WEBVTT 00:00:03.000 --> 00:00:09.000 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 00:00:09.000 --> 00:00:13.000 We are kind of approaching the halfway point. And now, Mr. 00:00:13.000 --> 00:00:26.000 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. 00:00:26.000 --> 00:00:28.000 Judy, Christopher. 00:00:28.000 --> 00:00:34.000 Thank you. I just wanted to start off by saying, this is a really exciting 00:00:34.000 --> 00:00:41.000 series of talks that start from the general overview of the Santa Clara Valley in Silicon Valley by Carl Wentworth. 00:00:41.000 --> 00:00:45.000 He's done a lot of really great work in the area. 00:00:45.000 --> 00:00:46.000 And then with Carol Prentice talking about the effects of the 1906 00:00:46.000 --> 00:01:03.000 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 00:01:03.000 --> 00:01:08.000 about the Silver Creek fault, which is a very interesting fault that we're learning a lot about. 00:01:08.000 --> 00:01:19.000 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. 00:01:19.000 --> 00:01:29.000 I am Judy Zachariasen, and I am a geologist at the California Geological Survey and looking forward to the session. 00:01:29.000 --> 00:01:36.000 So take it away guys. 00:01:36.000 --> 00:01:46.000 I've been asked to talk about the Quaternary basins beneath the South San Francisco Bay in Santa Clara Valley. 00:01:46.000 --> 00:01:51.000 There are actually two separated by a buried bedrock ridge. 00:01:51.000 --> 00:01:58.000 The basins are bounded on the southwest, by the San Andreas fault, and it's associated 00:01:58.000 --> 00:02:03.000 thrust system on the east side, the Foothills system and the Monte Vista thrust system. 00:02:03.000 --> 00:02:13.000 And on the east side by the left-stepping Calaveras-Hayward fault system. 00:02:13.000 --> 00:02:17.000 Underneath the Quaternary there are three older basins; Cupertino basin, partially overrun by the thrust 00:02:17.000 --> 00:02:36.000 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]. 00:02:36.000 --> 00:02:45.000 The Quaternary deposits at the surface are relatively simple mostly are late Quaternary and pale yellow alluvian 00:02:45.000 --> 00:02:53.000 and the pink notorious estuarine bay mud formed on the post-glacial sea level rise. 00:02:53.000 --> 00:03:03.000 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 00:03:03.000 --> 00:03:11.000 underneath this dune field indicating uplift to San Francisco, as well. 00:03:11.000 --> 00:03:27.000 There's also the Colma sand here, which is formed in the last interglacial and the Plio-Quaternary Marine Merced Formation here [pointing]. 00:03:27.000 --> 00:03:37.000 So if we move now to the Santa Clara Valley and schematic cross-section we see the Quaternary is just a thin skin. 00:03:37.000 --> 00:03:42.000 Here we have the Monte Vista fault overriding Cupertino basin, and in the east 00:03:42.000 --> 00:03:50.000 the deep strike-slip Evergreen basin, founded on the west by the Silver Creek fault. 00:03:50.000 --> 00:04:14.000 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 00:04:14.000 --> 00:04:31.000 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. 00:04:31.000 --> 00:04:34.000 Just to find a coarse fine layer in the coarse or in darker colors. 00:04:34.000 --> 00:04:35.000 The fine grain set intervals are in this pale. 00:04:35.000 --> 00:04:44.000 yellow, and there's a pattern to these course layering, and it's not random. 00:04:44.000 --> 00:04:56.000 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 00:04:56.000 --> 00:05:03.000 Of coarse sediment in a 50 foot thick column, and then run the column down the well 00:05:03.000 --> 00:05:17.000 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. 00:05:17.000 --> 00:05:27.000 And each of these major course peaks identifies a grouping of layers which are course at the bottom and fine at the top. 00:05:27.000 --> 00:05:46.000 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 00:05:46.000 --> 00:05:54.000 Grain section. These cyclic layers correlate very nicely 00:05:54.000 --> 00:06:07.000 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. 00:06:07.000 --> 00:06:30.000 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. 00:06:30.000 --> 00:06:33.000 We conclude that we have 00:06:33.000 --> 00:06:37.000 set of 8 finding upward Sedimentary cycles. 00:06:37.000 --> 00:06:41.000 They're produced as a result of the climate variation 00:06:41.000 --> 00:06:47.000 in each of these major climate cycles. 00:06:47.000 --> 00:06:54.000 With that background in mind, with our full set of 125 wells, including a 100 water wells 00:06:54.000 --> 00:06:55.000 what I've done mapped these 8 cycles around the whole basin and up onto the Nile's 00:06:55.000 --> 00:07:15.000 cone here. In cross section then, looking north to southeast, we see but the layering is nearly horizontal, subparallel, flat to the 00:07:15.000 --> 00:07:31.000 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. 00:07:31.000 --> 00:07:32.000 So now we'll summarize this whole section, looking across here from the Moffett, 00:07:32.000 --> 00:07:40.000 well-deep Moffett. Well, here across the Silver Creek fault to the Evergreen 00:07:40.000 --> 00:08:04.000 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. 00:08:05.000 --> 00:08:11.000 Interestingly, however, the Evergreen Well, which is east of the Silver Creek fault the cyclic section is thinner. 00:08:11.000 --> 00:08:19.000 This thinning is accomplished within the lower 3 cycles. 00:08:19.000 --> 00:08:30.000 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 00:08:30.000 --> 00:08:36.000 here to contour the basement in the Santa Clara Basin. 00:08:36.000 --> 00:08:54.000 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 00:08:54.000 --> 00:09:08.000 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. 00:09:08.000 --> 00:09:29.000 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. 00:09:29.000 --> 00:09:50.000 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 00:09:50.000 --> 00:10:04.000 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. 00:10:04.000 --> 00:10:09.000 Then, about 2 million years ago that system was reorganized 00:10:09.000 --> 00:10:28.000 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. 00:10:28.000 --> 00:10:44.000 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 00:10:44.000 --> 00:10:47.000 here by correlating with the Coyote Creek 00:10:47.000 --> 00:10:58.000 Well. What we see is that here's the Silver Creek fault separating the Franciscan basement from the fill of the Evergreen Basin. 00:10:58.000 --> 00:11:05.000 We see thrusts rampant flat structure here, indicating thrusts coming well out into the basin in the subsurface. 00:11:05.000 --> 00:11:16.000 Down here above the tip of the Silver Creek fault we have an extraordinary feature, a structural sag, which we'll look at next. 00:11:16.000 --> 00:11:36.000 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, 00:11:36.000 --> 00:11:54.000 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 00:11:54.000 --> 00:12:15.000 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 00:12:15.000 --> 00:12:20.000 Episodic thrusting is driven by similar behavior of the Calaveras 00:12:20.000 --> 00:12:31.000 fault itself or whether we're looking at some controls within the local thrust system. 00:12:31.000 --> 00:12:34.000 So now I want to turn to the northern basin. 00:12:34.000 --> 00:12:47.000 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 00:12:47.000 --> 00:12:51.000 Strait, and then down through the ancestral San Francisco Valley, 00:12:51.000 --> 00:13:08.000 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. 00:13:08.000 --> 00:13:11.000 And do that by looking at the bottom, at the bedrock surface. 00:13:11.000 --> 00:13:26.000 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. 00:13:26.000 --> 00:13:30.000 Similarly on the south, Hazel was refraction work. 00:13:30.000 --> 00:13:37.000 We can go through 152-250 leading down to about 300 meters 00:13:37.000 --> 00:13:39.000 here in the center of the basin, and that information comes from this reflection 00:13:39.000 --> 00:13:50.000 profile collected by Marlow, in which we see an unconformity of it's horizontal unconformity. 00:13:50.000 --> 00:14:02.000 At about 300 meters, overlined by flat layering, and in the Quaternary section. 00:14:02.000 --> 00:14:09.000 The other piece of information we have is bedrock sill in the Colma gap. 00:14:09.000 --> 00:14:20.000 A cross-section by Doc Bonilla which the bedrock sill has a bottom at about 150 meters below sea level. 00:14:20.000 --> 00:14:30.000 Well, if we put all this together, and the long cross section running through here, what we see is coming from Golden Gate 00:14:30.000 --> 00:14:37.000 we come down the bottom of the basin at 300 meters controlled by those reflection profile. 00:14:37.000 --> 00:14:43.000 Then up onto the Dumbarton Ridge, and the problem is, there's no outlet. Colma Gap is way up here. 00:14:43.000 --> 00:14:48.000 The stream couldn't have run through that, 00:14:48.000 --> 00:15:08.000 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 00:15:08.000 --> 00:15:22.000 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. 00:15:22.000 --> 00:15:36.000 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 00:15:36.000 --> 00:15:43.000 is much less than one degree. So it's imperceptible at any individual point. 00:15:43.000 --> 00:15:54.000 Thank you. 00:15:54.000 --> 00:15:59.000 Okay. That was an awesome talk. Thank you, Carl. 00:15:59.000 --> 00:16:17.000 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. 00:16:17.000 --> 00:16:19.000 Hi! Everybody! I'm Carol Prentice, and I'm going to just take a brief moment to thank Belle 00:16:19.000 --> 00:16:30.000 Phillibosian for asking me to put this talk together in her email to me. 00:16:30.000 --> 00:16:47.000 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 00:16:47.000 --> 00:16:59.000 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. 00:16:59.000 --> 00:17:08.000 So, thanks to Belle for giving me a good reason to put this talk together. It was a lot of fun. 00:17:08.000 --> 00:17:29.000 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 00:17:29.000 --> 00:17:33.000 the State Earthquake Investigation Commission put out its report, 00:17:33.000 --> 00:17:45.000 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. 00:17:45.000 --> 00:17:51.000 I don't think we would have any kind of coherent scientific study of this earthquake 00:17:51.000 --> 00:17:59.000 really. I also spent a lot of time in both the Bancroft Library at UC 00:17:59.000 --> 00:18:20.000 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 00:18:20.000 --> 00:18:31.000 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. 00:18:31.000 --> 00:18:36.000 This is a Landsat image, just to help you get oriented. 00:18:36.000 --> 00:18:53.000 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. 00:18:53.000 --> 00:18:57.000 The 1989 epicenter is shown in pink. 00:18:57.000 --> 00:19:06.000 The, 1906 epicenter is shown in orange, and that red line marks the surface trace of the San Andreas fault. 00:19:06.000 --> 00:19:14.000 So I've organized this talk so that after this very brief introduction we'll take a look at San Jose. First, 00:19:14.000 --> 00:19:18.000 we'll look at 1989 damage ground failure, liquefaction. 00:19:18.000 --> 00:19:21.000 Then we'll look at 1906 damage ground failure, liquorfaction. 00:19:21.000 --> 00:19:29.000 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 00:19:29.000 --> 00:19:39.000 it's not really an issue. We'll take a look at fault surface rupture instead. 00:19:39.000 --> 00:19:48.000 San Jose after the 1989 earthquake is exemplified by this building, which shows absolutely no damage. 00:19:48.000 --> 00:19:54.000 People who were working in this building described 00:19:54.000 --> 00:19:57.000 being very, very frightened by by the very strong shaking. 00:19:57.000 --> 00:19:58.000 But after it was all over they were able to just calmly walk out of the building. 00:19:58.000 --> 00:20:08.000 There was no damage, the San Jose Mercury news the day after the earthquake 00:20:08.000 --> 00:20:19.000 had this to say, "the new day also confirmed that San Jose escaped from the quake with relatively minor damage." 00:20:19.000 --> 00:20:30.000 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. 00:20:30.000 --> 00:20:36.000 Mostly by things falling on them. But there was very little structural damage. 00:20:36.000 --> 00:20:52.000 To the built environment that is underscored by this table, which appears in one of the Loma Prieta professional papers. 00:20:52.000 --> 00:20:59.000 The highlighted row here shows San Jose, and it shows that they were only 8 red tagged residential 00:20:59.000 --> 00:21:03.000 units in the entire city. 00:21:03.000 --> 00:21:09.000 Ground failure liquefaction this is zoomed in to part of a map that was compiled and put together by 00:21:09.000 --> 00:21:22.000 John Tinsley and others. I've circled the two places where they show liquefaction and ground failure near San Jose; 51d, 02:23:29.000 --> 02:23:40.00 just says it's evidence of possible soil, liquefaction near an electoral power station; 51E evidence of probable liquefaction. 00:21:33.000 --> 00:21:39.000 Both of these, by the way, are along the banks of the Guadalupe River. 00:21:39.000 --> 00:21:43.000 San Jose, however, in 1906, was a much different story. 00:21:43.000 --> 00:21:54.000 This is a view looking down South Second Street, you can see lots of building damage to multi-story masonry buildings. 00:21:54.000 --> 00:21:59.000 Sort of the potpourri of damaged photos. 00:21:59.000 --> 00:22:05.000 This is San Fernando Street. Here we have North Second Street. 00:22:05.000 --> 00:22:06.000 With this building collapse, blocking the street, another building collapse. 00:22:06.000 --> 00:22:23.000 Another building collapsed near Market and Post Street, and then this building, the facade collapsed on Santa Clara and First Street. 00:22:23.000 --> 00:22:33.000 I like this picture of the St. Patrick's Cathedral, especially because in the background you can see these apparently undamaged wood frame structures. 00:22:33.000 --> 00:22:40.000 Not all wood frame structures were undamaged. This is the Grant Grammar School, which collapsed completely. 00:22:40.000 --> 00:22:48.000 This is a lovely old Victorian home that apparently came off its foundation. 00:22:48.000 --> 00:23:05.000 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 00:23:05.000 --> 00:23:11.000 the fires and prevailing the kind of conflagration that we saw in San Francisco. 00:23:11.000 --> 00:23:22.000 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. 00:23:22.000 --> 00:23:33.000 Some wood frame homes damaged, and within San Jose City limits there were 19 deaths reported. 00:23:33.000 --> 00:23:48.000 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. 00:23:48.000 --> 00:24:13.000 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. 00:24:13.000 --> 00:24:25.000 Liquefaction and ground failure. Yes, as evidenced by these lovely sand boils seen near Coyote Creek. 00:24:25.000 --> 00:24:28.000 We're gonna take a look. Move on to the southern Santa Cruz 00:24:28.000 --> 00:24:37.000 Mountains. Now, this is an aerial, oblique view showing where the San Andreas fault cuts through the southern Santa Cruz Mountains. 00:24:37.000 --> 00:24:40.000 Here we're going to take a look first at 1989. 00:24:40.000 --> 00:24:42.000 Looking at damage, ground failure, and this time fault surface 00:24:42.000 --> 00:24:54.000 rupture, instead of liquefaction, and then do the same for 1906. Damage in the southern Sand Cruz Mountains typically looked like this. 00:24:54.000 --> 00:24:55.000 It's a pretty sparsely inhabited area. 00:24:55.000 --> 00:25:12.000 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, 00:25:12.000 --> 00:25:24.000 yes, there were some really big landslides. This is one of them that came down in blockbuster north bound lanes of Highway 17. 00:25:24.000 --> 00:25:28.000 As it turned out, it was very fortunate that there were no cars on the road in these lanes at the time. 00:25:28.000 --> 00:25:40.000 this landside came down. There were a lot of ground fractures up on Summit Ridge and Skyland Ridge. 00:25:40.000 --> 00:25:45.000 This one in particular was of interest, because it has left-lateral displacement. 00:25:45.000 --> 00:25:52.000 That was actually quite common. Many, many of these ground fractures. 00:25:52.000 --> 00:25:53.000 This is Morrell Road, and we're going to talk about that again. 00:25:53.000 --> 00:26:04.000 A little bit later. Here's another one of these interesting ground fractures up on Summit Ridge. 00:26:04.000 --> 00:26:08.000 This is now more than a kilometer away from the San Andreas fault. 00:26:08.000 --> 00:26:12.000 Was there surface rupture on the San Andreas fault? 00:26:12.000 --> 00:26:29.000 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 00:26:29.000 --> 00:26:43.000 of two different camps about what these big ground fractures up on Summit Ridge actually met. On one side of the story 00:26:43.000 --> 00:26:49.000 We're a lot of people who say, well, these are just one big ground, shaking features 00:26:49.000 --> 00:26:56.000 their official features. They don't have anything to do with the underlying tectonics. 00:26:56.000 --> 00:27:09.000 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. 02:29:16.000 --> 02:29:24.0 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. 00:27:17.000 --> 00:27:23.000 Okay. So the southern Santa Cruz mountains in 1906; 00:27:23.000 --> 00:27:25.000 yes, damage to single family homes such as this. One ground failure, 00:27:25.000 --> 00:27:35.000 lots of very similar features to what we saw on Summit Ridge in 1989. 00:27:35.000 --> 00:27:48.000 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. 00:27:48.000 --> 00:27:51.000 It's exactly the same place. But in 1906 it had a lot more of left-lateral displacement. 00:27:51.000 --> 00:27:59.000 So very similar feature, but much bigger in 1906. 00:27:59.000 --> 00:28:05.000 Here's another view of that same location showing the left-lateral offset of this fence. 00:28:05.000 --> 00:28:13.000 Now in the Lawson Report this is actually said to be the Saint Andreas fault. 00:28:13.000 --> 00:28:18.000 It's not. It's a half a kilometer away from the San Andreas fault. 00:28:18.000 --> 00:28:21.000 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. 00:28:21.000 --> 00:28:29.000 No, they were not printed backwards. I've been in the Bancroft Library. 00:28:29.000 --> 00:28:37.000 I've examined the glass plate negatives. These were printed correctly 00:28:37.000 --> 00:28:53.000 Well, it turns out that if you take all of the locations that are mentioned in wearings, we Lawson, about the ground rupture. 00:28:53.000 --> 00:28:58.000 It was that report was made by a student named Gerald Waring. 00:28:58.000 --> 00:29:05.000 What you'll find if you plot the locations that he mentions in his report on the oldest maps available for the area. 00:29:05.000 --> 00:29:12.000 You'll see that he was hardly ever even on the San Andreas fault. 00:29:12.000 --> 00:29:13.000 The astute observer will see that there is this one 00:29:13.000 --> 00:29:21.000 loocation. This is the Rights Tunnel, where he actually was on the fault. 00:29:21.000 --> 00:29:27.000 But all these other locations he was not. He really was nowhere near the fault. 00:29:27.000 --> 00:29:32.000 Many of these locations he reported as default. 00:29:32.000 --> 00:29:54.000 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 00:29:54.000 --> 00:29:55.000 fault. This is a map that kind of summarizes all of this. 00:29:55.000 --> 00:30:03.000 The 00:30:03.000 --> 00:30:15.000 yellow dots show the locations where Gerald Waring said he was on the fault and measured right-lateral 00:30:15.000 --> 00:30:24.000 Slip. You'll notice that only one of those was actually on the fault. And that's the Wright's tunnel. 00:30:24.000 --> 00:30:28.000 I wish I had time to tell you the story of the Wright's Tunnel. 00:30:28.000 --> 00:30:29.000 I really don't. I'm just about out of time here. 00:30:29.000 --> 00:30:42.000 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. 00:30:42.000 --> 00:30:46.000 One is that there was surface rupture in the Wright's tunnel. 00:30:46.000 --> 00:30:51.000 There was 1.8 meters of surface rupture across the San Andreas fault. 00:30:51.000 --> 00:30:52.000 It was distributed across a very narrow zone, most of it across a single fault 00:30:52.000 --> 00:30:59.000 plane the rest of it across no more than a few 100 meters. 00:30:59.000 --> 00:31:09.000 There was no broad zone of deformation that impacted the Wright's tunnel, and that tells us that in 1906, 00:31:09.000 --> 00:31:20.000 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. 00:31:20.000 --> 00:31:30.000 So I'm going to stop there and just summarize what we've seen here in San Jose in 1989. 00:31:30.000 --> 00:31:41.000 Not much damage, not much ground failure, not much liquefaction, lots of damage in 1906 and yes, ground failure and liquefaction, 1989. 00:31:41.000 --> 00:31:46.000 Sure damage in the southern Santa Cruz Mountains, ground failure for sure. 00:31:46.000 --> 00:31:52.000 San Andreas surface rupture, no. In 1906, lots of damage. 00:31:52.000 --> 00:32:06.000 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. 00:32:06.000 --> 00:32:11.000 San Andreas surface rupture, yes, probably. And I'll stop there. 00:32:11.000 --> 00:32:18.000 Thanks. 00:32:18.000 --> 00:32:26.000 Excellent talk. Thank you very much. So we are gonna move on to the next talk on the river structure 00:32:26.000 --> 00:32:38.000 fault-bounded mountains, how they can be used to inform seismic hazard assessments specifically in the South Bay by Felipe Aron. 00:32:38.000 --> 00:32:42.000 Good afternoon to everyone. On behalf of my co-authors, 00:32:42.000 --> 00:32:51.000 we appreciate the invitation to participate in this workshop, to speak about our work recently published at GRL. 00:32:51.000 --> 00:32:59.000 This Google Earth 3D view looking towards the Pacific Ocean shows about 60 kilometers long 00:32:59.000 --> 00:33:15.000 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. 00:33:15.000 --> 00:33:36.000 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 00:33:36.000 --> 00:33:42.000 reverse, thanks to the action of climate forces counteracting the tectonic uplift. 00:33:42.000 --> 00:33:54.000 Consequently, the incision pattern along mountain rivers should contain information about the past activity of the underlying relief generating faults, or study tests 00:33:54.000 --> 00:34:16.000 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. 00:34:16.000 --> 00:34:20.000 Two physical models are the key ingredients to our method. 00:34:20.000 --> 00:34:25.000 First, we need a geomorphic model that describes the landscape evolution, 00:34:25.000 --> 00:34:32.000 in this case the stream power law shown here by its integral form. 00:34:32.000 --> 00:34:45.000 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 00:34:45.000 --> 00:34:58.000 K, both unknown parameters, as well as other geometric parameters, such as the along river drainage, accumulation Area A and the channel concavity. 00:34:58.000 --> 00:35:10.000 In white, are all the known terms which can be extracted from the topography or the DEM. 00:35:10.000 --> 00:35:26.000 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. 00:35:26.000 --> 00:35:37.000 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 00:35:37.000 --> 00:35:45.000 using mechanical models. So today, I'm going to walk you through the main steps of our model. 00:35:45.000 --> 00:35:49.000 Starting at the study area, then explaining the couple geomorphic mechanic inversion to compute fault slip and moment accrual rates along 00:35:49.000 --> 00:36:08.000 relief generating faults, using the topography. And finally, I'll show what we have found for the zero- [indiscernible] folds flanking Silicon Valley. 00:36:08.000 --> 00:36:14.000 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. 00:36:14.000 --> 00:36:32.000 and the Chilean Science Funding agencies and the Chilean Research Center for Integrated Disaster Risk Management to which I'm affiliated to. 00:36:32.000 --> 00:36:42.000 Let's have a look first to the mountains flanking the southwestern-side of Silicon Valley. 00:36:42.000 --> 00:36:59.000 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 00:36:59.000 --> 00:37:04.000 rectangle in the States map shown here for reference. 00:37:04.000 --> 00:37:11.000 These two restraining bands produce localized shortening in this area, which is in turn accommodated by reverse 00:37:11.000 --> 00:37:20.000 reverse faults of the so-called foothills thrust belt or FTB affecting the Bay block. 00:37:20.000 --> 00:37:27.000 Sargent-Berrocal and the Shannon-Monte Vista faults, 00:37:27.000 --> 00:37:40.000 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 00:37:40.000 --> 00:38:02.000 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 00:38:02.000 --> 00:38:07.000 historic earthquakes along this portion of the Shannon-Monte Vista fault. 00:38:07.000 --> 00:38:18.000 So posing a potentially significant hazard to this important population and economic [indiscernible]. 00:38:18.000 --> 00:38:24.000 The map on the left shows the interpretative fault plane of the Shannon-Monte Vista 00:38:24.000 --> 00:38:29.000 fault responsible for a magnitude 6.5 historic thrust 00:38:29.000 --> 00:38:40.000 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 00:38:40.000 --> 00:38:56.000 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. 00:38:56.000 --> 00:39:01.000 Over the following slides, I walk you through our method 00:39:01.000 --> 00:39:09.000 starting by the geomorphic model of stream power 00:39:09.000 --> 00:39:17.000 as shown before. This expression describes the idealized geometry structure of a river profile 00:39:17.000 --> 00:39:28.000 assuming that the landscape is mostly in steady state, although there are not empirical measurements of erodability in this region 00:39:28.000 --> 00:39:41.000 as I mentioned before, this term, K, can be assumed to be dependent presently on rock time. 00:39:41.000 --> 00:39:59.000 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 00:39:59.000 --> 00:40:07.000 are color tag in the map below. 00:40:07.000 --> 00:40:19.000 Next I'll describe the mechanical model used to simulate surface deformation in response to fault slip. 00:40:19.000 --> 00:40:28.000 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 00:40:28.000 --> 00:40:39.000 matrix H. In the forward problem, far field plate boundary motion 00:40:39.000 --> 00:40:46.000 V separated in its shear vs. possibly for right-lateral and normal Vm 00:40:46.000 --> 00:41:00.000 possibly for extension components with respect to the relative geologic plate motion vector excites slip along the folds embedded in the model domain. 00:41:00.000 --> 00:41:04.000 This in turn produces rock uplift or subsidence. 00:41:04.000 --> 00:41:11.000 The surface of the model at rates depending on the imposed relative plate velocity. 00:41:11.000 --> 00:41:17.000 The inset of the upper left side shows a 3D close-up to the FTB 00:41:17.000 --> 00:41:25.000 structures of the model in front of the restraining bands. 00:41:25.000 --> 00:41:36.000 Now I'll show how we couple these two physical models to estimate slip rates. 00:41:36.000 --> 00:41:50.000 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. 00:41:50.000 --> 00:42:05.000 And then we set a joint linear, nonlinearing version, minimizing the misfit between predicted and measure channel elevations to estimate best fit errorability. K, 00:42:05.000 --> 00:42:13.000 Played, Velocity V, and so fault slip and uplift rates and output elevation Z, 00:42:13.000 --> 00:42:20.000 not model parameters. In order to constrain inversion, 00:42:20.000 --> 00:42:21.000 additional points that fall within each independent lithologic unit are forced to share the same errordability value 00:42:21.000 --> 00:42:40.000 K. Implying that rock type is the main controller on rock resistance to fluvial erosion 00:42:40.000 --> 00:42:46.000 Let's see some results. 00:42:46.000 --> 00:42:51.000 The map above shows the tunnel elevation data of all 00:42:51.000 --> 00:42:56.000 the river points detected in the Sierra Azul. 00:42:56.000 --> 00:43:09.000 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. 00:43:09.000 --> 00:43:18.000 As you know by the color scale or predictions result in an acceptable fit to the observations. 00:43:18.000 --> 00:43:31.000 Considering the model simplifications and epistemic uncertainty and the relatively large uncertainties proper of geologic data sets. 00:43:31.000 --> 00:43:39.000 Vs and Vn represent the obtained best fit shear positive for right-lateral, 00:43:39.000 --> 00:43:40.000 a normal positive for extension components of relative plague velocity along the San Andreas 00:43:40.000 --> 00:43:56.000 fault, in millimeters per year, and the ranges in square brackets shown on the left are documented values for those parameters. 00:43:56.000 --> 00:44:09.000 As you can see, results fall well within those previously published estimations. 00:44:09.000 --> 00:44:29.000 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 00:44:29.000 --> 00:44:31.000 per year. 00:44:31.000 --> 00:44:50.000 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. 00:44:50.000 --> 00:45:11.000 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 00:45:11.000 --> 00:45:18.000 caused by slip along the FTB faults. 00:45:18.000 --> 00:45:34.000 The next line shows the two model FTB fault planes looking towards the football in the direction of the gray arrow shown here. 00:45:34.000 --> 00:45:45.000 And here they are. They predicted, area weighted average slip rate for this structures range between 1.1 and 1.5 00:45:45.000 --> 00:45:53.000 million meters per year, with maximum slip-rate values around 2 and 2.5 mm per year 00:45:53.000 --> 00:45:59.000 for the Sergeant-Berrocal and Shannon-Monte Vista faults respectively. 00:45:59.000 --> 00:46:14.000 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. 00:46:14.000 --> 00:46:29.000 This slip-rates transferred into a dearly moment appropriate of 9.13 x 1023 9 cm for both structures of the FTB. 00:46:29.000 --> 00:46:40.000 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 00:46:40.000 --> 00:46:46.000 time as time passes since the last characteristic, stress-releasing event. 00:46:46.000 --> 00:46:54.000 As a reminder the most recent recorded significant earthquake that may have occurred along this structures of magnitude 00:46:54.000 --> 00:47:06.000 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. 00:47:06.000 --> 00:47:15.000 Consequently it appears that business structures have the potential to cause severe shaking in the adjacent Santa Clara Valley 00:47:15.000 --> 00:47:24.000 that could result in major human and economic loss. 00:47:24.000 --> 00:47:36.000 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 00:47:36.000 --> 00:47:42.000 accrual-rates along those really bounding relief [indiscernible] geologic faults, which is otherwise missing in traditional analysis of past fault behavior. 00:47:42.000 --> 00:47:59.000 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. 00:47:59.000 --> 00:48:06.000 So I leave you with those conclusions, and thank you very much again for the invitation and for your attention. 00:48:06.000 --> 00:48:11.000 Bye. 00:48:11.000 --> 00:48:31.000 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. 00:48:31.000 --> 00:48:32.000 Hi! I'm John Baldwin with the Lettuce Consultants International. 00:48:32.000 --> 00:48:43.000 One of many PI's that performed a fault rupture hazard investigation of the Silver Creek fault in downtown San Jose. 00:48:43.000 --> 00:48:54.000 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. 00:48:54.000 --> 00:49:12.000 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 00:49:12.000 --> 00:49:17.000 geotechnical evaluation for the proposed tunnel. 00:49:17.000 --> 00:49:29.000 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 00:49:29.000 --> 00:49:38.000 of the original study subsequent to that the USGS has performed a significant amount of research in Santa Clara Valley, including developing a Quaternary 00:49:38.000 --> 00:49:57.000 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 00:49:57.000 --> 00:50:07.000 active, then to characterize the location, width, in the style of faulting, and then further develop coseismic displacement estimates at the tunnel fault 00:50:07.000 --> 00:50:15.000 crossing for design purposes. The project site is located in a very seismically active area. 00:50:15.000 --> 00:50:24.000 We have the active San Andreas fault directly to the west we have the active Hayward and Calaveras fault zone directly to the northeast. 00:50:24.000 --> 00:50:39.000 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 00:50:39.000 --> 00:50:49.000 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. 02:52:56.000 --> 02:53:05.00 The Silver Creek fault also defines the western margin of aeromagnetic and gravity anomaly, called the Evergreen Basin. 00:50:58.000 --> 00:50:59.000 The Evergreen Basin is considered an ancient miocene 00:50:59.000 --> 00:51:15.000 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 00:51:15.000 --> 00:51:22.000 resulting in a series of thrust faults and reverse faults along the Eastern margin of the basin. 00:51:22.000 --> 00:51:25.000 The California Geological Survey does not consider the fault 00:51:25.000 --> 00:51:34.000 As Holocene active and thus it's also not zoned. 00:51:34.000 --> 00:51:40.000 This is a geologic map of the project area that shows the proposed tunnel alignment. 00:51:40.000 --> 00:51:47.000 It also shows some of the data that was used to characterize the Silver Creek fault that's shown here. 00:51:47.000 --> 00:51:51.000 And the multiple interpretations of false strand locations. 00:51:51.000 --> 00:51:52.000 We relied on a USGS seismic reflection profile 00:51:52.000 --> 00:52:04.000 north of the site, as well as two geophysical surveys that were collected as part of this study, closer to the tunnel alignment. 00:52:04.000 --> 00:52:19.000 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. 00:52:19.000 --> 00:52:29.000 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. 00:52:29.000 --> 00:52:37.000 So it's really only recognizable that the tunnel crossing by geophysical and closely spaced borehole data. 00:52:37.000 --> 00:52:38.000 This study had the advantage of utilizing Wentworth et al. 00:52:38.000 --> 00:53:00.000 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. 00:53:00.000 --> 00:53:06.000 They recognize as many as 8 cycles that spanned 750,000 years 00:53:06.000 --> 00:53:16.000 and we specifically use the uppermost cycles as strain gauges by which to assess the age and location of faulting. 00:53:16.000 --> 00:53:25.000 Previous studies performed in the area, include a USGS seismic reflection profile that's shown here in the Jachen's et al. 00:53:25.000 --> 00:53:42.000 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 00:53:42.000 --> 00:53:46.000 profile of Williams et al. is shown here on the right. 00:53:46.000 --> 00:54:00.000 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. 00:54:00.000 --> 00:54:13.000 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 00:54:13.000 --> 00:54:32.000 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 00:54:32.000 --> 00:54:49.000 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 00:54:49.000 --> 00:55:11.000 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 00:55:11.000 --> 00:55:17.000 is evaluating the upward projection 00:55:17.000 --> 00:55:36.000 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. 00:55:36.000 --> 00:55:47.000 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. 00:55:47.000 --> 00:56:01.000 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 00:56:01.000 --> 00:56:10.000 InSAR interpreted groundwater barrier of others. The profile shown here represents previously collected geotechnical borehole data, 00:56:10.000 --> 00:56:18.000 which we reinterpreted to identify Cycle 1, Cycle 2a, and Cycle, 2. 00:56:18.000 --> 00:56:22.000 Cycle 1, represents the Holocene boundary 00:56:22.000 --> 00:56:23.000 it's primarily fine-grained 00:56:23.000 --> 00:56:28.000 represented by this green color. The anomalous Cycle 2a 00:56:28.000 --> 00:56:37.000 course grain package of Wentworth et al. is shown here in yellow, with a couple different possible 00:56:37.000 --> 00:56:46.000 basil boundaries. One shown in blue, one's shown in orange, and then the base of the Cycle 00:56:46.000 --> 00:56:49.000 2a intersecting Cycle 2. The Holocene Pleistocene 00:56:49.000 --> 00:57:03.000 boundary is interpreted as undulatory, obviously with multiple vertical steps and it's unclear whether these steps are depositional or tectonic 00:57:03.000 --> 00:57:10.000 and from looking at these vertical steps, many of which are aligned with the structural sag. 00:57:10.000 --> 00:57:29.000 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. 00:57:29.000 --> 00:57:37.000 This is a typical geologic profile that we use to augment the geophysical survey program. With the geophysical survey 00:57:37.000 --> 00:57:57.000 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, 00:57:57.000 --> 00:58:05.000 And 2 boundaries. We used pedologic and textual characteristics to define those in part as well as age 00:58:05.000 --> 00:58:27.000 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 00:58:27.000 --> 00:58:39.000 years. We use this information to augment the seismic surveyed data to assess the age of potentially offset and reflectors 00:58:39.000 --> 00:58:48.000 Alright, this is an example of one of the seismic reflection profiles that we collected across the Silver Creek fault. 00:58:48.000 --> 00:58:58.000 It shows our interpreted geologic profiles where we have specific age information for the different cycles, both sides. 00:58:58.000 --> 00:59:08.000 It also shows a very broad zone of deformation and multiple closely spaced faults in which we used offset reflectors, 00:59:08.000 --> 00:59:18.000 abrupt termination of relatively strong reflection horizons and changes in apparent dips across the reflectors. 00:59:18.000 --> 00:59:21.000 In some cases specifically in Cycle 2 and Cycle 2a, 00:59:21.000 --> 00:59:26.000 we can see very clearly the potential for vertical separations 00:59:26.000 --> 00:59:40.000 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 00:59:40.000 --> 00:59:44.000 slightly higher up, and across the Holocene-Pleistocene boundary 00:59:44.000 --> 00:59:46.000 it's a little more difficult to project most of the faults across that Cycle 1. 00:59:46.000 --> 00:59:59.000 A lot of it has to do with the limited resolution of our reflectors, and just the poor 00:59:59.000 --> 01:00:12.000 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 01:00:12.000 --> 01:00:33.000 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 01:00:33.000 --> 01:00:38.000 mitigation design for for the tunnel. 01:00:38.000 --> 01:00:46.000 Now that we've established Holocene faulting ay be present along seismic line, too. 01:00:46.000 --> 01:00:59.000 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. 01:00:59.000 --> 01:01:18.000 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. 01:01:18.000 --> 01:01:23.000 This information is based on our seismic line just directly to the north of the tunnel. 01:01:23.000 --> 01:01:37.000 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. 01:01:37.000 --> 01:01:56.000 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 01:01:56.000 --> 01:02:12.000 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 01:02:12.000 --> 01:02:15.000 zone we need to design for fault displacement anywhere 01:02:15.000 --> 01:02:19.000 within this uncertainty. 01:02:19.000 --> 01:02:35.000 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 01:02:35.000 --> 01:02:42.000 youngest, most depositional cycles of Wentworth et al. Our geophysical profiles 01:02:42.000 --> 01:02:52.000 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. 01:02:52.000 --> 01:03:00.000 It's permissible to interpret vertical separation across Cycle 2a, that is, the 20 to 30,000 year old boundary. 01:03:00.000 --> 01:03:05.000 However, across Cycle 1, Cycle 2a, that applies to Pleistocene-Holocene boundary 01:03:05.000 --> 01:03:14.000 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 01:03:14.000 --> 01:03:24.000 there was at least one fault strand where there was the possibility of vertical separation across the Holocene-Pleistocene boundary. 01:03:24.000 --> 01:03:40.000 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 01:03:40.000 --> 01:03:45.000 Creek fault. Thank you. 01:03:45.000 --> 01:03:55.000 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? 01:03:55.000 --> 01:03:58.000 I believe, and we can try to sort those out to Judy. 01:03:58.000 --> 01:03:59.000 Do you want to dive in with a question to kind of get the you get things going? 01:03:59.000 --> 01:04:06.000 I've got one or 2 myself, but I don't want to monopolize 01:04:06.000 --> 01:04:19.000 Sure, I actually but we'll go ahead and ask yours, because the one that I had was also asked Bye, somebody else. 01:04:19.000 --> 01:04:20.000 Okay. 01:04:20.000 --> 01:04:21.000 Up here regarding to to morphic expression. So go ahead. 01:04:21.000 --> 01:04:22.000 If you have specific, okay. 01:04:22.000 --> 01:04:23.000 Yeah, I'm I'm really interested in this structural seg. 01:04:23.000 --> 01:04:30.000 And I wanna make sure that I understand it. My understanding is about a one kilometer. 01:04:30.000 --> 01:04:36.000 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. 01:04:36.000 --> 01:04:46.000 So I guess my question for Carl and John, as well as maybe explain. 01:04:46.000 --> 01:04:51.000 Is it? If it's a transpional feature that would be typical. 01:04:51.000 --> 01:04:52.000 What we see along a strike slip fault! It abandoned default. 01:04:52.000 --> 01:05:00.000 Or is there a component of extension 01:05:00.000 --> 01:05:02.000 Anybody hear me! 01:05:02.000 --> 01:05:03.000 We sure can 01:05:03.000 --> 01:05:12.000 Okay, well, I, it's transition, but a very, very small lateral extension is required to produce a stack. 01:05:12.000 --> 01:05:15.000 We're talking about tens of meters 01:05:15.000 --> 01:05:20.000 So is it, is it associated with the bend in the fault, or or okay? 01:05:20.000 --> 01:05:26.000 No. 01:05:26.000 --> 01:05:27.000 Yes. 01:05:27.000 --> 01:05:31.000 So. And it's the negative flower structure. Yes, okay, thank you. 01:05:31.000 --> 01:05:33.000 John. 01:05:33.000 --> 01:05:40.000 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. 01:05:40.000 --> 01:05:48.000 Both Carl's data and our data, the overall pattern of deformation across. 01:05:48.000 --> 01:05:56.000 What's the Silver Creek Falls hence to be defined in big big picture scheme? 01:05:56.000 --> 01:06:14.000 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 01:06:14.000 --> 01:06:21.000 Overall structural feature as you get up in the more shallow subsurface and you look at our Geo. 01:06:21.000 --> 01:06:27.000 Look at our geophysics. You're actually seeing all kinds of vertical separations down at the weeks. 01:06:27.000 --> 01:06:32.000 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. 01:06:32.000 --> 01:06:40.000 And that's how it's been generally modeled. 01:06:40.000 --> 01:06:56.000 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 01:06:56.000 --> 01:07:03.000 And so with maybe some having a transitional comma component and maybe others transp professional. 01:07:03.000 --> 01:07:09.000 But I think overall in the big scheme of things at least older it looks like it's a transential. 01:07:09.000 --> 01:07:13.000 So across the phone 01:07:13.000 --> 01:07:14.000 Thank you. 01:07:14.000 --> 01:07:17.000 Yeah. 01:07:17.000 --> 01:07:26.000 I'm not see any hands raised that might be my failure to see things. 01:07:26.000 --> 01:07:27.000 Yeah. 01:07:27.000 --> 01:07:31.000 There's Alex. Now I see. Alex. Do you have a question 01:07:31.000 --> 01:07:36.000 Hey? Everyone take a good time to call me. My dogs are going crazy for mail time. 01:07:36.000 --> 01:07:52.000 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. 01:07:52.000 --> 01:08:02.000 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 01:08:02.000 --> 01:08:22.000 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 01:08:22.000 --> 01:08:36.000 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. 01:08:36.000 --> 01:08:48.000 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. 01:08:48.000 --> 01:08:54.000 But then some that's something that can be tested I'm so. Most of the results of the method can be tested again. 01:08:54.000 --> 01:09:04.000 You know, nuclear cosmogenic erosion rates things like that, or or cosmogenic nucleus erosion rates are thermal chronology as well. 01:09:04.000 --> 01:09:10.000 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. 01:09:10.000 --> 01:09:16.000 So then the more, and you can better. You can. Input those constraints in the inversion. 01:09:16.000 --> 01:09:19.000 So so the more constraints you put in the inversion network constraints. 01:09:19.000 --> 01:09:27.000 Of course, the more realistic. Also the solution should be same, as there are many questions about the geometry as well. 01:09:27.000 --> 01:09:29.000 Of course the geometry that you want to doesn't change over time. 01:09:29.000 --> 01:09:33.000 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. 01:09:33.000 --> 01:09:41.000 And then and then that's why I say I'm the geologic map. 01:09:41.000 --> 01:09:42.000 So so we are assuming that all the channel points and transverse over a specific genetic unit should have the same enrollability. 01:09:42.000 --> 01:09:50.000 So again, assuming that this is the main controller, and we know that there might be rainfall changes across the mountains as well. 01:09:50.000 --> 01:10:00.000 So other factors can impact that parameter as well. 01:10:00.000 --> 01:10:07.000 So so so again, that goes into the uncertainty and the more information you have, the better geometric model you you get. 01:10:07.000 --> 01:10:13.000 The most, the the best of the better. The approximation should be. 01:10:13.000 --> 01:10:20.000 Although we in the paper we tested a simple case. Scenario which we assume no knowledge about the geology. 01:10:20.000 --> 01:10:25.000 So meaning a singular availability value. Sort of an area average value for the whole mountain range. 01:10:25.000 --> 01:10:39.000 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. 01:10:39.000 --> 01:10:51.000 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. 01:10:51.000 --> 01:10:54.000 What you get. So this is actually one of the outcomes of a research. 01:10:54.000 --> 01:11:13.000 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 01:11:13.000 --> 01:11:23.000 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. 01:11:23.000 --> 01:11:31.000 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. 01:11:31.000 --> 01:11:39.000 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. 01:11:39.000 --> 01:11:52.000 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 01:11:52.000 --> 01:11:54.000 Yeah, thank, you. 01:11:54.000 --> 01:11:55.000 Thanks. 01:11:55.000 --> 01:12:00.000 Alright. Thanks for that, Chris, you Madugo! 01:12:00.000 --> 01:12:02.000 You have a hand up 01:12:02.000 --> 01:12:07.000 I I think my question may have been partially answered. It was also to Aaron about. 01:12:07.000 --> 01:12:16.000 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. 01:12:16.000 --> 01:12:20.000 And my specific question was about fault. Geometries. I think that was discussed. 01:12:20.000 --> 01:12:29.000 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? 01:12:29.000 --> 01:12:35.000 Because you kept on saying that your geometries are fit in your mind 01:12:35.000 --> 01:12:40.000 Yeah, of course, if you have no constraints, it's difficult to set up any study value by the way. 01:12:40.000 --> 01:12:41.000 Okay. 01:12:41.000 --> 01:12:45.000 So so so I bet we saw the issueable blindfolds that they don't have surface expression. 01:12:45.000 --> 01:12:49.000 For example, this is an that that cannot be captured by this modeling. 01:12:49.000 --> 01:12:58.000 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. 01:12:58.000 --> 01:13:03.000 The best thing to my approach. That will be, test them all, and then we would. 01:13:03.000 --> 01:13:17.000 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 01:13:17.000 --> 01:13:26.000 That you can combine those pieces of information. And these principles, the physical principles, in order to achieve an unanswered like that. 01:13:26.000 --> 01:13:32.000 So so again, and then the more you have the well, not always, the more data means better. 01:13:32.000 --> 01:13:46.000 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. 01:13:46.000 --> 01:13:55.000 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. 01:13:55.000 --> 01:13:56.000 Okay. Thank you. 01:13:56.000 --> 01:13:59.000 Excellent question. 01:13:59.000 --> 01:14:05.000 Bill, you have your hand up. You have a question 01:14:05.000 --> 01:14:11.000 Yes, also, forfully, they kind of following on on the questions that we're just now. 01:14:11.000 --> 01:14:31.000 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 01:14:31.000 --> 01:14:32.000 Hmm. 01:14:32.000 --> 01:14:47.000 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? 01:14:47.000 --> 01:14:50.000 It seems like in in that case where your constraint is primarily on the vertical. 01:14:50.000 --> 01:15:03.000 But your solution is primarily horizontal. Would there be a significant component of the solution that is coming from the geometry of the model? 01:15:03.000 --> 01:15:08.000 That the geometry would have a significant influence on how much horizontal motion you need to produce. 01:15:08.000 --> 01:15:14.000 The vertical motion. That is why you have constrained 01:15:14.000 --> 01:15:21.000 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. 01:15:21.000 --> 01:15:22.000 So, yeah, so we we had address that program first of all. 01:15:22.000 --> 01:15:43.000 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 01:15:43.000 --> 01:15:46.000 In, in, rates, or those are strictly motions. 01:15:46.000 --> 01:15:47.000 Our basically in capture within the wavelength of the uplift rate field in the mechanical model. 01:15:47.000 --> 01:16:00.000 So they they have by the time range that this inversion is is is constrained for which is about half a 1 million year. 01:16:00.000 --> 01:16:13.000 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. 01:16:13.000 --> 01:16:18.000 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. 01:16:18.000 --> 01:16:40.000 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. 01:16:40.000 --> 01:16:58.000 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 01:16:58.000 --> 01:17:02.000 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. 01:17:02.000 --> 01:17:27.000 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 01:17:27.000 --> 01:17:38.000 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. 01:17:38.000 --> 01:17:46.000 The the physics needs to be work work works out, I guess, to incorporate that in the stream 01:17:46.000 --> 01:17:47.000 Yeah, if I could have one more kind of following on that. 01:17:47.000 --> 01:18:00.000 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. 01:18:00.000 --> 01:18:16.000 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 01:18:16.000 --> 01:18:19.000 Right, yeah. 01:18:19.000 --> 01:18:23.000 Thrust, and it's sort of peers to be partition based on the surface geology. 01:18:23.000 --> 01:18:24.000 Oh, of course! And 01:18:24.000 --> 01:18:27.000 So how am I? How about that? Impact your the results of your model 01:18:27.000 --> 01:18:31.000 Yeah, that also ties kind of in the question that Chris asked before before you. 01:18:31.000 --> 01:18:39.000 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. 01:18:39.000 --> 01:18:43.000 Yeah, of course. So so I wouldn't use this. That results. 01:18:43.000 --> 01:18:51.000 The outcome of of this paper specifically for, for, for for for app, or you know, a detail seismic hazard assessment in the area. 01:18:51.000 --> 01:18:57.000 Unless you redo the whole thing with a more realistic geometric mode, and that will affect, of course. 01:18:57.000 --> 01:19:03.000 But again, you're you're coming back to a very single number from all those sleep patches as well. 01:19:03.000 --> 01:19:10.000 So in that you relation, it might well be that the variation will not be really that significant. 01:19:10.000 --> 01:19:17.000 So only that you will add a a, an extended bracket for the uncertainties, probably on, on on the area. 01:19:17.000 --> 01:19:22.000 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. 01:19:22.000 --> 01:19:45.000 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. 01:19:45.000 --> 01:19:51.000 To, to cast. It's a real, real, real uncertainty embedded in this. 01:19:51.000 --> 01:19:53.000 Mycanigan Mall in the geometry of the model. 01:19:53.000 --> 01:19:59.000 And the other parameters, as well 01:19:59.000 --> 01:20:05.000 And and then so just to address one question by Alex here, yeah, the inversion is unique. 01:20:05.000 --> 01:20:06.000 And the, and then thank you for the comment at the end. 01:20:06.000 --> 01:20:22.000 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. 01:20:22.000 --> 01:20:39.000 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. 01:20:39.000 --> 01:20:46.000 So. So thank you for that coming, Alex, having in the chat 01:20:46.000 --> 01:20:49.000 Alright! Thanks for that! 01:20:49.000 --> 01:20:55.000 Very long and illuminating discussion, I'm wondering if we couldn't now. 01:20:55.000 --> 01:21:07.000 Maybe talk to some of the other speakers. If anyone has any questions for Carl or Carol 01:21:07.000 --> 01:21:11.000 I thought I would jump in with a question for for Carol that that kind of I thought would. 01:21:11.000 --> 01:21:16.000 Maybe. Is there like an optimal bias from 1906 along the fault? 01:21:16.000 --> 01:21:34.000 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 01:21:34.000 --> 01:21:35.000 Along the fault 01:21:35.000 --> 01:21:39.000 Well, so there! There's a gap in observations of about 20 kilometers, where nobody looked at the fault. 01:21:39.000 --> 01:21:48.000 Basically nobody reported it. And that's because Gerald Warren, who was a student. 01:21:48.000 --> 01:21:49.000 Right. 01:21:49.000 --> 01:21:57.000 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. 01:21:57.000 --> 01:22:01.000 Some had bright lateral displacement, some with left lateral displacement. 01:22:01.000 --> 01:22:14.000 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. 01:22:14.000 --> 01:22:20.000 So back. Then he had no tools to really tell the difference between something that was the fault and not the fault. 01:22:20.000 --> 01:22:25.000 A and B mostly he didn't have any maps. 01:22:25.000 --> 01:22:33.000 The oldest maps for most of that area, or if you looked at the figure I showed, or from like 1,915. 01:22:33.000 --> 01:22:40.000 So he had no maps to guide him either, so you know, and he was a student. 01:22:40.000 --> 01:22:59.000 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 01:22:59.000 --> 01:23:09.000 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. 01:23:09.000 --> 01:23:13.000 6. On the other hand, there wasn't a guy, you know. 01:23:13.000 --> 01:23:19.000 Lawson, that's a long story. I'm sorry I'm monopolizing the the talk here. 01:23:19.000 --> 01:23:20.000 But Lawson had to send somebody out along that part of the fault. 01:23:20.000 --> 01:23:37.000 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. 01:23:37.000 --> 01:23:43.000 So unfortunately, his aspirement wasn't to to talk about the displacement, or make any measurements or anything. 01:23:43.000 --> 01:23:56.000 It was just to describe the geomorphology, and doubly unfortunately, he wrote in a letter that his camera jams he didn't. 01:23:56.000 --> 01:24:09.000 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. 01:24:09.000 --> 01:24:12.000 So there you go. I I hope that answers your question. 01:24:12.000 --> 01:24:13.000 Oh, it does. Thank you very much. I thought David had a question. 01:24:13.000 --> 01:24:19.000 David Schwartz. 01:24:19.000 --> 01:24:23.000 Am I on? Can you hear me? 01:24:23.000 --> 01:24:24.000 We can. 01:24:24.000 --> 01:24:27.000 Carol. That was really really nice presentation 01:24:27.000 --> 01:24:33.000 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. 01:24:33.000 --> 01:24:36.000 I'd like to. I'd like to ask 01:24:36.000 --> 01:24:37.000 So thanks, Brooklyn, that 01:24:37.000 --> 01:24:42.000 I'd like to ask everybody to read Princess and Schwartz, which is a really really good paper, and Bsa. 01:24:42.000 --> 01:24:45.000 And really 01:24:45.000 --> 01:24:46.000 Oh, but you have to read the right stunnel paper, too. 01:24:46.000 --> 01:24:48.000 So apprentice and 01:24:48.000 --> 01:24:51.000 Oh, and the right side. Yeah, but with the 01:24:51.000 --> 01:24:54.000 Nobody reads anything. That's that old anymore. 01:24:54.000 --> 01:25:02.000 But what I wanted to say is, as far as I'm concerned, there definitely was rupture through there in 190. 01:25:02.000 --> 01:25:03.000 6, we 01:25:03.000 --> 01:25:08.000 Yeah, there's no question about it, and and sorry. Sorry I I shouldn't have implied that there was any question 01:25:08.000 --> 01:25:27.000 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 01:25:27.000 --> 01:25:32.000 Tim something or other. A fellow who lived on one of the ranches in the Santa Cruz 01:25:32.000 --> 01:25:35.000 Arnold, Tim Rohano, that the old guy? 01:25:35.000 --> 01:25:36.000 Yeah. 01:25:36.000 --> 01:25:40.000 Yeah. We interviewed A, 1906 survivor who described a lot of big, ground raptures. 01:25:40.000 --> 01:25:43.000 I don't think it was all that clear exactly. 01:25:43.000 --> 01:25:53.000 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. 01:25:53.000 --> 01:25:54.000 6 report. And yeah, the ranch is hit. 01:25:54.000 --> 01:26:03.000 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 01:26:03.000 --> 01:26:05.000 Yep with Diane Ranch, ruptured in 1890, and 1,906 ruptured the same place. 01:26:05.000 --> 01:26:18.000 I you know. I think Carol was exactly right. They didn't know what they were looking for. 01:26:18.000 --> 01:26:19.000 They ran into these big open fissures and landslides, and they just follow those along. 01:26:19.000 --> 01:26:29.000 They just were never really on the fall. So yeah. 01:26:29.000 --> 01:26:32.000 Accept it. Right? Stone. Yeah. 01:26:32.000 --> 01:26:36.000 And so anyway, there was a fascinating comparison. 01:26:36.000 --> 01:26:48.000 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. 01:26:48.000 --> 01:26:50.000 It's some other places. And you know, it's really our biggest city. 01:26:50.000 --> 01:27:03.000 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 01:27:03.000 --> 01:27:08.000 Yeah, it did. I agree? I left that that up in the air. 01:27:08.000 --> 01:27:15.000 That's no question about it. 01:27:15.000 --> 01:27:22.000 Well, we we have just a couple of minutes before we're supposed to wrap up this session. 01:27:22.000 --> 01:27:25.000 If anyone would like to throw in a last comment question. 01:27:25.000 --> 01:27:28.000 Judy. I have a couple of thoughts. This is Carl. 01:27:28.000 --> 01:27:30.000 Can you hear me? 01:27:30.000 --> 01:27:32.000 I can take it away 01:27:32.000 --> 01:27:54.000 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 01:27:54.000 --> 01:27:58.000 there's no tilting 01:27:58.000 --> 01:28:05.000 So I I it's not clear to me how to resolve that 01:28:05.000 --> 01:28:11.000 So sorry anybody have any thoughts on that 01:28:11.000 --> 01:28:12.000 So to follow them, and then, if what if you look at Marlow's work? 01:28:12.000 --> 01:28:23.000 I used a just one of his profiles. There are several others. 01:28:23.000 --> 01:28:37.000 He shows in the center of San Francisco Bay, folding that extends up into the caternary 01:28:37.000 --> 01:28:44.000 This is in the middle of a what's long be considered an intact block 01:28:44.000 --> 01:28:50.000 The only geologic features that I can see that might be related to this folding. 01:28:50.000 --> 01:29:06.000 Is the northwest southeast trending serpent tonight zone, which in the past has been called the Hunters Point, shears off 01:29:06.000 --> 01:29:19.000 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. 01:29:19.000 --> 01:29:25.000 It keeps us all busy, right? So I I personally, would like 01:29:25.000 --> 01:29:30.000 Well, I was just reading Key snow, like he says I should pursue my own question. 01:29:30.000 --> 01:29:31.000 Yep. 01:29:31.000 --> 01:29:34.000 I will now mute 01:29:34.000 --> 01:29:40.000 Well, thank you, Carl, thank thank all the speakers it's really been an excellent session. 01:29:40.000 --> 01:29:41.000 BC, 01:29:41.000 --> 01:29:44.000 A lot of really good information. So I just like to to say, Thank you. 01:29:44.000 --> 01:29:47.000 Thank you both. Thanks everybody. 01:29:47.000 --> 01:29:48.000 Okay, thanks everyone. So you have the afternoon later. 01:29:48.000 --> 01:29:54.000 These 2 faces, he says, the 2 01:29:54.000 --> 01:30:04.000 Thanks. Judy and Chris