ladies and gentlemen thank you for being here today it's my pleasure to introduce Karl Wegmann who's today's speaker
Karl hails from the Pacific Northwest from Washington state he got his undergrad there
at Whitman College and then he went to the University of New Mexico for his master's and then he spent five years
in the Washington State Survey before getting his PhD...Pennsylvania and then in 2008 Karl joined us here
at NC State as a professor Karl's talk today is going to be on the use of geospatial data along the lines of lidar and things like that
to help understand faulting and earthquakes and in particular these structures that weren't easily visible
without those kinds of data available in the Pacific Northwest and there's ...
of fission there that I don't understand and therefore I'm looking forward to that in his talk as well
so without further ado Karl Wegmann
thanks Paul thanks for for having me
today and if you I've changed the title
on you a little bit from what was
advertised hopefully that's okay so
we're gonna go on an adventure and it's
mostly going to be out in Washington
State which is what I want to talk to
you about today and we're gonna try to
get in mostly about topography faults
earthquakes geologic hazards and how
those things and how earthquakes and
landslides can rearrange topography and
landscapes and then how that might
relate to fish so when I first thought
when when John Vogler asked me if I'd
give this talk and I over the summer I
was thinking about what am I gonna talk
about what should a title be and at
first I came up with this title called
earth first we'll log the other planets
later digital lidar removal for
vegetation for earth surface processes and
hazards research to me that was maybe a
little funny and witty maybe to others
it's not I realize I'm in so I thought
well maybe maybe I'll take a little
opportunity to try to explain myself I'm
a geologist and I'll go into where I
grew up which is
part of this story in a moment but as a
geologist and someone who's ultimately
interested is the subfield I'm in is
geomorphology so I'm interested in
landscapes and the Earth's surface and
processes that generate topography and
processes that tear the topography down
landslides rivers glaciers right so for
me looking across a landscape like this
with a lot of trees and I know I'm now
in I've come up three floors and I'm
now in the College of Natural Resources
so I understand there's people who love
trees love vegetation I like trees too
except for be so nice it's like all the
landscapes were like this over here
without any trees and we could just see
the earth surface exposed that's sort of
this where this title came up right so
okay so here's here's the the part of
the world I grew up in in western
Washington it looks like this forested
forested hill slopes pretty much
everything in the landscape is a hill
slope and that's true everywhere in
terrestrial environments how many of you
got up this morning and thought geez I'm
gonna be traversing across hill slopes
most of my day today yeah it's not
really something we think about all that
much but I like to remind myself that
there really are kind of in the hill
slope business I mean in how - how is
topography forming and what are these
processes that are carrying it down
right so I had this little thing I say
in the geomorph class with the
undergrads if it's not a river or a
beach or a lake and you're on up above
the ocean you're on a hill slope and
one of the processes that happens on
hill slopes are landslides so I'm
particularly interested in those as
geomorphic and geomorphic
processes and geologic hazards we'll get
into landslides in a bit and so I put
that little primer on hill slopes
because it is Halloween thank you
for being dressed up it's Halloween
oh and over here too
oh and there
okay
it's Halloween there's three costumes I
have three chocolate bars you guys are
the winners and we're gonna be talking a
little bit about sediment moving
downhill slopes pretty rapidly later in
the talk during big landslides but I
thought it might be because it's
Halloween might be appropriate to talk
about a creep dominated hill slopes a
term how sediment moves down hill
slopes like creeping right really slowly
but a friend of mine made this a couple
years ago and sent it to me and I just
thought it was cute and now it's finally
Halloween and I can show this so thank
you all right that has nothing to do
with the rest of the talk but all right
so there's a fundamental relationship
between plate tectonics and topography
and I think no matter how many or
how few geology classes you've had you
realize that there plate tectonics it's
an active planet that we live on and
places where plates are colliding
together or pulling apart or grinding
next to each other kind of active
margins or collisional margins we call
them are places where there's where
we're creating new topography right
either through faults pushing rocks up
above the geoid or above sea level or
volcanoes injecting magma into the crust
or erupting stuff up onto the surface or
we're creating new topography and then
if we come over to a coastline where
like where we are here on the on the
Atlantic side much more of a passive
continental margin right and we're
mostly dominated by erosional processes
of processes that help to wear down
topography right these gravity driven
processes ok so as that is a primer
right we can look at the digital
topography of North America everyone
knows where we are right ok
over on this side what's the main what's
the main difference when you look at
North America from the topography of the
United States
oh come on
yeah there's a lot of elevation
differences right lots of hot
maybe if we think about topographic
wavelength there's a lot a lot higher
higher frequency of topography kind of
bouncing around over here in the western
part of the United States than certainly
in the middle portion and and here we
are we've got this fantastic mountain
range here a couple hours I've been told
three hours to our east no west is that
directional dyslexia gets me every time
right so was an active mountain range
250 300 million years ago no longer but
that topography persists we
still have landslides and debris flows
that occasionally kill people in these
mountains that's another story for
another day so have to invite me back at
some point we'll talk about those
processes in the Appalachians but really
what I want to talk about today are
seismic hazards and the seismic hazards
I guess the reason I put this underneath
this slide was sort of to say here's
this topography ultimately tectonics is
creating this topography part of that
are active faults and and their
associated earthquakes and if we look at
the seismic hazard map for the United
States warm colors equal higher seismic
hazard potential then cool colors
probably no big surprise you've all seen
things like this right California the
Pacific Northwest are areas that
lots of kind of active faults we're
building topography or moving topography
around on these faults and there's an
associated hazard so we're gonna go
spend some time up here in the Pacific
Northwest thinking about earthquake
hazards and the topography up there and
associated landslides that are being
caused by earthquakes okay so I was when
I first started putting this talk
together a couple days ago it said
today's story was going to consist of
three acts
but then a very smart PhD student came
to me this afternoon and said dude you
like to talk too much you cannot have
three acts so it was going to be Act One
here in the Pacific Northwest Act Two
Grand Mesa and kind of evolution of
topography in the Colorado Plateau and
then over here in the Appalachians those
are gonna be have to be different talks
for another day because I just can't do
it but it is my shameless pitch to let
you know that students and colleagues
we're working on using digital
typography to to interrogate landscapes
I'll show you stuff up here but also in
other parts of North America
I love digital typography and if at the
end of this class of this discussion
seminar if if you are using digital
topography in your own research
especially for for students in the in
the in the room if you want to chat
about that at any point
come find me I'm on the second floor of
Jordan Hall okay how many people use
lidar in their research but everybody
pretty much everybody knows what lidar
is right so just a really quick primer
and in my case I'm talking about
airborne lidar right this can be
collected from an airplane and I found
this video so the airplane flies around
it's shooting laser pulses down the ground
it's measuring the return and then
that's used to generate surface models
what's the elevation of whatever the
lidar's bouncing off of canopy trees
buildings the ground surface all right
have you guys seen this on from
Wikipedia just stole it okay and so
here's this airplane flying through over
the jungle in the Amazon and then they
do this fly through through the canopy
right so that the lidar is collecting
all this information about the canopy
mostly in this case not about so much
about the earth's surface maybe a few laser
points are are hitting the ground
surface one of the one of our PhD
students Julian "Nutman" Chestnut who's
not here today had a career in the
Air Force he was an F16 pilot before he retired
and decided that playing with digital
data sets like this would be more fun
and Julian will say that that stuff
that gets shot out of the back of an
airplanes it's called chaff right like
you're trying to so for me this is sort
of digital chaff like all these leaves
and I don't mean to offend anyone
because I know maybe there's some folks
that are interested in like structure of
canopies or or whatever but for me I
want to get rid of all that stuff I want
to see what's underneath right so here's
here's lidar data from Northern
California in this image here this is
like the first return and it's colored
by elevation so the darker the color
means the higher the trees the greens are
vegetation so you can see how much
vegetation is on this landscape right
and then we can digitally process that
use the last returns and just and
create a surface terrain model or
digital elevation model of the bare
earth right and that's a bit for me
that's what that's what we're really
interested in and this is why so this is
a little bit of a background on my
personal story because I think our
stories are all important in terms of
directing where we end up and where we
go in life so I grew up outside of a
small town called Port Angeles has
anybody been there before most people go
to Port Angeles because they're they're
trying to get to or come from Victoria
British Columbia which would be just up
up here right so there that's the main
reason you'd stop in Port Angeles unless
you really like trees we have a lot of
them so prior to the advent of lidar
prior to the development of lidar and
I'm old enough that I predate that at
least for kind of Earth's surface
process research I'm not sure I ever
really observed and this little thing in
here right I'm not sure I ever really
observed the true surface of the earth
growing up because it was always covered
in vegetation and that would be true I
think if you grew up in the mountains well
sometimes it's kind of true around here
if you grew up in the mountains of the
southern Appalachians
that much bare ground actually exposed
except for when they did log clearcuts
and I used to work in the summers in
college I worked for a logging company
as a summer job I loved going to see
these clear cuts in these places because
it was sort of like revealing what was
was like giving your dog a haircut you
kind of step back and all of a sudden
your dog looks different so now the
landscape looks different when you
remove that hair or giving oneself a
haircut okay so so lidar has allowed us
to do sort of digital clear cuts and
that's really where I came up with that
original title Earth first we'll log the other
planets later it was kind of digital
clear cutting used through lidar for Earth
surface process stuff okay so I grew up
in Port Angeles went off to college went
to New Mexico and then got a master's
degree and then came and then like lived
in my parents basement
for four or five months trying to find a
job anybody have that experience like
you guys are better than I was yeah okay
all right so good times eventually ended
up getting a volunteer position with the
Washington State survey saying uh and
I've got six years of geology training I
just need to get some some experience
under my belt so started out as a
volunteer mapping what's called a seven
and a half minute quandrangle I know
everyone know about USGS topo sheets
right okay so a standard map that
geology groups make are mapping the
earth at that one to twenty four
thousand scale or seven and a half
minute quadrangle the state of the
Washington State Geologic Survey was
making maps up along the North Olympic
Peninsula this was sort of a target area
for them my parents okay so I was living
in the basement of this house here and I
could drive over and help out the
geologist who was mapping this
quadrangle in the summer of 1999 and
after a few weeks I think he felt sorry
for me and decided that you know give me
a small salary and that began my my
career at the state survey for the next
five years the reason I put this
simplified geologic map up here what I
want to show you the dark line so this
is the Olympic Peninsula Seattle will be
right over here
the dark lines on here are faults right
and faults are just continuities between
different rock units and at at that
where the different blocks of rock have
moved relative to each other now there
could be faults we have faults all over
around us beneath our feet all the time
some of them here maybe hundreds of
millions of years old others of them may
be active well here they're not hundreds
of millions of years old cuz the Olympic
Peninsula didn't exist that long ago but
in Raleigh there may be faults that are
three four or five hundred million years
old that haven't moved since then in an
environment like this we knew that there
were faults we could map discontinuities
in the rocks across those faults but
nobody had an idea that that they were
active or potentially capable of
producing earthquakes at the Earth's
surface and so this is just my little
kind of acknowledgment to the folks who
did the original geologic mapping this
is a original geologic map for the
Olympic Peninsula done in 1960 it was an
oil and gas investigation map and they
had identified these faults and here's
here's one of them and there again is my
parent's house so if you notice the
basement I was living in for those
couple months it's right on one of these
faults so I started becoming kind of
aware of the geology of the surroundings where I grew up once I came back
from grad school and was living in their
basement and was doing this job for the
state survey certainly folks have known
that there been earth that there are
earthquakes in the Pacific Northwest
region for a long time and those those
sort those earthquakes are sourced in
three different places the Pacific
Northwest is an active plate margin so
I'm sorry I can't look at this screen
because of the glare all I see are the
buildings in the back so I'm gonna I
know this is kind of a timeout tangent
but it's okay for you guys if I talk off
that one okay okay so there's three
three different earthquake sources
it's the Juan de Fuca plate is
subducting beneath North America right
so we can generate the really
big earthquakes these megathrust events
happen on the subduction interface on
the Cascadia subduction interfaces to be
the subduction zone those are magnitude
up to magnitude 9 may be likened to Hoku
earthquake which happened in 2011 in
Japan something like that big earthquake
big tsunami shaking that goes on for
minutes we also have had historic
earthquakes that happen on the
subducting oceanic plate that's are
within the subducting oceanic plate
that's descending down beneath North
America and these are known as deep
locally deep Juan de Fuca earthquakes I
lived through one in 2001 that which is
locally known as the Nisqually or the
Olympia quake magnitude 6.8 so there
have been three of these in the last 50
plus years 1949 1965 2001 and these
caused a decent amount of damage so the
Nisqually earthquake caused about two
billion dollars worth of mostly
structural damage to buildings and
infrastructure and one fatality from
someone who had a heart attack and the
telephone lines to 9-1-1 were jammed and
they couldn't get emergency services to
that person what we also know that or we
anticipate that there are crustal what
are called crustal faults that
earthquakes that are embedded in the
North America and on faults in the North
American plate these are ones that when
they rupture they rupture right up
potentially to the ground surface and
cause displacement of the Earth's
surface and so these ones well they're
both magnitude seven maybe for deep
earthquakes and the crustal ones these
crustal ones are sourced essentially
right underneath our cities and our
infrastructure and the energy instead of
traveling 50 60 kilometers to the crust
before it reaches the Earth's surface
it's sourced essentially right at the
Earth's surface or a few kilometers
beneath and so there's the the potential
damage from these earthquakes while the
magnitude may be the same is potentially
quite a bit bigger okay so so we've
known about let's see the only ones that
have happened in historic time is maybe
a crustal earthquake back in eastern
Washington in 1872 we'll talk about this
one in 900 AD
there was no one living in this portion
of western North America that had a
written written language in 900 AD so we
don't have historical accounts and then
the subduction zone earthquake in 1700
the same thing that one was is recorded
in historical documents from the tsunami it
generated in Japan so so we need to
increase our understanding of the number
and how often and where are these these
earthquakes likely to happen in the
early 2000s lidar came along alright
okay so we're gonna do a little exercise
so for example this is a small island
just west of Seattle it's called
Bainbridge Island if you're in Seattle
and you ride the ferry or if you've
watched the Seahawks games because
they're the best football team ever and
I'm sure you all watch the Seahawks and
they always have a aerial shot with the
ferry going like in the foreground you
know and then I don't know what that was
anyways that was me cheering for the
Seahawks so okay so anyway so so the
ferry goes back and forth between
Seattle and Bainbridge Island this is the
southern part of Bainbridge Island
where's the fault who sees it
there coming down like here curb oh
okay so the fault's gonna be going to
east-west that's okay that's good all
right that's the whole point this is
what the Earth's surface look to us
before lidar geologists running around
it's not a jungle it's a temperate
rainforest jungle you can't you just
can't see the ground you're often not
walking on it there's the fault okay if
we use lidar and this is a really cool
really cool image made by the
cartographers at the Washington State
Survey where they they'll blend some of
the ortho photography in with the hill
shaded lidar now you can see that
discontinuity right that topographic
discontinuity coming through here here's
the earthquake fault
these north-south the north-south
topography this is glacial
glacially striated and formed bed forms
so so glacial at the Cordilleran ice
sheets coming out of British Columbia
and it's flowing south and it's kind of
sculpting this landscape so you get this
really strong north-south grain to the
topography in Puget Sound most of the
faults run more or less east-west so
they can crosscut that glacial
topography so we can use that as
evidence that this fault which is known
as the Seattle fault has ruptured since
the time that the glaciers receded about
14,000 years ago and in this case we
know now from from other work mostly
scientists with the USGS that there's
been seven meters of offset on this
fault so that's over 20 feet during one
earthquake so the Earth's surface right
you're standing there within 60 seconds
you're either 20 feet higher or 20 feet
lower if you happen to be right here
that would cause some problems it also
offsets the floor of Puget Sound what
happens when you displace a big body of
water essentially instantaneously you
generate a tsunami all right so there
was a tsunami in Puget Sound that was
generated by this event and probably
from my perspective most importantly
okay so there's the focal if we look a
little bit so here's the southern part
of Bainbridge Island if we look a little
further to the west that fault runs
right underneath downtown Seattle right
and I know you all love your Starbucks
you love Microsoft and their products
you all like Amazon instant delivery
whatever right that's all there but most
importantly it's where the Seahawks play
and the Sounders and the Mariners who
cares about them
anyways
okay so yeah so this lidar typography
allowed us as geologists and folks
interested in geological natural hazards
to start saying whoa we know there's
these faults that many of them have
created surface displacement since the
time of glacial retreat that lidar was
collected in 2002 here's a paper that
came out in 2003 in a in a little
geology publication called GSA today
see the first author was Ralph
Haugenud the USGS at University of
Washington high-resolution lidar
topography the Puget lowland Washington
a bonanza for Earth Sciences and that is
totally true
so here's let's see this would be the
same fault we were looking at and then
if you continue over to the west you can
see where the surface has been displaced
by that fault
on the next peninsula over and and just
continues and you can see the same
glacial striations and stuff right so
this allowed started allowing people to
go out and identify these things on the
lidar and then go find them on the
ground and figure out how much how often
they rupture how big the earth the
potential earthquakes might have been in
the past how big they're going to be in
the future
so here's kind of coming forward here's
now a map of all the faults that have
known to have ruptured the Earth's
surface in the Puget Sound region in the
last fourteen thousand years since the
glaciers melted away and kind of reset
that landscape and so we're gonna so
kind of we were just looking down here
on the Seattle fault zone
here's Bainbridge Island we were down we
were down there now we're gonna move up
to the northern part of the Olympic
Peninsula and I'm gonna share with you
some information some data we've been
collecting up here okay so we're gonna
go up here the town as we talked about
before is Port Angeles so in 2002 at the
the state of Washington and the USGS
collect lidar for much of Puget Sound in
the north part of the Olympic Peninsula
up to about Port Angeles here's this
2002 here's the digital surface model so
here with the lidar collection area at
this
time in 2003 I'm working for the state
survey I've been there about three years
and they said hey we want to do when I
first started I was volunteering we were
mapping this this area over here this
quadrangle and they said we're gonna map to
more quadrangles the Port Angeles and
the Elwha quadrangles would you like to
be involved we hear your parents have a
basement that you can live in for free
and we don't have to pay for an
apartment and I said sure I'd love to do
that that'd be awesome get to go work
on the geology where I grew up the lidar
comes out it's like oh my gosh look what
we missed when we did that map back in
the when we did this mapping a couple
years before one of the things we missed
was what we'll look at this okay so
we're gonna zoom in here back to my
basement okay so here's the digital
surface model overlying an ortho
photograph right and so this is a pond
and where there's water right there's no
returns from the lidar so you're seeing
kind of the green algae and some weeds
and then and the water there in the pond
and you can see the structure in the
trees right so here's this is like the
first returns anybody see oh there's
about my parents house okay now here's
the the last return the bare earth model
for this place and you might look at
this and say yeah it looks kind of what
like triangular facets it looks
a little pixelated I've seen lighter
that's way better
I agree this will remember this is early
days right like 2002 it's not maybe one
point every two meters or something like
that yeah not multiple points per meter
for sure like we have now okay do you
notice any topographic features of
interest there's a road roads you can see
the roads right faults are mostly
running east-west guess
you see any fault in here any subtle
hint that maybe the surface has been
displaced
there's the fault I didn't put a scale
bar on here that's about a hundred
meters so I spent like most of my life
first 18 years of my life in a basement
plus a couple months later like right on
top of this fault and that was a little
disconcerting now my so I show this to
my parents like check this out you guys are living on a fault and it's like oh my god do
we need to buy earthquake insurance I
don't know how do we know so all right so
here's we'll zoom out a little bit that
last slide was was where the little
white polygon a rectangle is we'll zoom
out a little bit can you see the the
feature now this sort of very faint sort
of linear feature running across the
landscape okay so let me highlight it
there okay so this is where there
surface rupture along this fault zone
that might just the parents happen to
live right on top of it so like the ones
in Puget Sound and this one here this
got geologists exciting because it's
kind of job security right
there's nothing if you're into the
earthquake business and you can't find
active faults then what are you gonna do
so this is this is job security for
folks at the state survey is job
security for folks at the USGS we're
going to go out and investigate these
faults so we're gonna we're gonna do some
paleo seismology we're going to trench
these faults we're gonna figure out how
often they rupture and how big the
earthquakes might have been in the past
and will be again in the future
so what magnitude might we expect and
and how best to answer these questions so
the USGS came out and let's see so that last
slide showed that that lasts what my
parents' house is like right here that by
the letter just just a little
west of the letter D USGS came out and
at that time the lidar only extended to
about here and so the USGS came out and
they put in trenches across these faults
with the backhoe they dig a trench
across
and they can look at offset in the
stratigraphic in the sediments offset in
the layers date those layers using
radiocarbon traditionally at least in
this environment and then use that to
figure out how old those sediments were
how much they've been displaced what was
the timing that they were displaced and
when they did this they came up with an
estimate of three to five earthquakes in
in the last maybe I didn't have that
written down the last 10,000 years and
the fault is slipping at a rate of about
one to two millimeters per year you may
say one to two millimeters per year so
what that's not that fast and I agree
it's not very fast right our finger how
fast our fingernails grow this is like
an important piece of information
everybody needs to know like 30 35
millimeters a year for your fingernails
okay so this fault's not slipping that
fast your fingernails are growing way
faster but if you because geology is
cumulative over time right what's a
thousand years to a geologist it's like
or to mother earth it's just like that
right so so a couple couple thousand
years now what if that if that slip is
is recaptured during during an
earthquake event you get several meters
of offset right one millimeter per year
equals a meter per thousand years so you
see that that accumulates this would be
kind of an example or a picture of a
backhoe trench into one of these faults
and looking at the sedimentary units
that are exposed and then collecting in
charcoal or organic material to
radiocarbon date that's not really part
of our story I just wanted to show you
how the USGS scientists collected this
data and then I'll present their results
compared to ours we're gonna go to this
nice pretty lake over here called Lake
Crescent to do our work here in just a
minute okay so the lidar allows first
for about 20 20 kilometers of surface
rupture over here along this this fault
which is known as the Lake Creek Boundary
Creek Fault since 20 kilometers of
surface rupture we can see that in the
lidar we can go out now and find it in
the field in 2015 the state collected
lidar this is Lake Crescent
which is Olympic National Park this is the
boundary of the lidar survey for some
reason no one wants to pay to collect
lidar data in national at least this
national park which I think is a tragedy
that should be fixed so write your
congressman or if you know anyone from
Washington State but the state of
Washington that owns all the timber land
around is really keen on having lidar
flown so they flew that in 2015 do you
see the fault in this image something
like that if I take it away can you see
that really faint line
okay now the quality now we have
multiple points per square meter and the
bare returned a much higher quality
lidar by 2015 okay so there's our
fault
okay so then let me just zoom in to show
you just one or two more because talk to
both of you about lidar so here's the
here's the trace of this fault right
here and we can start using things like
these little stream channels that have
been offset by that fault to figure out
how much displacement has happened along
that fault so here's here's the trace of
the fault and we can we can start to
reconstruct how how much it's slipped if
if we know the timing okay so see so so
putting this all together then so now
now we know in in 2000 we didn't know we
knew that there were faults in the North
Olympic Peninsula we've known that for
many decades but we didn't know that any
of them could generate earthquakes now
we know that there's a really big one
called the Lake Creek Boundary Creek and
then what we've what we've labeled the
Sadie Creek fault that have surface
rupture and they're capable of
generating earthquakes
okay and so the USGS in the state of
Washington takes this information and
they make seismic intensity models which
show okay here's a here's a fault this
would be our Lake Creek Boundary Creek
fault near Port Angeles the fault is
this long from our paleo seismic trench
studies we know that it slips on average
about a meter or 2 meters per earthquake
whatever the amount might be and then we
can estimate the amount of 
perceive shaking intensity at different
distances away from that fault
and so very severe would be an orange
here and then it dissipates away the
longer a fault is the greater the
rupture length that typically that the
bigger the earthquake so this fault
scenario was based on data before the
2015 lidar came out now we know that
this fault extends another 15 20
kilometers in this direction which would
allow us to increase the magnitude of
potential rupture based on there's some
scaling relationships between the length
of a fault and the size of the
earthquake that is capable generating so
that'd be a decent magnitude 7
earthquake up on the North Olympic
Peninsula okay so we're gonna go but we
really don't know how often these events
happened and what did they do to the kind
of the local landscape when they did
happen so we're gonna focus in and this
is work I've been doing with Del Bohnenstiehl and Lonnie Leithold in Marine
Earth and Atmospheric Sciences and a
number of graduate and undergraduate
students we're gonna go to this really
cool lake it's in an Olympic National
Park it's called Lake Crescent so are
you with me can we go on a on a virtual
field trip to Lake Crescent yeah okay
cool awesome and so we're gonna instead
of digging trenches into the fault with
a backhoe we're gonna use the sediments
that have accumulated in this lake as
our archive of past earthquakes so just
a little primer on I move this thing out
of the way no put it down over here okay
so the lake occupies parts of two
sort of east-west trending valleys it
was carved out by glaciers sometime in
the last couple million years as
glaciers advanced from British Columbia
there's British that's Vancouver Island
and that's the Strait of Juan de Fuca
this is the northern Olympic Peninsula
ice comes across and then it moves out
towards the Pacific and it's scouring
out these valleys the ice is advancing
and retreating on kind of hundred
thousand year timescales okay fourteen
thousand years ago the ice goes away
we've got this lake that's now one
hundred and ninety meters deep so it's
over 600 feet deep the bottom of the
lake's below sea level
it's about 20 square kilometers in size
it's got about a kilometer over a
kilometer of topographic relief from
like where I'm the person who took this
picture standing down to the bottom of
the lake so big steep hill slopes right
next to the lake and it's got these
faults that run through it and I promise
you there'd be a fish story even if you
wanted to hear it or not so there's two
endemic populations of freshwater fish
in this lake there's a rainbow trout and
there's a rainbow and cutthroat trout
that are endemic to Lake Crescent okay
and so since we're talking about fish
let's look at these fish so there's one
called the main one we'll focus on is
what's known as the beardslee trout the
beardslee trout is the local name that's
been given to a subspecies of rainbow
trout everybody know what rainbow trout
is you can buy them in the grocery store
they're commonly farmed they are endemic
they're not like here the rainbow trout
are introduced in the Appalachians right
but in the western part of North America
they're they're endemic okay they're
named the beardslee rainbow trout
because there was a we had a Navy Rear
Admiral this guy
Lester Beardslee who was stationed in
Port Angeles like in the late eighteen
hundreds and this guy liked to go out to
Lake Crescent and this is like his daily
catch so they're these for some reason
this lake the fish got really big so the
state records in Washington state for
both rainbow and cutthroat come from
Lake Crescent and then here's just a
picture of some kids that also caught
big fish big trout out of this lake
now it's protected in the National Park
the National Park and scientists that
are interested in these fish realized
that initially they were described by
phenotypic differences that they were
probably a separate species because
they're isolated in this lake and that's
been confirmed by genetic analyses and
I'll get to that a little bit at the end
and so now that the Park Service and
conservation biologists are you can't
you can no longer fish and we can fish
we can no longer keep them anymore
right they're trying to to maintain the
population okay and these fish
importantly they're anadromous
you guys know what that word means
what's an anadromous fish we thought
this was a talk about geology and
this is the College of Natural Resources
so an anadromous fish they're fish that
spent they spawn in freshwater and then
spend part of their lifecycle out in the
saltwater so these these fish initially
were anadromous and then they got
isolated in this lake Lake Crescent so
let me walk you through this story real
quickly I'll set up the fish story and
then we'll come back to it at the end
okay so right now Lake Crescent has one
outlet it drains through what's called
the Lyre River out to the Strait of Juan
de Fuca out to the salt water in the
past it used to be this this lake Lake
Sutherland and Lake Crescent were
connected they were one lake they were
joined together how are we gonna
separate two lakes what geologic process
would you do if you were gonna split a
lake in half landslides yeah okay cool
so there were there's a big some big
landslides that came down we're gonna
look at those in a minute so these big
landslides came down they separated the
lake and that caused so the outlet here
of Indian Creek is 24 meters lower than
where the Lyre River flows out here so
when these landslides separated Lake
Crescent from its former outlet the lake
level rose by 24 meters okay until it
spilled over a low divide and then
flowed out to the ocean unfortunately
for the fish that we're in this basin
they can go out but they can never come
back in there's a series of waterfalls
on the Lyre River that are about 10
meters high to prevent the fish from
getting back up into the lake so these
the ones that are in the lake the
thought is they were used to be anadromous like the other populations and
the streams around they they live partly
in the salt water and then they spawn in
the freshwater
these ones got trapped and now they just
spend their their life in this lake
okay so folks have known for a long time
that landslides separated Lake Crescent
and Lake Sutherland here's a map from a 1991
paper here's Lake Crescent the little
squiggly lines represent water these are
two a couple different landslides that 
geologists mapped back in the
in the early 90s and knowing that we
knew for sure that these lakes have
been separated by landslides but nobody
knew that the timing so there were two
estimates on the timing one was well
these landslides probably happened right
after the glaciers receded which was 14
to 13 thousand years ago and the
biologists said well that's okay because
the fish in Lake Crescent phenotypically
and this time they didn't have the
genetics yet but phenotypically they're
different than all the other rainbow
trout populations so we need some amount
of time for that to happen
some geologists went and they looked at
old growth stumps on these landslides
and they said well they're stumps that
are 500 years old so that provides a
minimum age for the landslides so that
age range was somewhere between fourteen
thousand years and five hundred years
the biologists said well we know for sure
that there fish have to have been
isolated for longer than 500 years but
we don't really know when when that
isolation happened okay so this is where
we're gonna come in to the rescue as
geologists and this we're gonna do some
lacustrine we're gonna look at sediments
lacustrine lakes so we're going to look
at lake sediments and reconstruct the
earthquake history along these faults
that we just looked at the lidar data we
could see that it ruptured the Earth's
surface over here and we know that fault
comes right underneath the lakes we're
gonna look in the lake for evidence of
displacement of the of the sedimentary
layers and okay so the important thing
and I'll show you this in a minute but
there's two types of sedimentary event
layers that we can see in the
stratigraphy of Lake Crescent and the
first one are what we call event layer
number one and that's what we're going
to focus on today these these record
ruptures of this Lake Creek boundary
Creek fault zone or the Cedar Creek
fault which would run right through this
upper portion of the of the lake okay so
there's layers in the lake sedimentary
layers that record rupture on that fault
and that's what we're going to focus on
today so let me show you some some data
so in 2013 or 2014 2012
no
time flies okay
Del and Lonnie and I had a grant from NSF
to study a different Lake out on the
Olympic Peninsula and our interest was
what do big earthquakes well we know
there's these big subduction zone
earthquakes off the west coast of
Washington State what happens to the
hill slopes in a forested drainage basin
when these big earthquakes happen and our
hypothesis was that they're gonna
generate lots of landslides and so we
went to a lake where we thought we would
see a record of that recorded in the
sediments where big earthquake the last
one in the year 1700 and then we'd see
this sort of drainage basin response
through landslides and then movement of
that sediment through the fluvial
system into a lake that's going to trap
that sediment that makes sense without
seeing a visual I'm trying to explain ok
so we went out there we rented some
equipment some expensive chirp sonar
equipment that's that pings sound down
in to the water column that sound goes
into the sediments and and bounces back
and we can generate velocity models or
maps cross-sections of the different
sedimentary layers as a function of
seismic velocity within the lake bottom
so and I know I just totally butchered
that but Del's gonna let it pass alright
okay so these so we we take that here's
the lake and we tow the the chirp device
back and forth across the lake and we
make maps of what the sub sub lake like
the subsurface below the bottom of the
lake what those sediments look like the
architecture of those sediments and
there's two things to know one is that
we see you will see how is this set up
okay we see kind of two packages of
sediment there's this this package up
here was kind of thinly layered material
and then there's these thick packages of
seismically what was called seismically
transparent material where there's no
energy returned from this package of
sediment we can see that in the western
basin over here we can see that in the
northern basin
here these are gonna be our event layers
okay so I guess to go back to the story
we were working in another lake but we
weren't because of gas in that methane
that's accumulated in the sediments of
that lake we were getting really poor
returns from the seismic data so we
ended up on a whim going to Lake
Crescent we had a few days left on the
rental towing the equipment around and
Lake Crescent and lo and behold it's got
this amazing stratigraphic record in it
and then that kind of leapfrogged into
everything else that we're talking about
so we collect that data a couple years
later we get a grant from the USGS from
the earthquake hazards group to come to
go out to Lake Crescent in collaboration
with the National Lucustrine Coring
Center from the University of Minnesota
they bring out their coring platform
which is kind of looks like a barge and
you put up a tripod or a frame on top
and then we're gonna send down piston
cores down into the sets of the lakes
190 meters deep right we want to get
that sediment out from the bottom of the
lake so we can look at those layers and
so I'm going to show you a video of how
that works so here's the piston core
think of this as like a long drinking
straw 30 meters 10 meters long it's about
30 meters long 30 feet long it's like a
big aluminum tube like an irrigation
pipe and it has maybe six to eight
hundred pounds of weight on the top that
gets lowered down on a winch from in the
middle of the coring platform there's a
smaller core called a gravity core when
the gravity core hits hits the bottom
it's only gonna penetrate maybe half a
meter or meter into the sediment when it
penetrates it causes this tripping arm
to go up and then that releases a little
hold on the on the wire and the piston
core drops like the last several meters
down into the sediments and those would
that one six to eight hundred pounds of
weight just drives it right into the
bottom of the lake right and then it's
because there's a vacuum on this like a
piston or a vacuum on the top of this
thing it's sort of like if you put a
drinking straw into your soda put your
thumb over the top you can lift it up
and there's still soda in your straw
right so we can do that and we can bring
it back up to the top and recover the
sediments so instead of me talking for a
minute you guys want to see a video we
thought it'd be cool to just just stick
a GoPro camera okay we thought it'd be
cool to stick a GoPro camera onto the
coring device and the water is really
clear in Lake Crescent so we're down
about maybe 50 feet in water depth
here's the gravity core it hits the
bottom it chips over it doesn't quite
work but it releases that tripping arm
boom and there's the main core barrel
with the weight stack on top it gets
driven down into the sediments alright
so we do this and then I'll fast forward
a little bit we don't need to watch the
whole thing then the winch pulls it back
up you can see that the tube the core
barrel and there's a lot of mud on the
outside and hopefully there's a bunch of
mud on the inside and we pull it back up
to the ship or to the to the barge and
then those then those cores end up
getting sent to University of Minnesota
to the National Lacustrine Coring Lab
and this is work that Lonnie Leithold
and her students have have kind of kind
of pioneered not the right word but but
it in our group have taken the lead on
the cores get split open cut it in
half and then photographed and we can do
chemical and sedimentological analyses
on these corse so let me show you okay
so here's our seismic image from the
lake here's one of these cores it
represents this portion we stuck a core
down into the sediments here this on the
bottom is an ISO pack thickness map so
here's our event layer just there's a
seismically transparent layer if we use
all the seismic data and we generate an
ISO pack or a thickness map for that
that event layer is up to almost two
meters thick in the deep portions of the
basins in the north basin and in this
southern basin of Lake Crescent so two
meters of sediment that accumulated I
mean we're gonna argue essentially
instantaneously I haven't talked about
that yet but accumulated almost
instantaneously here's what the
stratigraphy of one of these cores looks
like this is about a hundred and 140
centimeters
okay so just over a meter there's a
coarse sandy layer at the bottom so
here's the photograph of the core what
this is showing you is both grain size
the red lines are grain size so from and
this is microns at the top of 0.3
millimeters down to zero okay so very
fine so sand to most of the deposit it's
kind of in the silt and clay size
fraction at the bottom it's sandy kind
of a fine to medium sand and then it
that's this this dark area portion of
the core that dark portion of the core
also has let's see if this the mouse
work if I move yeah okay so then that
also correlates with magnetic
susceptibility so there's there's a
higher magnetic susceptibility of those
that coarse sand fraction and that has
to do with the geologic units that that
sand's derived from which is a story for
another day so we can differentiate
different parts of these event layers we
have a coarse sandy layer that we think
accumulates really quickly it's telling
us there's higher energy to get coarse
sand out into the middle of a lake and
then there's a big portion in the middle
that's just all the same grain size fine
grained very kind of fine grained silt
and then at the very top there's this
this light colored clay cap and this is
the sediment that's slowly dropping out
of the water column after a disturbance
event so it's just the stuff that takes
days to weeks to months to drop out of
the water column okay so
what are we gonna call these event
layers sounds good I heard it
megaturbidites who likes that word
what's a turbidite what the heck is a
turbidite the turbidites are underwater
turbid-- like underwater density flows
so think of them like kind of like an
underwater landslide but it's it's more
fluidized but it's you have dense
sediment that's moving down an
underwater slope and then as the slope
decreases that flow loses energy the
coarse particles accumulate first and
then you get a finding upward sequence
that's what defines a turbidite most
turbidites are on the order of
centimeters to maybe decimeters in
thickness this one especially in lakes
we have turbidites that are on the order
of meter to meter and a half to 2 meters
so we're gonna call those mega
turbidites right because it sounds
better
they sound bigger more powerful or
something so we've got these mega
turbidites and we can see them in the
seismic data here's the one we cored
through there these seismically
transparent units here's one here and
here's one we're calling it A B C D
probable fifth one down below the
punchline is we think each of these is
being caused by an earthquake and where
the fault comes underneath the lake
where where the the fault fault zone
comes underneath the lake we see
disturbance of these layers folding and
offset of these layers as we'd expect if
that fault is moving after the time that
the sediments below were deposited okay
so in are these are all of our cores
from the lake the important thing is
that we we were able to core four
different mega turbidites A B C and D
and they're in these colors green blue
red and yellow
and so these core photographs are
arranged from sort of west to east
across the lake
the important kind of the important
take-home thing from this is that we can
correlate four of these events across
the lake and all of these little black
numbers are radiocarbon dates that we
recovered from organic matter in the
cores and now we can put timing to when
these events happened and so we've got
four events we think all of them
triggered by movement on the Lake Creek
Boundary Creek fault and the most recent
one this upper green one based on our
dating happened about 3,000 years ago
okay three point one ka or three point
three what 3,000 years ago here if we
take our dating so on the top here are
our mega turbidites A B C and D for over
the last seven thousand years these are
the radio carbon okay time is on the
the x-axis zero would be to the right so
we're looking at the time interval 3000
or 2500 years ago to about eight
thousand years ago and these are the
radiocarbon these little wiggly lines are
the radiocarbon probabilities
probabilities age probabilities of the
radiocarbon samples we collected in the
core for each of the cores so four mega
turbidite A our estimated age is
3.2 to 2.9 thousand
years ago and goes back so earthquake
and mega turbidite in Lake Crescent
three thousand years ago one at four
thousand years ago one at about five
thousand and one at about seven thousand
years ago okay how does that compare to
the fault trenching record that the
folks in the USGS did over on the
eastern portion of the Lake Creek Boundary
Creek Fault we're working on the western
portion over right at Lake Crescent and
that probably means it's like time for
me to finish this story up real quick
okay so here's our here's our chronology
now I've switched just to make sure
you're staying awake I've switched the
time axis so now time is on the vertical
axis this is the Lake Crescent record
one two three four events they're pretty
well constrained in terms of the time
right the biggest often times there's
fairly large uncertainties with
radiocarbon
this is the time I don't know why we did
this but our events go A B C D the USGS
events go A B C D I apologize I'm sorry
just that's the way it worked okay so they
see an event about thirteen hundred
years ago that we don't record in Lake
Crescent we both see an event at three
thousand years ago so this is probably
saying the west the eastern portion of
the fault ruptured thirteen hundred
years ago but there's no evidence that
it ruptured underneath Lake Crescent so
what that would mean the way we would
interpret that is that was that
earthquake force probably magnitude six
and a half or something like that
whereas this earthquake at three
thousand years ago was probably more of
like a magnitude seven to seven and a
half because it probably ruptured the
entire 50 to 55 kilometers of the fault
zone and when we look at Lake Crescent
and and what do you notice in terms of
the sort of pattern I mean we have four
events what do you notice in terms of
the spacing between those events pretty
regular and then there's this block of
time well we haven't had one in the last
three thousand years and this gets back
to my parents' question they keep asking
me should we buy earthquake insurance
and I kind of looking at them now I'm
like no I don't think it's worth it
don't let them see this video I mean
what's the chance so we can calculate the
probability that based on the the
average recurrence interval out at Lake
Crescent which is about 1400 years
between these events and from that we
predict that in the next 50 years
there's about a 1 in 20 or about a 5%
chance that is that an earthquake will
happen out at Lake Crescent may not seem
like much but you know so do you buy earthquake insurance on a 1 in 20 chance
that in the next 50 years there'll be an
event I guess it depends on how long you
think you're gonna live and those sorts
of things right okay so that was that
part what
produced these what produced these mega
turbidites
let's do just one more thing and then
we'll end and then we can talk about
fish later it's kind of a cool story
this is where we get back to so the
lidar helped us identify these faults
then we've come out and we've cored this
lake we've come up with this paleo
seismic record and when we're looking at
the topography of cores unfortunately
right there's all the National Park they
didn't fly lidar but there's still some
pretty big landslides that are apparent
in the even the 10-meter DEM and you
can see them when you walk around in the
woods out here and we collected the
equivalent of lidar for the the bottom
of the lake we collected multi beam
bathymetry data with folks at the USGS
and lo and behold on the bottom of the
lake there's this beautiful land
underwater landslide deposit as it comes
from we think this subaerial void where
the landslide mass was now it's down
here at the bottom of the lake
Caitlin Joyner one of our former
students calculated the the area of this
and did some raster kind of subtraction
and calculation to figure out what the
probable volume of that landslide is
it's about seven million cubic meters of
material thats down on the bottom of that
lake that's significant what happens
when a big landslide we think triggered
by an earthquake goes into
