PubTalk 5/2021 - Where Earthquakes Hide in the Desert

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Title: Where Earthquakes Hide in the Desert: What we've learned from recent fault ruptures in the western U.S.

By Austin J. Elliott, USGS Research Geologist

  • Three large earthquakes since 2019 have ruptured incompletely mapped faults in the western U.S.
  • Both satellite and field measurements give extremely detailed maps of how the ground deformed.
  • Imaging these earthquakes and studying the previously unrecognized connectivity among the causative faults offers a rare window into the types of earthquakes that can occur, including how large and how often.
     

Details

Date Taken:

Length: 01:16:50

Location Taken: CA, US

Transcript

Hello everyone and welcome to

the US Geological Surveys pop

virtual public lecture series.

My name is William Seelig

and I will be your host.

And moderator today.

Before we introduce our speaker

tonight I have a few announcements

make for next month lecture.

We have Carolyn Driedger who is a USGS.

Hydrologist. Carol will be giving

you talk on Mount St Helens.

Called lives changed.

Lessons learned an legacies of 1980

that talk will be on Thursday.

June 24th at 7:00 PM Pacific,

so make sure to mark that in your calendars.

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We appreciate your.

Understanding in advance and

now for the exciting part,

so to introduce our speaker.

So tonight we have Austin Elliott

who will be discussing recent fault

ruptures in the western United States.

Austin received his bachelors in

Earth Sciences at the University

of Southern California.

He then received his PhD from UC Davis

where he researched from a geological

perspective how earthquake ruptures

are arrested along a fault system.

After that,

he spent five years in the UK working

on in post DOC research position

with the Center for Observation

and Modeling of Earthquakes,

volcanoes,

and tectonics at the University of Oxford,

where he studied large early and pre 20th

century earthquakes in Central Asia.

Which is one of the highest seismic

hazard reason regions in the world.

Austins first with USGS was actually

2003 as a high school intern where

he was given the opportunity to

find and analyze accounts of 19th

century earthquakes in old archival

newspaper film records mode.

More recently he joined the USGS in

2019 as a research geologist where

he studies the record of birth place

in the landscape at the Earthquake

Science Center in Moffett Field,

California.

And now I'm going to turn the mic over

to Austin Austin. The floor is all yours now.

Alright, thank you very much.

Let's get us started here.

Hi everyone, thanks for having me and

thank you for taking the time to watch

this talk about what we've learned from

recent earthquakes in the western US.

As well said, I work in the earthquake

geology project at the USGS Earthquake

Science Center at Moffett Field.

This means that I study the impact

effects and record of earthquakes

in the rocks the geology.

So let's familiarize ourselves

with the recent earthquakes

that I'll be talking about.

Well, there were a whole host of traumatic

things piling up at once last year.

You may or may not have noticed the

earthquakes did not stop bothering us

while we dealt with the devastating

impacts of a global pandemic.

Not long after the US,

cities began to shut down.

Salt Lake City was rattled by a magnitude

5.7 earthquake scarcely two weeks after that.

Much larger earthquake emanated

from the remote mountains of Idaho,

shaking many of those same folks an more.

The onslaught continued

with large earthquake,

an near Bodie Ghost town in the

eastern Sierra of California,

and as we were watching that

notable sequence unfold,

the widely felt needed 6.5

Monte Cristo range.

Earthquake occurred near Mina

in remote Western Nevada.

Just over a month after that,

magnitude 5.8 earthquake

struck beneath Owens Lake bed,

also in the eastern Sierra.

An aftershocks from the largest of these

earthquakes continued down the whole time.

Then in August,

North Carolina joined the party with a

widely felt earthquake of magnitude 5.1.

As succinctly stated on the Twitter

by the US Consumer Product Safety

Commission at the end of April 2020,

there was a lot going on.

This may seem like an inordinate

number of earthquakes,

but if we take a bigger picture

perspective of the active Western US,

we see that it's not really

abnormal at all for the place to

be lighting up with earthquakes.

Here we're watching a

fantastic animation by Noah,

specifically the Pacific

Tsunami Warning Center,

whose purview does include

earthquakes as well,

speeding us through four decades of

earthquake occurrence measured across the US.

As the animation continues,

it shows that modern,

moderate to strong earthquakes are indeed

quite common across the Western US.

Only a few of them make history when

they strike near population centers.

Many are long forgotten because the

western US is largely wide open,

sparsely populated space.

The animation continues for awhile and

I recommend that you search for Noah.

40 years of earthquakes on

YouTube to continue watching this

pretty spectacular animation.

The most recent of these large

but soon forgotten earthquakes

occur just a year ago, this month.

It's anniversary is the occasion for

which I'm invited to speak to you today.

That earthquake was on May 15th,

2020 at 4:00 in the morning was 96.5 so

called Monte Cristo Range earthquake

because of where its epicenter was.

Although the earthquake was widely

reported as felt as shown here in

this USGS shake map which contains

as well as instrumental records.

Did you feel it reports from the online

submission system that allows you to

report the shaking experience that you had?

The areas with the strongest shaking were

actually some of the least populated.

Areas in the entire country as shown

here in this USGS pager systems.

Population exposure map.

Pretty much the only impact from this

earthquake were to the tarmac and

roadbed on Nevada State Highway 95.

It's shown in this picture from

the Esmeralda County Sheriff.

Well, only this one of the western

US earthquakes during the year of the

pandemic ended up large enough to break

faults to the service and study geologically.

The prior year saw two surface rupturing

earthquakes in Eastern California which

were widely felt across the southwestern US.

At about 10:30 AM on the 4th of July 2019,

folks preparing their barbecues

from LA to Las Vegas,

where jostled by the long rolling

waves of a distant magnitude 6.4

earthquake which was centered near

the city of Ridgecrest.

Being so large,

it was the immediate target of

scientific investigation and a

host of seismologists and engineers

descended on the badly shaken town

of Ridgecrest to begin to study.

Literally,

just as they were wrapping up their

first date of reconnaissance on

the 5th of July,

a much larger magnitude

7.1 earthquake struck.

You can see the difference in scale and

impacts here between these two images.

Some of my colleagues were caught on

camera as they broke their wrap up

huddle just as the larger quake began.

What you're looking at is closed

circuit television captured

from a hotel in Ridgecrest,

where scientists had gathered to.

Stay the night as they studied

the impacts of this earthquake.

They've just wrapped up a day of

talking about what they've seen,

what their plans are.

And they are ready to head and

probably go to either dinner

or bed as they wrap up here.

Strong closes the door of his car.

He seems to trigger the earthquake.

The shading that you see here.

Ends up being quite dramatic.

There are a few things to notice.

The earthquake lasts many seconds.

This is characteristic of

a very large earthquake,

a magnitude 7.1 with shaking your

experiences somewhere 20 to 30 seconds

plus the ground motions are very strong,

but the buildings are nice and sturdy.

They stand up.

There are some panic reactions people

running around outside their buildings.

The recommendation is of course to

drop under sturdy furniture where

you are because running around risks.

Tripping, falling, being hit by things.

Nonetheless,

these are understandable reactions

to a really jarring event,

especially after they've already had one.

So this bunch of earthquakes out

in the desert I found the San

Andreas was our most famous threat.

In shaking potential maps like this one

prepared by the California Geological Survey,

the San Andreas is indeed

the hotspot or the hotline.

It carves, an ominous gash through

the landscape of coastal California,

as pictured here,

where it runs midway between San

Luis Obispo and Bakersfield.

But all of these recent

earthquakes that I've mentioned.

And others, which I'll talk about,

have happened away from the San

Andreas over in the interior desert.

Despite the despite the San

Andreas being the fastest.

Moving and posting the largest earthquakes.

The fault is not ruptured increase since

1906 in the North 1857 in Southern

California and even earlier at its

farthest southern end near the Salton Sea.

So all of these other earthquakes

and that we know about and have heard

about in our lives in California,

have happened elsewhere in the

state or in neighboring Nevada.

So what gives?

Furthermore the San Andreas

Plate boundary is a simple fault.

The recent fall appears elsewhere.

Some involve 2 to 5 volts single,

three or more.

The Ridgecrest earthquakes involved a

huge host of faults were not simple.

Each of these recent complex earthquakes

and many other recent well image

earthquake fault ruptures have been

considered by scientists unexpected

or surprising in their complexity.

So why were we caught off guard by

these will expand the question further

to where we actually caught off guard.

Or did we really have a fair idea

that these would happen or these

earthquakes really a surprise to us?

Well, it's essentially part of our job.

Is the US Geological Survey

to answer these questions.

This document outlines the USGS

Natural Hazards science strategy,

the mission of the USGS,

and natural hazards is to develop and

apply hazard science to protect the nation,

protect the safety,

security and economic well being

information to fulfill its mission

and meet statutory responsibilities,

the USGS must conduct geologic mapping

and acquisition of geophysical data

to enable a better understanding of

hazardous processes, including sources.

And impacts collect ephemeral data

during hazardous events that will

support future research to reduce loss

and develop long term chronologies with

associated magnitudes of hazardous events.

I'm reporting on these as

specific to earthquakes,

but you can imagine that these

apply to any number of the natural

hazards that our country faces.

A strategy document that was assembled

by the constituent agencies of

the national earthquake Hazards

Reduction Program makes clear what

role the USGS Science Investigations

play and understanding earthquakes.

USGS has the statutory responsibility

and authority to conduct post

earthquake investigations in order

to provide insight into how faults,

rupture, understand and predict

shaking and ground deformation and

document and improve performance

of the built environment.

I'm going to talk about how these

earthquakes applied all of these things.

After the puzzling observations posed

earlier about complex earthquakes

away from the main plate boundary,

you might be asking yourself,

like my colleague Chad here,

looking lost among the

fault lines in the desert.

What do we learn from

mapping all these fractures?

Why do so many large earthquakes

keep happening outside that map

zone of highest shaking probability?

And how have recent earthquakes informed

our expectations of future seismic events?

This is what we're talking about for

the next half hour or so I've already

spoken about our most recent earthquakes.

Before we go much further,

we're going to need to back way up and

make sure that the relationship between

earthquakes and fault lines is clear.

You've already heard me and you'll hear me

more using the words earthquake fault and

rupture a lot during the next half hour,

and I want to make sure that we're on the

same page about what I'm talking about.

The remainder of the talk will explore some

of the complex examples I highlighted,

so really see where mapping gets us,

culminating with a report on the

earthquake that happened just a year ago.

So let's jump back to the basics of

geology on Earth, the tectonic plates,

pieces of the broken up hard shell

of crust that surrounds Earth,

hotter interior.

The boundaries between these plates

are earthquakes and volcanoes occur

as they grind against each other.

The boundaries between the blades look

like well in our case the San Andreas Fault.

But there's more to it than that.

While the San Andreas runs up the

spine of California as pictured

in this astronaut photo from the

International Space Station.

Tectonic disruption of our crust extends far,

far inland from that thousands of miles.

Even where we still have tectonic action

splitting up our mountain ranges.

All that topography isn't just

there for nothing.

In fact,

the reason we have tectonic activities

so far inland is illustrated nicely by

this animation of plate boundary evolution.

Since 38 million years ago constructed

by Tanya Atwater of UC Santa Barbara,

with constraints from geological data.

As the Ferrell on plate disappears

beneath North America,

convergence at the plate boundary

stops and the margin of the North

American continent begins spreading

back out into the space that's open.

As the Pacific Plate slides northwestward.

The effect of this is to essentially open

up and create the entire state of Nevada,

among other areas.

These days we actually track this motion

in real time, which is astonishingly cool.

An array of GPS antenna installed

across the western US continuously

reads out their positions to

millimeter accuracy tracking where

they are and where they're headed,

mounted firmly in the crust,

this map shows their velocities.

From these data, scientists can calculate

the rate at which the crust is deforming,

displayed here in Matthew.

Does this look familiar?

It's a lot like the seismic hazard

map and this is no coincidence.

The deformity of the crust can

also be seen directly in the

terrain of the Western states.

Northward relative motion

of the Pacific Plate grinds.

These northwest aligned linear grooves in

the mountain ranges of coastal California.

The extension of the crust inland

breaks up Nevada into its famous

basin and range topography.

Much of the terrain can

be attributed to false.

The breaks in the crust,

which periodically slipped to

cause earthquakes.

USGS maintains a database of geological

faults and their associated fall folds,

in particular the ones that

demonstrate evidence of.

Deformation in large earthquakes

during the past 1.6 million years.

The Quaternary period of geologic time.

The Q files database.

Contains information on the recency

of slip and the frequency and the

frequency of recurrence of movement

in seismic events along these faults.

This data forms the basis of

our seismic hazard maps,

which I'll get to in a moment.

Uhm?

Because it involves the recency

of motion on the false.

It's also a great way to image

earthquakes that have in fact occur.

Dan been measured in the recorded

historical period or since about 1850.

Go wait earlier we saw earthquakes

as blinking dots.

Usually you see them as dots on a map.

But here we have all these big red

lines mapped out along the faults.

So what exactly is the relationship

between an earthquake and a fault?

This is pretty key to the rest

of what I'm going to talk about.

Fault,

as I've hinted or breaks in the

earths crust along which the opposite

sides slip in opposite directions.

They're usually stuck shut

by weight and friction,

but eventually tectonic forces

overcome that and force them to

lurch into a new position where they

continue loading to lurch again.

But the whole fault doesn't slip at once.

It breaks as a growing crack like

you might see in your windshield.

That crack nucleates somewhere

beneath the quakes epicenter and

begins to unzip the sides of

the fault across a growing area.

That area grows in either direction

at about 1 to 3 kilometers per second.

That's like 5000 miles an hour,

but the process only takes a few seconds.

The fundamental thing that controls

the magnitude of an earthquake is

how much of that fault slips in one

of these failures before stopping.

This is crucial to how we understand

and interpret earthquake geology.

So how do earthquake magnitudes

than correlate to that total

area of a fault that slips?

Recall that the earthquake

magnitude scale is logarithmically.

That means that each unit increase

from zero to one one to two,

two to three is actually a tenfold

increase in the size of the

earthquake metric units thus make

for an easy and natural way to

understand increasing fault rupture

size with earthquake magnitude.

And thankfully I have some

handy comparisons for you.

So we begin with a magnitude 0 earthquake.

You've probably never heard of these.

These are generally did

not perceptible by humans.

They produce very small ground

motions and are only detectable in

mines or places where you have really

sensitive instruments right next

to the source of the earthquake.

A man injured 0 earthquake is

produced by about 100 square meter

patch of a fault slipping that's 10

meters on a side or about the size

of a typical apartment magnitude.

One earthquake also way too small for

generally too small for people to

feel is the rupture of a portion of a fault.

That's about 30 by 30 meters on the side.

That's approximately the area of a

typical US home locked in this case,

what we're looking at is maybe.

15 by 45 meters,

but it balances out to give you 1000

square meter area of the patch of

the fault magnitude 2 earthquake.

Now we're getting into ones that you

might notice would be perceptible to humans.

They are caused by 100 by 100 meter patch

of a fault rupturing and slipping at once.

100 meters to be familiar to everyone

as the length more or less of a football

field 100 by 100 meters is maybe

technically 2 football fields side to side.

But we're only talking rough numbers here,

so next minute upamanyu three that

starts to rattle you 300 by 300 meters.

That's something like along city block

in America. Amended 4 earthquake.

This one you're really starting to

feel the shaking it makes sounds.

These are A1 square kilometer

patch of a fault,

roughly rupturing and slipping that

emanates seismic waves that is

roughly the size of a neighborhood

or subdivision in America or square

miles rather than square kilometers.

But we're talking ballpark numbers here.

Amanda did 5 earthquake is a 10 square

kilometer area that's approximately the

footprint of an International Airport.

So imagine the footprint of LAX

flipped on its side,

sitting across beside you.

That's how much of the fault

unzips to produce a magnitude 5

earthquake magnitude 6 earthquake,

10 kilometres on the side.

Well,

that's the size of the whole

city of San Francisco.

Something important happens

above a magnitude 6.

The brutal part of Earths crust is

only about 12 kilometres deep or so.

Below that, the earth gets warmer and

the rock like a two warm chocolate

bar bends instead of breaks,

so it doesn't support this strong

rigid seismic energy that creates

the earthquake once eruptions

diameter reaches 10 or 12 kilometers,

it's broken the entire depth of

the crispy part of the shell and

like a crack in your windshield,

it begins to propagate just

laterally to the side.

This is when ruptures are large

enough to break the surface

and false become expressed.

In the landscape.

Here's what that looks like Robert

Wallace and influential earthquake

geologist for decades within the

survey summarized the landforms

produced by horizontal motion along

a so-called strike slip fault.

There's no quiz on this for you,

but what's important to note is

that there are a variety of distinct

features that are diagnostic of a

tectonic fault sculpting the landscape.

There's this perpetual competition

between tectonic disruption of the

topography and rain and erosion

wearing it down,

but the eroded features themselves

also for markers that we can track over

time as they are offset by faults.

Here's what these look like in

real life as seen from satellites

orbiting our planet.

Any of these are visible to you on

virtual tours via imagery in your

favorite mapping app just fine.

Default map Ann and follow it to

your favorite corner of the world.

What you mainly see here is landscapes

carved or deposited by water gullies,

stream channels and big fans of

deposited gravel like this which

had been sliced and slid by lateral

motion along the faults.

You can see this faults slicing

through each of these individual images.

Very unnatural looking straight lines.

In this case,

it's very conspicuous how they've

shifted the deposits from the mouths

of these canyons off to the left here.

These landforms can be preserved for

10s of millenia in desert environments,

and they are fundamentally what

we use to measure earthquake size

and recurrence rate from the

history of ancient earthquakes.

This final one here is a Geo tourist

destination in Carrizo Plain National

Monument in Central California.

It's a great stop for you on a future

spring wildflower tour in the state.

The offset, an abandoned stream

channels across the fault here,

actually named for Wallace of the infamous.

Prior figure.

This is what the formation of one

of these landforms looks like as

a result of a single earthquake

you're seeing before and satellite

images of the 2019 Ridgecrest

earthquake in the Mojave Desert.

These gifts were put together

by Sotirios Vulcan notice from

which he posted on Twitter,

but these are representative of the

types of imagery that we look at

and that we use to map out where

these fault ruptures happened.

Here's another example.

In this one you can see how the

stream channel in the center is

offset and may preserve evidence

of this horizontal fault motion.

Another view shows how these offsets

impact anything built across them.

In this case roads.

In this case, pipelines.

This one is for water.

Handling these unavoidable infrastructure

crossings of active faults

appropriately is one of the principle,

economic and safety motivations for

detailed mapping of fault zones.

A more dramatic example of faulted

infrastructure comes from Palo Indonesia.

After the magnitude 7.8 earthquake

they had in late 2018.

You can clearly see what a hazard,

not just the shaking from

earthquakes represents,

but from the fault motion itself.

California has many faults underlying

these cities and has implemented

laws requiring set back zones for

large human occupied structures.

Plenty of things built before 1972,

however,

and some after still straddle our phones.

So if those last images weren't

compelling enough,

evidence that there's a need

to map and measure faults,

it's important to know that the location

and relative activity of faults

represent fundamental elements of

our modern seismic hazard assessments,

which the US updates every five

years with ever more and ever newer

information created by the USGS.

Information such as the location of faults,

possible earthquake size,

the recurrence interval of those earthquakes,

how often will a fault continue

to produce those?

Different rates of slip recurrence or

the amount of slip in an earthquake.

Implied different sized earthquakes

at different time intervals and

it's important to capture that

information that information so

that we understand the scope of

earthquakes that may happen in

the future along a given full.

We seek to understand the distribution

of those recurrence intervals

along our entire fault system,

as well as how large along are the

earthquakes that have can or will occur.

Our principle information about

what types of earthquakes may

occur is what the earthquakes,

what the earthquake ruptures are like,

that have a Kurd.

Unfortunately earthquake scientists

rarely get to choose when to set

up and conduct our experiments.

We have to wait on the whim of

nature in California and Nevada,

we have a pretty decent

and fascinating record,

and despite a few key

notorious events in history,

the Northridge earthquake

woman Prieta Sylmar,

so many of them have a curd in the remote

desert that we've gotten lots of information.

Too much impact society.

At least two dozen earthquakes since

1850 have ruptured the surface,

allowing us to measure them.

And these are just the biggest.

Let's look at one such example.

A Southern California classic,

at least among earthquake scientists.

The 1992 Landers earthquake.

When they start,

when the earthquake happened

at about 5:00 in the morning,

it left a 70 kilometer long gash through

the desert that's about 50 miles.

You can still see evidence of

the tectonic motions today

sharing the built environment.

If you're ever visiting

Joshua Tree National Park,

a short excursion northward takes you to

the land offset by the 1992 earthquake.

You can see these things yourself,

although looking on Google Earth recently,

I discovered that this road

has been re paved,

maybe smoothing over some of the offsets.

The farfield should still be visible.

Ann is evidence of ongoing active

deformation of our plate boundary.

In the era when that

earthquake occurred 1992,

scientists generally relied on

a basic concept that the length

of a map fault translated to the

likely maximum magnitude of an

earthquake that it could produce,

sort of like using that table.

I showed you a few slides back.

In 1990,

a pair of researchers published

a definitive paper summarizing

the recognized active faults

throughout the Mojave Desert.

Coining it, the Eastern

California Shear zone.

Here's the state of knowledge

of the Mojave Desert.

Active faults at the time

of the Landers earthquake.

If you travel between Los Angeles

and Las Vegas, you pass over a

regular succession of active faults.

These have been the source of

many of Southern California

is large rolling earthquakes.

In the last few decades.

Two important passages from

this paper stand out.

Number one.

The Eastern California Shear Zone,

because of its probable physical

connection to the San Andreas Fault system,

may have accommodated a significant

portion of the Pacific North American

transform motion these days.

We know this to be true.

We measure it with those GPS

monuments that I showed you earlier,

and we've had subsequent

earthquakes to validate this claim.

Another passage highlights the fact

that the false that they have been

identified here in 1990 are discontinuous.

None of them are too long.

Only one really appears to

straddle the entire Mojave Desert.

This passage implicitly suggests that

the individual faults will produce

limited earthquake magnitudes,

at least compared to the long

straight San Andreas Fault,

which is seen on the lower left of this map.

Then two years later,

the Landers earthquake struck.

Here's the pattern of surface

ruptures as mapped by whole teams

of researchers from universities

and government agencies.

You can see that it involves

more than one of these discrete

folds that was a wake up call and

remained the poster child of an

unexpectedly multi fault rupture.

But you can also see is that

only small portions of it were

previously unrecognized.

Scientists had actually done a great

job identifying the complete lengths

of the active faults along which

this earthquake rupture propagated.

Notably, seven years later,

another earthquake,

tangentially,

the first one that I ever experienced

at the new transplant to California.

Unzipped along a couple of adjacent faults.

While the smaller and less complex.

Earthquake the Hector mine again

illustrated that we need to

work harder on constraining how

propagating earthquake ruptures

navigate a fault system.

Which branch do they take?

How far can it connect adjacent

faults across an apparent gap?

Are the gaps between these faults

real or are they artifacts in our

maps of high sedimentation rates,

burying defaults from our view,

it takes a lot of different approaches

and tools to answer these questions.

And in the time since we've

made great progress,

here's the current query fault

map for Southern California,

the newest generation of seismic

hazard analysis takes into account

rules about how far between

disconnected fault tips of propagating

earthquake rupture can jump.

These rules are based on observations

such as those from the Landers earthquake,

but also on physics based

computer simulations,

and also laboratory experiments in

small scale analog sandbox models.

Every new Earth grade that we measure

helps us hone the expectations for

how earthquakes may propagate along

the fault system in the future.

The next example of an unexpectedly

complex earthquake rupture came

from just South of the border.

The rupture actually spanned

the US Mexico border on the

afternoon of Easter Sunday, 2010,

the so-called Elmira Kukupa earthquake,

named for the mountain range

and indigenous land in Wichita,

Curd ripped through the desert

forming these massive scars,

cars and swimming pools rocked

and rolled across Southern

California and northern Baja.

While this rupture propagated

along a set of 11.

Different faults.

In an intriguing parallel to the Landers

earthquake, almost two decades prior,

two researchers had published a paper

just the year before documenting fault

throughout the area and describing

how they might operate or linked

together during a large earthquake.

Here's that fault.

Mapping in the area at the

time of the earthquake.

I want to highlight that the black

lines in this represent fault

lines map throughout the bedrock.

And the paper described how

they may be activated together

above a low angle fault below.

Here are the faults that broke to

the surface in the 2010 earthquake.

A whole host of us mapped surveyed and

measured this rupture and it turns out

that the way it operated was almost

exactly as prescribed as described,

that it might in John Fletcher and Ronald

spells paper from just the year before

talking about other faults in the region.

So despite the apparent physical

complexity of all these false linking

together in a single coseismic rupture,

the prior tectonic mapping had already

recognized how this might occur.

The Rapture was unique, yeah,

but was it wholly unexpected

in hindsight now?

Next we move to Southern California's

most recent pair of large earthquakes,

the 4th of July Weekend Night 2019 Ridgecrest

sequence that I've mentioned earlier.

You're seeing a video of the aftershock

sequence that accompanied the two

largest main shocks of the sequence.

Aftershocks are just more earthquakes

responding to the dramatic,

abrupt changes in stress

introduced by a larger event.

Importantly,

they happen very near to the fault

that ruptured so they can be used to

illuminate its length and location.

As you watch all the recorded

aftershocks light up.

This intersecting a ray

of false that slipped.

You may recognize the same

old story playing out.

These earthquakes ruptured more

faults than we might have expected,

and in unforeseen configuration.

But we've gotten wise to

these seismic tricks,

and we've developed better

ways now of assessing just how

unexpected these events really were,

so that we can try and incorporate

their observed behavior in the

future seismic hazard models.

Here are some of the striking

examples of rupture through the

Mojave Desert at this point,

becoming familiar to you.

Among the scientists that you see,

measuring the amount of the

amount of these faults slipped,

or a group of my colleagues that embarked

on a study of the Ridgecrest earthquakes.

To quantify just how quote,

unquote,

unexpected these ruptures were.

Did we really know about these faults?

Their work after the Ridgecrest

earthquake evaluated how much of

the night 2019 Raptors were or

could have been known beforehand.

What you're looking at here is the

state of the Quaternary faults database

before the Ridgecrest earthquakes happened.

What's shown here are the fault that

ruptured during those earthquakes in 2019.

About 35% of the false that ruptured

in 2019 were in fact represented in the

Quaternary fault and fold database,

but you can see that a number of them aren't.

Nonetheless,

lots of faults were mapped throughout

this area prior to the 2019 earthquakes.

What was unclear was just exactly

how they might all link up together

to produce a larger earthquake.

To dig into this deeper,

I'm really show some results.

What you're seeing in the map here

is essentially showing you how

much of in the thick,

bold lines showing you how much of

the Ridgecrest 2019 ruptures had been

recognized previously in orange and yellow.

The black ruptures are all

ones that were sort of

newly discovered.

However, my colleagues looked

through satellite images,

air photos in high resolution digital

elevation maps from before the

2019 ruptures to try and identify

whether these faults could have been

detected and had just been missed in.

Compilation for the Customer fault database.

They found examples like this where

the red coseismic rupture runs

along a step in the landscape that

is in fact an uplifted surface.

That's pretty clear Taconic evidence of.

Pretty clear evidence of tectonic activity.

Sure enough, the 2019 rupture,

though it may be difficult to

see on this slide,

shows up right in front of this step

about where we would expect it to

form in a continuously active fault.

In the end. Well,

my colleagues identified is that

something around 70% of the rupture

was actually identifiable beforehand,

not just the 35% that was in equipment

in the queue files database.

That's actually pretty good,

and it underscores the continued

importance of hunting for ancient

fault scarps hiding in the desert.

As you can see here,

there are hundreds of them,

and their scattered across an area that

is 10s to hundreds of kilometers wide,

maybe even thousands.

When you count the whole desert.

So investigating each one of these scarves.

Is a massive project to understand how

they contribute to the seismic hazard.

This brings us to our most recent

surface rupturing earthquake,

for which I lead the USGS field

response in cooperation with the Nevada

Bureau of not of Mines and Geology.

The California Geological Survey

and a host of academic and industry

partners recall our tectonic setting,

plate boundary shear over to the West

Continental extension in the northeast.

Here's where the Quakes epicenter

sits for context with regional

tectonics and other historical events.

Phil teams were deployed to map the ruptures

to set up temporary seismometers and GPS

stations and to document any damage.

Mobilization at that point required

strict establishment of an

adherence to COVID safety protocols.

We were early in the pandemic.

I made it a challenge,

but the Nevada teams arrived in the

field the day of the earthquake and

most of the teams from California

arrived the following day.

When we got there,

we found ample evidence of the

strong shaking near the epicenter.

Most notably, these toppled rocks.

You can see the path coming

down the hillside here,

where the rock jumped bounced,

left divots and then split open

as it landed at the bottom.

And here this boulder that rolled down,

leaving a long trail through the sand.

We were also greeted by a pretty

vigorous string of aftershocks that

continued to rattle us several times

per hour for the first day or two.

The motivations for doing this

field response can be categorized

into 2 broad efforts, number one,

adding to our knowledge of how

coseismic rupture is look and behave

that spawns its whole its own

whole host of science questions,

but also doing a post mortem to understand

which faults participated and how.

Did Disruptor fit with our

models and our expectations,

or does it require a rethink?

So to begin that assessment,

we look at how this earthquake

fits in the tectonic context.

We're here in the so called Walker Lane.

The western edge of basin and range

extension bounding the shearing California.

It actually accommodates about 25%

of the San Andreas Plate motion of

the plate boundary plate motion.

Meaning that material on the West side

of this region is moving northward and

material on the Eastside moving southward

in addition to the East West extension.

The earthquake occurred

in the minor deflection,

which is a bend in that zone

of lateral slip faults.

You can see the change in the orientation

of the faults that are mapped here.

Shown on this colorful map are the

aftershocks in the first three months as

what you saw for the Ridgecrest earthquake.

The aftershocks cluster around and

align along the fault that ruptured,

helping delineate its location

an extent indeed.

These ones follow the orientation of the

nearby east West oriented left slip faults.

The next line of evidence is of

course whether there is any surface

rupture a magnitude 6.5 earthquake is

right on that cusp of having fully

reached the surface or not.

Indeed, there was plenty of surface rupture,

though it was nowhere near as

spectacular as those seen in the

magnitude 7 plus earthquakes that

I've been showing you so far.

We went around tracing,

surveying and measuring these

subtle yet traumatic fractures

which showed evidence of just a few

10s of centimeters like less than

a foot of tectonic deformation.

Here you can see the capable team

of Camille Collett Alley Pickering.

Alex hate him and Chad Trexler,

who accompanied me from both the

earthquake Science Center in the

Bay Area and the geologic Hazards

Science Center in Colorado.

We were just one of several teams

that converge to contribute mapping

and measurement of this vast array of

ground ruptures from this earthquake.

One of the best ways to see the

full scope of ground deformation

is from a high vantage point.

So we sent up an unoccupied

aerial vehicle UAV,

or more commonly known as drones.

In our case, a quadcopter.

Four rotors on each side.

To do comprehensive photography,

imaging and mapping of the Epicentral

fault zone of this earthquake.

These UAV surveys image the ground

at 1 centimeter per pixel resolution.

So and we use the varying vantage

points to reconstruct a detailed

3D terrain model using a process

called structure from motion.

The resulting data sets collected by

US and others allow the teams to map

ground rupture patterns in exquisite detail.

You can see here in one of the images.

What sort of patterns were looking at?

This wide array of fractures

formed above the fault zone.

The results were published earlier this year,

led by the Nevada Bureau

of Mines and Geology,

and illuminate a surprise surprise,

somewhat enigmatic pattern of faults

involved, but how unexpected was it?

Well,

here's the map of coseismic

ruptures plotted along with the

location of the epicenter.

And in Black previously mapped

Quaternary active faults from

that queue faults database.

While only a fraction of the red

and pink surface ruptures from this

earthquake followed previously,

mapped faults here and here for example,

there configuration suggests

that the faults were obscured by

sedimentary cover and burial,

not that they were newly formed structures.

I'll take you on a quick tour of

what some of these tiny fault

ruptures looked like in the Far East.

Safety from the Nevada Bureau.

Mines and geology is standing above

one of these little fractures.

Few centimeters wide that runs off

into the distance, but it actually.

Lies along the trace of this large

fault that you can see in the background,

offsetting this ancient lava flow

from its counterpart over here.

So we're seeing activation of big,

well known bedrock faults in a

minor way from this earthquake.

Similarly, deep in the sedimentary

basin over here you can see

this array of fractures running

through the desert gravel.

There's measurable offset across these,

and it lines up in between the

projections of two well known and

recognized faults on either side of

the center vent rebasing suggesting

that this is an expression of

the continuation of that fault.

On the East, sorry in the

West side we can see.

This small fracture that runs along the

base of a larger or it's frankly pretty

subtle unless you're geomorphologist,

but there's a step in the landscape

that's recognizable here as something

that must have been tectonic.

Sure enough, this rupture runs

right along the base of that,

so a lot of this is in fact

rupturing false that were previously

identified in the landscape.

Here in this main zona factors Alex

hate him is celebrating the discovery

of the main fault that really

ruptured to produce this earthquake.

It's still not that impressive.

Well, zooming into that Western

domain we can see what having

this low altitude aerial drone

imagery does for our ability to

see and map the rupture in detail.

Ongoing investigations are evaluating

just how much of this faulting

occur along faults that could have

been previously recognized and

are hunting for more evidence of

such features in the facility.

When we simplify the surface rupture

interpretation and simplify an ad

in mapped aftershock epicenters to

highlight where the deeper portions

of the fault that ruptured are,

we get a clearer picture of the

structure behind this earthquake,

rupture the portion of the

fault that broke was around 30

kilometres long from east to West,

following the buried continuation of the

previously identified Candelaria fault,

while rupture on that fault

didn't reach the surface.

Slip along it,

torqued these other intersecting

north South falls.

And made them tear open with minor

offset as we saw overall defaults

activated in this earthquake appear

to represent a microcosm of what we

expected from the regional tectonics.

Within the minor deflection

of the Walker leaning while it

ruptured newly mapped faults.

The pattern of faulting is

entirely consistent with how we

would have expected an earthquake

in this region to operate,

and the particular configuration

of this one shows us ways in

which the faults that we have

already mapped may link up.

This brings us to the present day and we

can revisit are confounded colleague Chad

here to answer some of his questions.

What do we learn from mapping all

these fractures? Well each earthquake.

Rupture that's mapped reveals more to us

about how seismics that propagates along a

fault system linking tectonic structures.

These in turn informed simulations

of the physical process so that we

can understand better the mechanisms

in the theory behind how earthquake

ruptures really work.

They also calibrate how to interpret

the magnitude of past events when

they are preserved in landscape,

so that we can interpret earthquakes

beyond our instrumental records.

Why do something larger is great,

keep happening outside the zone

of highest shaking probability.

Well, while the San Andreas and nearby

faults move fastest in geologic time,

which means in human time that

earthquakes recur most frequently.

The deforming part of the continent

is wide and diffuse hosting an

abundant set of false,

each one capable of producing

large earthquakes even if each

one produces an earthquake.

Rarely this huge collection of faults will.

Collectively produce large

number of earthquakes,

which is why most of the ones that

we've experienced in the last century

have come from off the same Andres.

How have recent earthquakes informed our

expectations of future seismic events?

Well, because each earthquake is different.

New earthquakes can surprise us by

a simulating all these examples of

modern ruptures and fleshing out the

longer term history of earthquakes

through mapping and excavation.

We have an ever improving handle on

which earthquakes may occur in the

future where they will strike and how

big they may grow to be understanding

the tectonics through studies of past

earthquakes and old bedrock faults.

Is critical to understanding how

contemporary meaning, future ruptures,

will navigate through the fault system,

allowing us to foresee where and

how large are the earthquakes

that society or face?

With that,

I'd like to thank you all for

listening and I'll be glad

to answer any of your burning

questions about these earthquakes.

Other earthquakes and earthquake geology.

Thank you.

Awesome, thank you so much. Awesome.

He's a fascinating election.

Hard to imagine, you know,

2020 with such a long year.

But seeing how how many large events happen

in the western US and such as torque,

short science man?

Yeah, great stuff.

So we're now going to.

We already have some really good

questions from the audience,

so we're going to open up to our

Q and a portion of the lecture.

So I've been.

I've been keeping an eye on some of

the questions that have been coming

through and just as a reminder,

if you would like to ask a question.

Remember to click that Q&A chat window.

I'll look for the question Mark icon on

the upper right hand corner of the screen,

and if you're on a mobile device or an iPad,

you can click on the question Mark icon,

which is also located on the upper

right hand corner of the screen

and submit your question there.

So our first question is from Januka,

who asked any of the 65% of the

unmapped faults in Ridgecrest,

new IE, not pre existing.

Could you repeat the first part of it?

Army.

Yes,

if if any of the 65% of the unmapped

faults in Ridgecrest or new.

That's right,

so only.

35% of them were in the Quaternary

faults database already.

An additional 35% of what

we saw rupture in 2019.

Were. In fact, recognizable

features that had simply been.

I wouldn't say overlooked there.

The desert is vast and there haven't

necessarily been studies of every

square foot of the desert so far, so.

What this earthquake sort of inspired

researchers to do was go back and really

interrogate was there were there.

In fact, features that could

have been recognized before if

we had dedicated studies here.

And So what they found is that that

additional 35% were there is in fact

a remaining sort of third of the

ruptures that had no expression previously.

That doesn't mean that there,

strictly speaking, new faults.

The Mojave Desert is characterized

by deep sedimentary basins.

Ann just piles and piles of

gravel shed off the mountains.

And over time,

those will tend to bury faults,

and so it's again this competition

between are the faults keeping up with

forming linear features and escarpments.

Or are they getting washed over,

washed away and buried by sediments,

and that's a perpetual challenge

that we face is studying the Jew

or the faults to morphic lean?

Great,

thank you.

And our second question of the

night about earthquake experiences.

So someone's asking if there,

hypothetically standing in a field

along a fault of when an earthquake happens.

When do they see date?

Does the offset motion happen in the

blink of an eye or over 2 seconds?

This is a fabulous question an I'm sure

one that fascinates all of my colleagues.

We all as we're standing out there

looking at these fresh scarps

that form just the day before.

We're all imagining what would it have

been like to see this process unfolding?

There are a small number of people around

the planet who have witnessed this happen,

and they've been lucky enough to,

and they've shared their experiences.

And we also know from the

physics of the process,

sort of what it would look like.

So the rubber tip itself,

as we saw in that simulation,

it moves at, let's say,

about a kilometer per second,

maybe faster,

and so that's pretty quick.

If you're standing on the ground

looking towards the fault.

The tip of that opening crack is

going to sort of zip by across your

field of view in a matter of of.

A couple seconds.

The actual we call it the rise time,

the time that it takes to fall

to then move is going to be an

additional couple of seconds.

The slip velocity default sort of catches up.

There is one video from an earthquake

in Taiwan a few years ago that

captures this process happening.

It was a closed circuit TV camera outside

of a shop under which a fault ruptured.

You don't exactly see default break,

but you can see over the course of.

Basically,

one or two seconds the house rides up over

the street and then sort of

parks itself there and so.

You would see the crack zipping open

and then you would see over the

course of just one to two seconds.

That's car perform in the midst of this.

Of course you would be experiencing

very violent shaking because

the shaking is produced by that

elastic motion of the ground,

and so the strongest shaking you

experience is probably going to come

right as the main rupture passes.

Awesome, thank you.

And our next question is about terminology.

Asking when do the term unzipped

for faulting begin being used?

I wouldn't necessarily say

it's a technical term.

I use it as a helpful analogy to the process.

That sort of unfolds overtime laterally,

and so the I think that that that

process of breaking down the frictional

bonds across the fault overtime as it

moves along is really analogous to

unzipping something sort of breaking

the bond between two sides of it

so that it can move independently.

Thank you. And our next question

from an audience member. They were

asking what created the MENA bend.

Well, that's a good question.

Going back so one of the diagrams.

There's my slides here.

Let me. Jump back if I can.

To our diagram here,

I glossed right over this,

but a model in that was sort of proposed

in 2005 for why this is happening.

What you got is again that Pacific

Plate boundary motion were in the West.

Stuff is moving northwest and in the east.

Stuff is moving southeast.

So these long faults that are

oriented to the Northwest are

strike slip faults that are

accommodating that sideways motion.

What's happening in the minor

deflection is that for.

Some reason the plate boundary

motion that strike slip gets

transferred out into the basin.

That may be because there are

more faults available over here

and it's starting to sort of Co

opt the extensional faults and

start to move them laterally.

That's one part of what may be happening,

and so in the middle there there's

this little zone of material that

is somehow having to accommodate

a bit of a gap in the motion.

If you're moving this stuff

southward and this stuff northward.

You're opening a bit of a gap here.

The model is proposed is that the

rocks in the middle are essentially

pinned between these two flat sides

of a wider fault zone and thus

sort of pinned and rotating like.

Like ball bearings,

essentially what that means is that in

between those you have faults with this

opposite left lateral sense of motion.

An quite truly that is exactly

what we're seeing here.

There's a stack of these left lateral faults

in the middle of the right lateral faults,

and so you can imagine that the two sides

of the minor deflection or sort of pinned,

and as this moves downward

and this moves northward,

it rotates the intervening bit like Domino's.

That means that when an earthquake happens.

It's navigating its way among

this evolving set of faults

that are rotating through time,

which may be why we see those surface

structures that are not exactly aligned with.

With the east West orientation

of these other faults.

Started things Austin.

Next question is from Bob who asked

is the Walker lane of possible

future San Andreas trace i.e.

A replacement for the San Andreas

Fault is another really great great

question and basically a subject of

ongoing hypothesising and research.

And there is a general consensus

that the there's a massive shear

zone there that accommodates 1/4

of the plate boundary motion,

and when you look at it in map view,

here's a small version I

can maybe jump us up to a.

The bigger regional picture here.

You can see that number one.

It's the most active part of

our big deforming belt, right?

All this sort of quakes happened

basically along this line that extends

down to the rifting Gulf of California,

and so essentially what we're seeing in

Southern California is the northward

propagation of this rift that is

separated Baja from mainland Mexico.

That same sheer extends up through the

Mojave Desert and then into the very

western edge of this extensional province,

and so there is an alignment of

things here that is growing.

These faults are maturing with everyone

of these earthquakes, as you can see,

the faults are linking together right there,

forming longer faults as they

produce this and so.

Over the next millions of years,

5 to 10 million years,

we probably will start to see

reconfiguration of the plate boundary

that's more accommodating of a simpler,

straighter boundary.

Not in our lifetimes.

It's another, thank you.

And our next question is from Steven

who asked is the goal the overall

goal to predict earthquakes or just to

understand their cause and effect better?

It's it's long, been a goal from the

public and a scientific perspective to

wish that we could predict earthquakes.

But there are so many complexities in

variables within the system that it does seem

a pretty unattainable goal in the meantime.

What we do is we try to forecast the suite

of earthquakes that may occur so that we

have a better handle so that we're not

surprised anymore when big ones happen

when we live on an active plate boundary,

earthquakes are always going to happen.

And the strategies with

for dealing with them.

There are much more strategy,

much more effective strategies than

predicting earthquakes in in advance.

If you were able to predict an earthquake,

you would still have to deal with that.

What would you do?

You have to evacuate a city.

What do you?

There are some real challenges conceptually

with dealing with the disaster.

That way when there are other measures

you can take to cope more robustly with

an earthquake and build infrastructure

and resilient communities that can

withstand them in the same way.

Basically that we withstand big rainstorms.

Thank you. And our next question

is from John who asked drones and

map details after the event and

aerial mapping showed faults that

could that could have been found.

But what is the value of using

these methods much more extensively

to map previously unknown faults?

Well, that's our favorite topic as

geomorphologists an earthquake geologists,

we would love to have high resolution

image ingane topography of every

corner of the planet and it is

in fact a big effort of what we

do in the USGS has a big program

to capture high resolution LIDAR,

laser imaging and topography and

to make it freely available for

researchers and the public to use.

The.

Some of the high resolution

topography that we have.

Some of the earliest high resolution

topography that was produced was

actually in in pursuit of the four event.

A fault line data,

so looking at specifically the

San Andreas Fault,

other big regional faults that we

knew to be threats.

The first LIDAR datasets.

Really captured in stretches along those

and have that have already been put to

use being measuring before and after.

Changes to the terrain from

some of these big earthquakes,

they give us a really detailed picture of

exactly not just where the fault traces are,

but the whole deformation field.

Because it's not just these

single cracks in the ground,

there's warping that extends over

a longer region and that gives us

also a better sense of both how

large the earthquake was and sort of

what structure is what subterranean

structures were involved in producing more.

So there's great value in.

High resolution topography.

We're always interested more.

Gotcha.

Anne got to have a really good question

about earthquake preparedness in general.

What actionable tasks based on

these new learnings can one take?

Living in the highly populated Bay Area,

California? A really great question.

So a lot of the research

that I discussed here,

the implications based on fault crossings.

All this fault rupture stuff.

The applications of these are

largely with larger infrastructure

and sort of city planning issues.

As individuals,

you're probably going to be more

concerned with the shaking itself

then with where the fault rupture,

but of course the shaking

is dictated by how large,

how long the fault rupture is, right?

So in the Bay Area, for example,

the Hayward Fault is this

massive threat to the East Bay,

and really the entire region.

The distribution of shaking from that from.

The eventual earthquake that it will produce.

Is going to depend on exactly how

much of that fault ruptures and so

understanding this distribution

of in any given earthquake,

how much of the fault ruptures?

Or are there particular features that

halt the rupture from propagating

doesn't control the distribution

of shaking and the sort of how

cities planned for and budget an an

insurance companies and infrastructure

utility companies and agencies deal

with those things as an individual.

Living in earthquake country,

the reality is always just that an

earthquake could hit at any time and

that's the reality that we live with.

And so getting yourself prepared making.

A plan with your community,

anticipating the affects the lingering

effects that large damaging earthquake

is going to have in the region.

The USGS.

A few years ago produced this massive report.

The Hay wired report.

You can look that up and it has rather

daunting set of prognosis about what

what may happen when the earthquake occurs,

but that's really the first step to starting

to get control of it and understand,

you know to anticipate what's going to happen

and be able to prepare yourself for it.

Because in reality most

people are going to survive,

lived through and and recover

from these earthquakes and they.

There are many societies around the world.

Think of Japan and Chile that

deal with earthquakes very well.

They take them in stride.

They deal with them like they're

just another rainstorm.

Which, by the way,

in California rain storms are

their own disasters, but we have.

Yeah.

The recommendation is gay prepared.

There are plenty of resources

looking to haywire report,

and I would emphasize the importance of.

Preparing within your community and

making sure that there are people around

you who are also aware so that the

problem is don't spiral out of control.

The pandemic has taught us a lot about that.

Absolutely thank you and I'll.

I'll put a link to the Halo report in the

chat window as well for that thank yous

are our next question comes from men.

Seeing if the continental extension

in Montana is any way related to the

California Nevada movements, that's right.

My talk is focused on this sort

of southwest corner of the US,

but if we jump back, I've gotta.

Let's just move that the.

What you can see here is that we're

basically looking at one big system,

so the extensional province that spans the

entire state of Nevada and reaches into Utah.

The watch fault is the famous eastern

boundary of that highly active

those faults project northward.

They crossed the volcanic

Snake River plain in Idaho,

and they extend up into northern Idaho.

This was actually the site of one of

those other big earthquakes last year,

as well as another large earthquake

in 1983, so.

Idaho is definitely also earthquake country,

as is southern Montana,

and these are indeed parts of

essentially the same fault system.

Technically speaking,

there are complexities introduced

because in the north we have

the Cascadia subduction zone.

There's convergence where the Pacific,

the Wanda Fuca plate here is colliding

with North America and pushing back inward.

You can see that in the velocities as the

continent is getting scrunched up here.

So some transition happens in this

zone around basically within Oregon,

but overall it's part of the

same extension belt.

Immutable.

Sorry about that, I didn't want

my typing to get in the way.

So our next question.

Is asking in the examples that you

presented the surface ruptures are complex,

could that be termed distributed faulting?

Yeah, there are a lot of permanent.

Pardon me like turn my lights on, there are.

The short answer is yes,

we would distribute.

We would determine we would

term that distributed faulting.

The exact relationship of all those

different factors with the sort of

main fault that was seismogenic

that produced the earthquake is

essentially still under investigation.

We were looking at these questions of.

Exactly what those smaller

fractions represent?

There's some manifestation of

deformation around the tip or

the edge of a major fault, and.

So yes. Great.

And then we have time we're going to

ask a few more questions and wrap

up our Q&A portion so our second

to last question is from Jeff,

who's asking the plate motion

networks provide any foresight

for these recent earthquakes.

Yeah, so none of these

earthquakes are have been.

Preceded by any sort of recognizable,

reliable precursor. In fact, we've really

never found any reliable precursors.

Certainly some earthquakes have foreshocks.

That happened months and months in advance,

but there's really no way of knowing

whether any given earthquake is

going to be a foreshock or not.

Only 5% of earthquakes end up

being four shocks, which is a

very small fraction of them. The.

No precursor geodetic signals have been

identified for any of these, so. Uhm?

That's basically it.

Other than the simply the notion

that this is a deforming region,

and we do expect earthquakes there.

That's what we can tell you another,

another feature that's worth noting

is the alignment of ruptures

that has happened there is.

Significance to this belt

of higher deformation,

and it is where an area where we would be.

Where we expect to earthquakes to be

more likely so we can see that over

time all these successive earthquakes

have started filling in the gaps.

There are less likely.

They don't necessarily happen on this in

the same place all right next to each other.

Although there are examples of that as well.

But you can see lots of filling

in the gaps along this belt.

It's almost complete.

Got it, thank you.

And are are less question of the night is

from Bill who's asking in satellite image.

Ng help discover these tiny

previously unknown features?

Or are you limited to drone

image ingane field studies?

If the former,

is USGS involved in the surface

biology and geology decade old survey?

Yeah so. First of all,

there are yes for identifying prior

geomorphic landforms in Providence.

Defaulting satellite image Ng is

one of the key things that we use.

The features that we're looking

for and they are generally,

but recognizable are captured

very well by orbiting satellites

which have imaging resolutions

of something like 30 centimeters

to a meter at their highest.

Features like we saw in the 2020 this

Monte Cristo Range earthquake are so small

that it's very unclear to us whether

those would be measured in the future.

So if we look back with hindsight,

even 10 years hence,

would we recognize that there had

been an earthquake rupture here?

These little factors that are

only a few centimeters across

get filled in really fast,

so again, we're talking about

this earthquake was right on that

cusp between earthquakes that get.

Lossed in the geologic record and

earthquakes that are preserved.

So the exact boundary there is something

we're really trying to dig into,

so collecting satellite data, however,

is really critical way that we have of

identifying any sort of active faults.

An making measurements across them.

The specifics of the program,

the cable surveys I'm going to

have to deflect that specifically,

but there are, uh? Number of.

Campaigns, data collection efforts,

data dissemination, and.

Generation that the USGS is involved in in

terms of high resolution terrain department.

Thank you. You know, I'm sorry.

I'm going to sneak in one more question,

'cause it's a really good question.

I'm curious to see what the answer.

So someone's asking,

how do these unmapped,

distributed fault traces that were

only mount after the earthquake affect

affect recommendations for fault

setbacks or fault avoiding zones?

Yeah, so that's a that's a great question.

While we cannot rely on being able

to map those for past earthquakes

because they're just so small.

There are a couple of things

that we're looking to do.

One of them is to identify whether there

are any broader signatures of them.

So maybe the discrete fractures

don't get preserved,

but maybe there are long sort of

longer wavelength warping of the

landforms or other things that could

be recognizable in past events or for

prior events before we recorded them.

But the other thing is that,

as I said, each of these.

New earthquakes that happens is one

of the key ways that we get new data

about how these ruptures occur,

and so there are.

That's why it's so important to

get out to the field rapidly and

collect as detailed surveys as

possible so that we understand the

distribution of this deformation,

because these datasets,

from the historic ruptures or what

go into this.

New emerging field of probabilistic

fault displacement hazard analysis

and this is used by especially for

infrastructure for highly vulnerable

or high how important facilities,

nuclear plants, other things of that nature.

They're really interested in where

exactly the ground is going to deform and

disrupt their infrastructure and life lines,

and so mapping out the distribution of

all these little fractures is really

critical to getting it right when we

build things that have to cross the fault,

whereas houses and buildings can

be set back from the fault roads,

railroads, pipelines can't be,

so we have to learn how to build across them.

Thank you for asking that and again,

that's that's all the time.

We can have four questions this evening.

I want to thank you again,

Austin, for the talk.

Today's super fascinating stuff and

just for filling all of our questions.

Really great questions from the

audience and thank you again to out

there everyone in the virtual world for

joining us tonight and just a reminder.

Austins lecture will be available

later for on demand viewing

on our website at usgs.gov.

Forward slash PLS.

And again we hope that we see you

next month on June 24th at same

time 7:00 PM Pacific for Carolyn

Driedger's lecture on Mount St Helens.

Until then, have a great night.

Thank you all for joining us.