Hello everyone and hello for the last time this is our very,
very, last session of the "Too Many Earthquake Anniversaries
edition."
Have we covered all the earthquakes?
No we have not.
So for this last session we have
asked everyone to submit their very favorite earthquake and the
very favorite lesson that they learned from each earthquake.
And we're going to do a rapid round- the-clock, round-robin of
people telling us what they learned from an earthquake.
And then we're gonna end with a little valedictory speech by
John Stewart telling us why we need to investigate earthquakes,
if we don't know that already.
But I think he knows all the good secrets.
So here we go with our last set of moderators, the wonderful
Lori Johnson and Mike Oskin. [Woohoo]
Good afternoon, everybody.
Im going to lead us off here welcoming you all to this
session.
Sarah just described it.
We have a potpourri of different earthquakes from the last 100
years and speakers. I will turn it over to my Co-moderator to
introduce the first speaker.
Thanks Mike.
Good afternoon everyone.
My name is Bob McPherson, and today I'd like to show you that
when we have large earthquakes near the Mendocino Triple
Junction they have a tendency to excite aftershocks along
features other than the initial slip plane.
And to show this, I'll present data from the 1992 magnitude 7.2
minutes Cape Mendocino earthquake.
Before I get to the story, I'd like to thank all of these
people here organizers listed alphabetically and also thank
John Grindle for operating the buttons and controls for this
meeting and of course the moderators for this session.
So thank you all for your efforts to putting on this
workshop.
This is a screen capture showing an uplifted wavecut marine
platform that was uplifted out of the surf zone after this
earthquake.
So the outline of my talk is shown over here.
I'm going to introduce the setting and show map views and
cross sections to support the argument that features are
reactivated after a large earthquakes and can make for
confusion.
And then apply the lesson to the Honeydew earthquake, which I
think has been misinterpreted.
So geographic setting here's False Cape, here's Cape
Mendocino, the concavity of the Mattole River going around Punta
Gorda down towards Shelter Cove where the San Andreas comes
ashore.
And one thing that you need to know is here comes the Mendocino
fault, the boundary between the Pacific and the Gorda plate, and
it ends about right here.
And then picking up the San Andreas in 19O6 rupture and
projecting it upwards to here.
I have now drawn the corner of the Pacific plate, so the
Mendocino fault doesn't extend beyond the corner
here is important information.
So here's the Honeydew earthquake, which I'm going to
apply the lesson to
and here's the '72 that ruptured toward the coast.
Also important to note is this is the area of the coast that
went up and right.
here was a 1.7g acceleration at McNutt Gulch.
Alright, so I just drew the corner of the Pacific Plate and
now I've removed it in this cartoon.
that's discussed in the FOP guidebook.
Anyway, a depth here.
The '92 about 12 km ruptured towards the coast and
upward along this slip plane, again lifting the coast and
causing strong accelerations along the coast.
Here's the response in the Gorda Plate in the cartoon shown by
a right-lateral vertical fault in the Gorda plate.
One other thing to note is as the Gorda plate descends or the
southern Juan de Fuca descends, this is the boundary between
Pacific and the Gorda plate, the very southern edge of the
subduction zone.
It's at a depth of about 17 km beneath the slip
plain.
And so you have the Mendocino fault here and then you have a
wedge in North America above it, which is going to be important
consideration.
So one other thing is these marine terraces shown here in
this image.
So the coast was uplifted from here down to Punta Gorda in the
distance.
And these terraces are evidence that this type of block movement
may have been occurring throughout whole of the
Holocene.
And one last point is here's the Anthony Lomax's relocations of
of earthquakes in the region and you can see the Gorda Plate
descending.
Here's the '92 slip plane,
and what I want to show on this is that these yellows and green
colors show that it has been reactivated in recent
earthquakes near the Trumbull Junction.
Alright, this data is was done by
Mike Pasyanos and the green represents 0 to 10 km
depth.
The red near the epicenter of the '92 and then it ruptured to
the coast,
and so this area is the slip patch corroborated by a campaign
GPS done by Mike Lisowski and Mark Murray.
And and then the response to that slip was two aftershocks and
one of them shown in red that are in blue that represent Gorda
plate vertical faults long right- lateral along a NW trend.
And over here in this inset of relocations, you can
see that these features have grown over time and they're
cutting the fabric of the Gordo Plate, which is
interesting in itself.
Alright, to show you a cross section.
So again, here's the map view I just showed you in the cartoon
for reference, this vertical line here, everything over here
is Pacific Plate
and this horizontal line, this is North American plate above
it, and this is Gorda plate beneath it.
So this vertical lineation here represents the Mendocino fault
at depth.
This blob represents activity in the wedge here above the
Mendocino fault.
So you have a fault above a fault.
Here's the slip area and we're looking out to the ocean,
so up dip and then here's these lineations seen in the North
American Plate.
So there was quite a bit of activity in the Gorda Plate and
all these other features.
So the lesson learned is that when you have an earthquake, it
can excite and look at the activity here and here.
You can excite other features with aftershocks that are
related to the slip, but confuse the interpretation of where the
slip occurred.
And so you need corroborative evidence.
And I would suggest that field evidence is one of the strongest
corroborative evidence.
Here's the Honeydew earthquake that I've spoke about,
and notice that the aftershocks of the Honeydew earthquake are
all to the West or offshore.
So the honeydew earthquake activated the
Mendocino fault and the future slip plane of 1992.
And so some people have suggested this is where the slip
occurred.
I would suggest to you that this is where the slip occurred and
this banana slug feature here is the result of a field
investigation of strong shaking and so this is the
interpretation.
It ruptured at depth and the nose of the hanging wall failed much
like shown in James Brune foam rubber models in the San
Fernando earthquake and such. The strong motion evidence was
displaced boulders in Honeydew Creek.
Here's a socket.
This cobble went up in the air and landed.
Here's a socket being pointed to and this cobble went up in the
air and is upside down.
So again the idea is this is strong evidence that this is the
case
the slip occurred at depth and ruptured upward to the east.
So in conclusion, when you're looking at the Mendocino Triple
Junction, be careful of using just aftershocks to infer slip.
You need other evidence such as now we have broadband's and
continuous GPS and of course field evidence.
Field reconnaissance is very important.
Thank you very much.
Thanks, Bob, for that really excellent talk.
This is really fascinating.
And of course, I want to talk about the Humboldt
earthquakes in 2022.
So we'll get to that in the questions.
Our next talk though is from Sue Hough, also with the Earthquake
Hazards Program at the USGS.
And her topic will be insights from the the one big lesson or
critical lesson from the Northridge earthquake.
Hello, thank you for tuning in and thank you to the organizers
for allowing 10 minutes to talk about a southern California
earthquake that hit the big 30 this year just a couple
weeks ago, the 1994 Northridge, California earthquake.
So Northridge had long-term impacts and in so many different
ways it impacted the building codes and construction
practices.
It led to retrofits of bridges and overpasses.
And within our field it really spurred the development of
seismic monitoring networks, broadband networks, real-time
systems and elements of data products
that are now very familiar.
If you look back at what happened at the time, science
really was different 30 years ago.
The initial overview publication was spearheaded by Lucy Jones.
It came out nine months later, presented some basic overview
results including some of the aftershock relocations.
It showed PGA values for about 200 free-filled stations that
recorded 1%g or higher
at the time.
That really was a landmark strong motion data set.
The ground motion map from that paper is shown here.
If you look closely there are some triangles there bend PGA
values and there is some other information on the map.
Well, around this time people were realizing that
moving towards a broadband seismic monitoring network would
allow networks to go from determining magnitude and
epicenter or hypocenter to actually mapping out the
distribution of ground motions.
And so that as things move forward, it was a project that
Dave Wald spearheaded to develop what became the ShakeMap system
that's now very familiar.
And around the same time ShakeMap's little sister Did You Feel
It? is a online system to collect user reports of earthquakes.
I'm going to get back to that in a minute.
So seismology has come so far in 30 years.
I wanted to take one of my 10 minutes to show this
animation, which was put together by Rob Graves (USGS).
So this shows predictions of shaking in a complicated 3D
velocity structure.
It's not a research grade simulation.
It's up to 1 hz.
But it's really fascinating to watch.
If you haven't seen it already, you can watch the
propagation effects in the northern LA basin.
You can see this amplification that was in the area of the I-10
collapsed as well as any number of other effects.
So if you haven't seen it, it's online.
I would encourage you to to go and play with it, but I'm gonna
move on.
Oops, not play it again and talk about the impact of the
Northridge earthquake on macroseismology.
Macrseismology is defined to mean the effects of earthquakes,
shaking on people, and the built environment, and so this is a
nice set of thumbnail illustrations that Remy Bossu's
group in France put together.
It shows the range of effects pictorially from Did I feel
something all the way to extreme damage and you're
thinking, wait a minute macroseismology, that's ancient and
it goes back to Robert Mallett in the 19th
century putting together early isoseismal maps.
In fact, it goes back even earlier than that.
So macroseismology has continued through the 20th
century, largely focused on historical earthquakes.
If you don't have any instrumental data,
macroseismology is is pretty much all you have.
But it continued through the 20th century for earthquakes, as
they happened putting together these intensity maps.
When Northridge happened, Jim Dewey led a project to do the
intensity survey.
They sent out 610 mail questionnaires to post offices,
54 to fire and police stations.
They got a 75% return rate, which is impressive.
They use those questionnaires to assign intensities manually.
It's essentially expert opinion and traditionally that's done.
People assign whole number intensities, 5, 6, 7, so forth.
Sometimes people would assign a range of intermediate values.
Well, following that, Lori Dengler teamed up with Jim Dewey
to cast a wider net with telephone surveys to about 6,000
adults and households.
They used the standard questionnaire.
Did you feel it?
How did you react all the way up to was there damage?
And they could have rolled up their sleeves and assigned
intensity values,
but they decided to use each question and turn it into an
index that they could treat numerically.
So the way this goes, they defined these indices.
Some of the answers lend themselves to fractions.
Did people feel the earthquake?
What percentage?
Some of them they used to define ranges of indices from 0 to
3 or 0 to 5, and then they put these terms together in
a clever way with scaling to define a community weighted sum.
And from that community weighted sum they determined community
decimal intensities that matched the intensities that were
assigned with expert opinion, Well, this really was the
landmark contribution.
This little equation brings macroseismology into the 21st
century, potentially into the big data era because it's
scalable.
You're not rolling up your sleeves to assign intensity
values, you're using an algorithm, and so you can
collect any number of questionnaires and analyze them
easily and objectively.
So that's at the stage very quickly for the Did You Feel It?
system, Dave Wall, Vince Quitoriano with Lori and Jim
developed the system to collect the report and determine
intensities.
I think it succeeded beyond wildest expectations.
This map was put together a few years
ago showing the maximum intensity values across the U.S.
over 20 years.
This information has been used for myriad applications
for ground motion investigations to early warning
systems.
I wanted to take a a quick detour to a historical event,
the 1886 Charleston earthquake.
We have a quite good intensity map.
This was Rossi Ferrell intensities for that earthquake
put together by Clarence Dutton and his his colleagues.
They were actually using a forerunner of the standard
questionnaire.
It was a USGS circular way back in 1886.
But there is an impressive compilation of of macroseismic
information for this earthquake.
So I went back to that, used it to assign ratified Mercalli
intensities, these black dots.
So there's a lot going on this panel.
There's some predicted intensities using the NGA East
relationships, but there's also red dots.
What are the red dots?
Well, because the information is so detailed, you can actually
use some of the accounts to feed the information into the Did you
Feel it?
algorithm and you end up with Did You Feel It? intensities and
it turns out that they match quite nicely with the values
that you assign subjectively. So these sets opens the door
to a did they feel it scale.
There's some issues here that are interesting that I don't
have time to get into.
I wanna come back and end with Northridge.
So for the anniversary we there were a number of activities,
mostly public facing to commemorate the event.
And the centerpiece of those efforts was asking the public if
they felt the earthquake.
So did you feel it was was developed in 99 but it can
collect reports for earthquakes that happened earlier.
People come back to the system.
A lot of people that done that before we started this, but we
started asking people if they felt it, please come in and tell
us and contribute to this
map and and we've gotten a a a pretty good response to that.
So we we put out calls via the media and social media.
There was a tweet that went out in Spanish because we're hoping
to catch cast a wider net and then the QR code.
If you can get your phone out.
I think there's 30 seconds left in my 10 minutes.
This QR code, if you were in the region, should take you to the
questionnaire to fill out your report for the Northridge earthquake
So I will
stop recording when my 10 minutes are up.
Thank you again to the organizers.
Getting my QR code there.
Thank you Sue for that great talk.
Next up is David Schwartz, who's going to be talking about the
Trans Alaska pipeline and the 2002 earthquake rupture.
in the one lesson from that take it away.
Hi everyone.
My name is David Schwartz.
I'm a scientist emeritus at the USGS.
And my example of a lesson learned from an earthquake, derise
from the magnitude 7.9 2002 Denali fault earthquake in South
Central Alaska.
It has critical implications for defining or characterizing fault
displacement across infrastructure like pipelines.
And in this case it was the Trans Alaska pipeline.
And this is of particular interest to me because in 1973,
I was a member of the fault study group for the pipeline and
I had the chance to go back after the 2002 event to map the
fault.
And as Yogi Bear said, "it's like deja vu all over again."
So what you're looking at on this slide is the rupture from
the 2002 earthquake along the Denali.
It propagated onto the Tachunda and these are aftershocks.
The earthquake or the rupture was 341km long with a
maximum displacement of 8.8 meters.
And on this chart, you can see how it compares with other
similar size shallow crustal strike-slip events that have
occurred historically.
It's right in there.
In the bottom part, you're looking at a distribution of
slip or offset along the rupture.
The Trans Alaska pipeline is right here.
And in these two little slides, you can see the rupture through
glacial ice.
It was 90km of that.
This hadn't happened before that we know of.
And in the bottom there's a 7m offset in alluvial deposits.
OK, this is the Trans Alaska Pipeline, extending
from Prudhoe Bay down to Valdez.
It was first proposed in 1969 to the Department of Interior.
It created a lot of questions, environmental and engineering.
The USGS in Menlo Park was heavily involved in this and
they were really questions of what would it do to the
permafrost, how would rivers be crossed?
Well, how would it affect wildlife migration like Caribou
and lastly earthquakes.
So these zones with a Richter zone, as you see, these are
zones developed by the USGS with the maximum expected earthquake
to be used in design.
The pipeline was authorized in '73.
It was constructed between '74 and '77.
It was almost 1,300 kilometers long and cost $8 billion, which
included the pump stations and the terminal at Valdez.
At the time it was constructed it carried 27% of U.S. daily oil
and today it carries 13%.
So you get some feeling for what the pipeline looked like and
what some of the issues were.
In 1973, a group was put together, a group of geologists
to fly the pipeline route and look for evidence of act of
faulting along its length.
This is the group that was headed up by Lloyd Cluff from
Woodward Clyde Consultants and really his second in command was
Burt Slemmons from the University of Nevada at Reno.
You may recognize some of the people, Gary Carver who became
chair at Humboldt State and many of you may have worked with Gary
or taking classes.
This guy in the yellow parker is Kerry Sieh, a young Kerry C, before
he went to Caltech to start his PhD.
And this guy right here, long hair and beard, is yours truly
from New York City.
It was a fantastic group of geologists.
One of the things we needed to do was to trace where the Denali
fault crossed the pipeline, and that was a problem.
We were able to see the fault on land, and the red line
represents the 2002 rupture.
But then there was the Delta River and there were soft
sediments, fluvial deposits from the Delta River, and then to the
east of the pipeline.
This whole area had been modified during the Alaskan
Little Ice Age between the 1300s and the middle 1800s, so there
was no expression of young faulting.
So there were fundamental questions raised.
Where does the fault cross the proposed pipeline route?
How much slip to accommodate in a design?
Because there were no data on the amount of slip from prior
earthquakes and actually how to design.
So this was the group of pipeline gurus that were put
together for the offset.
Lloyd Cluff from Woodward, Clyde; Burt Slemmons, Nevada,
Reno; and Clarence Allen from Caltech became part of this.
And even though there were no data, these guys had a lot
of experience.
They had looked at the 1906 rupture.
They had looked at the 1939 rupture in Turkey.
They had looked at other long strikes that faults.
So they had a pretty good feeling that with a fault like
the Denali, what type of offset to expect.
And then for the design, it was put together by Nate Newmark
from the University of Illinois and Bill Hall from the
University of Illinois and they came up with a very
innovative design for offset and shaking.
So the pipeline offset design, we didn't know where the Denali
fault crossed it.
So it was projected and there was a 600m wide corridor of
potential slip that was used in the design.
The consultants recommended 30 feet to the pipeline company
based on other earthquakes on other faults, and Alyeska, of
course, went smaller.
They designed for 20ft right lateral and 5ft vertical.
Here is a slide showing again the 2002 rupture in red.
The fault was projected from here in 1973.
This is the yellow zone, which is the projected corridor.
These features were mapped in 1973, but they were not part of
the faulting.
And you'll note that the pipeline crosses the very
southern end of this corridor for design.
And this is the pipeline and this is where it crosses the
Denali fault.
It was on supports coming into the zone.
These take heat from the pipe and pump it out and cool the
surface below it.
And then the pipeline itself sits on these steel sliders.
And these sliders are anchored with teflon shoes and this
allows the pipe to move back and forth in a fault displacement or
in shaking.
And the fault rupture was here at the South end of this zone of
design. So the 2002 rupture. It ruptured.
The rupture occurred only 36m from the South end of the
design corridor and all you can say is "Phew!"
Alyeska designed for 20ft or 6.1m of right-lateral and
5ft or 1.5m of vertical.
And the 2002 rupture was 5.8m of right-lateral and 1.6m
of vertical with the north side up.
This was just what the design ordered.
And what you can see here on the left is the pipeline prior to
the earthquake, the rupture, and I'll point out that it was
configured like this to allow for compression as a strike-slip
rupture went through it.
And on the right-side you can see the pipeline after the
earthquake and the yellow line is the pre-earthquake
construction.
So you could see how the pipeline was compressed and
bent.
So lessons learned, and I would say maybe learned again, is that
you can engineer for large fault displacement, but it requires
innovation, it requires experience, especially when you
don't have data on the amount of slip.
It takes into account uncertainty.
You have to account for uncertainty in the design.
And then there's serendipity.
There were two things.
If the rupture had occurred a little further South, the pipe
would have broken.
If the 8.8m of maximum slip occurred at the pipeline,
the pipe would have broken.
In the end, there was no black oil on white snow.
Thank you, David.
I have so many ideas and questions here.
I'm sure others do as well.
Let's keep moving forward so we can get to the questions.
Next is Anne Wine and Sarah McBride, both of the USGS and
they're going to talk about the Canterbury earthquake sequence.
Hello, One earthquake sequence.
The Canterbury earthquake sequence.
One opportunity to learn about long-term communications of
aftershock forecasts.
I am Anne Wine with the Western Geographic Science Center, USGS.
This research is with Sarah McBride in the Earthquake
Science Center et al., New Zealand colleagues at GNS
Science and Massey University.
The Canterbury earthquake sequence in Alterra, New
Zealand, initiated September 4, 2010, the green star on the map.
The activity of the sequence made for a bumpy road
to recovery.
The number of earthquakes slowed down on the pink part of the
sequence and recovery was able to take hold, a year and a half
later.
The earthquake sequence is unfortunately an example of an
aftershock causing more damage than the mainshock due to its
urban location and energy directed towards the city.
On February 22nd, 2011, the shaken city of Christchurch
exhibited a large cloud of dust.
This damaging and fatal aftershock occurred more than
5 months after the mainshock.
Prior to the February Christchurch aftershock,
thousands of aftershocks were expected and forecasted by
GNS Science, but it was hard to get people's attention when
they had survived a magnitude 7 earthquake during the night in a
rural area,
remarkably well after the fatal Christchurch earthquake.
The forecast gained more traction.
For example, in May 2011, GNS scientists forecasted that a
magnitude 5 aftershock would almost certainly occur, and
there was a 1-3 chance of a magnitude 6 aftershock
within the next year.
You can see from the blue and pink sequences that both of
those earthquakes did occur that year.
Residents were literally shaken up and aftershocks were the
number one cause of stress.
Finally, the pink sequence was leveling off. Was the damaging
effects of the Canterbury earthquake sequence over four
years later.
Five years into the sequence, there was still about a 50% or
1-2 chance of a magnitude 5 aftershock within the next
year.
Would you be surprised if such an earthquake occurred?
And would you be prepared for it?
The 50% chance magnitude 5 earthquake did indeed occur on
Valentine's Day in 2016.
This time, dust rose up from the sun cliffs.
By this time, people felt safer because they felt fewer
earthquakes and they figured building risks had been removed
or strengthened.
However, they were little aware of the residual risks of Cliff
collapse.
Also, the population had changed.
Residents had been displaced from red zones and people new to
the city had arrived who had not lived through the Canterbury
earthquake sequence.
So the population had diverged on earthquake knowledge and
experience.
This brings me to our study that followed an earlier one in 2013.
Our research question was to understand the effects of time,
in other words, during an earthquake sequence, what
aftershock forecast information and communication needs can be
revealed from the investigation of long-term experiences, in
this case six years of experience.
At the time there was very little study of longitudinal
risk communication, just some related to volcanic unrest.
We held four workshops with 21 participants in public health
and Emergency Management roles and interested members of the
public.
We learned about surprise or not of the Valentine's Day
earthquake, how time dynamics affected behavior and
preparedness, trust in the science agency, knowledge and
information needs, risk, perceptions and living with
uncertainty.
And thirdly, we receive feedback on the utility of aftershock
forecast scenarios, as in the possibilities of the sequence
slowing down, of a bumpy recovery like Canterbury
earthquake sequence, and of the worst to come with another
earthquake of similar or larger size.
The case of the 2023 Turkey earthquake sequence. We gathered
three types of surprise about the Valentine's Day earthquake.
There were people who had heard and retained the concept of an
earthquake sequence with spikes of activity.
They claimed to not be surprised by the Valentine's Day
aftershock except for the uncertainty of the exact time,
location and size of it.
An outcome of the lack of surprise was associated with
underestimating communication needs and their public health
and Emergency Management roles.
Consequently, the amplification of the DNS science message did
not happen through the networks and affected populations were
alerted by the media report of cliff collapse and supporting
each other and making sense of the event.
Within a social media platform, there were people who had become
less attentive to earthquake risks and had moved on with
their lives.
This is known as psychological adaptation and you can relate to
it from your multi-year experience of the pandemic.
This group acknowledged that they had set themselves up for
surprise.
The third situation identified was people new to the area and
an experience with earthquakes and earthquake sequences.
They were surprised, scared, upset.
The combination of moving on with lives and new people to the
area was sort of associated with a lapse in preparedness or
atrophy and vigilance.
An example was that hospital response procedures that were a
well-oiled machine a few years earlier were not implemented.
Workshop participants recognized the need then to sustain the
coordination of earthquake communication across roles and
down the line to divergent and diverse populations.
When the rate of earthquakes and the environmental queue slowed
down, they wanted to look to the science agency to periodically
prompt them to exercise and stay prepared.
This assumes that the lead agency has established a main
trust with diverse audiences.
Certainly there was evidence among the participants that
trust had been gained and their words they had watched the
forecast come true earlier in the sequence.
It was also clear that five years later people were not
following the forecast or checking them after the
Valentine's Day earthquake.
What was apparent that the spikes of earthquake sequence
behavior is an enduring concept that reduced the surprise factor
and helped make sense of the damaging aftershock for those
learning about earthquake sequence behavior for the first
time.
The other point to note is that some participants were seeking
deeper and broader information about earthquake hazards as
their risk perception shifted to larger sources of earthquakes.
We received feedback that suggested more appealing and
useful aftershock scenarios could be created.
Participants largely endorsed three scenarios and to include a worst
case.
They wanted to know the science underpinning the three
possibilities of a slowing rate of earthquakes, a bumpy recovery
and the worst still to come.
Further, they endorse communicating the uncertainties.
However, to be useful they need more information about the
impacts, not unlike the recent wave of impact based weather
forecasts.
So thinking ahead on collaborations for impact based
aftershock forecast, we can involve people in this workshop.
Scenarios like HayWire go through the translation of an
earthquake sequence and to engineering and societal impacts
to help build that capacity and the relationships.
One thing that was striking about the feedback on
aftershock scenarios was the alignment with McKinsey &
Company pandemic scenarios, and we could think about alternative
presentations like this one. In conclusion one earthquake
sequence,
one opportunity to learn about long-term communication of
aftershock forecasts.
We explored surprise when the possible happens and associated
Behavior, other time dynamics and strategies for preparing for
and communicating about aftershocks in the long-term.
There were very few studies on long-term hazard and risk
communication when we started the study in 2016.
The pandemic has stimulated a lot more research and there are
parallels that we can continue to use to reinforce our findings
and I thank you all for your attention.
Thank you.
Great talk.
The Mendocino Junction area with present the 2022 Ferndale
earthquake and how it activated the subduction
interface.
The Mendocino Triple Junction in Northern California is one of
the most seismically active regions in the U.S.
So this is the story of how the fault systems in the subduction
zone off the Mendocino Triple Junction are intertwined, how
the intraslab 2022 magnitude 6.4 Ferndale earthquake
triggered post seismic slip on the seduction interface.
And I'd like to thank all my co-authors from various parts of
the USGS.
First, let me start with the punchline.
This is a really weird and also important earthquake.
This earthquake is weird because it doesn't fit in the standard
categories of subduction zone earthquakes.
It's not an intermediate depth earthquake.
It's not an outer rise earthquake.
It's not, at least initially,
it's not an interplate thrust earthquake, it's a strike-slip
earthquake within the shallow part of the subducting slab.
It's also an important earthquake because after this
event occurs, we see post seismic slip on the subduction
interface showing this connection between the fault
systems within the slab and on the seduction interface.
So we usually consider these different categories of
earthquakes separately.
But this earthquake demonstrates that they are sometimes
connected, and that's important because this megathrust is
capable of generating magnitude 9 class earthquakes.
So we really need to consider the possibility that slip within
the slab might lead to slip on the megathrust,
and going along with the session topic, this is the critical
lesson learned from this earthquake.
Mendocino Triple Junction is very active and in fact has a lot of
complex earthquakes that rupture multiple faults.
The most recent example of this before the Ferndale earthquake
occurred just one year earlier the 2021 Petrolia earthquake
sequence.
This sequence initiated with a magnitude 6.1 right-lateral
strike-slip earthquake offshore along the Mendocino Transform
fault.
This is the pink mechanism.
11 seconds later it triggered a left-lateral strike-slip
earthquake within the mantle of the selecting gorgeous slab.
That's the purple mechanism.
And now one year later, an earthquake occurred about 20km
to the northwest of the onshore 2021 event.
That's this teal mechanism, the the magnitude 6.4 Ferndale
earthquake,
that is the focus of this talk.
So I'm going to start by looking at
the seismicity of the magnitude 6.4.
We're going to use a waveform template based approach.
We start using 309 routinely catalogued earthquakes from the
Northern California Seismic Network catalogue spanning about
a month starting just before the earthquake.
From these we are able to detect and relocate more than 7,800
total events.
We relocate these using hypoDD and we also use the cross
correlation measurements to help constrain the focal mechanisms.
So here's a look at this earthquake sequence.
This is the magnitude 6.4 mainshock focal mechanism.
It shows the strike-slip left- lateral motion striking toward
the east northeast.
Here you can see the zone of aftershocks denoting this
rupture.
In fact, these left-lateral strike-slip faults within the
Gorda slab are well known and they're thought to be spreading
center normal faults that have been rotated and reactivated in
a left-lateral strike-slip sense and these help accommodate the
compression the north-south compression experienced by the
Gorda slab.
So we see a pretty complex distribution of aftershocks.
We do see this main alignment of events along this main left-
lateral strike-slip fault, but we also see subsidiary faults,
some of these apparently striking nearly northward that
also seem to have left-lateral strike-slip motion on them.
Furthermore, we see some normal faulting, particularly the
purple group here and the dark blue group here.
I should say this these right hand plots are a zoomed view of
the map view and cross section shown on the left.
We estimate the Coseismic slip distribution from the GNSS
displacements as well as modeling the seismic data, and
we find different answers depending on whether we
force the slip to be deep within the slab.
If we don't do that, the model wants to put considerable slip
within the upper part of the slab.
However, we don't really see aftershocks within the upper
plate.
The slip distribution in this model goes up to about 5km
depth, and this is an area where we've had earthquakes
and many aftershocks in the past.
However, we can force the slip to be down at slab depths, in
this case 15km or deeper, and we fit the data
almost as well.
So in this case we consider that this depth constrained inversion
is the more likely or more realistic slip distribution.
With slip primarily confined within the slab.
If we look at the postseismic motion, things get even more
interesting.
This plot is showing three different GPS stations.
There's a red box here corresponding to this plot in
the upper right and the two purple boxes showing these two
stations on the lower right.
If I focus on station P158 here, that's this bold purple box
shown in the map view, we can see that the motion is steady
for several months prior to the earthquake.
This is a one-year time period spanning the earthquake.
Then we see there's sudden eastward motion with the
mainshock, the Coseismic displacement there.
And then a really strange thing happens.
If we look at the period of about two months following the
earthquake, this station actually rebounds back to the
West recovering most of that Co- seismic offset.
Now sometimes we see post- seismic slip that continues the
motion seen coseismically and this would make sense if you
have after slip on that same fault.
But the fact that this motion reverses the Coseismic motion
is an indication that this slip is occurring on a different
fault and that fault is likely the Cascadia megathrust fault.
So this plot on the left is showing the slip
distribution that we estimate to fit this postseismic motion.
It does a quite a good job of explaining that motion, and it
has up to 4 cm of slip on the interface, primarily
south of the rupture.
This is also an area where the coupling on the subduction zone
transitions from highly coupled to the north of the rupture to
less highly coupled to the south of the rupture.
So you may have this situation where the southern
part is creeping, the northern part is locked and it's
essentially tearing the slab apart and this earthquake could
help accommodate that relative motion.
If we look at the Coulomb stress transfer from the mainshock
expected onto the megathrust, we see up to 200 kilopascals of
encouraging stress for a slip on the megathrust primarily south
of the rupture, consistent with the region where we see
coseismic motion.
Coincidentally, we also see an episodic tremor and slip event
that occurs down dip during this time period.
It initiates about two weeks after after the rupture, but is
probably unrelated.
To help visualize this motion, we made these cartoons.
The left plot is showing the coseismic motion.
Is this Crimson zone of left lateral strike slip motion
within the slab this kind of tearing motion within the slab
and then the plot on the right shows the postseismic motion,
the Blue Zone on the subduction interface that essentially
accommodates this relative motion within the slab.
You can think of this almost as like a buried surface rupture at
the surface of the subducting slab.
So in conclusion, our primary results, we find that
aftershocks are primarily confined within the uppermost
Gorda slab, probably on hydrated faults and they're
notably absent from the subduction interface itself.
Our preferred slip model has coseismic rupture confined within
the slab and we identified postseismic deformation that is well
modeled by up to 4cm of slip on the subduction
interface consistent with the modeled stress transfer from
the coseismic slip distribution.
The implications of this are even more important.
This sequence demonstrates potential for interactions
between these different types of subduction earthquakes that we
usually consider separately, in this case intraslab earthquakes
and slip on the interface.
So we really need to consider the possibility that intraslab
earthquakes could be potential triggers for slip on the
subduction interface.
Now in the case of the Ferndale earthquake, this slip on the
interface was aseismic slow postseismic motion, but it
could also be seismic.
And in fact, it's conceivable that the next megathrust
earthquake on the Cascadia subjection zone could be
initiated by slip within the slab.
Thanks very much.
Thanks so much, David.
That's really excellent and scary.
So we are now, as Sarah mentioned, we're gonna turn to
Jon Stewart, who's down in New Zealand to kind of bring us home
here.
I was thinking, John, just about all the reconnaissance that I
know you've done with the GEER Association, but also just of
all the earthquakes that this panel collectively have
investigated over time.
So I think we have even though none of us were here
for the 1923 Kanto earthquake, we certainly have hundreds of
years of collective experience in this panel.
And thanks.
And we'll listen to John's presentation now.
Greetings, I'm Jon Stewart, I'm glad to be with you here today.
I'm going to be speaking about the benefits and impacts of post
events reconnaissance.
I'm a professor in UCLA Samueli Engineering, a board member with
EERI and the board liaison to the Learning from Earthquakes
Program and a Co-Pi of the Geotechnical Extreme Events
Reconnaissance (GEER) association.
I'll be talking about two main themes here today.
The first has to do with kind of the technical impacts of
reconnaissance, how reconnaissance findings
facilitate research and
that research then is the basis for improvements in our
understanding of earthquake processes and its impact on
infrastructure.
The second part of the talk will be more human focused.
It's about how participation and reconnaissance teams has
profoundly impacted many young researchers and I will presents
comments from a few examples.
So when we think about the impacts of reconnaissance on our
practice as earthquake professionals, one of the things
that we see repeatedly is that when we go out and we look at
what actually has happened, we're surprised and we may then
move our research in an entirely new direction.
So there's many examples of this.
I'll talk about one here, which is steel construction.
So this is the frame of a steel building.
Steel frame buildings have been with us for a very long time and
prior to 1994 had been through many earthquakes successfully,
or at least much more successfully then masonry
structures and concrete structures, particularly older
concrete structures.
And so there was kind of a prevailing feeling that steel
structures were relatively good, more earthquake resistant and
more reliable.
What we found in the Northridge earthquake; however, once people
broke through walls and took a look at some of the beams and
columns, is that cracks were showing up, an example of which
is shown here.
And these cracks have significantly weakened the
structure, making it more vulnerable to collapse from
future earthquakes.
In fact, there's been quite a bit of speculation of how much
more duration from the Northridge earthquakes would
have brought some of these buildings down.
So this realization that steel frame buildings do in fact have
some of these vulnerabilities spurred research that went on
for quite a long time.
It was called the SAC Steel Project and it ultimately led to
understanding that these problems were related to certain
welding practices and newer practices were derived to try to
solve the problem.
Not everything we observe after an earthquake, of course, is a
great surprise.
Sometimes we see the things we might have expected to see, and
one example is shown here, where we've had liquefaction on
saturated grounds from fairly strong shaking, the Nigata
earthquake just because we might have expected
this does not mean, however, that it's not valuable, because
it is possible in many cases to take the information derived
from our reconnaissance along with some subsequent
investigation, and come up with case history data that is
directly employed within models that we use.
And liquefaction is one such case.
So we take observations like this one where liquefaction
happened along with other observations where it did not.
We do subsequent investigations.
This is the log of a boring where we can see different soil
types and different soil properties, including
penetration resistance.
We find the layer within this profile that might have been
most likely to have produced the liquefaction, and by combining
the observation with the soil profile, some information about
the ground shaking in the earthquake, we can develop a
data point like this one in green on the graph.
That data point represents that case history, and the value on
the Y axis is a loading parameter.
It's related to the strength of the shaking at that site during
that earthquake.
And what's on the X axis is a soil resistance parameter that's
coming from that boring log.
And so we can position different case histories within this space
and then we can draw a boundary line separating the solid dots,
which are liquefaction, from open circles, which are
non-liquefaction, and that then becomes the model.
So this is a good example of how observations from earthquakes,
even if they're expected, are still very useful for model
development.
Another type of use of case history data is for validation.
Now what we're talking about with validation is we,
engineers and engineering seismologists and so on, we
create models for a certain phenomenon, and sometimes these
models can be fairly involved mechanistic models or finite
element models.
And we're not really sure that these models are going to be
accurate.
So we want to do a comparison of our model predictions to
observations.
This is really essential because these physics based models are
always a simplification of reality.
And so whether they actually are effective or the range of
conditions over which they're effective is very important to
establish.
So one example of this, this is an example of landslides from
the Northridge earthquake.
This is a map prepared by Randy Jibson and his colleagues, where
the dark blotches on the map indicate locations of
landslides.
And then he took a mechanistic model for Newmark sliding block
displacements, predicted the level of displacement as colored
for that same region on this plot, and then was able to
compare where the model predicts accurately the actual locations
of landslide displacement.
And in that way, he was able to come up with relationships for
how much Newmark displacement would be predicting the
occurrence of landslides.
The second thing I'd like to talk about is how participation
in reconnaissance teams has impacted young researchers.
Certainly impacted me and virtually everybody I know
that's been on these missions.
As part of this, I reached out to a few people who've done this
for the first time in the last decade or so.
And I've organized their comments to kind of convey a bit
about what is the kind of impact that this can have on a young
person early in their career.
I'd like to start with Ashley Cabas Mijares.
She's a professor at NC State and she wrote to me that
participating in reconnaissance.
Raised my awareness about the disproportionate effects of
earthquakes on vulnerable communities, she added.
I became increasingly interested in disaster resilience research
with the focus on the intersection of social
vulnerability, hazards, and engineering.
Paolo Zimmaro is associate professor at the University of
Calabria was very involved in reconnaissance following the
2016 Central Italy earthquakes.
He wrote that reconnaissance activities gave me increased
awareness of our role as earthquake engineers towards the
community.
Our work can make a tangible impact and change lives.
My first-hand reconnaissance experiences became part of my
teaching materials.
Students are more engaged when learning that I was actually
involved in doing the data collection.
Chukwuemeka Nweke, assistant professor at USC, has been involved in the
Ridgecrest earthquake and the 2022 Taiwan earthquake.
He wrote that learning how to conduct a proper reconnaissance
clarified my perspective on what's important in reality
versus what we may think is important in our academic work.
And I've gained an appreciation for the perishable nature of
field performance data and the need for being timely in our
reconnaissance work.
Sean Ahdi, an engineering seismologist with AECom was
involved in the 2019 Ridgecrest earthquake.
He writes that seeing damage first-hand, speaking to people
and getting their perspectives is critical to doing good
reconnaissance.
Having discussions with locals who are truly scared while
trying to exercise appropriate restraint in our excitement
regarding our scientific endeavors provides a great
opportunity to learn appropriate science communication.
And we need to be cautious to not come across as big shots
that are swooping in to profit off the suffering of others.
We'll do a better job to improve our image in this regard.
So I really appreciate these comments from these folks who
I reached out to and I think that provides a nice perspective
on how reconnaissance has impacted their careers and
also some good advice for those to follow.
With that, I will wrap it up and I appreciate the opportunity to
share these thoughts with you today.
Thank you, John and thank you everybody for the great talks.
Now we're starting the discussion part of this last
session and Sarah has informed me that we can run over 4:00 if
we get excited and need that time.
If you'd like to ask a question or make a comment, please raise
your virtual hand using the raise hand button.
You can also ask questions using chat, but they might get missed.
It's much better to turn on your video and interact verbally.
And speakers, please also turn on your video during this
Q&A session.
I have a question.
I asked it in the chat, but I'm going to put one of the Dave's
on the spot here.
How did Alyeska justify not taking the design criteria full
face value?
Did they give any excuse whatsoever?
You know, I can't really.
They got lucky.
I was not involved in the discussions of the final design.
You knew you would have to ask Clarence or Burt or Lloyd.
Those were the three guys and very few of us peons who were
involved in the actual field mapping had any real say in the
design of the offset.
Okay.
Yeah, I was curious about that as well.
Oh, sorry, Mike.
I was going to say this worries me because if we get better at
our understanding of what we might forecast, that means we're
more likely to have the real value ignored.
[noise] Alyesco was you know just a
world unto itself and why they thought they
could only designed for a little over 6 m.,
I don't know, but that's a good question and I think that's
something maybe I will spend a little bit of time trying to
follow up on.
When I do, I'll let everybody know.
You know Dave if I may ask were those estimates of mean
or medium or an upper bound.
It was
a number.
You know there were just no real uncertainties put on
them.
You can imagine Burt and Lloyd and Clarence sitting around and
saying, hey, you know these other big faults
ruptured 10 m.
We'll use that as the design and beyond that, I can't,
go any further.
There were no other uncertainties.
It wasn't done the way statistically you would develop
a design today.
And it was seat of the pants.
Thank you.
I see we have some raised hands.
Yeah.
I was just gonna note there's a comment by Lori Dingler in the
top that Lloyd Cluff did get them to expand the zone.
So yeah, you know the we didn't know where the fault was.
And today there were any number of subsurface techniques
you could use to try and see where the fault was under that
relatively unconsolidated material.
But at the time there was just a lot of question marks.
And I will say that one thing that was not known at the time,
and I don't know how that would have changed the design.
But in 1912 there was a large earthquake South of the
Denali Range and Diane Dozer put M7.3-M7.4 on it and suggested it was
on the Denali fault.
After the 2002 earthquake, Gary Carver spent time looking at
trees along the location of the fault in the soft alluvium
to the west.
And some of the trees were split.
And he noticed that in those trees there was evidence of a
prior damage and the trees were cored and they were
dated and they came out in 1912.
So we didn't know at the time that there had been a large
earthquake that probably extended under the pipeline in
1912.
How that would have changed the design, I don't know, but there
really were, there were a lot of data that were not available at
the time that the pipeline was constructed and the design was
made.
It was amazingly innovative
design a pipeline that had never been designed to slide back and forth
and you know, in the end, maybe even if there was more
displacement, it would have been accommodated.
The pipe wasn't damaged, but the shoes that it was on, the
teflon shoes, a few of those almost came off the ends of
the steel sliders.
And finally, I just say that because the pipe was unbroken,
Alyeska reset it for its original design configuration
with the idea that another large event wouldn't occur for several
100 years and the pipe had a 50- year design lifeline.
So lot of serendipity across the board.
Thank you, David.
Let's see who is up next here.
Laura, did you have a question?
Oh, I just wanted to comment that I spent many hours talking
with Lloyd Cluff, oh probably 6-7 years ago,
and also Gary Carver.
And my understanding from Lloyd was that it wasn't a yes or no,
it was an incremental discussion and that Lloyd said they were
able to expand it particularly to the north to the edge where
the displacement actually occurred.
They didn't get everything they wanted, but they did managed
to capture the part that actually slipped.
That's just according to my recollection of talking with
both Lloyd and Gary.
Yeah, I would just say that the because it was really uncertain
where the fault was.
As I said, a projection was made from the west and that took into
account the variation in the strike of the fault itself.
And that 600m wide zone was really based on uncertainty in
the projection.
Now maybe behind closed doors they had decided to, you know,
expand it.
I just don't know.
And unfortunately, Lloyd has passed and we can't go back and
ask him that again.
Although knowing Lloyd, he may send an answer down.
I say we have a few more questions.
People raised hands.
I'm curious, just a question for one of our other speakers just
to sort of spread out the joy here.
Yeah, Gordon, you have a question for somebody else or is
it directed towards David?
I think he answered it.
Okay. Charles.
Yeah.
I this is just a comment for Jon Stewart. First of all, I want to
thank all the speaker's for a great Session. Jon?
Do you emphasize the value of reconnaissance to
young researchers?
I also just want to help like that.
Young practitioners and all the engineering firms went out of
each league, also dating gold and so on.
I'm among all firms.
I've always sent the younger engineers out when events occur
because it has a tremendous impact on their understanding of
important seismic design, and this point is worth making
across.
Many of the reconnaissance efforts are led by academic.
It's important that they also bring along their [indiscernible] and
practitioners and continue their education after the
graduation of the classroom. Thank you. Perry, turn your
camera on.
Oh yeah, I think, Oh, is it on?
Is it on now?
Oh, Okay. Whoops, A little bit.
Sorry about that.
I'm not sure who among the group could answer it, but I'm hoping
this is a wide enough swath, both yesterday and today.
I'm back to the fires again, because they seem to have such a
tremendous impact.
And if you're gonna be saving, I don't know it just seems like a
tremendous way to maybe do something about all this.
So what I what I was wondering was, is anyone aware of any
plans to go.
I mean one of Carl's main suggestions was to have
automatic cut-off valves for the gas perhaps PG&E
has a representative onboard here or if anyone has any industrial
connections or has been talking.
Are there plans to sort of think about this and address
some of those top two mitigation issues and I guess
the other one was the water but it seems to me that the
automatic shut off could be particularly valuable.
Yeah anyway. If there's some one from PG&E here they
should respond to that otherwise I can respond. Yeah this is
Jeff Bachhuber, I'll jump in on that.
We do have automatic shut-off valves at regular intervals on
our gas transmission lines.
One thing we're looking at because we keep getting asked
about is integrating earthquake early warning to shut-
off the gas systems.
But it's important not to have false positives because when we
shut-off parts of our gas system, it's a major effort for
gas and line inspections and relighting and such.
So when we do need to have control that's
automatically tripped, it's better to have a seismograph at
that control location and then set a trigger,
appropriate for the engineering design.
For our distribution system, we do have cut-off valves.
A lot of them are still manual, but on the transmission lines we
do have automated shut offs and they're typically triggered by a
drop in the flow velocity or an increase in the flow velocity
recording.
You actually have damage and a rupture or a split in the pipe.
And so it's a positive way.
Yeah, we had damage and it shuts it off.
Thank you.
Thanks so much for your answer.
Charlie, go ahead if I may.
Charlie you might turn off your video,
we're having trouble hearing you.
Let me.
Sorry, just a second.
Okay.
Can you hear me better now, I hope. Yeah, much better.
Okay.
Thank you.
Much better.
[noise]
Let me just speak to Jeff's points.
The shut offs in the transmission lines are spaced
many kilometers apart and as we saw in the 2010 San Bruno
explosion, the residual pressure will continue to feed a flare
for hours.
As he pointed out the distribution system shut offs
there are about maybe a dozen or 20 in San Francisco
for example.
They are manual and we saw in 1984 puncture of a
distribution line in downtown San Francisco near Embarcador
Center that valve was paved over and it took them over an
hour to find it.
So the ability to control the system after an
earthquake is actually quite inadequate.
Now it's my understanding and Jeff might comment on this that
I do know that previously PG&E replaced all their gas
meters with smart meters but without including a seismic shut
off.
They now have a pilot program I believe to examine the
efficacy of including a seismic shut off in the gas meters,
but it's a very small power program.
I just was involved in an effort in British Columbia to try and
get the Canadian insurance industry to try to get
the gas utility there to include a seismic gas shut off
device.
A seismic device in their gas meters which they were going to
replace wholesale, which they are replacing wholesale for the
same smart meter elimination of the meter reader job purpose and
they fought that tooth and nail and we failed.
On the other hand in Japan as Jeff knows well Tokyo
has 12,000 seismometer connected automatic shut off devices that
in their grid within the city that isolate the brakes within a
block or two.
And every customer in Japan about 20 million people
has a seismic device incorporated in the gas heater.
These were all switched out following Kobe earthquake.
So just like an early earthquake warning has been implemented 10
years earlier in Japan, actually 15 years earlier in Japan than
it has in the United States.
The safety for gas systems in Japan is decades ahead of what
it is in the United States.
Yeah.
Jeff.
Yeah, the Japanese definitely are on the cutting edge there.
A lot of the damage to gas pipelines occurs on the service
line, so on the customer side of the meters.
So I saw in the chat that mentioned that some folks have
installed those.
I actually have one on my house too.
And so you know, right after the meter, it's a ball valve that
typically drops down.
Those are really cheap.
That's a good way for customers to have some level of protection
feeding right into their house where it probably is the most
vulnerable part of the gas pipeline system.
Actually, Jeff, there's the most inefficient way to mitigate this
risk.
Yes.
Yeah.
I just want to move us on just because we're running out of time.
Well, if I can.
All right, fine.
So I can think.
Let me add one thing to that, which is Japan has
mandatory cut off valves;
they still have fires.
So it's not the only source of fires. Yeah that's
yet another challenge.
Absolutely.
I'd like to ask the question of both Bob and Dave Shelley about
the 1992 earthquake.
Do you think we had the more modern observations that of the
quake happened now that Bob you might reinterpret what's going
on about what faults were just lit up by aftershocks versus
maybe was a multi-fault rupture?
That's a good question.
I think in 1992 when we're going from analog to broadband,
you know of course there was no continuous GPS and so it was
campaign GPS that actually came up with a slip plane that
corroborated with the hypocenter locations and then you add to
That field
observations of strong shaking at the nose, of the hanging
wall.
You put all those together and it's fairly confident of the
slip plane.
So, yeah, now with David doing his wave led locations and such,
I don't think there's any problem now with the new
coverage and the earthquake early warning system.
And we're instrumented now a continuous GPS.
And you saw Dave's work, you know, interesting, I wanted to
make a comment, I've written some posters on our offshore
earthquakes and so we had 2005, 2010, 2014, and all of those
earthquakes moved the GPS stations on the surface of North
America.
So those are offshore earthquakes and they move
the stations through the megathrust through the surface.
And then you have what Dave just saw or documented that we
have triggering on the megathrust, which doesn't
surprise me at all.
I think the big question of the triggering of the Cascadia was
written by Goldfinger and his people about the 1906 triggers of
the Cascadia, you know where where you have a 8m slip coming
up through Shelter Cove and then the Coulomb stress projections
onto the surface initiate a megathrust event.
Dave could probably talk more on that, but I think these
intraplate earthquakes, it doesn't surprise me at all
because basically a little triangular piece moved under the
subduction zone.
So that doesn't surprise me, what Dave just documented.
Dave, do you think that earthquake would look more
complex from 1992 if we had 2022 observations?
Yeah, I'm sure it would, but it's complex enough even
with the 1992 observations.
So we would of course love to have more data for that.
But you know, Mendocino is just, a highly active area and
it's a really complicated area.
So it seems like the kind of place where we can look over a
relatively short period of time and kind of get an idea of
scenarios that may happen that we might not have thought of
otherwise.
You know, just another comment is the 2022 which we also have a
paper in the process.
It initiated the Mendocino fault. It initiated the wedge above
the Mendocino fault.
It initiated some of the right-lateral, these new
right-lateral that are cutting across. So these earthquakes
initiate many features in the area.
It is complicated.
Thank you Bob.
I wanted to give
Anne and Sarah a chance and
for folks to ask a question if they have one,
as well as Susan. I wanted to ask in particular
your work with the HayWired scenario especially the follow-
on work whether emergency managers in particular are
thinking more about aftershocks.
I know when we started the HayWired work back in the mid-
teens, many emergency management plans really always just had
sort of one earthquake scenario, a major event with very little
consideration of an aftershock sequence.
So curious what your observations have been and the
outreach you've been doing post- scenario.
Thanks for that.
PG&E, I think were the first users to run a exercise
including some aftershocks early on.
So that was great.
And most recently we've got the HayWire tool kit, which Mark
spoke to yesterday.
So there is a tool on aftershocks and afterslip and
then it's brought up periodically within some of the
other subjects that are offered for exercises.
So in our workshops, we've been bringing it up and having people
think about it.
David Wald, I think you had your hands up.
Yeah, unfortunately Jon Stewart snuck out.
I'm going to give him his question anyway, maybe you can
answer it.
And you know, we always learn things from the field and really
surprised, as Jon said, but you know, he talked about 1994 in
steel buildings and yet, you know, we had some pretty
extraordinary collapses in Mexico City in 1985.
So you know,
did we just ignore those because those were not our structures or
was that lesson never absorbed without steel
structures in 1985.
Actually I was there.
There was no steel structures that collapsed.
The steel structure, the high rise buildings that
collapsed Parte Loco and some of the others were all
reinforced concrete.
The Piño Suarez building was a 3 high
rise steel frame.
They did not collapse.
The columns buckled.
They were virtually on the edge of collapse,
but they did not collapse.
I'm looking at Astras's paper on steel structures collapsing,
Charlie.
Oh well,
I'll do my homework.
Which ones is named?
The
I don't.
The Piño Suarez.
Piño Suarez did not collapse.
Severely damaged, 21-story building collapsed and a 14-
story building collapse.
So that's pretty nice.
Really.
But they did not collapse.
Okay. [noise]
Yeah.
OK, Dave, I have a question for you.
Okay. Is there any consideration for
incorporating fire following into pager estimates?
No.
That's a really tough one.
I mean it's right there with tsunami where, you know,
the shaking's over and we're done.
You know the most of the problems over the damages done,
tsunami's going to come at some later time and that's an
evolving process. With fire following,
it's also an evolving process that is, as Charlie knows, it's
really, it's difficult to model and it's more really
observational.
I mean you got to pay attention to what's happening
on the street and that's what the new fire departments do.
Yeah.
So I think from a mitigation of planning perspective, it would
be better to have better models for scenario earthquakes so that
we can we can do that, but it's a tricky business
and we stick with shaking base damage which is still tricky but
still a little bit more viable.
I have a question for Sue.
It's really interesting to be able to use the historical
reports from Charleston.
How far back can we reliably go?
I mean, there's some really long earthquake records in, say,
Turkey and China, but the reports are really sparse and
from a very different era.
So yeah, I mean, there's the whole realm of of historical
seismology that depends on the history.
Japan, I mean, the history has to exist, written history.
And a lot of the native tribes in North America didn't have a
written language.
So they were around, but there there weren't any records that
we can find.
Ruth Ludwig's done some great work going back to to
transcribed oral histories to tease out some information about
Cascadia.
Really remarkable work.
It just depends on the country how far back the written records
go.
And then, you know, finding them.
1886 really is exceptional because of Clarence Dutton and
the report that was done on that earthquake is a remarkable
compilation of information.
If you go back to New Madrid or earlier earthquakes and you're
rooting around for newspaper articles for the most part.
May I mention that in the 1980's Muir Wood would develop
the catalog of British earthquakes going back over 1000
years by looking at not only the literature but also the damage
the churches in the UK or in Britain.
So it's similar thing and I enjoyed your presentation very
much soon.
Thank you.
Yeah, I mean the Britain, England has a long history.
Italy, Italy has a very active historical seismology community
with a long history.
I think with some of the work you really need to have
the language becomes an issue.
So it's not something like looking at the Chinese record,
it's not something that someone from the outside could could do.
So I wanted to check with everybody.
Is there any last questions for our speakers?
Thank you all for your participation.
I'm going to hand this off to Sarah.
Thank you so much to our speakers, our moderators, and our
wonderful, wonderful participants.
That was a great closing session and a lively discussion.
I hate to interrupt, but it is the end of the third day and I
feel like I should release everyone to the world.
But I want to say that we I need to interrupt you.
I've been instructed that I'm allowed to do that.
Okay.
Of course we will because we "otter" thank you for your
utterly important contributions as a fearless leader for
everybody in the workshop.
And thank you so much.
So everybody, a round of applause for Sarah and everybody
in the speakers and the and everybody who got engaged and
moderators.
But really, Sarah, thank you so much for putting this together.
And now I'm retreating politely so you can finish your
spill.
Thank you, Sarah.
No, thank you everyone.
You know, this is a group activity all the organizers do
with so much.
But also, you know, it's all of you being wonderful and
participating wonderfully that make the workshop.
So give you all, Give yourselves a big round of applause.
for Sarah.
So we learned climate change and how
hazards are gonna be more seasonal in the future as
climate becomes more extreme in its seasons.
We learned about the importance of different communications
methods and basic earthquake education.
And then, in fact, people may need basic earthquake education
to be able to take advantage of earthquake early warning.
We talked about the extinction of the passenger pigeons, which
I was not expecting us to do.
We made a lot of otter puns.
We managed to cause both an atmospheric river during a
climate change session and a a swarm on a creeping faultt during
a a creeping fault session.
So we're really, really powerful in a way that we weren't
expecting to be.
We've developed an important theory about earthquakes
happening in the years 4 and 9, except for the Triple Junction
where it's the years ending in 2.
And I think most importantly of all, I want to end with the
really, really important words that Christy Rose gave us
yesterday.
Trees are not weeds.
And I think that's it.
Thank you so much everyone.
Have a wonderful, wonderful time.
Till next year or actually until next month.
Come back March 4th through 5th for our community modeling
workshop.
More information to come.