WEBVTT
Kind: captions
Language: en-US

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[Silence]

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[intermittent beeping]

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Okay, let’s start.

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So, good morning, everyone.
Thanks for joining us.

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Please remember to keep your cameras
off and your microphones on mute.

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And, at the end of the presentation,
you will have a chance to type in your

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questions into the chat – meeting chat,
or just unmute yourself and ask.

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If you would like to join our
distribution list, my and Kathryn’s

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contacts are on
the center web page.

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Email us, and we will add you to
the seminar’s distribution list.

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And now I pass it on to Mehmet
to introduce today's speaker.

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- Okay. Well, I’m happy
to introduce Eduardo today.

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And maybe most of you know,
there are … [background noise]

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[inaudible] Mexico
[noises in background] …

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[voice inaudible due
to background noise]

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… in Mexico. Then, after the
[inaudible], he came to UC-Berkeley

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to complete his master’s
and Ph.D. degrees.

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He was very much interested in
earthquakes, particularly starting

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with the 1985 earthquake which
was a very significant event.

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And he’s now at Stanford
as a full professor.

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He’s been at
Stanford two decades.

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Tom Hanks and I joined this team
in 1985 to study the 1985 earthquake,

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and that’s when we
first met Eduardo.

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So it was a pleasant surprise to see
him back in the Bay Area for his

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graduate degrees and [inaudible].
[multiple beeps and background sounds]

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I want to add that Eduardo is known at
Stanford as a earthquake encyclopedia.

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So everybody runs to
him for information.

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He is interested in earthquake
engineering with emphasis

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on performance-based design
and also seismic response studies

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of structures built on
soft soil deposits.

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He also has extensive studies
done on analysis of records

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from instrumented structures.

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He is not a stranger to the USGS.
He has served at the

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ANSS Steering Committee
as representative of

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Earthquake Engineering
Research Institute.

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And he currently serves also as advisory
committee subcommittee member of

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CSMIP, which is California Strong
Motion Instrumentation Program.

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And he’s been
doing that for 15 years.

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So, in order not to take any more
time from his interesting presentation,

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I am sure, so I turn it
over to Eduardo. [beep]

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Thank you, Eduardo.

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- Thank you very much, Mehmet,
for that nice introduction.

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It’s really a pleasure for me to be
part again of this seminar series.

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Unfortunately, I’m not able to do it in
person in the new Yosemite room in

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Moffett Field, but I hope, in the near
future, to have an opportunity to do that.

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So I’ll start by thanking
a number of people.

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Before I would like to thank the
John A. Blume Earthquake

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Engineering Center at Stanford
University and StEER, who provided

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the funding for us to go to Puerto
Rico right after the earthquake.

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And, in particular, the John A. Blume
Center, it’s – it was initiated as part

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of an endowment that was left
by Dr. Blume and his family.

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And they allow us to fund a number
of fellowships and a number of

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very important activities, such
as earthquake reconnaissance.

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I also would like to thank, you know,
of course, USGS for the hospitality to

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participate in this – in this seminar,
in particular Mehmet Celebi, Kathryn,

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Noha, and Susan, who have been,
you know, taking care of

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all the logistics
aspects of this seminar.

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We originally were going to do it
in person back in March, and then

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unfortunately it got postponed,
and fortunately now we’re

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able to do it online.

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And also would like to thank Professor
José Antonio Martinez-Cruzado,

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a former classmate at Berkeley who
is a professor at the University of

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Puerto Rico-Mayagüez, who has helped
us, as soon as the earthquake happened,

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in gathering information and a lot of
logistics while we were there, and has

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continued to work, as I will mention,
with us learning from this event.

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The team that I was part of
was composed by myself

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and these four individuals
that I list over here.

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A Ph.D. student at UC-Berkeley,
Jorge Archbold.

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And then a postdoc from
Stanford, Pablo Heresi.

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And then Ph.D. students
Armando Messina and Isamar Rosa.

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By the way, Isa just had her
Ph.D. defense last Monday.

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So the main goals of our reconnaissance
were primarily to document the

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performance of instrumented structures,
to document performance of engineered

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structures that are close to
free-field stations, and then

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to document the performance
of other structures.

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Of course, we’ve had earthquakes for
centuries, but our ability to learn

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from them, it’s rather limited
if we don’t have instruments

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that enable us to create a pair in which
we can sort of observe and document

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what kind of performance was produced
by what kind of ground motion.

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So, in this case, one of – one of the
things that I usually look at as soon as

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I receive some of the U.S. notifications
that there’s been an earthquake,

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I quickly try to find out whether –
where there were recording stations.

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And then, if so, what kind of
intensities did they measure.

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And that’s a key component of making
the decision of whether to go or not.

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So, in this case, we quickly learned –
I mean, I already knew about

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the network over there,
about their interesting instrumented

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soft soil sites, as I will
mention in a moment.

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So I knew that there were going to
be good records from this event

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that would really allow
us to learn more from it.

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Very quickly – I won’t go into
the details, but just very quickly,

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for those of you who are not familiar
with the seismicity of the Caribbean,

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it’s a rather complicated
seismic environment.

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Mainly because it’s at the edge of
two plates, like we – often occurs.

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In this case, between the Caribbean
Plate and the North American Plate.

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And you see Puerto Rico
is this small island over here.

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But it’s – you know, even though
the island is – or, part of the island

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that it’s above the sea level,
it’s rather small, it’s actually –

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that platform, it’s rather large,
as you see over here.

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And that actually extends along
the Antilles arc with pretty much

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what we see above sea level
is just a few volcanoes.

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But the platform is –
it’s much, much larger.

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The region has seen
many, many earthquakes,

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many of which
are very large.

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I think, in the USGS surveys,
there’s a number of people

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who really specialized in
the seismicity in this area.

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And not only of Puerto Rico,
but all of the neighboring islands,

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including La Española, which, as you
all know, had a big earthquake in 2010.

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What's interesting about this situation is –
I think I would call it, like, a perfect

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example of multi-hazard risk.
So nowadays, not only the United

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States, but worldwide, there’s a lot
of interest to study multi-hazards.

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And, when we think of the Caribbean,
probably most of us, we think of

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the yearly dozens of hurricanes.
And that’s perhaps the largest hazard

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in the area, or certainly the hazard
that is more in the minds of people.

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And certainly everybody remembers
Hurricane Maria in recent years.

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But there are many other risks.
I mean, volcanic risks throughout

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the Caribbean. And certainly
earthquakes – and big earthquakes.

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And I will just – I would like to
point one in particular, which is

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really the largest earthquake
in the island in recent years –

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or, a little off from the island –
the October 11, 1918.

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So about 200 years ago, the
San Fermín earthquake occurred.

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And it’s important to highlight this
event, which is – occur, as you see,

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over here, and affected the whole island,
but in particular, the west side of

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the island and Mayagüez.
And there were important tsunamis

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in several locations there
that are well-documented.

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And here, I just wanted to show
you a couple of images of the

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damage that it produced
in Mayagüez.

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And the reason why I bring this up
is that, pretty much after this event,

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even though there’s been several other
earthquakes, there was not really

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any recent event in – sort of in the
memory of any person that’s alive

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today that would recall severe
damage from earthquakes.

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And this very important because, as
people are designing and building their

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constructions – their bridges and so on,
their primary worry are hurricanes.

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And perhaps not so much earthquakes,
even though, of course, earthquakes

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are part of the building code,
and you have to design for that.

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But especially for a lot of the
self-construction that takes place in

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the island, the main worry is hurricanes.
And very often, that means that you

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would like to have a big, heavy roof
that will protect you from the sun,

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that will protect you from the rain,
that will certainly not be lift off

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by hurricane.
But that works against you

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when it comes to inertial forces
that are proportional to the mass.

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So, in that case, maybe something
lighter would work better.

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This is an image from Temblor that
was produced at the end of January

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that reflects the pretty productive
activity that has been taking place

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in the still-ongoing sequence.
It happened, just as you see here,

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in the edge of this platform but
south [voice in background]

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of the island with many
thousands of earthquakes.

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This image, also from Temblor,
produced by Lopez, Vanacore,

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and others, highlights, you know,
the location of the earthquakes

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within the island. And, as you can see,
most of the events offshore, but there

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were a number of them that were very
close to the heavily damaged towns.

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In terms of the space,
the largest city in –

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near the epicenter is Ponce,
which is located over here.

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And the second-largest city
is the area is Mayagüez,

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where the networks
are operated from.

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I put together these slides last night from
ComCat just to highlight, you know,

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the large activity that is taking place.
So, as of last night, there were

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close to 1,300 earthquakes
with magnitudes larger than 3.

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And here you see how they
have spread out quite a bit.

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For, you know, more than
50 kilometers in length and –

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but even if you take magnitudes larger
than 4, there are 95, as you see here.

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And has produced a fairly
large number of earthquakes

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of magnitude 5 and greater.
And the sequence – I won’t

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go into the details, but it’s been
described as one of the most productive

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earthquakes in terms of aftershocks
relative to the magnitude of the event.

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I’ll just point out a few of them.
The sequence started on December 29

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of last year with a magnitude 5 event.
And that was – you know, for the

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typical activity, that was already
fairly large and alerted the people

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that something was going on.
And the sequence continued

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to the beginning
of this year.

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The largest event prior to the
main shock took place on the

00:15:20.439 --> 00:15:30.119
Day of Epiphany on January 6, 2020.
And so, fortunately, schools were not –

00:15:30.119 --> 00:15:38.639
because of this – it’s a national holiday,
so they were not in operation that day.

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But that was followed by the main
event on the following day

00:15:42.260 --> 00:15:51.980
on January 7 with a magnitude 6.4.
This particular combination,

00:15:51.980 --> 00:15:59.670
or sequence, actually, I believe,
played a major role in diminishing

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the number of lives that were lost
and some other consequences,

00:16:05.250 --> 00:16:12.269
basically because, after this event
that I told you – the 5.8 – a lot of the

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people stopped staying in their houses.
They were living in the outside in

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their yards in front of their houses
or going to some shelters.

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And therefore, at least all of the
structures that were damaged in this 5.8,

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most of those were empty
when the large 6.4 occurred.

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In terms of aftershocks,
well, we were there.

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We experienced
many aftershocks.

00:16:43.960 --> 00:16:48.389
But this one was, relative to
the main shock, fairly strong.

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We were at Ponce at the time.

00:16:51.020 --> 00:17:00.439
And I remember, after a very long day –
we had slept very little when we finally

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arrived to Ponce after many hours of
being in aiports and planes and having

00:17:07.560 --> 00:17:12.600
visited San Juan and Ponce,
and we were exhausted.

00:17:12.600 --> 00:17:17.200
And the first thing that – you know,
we made the reservations in this hotel

00:17:17.200 --> 00:17:20.750
in Ponce through the internet.
And obviously, it’s not like they

00:17:20.750 --> 00:17:25.270
were going to advertise on their
web page, you know, what is their –

00:17:25.270 --> 00:17:30.190
when it was built and
seismic resistance and whatnot.

00:17:30.190 --> 00:17:35.730
But the – we came from the back
of the hotel through an annex that –

00:17:35.730 --> 00:17:41.810
it was, you know, newer construction.
But, as we went into the – into the

00:17:41.810 --> 00:17:49.040
actual hotel through a beautiful
interior yard, and then the main

00:17:49.040 --> 00:17:54.590
advertising of the hotel was saying,
you know, this is the oldest hotel

00:17:54.590 --> 00:17:59.850
in Puerto Rico. And soon after that,
we had, in the evening, a very strong

00:17:59.850 --> 00:18:05.000
aftershock. And then this other one,
even stronger, in the morning.

00:18:05.000 --> 00:18:10.150
So I knew right away – and maybe
retrospectively, I should have paid

00:18:10.150 --> 00:18:14.780
more attention, that something
was going to happen this year.

00:18:14.780 --> 00:18:18.860
Because, as soon as the earthquake –
I start to find out whether we were

00:18:18.870 --> 00:18:24.110
going to go and make the plans to go,
and we had just taken off from

00:18:24.110 --> 00:18:30.650
here from SFO in a fairly –
almost brand-new 787.

00:18:30.650 --> 00:18:38.100
And the pilot said, we just had
a fracture in the – in the windshield

00:18:38.100 --> 00:18:42.860
of the – of the – in the cockpit
on the co-pilot side, so we’re

00:18:42.860 --> 00:18:45.380
heading back
to San Francisco.

00:18:45.380 --> 00:18:48.450
So that’s how our
reconnaissance trip started.

00:18:48.450 --> 00:18:51.900
And retrospectively,
I said, you know, this –

00:18:51.900 --> 00:18:55.280
2020 is going to
be full of surprises.

00:18:58.180 --> 00:19:02.940
This sequence, as I mentioned,
it has been still ongoing.

00:19:02.940 --> 00:19:08.560
And recently, on June 2nd,
they had a strong – another strong

00:19:08.560 --> 00:19:14.000
aftershock – a magnitude 5.4.
And the personnel over there at the

00:19:14.000 --> 00:19:19.600
university have continued to work
despite of the – of the quarantine and

00:19:19.610 --> 00:19:24.980
been able to retrieve many important
records from this other event.

00:19:24.980 --> 00:19:29.340
In some of the stations in Ponce,
they recorded larger intensities

00:19:29.340 --> 00:19:33.240
than in the main event.
Of course, this is closer to Ponce,

00:19:33.240 --> 00:19:38.050
which is located in
this area over here.

00:19:38.050 --> 00:19:45.900
And that, in combination with soft soils,
probably led to those high intensities.

00:19:45.900 --> 00:19:50.440
I’ll briefly mention something about the
networks that are operated over there.

00:19:50.440 --> 00:19:52.720
There are two very
important networks.

00:19:52.720 --> 00:19:56.740
Here I’m just showing you the
ones located in the island.

00:19:56.740 --> 00:20:02.220
But actually, they operate networks
across five different countries,

00:20:02.220 --> 00:20:07.020
including in the neighboring
República Dominicana and

00:20:07.020 --> 00:20:12.140
several other Virgin Islands
and other – and other islands.

00:20:12.140 --> 00:20:18.000
So they have a first network
of strong motion programs.

00:20:18.000 --> 00:20:20.870
And that’s operated by
Professor José Antonio

00:20:20.870 --> 00:20:26.760
Martinez-Cruzado and his team.
I’ll mention some of them in a moment.

00:20:26.760 --> 00:20:33.640
And then there’s another one –
the Puerto Rico seismic network

00:20:33.640 --> 00:20:38.080
that it’s operated by Professor
Elizabeth Vanacore and her team.

00:20:38.080 --> 00:20:44.500
And that has more instrument that’s
distributed throughout the island.

00:20:44.500 --> 00:20:50.590
The one of strong motion stations,
they operate also distributed stations,

00:20:50.590 --> 00:20:55.910
but in particular, they have two very
interesting networks in the city of

00:20:55.910 --> 00:20:59.210
Mayagüez and in
the city of Ponce.

00:20:59.210 --> 00:21:03.100
And I’ll be describing some of the
records that were obtained over there.

00:21:03.860 --> 00:21:08.760
There’s another one of these
local networks in San Juan,

00:21:08.760 --> 00:21:12.820
and most of the instruments
were triggered in this event.

00:21:12.820 --> 00:21:18.300
Although that’s further away
from this event at distances

00:21:18.300 --> 00:21:24.780
close to 100 kilometers.
So the intensities there were very small.

00:21:26.530 --> 00:21:31.900
So this is part of the – of the
Red Sismica de Puerto Rico –

00:21:31.900 --> 00:21:37.210
the Puerto Rico seismic network
operated from the University of

00:21:37.210 --> 00:21:40.950
Puerto Rico-Mayagüez and showing
some of the stations in the island

00:21:40.950 --> 00:21:46.220
and then in some of the other islands,
as you see here, in Punta Cana,

00:21:46.220 --> 00:21:52.860
in República Dominicana, you can
see just barely in this close-up view.

00:21:54.260 --> 00:21:57.560
Some of the people that I would
like to acknowledge here that have

00:21:57.560 --> 00:22:03.200
been key over the years, in not only
the installation, but the maintenance

00:22:03.200 --> 00:22:08.820
and reconstruction of a network.
Because their network and many

00:22:08.820 --> 00:22:14.260
of their stations suffered damage,
either on the telemetry or antennas

00:22:14.260 --> 00:22:20.280
or batteries, whatnot, as a
result of Hurricane Maria.

00:22:21.120 --> 00:22:24.140
But, as I said, this has been led
for a number of years by

00:22:24.150 --> 00:22:29.030
Professor Martinez-Cruzado.
But these other individuals that

00:22:29.030 --> 00:22:36.380
I list here have been key over the years
to maintain and really trying to leverage

00:22:36.380 --> 00:22:43.040
their funding from local sources
with federal resources,

00:22:43.040 --> 00:22:46.860
resources provided in
incorporation with the USGS.

00:22:46.860 --> 00:22:53.200
And USGS has played a major role
in assisting the island in the installation

00:22:53.200 --> 00:22:57.080
of many of these and in
the reconstruction here.

00:22:57.080 --> 00:23:02.640
I’m showing a photograph of one
of them while installing some of

00:23:02.640 --> 00:23:08.660
the instrumentation at Lucchetti Dam
that I’ll talk about in a moment.

00:23:08.660 --> 00:23:16.820
In terms of – in terms of records, this –
of course, it’s an image from USGS.

00:23:16.820 --> 00:23:25.000
A ShakeMap showing the locations of
instruments and in colors – color-coded,

00:23:25.000 --> 00:23:31.740
the intensity of some of these.
I’ll just point out a few of these.

00:23:31.740 --> 00:23:38.680
The largest peak ground accelerations
was recorded at this UUPR station that

00:23:38.680 --> 00:23:44.350
exceeded half a g, which is remarkably,
as you will see in a moment, I mean,

00:23:44.350 --> 00:23:47.580
given the magnitude
and distance.

00:23:47.580 --> 00:23:53.130
You know, this is significantly higher
than what we would have expected.

00:23:53.130 --> 00:23:59.640
And another one was at the
campus of the University at Utuado,

00:23:59.640 --> 00:24:04.710
where a peak ground acceleration
of 0.45 g was recorded.

00:24:04.710 --> 00:24:09.080
This is – this was not entirely
a surprise for the people who

00:24:09.080 --> 00:24:12.130
operate these networks.
This particular station has

00:24:12.130 --> 00:24:17.730
measured large accelerations
in a number of events.

00:24:17.730 --> 00:24:20.640
In particular in several of the
events has been – the largest

00:24:20.640 --> 00:24:25.020
intensity has been recorded.
And it’s probably due to

00:24:25.020 --> 00:24:29.830
a combination of some topographic
and local site effects that lead to

00:24:29.830 --> 00:24:34.140
these large amplifications
of motion.

00:24:34.140 --> 00:24:39.740
The Lucchetti Dam that I just
mentioned, that is – measure

00:24:39.740 --> 00:24:46.700
an intensity of 0.4. As you would
expect, it’s located in the mountains.

00:24:47.860 --> 00:24:51.860
And then, in Puerto Rico,
peak ground accelerations

00:24:51.860 --> 00:24:59.140
oscillated somewhere
between 0.16 and 0.25 g.

00:24:59.140 --> 00:25:05.640
And the higher accelerations were
all recorded on soft soil sites.

00:25:06.660 --> 00:25:13.840
And then, in the city of Mayagüez,
accelerations had even larger variations,

00:25:13.840 --> 00:25:20.780
varying from about 4% of g to 19% of g.
Again, the lower ones for rock stations

00:25:20.780 --> 00:25:25.400
and the larger ones for
stations located in soft soil sites.

00:25:26.320 --> 00:25:31.820
These are just plots of the attenuation
of intensity with distance.

00:25:31.820 --> 00:25:36.840
I plotted in the left sort of the more
common way in which engineers

00:25:36.840 --> 00:25:40.770
look at this, and on the right,
the way seismologists look at this.

00:25:40.770 --> 00:25:46.500
So I say, you know, you look at the
one that you are more familiar with.

00:25:46.500 --> 00:25:51.970
But both clearly show, you know,
the expected decay in intensities

00:25:51.970 --> 00:25:55.430
with increasing distances.
Again, I’ll just highlight

00:25:55.430 --> 00:26:03.140
a few of these intensities.
The largest, again, 0.52.

00:26:03.140 --> 00:26:08.240
And you can see significantly larger
even for stations that were located at

00:26:08.240 --> 00:26:15.190
similar distances from the epicenter.
The one at the campus of the

00:26:15.190 --> 00:26:20.520
University of Puerto Rico in
Utuado, 0.45. Lucchetti Dam, 0.4.

00:26:20.520 --> 00:26:24.760
And then Ponce, which is located
about 20 kilometers from the epicenter

00:26:24.760 --> 00:26:31.840
of the main shock saw accelerations
between 7 and 0.24 g.

00:26:31.840 --> 00:26:38.370
So that’s a ratio of about 3-1/2
from the lower to the highest,

00:26:38.370 --> 00:26:41.200
which is not uncommon.
We see this all the time.

00:26:41.200 --> 00:26:47.440
As a matter of fact, in my recent course
at Stanford, in a quiz, I asked the

00:26:47.440 --> 00:26:52.880
students if you would think that it’s
normal that, at the same distance and

00:26:52.880 --> 00:26:56.720
same magnitude and same event,
you would be able to measure

00:26:56.720 --> 00:27:02.180
4 times the intensity. And only a few of 
them – even though I had shown them

00:27:02.180 --> 00:27:06.860
several examples, just a few of
them answered that correctly.

00:27:06.860 --> 00:27:13.540
And same thing occurred in Mayagüez.
Mayagüez, located about 45 kilometers

00:27:13.550 --> 00:27:19.000
from the epicenter – again, big variation
of ground motion intensities with the

00:27:19.000 --> 00:27:24.000
lower ones corresponding to the rock
sites and the high ones to soft soil.

00:27:24.000 --> 00:27:31.720
In particular, this higher one with 0.2 g,
it’s a free-field station that was recorded

00:27:31.720 --> 00:27:37.450
right next to a viaduct that
suffered significant damage.

00:27:37.450 --> 00:27:41.060
And I’ll show you some
photographs of that afterwards.

00:27:41.060 --> 00:27:47.320
In terms of peak ground velocities,
also some of the stations recorded

00:27:47.320 --> 00:27:51.420
fairly large peak
ground velocities.

00:27:51.420 --> 00:28:00.630
[inaudible] six stations here with
intensities larger than 25 centimeters

00:28:00.630 --> 00:28:06.260
per second, which are definitely capable
of producing quite a bit of damage.

00:28:09.530 --> 00:28:14.800
In terms of design spectral
intensities, the Puerto Rico building

00:28:14.800 --> 00:28:22.940
code is based on ASCE 7, like just
the rest of the – of the U.S.

00:28:22.940 --> 00:28:28.120
And I’m showing you here the
spectral ordinates as a percentage

00:28:28.120 --> 00:28:34.520
of g for what we refer to as the
maximum considered earthquake

00:28:34.520 --> 00:28:39.420
that would have a
probability of 2% in 50 years.

00:28:39.420 --> 00:28:44.720
And you can see that, in this –
the southwestern part of the island

00:28:44.720 --> 00:28:50.660
is where the largest spectral
accelerations would occur,

00:28:50.660 --> 00:28:57.160
many of which
are larger than 1 g.

00:28:57.160 --> 00:29:01.530
But especially for the engineers
in the audience, as you know,

00:29:01.530 --> 00:29:07.810
we don’t really design for this level,
but typically for two-thirds of this.

00:29:07.810 --> 00:29:10.700
So, in many stations,
we would be designing

00:29:10.700 --> 00:29:19.800
for about 80% of g at 0.2 seconds.
And then, at 1 second, for values at the

00:29:19.800 --> 00:29:28.060
MCE level, about 1/2 a g and two-thirds
of that for the design base as earthquake.

00:29:29.240 --> 00:29:37.360
These are just representative examples
of some of the design spectra for

00:29:37.360 --> 00:29:41.450
some of the cities that I’ll be
showing you in the photographs.

00:29:41.450 --> 00:29:46.350
Ponce, Guánica, Guayanilla,
and Mayagüez.

00:29:46.350 --> 00:29:50.630
And I plotted here the values
corresponding to

00:29:50.630 --> 00:29:56.980
Site Classes C and D, which are
alluvial sites that are relatively soft.

00:29:56.980 --> 00:30:00.160
Although I would like to mention
that several of the sites are

00:30:00.160 --> 00:30:05.040
actually softer, and they would
correspond to Site Class E.

00:30:08.720 --> 00:30:12.960
This is an image, again,
of the island of Puerto Rico

00:30:12.960 --> 00:30:18.540
showing the location of some
of the recording stations.

00:30:18.540 --> 00:30:22.330
And, in the squares, I’m showing
you some of the close-up views

00:30:22.330 --> 00:30:28.630
that I will show you with some of the
local instruments and some of the red

00:30:28.630 --> 00:30:33.040
squares represent some of the structures
that we visited and documented.

00:30:33.040 --> 00:30:38.320
I won’t have time to go into details
of all of them, but I’ll give you

00:30:38.330 --> 00:30:42.750
some references of some – a couple of
reports that we have published for any

00:30:42.750 --> 00:30:47.810
of you that would like to have
more information to look at that.

00:30:47.810 --> 00:30:50.850
This is one example.
This is in the city of Ponce.

00:30:50.850 --> 00:30:55.690
Again, this is the largest city
that is close to the epicenter –

00:30:55.690 --> 00:31:02.220
about 20 kilometers from the epicenter.
The triangles represent strong motion

00:31:02.220 --> 00:31:08.980
stations. And there’s one here at the
University of Puerto Rico in Ponce.

00:31:08.990 --> 00:31:14.130
That – actually, that’s where we started.
and we knew that there was a station

00:31:14.130 --> 00:31:18.630
there, so the first thing we did was to –
when we arrived to Ponce,

00:31:18.630 --> 00:31:24.620
was to visit that – not only the station,
but to visit all the – all the structures

00:31:24.620 --> 00:31:31.340
on the campus that were located
very close to that station.

00:31:31.340 --> 00:31:36.910
We also visited two nearby stations –
a bridge that is instrumented,

00:31:36.910 --> 00:31:43.610
and I’ll show you, and then a toll plaza
that actually recorded the largest

00:31:43.610 --> 00:31:48.340
acceleration in the event.
It’s partly – that toll plaza is partly

00:31:48.340 --> 00:31:53.460
located on a fill that I’m sure must
have played a role in the slightly

00:31:53.460 --> 00:31:57.460
larger intensity compared to the
one of the bridge or the one that

00:31:57.460 --> 00:32:03.400
was located here on the campus.
But there are several other stations,

00:32:03.400 --> 00:32:08.650
especially near downtown in the
offices of an engineering firm

00:32:08.650 --> 00:32:12.050
in the [inaudible] and many others.

00:32:12.050 --> 00:32:19.000
So we visited a lot of
interesting sites over there.

00:32:19.000 --> 00:32:25.850
Just representative – this comes
from a USGS Open-File report that

00:32:25.850 --> 00:32:33.680
was produced some years ago of
people that conducted investigations

00:32:33.680 --> 00:32:38.450
of the soil profiles in several
locations in Puerto Rico.

00:32:38.450 --> 00:32:43.450
And that included this particular
location in the campus of the

00:32:43.450 --> 00:32:49.980
Catholic University of Puerto Rico.
It’s a private university there in the city.

00:32:49.980 --> 00:32:57.140
And what’s interesting about this one is,
as you can see, it has a couple of layers

00:32:57.150 --> 00:33:02.230
of very soft soil – alluvial deposits
with shear wave velocities of

00:33:02.230 --> 00:33:07.920
140 and 160 meters per second.
And that sits on top of a Ponce

00:33:07.920 --> 00:33:16.110
limestone that – it’s much, much
stiffer with shear wave velocities

00:33:16.110 --> 00:33:22.650
in the order of 505 meters per second.
But it’s relatively shallow.

00:33:22.650 --> 00:33:27.660
And then, even if you, you know,
take this into consideration in

00:33:27.660 --> 00:33:34.870
computing the Vs30, you still
lead to a value smaller than 180,

00:33:34.870 --> 00:33:39.080
and therefore it’s classified
as a Site Class E.

00:33:41.900 --> 00:33:45.230
These are just representative
examples comparing the

00:33:45.230 --> 00:33:50.500
design spectra with some of the
response spectra computed from –

00:33:50.500 --> 00:33:56.300
5% response spectra computed from
some of the ground motions in the city.

00:33:56.300 --> 00:34:03.470
As you can see, the design spectral
ordinates were exceeded, both in the

00:34:03.470 --> 00:34:08.879
high-frequency region, but in particular,
you know, in terms of displacement

00:34:08.879 --> 00:34:13.050
demands, which are primarily
responsible for damage to both

00:34:13.050 --> 00:34:19.160
structural and non-structural
components, it’s a lot more worrisome,

00:34:19.160 --> 00:34:26.080
this large spectral ordinates
occurring at periods larger than 0.5,

00:34:26.080 --> 00:34:30.320
which give rise to fairly
large displacement demands.

00:34:34.590 --> 00:34:39.800
This is some of the –
some of the instruments located

00:34:39.800 --> 00:34:44.020
in the city of Mayagüez.
Again, Mayagüez is located about

00:34:44.020 --> 00:34:49.840
45 kilometers from the epicenter.
The campus of the university where

00:34:49.850 --> 00:34:56.130
our friends are located is right here.
There’s a couple of stations there.

00:34:56.130 --> 00:35:01.610
This is up in the hills.
And this region is – it’s relatively flat.

00:35:01.610 --> 00:35:07.640
Downtown, it’s around here,
and that’s also on a hill.

00:35:07.640 --> 00:35:13.520
And I’ll be showing you some images –
this is the viaduct that I mentioned

00:35:13.520 --> 00:35:17.950
previously that suffered damage.
And I’ll be showing some images

00:35:17.950 --> 00:35:25.170
of that. And this is a very nicely
instrumented condominium tower,

00:35:25.170 --> 00:35:31.990
El Castillo, which is – we also visited
and we’ve been working with some of

00:35:31.990 --> 00:35:36.250
the records that were obtained there.
Just like I did for Ponce, I wanted to

00:35:36.250 --> 00:35:42.850
show you some of the information we
know about the soils in Mayagüez.

00:35:42.850 --> 00:35:52.060
Again, in many locations, you find
alluvial soil deposits that are –

00:35:52.060 --> 00:35:58.360
with low shear wave velocities
of about 145 meters per second.

00:35:58.360 --> 00:36:03.800
In this case, [inaudible] bedrock
at about 18 meters’ depth with

00:36:03.800 --> 00:36:07.820
shear wave velocities
in the order of 355.

00:36:07.820 --> 00:36:13.700
And this one just barely
classifies as Site Class D.

00:36:13.700 --> 00:36:17.610
As you all know, you know,
the site classification has worked well,

00:36:17.610 --> 00:36:25.030
and it helps us in a number of things.
But also, you know, it’s not the same as,

00:36:25.030 --> 00:36:26.910
you know, doing a
site response analysis.

00:36:26.910 --> 00:36:34.010
You see this kind of information
from [inaudible].

00:36:34.010 --> 00:36:38.840
This is another example.
This is at the track on the campus of the

00:36:38.840 --> 00:36:44.520
University of Puerto Rico-Mayagüez
where there you have an impedance,

00:36:44.520 --> 00:36:50.390
or contrast – a much sharper contrast
there where you go basically from

00:36:50.390 --> 00:36:57.580
deposits of 140 meters per second
to fairly good rocks, which are

00:36:57.580 --> 00:37:02.020
velocities of up to more than
2,000 meters per second.

00:37:02.020 --> 00:37:08.430
So when you – when you classify this
according to NEHRP classifications,

00:37:08.430 --> 00:37:15.740
you end up classifying this as to –
as a NEHRP Site Class D, but would

00:37:15.740 --> 00:37:22.740
not necessarily produce motions of
your typical Site Class D, but rather,

00:37:22.740 --> 00:37:29.840
they’re more representative of
a soft layer of soft soil on rock.

00:37:29.840 --> 00:37:36.940
And these are some examples, again,
comparing design spectrum with 5%

00:37:36.940 --> 00:37:41.060
response spectra computed from
some of those ground motions.

00:37:41.060 --> 00:37:48.320
And similarly, to – oh, sorry.
I put this image – these are actually

00:37:48.320 --> 00:37:52.480
the ones – it says “Mayagüez,”
but I copy again the once of Ponce.

00:37:52.480 --> 00:37:54.960
I apologize.

00:37:55.460 --> 00:38:00.220
But, in my report,
I’ll show those.

00:38:01.520 --> 00:38:06.120
This is in Yaucos.
This is closer to the epicenter.

00:38:07.100 --> 00:38:14.460
This had a peak ground acceleration 
[echoing] a little bit [inaudible] 0.35 g,

00:38:14.460 --> 00:38:19.720
if I recall correctly. [echoing stopped]
And you can see that it exceeded

00:38:19.720 --> 00:38:24.580
spectral ordinates on a wide range
of periods and frequencies.

00:38:29.100 --> 00:38:35.980
These are some of the risk that was
estimated by USGS PAGER, where,

00:38:35.980 --> 00:38:41.460
I believe, correctly identified
the small number of fatalities.

00:38:41.460 --> 00:38:44.800
There’s only one fatality
that we know of.

00:38:44.800 --> 00:38:49.780
But, again, I believe that we –
it really played a big role,

00:38:49.780 --> 00:38:56.580
the occurrence of these two events.
That’s why I put both of them here,

00:38:56.580 --> 00:39:03.660
that having had that 5.8 the day before
allowed a lot of people just not to

00:39:03.660 --> 00:39:09.700
be living in their – in their
houses when the main occurred.

00:39:09.700 --> 00:39:17.710
And that, I’m sure, saved a lot of lives.
You know, this is just my educated

00:39:17.710 --> 00:39:23.600
guess, but I think we would have
definitely exceeded the 10 and possibly

00:39:23.600 --> 00:39:30.600
even 100 fatalities if it wasn’t for this
sequence, the way it played out.

00:39:32.700 --> 00:39:40.430
I believe that the largest impact
was on the residential construction.

00:39:40.430 --> 00:39:45.580
These are just a few images taken
from some social media and from

00:39:45.580 --> 00:39:52.000
reporters that we all saw in the
days following the earthquake.

00:39:52.000 --> 00:39:59.960
And they are representative examples
of the type of construction that you see.

00:39:59.960 --> 00:40:05.340
Not only in the epicentral region,
but throughout Puerto Rico,

00:40:05.340 --> 00:40:12.330
to a certain extent, in which it’s very
common to have these two-story houses,

00:40:12.330 --> 00:40:18.980
but that the ground level is used for
parking and for protection from the sun.

00:40:18.980 --> 00:40:23.940
And then people actually live
in the – in the upper level.

00:40:23.940 --> 00:40:29.200
And I mentioned this because,
in a recent study we did at Stanford,

00:40:29.200 --> 00:40:36.520
we found that two-story houses
are substantially more risky

00:40:36.520 --> 00:40:39.690
than one-story houses.
And, as we were doing our

00:40:39.690 --> 00:40:44.050
reconnaissance, we had just
recently published this paper.

00:40:44.050 --> 00:40:48.430
We had this fresh in mind, and it –
you know, of course it – you could say

00:40:48.430 --> 00:40:51.840
it’s expected when you
have these soft stories.

00:40:51.840 --> 00:40:55.480
But, as I’ll show you in some of the
images, this also occurred not only

00:40:55.480 --> 00:41:04.180
in soft stories, but it was pretty
evident throughout the region.

00:41:05.410 --> 00:41:11.880
The fact that you have the soft story,
or the parking, also played a role in the

00:41:11.880 --> 00:41:17.700
sense that, even if these collapse,
as you can see here, people would

00:41:17.700 --> 00:41:23.940
be able to walk and be alive if
they were in the upper level.

00:41:27.700 --> 00:41:32.380
This is another example
taken from social media.

00:41:32.380 --> 00:41:35.340
This was – it looks like
a one-story, but at one point,

00:41:35.340 --> 00:41:40.480
it was a second –
two-story house.

00:41:42.960 --> 00:41:46.760
And this is
another example.

00:41:46.760 --> 00:41:52.820
I’m just going to be showing you a few,
but this is interesting in the sense that,

00:41:52.820 --> 00:41:58.820
you know, you could clearly see that
many of these had engineering designs,

00:41:58.820 --> 00:42:03.460
and in some cases, fairly large columns.
You know, in some cases, you do see

00:42:03.460 --> 00:42:08.119
some problems, but here,
as you see, there were fairly large

00:42:08.120 --> 00:42:11.040
columns in this
particular house.

00:42:11.040 --> 00:42:19.160
And so relative to the mass,
you would say it’s a fairly strong

00:42:19.160 --> 00:42:22.880
soft story, if you will, but you
see there the close-up view of

00:42:22.880 --> 00:42:30.420
that interior column and the
severe damage that that caused.

00:42:30.420 --> 00:42:41.440
And one thing that I would like to point
out is that we were there a little less

00:42:41.440 --> 00:42:49.750
than 48 hours after the main shock.
And we stayed there for four days.

00:42:49.750 --> 00:42:55.000
And so that basically means that,
for about six days, we basically see –

00:42:55.000 --> 00:42:59.950
we saw no tagging.
And most people, you know,

00:42:59.950 --> 00:43:05.020
just basically were making decisions
on their own whether to stay or not.

00:43:05.020 --> 00:43:10.500
And, while many people were living
outside, we saw many houses that

00:43:10.500 --> 00:43:15.560
were being occupied that probably
they shouldn’t have been occupied.

00:43:15.560 --> 00:43:21.070
And that’s one of the
lessons that I would say.

00:43:21.070 --> 00:43:27.770
We need to learn, or relearn,
the importance of starting the

00:43:27.770 --> 00:43:32.800
tagging right away.
And this earthquake certainly

00:43:32.800 --> 00:43:37.170
highlighted how we’re
often slow in doing that.

00:43:37.170 --> 00:43:44.230
And particularly challenging in places
like Puerto Rico, where, again, because,

00:43:44.230 --> 00:43:48.100
for essentially a hundred years,
they had not seen this.

00:43:48.100 --> 00:43:53.460
Even though there are some engineers
who have been trained in this type of

00:43:53.460 --> 00:44:00.359
post-earthquake evaluation of existing
structures, it was difficult to do the

00:44:00.360 --> 00:44:02.860
coordination and get
this process started.

00:44:02.860 --> 00:44:10.680
Eventually, it started, but took
some days to get it going.

00:44:10.680 --> 00:44:16.420
This is – this is one example of the
type of damage in two-story houses.

00:44:16.420 --> 00:44:21.090
But again, it’s – this is representative
of something that we saw very often,

00:44:21.090 --> 00:44:26.210
which is – you know, you wouldn’t
say that it’s such an obvious soft story

00:44:26.210 --> 00:44:32.480
as the previous one. But if you compare
what went on in the upper level with

00:44:32.480 --> 00:44:37.860
respect to the lower level, you know,
it’s remarkable, the contrast.

00:44:37.860 --> 00:44:44.520
And very often, if you – if you look at
many documents throughout the years,

00:44:44.530 --> 00:44:49.470
we have classified one- and two-
and sometimes even three-story

00:44:49.470 --> 00:44:54.280
houses under the same category.
And this started after the

00:44:54.280 --> 00:45:02.040
1906 earthquake in California.
But there are many documents that –

00:45:02.040 --> 00:45:10.740
whether it’s for tagging, for rapid
evaluation, for rapid screening,

00:45:10.740 --> 00:45:16.940
for actual loss estimation, they
being lumped into the same category.

00:45:16.940 --> 00:45:22.720
And we strongly believe that this –
we should stop doing that.

00:45:22.730 --> 00:45:27.310
Even with relatively simple
calculations, you can show that,

00:45:27.310 --> 00:45:33.330
because of the difference in vibration
characteristics, simply one is going to

00:45:33.330 --> 00:45:39.119
have a period about twice the other.
And that gives to very large differences

00:45:39.119 --> 00:45:42.700
in displacement demands.
But then those displacement demands

00:45:42.700 --> 00:45:47.800
essentially concentrate in the
lower story and making

00:45:47.800 --> 00:45:53.580
two-story houses far more
vulnerable than one-story houses.

00:45:53.580 --> 00:45:58.040
And I think we need to
do a better job in recognizing this

00:45:58.040 --> 00:46:00.940
in the engineering community.

00:46:02.720 --> 00:46:06.340
Moving now to damage
to school buildings.

00:46:06.340 --> 00:46:13.580
I’m sure you all saw the images
in the TV and in newspapers

00:46:13.580 --> 00:46:20.090
about the collapse of this structure.
This structure collapsed on the

00:46:20.090 --> 00:46:24.540
January 6th – or, partially collapsed
on the January 6th event.

00:46:24.540 --> 00:46:30.200
And fortunately, Professor Martinez-
Cruzado visited the structure on that day

00:46:30.200 --> 00:46:36.860
and essentially closed it and made sure
that nobody would get anywhere near it

00:46:36.869 --> 00:46:43.210
and then suffer further damage
and collapse in the main shock.

00:46:43.210 --> 00:46:48.880
But by then, you know, nobody
was close to this structure.

00:46:50.840 --> 00:46:57.040
Here it’s another view. As you see,
it has a number of buildings in it.

00:46:57.040 --> 00:47:02.020
This is the main courtyard.
The entrance is here on the right.

00:47:02.020 --> 00:47:07.300
And, in particular, this …

00:47:10.660 --> 00:47:16.500
… this structure was the one that
collapsed in the – in the main shock.

00:47:17.760 --> 00:47:21.780
These are some images.
It’s fairly complex.

00:47:21.780 --> 00:47:25.460
You know, sometimes when
I do earthquake reconnaissance –

00:47:25.460 --> 00:47:29.540
or, I should say, not sometimes,
but almost always, as I’m taking

00:47:29.540 --> 00:47:32.860
photographs, I’m reflecting, you know,
to what extent I would have been

00:47:32.860 --> 00:47:40.660
able to predict such a performance.
And you do see a number of views

00:47:40.660 --> 00:47:45.920
with this structure that perhaps the most 
important one that led to this collapse

00:47:45.920 --> 00:47:52.670
is the presence of short columns,
or captive columns, as we call them.

00:47:52.670 --> 00:47:56.770
But interestingly enough – and when
you go to conference, people say,

00:47:56.770 --> 00:47:59.530
oh, you know, it failed
because of short columns.

00:47:59.530 --> 00:48:03.900
But what people don’t tell you very
often is that, in the same location,

00:48:03.900 --> 00:48:06.650
there were plenty of other
structures with short columns,

00:48:06.650 --> 00:48:09.280
and they were intact.
As a matter of fact, this particular,

00:48:09.280 --> 00:48:12.820
you know, one-story structure
right next to it, we visited,

00:48:12.820 --> 00:48:16.880
and we looked very careful at it.
There you see the short columns.

00:48:16.880 --> 00:48:21.619
And essentially had no damage.
And it was not the only structure there.

00:48:21.619 --> 00:48:24.880
I mean, there were others.
And I’ll show you a video in

00:48:24.880 --> 00:48:32.869
a moment that highlights, you know,
the selective nature of earthquakes

00:48:32.869 --> 00:48:38.790
but also how complicated is
really the task of evaluating

00:48:38.790 --> 00:48:42.480
which ones are at risk
and which ones are not.

00:48:42.480 --> 00:48:48.340
This was not a very old structure.
Yes, you know, the detail is not perfect.

00:48:48.340 --> 00:48:52.980
And, you know, short –
you would point out the large spacing.

00:48:52.980 --> 00:48:57.480
I mean, it had good separation
at the ends, you know, improving

00:48:57.480 --> 00:49:01.859
a little bit the confinement
at the end of the columns.

00:49:01.859 --> 00:49:11.080
But, you know, larger spacing
with 90-degree bends in the corners,

00:49:11.080 --> 00:49:16.960
which of course, we would not
use or recommend nowadays.

00:49:16.960 --> 00:49:21.380
But still, if you look at the longitudinal
reinforcement, the quality of the

00:49:21.380 --> 00:49:25.620
concrete, and the size of the columns,
you know, on the back of the

00:49:25.620 --> 00:49:28.460
envelope, you can do some
calculations of what is – what is

00:49:28.460 --> 00:49:32.869
the amount of shear force that it
takes to shear one of these

00:49:32.869 --> 00:49:37.600
large columns the way it did.
And then, times the number of columns.

00:49:37.600 --> 00:49:42.720
And then you quickly come to
realize the very large forces

00:49:42.720 --> 00:49:46.060
that act on these structures
during these earthquakes.

00:49:47.570 --> 00:49:52.160
These are just some close-up
views in high-resolution so you

00:49:52.160 --> 00:49:56.870
can see some of the details.
There you see the closer spacing

00:49:56.870 --> 00:50:03.420
that I mentioned in the top.
There were number 4s at 4 inches apart

00:50:03.420 --> 00:50:11.320
and longitudinal enforcement that were
number 8 rebars with very good quality,

00:50:11.320 --> 00:50:15.720
no evidence of corrosion.
And here you see a close-up

00:50:15.720 --> 00:50:21.100
view of some of the 90-degree
bends in the corners.

00:50:22.600 --> 00:50:28.599
And, you know, sometimes we say, well,
you know, these are – we sometimes

00:50:28.599 --> 00:50:34.190
create these binary classifications,
especially here in California.

00:50:34.190 --> 00:50:36.940
We like this simple binary
classifications, right?

00:50:36.940 --> 00:50:39.960
We say, oh, this was a
pulse-like ground motion.

00:50:39.960 --> 00:50:42.670
This was an ordinary
ground motion.

00:50:42.670 --> 00:50:46.530
This is near-fold.
This is far.

00:50:46.530 --> 00:50:50.760
And similarly, we would say, oh,
this is non-ductile. This is ductile.

00:50:50.760 --> 00:50:55.010
When, in reality, you know,
this is far from a binary classification,

00:50:55.010 --> 00:51:00.540
and this is just sort of like for human
beings to feel happy that they have

00:51:00.540 --> 00:51:03.430
classified these structures
or these ground motions.

00:51:03.430 --> 00:51:06.869
But, in reality, there’s a
full continuum in between.

00:51:06.869 --> 00:51:11.740
In reality, it’s a lot more
complex than we sometimes think.

00:51:12.680 --> 00:51:16.000
This is a video that I took.
It’s the only one that I’ll show you.

00:51:16.000 --> 00:51:20.520
But I think it’s sort of representative
of the selective nature of earthquakes.

00:51:20.520 --> 00:51:26.940
So I first start by displaying
that school that you just saw.

00:51:26.940 --> 00:51:30.800
But then I’m panning around
the structures in the surrounding

00:51:30.800 --> 00:51:35.560
of the school.
And you essentially see no damage.

00:51:39.860 --> 00:51:43.420
There on this structure –
it’s a museum.

00:51:43.430 --> 00:51:47.660
There you see that sort of tower.
It actually has, like, a clock tower.

00:51:47.660 --> 00:51:49.130
It had no damage.

00:51:49.130 --> 00:51:51.910
The only damage that I saw
on that structure were some of

00:51:51.910 --> 00:51:57.880
those ornaments on the parapet,
that a couple of them collapsed.

00:51:57.880 --> 00:52:01.490
But, again, you would say, well,
you know, this is a non-ductile

00:52:01.490 --> 00:52:04.540
reinforced concrete school,
so what do you expect?

00:52:04.540 --> 00:52:07.560
Well, you know, if you actually
were to look at the drawings of

00:52:07.560 --> 00:52:11.900
all of these structures, I guess,
in this simple classification,

00:52:11.900 --> 00:52:14.470
you could probably also call
them non-ductile reinforced

00:52:14.470 --> 00:52:18.180
concrete construction,
and still, they were intact.

00:52:18.180 --> 00:52:26.450
So, again, it highlights the often
selective nature of what the

00:52:26.450 --> 00:52:30.620
earthquakes choose to
destroy and what not.

00:52:31.460 --> 00:52:36.700
This is another example.
This is in Ponce.

00:52:36.700 --> 00:52:39.870
Like many schools, sort of the
geometry – and because of the

00:52:39.870 --> 00:52:42.770
purpose and the classrooms
next to each other, they share

00:52:42.770 --> 00:52:49.380
a very different – I mean,
very similar configuration.

00:52:49.380 --> 00:52:53.660
And you can see the presence of
short columns in this case

00:52:53.670 --> 00:53:00.010
with these architectural parapets.
Masonry walls that essentially

00:53:00.010 --> 00:53:06.410
prevent lateral deformations in
the column and therefore essentially

00:53:06.410 --> 00:53:10.360
double the shear demands for
the same lateral deformation.

00:53:10.360 --> 00:53:14.900
And there was no damage.
I mean, I took lots of photos

00:53:14.910 --> 00:53:19.010
of each column with close-up
views, which I won’t show you.

00:53:19.010 --> 00:53:25.600
But many structures nearby, including
this one that you see here on the left,

00:53:25.600 --> 00:53:29.880
and within the structure – within
100 yards of this structure, there was

00:53:29.880 --> 00:53:37.220
severe structural damage. And this one
with short columns had no damage.

00:53:37.220 --> 00:53:42.170
It’s located on soft soil.
This is just a close-up view

00:53:42.170 --> 00:53:48.900
of that short column in the corner.
And you would say, well, you know –

00:53:48.900 --> 00:53:51.620
maybe in one of these
pre-screenings, you would say,

00:53:51.620 --> 00:53:55.760
oh, yes, this is the first
column that is going to go.

00:53:55.760 --> 00:54:02.780
And it just – sometimes I show some of
these in classroom to tell the students,

00:54:02.780 --> 00:54:07.020
you know, that we need to remain
humble and don’t believe that –

00:54:07.020 --> 00:54:09.619
for a minute that we understand
everything about earthquakes

00:54:09.620 --> 00:54:11.480
and what earthquakes
do to structures.

00:54:11.480 --> 00:54:17.660
Because every earthquake teaches
that it’s more complicated than that.

00:54:17.660 --> 00:54:25.640
So moving on to residential
constructions, but taller ones.

00:54:25.640 --> 00:54:30.500
There – you know, like many
urban areas, when land starts to

00:54:30.500 --> 00:54:34.200
be scarce and starts
to go up in price,

00:54:34.200 --> 00:54:41.480
developers find more economically
attractive to go in the vertical direction.

00:54:41.480 --> 00:54:48.040
And this is one of those structures
that – so, for in the – in the main façade,

00:54:48.040 --> 00:54:51.240
you could see some
damage but not a lot.

00:54:51.240 --> 00:54:55.340
But then, on the back,
there was quite a bit of damage.

00:54:55.340 --> 00:55:00.550
And I’ll show you some views of that.
In particular, there was a ramp

00:55:00.550 --> 00:55:05.050
to go on the upper level of
a parking garage, which, on either

00:55:05.050 --> 00:55:09.550
side of the building – on the right-hand
side, you access the lower level.

00:55:09.550 --> 00:55:10.950
On the left-hand side
of the building,

00:55:10.950 --> 00:55:14.220
you access the upper
level through this ramp.

00:55:14.220 --> 00:55:19.380
But unfortunately, this ramp was
not separated from the main structure,

00:55:19.380 --> 00:55:23.200
creating this short
column that you see there.

00:55:23.200 --> 00:55:29.140
It has been completely sheared off.
And being a corner column, you know,

00:55:29.140 --> 00:55:36.760
it probably has lost part of its
vertical carrying capacity, making

00:55:36.760 --> 00:55:46.140
this particular damage – even if it’s
just in one element – very severe.

00:55:48.220 --> 00:55:54.780
This is an example about 50 yards
from the – from the previous one,

00:55:54.780 --> 00:56:00.960
actually just on the back of the previous
one, also near downtown Ponce.

00:56:00.960 --> 00:56:05.070
It’s called the La Abolición –
El Condominio Abolición.

00:56:05.070 --> 00:56:11.350
And there you see the front on the left
and the back of the building on the right.

00:56:11.350 --> 00:56:17.260
It’s interesting that it’s very common
in Puerto Rico to have a concrete

00:56:17.260 --> 00:56:22.970
structure – a concrete frame structure
but combined with a steel floor system.

00:56:22.970 --> 00:56:28.980
This is not so common in other
Latin American countries.

00:56:28.980 --> 00:56:31.920
But here they combine
sometimes joist systems

00:56:31.920 --> 00:56:36.280
with steel deck
and concrete slab.

00:56:40.120 --> 00:56:45.480
In this case, the most severe damage
occurred at the ground level.

00:56:45.480 --> 00:56:53.200
It has a soft story, as you see there.
But in particular, this corner column

00:56:53.200 --> 00:57:00.780
suffered this severe shear failure and
therefore, just like the previous building,

00:57:00.780 --> 00:57:06.200
jeopardizes that vertical carrying
capacity in that location.

00:57:07.680 --> 00:57:12.420
This is another corner column,
also on the back of the building.

00:57:12.420 --> 00:57:16.280
On the image of the left,
you don’t see it that bad.

00:57:16.281 --> 00:57:23.540
But if you were to zoom in and –
that’s what you would see

00:57:23.540 --> 00:57:26.060
over there on the right.

00:57:30.040 --> 00:57:34.720
I’ll take advantage of this image
to say, you know, the importance

00:57:34.720 --> 00:57:39.650
of the interaction of masonry
infills with frame structures.

00:57:39.650 --> 00:57:45.910
Very often, when we design the
structures, we model the frame

00:57:45.910 --> 00:57:50.530
but not the infill.
And – or, even when we model

00:57:50.530 --> 00:57:58.440
this infill with an equivalent diagonal,
we don’t take into account that these

00:57:58.440 --> 00:58:04.200
compression struts that form in
this could lead to localized crushing

00:58:04.200 --> 00:58:08.680
of the masonry. And even if you
don’t have a short column, you end up

00:58:08.680 --> 00:58:13.240
developing a short column once
the masonry infills have failed.

00:58:13.240 --> 00:58:19.940
This is another example in Ponce
again that suffered severe damage.

00:58:19.940 --> 00:58:24.400
And, you know, look at the size of
these buildings and think about the

00:58:24.400 --> 00:58:30.040
number of units that it has – the
number of families that are displaced.

00:58:30.040 --> 00:58:35.720
And some of which, I’m sure they’re
still displaced because probably

00:58:35.720 --> 00:58:41.550
these structures are not – still
cannot be occupied to this date.

00:58:41.550 --> 00:58:45.570
So sometimes some of us, you know,
we complain in this quarantine that,

00:58:45.570 --> 00:58:50.369
oh, you know, I’m not able to go to
my office. Or I’m not able to do this.

00:58:50.369 --> 00:58:52.840
Well, you know, we’re lucky
compared to these people

00:58:52.840 --> 00:58:55.770
when you think about, you know,
just being displaced for your residence,

00:58:55.770 --> 00:58:59.080
and you may not be
able to return to it.

00:59:02.820 --> 00:59:09.910
Some examples of what earthquakes do
and things that we engineers often miss.

00:59:09.910 --> 00:59:14.170
Again, because we model frames
and not infills and non-structural

00:59:14.170 --> 00:59:16.960
components that will
actually be placed there.

00:59:16.960 --> 00:59:21.760
In this case, you see a number of infills
on the left, but I took these images –

00:59:21.760 --> 00:59:31.050
close-up images of the infill where
you now open an area for placing

00:59:31.050 --> 00:59:35.300
these air conditioning units, which
of course are very necessary in

00:59:35.300 --> 00:59:39.280
Puerto Rico, especially, I suppose,
this time of the year.

00:59:39.280 --> 00:59:44.520
And because of that, you create
all sorts of stress concentrations.

00:59:44.520 --> 00:59:50.080
And the earthquake will be a very good
inspector in finding all of these things

00:59:50.080 --> 00:59:56.760
that the engineer didn’t model and
some of the problems that it creates.

00:59:59.400 --> 01:00:02.230
In terms of non-structural
components in some of these units,

01:00:02.230 --> 01:00:07.060
I won’t go too much into details.
Just wanted to highlight glazing.

01:00:07.080 --> 01:00:13.880
We saw a lot of damage from glazing.
And it’s a very common occurrence.

01:00:13.880 --> 01:00:20.440
And we often don’t think about the
hazard that this glazing represents.

01:00:20.440 --> 01:00:26.500
Some of this glazing may be falling off
from five, seven, eight stories above.

01:00:26.500 --> 01:00:31.320
And when it’s falling, very often,
it’s not falling in these little pieces

01:00:31.339 --> 01:00:36.180
that you see in this – in this image.
But rather, large pieces.

01:00:36.180 --> 01:00:39.630
And very often, the way they fly,
it’s not in the horizontal position

01:00:39.630 --> 01:00:42.720
but in the vertical.
And, you know, don’t need

01:00:42.720 --> 01:00:48.600
to go into more description,
but it’s obvious what it can happen.

01:00:50.900 --> 01:00:54.450
These are some close-up views
of the damage on the other side of the

01:00:54.450 --> 01:01:01.960
building that, again, leads to, you know,
a red tag in this case for this building.

01:01:01.960 --> 01:01:06.170
There was not really official red tag
on this building when we visited.

01:01:06.170 --> 01:01:11.440
But clearly some engineers had
previously visited this and had put

01:01:11.440 --> 01:01:19.140
some informal tagging and not
allowing people to go into the structure.

01:01:19.140 --> 01:01:23.170
You do see a number of
problems in the detailing of this.

01:01:23.170 --> 01:01:26.349
These columns, for example,
you see a rebar showing that the

01:01:26.349 --> 01:01:31.270
splice was done not at [inaudible]
height as we often would like to see,

01:01:31.270 --> 01:01:36.090
but rather at the
beam-column level.

01:01:36.090 --> 01:01:43.130
You see no stirrups near the
beam-column joint and so on.

01:01:43.130 --> 01:01:49.480
This is the neighboring structure –
a three-story building with a soft story

01:01:49.480 --> 01:01:53.820
created by the parking garage.
But there were several of these, again,

01:01:53.820 --> 01:02:00.540
highlighting how, you know, not only
in those residential construction

01:02:00.540 --> 01:02:04.910
of single-family houses that I showed
you at the beginning, but it also,

01:02:04.910 --> 01:02:11.450
in these multi-units, where there’s
clearly engineering, architecture, and

01:02:11.450 --> 01:02:17.920
good firms that were involved, still they
saw significant amount of damage.

01:02:17.920 --> 01:02:23.970
These are some close-up views of the
damage of the shear failures that took

01:02:23.970 --> 01:02:31.460
place, and it’s evident the danger in the
structure as a result of these failures.

01:02:34.080 --> 01:02:36.640
Moving on to bridges.

01:02:36.640 --> 01:02:43.860
This is the bridge that is
instrumented in the city of Ponce.

01:02:43.860 --> 01:02:50.280
It’s an intersection of the main –
or one of the main highways –

01:02:50.280 --> 01:02:52.980
toll highways
in the island.

01:02:52.980 --> 01:02:58.560
And an intersection that connects the
downtown with the Port of Ponce.

01:02:58.560 --> 01:03:01.460
That’s where this
bridge is located.

01:03:01.460 --> 01:03:07.280
And it’s instrumented by the
University of Puerto Rico in Mayagüez.

01:03:07.280 --> 01:03:13.020
And these are some images that –
one of the instruments.

01:03:13.020 --> 01:03:18.460
And so there’s sensors
also located over here.

01:03:18.470 --> 01:03:22.790
And this structure
in general behaved very well.

01:03:22.790 --> 01:03:27.930
We saw relatively little evidence
of motion and deformations

01:03:27.930 --> 01:03:33.240
in this structure.
With the exception of some

01:03:33.240 --> 01:03:40.030
small diaphragm elements that
are trying to prevent the twist

01:03:40.030 --> 01:03:44.920
and provide lateral torsional
resistance to these [inaudible] beams.

01:03:44.920 --> 01:03:49.600
And several of those – or, I would
say most of them suffer some damage.

01:03:49.620 --> 01:03:55.420
Here you see some of these little
elements that I – that I was referring to.

01:03:55.420 --> 01:03:58.800
And there were
several along the span.

01:03:58.800 --> 01:04:02.420
You can see here it’s
fairly long-span bridges.

01:04:02.420 --> 01:04:06.640
And that’s where
damage occurred.

01:04:06.640 --> 01:04:11.800
The motion recorded at
this place was about 0.2 g.

01:04:11.800 --> 01:04:15.390
And, as I mentioned before,
in the nearby toll plaza,

01:04:15.390 --> 01:04:17.680
a little bit higher – 0.24.

01:04:17.680 --> 01:04:24.720
This is another view of the bridge.
[audio garbled] at the beam.

01:04:24.730 --> 01:04:29.680
Very similar to what you see in
older bridges here in California.

01:04:29.680 --> 01:04:36.210
For example, on Highway 101
here on the Bay Area, you see many

01:04:36.210 --> 01:04:41.050
bridges that are very similar to this.
This is an example of that damage

01:04:41.050 --> 01:04:45.370
that I was referring to.
You know, it doesn’t really create

01:04:45.370 --> 01:04:51.010
a big damage, but some of these chunks
of concrete that came off landed on

01:04:51.010 --> 01:04:59.369
the roadway and certainly those pose
a hazard to the people driving

01:04:59.369 --> 01:05:05.380
underneath if they were to be driving
at the moment of the earthquake.

01:05:05.380 --> 01:05:12.980
This is an image I took from the roof of
a condominium building with a nice

01:05:12.980 --> 01:05:20.180
view of the city of Ponce where you see,
you know, these small hills, but fairly

01:05:20.180 --> 01:05:29.579
flat city that it’s – it originally had
very good – it was an agriculture area

01:05:29.580 --> 01:05:36.980
with very good agricultural soil.
But now the city is just growing.

01:05:36.980 --> 01:05:42.200
But, as I mentioned before, many
of these sites are Site Class E.

01:05:42.200 --> 01:05:46.270
This viaduct over here, it’s similar
to the one that I just showed you.

01:05:46.270 --> 01:05:50.600
This one is not instrumented.
But we also carefully documented

01:05:50.600 --> 01:05:56.119
the performance of it.
In recent years, in California,

01:05:56.120 --> 01:06:01.480
once heard the chief engineer of
Caltrans say that the best joint –

01:06:01.480 --> 01:06:05.760
you know, there are many different
types of joints that we use in bridges.

01:06:05.760 --> 01:06:12.240
And he said the best joint is a no joint.
Meaning that Caltrans, over the years,

01:06:12.240 --> 01:06:16.369
starting from February 1971
San Fernando earthquake,

01:06:16.369 --> 01:06:19.720
we’ve learned that there’s
a lot of problems with joints,

01:06:19.720 --> 01:06:23.940
relative motions, pounding.
If the – if the supports are

01:06:23.950 --> 01:06:28.410
not large enough, that the beams
come off from the support and so on.

01:06:28.410 --> 01:06:32.750
Many of that has been retrofitted,
but in recent bridges, we tend to

01:06:32.750 --> 01:06:40.839
avoid or put at least as possible joints.
So this is sort of older designs.

01:06:40.839 --> 01:06:45.140
And it’s sort of reflected of, you know,
not having experienced large

01:06:45.140 --> 01:06:51.370
earthquakes for a hundred years.
And perhaps not following

01:06:51.370 --> 01:06:55.010
so closely some of the things
we do here in California.

01:06:55.010 --> 01:06:59.780
There you see, with arrows,
I’m pointing to the – to the joints.

01:07:01.940 --> 01:07:06.960
And similar to the retrofit that was
done in the ’80s in California,

01:07:06.970 --> 01:07:13.450
many of these – we saw some
evidence of steel cables to

01:07:13.450 --> 01:07:19.440
prevent the beams
coming off from the supports.

01:07:19.440 --> 01:07:23.660
And some of that worked
fairly well in this event.

01:07:23.660 --> 01:07:27.660
But in general, we saw little
evidence of pounding.

01:07:27.660 --> 01:07:33.980
And this is the bridge from underneath.
There you see the retrofit in

01:07:33.980 --> 01:07:38.720
all of these locations.
These sort of V-shaped steel cables.

01:07:38.720 --> 01:07:45.680
And the main damage that we
documented in this structure was,

01:07:45.680 --> 01:07:49.680
again, damage in some of
these elements preventing

01:07:49.680 --> 01:07:56.640
lateral torsional motion
in these – in these beams.

01:07:56.640 --> 01:08:02.080
But also, in some of the shear keys,
that basically transmit the inertia

01:08:02.080 --> 01:08:07.230
forces that are generated mainly
on the road surface, and where most

01:08:07.230 --> 01:08:10.480
of the mass – and they bring
it down to the [inaudible].

01:08:10.480 --> 01:08:12.500
And that’s done through
these shear keys.

01:08:12.500 --> 01:08:17.370
And most of the shear
keys were sheared off.

01:08:17.370 --> 01:08:21.690
Meaning that they didn’t
have enough shear capacity.

01:08:21.690 --> 01:08:27.270
But fortunately, the vertical
carrying capacity, it’s provided

01:08:27.270 --> 01:08:30.760
mainly by the beams.
And this prevented the

01:08:30.760 --> 01:08:34.949
lateral motion to – you know,
some deformation obviously

01:08:34.949 --> 01:08:38.790
took place to produce this failure,
but it was small enough not to

01:08:38.790 --> 01:08:42.560
cause problems, and there
was no partial collapse.

01:08:42.560 --> 01:08:45.739
And actually,
as you saw in that image,

01:08:45.739 --> 01:08:53.940
the bridge was not closed, and traffic
was still running through the viaduct.

01:08:53.940 --> 01:08:57.969
There you see other examples
of damage in the shear keys.

01:08:57.969 --> 01:09:06.860
And in all of this, it also created a lot of
interesting new residents on the bridge.

01:09:06.860 --> 01:09:12.529
There were a lot of pigeons who
now have their house next to this –

01:09:12.529 --> 01:09:17.839
to the shear keys.
Other examples of bridges we visited.

01:09:17.839 --> 01:09:28.549
This is an important bridge
that crosses the main toll bridge

01:09:28.549 --> 01:09:32.270
that runs in the south
in this part of the island.

01:09:32.270 --> 01:09:38.960
And it has some rocker bearings.
It’s supported on these rocker bearings.

01:09:38.960 --> 01:09:42.770
And I’ll show you some details of that.
There was evidence of soil

01:09:42.770 --> 01:09:48.049
deformations in the abutments.
And some motion in the supports.

01:09:48.049 --> 01:09:56.700
So here you see the vents and
cast-in-place superstructure.

01:09:56.700 --> 01:10:00.690
And I’ll show you some details
of the rocker bearings whose

01:10:00.690 --> 01:10:05.170
main function is to transmit the
vertical load but allow some small

01:10:05.170 --> 01:10:14.120
lateral deformation produced by thermal 
stresses from changes in temperature.

01:10:14.120 --> 01:10:17.780
And they basically – from their name,
they rock back and forth

01:10:17.790 --> 01:10:21.800
and they allow this deformation.
But those – especially on their

01:10:21.800 --> 01:10:26.280
larger seismic deformations,
they don’t work very well.

01:10:26.280 --> 01:10:30.160
And they may have problems.
So, in this case, you see the

01:10:30.170 --> 01:10:35.780
typical view of how these were done.
So it’s essentially a very thick

01:10:35.780 --> 01:10:41.980
rectangular steel plate that is
able to rock when you impose

01:10:41.980 --> 01:10:43.850
some lateral deformations.

01:10:43.850 --> 01:10:49.370
So these deformations, say,
are in the order of 5 millimeters or so,

01:10:49.370 --> 01:10:53.350
there’s absolutely no problem.
But, in this case, I estimate that

01:10:53.350 --> 01:10:57.739
something as little as
10 millimeters or half an inch

01:10:57.739 --> 01:11:00.060
would start causing
more severe problems.

01:11:00.060 --> 01:11:06.140
The other is they work sort of
conceptually well under longitudinal

01:11:06.140 --> 01:11:11.420
deformations that are orthogonal
or perpendicular to the plate,

01:11:11.420 --> 01:11:15.580
but they don’t work correctly
in the plane of the plate

01:11:15.580 --> 01:11:19.730
and certainly not under
torsional deformations.

01:11:19.730 --> 01:11:26.020
So this often manifests, or gives
you trouble, at the abutments.

01:11:26.020 --> 01:11:32.800
And the abutments usually will suffer
a lot of damage from pounding.

01:11:32.800 --> 01:11:36.860
Here you see some of that.

01:11:36.860 --> 01:11:41.260
But some of the rocker bearings
underneath, they can suffer a lot more.

01:11:41.270 --> 01:11:45.110
In particular, this one, we were
very careful when we went

01:11:45.110 --> 01:11:49.480
underneath the bridge. Because this
was, you know, very close to go.

01:11:49.480 --> 01:11:52.260
And told my group, I said,
you know, just be ready.

01:11:52.260 --> 01:11:58.480
If this comes down, you know, it’s not
going to go farther than these 4 inches.

01:11:58.480 --> 01:12:03.719
But make sure that your hard hat
is lower than 4 inches

01:12:03.720 --> 01:12:09.100
from those beams in case
we experience a strong aftershock.

01:12:10.160 --> 01:12:15.000
This is another example.
This is an important bridge that

01:12:15.000 --> 01:12:21.190
essentially exits the main toll road
and gives access to – is the main

01:12:21.190 --> 01:12:23.620
access to the city of Guayanilla.
[small child heard in background]

01:12:23.620 --> 01:12:30.230
It goes above this river.
There was some damage here

01:12:30.230 --> 01:12:35.500
as a result of Hurricane Maria.
[background quiet again]

01:12:35.500 --> 01:12:38.020
But in this earthquake,
we saw some damage.

01:12:38.020 --> 01:12:40.830
On the left abutment,
the bridge suffered major damage.

01:12:40.830 --> 01:12:45.300
As a matter of fact, when we got there,
it was already being demolished.

01:12:45.300 --> 01:12:50.180
And on the – on the right, we saw some
evidence of liquefaction at the base of

01:12:50.180 --> 01:12:58.280
these piers as well as part of the – of the
viaduct that gives access to the bridge.

01:12:59.500 --> 01:13:03.460
Very similar to some of the other
bridges that I showed you, there

01:13:03.460 --> 01:13:09.420
was significant amount of damage
concentrated on the shear keys.

01:13:09.420 --> 01:13:14.880
And almost all of the shear keys
exhibited this type of damage.

01:13:14.880 --> 01:13:17.730
Here I’m just showing
you some examples.

01:13:17.730 --> 01:13:22.030
These shear keys, I would say they
were done, you know, with fairly large

01:13:22.030 --> 01:13:27.780
dimensions, good reinforcement,
good confinement, as you see

01:13:27.780 --> 01:13:32.010
in some of these images.
And this is not an old bridge,

01:13:32.010 --> 01:13:36.500
and still, it suffered damage.
Again, on the back of the envelope,

01:13:36.500 --> 01:13:40.460
you can estimate the shear capacity
of some of these, and you can

01:13:40.460 --> 01:13:45.340
corroborate that it’s very large.
And you can, you know, essentially

01:13:45.340 --> 01:13:50.670
visualize the large inertial forces that
are generated in these structures that

01:13:50.670 --> 01:13:57.200
very often exceed by far some of the
forces for which they were designed for.

01:13:57.200 --> 01:14:05.280
And the – something that
I teach in my – to my students

01:14:05.280 --> 01:14:09.290
is that the forces don’t really
come from this design spectra,

01:14:09.290 --> 01:14:11.170
but they really come
from the deformation.

01:14:11.170 --> 01:14:14.300
They’re restoring forces
that the structure –

01:14:14.300 --> 01:14:19.180
they’re generating in the structure.
There’s no equivalent static loads

01:14:19.190 --> 01:14:23.040
or dynamic loads that are being
applied laterally, but rather,

01:14:23.040 --> 01:14:28.040
these are internal forces that
are generated as a result of the

01:14:28.040 --> 01:14:31.400
deformations in the structure.
So it’s all about estimating

01:14:31.400 --> 01:14:34.460
those deformations.
And if you impose those deformations

01:14:34.460 --> 01:14:39.830
on this very stiff element, the result is
you generate gigantic forces that very

01:14:39.830 --> 01:14:44.410
often are going to be much larger
than then ones we designed them for.

01:14:44.410 --> 01:14:47.040
Here is some
evidence of pounding.

01:14:47.040 --> 01:14:51.660
And some evidence of plastic
hinging in the top of piers.

01:14:51.660 --> 01:14:57.900
Again, illustrating very good-
quality concrete, good detailing,

01:14:57.900 --> 01:15:01.340
excellent confining with
helicoidal reinforcement.

01:15:01.340 --> 01:15:07.420
And this is what, you know,
you would expect to see in these –

01:15:07.430 --> 01:15:12.340
in these kind of events.
But unfortunately, in the abutment

01:15:12.340 --> 01:15:18.200
did not prevent a portion of
the bridge to be closed.

01:15:19.620 --> 01:15:24.360
Moving on to more bridges.
This is the viaduct in Mayagüez

01:15:24.360 --> 01:15:28.440
that I told you that
it was instrumented.

01:15:28.440 --> 01:15:33.540
Unfortunately, the sensors on
the structure did not function.

01:15:35.940 --> 01:15:39.590
The main person that, you know,
was behind instrumentation and

01:15:39.590 --> 01:15:43.880
the maintenance of the – of the –
of this instrumentation unfortunately

01:15:43.880 --> 01:15:50.840
passed away. And perhaps
partly of that – as a result of that,

01:15:50.840 --> 01:15:57.440
the instruments did not work,
which would have been very valuable.

01:15:57.440 --> 01:16:00.900
But fortunately, the free-field
instrument at this location did work.

01:16:00.900 --> 01:16:04.140
And that’s where
this 0.19 g was recorded.

01:16:04.140 --> 01:16:08.420
So there are two viaducts at this
location – a new and an older one.

01:16:08.420 --> 01:16:12.920
And you see, you know,
clearly the difference in diameter

01:16:12.930 --> 01:16:15.930
of the old piers
versus the new ones.

01:16:15.930 --> 01:16:20.670
There was some slight damage
on the new bridge, but the heavy

01:16:20.670 --> 01:16:25.680
structural damage occurred in some
of the vents in the old bridge.

01:16:26.580 --> 01:16:31.300
And here you see a little bit of
the difference between the two.

01:16:31.300 --> 01:16:35.800
And I’ll show you some images
of the type of damage.

01:16:35.800 --> 01:16:40.840
This was the pier that saw
the largest damage of shear failure,

01:16:40.840 --> 01:16:45.710
as you see there. Pretty severe.
These kind of failures, again,

01:16:45.710 --> 01:16:50.260
may put in – reduce the vertical
carrying capacity of the bridge.

01:16:50.260 --> 01:16:54.720
So that’s why the
bridge was closed.

01:16:57.200 --> 01:17:03.520
But similar damage occurred,
or at least a little bit less,

01:17:03.530 --> 01:17:07.390
but, you know, with careful inspection,
you would see the initiation

01:17:07.390 --> 01:17:10.960
of shear failure in many
of these bridge piers.

01:17:12.600 --> 01:17:16.820
This damage led to many bridge
closures and traffic disruptions.

01:17:16.820 --> 01:17:23.640
In the case of this main toll highway
bridge, they were very lucky that,

01:17:23.640 --> 01:17:28.970
in most locations, there was sort of
a local non-toll road that would run

01:17:28.970 --> 01:17:33.120
in parallel, or approximately in parallel,
such that people could use that

01:17:33.120 --> 01:17:41.020
other road instead of the main road.
But there was one location just west

01:17:41.020 --> 01:17:44.640
of Ponce where there
were some landslides,

01:17:44.640 --> 01:17:51.040
and there was no alternate route there.
And there were some complete closures

01:17:51.040 --> 01:17:54.910
of the highway for many, many hours.
And we were there –

01:17:54.910 --> 01:18:00.489
they were still working on it.
But what we did was to try to

01:18:00.489 --> 01:18:06.060
go there in hours where we
were expecting less traffic.

01:18:06.060 --> 01:18:11.060
But it took almost a
week to clear that area.

01:18:11.060 --> 01:18:16.040
And it just highlights the
importance of – you know,

01:18:16.040 --> 01:18:21.100
that it’s not just about avoiding
collapse, but many of these bridges,

01:18:21.100 --> 01:18:25.530
we need to study, you know,
alternate routes and so on.

01:18:25.530 --> 01:18:28.130
And, based on those,
really decide the level of

01:18:28.130 --> 01:18:31.390
performance that they should have.
And, in many of these, the level of

01:18:31.390 --> 01:18:35.590
performance should be that they
should allow – continue to work,

01:18:35.590 --> 01:18:41.420
especially if there’s no alternate route.
Because this is very important for first

01:18:41.420 --> 01:18:49.080
responders, but even for the rest of
the population to move to safer –

01:18:49.080 --> 01:18:58.360
to move to shelters, to have their food
and supplies, that they reach them.

01:18:59.680 --> 01:19:01.100
I just have a few more slides.

01:19:01.100 --> 01:19:05.920
I wanted to show you some of the
structures that are instrumented there.

01:19:05.920 --> 01:19:08.400
These are three buildings
that are instrumented.

01:19:08.400 --> 01:19:11.280
But there are a few others.

01:19:11.280 --> 01:19:14.320
First two are in San Juan.
And we visit them.

01:19:14.330 --> 01:19:20.420
And the – and the third one is in the city
of Mayagüez – this condominium tower.

01:19:20.420 --> 01:19:22.300
The first one,
it’s a government building.

01:19:22.300 --> 01:19:25.280
The other two are
condominium towers.

01:19:25.280 --> 01:19:28.560
I’ll show you a few
details of this structure.

01:19:28.570 --> 01:19:31.739
There are two almost
identical towers at this location,

01:19:31.739 --> 01:19:34.940
and only one of
them is instrumented.

01:19:34.940 --> 01:19:38.460
It’s only instrumented
at the base and at the roof.

01:19:38.460 --> 01:19:44.100
And, of course, we would like to
see more sensors and so on, but still,

01:19:44.110 --> 01:19:47.570
having the availability of these
few sensors allows to understand

01:19:47.570 --> 01:19:52.110
a lot of things
about this structure.

01:19:52.110 --> 01:19:55.230
There you see that
layout of the sensors.

01:19:55.230 --> 01:20:00.740
Has a triaxial at the – at the
basement level and then several ...

01:20:00.740 --> 01:20:03.420
[audio cuts out]

01:20:03.420 --> 01:20:06.920
... to measure longitudinal motion,
and then two in the transfer direction

01:20:06.920 --> 01:20:11.960
that allow you to
capture torsional response.

01:20:11.960 --> 01:20:14.111
We’ve been working in
cooperation with the

01:20:14.111 --> 01:20:19.940
University of Puerto Rico-Mayagüez
and with USGS mainly with

01:20:19.940 --> 01:20:23.610
Mehmet Celebi and José Antonio
Martinez-Cruzado and his team

01:20:23.610 --> 01:20:28.360
on the system identification
of these buildings.

01:20:28.360 --> 01:20:32.940
And here I’m just showing you
comparisons of recorded and computer

01:20:32.940 --> 01:20:38.440
response that we’ve been computing
in this – in this building.

01:20:38.440 --> 01:20:42.750
And these are relative displacements
relative to the basement.

01:20:42.750 --> 01:20:49.960
And then these are absolute
accelerations where you see interesting

01:20:49.960 --> 01:20:56.330
beating happening and higher frequency
at the initiation of the motion.

01:20:56.330 --> 01:21:01.800
Here you see the arrival
of the P waves, the S waves.

01:21:01.800 --> 01:21:06.740
Far more participation of higher modes
in these 15 seconds than in the rest.

01:21:06.750 --> 01:21:12.290
And these are 1% floor spectra
illustrating how we’ve been able to

01:21:12.290 --> 01:21:16.429
capture the response with
some of our identified models.

01:21:16.429 --> 01:21:18.520
These are some of the
dynamic properties that we’ve

01:21:18.520 --> 01:21:23.530
been identifying in recent years.
Some of you have been very interesting

01:21:23.530 --> 01:21:29.900
to learn more about energy dissipation
and damping in structures. And this kind

01:21:29.900 --> 01:21:36.540
of instrumentation helps us to further
improve our understanding of this.

01:21:36.540 --> 01:21:39.940
This is the structure –
the condominium in Mayagüez.

01:21:39.940 --> 01:21:42.900
Very nicely instrumented.

01:21:42.900 --> 01:21:48.740
The people at the University of
Puerto Rico-Mayagüez allow us

01:21:48.740 --> 01:21:53.980
through their contacts to have access
to this structure and visit it

01:21:53.980 --> 01:22:00.140
and have access to the records,
which are publicly available at the –

01:22:00.140 --> 01:22:05.060
at the StrongMotionCenter.org
website.

01:22:05.060 --> 01:22:14.520
And, after this earthquake, USGS has
produced this very nice sensor map with

01:22:14.530 --> 01:22:20.520
the location of all the instrumentation
that allow us to study the structure.

01:22:20.520 --> 01:22:24.080
And these are some of the results
that have been produced by

01:22:24.080 --> 01:22:30.960
Dr. Celebi from the structure.
And we – independently done the

01:22:30.960 --> 01:22:35.810
system ID, and we have come to almost
identical dynamic properties, both in

01:22:35.810 --> 01:22:43.290
terms of frequencies and damping
ratios, including torsional response.

01:22:43.290 --> 01:22:47.969
So with this, you know,
I would like to wrap up and just

01:22:47.969 --> 01:22:52.880
with a few – leave you with a
few observations and conclusions.

01:22:52.880 --> 01:23:00.290
I believe that the occurrence of the
sequence provided some sort of,

01:23:00.290 --> 01:23:08.960
you know, benefit, especially the fact
that there was that 5.8 on January 6,

01:23:08.960 --> 01:23:14.140
as I mentioned, played a major role
in having many of those damaged

01:23:14.140 --> 01:23:17.350
structures – or, even if they were
not damaged, people simply

01:23:17.350 --> 01:23:22.719
not living in them – and that
resulted what I would describe

01:23:22.720 --> 01:23:27.400
as an outlier on the statistics
of collapse-to-fatality ratios.

01:23:27.400 --> 01:23:32.920
And usually we see far more fatalities
for that number of collapses that we saw

01:23:32.929 --> 01:23:39.420
in this earthquake. So that’s, you know,
a piece of good news from this event.

01:23:39.420 --> 01:23:45.430
I believe that both the free-field and the
instrument records that were obtained,

01:23:45.430 --> 01:23:49.420
and that continue to be obtained,
are extremely valuable, not only

01:23:49.420 --> 01:23:54.830
for earthquake resistance design in
the island, but for many other locations,

01:23:54.830 --> 01:23:59.929
in particular, very valuable for further
understanding of structures located

01:23:59.929 --> 01:24:08.640
on soft soil – so these Site Class E –
that are very tough to – and give rise

01:24:08.640 --> 01:24:11.739
to very large amplifications,
in particular, very large

01:24:11.740 --> 01:24:14.800
displacement and
deformation demands.

01:24:16.000 --> 01:24:19.040
The largest damage occurred
in residential construction.

01:24:19.040 --> 01:24:29.090
And it was really heart-breaking to see
so many families living outside and –

01:24:29.090 --> 01:24:36.140
you know, in the initial days
with no water, no food, no power.

01:24:36.140 --> 01:24:41.460
And especially after what
they have suffered after Maria.

01:24:41.460 --> 01:24:45.360
And to basically see
this happening again.

01:24:45.360 --> 01:24:51.420
And, as we were talking to people
in the island, you know, it was very –

01:24:51.420 --> 01:24:57.230
I visited many place after earthquakes,
and it was very evident that it was

01:24:57.230 --> 01:25:04.800
sort of like a generalized post-traumatic
syndrome kind of situation in which

01:25:04.800 --> 01:25:09.760
people would obviously contrast
their experience with hurricanes.

01:25:09.760 --> 01:25:12.440
And people would tell you, you know,
with hurricanes, we more or less

01:25:12.440 --> 01:25:15.710
know when it’s going to hit us.
With this thing, we don’t.

01:25:15.710 --> 01:25:19.440
And it’s – and the other
thing is that, with hurricanes,

01:25:19.440 --> 01:25:22.980
once the eye goes
over the island, that’s it.

01:25:22.980 --> 01:25:24.940
Whereas, with this, you know,
it’s, like, we don’t know

01:25:24.941 --> 01:25:27.480
when it’s going to be over.
And we just keep feeling

01:25:27.480 --> 01:25:29.750
these strong aftershocks.
We have no idea when we’re

01:25:29.750 --> 01:25:33.130
going to be able to go back
to our houses, when we’re going to

01:25:33.130 --> 01:25:36.610
be safe, if our houses
are safe, and so on.

01:25:36.610 --> 01:25:40.400
So I strongly believe that one
of the big lessons from this

01:25:40.400 --> 01:25:43.360
is to pay more attention
to the level of performance

01:25:43.360 --> 01:25:46.360
for which we design
residential construction.

01:25:46.360 --> 01:25:50.440
There has been many, many examples
of the thousands of people that are

01:25:50.440 --> 01:25:56.699
displaced from the residences.
And I believe that we need to find ways

01:25:56.699 --> 01:26:00.290
of designing for better performance,
such as what we now refer to as

01:26:00.290 --> 01:26:03.900
functional recovery, in particular,
what in San Francisco we call shelter

01:26:03.900 --> 01:26:07.870
in place, that, even if we allow
some damage to take place,

01:26:07.870 --> 01:26:11.320
it’s a smaller amount of damage
that allows the residents to

01:26:11.320 --> 01:26:16.380
remain in their houses in
the days after the earthquake.

01:26:16.380 --> 01:26:21.730
And I think this is, again,
one of the big lessons from this event.

01:26:21.730 --> 01:26:25.840
And finally, something similar
in terms of functional recovery.

01:26:25.840 --> 01:26:27.800
It’s for highway bridges.

01:26:27.800 --> 01:26:31.980
And I was very involved in the
evaluation of damage to highway

01:26:31.980 --> 01:26:37.110
bridges after the October 17, 1999,
Loma Prieta earthquake here

01:26:37.110 --> 01:26:41.699
in the Bay Area. I did some study
with some of my classmates

01:26:41.699 --> 01:26:46.150
on the Cypress Street Viaduct.
And, to me, it was, you know,

01:26:46.150 --> 01:26:51.730
very revealing that there was
not really any – prior to that earthquake,

01:26:51.730 --> 01:26:56.210
there was no classification of the
importance of bridges, with exception

01:26:56.210 --> 01:27:00.630
of some of the major, you know,
suspension toll bridges.

01:27:00.630 --> 01:27:03.290
The rest of the bridges
had the same importance.

01:27:03.290 --> 01:27:08.920
And clearly, depending on the –
on the traffic, their location,

01:27:08.920 --> 01:27:14.600
the alternate and redundancy of the
network, they should be designed

01:27:14.600 --> 01:27:17.670
for different levels of performance.
And many of these, they should

01:27:17.670 --> 01:27:22.920
be designed not to – to remain
functional after earthquakes.

01:27:24.030 --> 01:27:28.100
You know, even if that means,
you know, reduced space or reduced

01:27:28.110 --> 01:27:34.150
volume of traffic. But allowing some
level of traffic is very important.

01:27:34.150 --> 01:27:36.900
And the last point that I –
that I mentioned and I would

01:27:36.900 --> 01:27:40.940
like to leave and that you all
remember from this presentation is the

01:27:40.940 --> 01:27:46.760
importance of initiating the structural
evaluations as soon as possible.

01:27:46.760 --> 01:27:50.950
We often think of other
things that are more important.

01:27:50.950 --> 01:27:55.760
You know, certainly, you know,
hospitals, medical attention, rescue

01:27:55.760 --> 01:28:00.820
in the case of collapses, and so on.
But equally important to initiate these

01:28:00.820 --> 01:28:06.260
structural evaluations as soon as
possible because the sooner we initiate

01:28:06.260 --> 01:28:12.140
these, they will allow thousands of
people to remain in their houses.

01:28:12.140 --> 01:28:17.570
And very often, what you see are people
that are not living in houses that they

01:28:17.570 --> 01:28:20.210
could be occupying, and therefore,
they’re taking the place of other

01:28:20.210 --> 01:28:23.350
people in the shelter that
they need it more than them.

01:28:23.350 --> 01:28:27.140
But, on the other hand, you have
people that are living in residences

01:28:27.140 --> 01:28:32.530
that they shouldn’t be living in.
And we need to sort of be better

01:28:32.530 --> 01:28:41.820
prepared in training the people and
have the organization to get this going.

01:28:41.820 --> 01:28:49.660
And fortunately, FEMA has done a great
job in improving this as a result of this.

01:28:49.660 --> 01:28:53.080
And they’re doing
a great job in the island.

01:28:53.080 --> 01:28:57.160
There’s a couple of reports of,
some of you want more information

01:28:57.179 --> 01:29:01.489
that StEER – this Structural
Extreme Event Reconnaissance

01:29:01.489 --> 01:29:05.760
organization that I’m proud
to be part of – produced.

01:29:05.760 --> 01:29:12.200
The first one on the left was
a Virtual Reconnaissance Report.

01:29:12.200 --> 01:29:17.290
This organization does virtual
reconnaissance, and they’ve been

01:29:17.290 --> 01:29:21.810
doing it for a long time, even before
this quarantine or before doing

01:29:21.810 --> 01:29:27.640
virtual everything was trendy.
We were already producing these ones.

01:29:27.640 --> 01:29:30.600
And we simply gather and organize
the information available from

01:29:30.600 --> 01:29:36.030
different sources but put them in the
same place in an organized way and

01:29:36.030 --> 01:29:41.670
gathering information for newspapers
and technical sources and whatnot.

01:29:41.670 --> 01:29:47.020
And then the Early Access
Reconnaissance Report that

01:29:47.020 --> 01:29:50.630
resulted form our visit there
that you see on the right.

01:29:50.630 --> 01:29:53.310
Both of them are publicly
available from different sources.

01:29:53.310 --> 01:29:58.630
You can download this from
the StEER – the DesignSafe website.

01:29:58.630 --> 01:30:01.730
Also from the Stanford
Blume Center and from the

01:30:01.730 --> 01:30:05.870
EERI Clearinghouse
for this event.

01:30:05.870 --> 01:30:09.690
And with that, I thank you
very much for your attention.

01:30:09.690 --> 01:30:15.820
And if you have some questions,
I’ll be happy to try to answer them.

01:30:18.020 --> 01:30:23.880
- Thank you very much.
Thank you to everyone for attending.

01:30:23.880 --> 01:30:27.770
I just wanted to let our speaker and
everyone else know that this was a very

01:30:27.770 --> 01:30:33.980
well-attended seminar that, at certain
points, we had up to 180 people on.

01:30:33.980 --> 01:30:41.780
And they came from as far away as
Puerto Rico, Mexico, even Japan.

01:30:41.780 --> 01:30:45.480
So this was pretty great.

01:30:45.480 --> 01:30:52.050
We have a question for Eduardo,
which is from one of our attendees.

01:30:52.050 --> 01:30:56.760
How important is multi-hazard planning
now in this era of multiple hazards?

01:30:57.340 --> 01:31:02.920
- I think it’s always important,
but, you know, if I – if I would say

01:31:02.920 --> 01:31:07.260
sort of like the poster
example of multi-hazard,

01:31:07.260 --> 01:31:09.460
it’s got to be the Caribbean.

01:31:09.460 --> 01:31:15.480
This became very clear after
I visited Port-au-Prince in 2010.

01:31:15.480 --> 01:31:21.290
But it reminded me again
on this trip to Puerto Rico.

01:31:21.290 --> 01:31:24.739
But there are many other
locations where this happens.

01:31:24.739 --> 01:31:29.260
Hawaii is another perfect example,
where you have tsunamis,

01:31:29.260 --> 01:31:34.480
volcanoes, earthquakes,
and hurricanes as well.

01:31:34.480 --> 01:31:40.010
And it’s very challenging because
very often what you need to protect

01:31:40.010 --> 01:31:46.630
for one comes – sort of
doesn’t help you for the other,

01:31:46.630 --> 01:31:50.760
especially with aspects related
to mass, as I mentioned.

01:31:51.680 --> 01:31:57.180
You know, one of the things – I had the
opportunity to visit the Port of Ponce

01:31:57.180 --> 01:32:03.440
and still document some of the damage
from Maria in some of the warehouses.

01:32:03.440 --> 01:32:10.260
And I was telling my colleagues
who teach steel structures – I was

01:32:10.260 --> 01:32:14.679
just taking – I took, I think, over
200 images from this – from this

01:32:14.679 --> 01:32:20.190
warehouse, which I sort of
refer to as the museum of buckling.

01:32:20.190 --> 01:32:25.870
And I think this [audio garbled]
Euler, you know, it was

01:32:25.870 --> 01:32:29.410
well-represented in this.
And it was just like seeing

01:32:29.410 --> 01:32:34.240
all his theories on buckling
represented in every diagonal,

01:32:34.240 --> 01:32:40.040
every element, of all these
trusses in this structure.

01:32:40.040 --> 01:32:44.860
And the amount of destruction
that took place in what otherwise

01:32:44.860 --> 01:32:49.220
looked like very strong and
well-designed steel trusses.

01:32:51.200 --> 01:32:57.120
- Great. Well, that seems to be it.
That wraps up our seminar today.

01:32:57.120 --> 01:33:02.060
Thank you, everyone, for attending.
Hope to see you again.

01:33:03.140 --> 01:33:05.360
- Thank you.
- Thank you, everyone.

01:33:05.360 --> 01:33:07.540
- Thank you.
- Thank you.

01:33:08.260 --> 01:33:11.720
[Silence]

01:33:11.720 --> 01:33:12.820
- Thank you.

01:33:14.180 --> 01:33:15.440
- Thank you.

01:33:15.780 --> 01:33:17.140
- Thank you.

01:33:17.140 --> 01:33:18.840
- Thank you from Puerto Rico.

01:33:18.840 --> 01:33:20.760
- Thank you.
- [inaudible]

01:33:21.240 --> 01:33:23.500
- Thank you from Ecuador.
- Thank you from Mexico.

01:33:24.140 --> 01:33:26.700
- Thank you, Professor Miranda.
See you.

01:33:28.400 --> 01:33:29.600
- You’re welcome.
- Thank you all.

01:33:29.600 --> 01:33:31.380
Wonderful job. Love it.
- Good seeing you all.

01:33:31.380 --> 01:33:32.140
- [inaudible]