[silence]
Hello everyone and now the event that everybody came for, the top of the top, the cream of the crop, the "Thunder Talks" and they will be moderated for you today
by none in all, the one, the only, the incomparable, Austin Elliot!!
Hi everybody, welcome to the third session of Thunder Talks. These ones are going to have a geological and tectonic bent.
What you're going to see is that I think in general we'll be marching from South toward the north in Northern California.
So let's kick it off with Christie Rowe. There you go.
Thanks, Austin. Okay, how wide is the fault and when does it matter? This is some compilation magic I've been working on with
your colleague Alex Hatem. First of all, when does it matter? A false width matters when we want to look at the width of the zone that is potentially subject to surface rupture damage.
It matters when we want to think about the rheology of creep and slip because slip rate, it can be related to strain rate by the width of the deforming zone
and fault tough thickness, we all know that, so sometimes it's small, sometimes it's, thicker.
It doesn't matter probably when we're thinking about dynamic rupture models or ShakeMaps because in those kind of falter essentially thickness list.
So we're not worried about those. So, this is a plot of the thickness of a fault during one earthquake and its aftershock sequence.
So this is actually Airport Lake fault, near Airport Lake. So this is Ridgecrest M7.1.
The depth scale is linear in kilometers and on the x-axis we have thickness in log, in meters.
So the three color bars at the top represent three different people's measurements for when they map the individual rupture strands for this event.
How much across fault width was populated and the reason why the range is so great is because sometimes the zone is narrow and has few strands and sometimes it's broader and has more strands.
So that is the co-seismic thickness and then these gray bars represent the breadth of the aftershock zone resolved at different depths.
So higher resolution. So this gives us an idea of like how thick a fault zone is for a single event.
To correlate that to information from deeper, older, exhumed faults we need to come up with some equivalencies or at least comparisons that allow us to compare a single event or surface observation or geophysical observation of an active fault with the rocks that are left over from the activity of
deeper faults. So our instantaneous and recent events are near the surface, and then at the, from deeper and zoom faults, we get this cumulative depth of the lifetime of a fault and how much deformation there is in that zone.
So here's some examples. I've expanded these on the depth access, but these are surface maps similar to what I just showed you for Ridgecrest.
For Iszmit, Hector Mine, Ridgecrest, Landers, a whole bunch of earthquakes the little triangles show kind of the average or typical width of the fault zone so tens to hundreds of meters but they range from one meter to even greater hundreds of meters.
And just from comparison, about 300 meters is the width of the AP zone in California law.
Okay, so collapsing those back to the depth of 0 where they were observed, we can compare that to the width of the creeping zones of a whole bunch of actively creeping faults,
so this is from like nail arrays, photogrammetry, lots of repeat surveys at the surface,
and the the key thing to notice is these actively creeping faults, particularly the ones in California, tend a little bit narrower than the zone of rupture of a single earthquake, which is kind of interesting.
We have a couple of creeping zone thickness observations at depth, for example, from SAFOD.
Okay, then we're going to compare that to the ultra myelonite zones that are measured up faults that have been exhumed from lots of different depths down to tens of kilometers and these are ultramyelonites are formed at high stress, very fast creep in the ductile field.
And the interesting thing about this is even though they form over the lifetime of default, they populate the same range of widths.
That is less than a meter up to several tens of meters as creeping zones in active faults do right now.
So instantaneous, same as long-term, which is kind of cool. Okay, now let's look at the damage zone estimates.
So these gray dots are the damage done with estimates like the one I showed you from Ridgecrest that are from velocity. Active
aftershock relocations and from slow velocity zones that are resolved on faults and they populate the same width as big mylonites zones from the lower crust indicating that the fault has the same kind of macroscopic width all the way down.
So the key, oh yeah, and then the one I showed you in Ridgecrest fits that kind of average pattern.
So the patterns arising are that these magnitude 6 to 8 single earthquakes are multi-stranded;
they are hundred meters wide; they're surface displacement over hundreds of meters-wide. Falls which creep at high detectable rates are somewhat narrower than a single rupture zone, which is interesting.
And then the damage zone maintains the width in the hundreds to a kilometer or 2, even as deformation style changes with that from brittle to ductile.
Thank you very much.
So can everyone hear me? Okay, okay, awesome. So hi everyone.
My name is Dana Marino. I'm an undergrad at McGill University. I actually work with Christie Rowe who just presented and today I'll be talking about my research project which exports the geomorphic expression of the Northern Calaveras fault.
Okay, so motivation behind this project is the changing distribution of creep along the Calaveras fault.
As some of you might know, the Calaveras fault has creep that decreases along trace from south to north.
And in addition to this, the Q Faults entry for the Central-Northern Calaveras fault creates a lot of Lidar and field investigations.
So in hopes to better understand this creep, my project tries to define a newer fault trace which hopefully one day could help in earthquake hazard assessment.
So to start off I did a literature review which amounted to a pretty hefty annotated bibliography.
And just a quick thank you to Keith Kelson for so much unpublished data. So far this is what I've been working on.
I've been doing a lot of stuff on QTS. And comparing it to Q faults.
So on the left we have an example of the Calaveras reservoir and here the geomorphic fault indicators match up pretty well with Q faults and so do the trenches from other field investigations.
On the right, however, we have an example where Q Fault is a bit iffy. The geomorphic fault indicators don't quite line up and there aren't that many trench sites and doesn't really line up with the underlying georeference.
It's possible though that this lower resolve slip-rate is related to more diffuse fault zone and hence a less pronounced surface expression making Q faults maybe just a bit more uncertain.
Here is another example. This is Animas Creek, and here we have an example where Q faults does a good job and questionable job, so the more western trace once again aligns with the geomorphology whereas the eastern trace is a little bit more uncertain and doesn't really match up with
geomropology, georeference maps. So yeah, the general takeaways is that differences
do exist. Q faults does a pretty good job for the most part though. Areas with housing or diffuse fault zones like I showed earlier around Pleasanton Ridge do challenge the observation of geometric fault features so that can lead to uncertain fault traces and I'm currently working on it but some areas deserve more investigation like Coyote Reservoir and Animas Creek and other places that have more research to be
done on. So that's it. Thank you.
If you speak, unmute yourself.
[No, I'm ready to go.] Hey everybody, this is Chris Bloszies, Lettis Consultants International, Inc.
If you mind going back one slide. I just want to thank cllaborators and the USGS.
So nice job on this and funding this research. So this is research into the Contra Costa Shear Zone.
It's sort of an uncharacterized structure in the middle of the East Bay Hills.
[So if you wouldn't mind advancing a slide.
I don't have control. I'm on my phone. I apologize. There we go.
Keep going back.
One more if you wouldn't mind.]
Okay, so what is the Contra Costa Shear Zone? So it relates very closely to the Northern Calaveras fault.
As the Northern Calaveras fault branches off from the Hayward it's directed northward and it slip gradually diminishes until the active trace it's essentially not active north of Danville.
And it's sort of a mystery in terms of where that slip is directed to the north.
One option is it could go. You know, right releasing step onto the Concord fault ultimately.
But that's not well supported in terms of the geomorphic in the area which is sort of a topographic positive area.
The other option is that it could get directed to the west into the Contra Costa Shear Zone and then ultimately make it up under the West Napa fault. [Next slide, please.]
So, what is the Contra Costa Shear Zone? [If, if you wouldn't mind advancing a slide, please.]
[One back. There we go.] So the Contra Costa Share zone is a collection of Northwest trending folds and North striking bedrock faults
that collectively are about 15 km wide. None of these are very well understood, but there are seismicity trends associated with each.
In terms of investigating this it's a little bit of a puzzle. A lot of this area is pretty well developed.
So, in looking for a trench location we tried to find the the best expressed and least developed structure which ended up being the Lafayette Ridge site [if you wouldn't mind advancing a slide please.]
This bedrock mapping on the right is Grammar's map, by the way. So we chose, the Lafayette Ridge site, which was actually chosen by Keith Kelson and Jeff Unruh in a NEHRP, the late 1990s, early 2000.
It's a ridge top site that's defined by a steep ridge to the west and to the to the east it's a low ridge.
Interpreted as sort of a mountain depot center that might accommodate offset channels in a right-lateral sets.
[Next slide, please.] So the red lines here are lineament interpretation through the site and the orange lines are lineament mapping is the result of Unruh and
Kelson, NEHRP study. We excavated two trenches here to shadow the site sort of ala, AP style, site clearance investigation.
[Next slide, please.] So this is flipped, just so you know, this is trench one.
Trench one exposed old landslide debris to the west and an anomalous zone in the center.
And a series of alluvial deposits that progressively get younger and more organic-rich
to the east. [Next slide please.] So this is zooming in. We have this old landslide debris.
We just got our radio carbon results back. And that one sample right in the middle of the screen is about 40,000 years old.
So effectively this clears that portion of the trench of faulting, at least Holocene active faulting,
and it calls into question this anomalous zone, because it's closely very adjacent to the landslide debris.
[Next slide please.] T-2 is effectively the newer portion of the trench one Strat column, very organic rich.
But very similar, Stratography. [Next slide, please.] Here's the zoom in of what we're calling the Eastern Anomalous Zone, vertical features that displaced, organic-rich sediments and sediments
lower but we weren't really definitively able to track them into the sediments at the base of the trench.
So juries still out on what these are. Radiocarbon results here came back about 500 years ago.
Is that that surface most deposit? So we're still compiling data, but we feel like this is promising.
Thank you. I know a lot of you are on this call that came out and reviewed the trenches.
So I really appreciate your input. Thank you.
Hi, I'm Kim Blisniuk and I'm from San Jose State University. Today in this "Thunder Talk" I will briefly summarize some field sites that colleagues and I have been working on on the northern San Andreas Fault System.
Where we have updated slip rates and field observations that may have implications on kinematic and earthquake probability models for California.
This is the map of the northern San Andreas Fault System from west to east. The main fault
of the system include the San Gregorio fault, the San Andreas, Rodgers Creek, Hayward, Calaveras, Concord, and Green Valley faults.
The northern San Andreas fault is partitioned from north to south into the North Coast section,
the Peninsula section, and the Santa Cruz mountain section and most kinematic models suggest that from the North Coast section to the Santa Cruz Mountain section
the northern San Andreas fault decrease in slip as slip is partitioned onto the San
Gregorio fault and to the Hayward-Calaveras fault.
And so the first site I'm gonna summarize talks about the policy and slip rates that we were able to constrain that show both
temporal and spatial consistency along the entire length of the northern San Andreas Fault System.
And this is work that I've been doing with Katherine Gunn at USGS and Roland Burgmann at UC Berkeley.
I'm here, what we did was we dated offset alluvial fans and debrief flows that are offset and we have three different offsets over the Holocene time period at about 12,000 years, 8,000 years, and 2.5 thousand years with displacements of 320, 170 and about
50 meters. When we take this data and we combine slip rates over these three different time intervals, we get, slip rates of about 25mm a year.
This rate is faster than the previously estimated slip rate of about 17mm a year that had been constrained.
to the north on the Peninsula section which may suggest higher rates on the fault at this location. Suggesting possible temporal and spatial consistency or high-
low and then high, but that's a different discussion. I'm just highlighting a bunch of work that we've been doing.
The next site is looking at the structural evolution and potential creep both landslide and aseismic on the San Gregorio fault at Pillar Point Bluff.
So we are moving just west of the main San Andreas at this yellow star here.
And at this site, we've been able to identify three main strands of what we define as the San Gregorio fault.
These main strand offset both the surface and subsurface sediment. It also offsets bedrock.
So this is a excellent example where we can see how the fault cuts bedrock, sand, and the surface.
Here is just an exposure of one of the strands and all that's many displays and we're working hard to clean out the site and Look at how deformation patterns may be
affecting both the surface and the bedrock and sands. And our new, faulty shows, multiple
Fault strands forming a positive flower structure along the left step or bend that may connect up to the Seal Cove fault.
We have dates that range from 50 to 11,000 years. So it's pretty exciting. And a beautiful sight.
And then finally, we're going to move to the Maacama fault where you can see lineations of grass and sandy patches.
Suzanne Hecker and I were just there this summer and what we noticed is that as we follow these lineations along we get to an offset channel that Suzanne is standing on and we think this may be the most recent event,
so that's really exciting. And so I just want to talk about how all these field observations that my students, colleagues, and I have been doing on the northern San Andreas fault as far really tells us that we can learn so much by walking the fault, identifying,
new fault strands, getting new slip rates, and even the most recent event.
Alright. My name is Tyler Ladinsky with the California Geological Survey.
I'm just gonna briefly provide a little bit of information on updated, obvious Alquist-Priolo Fault Zoning for the southern Rodgers Creek fault.
So as we determine these Alquist-Priolo Fault Zones, we have in the company, fault evaluation reports or FER.
In this case it was a 60 km long reevaluation of the Rogers Creek that included 5 quadrangles
as shown in the image on the right. We started down in the southeast at Sears Point and continued up through Santa Rosa and the Santa Rosa quas to the northwest.
Our reevaluation was primarily based off of LIDAR data, previous geomorphic mapping, and contemporary research.
For those who are unfamiliar with the Rodgers Creek, it's thought to be the northern extension of the Hayward fault.
Culminates about 20% of the overall slip budget across the SF Bay Area, and it has the most recent historical earthquake that has thought to occur on the southern Rogers Creek was the 1898 Mare Island which was estimated to be about a magnitude 6.5.
There's been a couple smaller events in the late 1960's that are around magnitude 5.5.
[So.
Wait for it, there we go.] So just the background on what the Alquist-Priolo Fault Zone is
basically intended to prohibit the location or prohibit the developments of structures for human occupancy across active faults.
Two of the keywords there are sufficiently active and well defined. Those are the two keywords that I'll focus on on.
So to do this study, basically followed these four steps to essentially assess whether the traces are sufficiently active and well-defined.
In this case, sufficiently active would mean within the Holocene. So first, just review previous geomorphic mapping, geologic mapping, and compile Paleoseismic studies.
Then we do interpretation of the lidar data to identify tectonic geometric features. Field checking spots along the fault that's available and then using the geomorphic expression as a proxy for recency where the age of Quaternary deposits are unknown or Quaternary deposits are nonexistent.
[Okay. Come on.
There we go.] Mapping products we have on the left, in image we have the tectonic geomorphic mapping that's a snippet of some of our mapping.
It also includes the area photo review on the Sonoma County lidar base map. Image on the right is a compilation mapping of the previous geomorphic mapping.
In addition, there's also site specific studies that you can see locality 2, 3, and 4
those are either Alquist-Priola Fault Zone studies or paleoseismic studies that we incorporate.
Essentially, we kind of take the compilation mapping, the tectonic geomorphic mapping, smash it together, combine it together and we get our AP zones.
And in this case.
It looks like that. So just to orient the image on the upper left is the northwestern part of our site, our field study area, north of Santa Rosa, and an image on the far, lower right is the southeastern.
Extent of our field study, which would be by Sears Point. Obviously the yellow zones are or the yellow is the zones and the black lines are the faults that the zones are based off of.
So feel free to reach out if you have any questions to myself or to Judy Zachariasen.
Thanks a lot.
Hey everyone. My name is Ben Melosh from the USGS in Moffett Field.
This is work I've been doing over the last several years up in the Northern Coast Ranges surrounding the Maacama fault.
Location figure here is on the left and we're focusing in on the black box.
So it's the central part of the Maacama, the fault zone, and includes the city of Ukiah
just west of Clear Lake,
And then on the right here, you'll see this, a geologic map compiled from previous sources and showing some of our new mapping.
Right in the middle in the gray box where we've identified two new faults
from the bedrock mapping we strike northwest and follow the regional structural fabric in a lot of this part of the Coast Ranges.
The full extent of those faults is yet to be fully mapped but it does appear that they continue to the south and connect up with other thrust faults in the bedrock, including the Chicken Springs Fault Zone, which is shown at the bottom of that map there.
And that continues out of the map here down into the Geysers area
where a series of thrust faults has been mapped by Bob in previous work.
So yeah, we've, focused on looking at some of the active tectonics in this area I'm showing the geology here for reference.
On the left and then on the right is a channel steepness index map. And those brighter colors correspond to higher values you see those correlate to the position of the Maacama fault zone itself and also fall just to the east of the fault zone
along the west side of the Maacama Mountains there. In places some of those steepness index values do correlate to changes in the bedrock geology,
but for the most part, we are seeing a signature of active uplift, and reactivation of these older bedrock faults along the west side of the mountains there.
We also took a look at some of the micro-seismicity data starting in the southern area along profile C to C prime.
You'll see these two distinct splays on our micro-seismicity clusters within the Maacama Fault Zone
and then along profiles A prime and B to B prime to the east of Maacama fault, you see a much more gently east dipping cluster of micro-seismicity that extends for about 7km and when you trace that, up to the surface, it corresponds to the position of these newly identified faults that you see in the geology.
So we are inferring that this is an older Franciscan age bedrock thrust fault that's reactivated in the modern stress field.
We took the micro-seismicity data and created a 3D model, of the area.
What you're seeing here. In red, these are faults or fault splays within the Manama Fault Zone,
itself and then in orange this is the more gently stepping reactivated Franciscan age fault, that we just identified.
I performed a static stress analysis. On faults in this model and I'm showing those results here on the right in the stereo net.
We see in general. I should say this is slip tendency values, which is the ratio of sheer stress to normal stress.
And in general, we see low slip tendency values. Ranging from about 0.5 to 0.4 and the lowest of those occur on this reactivated bedrock fault.
So in summary, we find a much more complicated fault geometry then we, previously anticipated, and that is in part due to these reactivated Franciscan age structures.
Active faulting and uplift extends east of the main trace of the Maacama faults in the area in the western Maacama Mountains.
These low slip tendency values that we calculate suggest the faults are not ideally oriented for slip.
And also match previous work that shows a correlation between these slow slip tendency values and increased geometric fault complexity and increased fault width.
So that's as it stands, if you're interested in more of this work it was just submitted to Geosphere, look for that and thank you very much.
Hi everybody! This is Don higher up. I'm having some video transmission problems. So you're just gonna get my voice here.
I'm Don High up with engineering geologist with California Department of Water Resources. DWR owns and operates the California State Water Project.
The three headwater dams, statewater project are Antelope, Frenchman, and Grizzly Valley Dam, which is located at Lake Davis.
These 3 earthen bake the dams are in the upper Feather River Basin of Plumas County, California within the northern Walker Link shear zone.
For last 16 years DWR has been studying these faults near these 3 dams, but the most attention given to the Grizzly Valley Fault located about 300 meters east of the dam.
Today I'm going to give you an update on the most recent work from last October along the Grizzly Valley Fault.
It involved additional mapping and paleo seismic investigation work on the East shore like Davis. 4 trenches excavated and a little bit of disappointment.
A little overview. Bedrock geology is primarily cretaceous. Grenadier, right?
Overly by Mysql mechanics, along with caternary cue deposits.
This is our area. This is our transit area, lightning tree boat launch ramp along the northeast shore of Lake Davis.
Note the broken blue line represented by the approximate location of the Pleistocene Grizzly Lake Paleo shoreline.
This is our Q deposit map of the fault trench area in relation to the main traces of the suspected Grizzly Valley fault dashed red lines.
Q deposits include place to see lucustering deposits and alluvial colluvial deposits.
The next slide is the area within the black box. It was these 2 morphic features seen in the lighter that brought us to location as a preferred trench site area.
Note the offset deflected drainages and ridge line spurs. We had ranked 4 possible trench locations T one through T 4 early on.
The actual excavated trench locations are T one and T 4, T 4 A and T 4 B.
This is a photo of the landscape, a T one prior to excavation, to the southwest towards Lake Davis.
And photo of T one wall clearing.
Come on, you can do it. Well, cleaning. And then next photo is photo of T one wall.
It's jumping.
There is definitely a lag ear, isn't there?
That's a bummer.
T. Well, this is the T one wall excellence stratigraphy and there was some description on that but in light of time.
Next is.
Okay.
Still base killing me. Sorry everybody. This is the photo imagery of T one, T 4 self well, massive fine sand, still to bottom of bread change and, texture and blocking with suspected texting.
This next photo is T 4 photo, but with interpretation yellow boxes are tifer samples. White boxes, carbon, green boxes, OSL.
39 samples were taking, lab results penning, although one C 14 sample was dated about 1,050 years before present in the upper unit.
Preliminary conclusions, previous geomorphic mapping the Grizzly Valley Fault is robust and provides strong evidence that the fault extends along the eastern shore like Davis.
The site depicts the fault as a series of distributed discontinuous traces that are each locally defined by a parent fault related to your morphic expression.
The other seismic trenching did not find conclusive evidence of fault rupture. All trenches displayed continuous.
Mostly uninterrupted stratography at their base. Geomorphic features did not appear to be produced by faulty.
Possible explanations, Grizza Valley Font may be highly distributed across the project area. And not easily identifiable by the geographic expression, geomorphic expression and or the fault is located further to the, you know, the base of the range front located about 100 meters northeast of the project site.
Future work, tail additional trench work in the north of the area and study of offset marine and cut with cosmogenic dating.
And lastly, I want to say that much of this work has been supported by our consultants at Infrterra, let us consulting international by the California Geologic Survey through interagency agreement with field assistance by Nevada Bureau of Mines and Geology, U.S. Forest Service and Pacific Gas and Electric.
Thank you.
[All right. Hey, everybody. Hope you can see me, Yes, you can.]
Alright, so my name is Allyson Carroll from Cal Poly, Humboldt and I will introduce our ongoing work.
"Earthquake indicators and coast redwood tree rings along the North Coast San Andreas fault,"
and this is collaborative work funded by USGS.
So our goals are used tree rings to document indicators of the 1906 earthquake and to constrain the timing of the penultimate earthquake which has a rough constraint of about 1660 to 1812. So we want to use growth rings because they could provide annual resolution and dating is based on ring with patterns from a shared climate signal in the region.
Okay, so earthquakes impact trees we could have fracturing, twisting, tilting,
loss of structure and co-seismic change and that could lead to signatures on the tree rings.
Okay. So we could have growth reductions,
releases, and wood anatomical indicators. You can see this fracture tree growing on the fault
after the 1906 earthquake at Fort Ross and that's our primary study location.
Coast Redwood is an ideal species due to its great age to reach ages over 2,000 years. You can see in red the range of Coast Redwood.
With a very rough overlay in green of the northern San Andreas fault, but only 5% of primary forest remain.
So it's a challenge to find trees old enough to capture the penultimate event and we focus in on the Sonoma Mendocino coast.
Coast Redwood is extremely challenging to cross-state old trees. Cross-state or annually resolved they can have tight rings,
wedging or discontinuous rings as well as abnormal growth at the big buttress at the bases of these large old trees.
Recently, our team completed the first systematic cross-dating of Coast Redwood. We did this by taking replicate, pencil thin increment cores along the main trunks of
standing trees accessed by rope climbing techniques. We published 47 reference chronologies across the range.
Including an over 800 year old reference less than 14 kilometers from Fort Ross. So now we have references to compare newly collected samples.
Right, so far we have sampled 6 trees at Fort Ross and we plan to sample 3 more when the weather lets us.
We're looking for trees on or near the fault with external indicators of disturbance with the goal of dating these disturbances.
The caveat is that we cannot conclude the cause; we're looking for a coincidence of dates.
So I'm just going to introduce you to a couple of our study trees. Check this one out.
You can see on the top. so disturbances such as earthquakes can cause tops to snap off of trees.
And coast redwood could then grow reiterated trunks. So our climbers Steve Sillit and Marie Antoine climbed and sampled the top of these trees.
We're able to date the initiation of this reiteration to post 1906. So you can see the power of our sampling technique is that we can access these features.
Here's another tree. It has forked reiteration on top that we were able to sample.
This tree has a strong lean. You can climb and sample at multiple locations. The goal is to date the rightening of the lean as well as the initiation of reaction wood on the lean.
This tree has a kink likely caused by an earthquake that fractured the main trunk so we can sample below on and above. And we also have a tree at Gualala Redwood Timber Company that's leaning over a sag pond as well as 23 stumps
that were sampled on the fault. So this is ongoing work. I want to thank you for your time and we will keep you posted on our results.
Thank you.
Hi everyone, I'm Steve DeLong and I'd like to describe for you some new research that we started at the USGS recently.
Much of this initial work has been done by Jessie Vermeer. So the long-term goals of this work include better standing of the onshore fault network and the greater Mendocino Triple Junction region which spans southern Cascadia and the northern San Andreas Fault Network.
We should learn more about how the shear from the San Andreas Fault System transitions up to the subduction regime in Cascadia.
Faults in this area are part of the express due to steep landslide from
slopes, thick vegetation, until recently a lack of Lidar topographic data. The recent Ferndale earthquake in the 1992 Cape Mendocino earthquake remind us of the regional seismic hazard in this area.
And of course, we hope to eventually improve the fault mapping and models and to provide and improve parameters for national seismic
hazard model and future uniform earthquake rupture models. So lots of folks have been here for a long time.
These include people like Jay Patton, Tom Leroy, Harvey Kelsey, Mark, Haley, and there are many students who have been working this area for years.
So our approach is collaborative. And we're first developing a geomorphic and geochronological framework, while these local researchers continue to lead the important site specific investigations.
In general, we're working intergrator Mattole River watershed at first and this area includes the rapidly uplifting and fairly well studied Coastal King Range, which is that band of mountains to the southwest of the Mattole River on the figure on the screen and those are uplifting about 4mm per year.
San Andreas fault comes back onshore at Shelter Cove and perhaps elsewhere, but we don't know how it crosses the King Range or the Mattole River watershed in any detail.
The Mattole River itself may indicate the spatial variability of uplift rates farther onshore, sharp variations in that elevation age relationships are better at fluvial terraces and the presence of channel zones having contrasts in channel steepness.
Along the coast uplifts are recorded in the elevation age relationships of marine terraces.
And in addition, you know, in general, this area, tectonic fluvial and coastal processes
appear to conspire to drive shifts in drainage divide like locations, which can complicate our understanding of the geomorphology.
So in order to develop better spatial and perhaps temporal understanding of the geomorphic framework of this complex tectonic system.
We're analyzing many watersheds for mono scale erosion rates using cosmogenic methods and we're dating marine and fluvial terraces with cosmogenics and luminescence dating.
We've extracted channel steepness and chi values, which we can be correlated to rock uplift, but may also indicate the influence of coastal of drainage divide shifts and other processes.
So I'm tailing the fluvial, coastal, and tectonic influences on Alaska will be challenging.
This area provides considerable opportunity to develop new understanding of these relationships. Do the remarkable suite of land forms available for study.
And this framework will be useful as we look for the expression of individual faults and zones of deformation.
On the left is an example of a suite of fluvial terraces along the Mattole River.
It's apparent that the tectonics of the Mattole River region implications not only for seismic hazard, but also for things like critical habitat for fish.
Upstream and mid-base and low gradient reaches our key habit of these fish and these could be identified using the tools that are intended for tectonic analysis.
On the right is an example of a beautiful paleoseismic site. This one along the Eel River, which has been identified and is being led by Jay Patton at CGS and Tom Leroy from Pacific Watersheds.
This offset flight of fluvial terraces and previous to lidar our unrecognized fault strand is a great example of the location where we learn about past earthquakes, fault slip rates, and get new insight into the connectivity of the fault network in the greater Mendocino Triple Junction. And development of sites such as these will have the most direct impact on reducing uncertainty of seismic hazards in the greater Humboldt region.
Thanks.
Hi, I'm Clara Yoon from USGS and I've been looking at some recent moderate magnitude earthquakes and the Mendocino Triple Junction all with the strike-slip mechanisms.
I've done this work with David Shelley. Please check out his talk tomorrow.
[Hey, just waiting for my slide.]
Okay, so on December 20, 2021 the Petrolia doublet earthquake happened. So it started with a magnitude 6.1 offshore earthquake shown by the blue mechanism and then 11 seconds later there was a second magnitude 6.0 onshore earthquake shown by the green that was located 30km away from the first earthquake.
And then exactly a year later in December, 2022, the magnitude 6.4. Ferndale earthquake happened not too far away that's this black mechanism.
And so we wanted to know how, first of all, how are these earthquake sequences related and also what faults did they rupture.
So our strategy to answer these questions was to come up with an enhanced and relocate high resolution earthquake catalog for the Mendocino area spanning both sequences that was created using a completely automatic workflow using seismic data
from these stations shown by triangles and then using a deep learning based and phase picker EQ transformer followed by association, location, magnitude, and relocation.
So what did we find? Well, on the left, I'm showing your earthquakes from only the petroleum sequence.
In the middle are earthquakes from only the Ferndale sequence. And on the right are, both earthquake sequences combined and here all the earthquakes are colored by that.
So what we saw was that the Petrolia and Ferndale sequences were very distinct in space;
they did not overlap much, but they are located near each other; they're adjacent and there's only a small spatial gap between them.
Alright, so now let's take a look at what's happening at depth. So on this slide I'm showing you their earthquakes that are colored by time.
And then there's two at depth cross-sections. There's a prime kind of along the Ferndale afershocks on the top right.
And then there's EDE prime from north to south on the bottom right. And we found that the Petrolia and Ferndale sequences both occurred in the downg-going Gorda plate slab, but they were at different depths where conditions like temperature and pressure can be different.
The Petrolia onshore earthquakes, which are shown in red we're deeper and in the mantle, whereas the Ferndale earthquakes aftershocks were kind of confined to the uppermost part of the Gorda slab and near
but not on the subduction interface.
The Petrolia and Ferndale sequences were also distinct in time, but they were much more widely separated by a year
and that's because both of these sequences, similarly decayed very quickly with low aftershock productivity that's pretty typical of the Mendocino region.
Zooming in on the first couple of days after the mainshock we saw that the Petrolia sequence decayed really quickly;
most of the aftershocks happened within the first 2 hours of the doublet.
So looking at the bigger picture, the Petrolia and Ferndale sequences are really examples of the diverse earthquake
sequence and rupture behavior in the Mendocino area this complicated triple junction. If we think of Petrolia and Ferndale as distinct sequences. They were separated by longer time period of a year that had a very short spatial gap between them less than 5 km,
but on the other hand, if we think of the Petrolia doublet ruptures, the magnitude 6.0's earthquakes,
they were separated by a short time interval of 11 seconds, but had a much larger spatial gap of 30 km between them
and a Cape Mendocino sequence from 1992 was another example where there were 2 aftershocks a day after the magnitude 7.2 mainshock they occurred 30km away and a deeper depth offshore.
And so it's really important to consider the full range of possible earthquakes in a complicated region like Mendocino Triple Junction. Thank you.
Hi, I'm John Eidinger. I'm gonna talk about faults but these are electrical faults.
And not earthquake faults directly.
This is a ShakeMap of the magnitude 6.4 Ferndale or Fortuna earthquake.
All little black dots shows where there were electrical power outage related issues in this earthquake.
The yellow areas are to urbanized areas. One of the surprising things is that everybody from Rio Dell as far north as Orric lost power.
That's about 70,000 customers, Pacific Gas & Electric customers that's one customer equals one billing account.
and a hundred percent of the community had outages. From anywhere from PGA, point 0.03g to 0.60g+ or higher.
However, only about 5,000 of these 70,000 customers had outages due to something physically breaking like a wire broken.
The other, 95% or so, 65,000 customers lost power due to phase-to-phase or phase-to-ground faults.
On earthquake faults, these are electrical faults. I'll talk about them in a second. So what are these faults?
So when you have ground shaking, the towers or wooden poles, they vibrate which in turn cause vibration of the electrical conductors, the wires.
Most circuits have three phases, if the wires swing out-of-sync
or get too close to each other they will fault, the power from A phase jumps to B phase the circuit breaker says ah, electrical fault and it shuts down the line.
And statistically something on the order of 1/1,000 spans are having faults. Here it is from the earthquake, how many Pacific as an electric transmission towers and poles were exposed to various levels of shaking.
And we saw actually 3 or 4, faults. Actual faults, electrical faults, which then shut down 25 circuits, which then led to the bulk power outages.
So I have here we did some full-scale testing over Buffalo a couple years ago.
We built a transmission line, we shook the heck out of it. I didn't show a movie here, but I have a couple snapshots of what this line does when you shake it on the left side we have a shake table,
On the right-side we have an actuator shaking the wires representing an earthquake. And if you're an earthquake, a big shake
these wires are conductors can easily move 5 feet. I mean, that's a lot of movement.
And the jumpers at transmission towers can move a couple of feet. And if the wires move out of phase and get too close to each other and they're going to short out and you're gonna have a power outage.
So the conclusions are in this earthquake. 95% of all the power outages were due to
faults in the transmission network, the power lines. Nothing broke. It just, intermittent faulting.
In the past, well, the forecast, these are all 2 or 3 sigma events. You have to get the wires shaking.
You have to go out of phase. It's a rare phenomena but you have thousands of spans it does happen.
To eliminate all these power outages require some sort of mitigation to prevent the wires from shaking side-to-side to touch each other.
Now in the past up to about 6, 7 years ago, our wildfires in California in the past the circuit breakers refilled these faults you would see at your house a little lights would flicker and then the lights would go back on.
Now, Pacific Gas & Electric and all the investor utilities in California take a different approach. It says if there's a fault, they're not going to re-energize the circuit until somebody, a human being walks down the line from end-to-end to make sure nothing fell on the lines because they don't want to put power through on a short circuit, which then create an ignition. This is a very time
consuming process. The average outage time in this particular earthquake was on the order of 14 hours and that was basically the time necessary
for PG&E staff walk down the lines to confirm there were no physical trees. Or branches fallen on to the lines.
They did all those serve as patrols or surveys and the answer was there were no branches or trees fallen on the lines.
Thank you very much.
As someone who experienced that power outage on December, 20th, 2022. I appreciate that talk and it's a great segue into our most recent outreach project here on the North Coast.
So, we've been dealing with earthquakes since I first arrived here in 1978 and millennia beforehand.
But it didn't take too long for me living on the North Coast to experience strong earthquakes.
And in 1993, we published our first "Living on Shaky Ground" magazine.
And since then, we've had basically 7 editions, our most recent addition we released on the one year anniversary of our last strong earthquake.
So I'm going to talk a little bit about the purpose of these magazines and why we felt there was a need to improve it.
Obviously there's a need for outreach to the general community, but these magazines also serve as a guide
for anyone, in the public sphere talking about earthquakes. We're fortunate here on the North Coast to have the Redwood Coast tsunami work group,
a very active CERT program and a lot of different outreach programs. And our "Living on Shaky Ground" basically serves as our guidebook so that we are all on the same page.
Our audience is Northern California; north of Santa Rosa. So a predominantly rural and many different kinds of communities,
and extremely vulnerable to landslides, ground shaking, and so forth. From the very first magazine, I was fortunate to work closely with Dennis Molletti in terms of getting the right social sciences message.
And from the very beginning, we've been always positive. There are essentially no images of death and destruction
and it's focused on what you can do to make yourself safe. We also make it clear that this is a work in progress that the next edition may have different information
because every earthquake and every tsunami is an opportunity to learn more. So why a new addition?
First, the need to update earthquake and tsunami information. Unlike most places.
In the U.S., we actually have very frequent earthquakes and our last edition missed the last 4 earthquakes.
Of magnitude 6 or larger especially the most recent one a little over a year ago. There is also a need.
To update our tsunami information and in particular, we learned a lot about a new kind of tsunami hazard back in 2022 with the Tonga volcanic eruption.
And these images are just screenshots straight out of the magazine. We were also able to include QR codes throughout to provide additional information.
There's also been a fair amount of technology, new technology and new programs, in particular ShakeAlert.
And we've had, I think I counted 7 ShakeAlerts since it went live in California.
So we have a lot of experience with it. Earthquake, Brace and Bolt, CERT programs and so forth.
And finally, the need to really improve readability and inclusiveness. Here you see two pages side-by-side in the 2014 edition.
The font was 8 which i can't really read anymore our smallest font now is 10 and many more illustrations.
to make it much more accessible. This is a project funded through CalOES and NEHRP, and NTHMP.
Funding and many of you in the audience help to review it. And I thank all of you.
Right now it's only available online. But we will have print copies. Hopefully by the end of February.
Thank you.
Awesome, thank you everybody. Let's have a big round of applause for all the speakers.
I hope everyone has thoroughly energized by our journey from the Bay Area up to Cape Mendocino.
I will open it for questions now. We're at the allotted end of our time, but we want to give some people the opportunity to ask.
Any questions that may have come up, there's no quite lively chat going on. So if people have any questions
go on and interrupt me. Throw your camera on. Start talking or raise your hand and do it politely.
I see Bob's got his hand up. Go ahead, dive in.
By unmuting. There you go.
Bye, unmute your mic. Sorry.
Yes. Sorry about that. I was gonna ask Carol is she gonna target the Candelabra trees in well gulch?
There's a whole series of trees, it looks like the tops have been broken out. It might be a really nice place to see the northern end of the San Andreas.
Hello, so far we don't have that as a target, but we do have some leeway with this year so I will give you my email.
I'd love to be in touch with you about which trees you're talking about because we're finding that the Candelabra trees are a little bit more clear-cut.
To date the top snap as opposed to trying to as we're talking about in the discussion when did a lean start and those type of things are a little bit harder to resolve.
I'm gonna put my email in the chat. Thank you very much.
Yeah, the Candelabra trees are on well gulch and I think they'd be a great
study. Yeah. Yes.
Are you at Humboldt as well, right? And so am I. Yeah, maybe we can.
I'll talk to you. I'll talk to you.
Maybe we can meet up. That'd be, fantastic. Thanks.
Yep.
I just put Bob's email in the chat.
Thank you so much.
Thanks, Dave, for covering my ass.
Not the last.
Not the first time. Yeah.
Ruth's got her hand up, hop in.
Yeah. So I, I'm like thinking about fire because we have it with and without earthquakes does undergrounding our power lines help.
I know that having our power lines above ground has caught a lot of problems even without earthquakes.
Is that a possibility? I know the city I live in, they have only underground it a little bit and they're not planning on undergrounding anymore.
So when we're thinking about you know earthquake induced hazards, we talked about fire, is that a possible fix?
Or maybe not. I was wondering in terms of the earthquake that I've been studied so far.
And the Ferndale experience. Thank you.
Okay. This is John Eatinger. So I've been studying this underground overhead lines from earthquakes.
As well as fires. There's no question underground power lines do much better than overhead power lines in earthquakes.
On the order of 90 to 99% more rugged. However, undergrounding transmission lines is 50 million dollars a mile.
And undergrounding low voltage distribution, your wood poles going to your house, something like 4 million a mile in urban environments.
Pacific Gas & Electric has 100 and 75,000 km of wires systems of which 80% is overhead, especially in rural areas where we have very few customers per mile.
So the cost on the ground is not $10 billion if you want that underground whole system we're talking Well over a $100 billion and moving towards a trillion dollars. 01:02:37.0$00 --> 01:02:45.000 The utility at Southern California Anderson or San Diego as an electric, PG&E, everybody is aware of the issue.
If you want your electricity rates to triple, stand up and say we want on the ground, but someone has to pay for that.
It's very expensive.
Thank you.
Hey John, a quick question. What were the voltages on those lines that tripped and also what was the voltage that you wanted to.
Simulate that you simulated up above flow.
So in the, Ferndale, Eureka, Rio Dell area, the highest voltage is a 115,000 volts.
There is some 115 lines, some 60,000 volt lines, and most low voltage distribution is at 13,000 volts.
There are no 230 or 500 in that area.
What was the breakdown though? Do you have it?
You don't have Okay. Okay.
I have the data. Roughly, 115 is about, 25% of the transmission.
And 60 KV is the the rest of it up there.
Okay, and what were you simulating with these experiment in Buffalo? What voltage?
Well that was a bluebird conductor that you saw there. That is a common line used for Southern California Edison.
We had SEE build that line. So that would be commonly used at 230 KV. That particular line that was in that take shake table test.
Thank you.
Oh, hop in.
Hey, I have a couple of questions for Tyler. You're really interesting new work on the Rogders Creek fault and I wondered what was the major impact of the new work on the, so they generally get, bigger, did they get smaller anywhere?
And I was also, interested in the question that they get smaller anywhere. And I was also interested in the question that David Schwartz brought up in the chat about how your new work, seemed to support.
Assigning the Mayor Island-like to Roger's because I don't think I've seen that before either.
More typically assigned to the Franklin fault.
Yeah. Well the Yeah, sure. So for the
the zone changes from I think it was initially done in 82 to what we're gonna release the final zones coming out and like in February.
Most of them got bigger. I don't think there's really any case where it got smaller.
Basically, you know, the lidar data supports these complex step overs. The Rodgers Creek, I thought was gonna be a little bit more.
Linear, but there's actually quite a lot of change in strike orientation along the fault, which creates these kind of restraining bends and complicated step over zone.
So, and then additionally, kinda what, Suzanne Hecker's done in the city of Santa Rosa, which was big impetus for us to rezone it, definitely widened the zone as it goes through the city of Santa Rosa.
So yeah, I would say overall it's probably been widened in some cases is about the same.
And I don't think there's really any case where it got smaller. As far as
the Mayor Island earthquake. It's really kind.
It's a seedling of a possibility. So first off, there's obviously been work that's been suggestive that the Mayor Island earthquake happened somewhere that that has been a attributed to the Southern Rogers Creek.
Now obviously it's an interpretation based off of kind of the shake maps to kind of felt reports and stuff like that.
So it's not certainly positive or conclusive. Interestingly what I found in the mapping that I did that's again something I really haven't spent much time really looking into it. Do you amorphic expression of the Rogers Creek was strikingly more robust for like the like the most southern extent of it.
So basically going from Sears Point. To kind of like Gravely Lake area. It was
the most distinctive. That I saw as far as the expression of it in the landscape, which to me suggests that it's more Either it's just more confined to one trace.
Or it's more, there might be expression of a event there that could be related to the Mare Island.
Again, I It's conjecture at this point, but there it was distinct in my mapping something that I took note of of how.
Basically from the north of Gravely Lake, which is like 10 kilometers north or 8 kilometers north of Sears Point.
It basically bifurcates in the 2 strands and it's actually not that well distributed or expressed, excuse me, not that well expressed across most of the landscape, which I was surprised to see.
I thought it would, especially with the slip that you would attribute to it, you think would be a little bit more.
Kind of distinct in the landscape. So that was kind of my thought around why you could say that the Mir island earthquake may have ruptured a small portion.
Just a smaller portion, but that would also require. It going offshore into the bay, which there was evidence of a small tsunami from the Maryland earthquake.
So and then that also kind of is conflicting with other data that Rogers Creek does not extend into S.
Pablo Bay. So it definitely is one of those things where. There's a lot to kind of sort out there, but.
The geomorphic expression was notable when I was doing the mapping.
Oh, that's interesting. And maybe if not, that is quick, at least a more recent earthquake than the part to the north.
Yes, yeah, yeah
Is that? Thank you. I guess I would also bring up the question, but of that earthquake rupture going unnoticed.
In 1898 if it were. There. I don't know much about the head. How likely it is that it.
Would have been not noticed had it ruptured that part of the fall at that time.
Yeah, I mean, that's a good point. And also, I don't know, is estimated to be.
6 and a half. So maybe there wasn't much, may not be much slip on it either.
So yeah, as a combination of things that it's kind of, I don't know if it's gonna be I don't know if you had a trench you would actually see it in your fault drench essentially so ideally you would but yeah maybe to your point it would be more of a more recent then the northern part of it.
So yeah.
Thanks a lot.
Thanks for indulging this discussion and there's also a good little bit of chat, some references about this.
If everyone scrolls up and wants to dig into that further. We're closing in on, we've exceeded our time.
I wanted to give sort of a 10 min period to answer questions. If anyone has any, burning final question, jump.
In I did I wanted I have a question actually for Ben Milosh and I'm hoping that this is potentially sort of broad and generalizable in a way that rounds out this session kind of nicely, which is in constructing these.
3d fault. Planes or surfaces, what sort of considerations did you need to factor in what tools you used to do it and how might we you know as we try and translate taking this sort of from the first talk in the session with says Christy's fault zone dimensions with depth.
What are we gonna need to consider when we translate our geological knowledge into the third dimension?
Yeah, thanks for the question. That's That's interesting. Yeah, I think.
For that particular. Area that I presented on. There's little to no subsurface data. Not for wells or anything.
That might help pinpoint the fault geometry more accurately at depth. So I was basing that model on the micro says, and in places where, in the cross sections, for example, I showed.
Some places you could very clearly see. Well defined A fault within the Microsoft. I mean other places you couldn't as well and it was sort of more diffuse in those areas or sort of zones or there'd be more uncertainty or you could take.
You know, several geologists and they give you slightly different. Results. And for what I did, I was relying on those areas where I was well constrained.
I was very confident about the orientation. Yeah, the micro-size Micity stretched for several kilometers.
In 3 dimensions. And the zones where I was less certain. Recognizing that there's perhaps several different interpretations and then relying on interpolation within the 3D modeling software to help.
As well as doing simultaneously I made two dimensional cross-sections every 4 or 5 km.
And then sort of constructing my interpretations based on that and then extrapolated between the different.
2D cross sections. So, so obviously, you prefer to have more subsurface data.
But in some of these areas you just sort of have to apply what you have and Learn what you can.
Thanks, Ben. And thanks to everyone for this really interesting session and for the geologist for digging into the weeds and for the sushi's and engineers for taking us up to Darling, California.
I will. Thank you everyone for attending for sticking out this late. We're almost at the top of the hour, so I'll hand it back to Sarah.
Thank you.
Hello, hello, hello, thank you everyone. Excellent talk, speaker was moderator. Thank you so much.
And on the final votes of Christie Rowe, trees are not weeds. I'd like to call today's session to an end.
Thank you so much for coming. Please come back tomorrow morning. We have another action packed day set up for you.
We will start at 9 30 a.m. Pacific time and as always invite our speakers and moderators to come 15 min early at 9:15 a.m.
So we can get you set up.