Hi, there. I’m Steve DeLong from the USGS Moffett Field.
And I’m going to be reporting on some recent ongoing and future
research in northern California. And the sort of thread that ties
the talk together today is research that is maybe beyond our sort of
bread-and-butter emphasis on paleoseismology and looking at
secondary faults and creeping faults – that sort of thing.
Lots of co-authors on the left there. Most of them are the USGS folks at
Moffett Field – the geology group. Also Yann Gavillot from
Oregon State who is a collaborator. And other collaborators and other folks
who aren’t on this list have material in this talk as well.
I’ve done my best to give them credit when I’ve included their work.
So the sort of three things I’ll talk about are recent updates to the National
Seismic Hazard Map fault model and the research questions that kind of
came out from that process. And then I’ll zoom in a little bit
on the San Joaquin-Sacramento Delta and talk about seismic hazard there
and research that’s in that area. And then I’ll finish up by talking
a little bit about sort of an update to our longstanding effort
to understand creeping faults in northern California.
So first, recent updates to the National Seismic Hazard Model, Hazfaults.
This is the generalized fault model used in the National Seismic
Hazard Map and UCERF models. This is a more general model
than Qfaults or AP maps. And the fault geometries are
not meant to be fully detailed or accurate, but the overall geometry
has really important implications for fault connectivity,
earthquake rupture propagation, and maximum earthquake magnitudes and
how these things are handled in models. And there’s lots of discussion
about how this is done. You can see, of course,
the UCERF publications, and then sort of some discussions that have
come up more recently include Dave Schwartz’s paper from 2018
and Morgan Page’s paper from 2020.
So this has been updated. And thanks to Alex Hatem
out of USGS Golden for leading this national cat-herding effort.
It was done really efficiently with, I think,
a lot of participation from important folks.
And that model is available at ScienceBase.
You can contact Alex or me if you want to get that sent to you.
So, over on the right here is northern California.
Bay Area, Central Valley, Sierra, Mendocino Triple Junction.
And the orange faults are unchanged from previous versions of this model.
Red faults have been removed and refined.
And green faults are new additions to the model.
So you can see not big structural changes to the model,
but there are some details that are interesting to talk about, I think.
So, north of the Bay Area, northern California really worked mostly by
folks not in the Moffett Field office, include the offshore San Andreas
Fault – just a little refinement there just to kind of sandwich the map trace
inboard of where marine surveys basically didn’t find it.
And how this fault, as it comes offshore from Point Arena, interacts with the
rapidly deforming uplifting King Range and the Mendocino Triple Junction
is not super well-understood. So this is a slightly more likely
alignment of the fault, but there’s still work to be done up there.
Northern Central Valley – I think this is largely due to Steve Angster,
USGS, from his thesis work. Added the Red Bluff Fault
and the Inks Creeks folds. And I believe he’s got a recent – well,
he does have a recent geology paper where you can get some of the details
that led to these changes in the model. So you can reach out to him.
And then northern California – or, northeastern California, way up here,
sort of south of Mount Shasta, northern Walker Lane.
Added the Pondosa Fault Zone. If you want to learn about that –
if that’s not something you’ve heard about, Jessie Thompson Jobe
will be describing that is a lightning talk in this meeting.
And then lots of other refinement thanks to PG&E, consulting groups,
and other researchers on Hat Creek fault, McArthur Fault, faults in the
Big Valley, Honey Lake, and just a – sort of a large number
of faults in this area have been added to the model.
Zooming in now on the Bay Area – so here we are, San Francisco.
Here’s the bay. Here’s the edge of the delta.
You know, really – a few faults have been added. Most refinements.
And lots of folks were involved in this – Tim Dawson, Jeff Unruh,
Vicki Langenheim, and Russ Graymer, largely via their forthcoming Mount
Diablo work – paper that’s coming out in a GSA special paper soon.
And our collaborator Yann Gavillot as well.
So Contra Costa shear zone has always been this enigmatic area
of faulting and map lineaments. And we’ve just basically simplified
this into the – what is this – the Southampton and the Franklin Faults,
trying to put likely traces of where the faulting moves forward –
moves northward into Napa Valley.
Still not well-constrained. The old version’s not in here,
but it was a little bit more complex in how it connects down
from the Calaveras or up from the Calaveras.
Refined the – Mount Diablo is these two green arcuate thrusts.
And added this little Midway Fault and the West Tracy Fault, which we are
confident have Quaternary activity – Holocene activity, most likely.
And made some other refinements to geometries based on things like where
creep is mapped out and looking at Lidar and that sort of thing.
And you can see those refinements are sort of up and down here.
So no big changes to the principal San Andreas, Hayward, etc., etc.
So this all sort of inspired us to talk about current research and
future research interests. Some of this stuff, of course, is ongoing.
And so I will talk about the things in bold – San Joaquin-Sacramento Delta.
But other things that have been going on, Belle Philibosian and Mike Oskin
and the Davis group have both independently been working
in Napa for quite some time. Mike was – Mike was out there
before the 2014 earthquake. He knew something.
So fault mapping updates are forthcoming for Napa, for sure.
Rodgers Creek-Maacama connectivity – oh, I’ve got some
ovals to show you here. There’s Napa.
And so the connectivity to the Maacama and the Rodgers Creek,
Suzanne Hecker is working on this, and there will be forthcoming
mapping that gives some more details on that.
Nothing’s been including in the fault update, but that’s happening.
Farther north, we’re interested in the northern Maacama, and I mostly put
this in because there’s a whole session on this issue in this meeting,
and it’s something I’ve spent a little time looking at, and it’s interesting to
see how these faults become more complex as you move northward
towards the Mendocino Triple Junction. And its recent seismicity really
indicates that the faulting is complex, which others have observed as well.
So it’d be nice to – there is ongoing work to better understand that.
Connections between the Greenville Fault, which –
you know, the Greenville Fault is here east of Livermore –
had an earthquake in 1980.
And we don’t really know what happens to the slip as it moves
north from Livermore Valley. Does it stay to the east of Mount
Diablo, where there’s not really great evidence for active faulting?
Or does it move through Mount Diablo up onto the Concord,
which we know is a pretty active fault?
Still an open question.
More work can be done there.
We have ongoing – oh, yeah, so also the connection for
the Calaveras – so here’s the Calaveras Fault.
Where does this go? It probably doesn’t go through the
Contra Costa shear zone up to Napa. It just doesn’t seem like this is
the most active faulting area. But the Concord is certainly more
active, so perhaps it actually – slip is transferred to the Concord
somehow through this area. So that’s an area lots of folks
are working on and thinking about.
Farther north – Bartlett Springs Fault. We want to understand creep,
slip rate, event chronology. So we’re pushing forward on that
as well as – we have a plan to update fault mapping as well
now that we have Lidar. The last real effort was photo-based.
And then I’ll talk a little bit about this issue of maybe possible fault
connectivity from these sort of Mount Diablo-Great Valley thrust systems
through the Midway Fault and farther up, and this question of where –
how does this all work kinematically? And, more generally, we’re interested
in the distributions and implications of fault creep.
And I’ll talk about that as well.
So in the delta, Chad Trexler is leading a lot of this work, but I’m involved.
Yann Gavillot is involved. Belle Philibosian is involved.
And we’ve got lots of – a list of things to do once
we can get back out in the field, for sure.
So the Montezuma Hills are an area of interest.
This is the sort of actively deforming low range of hills north of the delta.
We know there’s these geomorphically interesting wind gaps where streams
used to go through, and now they don’t.
And so this is certainly a likely indication of active deformation
in this area. So we’d like to better understand that.
And then Chad is really working – and he’s got a lightning talk,
and he can give you the details. I’m using a combination of the bedrock
geology and the geomorphology, including things like zones of possibly
active uplift and how that interacts with a fluvial system.
And he’s identified all sorts of interesting stuff there that can
indicate tectonic activity and faulting.
Zooming in just a bit – Yann Gavillot is going to give a lightning talk on
sort of the trenching – most recent trenching in this area,
but we’re also working on looking at – so starting here.
This is the Diablo Range, zooming into the Black Butte Fault and San Joaquin
Fault in this area and some active structures to the north of that.
Then zooming in a bit more, we can see that there are these places where
faults offset these alluvial surfaces. So there’s a – you know, we’ve done
a bunch of mapping of this suite of alluvial fan and fluvial terrace surfaces
at both Lone Tree Creek and Corral Hollow and analyzing those.
Getting – we’re starting to get ages – luminescence and cosmogenic ages.
More are forthcoming. But initially, you know,
correct for geometry, and we can see that these faults are probably
deforming at something like that 1.5 to 3.5 millimeters per year.
And this has implications for seismic hazard to the delta, which we know
is ecologically and, in terms of infrastructure, vulnerable.
And then how these faults sort of interact.
So here we are in – here’s Tracy, and this is the Qfaults and Hazfaults
and how these – how the faulting works on the range front and how that
might transfer through the Black Butte anticline up here onto the Midway Fault
and then possibly, from the Midway Fault, does this slip actually transfer
on the east side of Mount Diablo? Or does it work through this network
of faults southeast of Mount Diablo and even onto Mount Diablo?
So the larger-scale kinematics in this area are interesting to the think about,
and we’re just trying to understand those, as well as
the activity of the Midway Fault here.
So just wrapping up, so creeping faults are something that we have studied for
a long time in northern California. And recently, we’ve really been
aided by our geodetic friends. Gareth Funning and his group,
in particular, but lots of other folks as well who have helped us
understand the distribution of fault creep.
So this is information that we really like to receive so we can guide our
geologic studies and help us interpret our observations in light of what
the remote sensing work tells us. And so recently, they’ve highlighted
zones on the Rodgers Creek Fault that are creeping.
And this is from things like spaceborne SAR – InSAR –
and repeating earthquakes. Down here, we see evidence
from repeating earthquakes.
Looking at seismicity, we can get at fault creep and geometry of structures
and all sorts of interesting things over on the right as well.
So creep rates in the colored boxes from repeating earthquakes as well.
And then, of course, the satellite SAR has really been great for
showing us where faults creep. So what kind of stuff do geologists
do with fault? Well, quite a bit. Because we want to understand
how much moment and slip rate is taken up aseismically.
We want to understand how we distinguish creep
in the paleoseismic record. And we want to think about what
the implications are for fault rupture propagation, especially when you think
about big players like the central San Andreas and the Hayward.
And so, you know, I mentioned InSAR and seismicity.
In our group, we use alignment array re-occupation, repeat terrestrial Lidar,
UAV surveys, repeat airborne Lidar, image analysis using things like
COSI-Corr, and, of course, direct observation, which you
have a couple examples of here. This is Suzanne Hecker’s trench –
recent trench on the Rodgers Creek. She’ll have a lightning talk about that.
And our – the crew did a trenching investigation, and then, as we were
wrapping up, the area burned. We lost a lot of gear, but it was
interesting to go back out after the fire and observe that what is
most likely the creeping trace of the fault has these opening cracks.
And here’s Ali in the latest post-fire apocalyptic field gear surveying out
those cracks. And then this is just an example of re-occupation
of an alignment array that Belle Philibosian and
Dan Mongovin worked on on the Sargent Fault.
And we’ve looked at these elsewhere, of course.
And just a quick update. You know, our longstanding
monitoring of the northern California alignment array system.
Jim Lienkaemper recently retired, and we’re carrying this on.
We’ve got new instrumentation. This is, you know, driven by San Francisco
State and Jim in the past, and now Austin Elliott is picking this up.
And so we’ll be continuing to monitor all this.
And then we’ve got – of course, always trying to figure out
new fancy ways to measure creep. And to learn about this cool figure
in the lower left, check out Chelsea Scott’s talk, which I believe is just
after this one, or a few after this one.
And you can learn all about using Lidar to measure creep.
So I’ll tie this all together.
You know, updating the Hazfaults model indicated areas in which fault activity
and connectivity needs to be better understood.
These secondary low-slip-rate,
long-recurrence faults are particularly challenging to study.
Understanding kinematics from, not just faults, but folds and, you know,
things apparent in geomorphic analysis can be a way forward.
And examples are, like, interactions between the thrust faults adjacent to
Mount Diablo and the strike-slip faults – the Greenville,
the Calaveras, etc., etc., may help us eliminate
more complex kinematics and fault connectivity.
Fault creep detection really helps us observe creep evidence in paleoseismic
investigations and are good indication of where the active faulting is.
And we’re going to continue creep monitoring and measurement
using proven, like, alignment arrays and survey instruments
and emerging methods like I described.
Thanks for listening.