Well, I hope everybody good lunch and a good dance break in there. Welcome back to the afternoon of the second day of the workshop
We are kind of approaching the halfway point. And now, Mr.
Bond, we return to our next session, during which Chris and Judy will lead us through a long series of monologues about Silicon Valley, during which I am sure you will not escape.
Judy, Christopher.
Thank you. I just wanted to start off by saying, this is a really exciting
series of talks that start from the general overview of the Santa Clara Valley in Silicon Valley by Carl Wentworth.
He's done a lot of really great work in the area.
And then with Carol Prentice talking about the effects of the 1906
and Loma Prieta earthquakes. A talk by Felipe Aron on using geomorphic tools to evaluate the uplift of the ranges on both sides of the valley, and then a talk by John Baldwin which is more specific
about the Silver Creek fault, which is a very interesting fault that we're learning a lot about.
So I'm Chris Hitchcock. I'm a geologist that's practicing in the area, and I'd like to hand it off to Judy to introduce herself.
I am Judy Zachariasen, and I am a geologist at the California Geological Survey and looking forward to the session.
So take it away guys.
I've been asked to talk about the Quaternary basins beneath the South San Francisco Bay in Santa Clara Valley.
There are actually two separated by a buried bedrock ridge.
The basins are bounded on the southwest, by the San Andreas fault, and it's associated
thrust system on the east side, the Foothills system and the Monte Vista thrust system.
And on the east side by the left-stepping Calaveras-Hayward fault system.
Underneath the Quaternary there are three older basins; Cupertino basin, partially overrun by the thrust
fault system here [pointing]; San Leandro basin here, one day it probably late Tertiary and the 40 kilometer long strike-slip Evergreen basin here [pointing].
The Quaternary deposits at the surface are relatively simple mostly are late Quaternary and pale yellow alluvian
and the pink notorious estuarine bay mud formed on the post-glacial sea level rise.
There are some older deposits most particularly for this story, the uplifted marine terraces here on the outer course, west of the San Andreas, and then also in San Francisco
underneath this dune field indicating uplift to San Francisco, as well.
There's also the Colma sand here, which is formed in the last interglacial and the Plio-Quaternary Marine Merced Formation here [pointing].
So if we move now to the Santa Clara Valley and schematic cross-section we see the Quaternary is just a thin skin.
Here we have the Monte Vista fault overriding Cupertino basin, and in the east
the deep strike-slip Evergreen basin, founded on the west by the Silver Creek fault.
In a little more detail now we're looking at Wells with the dots together with the three seismic reflection profiles here. Evergreen here, and here that's our source of subsurface control. Looking at that subsurface I will start with these two wells GUAD-CCOC which are
about 7 kilometers apart, and in those wells we can define the coarse fine layering, using the gamma log, the resistivity log, and the cores that we took while we were drilling.
Just to find a coarse fine layer in the coarse or in darker colors.
The fine grain set intervals are in this pale.
yellow, and there's a pattern to these course layering, and it's not random.
And to bring out that layering pattern I've designed a curve that I call a coarseness curve here in red, which is measuring the amount
Of coarse sediment in a 50 foot thick column, and then run the column down the well
result which we can say over here, the coarseness curves here in black define eight prominent coarse peaks running down the well to adapt to 300 meters.
And each of these major course peaks identifies a grouping of layers which are course at the bottom and fine at the top.
So we define a series of eight finding upward Sedimentary cycles or sequences. Placing the base of each cycle at the bottom of the bottom coarse layer like this, and although the wells a 7 kilometers of fart and guad apart, and clad is much finer
Grain section. These cyclic layers correlate very nicely
If we part, the depth of the base of these layers against time here measured, represented by the marine isotope curve, which shows us the the glacial ventilation variations.
We see a very simple, almost straight line relationship, which defines a subsidence rate of the basin of 0.4 millimeter/year, and it's not subsidence which provided the accommodation space in which these 8 cycles were preserved.
We conclude that we have
set of 8 finding upward Sedimentary cycles.
They're produced as a result of the climate variation
in each of these major climate cycles.
With that background in mind, with our full set of 125 wells, including a 100 water wells
what I've done mapped these 8 cycles around the whole basin and up onto the Nile's
cone here. In cross section then, looking north to southeast, we see but the layering is nearly horizontal, subparallel, flat to the
topographic surface actually. And the abundance of course material is least near the Bay here in greatest down in the center of the Santa Clara Basin.
So now we'll summarize this whole section, looking across here from the Moffett,
well-deep Moffett. Well, here across the Silver Creek fault to the Evergreen
well here. What we see are these 8 finding upward cycles come about 300 meters thick, underlined by a mid-Quaternary on conformity. Underlined that underlined by a finer grain section at maximum about 150 meters thick, amounts which we know very little.
Interestingly, however, the Evergreen Well, which is east of the Silver Creek fault the cyclic section is thinner.
This thinning is accomplished within the lower 3 cycles.
We can use all the well and reflection record information together with a large set of refraction surveys that were made by Hazelwood early in the history of the Earthquake Program
here to contour the basement in the Santa Clara Basin.
What we see is erosional topography dropping down from Dumbarton Ridge on the west side of the basin and Oak Hill on the south side to the edge of the Dumbarton Bay, at the Evergreen Basin. So the drainage system that eroded
this hole drained out through the Evergreen Basin, and must have gone out to the southeast to Monterey Bay before the [indiscernible] was closed by thrusting.
So now let's look at the Evergreen Basin founded on the west by the large Silver Creek fault thrust overriding it from the east, and underneath those thrusts, the fault we call Mt. Misery, which is present east side of that basin.
Look at how that basin formed early on we had a right-step between the Silver Creek fault and the early Hayward fault, and as that puller part basin grew, ultimately it was cut across more by a more efficient ruptured direction, we call that the Mt. Misery fault which
is right here, and most of the 175 kilometers of right-slip that has come up Calaveras fault into the East Bay has moved up on to this Mt. Misery fault.
Then, about 2 million years ago that system was reorganized
to a left-stepping system from an extended Calaveras fault to the Hayward fault, with the earthquakes moving in a very simple fashion, and in this constraining bin, then the thrusting developing and moving south across here the whole basin.
So if we look at a inflection profile right here, which images the evergreen basin to a depth of about 1 km, we identify as a shallow horizons
here by correlating with the Coyote Creek
Well. What we see is that here's the Silver Creek fault separating the Franciscan basement from the fill of the Evergreen Basin.
We see thrusts rampant flat structure here, indicating thrusts coming well out into the basin in the subsurface.
Down here above the tip of the Silver Creek fault we have an extraordinary feature, a structural sag, which we'll look at next.
So here, with a more realistic vertical exaggeration, we have this special sag or negative flower structure formed above the Silver Creek fault, and a shallow depth is about 700 meters wide, with an amplitude of 30 meters, formed both by bending, tilting,
and small fault-offs offsets, and although those offsets are small, they are sufficient to create a prominent groundwater barrier along the Silver Creek fault evident here in this InSAR image. Now, if we move to the east side of the basin, and look at these
thrusts we have a very interesting situation of thinning particular intervals here and here, against the rising fold underneath the thrust which seems to indicate that we're looking at episodic thrusting on a scale of hundreds of thousands of years. An interesting question here is whether this
Episodic thrusting is driven by similar behavior of the Calaveras
fault itself or whether we're looking at some controls within the local thrust system.
So now I want to turn to the northern basin.
Last year Andrei Sarna-Wojcicki wrote that after the Carquinez Strait was opened in about 630,000 years ago, drainage from the great Central Valley, could come through the Carquinez
Strait, and then down through the ancestral San Francisco Valley,
our stream system, as he called it, and out through the Colma gap. What I want to do is as think briefly about the formation of that ancient San Francisco Valley.
And do that by looking at the bottom, at the bedrock surface.
Here we have the sill at the Golden Gate at about 110 meters down below sea level, and then using wells that contouring takes that down through 200-250 meters.
Similarly on the south, Hazel was refraction work.
We can go through 152-250 leading down to about 300 meters
here in the center of the basin, and that information comes from this reflection
profile collected by Marlow, in which we see an unconformity of it's horizontal unconformity.
At about 300 meters, overlined by flat layering, and in the Quaternary section.
The other piece of information we have is bedrock sill in the Colma gap.
A cross-section by Doc Bonilla which the bedrock sill has a bottom at about 150 meters below sea level.
Well, if we put all this together, and the long cross section running through here, what we see is coming from Golden Gate
we come down the bottom of the basin at 300 meters controlled by those reflection profile.
Then up onto the Dumbarton Ridge, and the problem is, there's no outlet. Colma Gap is way up here.
The stream couldn't have run through that,
but what I suggest is just as here in the Santa Clara Basin, the drainage outlet was to the east and southeast, through the Evergreen Basin that would be here in the southern Basin, out here and across the Hayward fault, and then back into the Evergreen Basin
and then out down here. The final point I'd like to make is how did this space and to fill up what was the cause of the subsidence and the simplest explanation.
There are no faults, there are no cross-faults is one that Bob Jackson suggested long ago, and that is that we're looking at tilting. Tilting down from northwest to the southeast and that tilt angle for this 80 kilometer length
is much less than one degree. So it's imperceptible at any individual point.
Thank you.
Okay. That was an awesome talk. Thank you, Carl.
So next we have up Carol Prentice, talking about the effects of the 1906 and 1989 earthquakes in the southern Santa Cruz Mountains, and San Jose area.
Hi! Everybody! I'm Carol Prentice, and I'm going to just take a brief moment to thank Belle
Phillibosian for asking me to put this talk together in her email to me.
Belle said, well, we just never hear about what happened in San Jose or in the southern Santa Cruz Mountains in either the 1906 earthquake, or the 1989 earthquake, and would you be willing to give a talk about this at the Northern
California Workshop. It's been a lot of fun putting this talk together going back to the very early tastes of my career, and some of the earliest work that I did for the USGS.
So, thanks to Belle for giving me a good reason to put this talk together. It was a lot of fun.
Sources used for 1989 include newspapers and the many, many scientific publications that are out there, but especially the USGS Loma Prieta earthquake professional papers, which are just a veritable fire hose of information. For the 1906 earthquake
the State Earthquake Investigation Commission put out its report,
I just called it the Lawson report because it was spearheaded by Andrew Lawson, shown here in this photograph taken in 1901, without Andrew Lawson.
I don't think we would have any kind of coherent scientific study of this earthquake
really. I also spent a lot of time in both the Bancroft Library at UC
Berkeley and in the Green Library at Stanford, in the archives looking for archival material and correspondence, newspaper accounts, field notes, photographs, etc., etc., to help better understand the 1906 earthquake especially in the southern Santa
Cruz Mountains. Oh, and of course I had to go back and re-read my own papers from that time, which is always quite an adventure.
This is a Landsat image, just to help you get oriented.
This is part of the coast of northern California with hopefully some familiar place names to help you figure out where we are we're going to be talking about San Jose and the southern Santa Cruz mountains here.
The 1989 epicenter is shown in pink.
The, 1906 epicenter is shown in orange, and that red line marks the surface trace of the San Andreas fault.
So I've organized this talk so that after this very brief introduction we'll take a look at San Jose. First,
we'll look at 1989 damage ground failure, liquefaction.
Then we'll look at 1906 damage ground failure, liquorfaction.
Then we'll go to the southern Santa Cruz Mountains and do the same thing except instead of liquefaction, because we're up in the mountains
it's not really an issue. We'll take a look at fault surface rupture instead.
San Jose after the 1989 earthquake is exemplified by this building, which shows absolutely no damage.
People who were working in this building described
being very, very frightened by by the very strong shaking.
But after it was all over they were able to just calmly walk out of the building.
There was no damage, the San Jose Mercury news the day after the earthquake
had this to say, "the new day also confirmed that San Jose escaped from the quake with relatively minor damage."
Further down in that article, San Jose's two major trauma centers, San Jose Medical Center and Valley Medical Center reported no serious structural damage and were treating numerous patients for broken bones and abrasions suffered during the earthquake so people were definitely injured.
Mostly by things falling on them. But there was very little structural damage.
To the built environment that is underscored by this table, which appears in one of the Loma Prieta professional papers.
The highlighted row here shows San Jose, and it shows that they were only 8 red tagged residential
units in the entire city.
Ground failure liquefaction this is zoomed in to part of a map that was compiled and put together by
John Tinsley and others. I've circled the two places where they show liquefaction and ground failure near San Jose; 51d,
just says it's evidence of possible soil, liquefaction near an electoral power station; 51E evidence of probable liquefaction.
Both of these, by the way, are along the banks of the Guadalupe River.
San Jose, however, in 1906, was a much different story.
This is a view looking down South Second Street, you can see lots of building damage to multi-story masonry buildings.
Sort of the potpourri of damaged photos.
This is San Fernando Street. Here we have North Second Street.
With this building collapse, blocking the street, another building collapse.
Another building collapsed near Market and Post Street, and then this building, the facade collapsed on Santa Clara and First Street.
I like this picture of the St. Patrick's Cathedral, especially because in the background you can see these apparently undamaged wood frame structures.
Not all wood frame structures were undamaged. This is the Grant Grammar School, which collapsed completely.
This is a lovely old Victorian home that apparently came off its foundation.
And here we have a photograph showing that there were fires that started several fires started as a result of the earthquake, however, the water source was not cut off, so firefighters were able to very quickly put out
the fires and prevailing the kind of conflagration that we saw in San Francisco.
This excerpt from the Lawson report, I think very nicely sums up what happened in in San Jose that there were brick and stone buildings damaged.
Some wood frame homes damaged, and within San Jose City limits there were 19 deaths reported.
However, that's not the whole picture, because just outside of San Jose City limits there was this facility which was known as the great asylum for the insane in Agnews.
Agnews is now part of Santa Clara, but it's not very far from the San Jose City limits, and it suffered multiple collapses and at least a 112 people were killed at this sight a 101 patients and 11 staff members.
Liquefaction and ground failure. Yes, as evidenced by these lovely sand boils seen near Coyote Creek.
We're gonna take a look. Move on to the southern Santa Cruz
Mountains. Now, this is an aerial, oblique view showing where the San Andreas fault cuts through the southern Santa Cruz Mountains.
Here we're going to take a look first at 1989.
Looking at damage, ground failure, and this time fault surface
rupture, instead of liquefaction, and then do the same for 1906. Damage in the southern Sand Cruz Mountains typically looked like this.
It's a pretty sparsely inhabited area.
Lots of single family wood frame homes. Many of them did just find some of them, such as this one with a software story collapsed. Ground failure,
yes, there were some really big landslides. This is one of them that came down in blockbuster north bound lanes of Highway 17.
As it turned out, it was very fortunate that there were no cars on the road in these lanes at the time.
this landside came down. There were a lot of ground fractures up on Summit Ridge and Skyland Ridge.
This one in particular was of interest, because it has left-lateral displacement.
That was actually quite common. Many, many of these ground fractures.
This is Morrell Road, and we're going to talk about that again.
A little bit later. Here's another one of these interesting ground fractures up on Summit Ridge.
This is now more than a kilometer away from the San Andreas fault.
Was there surface rupture on the San Andreas fault?
No, there was not, but there were all of these great big, and very interesting ground fractures up on the ridge top now some of these had a component of left-lateral displacements, some of them right-lateral displacement, some of them were purely extensional and they were kind
of two different camps about what these big ground fractures up on Summit Ridge actually met. On one side of the story
We're a lot of people who say, well, these are just one big ground, shaking features
their official features. They don't have anything to do with the underlying tectonics.
And then there were people who came up with models suggesting that these were actually the surface manifestation of deep shear, across a shear zone beneath Summit Ridge.
So we thought that if we took a careful look at what happened in 1906, we might be able to shed some light on this.
Okay. So the southern Santa Cruz mountains in 1906;
yes, damage to single family homes such as this. One ground failure,
lots of very similar features to what we saw on Summit Ridge in 1989.
These great big ground fractures. This is the same location as that little ground fracture I showed you crossing Morrell Road with the left-lateral slip in 1989.
It's exactly the same place. But in 1906 it had a lot more of left-lateral displacement.
So very similar feature, but much bigger in 1906.
Here's another view of that same location showing the left-lateral offset of this fence.
Now in the Lawson Report this is actually said to be the Saint Andreas fault.
It's not. It's a half a kilometer away from the San Andreas fault.
It's got left. Lateral slip. And just in case you might think that these photographs were printed backwards, and really they're right. Lateral.
No, they were not printed backwards. I've been in the Bancroft Library.
I've examined the glass plate negatives. These were printed correctly
Well, it turns out that if you take all of the locations that are mentioned in wearings, we Lawson, about the ground rupture.
It was that report was made by a student named Gerald Waring.
What you'll find if you plot the locations that he mentions in his report on the oldest maps available for the area.
You'll see that he was hardly ever even on the San Andreas fault.
The astute observer will see that there is this one
loocation. This is the Rights Tunnel, where he actually was on the fault.
But all these other locations he was not. He really was nowhere near the fault.
Many of these locations he reported as default.
He reported right lateral offset across the fault at these locations that are not on the fault, and it's kind of important to recognize that the many of the locations were quote unquote, right-lateral fault the rupture was measured were actually not on the San Andreas
fault. This is a map that kind of summarizes all of this.
The
yellow dots show the locations where Gerald Waring said he was on the fault and measured right-lateral
Slip. You'll notice that only one of those was actually on the fault. And that's the Wright's tunnel.
I wish I had time to tell you the story of the Wright's Tunnel.
I really don't. I'm just about out of time here.
I will mention that our research into the archives and looking very carefully at the map of the Wright's Tunnel showed us several things.
One is that there was surface rupture in the Wright's tunnel.
There was 1.8 meters of surface rupture across the San Andreas fault.
It was distributed across a very narrow zone, most of it across a single fault
plane the rest of it across no more than a few 100 meters.
There was no broad zone of deformation that impacted the Wright's tunnel, and that tells us that in 1906,
all of those great big ground fractures up on Summit Ridge were, in fact, shallow, surficial features, and we think they were the same thing in 1989.
So I'm going to stop there and just summarize what we've seen here in San Jose in 1989.
Not much damage, not much ground failure, not much liquefaction, lots of damage in 1906 and yes, ground failure and liquefaction, 1989.
Sure damage in the southern Santa Cruz Mountains, ground failure for sure.
San Andreas surface rupture, no. In 1906, lots of damage.
Also up in the southern Santa Cruz mountains and lots of ground failure as well, including those mysterious big cracks up on Summit Ridge and Skyland Ridge.
San Andreas surface rupture, yes, probably. And I'll stop there.
Thanks.
Excellent talk. Thank you very much. So we are gonna move on to the next talk on the river structure
fault-bounded mountains, how they can be used to inform seismic hazard assessments specifically in the South Bay by Felipe Aron.
Good afternoon to everyone. On behalf of my co-authors,
we appreciate the invitation to participate in this workshop, to speak about our work recently published at GRL.
This Google Earth 3D view looking towards the Pacific Ocean shows about 60 kilometers long
section of about 1 kilometers high southern Santa Cruz Mountains or Sierra Azul, located in the North American block along the San Andreas plate boundary flanking the Santa Clara Valley.
As you can see, the activity of geologic faults promoting burning on motion of rocks produces uplift of the earth surface, which over geologic time and over thousands of earthquake cycles builds up mountain ranges. That relief is in turn carved by river
reverse, thanks to the action of climate forces counteracting the tectonic uplift.
Consequently, the incision pattern along mountain rivers should contain information about the past activity of the underlying relief generating faults, or study tests
this fundamental idea, integrating the topography with mechanical and erosional modeling to estimate the cruel of earthquake magnitude potential over time along crustal faults fundamental component to probabilistic seismic hazard assessments.
Two physical models are the key ingredients to our method.
First, we need a geomorphic model that describes the landscape evolution,
in this case the stream power law shown here by its integral form.
This equation predicts the elevation of all channel points along the river bed as a function of rock uplift rate U and the rock resistance to fluid erosion
K, both unknown parameters, as well as other geometric parameters, such as the along river drainage, accumulation Area A and the channel concavity.
In white, are all the known terms which can be extracted from the topography or the DEM.
We can constrain K, assuming that the first order control erodibility is given by the lithology in general, it's easier to carve into an unconsolidated mudstone than into a granite.
And how knowledge about the structural and tectonic setting of the area allows us to simulate the rock uplift patterns that result from fault slip
using mechanical models. So today, I'm going to walk you through the main steps of our model.
Starting at the study area, then explaining the couple geomorphic mechanic inversion to compute fault slip and moment accrual rates along
relief generating faults, using the topography. And finally, I'll show what we have found for the zero- [indiscernible] folds flanking Silicon Valley.
Before I move forward I would like to give us special thanks to the people listed on this slide, and also acknowledge the continuous support through the years from the U.S.
and the Chilean Science Funding agencies and the Chilean Research Center for Integrated Disaster Risk Management to which I'm affiliated to.
Let's have a look first to the mountains flanking the southwestern-side of Silicon Valley.
This map shows the more structural setting of the right-lateral transform plate boundary on the rate between the Pacific and North American plates or the Bay block over a section of the San Andreas fault along the Santa Clara Valley in Central California which is outlined by the red
rectangle in the States map shown here for reference.
These two restraining bands produce localized shortening in this area, which is in turn accommodated by reverse
reverse faults of the so-called foothills thrust belt or FTB affecting the Bay block.
Sargent-Berrocal and the Shannon-Monte Vista faults,
the two major structure model in this work. This is localized shortening have led to the construction of the southern Santa Cruz Mountains or Sierra Azul, which pops up similarly
to when a watermelon seed is pressed between two fingers. This areas makes up an ideal case to test our method because of the excellent topographic geologic and geophysics information available, and as I show the next slide there is evidence of quaternary deformation and
historic earthquakes along this portion of the Shannon-Monte Vista fault.
So posing a potentially significant hazard to this important population and economic [indiscernible].
The map on the left shows the interpretative fault plane of the Shannon-Monte Vista
fault responsible for a magnitude 6.5 historic thrust
event; the right from surface displacement, captured by a leveling station located in the highest peak of the ridge, and along the trace of the structure
reverse faults have been mapped affecting young Quaternary alluvial fan deposits at the [indiscernible] of the ranch, as shown by the picture on the right.
Over the following slides, I walk you through our method
starting by the geomorphic model of stream power
as shown before. This expression describes the idealized geometry structure of a river profile
assuming that the landscape is mostly in steady state, although there are not empirical measurements of erodability in this region
as I mentioned before, this term, K, can be assumed to be dependent presently on rock time.
For this case the identified tunnels of the Sierra Azul transverse across 21 bedrock units comprising of sedimentary, metamorphic, volcanic, and intrusive rocks, ranging from Jurassic to Neogene times, which
are color tag in the map below.
Next I'll describe the mechanical model used to simulate surface deformation in response to fault slip.
This is our numerical sandbox of the plate boundary constructed using the boundary elements method with geometric and mechanical properties encapsulated in the green's functions
matrix H. In the forward problem, far field plate boundary motion
V separated in its shear vs. possibly for right-lateral and normal Vm
possibly for extension components with respect to the relative geologic plate motion vector excites slip along the folds embedded in the model domain.
This in turn produces rock uplift or subsidence.
The surface of the model at rates depending on the imposed relative plate velocity.
The inset of the upper left side shows a 3D close-up to the FTB
structures of the model in front of the restraining bands.
Now I'll show how we couple these two physical models to estimate slip rates.
We re-express the stream power law. So the linear dependency of channel innovation on U is recast in terms of play velocity via the mechanical model.
And then we set a joint linear, nonlinearing version, minimizing the misfit between predicted and measure channel elevations to estimate best fit errorability. K,
Played, Velocity V, and so fault slip and uplift rates and output elevation Z,
not model parameters. In order to constrain inversion,
additional points that fall within each independent lithologic unit are forced to share the same errordability value
K. Implying that rock type is the main controller on rock resistance to fluvial erosion
Let's see some results.
The map above shows the tunnel elevation data of all
the river points detected in the Sierra Azul.
The map below represents the channel elevations predicted by the model, and finally, the map of the bottom shows the absolute receivers of channel elevation.
As you know by the color scale or predictions result in an acceptable fit to the observations.
Considering the model simplifications and epistemic uncertainty and the relatively large uncertainties proper of geologic data sets.
Vs and Vn represent the obtained best fit shear positive for right-lateral,
a normal positive for extension components of relative plague velocity along the San Andreas
fault, in millimeters per year, and the ranges in square brackets shown on the left are documented values for those parameters.
As you can see, results fall well within those previously published estimations.
Having estimated best parameters of play motion, we can run the forward problem of the boundary elements model to estimate rock uplift rates, which in this case are on average 0.5 mm per year with maximum values of about 1-1.5 mm
per year.
The only natural proxy for rock uplift in this area corresponds to an exclamation rate of 0.8 mm/year, obtained from apatite fission tracks from samples of Loma Prieta shown here by the green star.
Our model predictions for rock uplift rate also coincide quite well with what's been documented with the advantage of having been [indiscernible] to the other lift rate field instead of a single point measurement and of more relevance to this workshop this rock uplift rate field is
caused by slip along the FTB faults.
The next line shows the two model FTB fault planes looking towards the football in the direction of the gray arrow shown here.
And here they are. They predicted, area weighted average slip rate for this structures range between 1.1 and 1.5
million meters per year, with maximum slip-rate values around 2 and 2.5 mm per year
for the Sergeant-Berrocal and Shannon-Monte Vista faults respectively.
High slip-rates, tend to concentrate and localize in patches that we refer to as long-term asperities such as this, and this section here.
This slip-rates transferred into a dearly moment appropriate of 9.13 x 1023 9 cm for both structures of the FTB.
And if we assume as slip predictable and member model of the earthquake cycle, we can estimate what will be the earthquake magnitude for a given recurrence
time as time passes since the last characteristic, stress-releasing event.
As a reminder the most recent recorded significant earthquake that may have occurred along this structures of magnitude
6.5 was in 1865, which could have rupture the high slip-rate patch of the Shannon-Monte Vista fault, and close by the pink ellipse.
Consequently it appears that business structures have the potential to cause severe shaking in the adjacent Santa Clara Valley
that could result in major human and economic loss.
So in conclusion, coupling mechanical and geomorphic models to extract information from the landscape, provides a powerful tool to estimate long-term slip and moment
accrual-rates along those really bounding relief [indiscernible] geologic faults, which is otherwise missing in traditional analysis of past fault behavior.
And as most of the people in this audience is very aware of long-term slip and moment, a world accrual- rates are a primary and fundamental input to any probabilistic seismic hazard assessment.
So I leave you with those conclusions, and thank you very much again for the invitation and for your attention.
Bye.
Thank you. Excellent talk and very, very interesting subject. Our next presentation is by John Baldwin, of Lettuce Consultants International on the fault rupture hazard investigation of the Silver Creek fault which runs through and underneath San Jose.
Hi! I'm John Baldwin with the Lettuce Consultants International.
One of many PI's that performed a fault rupture hazard investigation of the Silver Creek fault in downtown San Jose.
What's kind of fun about this project is that it relied on some excellent research conducted by multiple geologists and geophysicists at the USGS.
And this is essentially a summary of using that information to further characterize the fault. This bulk evaluation represents a due diligent study for proposed transportation tunnel in downtown San Jose that intersects the Silver Creek fault, the original
geotechnical evaluation for the proposed tunnel.
New of the Silver Creek fault, however, there was very little information about that activity, and the location and the style of deformation associated with that fault at the time
of the original study subsequent to that the USGS has performed a significant amount of research in Santa Clara Valley, including developing a Quaternary
geologic model, as well as identifying varied structures. So as part of the due diligence study, it was deemed appropriate to further assess the presence or absence of Holocene faulting associated with this fault and if it is deemed to be Holocene
active, then to characterize the location, width, in the style of faulting, and then further develop coseismic displacement estimates at the tunnel fault
crossing for design purposes. The project site is located in a very seismically active area.
We have the active San Andreas fault directly to the west we have the active Hayward and Calaveras fault zone directly to the northeast.
We have the Silver Creek fault shown here, merging with the Calaveras fault zone to the southeast, and with the Hayward fault to the northwest. Micro-seismicity tends to be a show associated with the southern end of the fault near the
Calaveras fault. There are two very poorly located magnitude 6 earthquakes that are thought to have occurred either along the fault or very close to the fault.
The Silver Creek fault also defines the western margin of aeromagnetic and gravity anomaly, called the Evergreen Basin.
The Evergreen Basin is considered an ancient miocene
pull-apart basin. It's no longer active, due to the reorganization of the Hayward and Calaveras faults with the exception of the eastern margin of the basin where the Calaveras and Hayward faults transfers slip in a left-step
resulting in a series of thrust faults and reverse faults along the Eastern margin of the basin.
The California Geological Survey does not consider the fault
As Holocene active and thus it's also not zoned.
This is a geologic map of the project area that shows the proposed tunnel alignment.
It also shows some of the data that was used to characterize the Silver Creek fault that's shown here.
And the multiple interpretations of false strand locations.
We relied on a USGS seismic reflection profile
north of the site, as well as two geophysical surveys that were collected as part of this study, closer to the tunnel alignment.
We also relied on existing geotechnical borehole and CPT data collected along the tunnel, as well as our own specific borehole and CPT data across our own profiles.
The fault itself in this area is obviously buried. It's buried by thick sequence of Quaternary alluvium, and then obviously obscured by the urban development.
So it's really only recognizable that the tunnel crossing by geophysical and closely spaced borehole data.
This study had the advantage of utilizing Wentworth et al.
2015 that showed the Santa Clara Valley alluvium typically correlates with these global climatic oscillations or depositional cycles, that these cycles are noted by upward finding sequences and buried soils.
They recognize as many as 8 cycles that spanned 750,000 years
and we specifically use the uppermost cycles as strain gauges by which to assess the age and location of faulting.
Previous studies performed in the area, include a USGS seismic reflection profile that's shown here in the Jachen's et al.
arrow magnetic map. The Evergreen Basin shown here in light blue, the profile also intersects the Silver Creek fault shown here is this black dotted line, and is directly north of our proposed tunnels shown here in blue. The interpreted
profile of Williams et al. is shown here on the right.
It shows Franciscan complex on the west, against Evergreen Basin deposits on the east and multiple thrust faults projecting off of the Calaveras and Hayward faults up into the basin.
It also shows the interpreted location of the Silver Creek fault where it offsets the base of the Quaternary deposits down to the east across the Silver Creek fault. Up section
the faulting is less well defined, due to the resolution of the geophysical data, so subsequently in 2015, Wentworth et al. reprocessed the size, make data, as shown here, and reinterpreted the upward projection of faulting into
the younger sediments. Importantly, this well right here called CCOC also shown here roughly, right about here, is one of the wells that Wentworth et al. used to develop their depositional cycle model for Santa Clara Valley recalled as many as 8
cycles. Here are some of those shown here in blue. Wentworth et al. interpret faulting potentially extending up into about a 140,000 year old deposits as a structural sag, as shown here, and which is suggestive of evidence for transtensional deformation. Our study
is evaluating the upward projection
beyond this 140,000 year old deposit into material that's perhaps as young as 11,000 years old to establish Holocene activity for faulting here near the tunnel.
We used existing geotechnical data, borehole data collected along the tunnel alignment, shown here in blue to interpret the location of the Silver Creek fault.
Our profile spans this distance shown here below and vertical exaggeration of 10 times spans the Wentworth et al. structural sag, and also intersects the
InSAR interpreted groundwater barrier of others. The profile shown here represents previously collected geotechnical borehole data,
which we reinterpreted to identify Cycle 1, Cycle 2a, and Cycle, 2.
Cycle 1, represents the Holocene boundary
it's primarily fine-grained
represented by this green color. The anomalous Cycle 2a
course grain package of Wentworth et al. is shown here in yellow, with a couple different possible
basil boundaries. One shown in blue, one's shown in orange, and then the base of the Cycle
2a intersecting Cycle 2. The Holocene Pleistocene
boundary is interpreted as undulatory, obviously with multiple vertical steps and it's unclear whether these steps are depositional or tectonic
and from looking at these vertical steps, many of which are aligned with the structural sag.
It's permissible to interpret vertical separations from 0.6 meters to as much as 3 meters in places with vertical separation decreasing overall up section into the younger overlying deposits.
This is a typical geologic profile that we use to augment the geophysical survey program. With the geophysical survey
roughly shown here spanning the width of the Silver Creek fault zone, as well as the different fault strands mapped by others, and this profile shows CPT and continuous bore hole data that we use to further define and refine the Cycles 1 and 2a,
And 2 boundaries. We used pedologic and textual characteristics to define those in part as well as age
information from the continuous core in which we sampled and analyzed [indiscernible], as you can see here in Cycle 1, we have age information showing that Cycle 1 is at or near the Holocene-Pleistocene boundary of about 11 to 12,000
years. We use this information to augment the seismic surveyed data to assess the age of potentially offset and reflectors
Alright, this is an example of one of the seismic reflection profiles that we collected across the Silver Creek fault.
It shows our interpreted geologic profiles where we have specific age information for the different cycles, both sides.
It also shows a very broad zone of deformation and multiple closely spaced faults in which we used offset reflectors,
abrupt termination of relatively strong reflection horizons and changes in apparent dips across the reflectors.
In some cases specifically in Cycle 2 and Cycle 2a,
we can see very clearly the potential for vertical separations
across these different reflectors, some down to the east, some down to the west, and so at least bringing faulting up into the 20 to 30,000 year old deposits of Cycle 2a
slightly higher up, and across the Holocene-Pleistocene boundary
it's a little more difficult to project most of the faults across that Cycle 1.
A lot of it has to do with the limited resolution of our reflectors, and just the poor
resolution of the data in the upper 10 meters or so. However, it is permissible to interpret about 5 meters of vertical displacement across this false strain
B, which is really important because it now suggests that at least across some of these fault strands there's a suggestion that the Silver Creek fault is potentially active, which then leads us down the road to consider and develop fault rupture
mitigation design for for the tunnel.
Now that we've established Holocene faulting ay be present along seismic line, too.
We need to establish the potential for primary and secondary fault in across the tunnel alignment shown here in purple, and we need to develop what's called fault location uncertainty zone.
That is a zone in which, anywhere within this zone, either primary or secondary faulting could occur where it intersects the tunnel. Clearly based on the information that we have at or near the tunnel, the fault is relatively poorly constrained.
This information is based on our seismic line just directly to the north of the tunnel.
The USGS line and then our more well-constrained data further to the south, along seismic line 2. We define a uncertainty zone on the order of 2.200 at 2,400 feet wide.
Fault crossing angles ranging between 60 and 90 degrees in interpreting the fault primarily as a dexteral strike-slip fault where vertical separation can either be east-side down or west-side down. Within this zone faulting could be as narrow as a
foot or it could be much broader to be more consistent with the negative flower structure and the multiple fault strands that we've seen in seismic line 2. Essentially, what needs to occur is at this tunnel where it intersects the silver creek fault zone and our uncertainty
zone we need to design for fault displacement anywhere
within this uncertainty.
In summary, the study identified shallow laterally continuous late Pleistocene to Holocene stratigraphy that we could correlate with the depositional cycles of Wentworth et al. Through age dating we were able to further refine the uppermost ages of those
youngest, most depositional cycles of Wentworth et al. Our geophysical profiles
we were able to interpret multiple anomalies that coincide with the structural sag of Wentworth et al. as well as to finding a broad zone of deformation.
It's permissible to interpret vertical separation across Cycle 2a, that is, the 20 to 30,000 year old boundary.
However, across Cycle 1, Cycle 2a, that applies to Pleistocene-Holocene boundary
ultimately there was very little vertical separation of the reflectors; however, most of this had to do with the limit resolution of the data, and recall
there was at least one fault strand where there was the possibility of vertical separation across the Holocene-Pleistocene boundary.
That's Holocene faulting cannot be precluded at the site which led to the study being followed by a fault displacement hazard analysis, where design recommendations for fault, rupture, and ground motions were developed for the tunnel where it intersects the Silver
Creek fault. Thank you.
Excellent talk. Thank you, John. So Judy and I are now going to attempt to field questions, and you can you put your hand up?
I believe, and we can try to sort those out to Judy.
Do you want to dive in with a question to kind of get the you get things going?
I've got one or 2 myself, but I don't want to monopolize
Sure, I actually but we'll go ahead and ask yours, because the one that I had was also asked Bye, somebody else.
Okay.
Up here regarding to to morphic expression. So go ahead.
If you have specific, okay.
Yeah, I'm I'm really interested in this structural seg.
And I wanna make sure that I understand it. My understanding is about a one kilometer.
Basically dip that we see in the reflector that's localized on the east side of the Silver Creek fault, basically bounded by the fault, not the entire evergreen basin.
So I guess my question for Carl and John, as well as maybe explain.
Is it? If it's a transpional feature that would be typical.
What we see along a strike slip fault! It abandoned default.
Or is there a component of extension
Anybody hear me!
We sure can
Okay, well, I, it's transition, but a very, very small lateral extension is required to produce a stack.
We're talking about tens of meters
So is it, is it associated with the bend in the fault, or or okay?
No.
Yes.
So. And it's the negative flower structure. Yes, okay, thank you.
John.
Yeah, I, so so Carl's looked at this extensively along the entire length of of the Silver Creek fault, based on the geophysical data.
Both Carl's data and our data, the overall pattern of deformation across.
What's the Silver Creek Falls hence to be defined in big big picture scheme?
A a structural sag. It's unclear within that structural sag, whether all of the features and anomalies that are identified in the geophysics are actually active in controlling that sag, or whether there's a single primary strand that could be controlling that that
Overall structural feature as you get up in the more shallow subsurface and you look at our Geo.
Look at our geophysics. You're actually seeing all kinds of vertical separations down at the weeks.
Add down to the east, as well as down to the west, so I think in the big scheme of things definitely looking long-term, it looks transitional.
And that's how it's been generally modeled.
However, looking at the more recent geophysics that are in the shallow subsurface and the recent deposits, it's a little harder to define that all as a basin other than it's a broad zone of several 2,000 feet wider zone a potential faulting
And so with maybe some having a transitional comma component and maybe others transp professional.
But I think overall in the big scheme of things at least older it looks like it's a transential.
So across the phone
Thank you.
Yeah.
I'm not see any hands raised that might be my failure to see things.
Yeah.
There's Alex. Now I see. Alex. Do you have a question
Hey? Everyone take a good time to call me. My dogs are going crazy for mail time.
Sorry if they're yelling. I am. I have a question for I was wondering about the slip rates that you get from your from your geometry observations and the modeling correct me if I'm wrong.
But they seemed rather similar to the other observations from geology and geodesy is that, did I interpret that quickly from the slide, that they're pretty similar to what we already knew
Yeah, so so real sleep rates on those folks are not widespread, as you know, and and there are a few some geologic estimates by Bob Mccoy, probably here in the audience, and it's also by that this paper by on Bergmann, where they thanks to molding I I
I I don't have the exact details on top of my head now, but they estimated ballpark numbers in the same range again with as well. So I'm not not really measurement.
So with those very few data points, or or or or or proxies, they sort of agree in in, in, in, in in, in the ballpark.
But then some that's something that can be tested I'm so. Most of the results of the method can be tested again.
You know, nuclear cosmogenic erosion rates things like that, or or cosmogenic nucleus erosion rates are thermal chronology as well.
So so you can select locations where you can sample and abstain those metrics and compare with the results of the of the model as well.
So then the more, and you can better. You can. Input those constraints in the inversion.
So so the more constraints you put in the inversion network constraints.
Of course, the more realistic. Also the solution should be same, as there are many questions about the geometry as well.
Of course the geometry that you want to doesn't change over time.
For example, this is just a binary element method, sort of a quasi-static simulation, so that that can add to someone certainly as well.
And then and then that's why I say I'm the geologic map.
So so we are assuming that all the channel points and transverse over a specific genetic unit should have the same enrollability.
So again, assuming that this is the main controller, and we know that there might be rainfall changes across the mountains as well.
So other factors can impact that parameter as well.
So so so again, that goes into the uncertainty and the more information you have, the better geometric model you you get.
The most, the the best of the better. The approximation should be.
Although we in the paper we tested a simple case. Scenario which we assume no knowledge about the geology.
So meaning a singular availability value. Sort of an area average value for the whole mountain range.
Most of the units, all of the units in capsule, in a single value, and also with a simplified geometry of the foot hills thrust belt of other folks, and then we obtain at the end.
So the moment I exponential rate, which is a single number, you know you have a huge 3D model that then comes down to a single number also in in 9 cm per year, is very similar.
What you get. So this is actually one of the outcomes of a research.
We say that although the more information you have of the system, so you can make your case based scenario more realistic, the best approximation will be that can be even useful as a sort of like a first step approximation for session hazards in regions for example, in the developing world where you
Don't have that much information about the natural system. So this is the perfect scenario to test this thing, because you will know how data reach the Bay area is.
But then but then our our claim is that we can expand that to other places, and then and then that you don't really need perfect.
Join me, or a perfect knowledgeable about the because already they'll be semi concerning in caption makes that, and and again you're you're collapsing that's a single number to a moment.
Manual rate. So so this, this, those are some of the outcomes that somewhat related to your question, and others that they saw in in the chat
Yeah, thank, you.
Thanks.
Alright. Thanks for that, Chris, you Madugo!
You have a hand up
I I think my question may have been partially answered. It was also to Aaron about.
I think from reading the paper my takeaway was that the method works really well in an area with lots of data and then it's potentially useful for an area with not very much data.
And my specific question was about fault. Geometries. I think that was discussed.
I think I added a question in the chat what if you really have no constraints or a bunch of different conflicting models on on fault geometries? What would you do?
Because you kept on saying that your geometries are fit in your mind
Yeah, of course, if you have no constraints, it's difficult to set up any study value by the way.
Okay.
So so so I bet we saw the issueable blindfolds that they don't have surface expression.
For example, this is an that that cannot be captured by this modeling.
Of course, because you, you need. You need relief to be constructed and eroded by rivers to apply this methodology so, and then and then, and then you have many constraints.
The best thing to my approach. That will be, test them all, and then we would.
You can stay. You can get a rent at least of, and and still that will be a better that nothing approximation of those slip rates but then I'm not claiming for having the the perfect geometric or geological model of the area that's not the idea of the style is showing
That you can combine those pieces of information. And these principles, the physical principles, in order to achieve an unanswered like that.
So so again, and then the more you have the well, not always, the more data means better.
By the way. So with a but, by the way, so so in the case that you present that if you have many conflicting models, I would try them all and estimate Reanges, and then I'm pretty sure they they will full I hope that so we haven't tested anywhere else.
So so they should fall in a range that again would be another piece of information to incorporate with a specific on certainty which can give you, even by that branch as well.
Okay. Thank you.
Excellent question.
Bill, you have your hand up. You have a question
Yes, also, forfully, they kind of following on on the questions that we're just now.
Your, if I understand correctly, from the gomorphic model your constraint is dominantly on the vertical motion of the mountain ranges, whereas I was struck by in the the figure that you plotted with the that showed the rake of motion on the faults but the motion on on all of the
Hmm.
falls, kind of surprisingly, even the ones that are out on the range front that we kind of expect to be more thrust like the dominant motion, appeared to be mostly strike, slip, so can you comment on that?
It seems like in in that case where your constraint is primarily on the vertical.
But your solution is primarily horizontal. Would there be a significant component of the solution that is coming from the geometry of the model?
That the geometry would have a significant influence on how much horizontal motion you need to produce.
The vertical motion. That is why you have constrained
Yeah, sure what? Well, I'm wondering if you were one of the reviewers that asked the same question, and when we submitted the paper.
So, yeah, so we we had address that program first of all.
By inspecting the geologic maps for deflections, for example, of rivers, river beds, we couldn't find any, and and and and also if if you look at the scale of the model which is about like a 100 by 100 kilometers, more or less so those deflections
In, in, rates, or those are strictly motions.
Our basically in capture within the wavelength of the uplift rate field in the mechanical model.
So they they have by the time range that this inversion is is is constrained for which is about half a 1 million year.
So, not enough displacement could have been really affecting this input of uplift rate constraints on the on, the on the geometric model, which is 100 ms, also the rivers.
They, when you have slow sleep, rates. In this case, obstruction, motion, the they tend to capture the heads, and then continue flowing along the same path as well.
So that's probably another reason why they the the geometry of the rivers, remains sort of a stationary with respect to the specific red, the formation feel impulse at the specific part of the band or the folds where they are located.
But then but but even though those explanations can be sort of like a way to justify this, the way of not accounting for this, allowing the geomorphic model to also incorporate a horizontal displacements will be a great AD especially
Instructively, motion environments. So them all, because again, you, you will be able to reconstruct as well the geometry over time and things like that.
But then right now they they, the simple expression we have to describe the landscape evolution in terms of the stream power law only only accounts for up and rate, and and and we really wanted to keep it simple for the beginning so assuming that as you know, is that there's a lot of stressing motion on those those thresholds as well but then but then the
The most of this sleep is concentrated in areas where they displacement is, is is in the vertical direction kind of so so so again, those those improvements can be done.
The the physics needs to be work work works out, I guess, to incorporate that in the stream
Yeah, if I could have one more kind of following on that.
Obviously you had to make some choices in simplifying the model from what is known about the other salt and raft at the surface right now, but I wondered how much that influence that might have had on the model. Results.
So, for instance, you've combined the sergeant fault in the barrack all fall into the single structure, whereas, especially toward the northern end, they are definitely 2 separate faults for the sergeant fault clearly has a very strike slip, surface expression on the vertical is is more the
Right, yeah.
Thrust, and it's sort of peers to be partition based on the surface geology.
Oh, of course! And
So how am I? How about that? Impact your the results of your model
Yeah, that also ties kind of in the question that Chris asked before before you.
So how much the geometry will affect that if you have conflicting models, for example, all that geometry will be the connectivity of phones, etc.
Yeah, of course. So so I wouldn't use this. That results.
The outcome of of this paper specifically for, for, for for for app, or you know, a detail seismic hazard assessment in the area.
Unless you redo the whole thing with a more realistic geometric mode, and that will affect, of course.
But again, you're you're coming back to a very single number from all those sleep patches as well.
So in that you relation, it might well be that the variation will not be really that significant.
So only that you will add a a, an extended bracket for the uncertainties, probably on, on on the area.
But then something that needs to be tested. We wanted to show again that this could be done, and then and then those improvements, of course, for each.
Specifically, if you're using this in an operational manner, or or for real estimated outside the scientific paper, you know, when when you really want to put this into application, you will have to do a case specific study and and for that and then I probably assume or alternative scenarios as well, and things like that in order.
To, to cast. It's a real, real, real uncertainty embedded in this.
Mycanigan Mall in the geometry of the model.
And the other parameters, as well
And and then so just to address one question by Alex here, yeah, the inversion is unique.
And the, and then thank you for the comment at the end.
So also also something that we conclude. So we compare this with, intersize, make GPS, velocities of the area, assuming for the locking of some of the folks, and and then and we have time, very similar rates for that so so so we we think that these results.
Can sort of reach a gap between geologic data sets and all the way down to geodetic data sets as well with kind of like similar estimations of grades.
So. So thank you for that coming, Alex, having in the chat
Alright! Thanks for that!
Very long and illuminating discussion, I'm wondering if we couldn't now.
Maybe talk to some of the other speakers. If anyone has any questions for Carl or Carol
I thought I would jump in with a question for for Carol that that kind of I thought would.
Maybe. Is there like an optimal bias from 1906 along the fault?
In terms of the observations being to the west the fault, and not along the fault of that factor of maybe the road access back then or with it, is something that there may have been rupture, and they didn't make it, or or they were in they were out there and they just didn't see anything
Along the fault
Well, so there! There's a gap in observations of about 20 kilometers, where nobody looked at the fault.
Basically nobody reported it. And that's because Gerald Warren, who was a student.
Right.
You have to remember that back in the days they really didn't have a clue about strip faulting, or what they were looking for, and he came across all these huge you know, gaping fractures.
Some had bright lateral displacement, some with left lateral displacement.
He thought those were the fault. So so he was operating without it's sort of the background that we all have to be able to recognize the difference, and even some of us have trouble recognizing the difference right today.
So back. Then he had no tools to really tell the difference between something that was the fault and not the fault.
A and B mostly he didn't have any maps.
The oldest maps for most of that area, or if you looked at the figure I showed, or from like 1,915.
So he had no maps to guide him either, so you know, and he was a student.
He just started at Stanford, he actually went on to have a very distinguished career as a as a hydra geologist, but he really kind of blew it in terms of identifying and reporting on fault slip as it turns out and it's not surprising it's just I think
it's a good good, you know, lesson in in the importance of of really going back into the archives and understanding what happened in 190.
6. On the other hand, there wasn't a guy, you know.
Lawson, that's a long story. I'm sorry I'm monopolizing the the talk here.
But Lawson had to send somebody out along that part of the fault.
A year later, cause he couldn't get Branner's description of the geomorphology, so he sent one of his students, whose name was Larson, down there, and Larson had no trouble following the fault.
So unfortunately, his aspirement wasn't to to talk about the displacement, or make any measurements or anything.
It was just to describe the geomorphology, and doubly unfortunately, he wrote in a letter that his camera jams he didn't.
He wasn't even able to take any picture, so he he may have actually been following surface references. I suspect he was given his description, but that's not what he was asked to talk about and that's not what he reported on.
So there you go. I I hope that answers your question.
Oh, it does. Thank you very much. I thought David had a question.
David Schwartz.
Am I on? Can you hear me?
We can.
Carol. That was really really nice presentation
Thanks, David. I I didn't mean to imply that I didn't take this rapture on the fault. Sorry that was kind of a probably there.
I'd like to. I'd like to ask
So thanks, Brooklyn, that
I'd like to ask everybody to read Princess and Schwartz, which is a really really good paper, and Bsa.
And really
Oh, but you have to read the right stunnel paper, too.
So apprentice and
Oh, and the right side. Yeah, but with the
Nobody reads anything. That's that old anymore.
But what I wanted to say is, as far as I'm concerned, there definitely was rupture through there in 190.
6, we
Yeah, there's no question about it, and and sorry. Sorry I I shouldn't have implied that there was any question
There's been postaluma created trenching done along the rupture, and you can see 1,906 at multiple places like grizzly flat and Hazel Dell and some other trenches to the north and we had I don't remember his name it was
Tim something or other. A fellow who lived on one of the ranches in the Santa Cruz
Arnold, Tim Rohano, that the old guy?
Yeah.
Yeah. We interviewed A, 1906 survivor who described a lot of big, ground raptures.
I don't think it was all that clear exactly.
But he took us through like because took place. He said, Yeah, the call came right through here, and then you have something like Nylon Ranch, which was described in the Yo.
6 report. And yeah, the ranch is hit.
Oh, yeah, that's way far south, David. If there's just that 20 kilometer gap, you know where, where we didn't have 1906 observations of faults, that's all always been
Yep with Diane Ranch, ruptured in 1890, and 1,906 ruptured the same place.
I you know. I think Carol was exactly right. They didn't know what they were looking for.
They ran into these big open fissures and landslides, and they just follow those along.
They just were never really on the fall. So yeah.
Accept it. Right? Stone. Yeah.
And so anyway, there was a fascinating comparison.
And I really liked what you did with San Jose, because San Jose gets left out of the equation when we talk about the Bay Area all the time San Francisco it's Oakland.
It's some other places. And you know, it's really our biggest city.
So that was really really good. So I wanted to thank you for the talk and just reiterate, oh, 6 broke through the all the way down
Yeah, it did. I agree? I left that that up in the air.
That's no question about it.
Well, we we have just a couple of minutes before we're supposed to wrap up this session.
If anyone would like to throw in a last comment question.
Judy. I have a couple of thoughts. This is Carl.
Can you hear me?
I can take it away
Well, I'd like to point out that we have a fundamental conflict in San Francisco, and to pay to the East San Francisco is rising, and the payoff is subsiding, and there are no intervening faults and marlow's reflection record says
there's no tilting
So I I it's not clear to me how to resolve that
So sorry anybody have any thoughts on that
So to follow them, and then, if what if you look at Marlow's work?
I used a just one of his profiles. There are several others.
He shows in the center of San Francisco Bay, folding that extends up into the caternary
This is in the middle of a what's long be considered an intact block
The only geologic features that I can see that might be related to this folding.
Is the northwest southeast trending serpent tonight zone, which in the past has been called the Hunters Point, shears off
This is a good way to end this discussion, perhaps, is this is a really interesting question, and that we're just so much we still don't know which is, which is always kind of rewarding in itself.
It keeps us all busy, right? So I I personally, would like
Well, I was just reading Key snow, like he says I should pursue my own question.
Yep.
I will now mute
Well, thank you, Carl, thank thank all the speakers it's really been an excellent session.
BC,
A lot of really good information. So I just like to to say, Thank you.
Thank you both. Thanks everybody.
Okay, thanks everyone. So you have the afternoon later.
These 2 faces, he says, the 2
Thanks. Judy and Chris