Hi Everybody! Welcome back for our next session as a appetizer before our lunch break we're going to have a grab bag of talk, so these will be short talks of 3 minutes each.
We've tried to arrange them roughly, based on similar topic, but unlike the Ferndale session yesterday, they are not organized around cohesive theme.
It's a grab bag of topics for all northern California earthquake
science, so there will be some time for questions at the end, but otherwise please listen to all the talks and hold your questions until the end. Thank you.
Are we ready?
Okay. Hi, I'm Craig Hartline. I'll be discussing 3D structural model building, constrained by a new seismicity
pattern at the Geysers Geothermal Field.
Induced seismicity occurs as
Full water. Free falls in the hot rock and activate fractures.
While this pressure increases, also reactivate fractures as water falls to the top of the standing water on and exits into the steam reservoir
I was just power company as well developed community devices, programs and worldwide size missity research collaborations to address undue size, Missy at the Geysers.
An excellent example is segment. And that information online in real time to a value collaboration with the United States Geological Survey and Lawrence Berkeley National Laboratory.
The permanent sizing, monitoring network supervisors consist of once Berkeley National Laboratory network of 34 stations, and the recent addition of trauma motion accelerometers on the Eastern front corner of the field 4 of them the record Pete ground Accelerations
near the communities along with the Usgs regional network.
Sorry. That was okay. And and now I'd like to talk about cumulative water andjections volume and seismicity progression and a map view from January 1985, to the present at a fiber in the wall and the purple dis radi are skilled to the cumulative water injection
Point. As I progress through this from 1985 to the present, at a 5 year interval, important point to be made is that there is a goal of improved water distribution spatially and temporarily to assist with seismicity mitigation at the geysers.
And we are 14,01520, and you're the present day now, looking from the southwest at the entire field.
I'll introduce several of the fault with logic surfaces along with the Pop steam reservoir and the base team reservoir and the goal.
Here just to show, as I progress through this once again, that the seismicity patterns are indicative of steam reservoir that is structurally complex, with the same hydraulic discontinuity, and also a highly variable in thickness and permeability, and to the present day looking
at a depth slice from 7,500 to 8,500 feet in the North guysers.
Promise to be made are with the Indu seismicity.
Patterns are indicative of fluid flow. Pathways include flow boundaries.
Yeah. The steam reservoir appears to be subdivided by intersecting zones falling and fracturing, resulting in steam, reservoir compartmentalization.
We're about 400. Surface is interpretive from seismicity patterns.
And these are refined continually during re drilling project analyses here we're looking at the aspen texts. You go CAD 3.
Project for the geysers, which includes mythology, logs for 950 well segments, and this view is from the southeast of a slicer that's extracted from the the full volume now we add the interpretation of primary let's logical surfaces.
Within the 3D model. Yeah, the comments to be made now, or the 3D structural model.
Has has many data, constraints, and are a fine understanding of fluid flow pass to a boundaries, reservoir, hydrogenity, and reservoir come up.
Compartmentalization assist with well planning, targeting, real-time drilling, analysis press for management and provides the potential for and do seismicity, mitigation quickly fly through some final images with a map view on the left and the over cross second view is on the right and the
point to be made from this pre drilling analysis project that slicer reviews are added.
Here is that these that slices, and the cross-sectional spices you from various angles highlight the steam resort complexity.
So we're looking at different angles in Matthew, showing the slicer and then resolving image on the right.
Thank you.
Everyone. My name is Mike Floyd. I'm gonna be introducing some of the Gnss.
Surveys and continuous observations, that I, along with Garth, funny at Uc.
The other side, with the help of people like Craig and many others Lawrence Berkeley and Uc.
Berkeley as well. We've been collecting observations over many years now.
So this complements quite nicely. What, Craig just talked about, I think because we're observing defamation directly here with the Gnss.
And this gives you a bit of an overview of the result of survey measurements.
In the 1990 S. And 2 thousands a lot of this stuff was published by Mossipin Siegel in the late 1,900 and Ninetys.
We've since done additional measurements by survey, and continuous stuff.
So you can see here the general pattern of inward contraction around the Guises.
Should be noted that this is in a reference frame that is basically a regional reference frame around the geysers.
And you can see there they gate the notor site. P.
2, 0, 3 in the north, west, outside, the Guises, essentially has a 0 velocity relative to this frame server.
Everything, you see is sort of relative to the to the outside of the Guises.
If we look at the vertical rates here on the left, you have the vertical rates estimated from data solely taken during the ninetys, the nineteenth ninetys.
This is Pre. The initiation of some wastewater injection pro projects in the late nineties, and early 2,000 on the right hand side you can see the vertical velocities taken from data in the 2 thousands only, and you'll see that there is a reduction in the rate
Of substance between those 2 time periods, essentially ten-year periods.
We can plot those on 1 one ratio plus, just to show that point a little bit.
It's the top there. There are some data from 2,000, 2,001, which would taken with very, very short sessions.
So they're quite imprecise data excluding those data.
And just using the re precise stuff taken over long observation times that's the bottom plot.
There. So there's a little bit less data. The the it's a little bit less precise.
But you can still see the same trend that the dots falling above the one to one ratio line shows that there was a slowing of the rate of subsidence as we move into the 2 thousands.
So we were interested in this and started looking at continuous observations to see if those surrounding sites that the notice sites could see the same thing.
And we are looking here at a time series of that p 2, 0 3.
Site up in the northwest corner, well outside the geysers, I have trended this time series relative to the the velocity that it had prior to 2,008, which is when the enhanced geothermal systems demonstration project was was initiated and you can see
There, the change of velocity at that time Gonath and I install 3 more continuous stations inside the Guises itself in the, in the yellow stars.
Here, and those Time series show all sorts of things. One thing that you will notice is that we seem to have see a second reversal of that vertical rate.
We were going up a little bit after 2,011 we're going back down again now, after 2,014, and just to summarize what we have available here.
We've got 3 potential velocity changes that are observed geodetically.
We have these 3 continuous Gnss sites operating.
They do operate at high rate, they have captured local earthquakes, and we haven't had very much time or support to really announce this stuff.
But it's there. And we continue to collect data. Thanks
Hi! I'm Durham with the brand New Earth School consortium, and I will talk to talk about the Nodea Gnss. Network
First of all, as of January first, I was in, you know, who have joined forces and have officially merged to become a scope.
Many of you were familiar or actively involved. This Irish and UN Africa in the past, and we invite you to remain or become active.
Within the oscilloscope community as well. And opportunity is coming up in late March, when we'll hold our annual community science workshop in Pasadena and registration is now open as a scope.
We will continue to operate, sage, engage, which are the seismic and geodetic facilities founded by funded by Nsf.
Zoom, largest project. This engage is the network of the Americas of Nota, which consists among some other senses of 1,150, continuously operating gns.
Stations across the Us. Mexico and Caribbean.
In California and along the west coast. The network is especially dense, at least in terms of permanent stations, and then coastal northern California.
All stations have been upgraded to full constellation.
Gnss. Receivers with onboard positioning. This process was completed as Usd.
As shake a load funding in 2,021
Geodetic data are available from the nodal network. At different processing levels and in various sampling rates and real-time data streams are also available for almost all of these stations.
While we are exploring a fee-based system for the commercial use of real time data, academic, educational and humanitarian data, access to the remain free and open.
In addition to operating the network. On providing these data products, we provide a number of other services, for example, support for pi field projects for custom, data, acquisition
We also routinely initiate an event response to earthquakes married to the 6 or larger.
Anywhere within the node of footprint, which consists of downloading.
High rate data for stations. When it's within a certain radius of the epicenter depending on expected surface displacement a stereotype pointed out yesterday Hi, rate data like 5 routes are quite useful for analysis of these events.
Sean heel. On the left is just a download status for such a response.
He posed a frontal earthquake, showing that almost all highway data from notice stations in the area, but successfully downloaded within a date
So whether you are already involved. This we are already involved person African Iris.
And now earthquakes were not. Please check out. What's new?
To support your research. Thank you.
Hello, everyone! I'm Mashine. Today I'm gonna have a brief overview on our recent efforts on the Senators and Southern Colorado spots using in.
Zoom. So we you
So we use, okay, so we use 5 years of sentinel.
One data from 2,015 to 2,020, and perform time series.
Analysis. Here. Red color shows the motion towards the satellite, and blue indicates motion away from the sound.
Many features show up in the map. So here, with both Titanic platform motion and water revound at the Santa Clara Valley, and also Lily, like substance at the central value, and with the with the high resolution velocity, map, we are able to extract the surface creep rates on
The both the San Andreas spot Calvars fault, Sergeant thought, and the Queens a bit fault, and by comparing the surface, creep rates and the tectonic stress loading rate, we found that the fat tree acts as a first other control on the creeperate
Distribution on the post lots. We've sort of found that the thought creep is not space available in time, and we captured a coupling decrease.
That is, cooperates a coupling increase that is creepy, decrease during 2,016 to 2,018 on both San Andres and Calvara spots, with evidence from both repeating earthquake and insart time series, as well as b-value time series worth
Noting that the temporal behavior of the San Andreas spot precedes the Calavera spot by about 6 months, indicating possible interactions between the 3 2 parts
And it's not advancing.
Okay. One thing to note that when looking at the seasonal patterns of the time series, the timing of the peak is more uplift, which is, is a review of the deformation mechanisms in fine scale, for example, on the top left at brown water basins we see a peak seasonal
Update in early spring that corresponds to the pro elastic response.
Where in the brother region, we see pixies? No athletes.
In late bar corresponds to elastic and loading response to the total loss of water storage.
In the summer. So with the inside analysis, we are able to see more information in fine scale, fine detail, but in large scale.
So more information can be found in our recent published paper and Roland's presentation in the afternoon will also touch on this topic again, and just to note that all the insar products for time series, and also velocity products are freely available to download at the new link before below so
Preferred to email me if you have any questions or would like to check on the data. Thank you.
Hi! I'm I'm going to describe an intriguing observation that does not yet have a a clear explanation.
So we're hoping to get some feedback and ideas from this group, as most of you know, the send address, fault segment south of sand.
Long, a potatist has both creep and ongoing seismicity with less creep and more earthquakes.
To the north, and we just heard about the creep and heather also talked about the creep earlier this morning.
We looked at a calendar event since 1,981, and the box shown on the left.
And specifically, we look for event pairs that are close in time less than 50 s apart.
But they're separated in a distance by at least 5 kilometers, and this time versus a distance plot shows the pairs that we found, and it gives our key result.
Note that a a positive distances on the right are those in which the second event in the pair is on northwest of the first event, and negative distances, or when it's to the southeast, as you can see, the vast majority of the pairs in this in in the box up
Jump to the northwest. So there's a fundamental space-time asymmetry in these pairs which is not easily explained, as most triggering scenarios at these distances would predict, equal numbers in either a a direction so this slide shows details of exactly where and when
These quakes occurred with blue for the Northwest, propagating pairs, and read for the southwest, propagating pairs.
If you are intrigued by this and want more details, please send me an email to request a pre-print, and if you have any ideas about what might be up ha causing this, please let us know.
Thank you.
Okay. Hi, I wanted to take a few minutes to talk about the 1906 San Francisco earthquake.
So you've probably seen the map on the left which results from the nice work by Jack Boat Wright and Howard Bundock some years ago the shaking intensities from from felt reports you may not be familiar with the map upper right which is from detailed mapping by Harry Wood immediately after the
earthquake? Who mapped out the severity of shaking in San Francisco.
Not before the the effects of the fire so early in the pandemic.
I did some data mining. Put those 2 together to come up with a 1,906 equivalent of a did you feel it?
Map. Lower right next slide, please. I can't advance my own slides.
So next slide, okay, so going back 15 years or more, it will constrained intensity.
Distributions have been used as targets to develop rupture scenarios for various earthquakes.
There's different methods that have been used. One of them uses ground motion models that are determined from.
For example, the Nga project which results from extensive global compilations of of data.
So one approach is to use a ground motion model, together with a ground motion, intensity, conversion, equation, to to produce an intensity, prediction, equations shown at upper left, and to use that to explore rupture, scenarios, 1,906 is a good event to look at because we pretty
Much know where the rupture was, so you can use the ground motion model to explore the magnitude that best explains E directly estimated intensity, distribution.
The answer turns out to be 7.9, which is the same value that was estimated by song at all.
Looking at all of the instrumental data next slide.
So that's the good news. The less good news. There are some caveats, and I just wanted to highlight, too, so I've squished 1906 the map, and then the top panel shows intensities versus join or poor distance.
So that's the nearest distance to the surface projection of revolt.
And then, if you advance, there'll be another panel for the similar plots for the 1989 lumber created earthquake, and I think you can see that in terms of overall trends.
Looking in terms of join a board distance 1,989 looks an awful lot like 1,906, so that highlights, one of the limitations of using join or board distance does a distinct as a metric for this kind of this kind of study you basically lose any
Information in the observations that might constrain the overall dimensions of the rupture.
There's another fundamental uncertainty, that's been discussed going back 40 years.
Now that shaking intensities are primarily a reflection of high frequency.
Shakes, which depends only weekly on seismic moment and quite strongly on stress drop or in grambushion terms, and the event term so, as you can see, the 2 events can be different in magnitude by a full unit.
But have comparable shaking intensities, and that's a potentially irreducible uncertainty.
Next slide. Oh, these, these issues are discussed in a paper that was just submitted to Ahsl.
So if people are interested to hear more about the analysis of intensity, information, and some of these issues, I'm giving a seminar.
So this is an advertisement at the end of March.
It's focused on the Long beach earthquake.
The 30 eighth anniversary of which is this year.
But I'm gonna be talking about some of the modern science in in that talk, for now next slide, I'd just like to thank everyone for tuning in, and especially the organizers, for all of their hard work
Oh, I'm there to Kitty
Alright, thanks soon thanks, all of our speakers, so that grab back toxic question for any of the speakers.
Please raise your hand.
Is to get things started. I have a question for about the I I noticed you on your on your map.
You had a. You talked about the sergeant phone briefly.
I've worked on that a little bit in the past, so I wondered how well you were able to resolve the prep on that phone, which is a little studied despite it's interesting.
Yeah.
Yeah, yeah. So the idea kind of we look at Sergeant as well as Queen Survey is so sharp.
Answer is, we beat, found around like 4 maximum, 4 per year.
Shallow Creek on Sergeant Fault. But when you look at the map, close the it is kind of like one location around searching that point so the 6 point I east that have that group and the majority of the thought seems to be like with really low corporate.
And the insar study kind of acts as a. We kind of want to provide the upper bounds of what's the possible crop rates on the.
And mostly it was
Oh, that's very interesting. So it's a limited area.
Does that area correspond to the places where where there's an actual
Yeah. Yeah. But I correct, I do not have the exact logic, but it seems to be near vicinity, like the location where they reported. Shallow curve is close to the region we reported for me in some
Oh, excellent! I'll be sure to check out your paper about that
Awesome? Has a question
Hi! I have a question for the gentleman that that gave a talk on the geysers.
Subsidence, or related to injection over the over the steam field.
My my understanding from your talk was that you're seeing since 2,014.
The the subsidence increasing again. And I'm wondering if you have a a tentative explanation for that at this point.
Is it drought related, or has injection decreased? Or I'm just curious
Yeah, I I haven't looked closely at exactly what the injection rates and the extraction rates to balance it have been since then, but I do suspect it may be due to the demonstration Egs project winding down.
I don't know quite how far that went, but I think it was around 2014 that it it wound down a little bit.
Create could probably provide more details on that. But I I do suspect that it is. That is something to do with that demonstration project in the Northwest causes. Yeah.
Okay. Thank you.
Some discussion in the chat about 2 house talk on the magnitude, do you?
Wanna pop in and what's being discussed
Yeah, so there is this paper that was just submitted to Sl. And if anyone's interested and we're in the market for an internal reviewer, just that, I'd say that.
But yeah, if you use a well-constrained intensity, information to try to recover magnitudes, using approaches like I showed you, there.
Results are generally good on average, but the individual event, magnitude can be off, by as much as a unit, and that has to do with this stress drop issue, which was first or a discussed by Hanks and Johnston back in 1992 so yeah, for longer.
Period. If you, we, you can recover the magnitude of of 1906, assuming 7.9 is the right answer.
But if you use the same approach for longer Creator, you also get 7.9 because it was a high stress drop event
Alright unless anyone has an additional question for any of our speakers, so probably all getting hungry and ready for lunch.
Okay, then. So everybody, let's take a lunch break.
We're gonna take a break for an owl and come back at trial 45, and get ready with your best.
James Bond jokes for the next session
The moan seed in the foyer number. I was like Nick before the thunder
He doesn't thunder
And and
She's with laughing in my classes. While I was scheming the massive you dream about being a big child.
To say your basic say, you're easy. You've always tried the back scene.
Now I'm smiling. 5
I'll turn the music down, and you can go
I get killed, so feel that, and it drops. Can't say my been so phenomenal leads you more like
Well, I hope everybody got a good lunch and a good dance.
Break in there. Welcome back to the afternoon of the second day of the walkshop.
Well, 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, doing which I am sure you will not escape.
Judy, Christopher.
What's it? Thank you. I just wanted to start off by saying, This is really exciting.
Series of talks that start from the general overview of the Fantasy Valley in Silicon Valley by by Carl Wentworth.
We've done a lot of really great work in the in the area.
And then with Karl Prentice talking about the effects of the 190.
6, and in lom Frita Earthquakes a talk by Flip a Aaron on a using geomorphic tools to evaluate the the uplift of the 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 without I'd like to hand it off to Judy to introduce yourself
I am Judy Zacharias, and a 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 fraternity basins beneath the South San Francisco Bay in Santa Clara Valley.
There are actually 2 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 monovesal system.
And on the east side by the left, supping Calaveras Heyward fault system
Underneath the Quaternary there are 3 varied older basins, Scooper being on cupertino basin, partially overrun by the thrust.
Fold system here Santa Lindral Basin. Here one day it would probably late tertiary and the 40 kilometer long. Strike, slip evergreen basin. Here
The Turner deposits at the surface are relatively simple, mostly our latest quaternary and pale yellow alluvian and pink.
The notorious Esterine Bay mud formed on the postclass will 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, in the uplift of San Francisco, as well.
There's also the Come on a sand here, which is all informed in the last. In relation, the peculiar player, quaternary eminence, and marine Merced formation here
So if I moved out to the Santa Clara Valley and schematic cross-section, we see the Returnery is just a thin skin.
Here we have the Monovist default overriding Cupertino Base, and then 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 with our, together with the 3 seismic reflection profiles here, evergreen hair, and here that's our source of subsurface controlled looking at that subservice will start with these 2 wells quad and 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, the cores that we took while we were drilling
Just to find a coarse, fine layer in the course, or in darker colors.
The fine grain set intervals are in this pale.
He, and there's a pattern to these layer in the course layer, and it's not very random.
And to bring out that layer of pattern. I've designed a curve that I call a coarseness curve here in red, which is measuring the amount.
Of course, 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 8 prominent course peaks running down well to adapt to 300 meters.
And each of those these major course peaks identifies a a grouping of of layers which are course at the bottom and fine at the top.
So we define a series of 8 finding upward sedimentary cycles or sequences, placing the base of each cycle at the bottom of the bottom, curse layer like this, and although the welles 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 ox is an isotope curve, which shows us the the glacial ventilation variations.
We see a very simple, almost straight line. Relationship was design defined, a subsidence rate of the basin of 4 tens of a millimeter per year, and it's not subsidence which provided the accommodation space in which these the 8 cycles were were preserved
We conclude that we have
Set of 8 finding upward sedimentary cycles.
They're produced as a real 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 from north to southeast, we see but the layering is nearly horizontal, subparallel, flat to thee.
Topographic surface actually. And the advance, of course, material is least. There's a bay here greatest down in the center of the Santa Clara Basin
So now we'll summarize this whole section, looking across here from the Monet.
Well-deep Moffat. Well, here cross the Silver Creek, fold to the evergreen.
Well, here what we see are these, 8 finding upward cycles come about 300 meters thick, underlined by a midpointary on control, underlying that underlined by a finer grain section, at maximum about 150 meters thick amounts which we know very little
Okay.
Interestingly, however, the evergreen well, which is east of the Silver Creek fault, cause the cyclic section is thinner.
Destining 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 Bombardon Ridge on the west side of the Basin and Oak Hill on the south side to the edge of the Dumbardon Bay, at the Evergreen Basin, so the drainage system that Eroded
This whole trained out through the thumb of the evergreen basin, and must have gone out to the southeast to Monterey Bay before the sowler was closed by thrust
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 fall we call mal Misery, which is a present east side of that basin
To look at how that base, informed 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 mal misery fold which
is right here, and most of the 175 kilometers of ride slipped that has come up Calaver's fault into the East Bay as moved up on this misery fault.
Then, about 2 million years ago. That's systems reorganized.
To a lift. Stepping system from an extent caliber is fold to the Hayward fold, 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 one kilometer, we heard, we identify as a shallow horizons.
Here by correlating with the Coyotic Creek.
Well know. What we see is that here's the silver trig fault separating Franciscan basement from the fill of the evergreen basin
Let me see! Thrusts rampant, flat structure here, indicating thrusts coming well out into the basin in the substurface.
Down here above the tip of the silver Creek, fall we have an extraordinary feature, a structural sag, which we'll look at next.
So here, with a more realistic vertical exaggeration, we have the 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. Mossets, and although those offsets are small, there are sufficient to create a prominent groundwater barrier along the silver tree fault evident here in this insar image, now, if we move to the east side of the basin, and look at these
Throats. 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 well a scale of hundreds of thousands of years, interesting question here is whether this
Epicenticity is driven by similar behavior of the Calaveras.
Fault itself whether we're looking at some controls within the local thrust system
So now I want to turn to the norm and basin.
Last year Andre Sarna wrote that after the Corkunus trait was opened in about 630,000 years ago, train is from the great of the central Valley, could come through the car.
Serious trade, and then down through the H. Ancestral San Francisco Valley.
Our our stream system, as he called it, and out through the Kolmogat. What I want to do is as think briefly about the formation of that ancient was San Francisco Valley.
And do that by looking at the bottom, at the bedrock surface.
Here we have the still at the Golden Gate at about 110 meters down little sea level, and then we, using wells that contouring has takes that down through 200 250 meters.
Similarly on the south. Hazel was refraction worked.
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 corrupted by Marlowe, which we see an unconformity of it horizontal, and conformity.
At about 300 meters, overlined by flat layer, and in the Quaternary section
The other piece of information we have is, bedrock sill, and in the coal macap.
A cross-section by Tac vanilla, and which the bedrock still it 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 Feet.
We come down. The bottle is based at 300 meters controlled by those reflection profile?
Then up onto the Tombardon Ridge and the problem is, there's no outlet coma Gap is way up here.
That extreme 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, 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 crossfalls, is one that Bob Jackson suggested long ago, and that is that we're looking at tilting, sitting 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 1,906 and 1989 earthquakes in the southern Santa Cruz Mountains, and San Jose Aaron
Hi! Everybody! I'm Carol Prentice, and I'm going to just take a brief moment to thank Bell.
Philipposian for asking me to put this talk together in her email to me.
Bell said, well, we just never hear about what happened in San Jose or in the Southern Santa Cruz Mountains in either the 1,906 earthquake, or the 1,989 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 it for the Usgs.
So, thanks to Bell for 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 Usgsloma Prieta Earthquakes, professional papers, which are just a veritable fire hose of information for the 19 OS 6 earthquake
The State Earthquake Investigation Commission put out its report.
I just called out the Lawson report because it was spearheaded by Andrew Lawson, shown here in this photograph taken in 1,901, 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 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 1,906 earthquake especially in the Southern Santa
Cruz Mountains. Oh, and of course I had to go back and reread 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 the coast 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, 1,906 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 1,906 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 Balt surface rupture instead
San Jose after the 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. 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 2 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.
Yeah, in the entire city
Ground, failure, liquefaction. This is zoomed in to part of a map that was compiled and put together by tint.
John Tinsley and others. I've circled the 2 places where they show liquefaction and ground failure near San Jose 51 d.
Just says it's evidence of possible soil, liqufaction near an electoral power station 50 onee evidence of probable liquefaction.
Both of these, by the way, are along the banks of the Waalupe River.
San Jose, however, in 1,906, 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 poor pouri of a 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 Agnus.
Agnes 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
Liqufaction 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.
Mains. 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 1,989.
Looking at damage, ground failure, and this time fault surface.
Rupture, instead of liquefaction, and then do the same for 1,906 damage in the Southern center cruise mountains typically looked like this.
It's a pretty sparsely habitat, 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.
The sland side 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 Morel 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 was. We're all of these great, big, and very interesting ground fractures up on 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 extensive and they were kind.
Of 2 different camps about what these big ground fragments up on Summit Ridge actually met on one side of the of of the story.
We're we're a lot of people who say, Well, these are just 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 share across a shear zone beneath Summit Ridge.
So we thought that if we took a careful look at what happened in 1,906, we might be able to shed some light on this.
Okay. So the southern Santa Cruz mountains and 1906.
Yes, damage to single family, homes such as this. One ground failure.
Lots of very similar features to what we saw upon Summit Ridge in 1,989.
These great big ground fractures. This is the same location as that little ground fracture I showed you crossing Morel Road with the left lateral slip in 1989.
It's exactly the same place. But in 1,906 it had a lot more of left lateral displacement.
So very similar feature, but much bigger in 1,906.
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 Santa 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 in in the Report public in 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.
Location. 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 default at these locations that are not on the fault, and it's kind of important to recognize that the many, many of the locations were quote unquote, right lateral fault, 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 rights tunnel
I wish I had time to tell you the story of the rights 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 Rights Tunnel, showed us several things.
One is that there was surface rupture in the rights 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 a broad zone of deformation that impacted the rights tunnel, and that tells us that in 190.
6, all of those great big ground fractures up on some at Ridge were, in fact, shallow, surficial features, and we think they were the same thing in 1,989.
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 1,906 and yes, ground failure and liquefaction, 1,989.
Sure damage in the southern Santa Cruz Mountains Ground Failure for sure.
Sanadressed surface rupture. No, in lots of damage.
Also up in 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, Anne, 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 in form. Slip Mac, Catherine's deathman specifically in the South Bay by Flip Aeron.
Good afternoon to everyone on behalf of my golfers.
We appreciate the invitation to participate in in this workshop, to speak about or work recently published at Grl.
This Google Earth, threed view, looking towards the Pacific Ocean shows, and about 60 kilometers long.
Section of the about one kilometers high southern Santa Cruz Mountains or Cr Zoom, located in the North American block along the Sun andresplate 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 source 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 contrasting the tectonic uplift.
Consequently the incision pattern along mountain rivers should contain information about the pass activity of the underlying relief generating folks, or study tests.
This fundamental idea, integrating the topography with my mechanical and emotional modeling, to estimate the cruel of earthquake magnitude potential over time, along crossroads, fundamental component to probabilistic seismic hazard assessments.
2 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 web as a function of rock uplifrate U and the rock resistance to fluorine erosion.
K both unknown parameters, as well as other geometric parameters, such as the along river drainage, accumulation Area A and the channel can carry theta in.
White, are all the known terms which can be extracted from the topography or the Ddf.
We can constrain K. Assuming that the first order control owner will be given by the ethology in general, it's easier to card into an unconsolidated maximum 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 full sleep.
Using mechanical models. So today, I'm going to work you through the main steps of our model.
Starting at the study area, then explaining the couple, geomorphic, mechanic inversion to compute false sleep and moment accrual rates along.
Relief, generating faults, using the topography. And finally, I'll show what we have found for the zero-sool folds flanking silicon value
Before I move forward I would like to give us special things to the people listed in this slide, and also acknowledge the continuous support through these years from the Us.
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. So the mountains flanking the southwestern side of Silicon Valley
This map shows the more for structural setting of the right lateral transform plate 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 Para Valley in Central California which is outlined by the Red
Rectangle in the States. Map shown here for reference.
These 2 restraining bands produce localized shortening in this area, which is in turn accommodated by reverse.
Folds of the so called foothills, and thrust belt or Ftb.
Affecting the blog such as the sergeant, baroque, and the Channel Monte Vista Falls.
The 2. May your structures model in this work. This is localized shortening have led to the construction of the Southern Santa Cruz Mountains or Sierra Zoo, which pops up similarly.
So when a watermelon seat is pressed between 2 fingers, this error makes up an ideal case to test our method because of the excellent topographic geologic, and geophysics information available, and I said showing the next slide there is evidence of quaternary deformation and
Historic earthquakes. Along this portion of the Shannon Montevi Staffold.
So posing a potentially significant hazard. So this important population and they're gonna recap
The map on the left shows the interpreted fold plane of the Shannon Monte Vista.
Fault responsible for a magnitude 6.5 historic thrust.
Events, the right from surface displacement, captured by a leveling station located in the highest peak of the ridge, and then the trace of the structure.
Reverse. Fools have been mapped affecting young. What terminally alluvial fan deposits at the python of the ranches, as shown by the picture on the right
Over the following slides, I woke you through our method.
Starting by the geomorphic model of Channel musician
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 soul transverse across 21 bed drug geologic units comprising 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 seem used to simulate surface deformation in response to phone slate
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, Farfield, Farfield pay bond or motion.
V. Separated in its shear vs. Possibly for railroad and normal Vm.
Positive for extension components with respect to the relative geologic plate motion vector excites sleep 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 threed close-up to the Ftb.
Structures of the model. In front of the restraining bands
Now I'll show how we couple these 2 physical models to estimate slip rates
We re-express the stream power law. So the linear dependency of channel innovation on you 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 abroadability. K.
Played Velocity V, and so full 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 errorability value.
K. Inlying. That rock type is the main controller on rock resistance to flual erosion
Let's see some results.
The map appalled, shows the tunnel elevation data of all 3.
All the river points detected in the 0 zoom
The up below represents the channel elevations predicted by a mall, 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, a geologic data sets
Vs. And Vn. Represent the obtained best fit, shear positive for redilateral.
A normal positive for extension components of relative plague velocity along the sun and grass.
Fault, in millimeterers 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 bested parameters of play motion, we can run the forward problem of the boundary elements model to S estimate, rock uplif rates which in this case are on average 0 point 5 per year with maximum values of about 1 1.5
Per year
We only natural proxy for rock uplifrate in this area corresponds to an exclamation rate of 0 point 8 per year, obtained from appetite fission tracks from samples of long ariada shown here by the green star
Or model predictions for rock uplifray also coincide quite well with white spin documented with the advantage of having been tired to the otherlif rate field instead of a single point measurement and of more relevance to this workshop this rock uplift breakfast is
caused by sleep along the Ftb. Faults
The next line shows the 2 model Ftb phone planes looking towards the football in the direction of the Gray Arrow shown here
And here they are, they predicted, area weighted average sleep rate for this instructor structures range between 1.1 and one.
Point 5 million meters per year, with maximum sleep rate values around 2 and 2.5 per year.
For the sergeant Baroque and Shannon, Monte Vista folds resp.
High slick rates, 10 to one trade, and not 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 on 1310 to the 23, 9 cm for both structures of the Ftb.
And if we assume as sleep predictable and member model of the earthquake cycle, we can estimate what will be the earthquake magnitude for a givens 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 money.
On 6.5 was in 1,865, which could have rupture the high sleep ray patch of the Shannon Monte Vista Fall, and close by the pink ellipse.
Consequently it appears that business structures have the potential to cause severe shaking in the Json Santa Barbara.
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 execute long-term sleep and moment.
A quarrel rates along those really bounding relief, generating juroric falls, which is otherwise missing in traditional analysis of past full behavior.
And as most of the people in this audience is very aware of long-term sleep and moment, a world 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.
Right.
Thank you. Excellent talk, and very, very interesting subject. Our next presentation is by John Baldwin, of lettuce consultants International on the fault, rupture, and how they're investigation of Silver Creek fault which runs through an underneath that a day
Hi! I'm John Baldwin with the lettuce consultants International.
One of many pi's that performed a thought, rupture, hazard investigation of the Silver Creek vault 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 phone this bulk evaluation represents a due diligent study for proposed transportation tunnel in downtown San Jose that intersects the Silver Creek Fall the original
geotechnical, he value 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.
With the original study subsequent to that the Usgs has performed a significant amount of research in Santa Clara Valley, including developing a Quaternary.
Geoic 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 hold a seat vaulting associated with this phone and if it is deemed to be holocene
active, then to characterize the location, width, in the style of faulting, and then further develop cosmic displacement estimates at the tonal 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 caliber's 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 fall near the
Calaveras fall, there are 2 very poorly located magnitude 6 earthquakes that are thought to have occurred either along the fault or very close to the phone.
The Silver Creek fault also defines the western margin of aeromagnetic and gravity andomaly, called the Evergreen Basin.
The evergreen basin is considered an ancient miocene.
Polar Park, 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 transferred in a left Step
Resulting in a series of thrust faults and reverse faults along the Easter margin of the basin.
The California Geological Survey does not consider the fault.
This Holocene active. And thus it's also not sound
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 Fall 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 2 geophysical surveys that were collected as part of this study, closer to the tonal alignment.
We also relied on existing geotechnical borehol and cpt data collected along the tunnel, as well as our own specific borehol and cpt data across her 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 the tunnel crossing by geophysical and closely spaced borehol data.
This study had the advantage of utilizing Wentworth at all.
2,015 that show the Santa Clara Valley of Louvian 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 fault
Previous studies performed in the area, include a Usgs seismic reflection, profile that that's shown here in the Yawkins at all.
Arrow of magnetic map. Yep, evergreen basin, shown here in 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 at all 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 Heyward 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, Fall up section.
The faulting is less well defined, due to the resolution of the geophysical data so subsequently, in 2,015, Wentworth and all reprocessed the size, make data, as shown here, and reinterpreted the upward projection of faulting into
the younger sediments. Importantly, this, this well right here called Ccoc, also shown here roughly, right about here, is one of the wells that Wentworth and all 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, and all interpret fault team 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 transtentional deformation our study
Is important, is, 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 faultine had, or near yeah, the tunnel
We used existing geotechnical data, or whole data collected along the tunnel tunnel Linux, shown here in blue to interpret the location of the Silver Creek Fall.
Our profile spans this distance shown here below, and vertical exaggeration of 10 times spans the Wentworth at all structural sag, and also insects.
Insar, interpreted, groundwater barrier of others, profile shown here represent previously collected geotechnical borhol data.
Which we reinterpreted to identify Cycle one cycle, 2, a and cycle, 2.
Cycle, one represents the holocaust boundary.
It's it's primarily fine-grained.
Represented by this green color. The anomalous cycle, 2.
A course grain package of Wentworth in all is shown here in yellow, with a couple different possible.
Basil boundaries, one shown in blue, one's shown at Horn, and then the base of the cycle.
2, a intersecting cycle. 2. The whole scene plays.
To see the holocaust scene. 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 them are lying with the structural sag.
It's permissible to interpret vertical separations from 0 point 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 cycle one and 2 a
And 2 boundaries we use pedologic and textual characteristics to define those in part as well as age.
Information from the continuous core in which we sampled and analyzed sticks out albums and detrital, as you can see here in Cycle one, we have age information showing that cycle one 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 sites, 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 2, a.
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, 2.
A slightly higher up, and across the Holocene plies to see boundary.
It's a little more difficult to project. Most of the faults across that cycle.
One. A lot of it has to do with the limited resolution of our reflectors, and just the poor reflector.
The the poor resolution of the 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 Fall 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 fault team may 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 perfect and we need to develop what's called fault location, uncertainty zone.
That is a zone in which, anywhere within this zone, either primary secondary faulting could occur where it interrupts 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, too, 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 full where vertical separation can either be eastside down or west, side down within this zone faulting could be as narrow as a
Foot work could be much broader to be more consistent with the negative flower structure and the multiple fault strands that we've seen in seismicleine, too, 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 anymore.
Within this uncertainty.
Summary, the study identified shallow, laterally, continuous lake plies to seen the whole scene start, take a feature that we could correlate with the depositional cycles of Wentworth at all through age dating we were able to further refine the uppermost ages of those
Youngest, most depositional cycles of Wentworth at all geophysical profiles.
We were able to interpret multiple anomalies that coincide with the structural sag of what we' at all, as well as to finding a broad zone of deformation.
It's permissible to interpret vertical separation across Cycle Twoa, that is, the 20 to 30,000 year old boundary.
However, across cycle one in Cycle twoa, that applies to seeing Holocene boundary.
Ultimately there was very little vertical separation of the reflectors, however, most of this had to do with the limit of resolution of the data, and recall.
There was at least one fault strand where there was the possibility of vertical separation across the holocaust pistine 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 fall. 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.