Slow Earthquakes

all righty this was the topic of last week a collision between two plates along the west coast of Washington this is the North American plate moving west this is the JDF plate the Juan de Fuca plate an oceanic plate moving east and diving beneath Washington most of us know about this this is not new information here's some water here here's coastal communities okay part of what we did last week was talking about evidence that Brian Atwater found for a magnitude 9 earthquake that struck 310 years ago on a winter night in the year 1700 he found trees at the coast that were dead he found trees at the coast that were dead that were lower than they should be and he found a sand layer that was evidence of tsunami so we then dug into Chris Goldfinger's work in submarine canyons offshore remember this and we realized hey it wasn't just one magnitude 9 earthquake that we have dealt with in our past we've had a whole series of magnitude 9 earthquake happen repeatedly at this same place involving these same two plates and due to Goldfinger's work and out waters work we concluded that there was an average of 500 years between magnitude 9 earthquake and it's been 310 years so maybe we're ok but maybe we're not that's an average number and maybe we're wrong on that number as we learn more as we go part of last week's lecture also was the model that we have to explain why these magnitude 9 earthquake SAR happening and that's what I really want a diagram for you it might not have sunk in I think it was just animations that we did last week so I want to make sure you've got that and I should have done this on the whiteboard because I want to use different colors oh well I'll just have to be extra clear why do we have magnitude 9 earthquake at our coast that's the question our best guess is this and let's do it this way let's let's talk about up peacetime and quake time quake time is when the actual event happens the big magnitude 9 earthquake and peacetime are those 500 years between big earthquakes ok willing to play along with that quake time and peace time so what happens during peace time with this picture what we think is going on is very slow but gradual lifting of the land right at the coast and in fact we have equipment that can measure this uplift now that's part of the topic of tonight's talk which we'll come to in a second so we're pretty clear that during peacetime there is a very slow and gradual lifting of the crust at the coast and during the quake time the magnitude 9 event what happened at the coast boom all at once right so at the coast during quit during peacetime we have 500 years a slow gradual uplift and then during the magnitude 9 event could chunk the land goes all the way back to the way that it was originally and we start the whole process over so we can do that gradual uplift and sudden drop gradual uplift and sudden drop that's what we observe with the dead trees and the tsunami sand and the instruments that we now have that we're using today the model is why is this happening why is the land going up and then suddenly dropping our idea this might change but the idea we have now involves the Juan de Fuca plate as its abducts or as it dives beneath North America our idea and it's an idea because we haven't been down there to see it but our idea is that the boundary between the Juan de Fuca plate and the North American plate is locked during peacetime during peacetime so we're going to subduction oak uestion there the subduction is happening but as we subducting to pull the edge of the North American plate down with it in that locked zone and the North American plate is rigid kind of like this pointer here and so what happens if I pull down on the edge of this meter stick or this this pointer what's happening in the interior at the coast okay and then we finally have enough energy in the plate interface where we have a failure of the locked zone it becomes unlocked and suddenly this land is dropping this is not the best example I've got more animations for you tonight but here it is we're pulling the edge of the North American plate down and while we're pulling it down we're lifting the middle or the coastal area of North America and then everything gets restored when we have the big earthquake got that that's important for tonight's lecture actually so during quake time the locked zone suddenly becomes unlocked this North American plate that was pulled down is suddenly flipped back to its original position we have a big tsunami everybody gets hurt it's a sad story and that is continually taking place why because as soon as we unlock and have our big earthquake the subduction starts again and we start pulling the whole thing down again that's the cycle 500 years of a locked zone and then release it 500 years of a locked zone and then release it that's our current understanding and that was last week's lecture okay let's break new ground what are the instruments that we have that measure this gradual uplift and what are the instruments that we use to measure these plates actually moving how do we know these plates are moving well before I get to what the sar let's do some stuff from the 1970s and 80s about geologic evidence that we have for plates moving let's try this see how this goes uh-huh this is where we need some music doubt it up down and on and on they're not down - no no no no no no no no no no no okay Washington Oregon California Idaho Montana brain problem Montana Wyoming Utah Nevada okay great let's put some colors on here Yellowstone National Park is a volcano it's in Wyoming it's a supervolcano we haven't talked much about it here but it's a volcanic system that's very different than our cone-shaped volcanoes but the reason we're talking about right now is beneath Yellowstone Park is a hot spot is a stationary fixed leak where heat is coming from the middle of the earth and cruising to the surface and it's fixed the fixed spot okay put that on hold for a second what's this thing here that's right this is the San Andreas Fault which is a plate boundary between the North American plate and the Pacific plate now I'm going to get my use out of these colors here today plates are big chunks of the earth crust moving in different directions and there's another plate right over here what's that Juan de Fuca great so let's go back here and and now we're putting in the Juan de Fuca plate which is is next door to us that was the plate we have here so there's three plates interacting with each other in the western North American plate how do we know that the North American plate is actually moving one way before we had these fancy instruments I'm about to tell you oh oh oh I will be falling tonight I will be falling facedown and might bounce a couple times when I land just I'm just this camera guy be ready for that okay great what evidence do we have that North America is moving well this is a fixed hot spot at Yellowstone but there are progressively older volcanic deposits that stretch into Northern Nevada brand-new lava here up to about 17 million year old lava in extreme Northern Nevada it's a fixed hotspot but it's a moving plate over a fixed hotspot you get the rationale there so that evidence tells us and we've done some math with it whoops I need another color blue that tells us that the North American plate is moving kind of to the southwest mostly to the west but a little bit to the southwest at an average speed of 3 centimeters per year 3 centimeters per year that's not much right but but that actually is a lot in geology if you can measure something annually and you can measure a difference in 12 months that's a substantial 12 12 3 centimeters now that's based on this fixed hot spot in this moving plate now similar type features have been used to get the plate velocities or the speed of these plates involving Pacific and Juan de Fuca as well the Juan de Fuca coming at if that's not a surprise because we know it's abducts beneath us right we have a rate there as well 3 centimeters per year towards us and the Pacific plate which I'm going to make a longer arrow here and that will get us used to this there's going to a lot of arrows tonight and the longer the arrow the faster the annual speed and the shorter the arrow the slower the movement per year okay so we're going to make this a much longer arrow because the Pacific plate actually moves nine centimeters a year okay so it's cruising and by the way Los Angeles and San Francisco are on that Pacific plate so they're moving a slightly different direction than the rest of us okay so that's 1970s and 1980s geology what just happened that's an unsettling feeling everybody's in on a joke except me all right okay all right I'm glad you're having a good time okay now come to 1990s we get GPS now when I ask a freshmen in college what GPS is they say yeah well you use it to get to the mall and stuff it's like it's like in your car GPS like well okay yeah that's a use of GPS but what is GPS we have satellites in space and the satellites have the ability to measure distances between the satellite and a fixed place on North America let's say and we can take a GPS receiver which is actually quite large bigger than me and we can anchor it in some bedrock and we can have three satellites measure distances one satellite there's the distance between the satellites and the GPS receiver another one another one we can have three satellites three different distances and we can precisely locate the latitude and longitude of that GPS receiver down to fractions of millimeters incredibly precise for scientific use that technology of determining precise latitude longitude locations of spots on our crust have given us more precision on how to measure the movement of these plates and that's what we're talking about tonight without GPS technology and making these very detailed measurements we wouldn't know about these things called slow earthquakes which nobody can feel but yet happen at a spooky regular interval ok so what have we learned let's see I'm going to go here I guess I'm going to try to make Washington now just Washington and I want to start plotting basic GPS information I got to go to my notes now baby right ok good so let's try Washington over here primarily Western Washington would be good so here's Ellensburg and let's put a bunch and we'll actually put Vancouver Island in here because the British Columbia folks are involved in this story so what are these dots this week last week the dots were something else right they were they were dead trees and they were turbidites and stuff like that the dots this week are GPS receivers that have been installed and anchored into bedrock and there is daily readings off of these GPS receivers every day and that information is processed and averaged and all sorts of math I don't understand and so we finally have very detailed movement recorded within a plate it's not good enough now for us to say North America is moving southwest we want to know detail movement within the North American plane ok ok so by the way if we use GPS stations in eastern Washington they show what we talked over there three centimeters or thirty millimeters per year that's the same right three centimeters and 30 millimeters same number same distance ok great so it gets a little confusing right here so I'm just going to say we're going to ignore this because we're not disagreeing that this whole North American plate is moving three centimeters a year we're now focusing on stuff in western Washington that is not doing that that's doing something slightly different than theirs three centimeters per year let me try to explain that the story starts how do I want to do this yeah let's do it this way this story starts in the summer of 1999 that's not that long ago 11 years ago and herb braggart a guy that's up in British Columbia scientist geologists had a few GPS stations on Vancouver Island and even across the Strait of Juan de Fuca on the Olympic Peninsula and he started getting these annual monthly than even daily solutions on what the GPS stations were doing and what he noticed first of all was this which should surprise you each of these stations each of these GPS stations and by the way if you're having a hard time picturing a GPS receiver I've got some images to show you shortly okay what is this showing this is showing the GPS stations are moving northeast not Southwest and there's numbers on this 15 millimeters per year to the Northeast and that's just not him that we realize that's also happening all through Western Washington an average number today an average number for annual movement of specific points of crust in western Washington is this I'll write it bigger fifteen millimeters per year now that seems to conflict with what I just said why do you think these GPS receivers are going to the Northeast any idea yeah that's it because the Juan de Fuca plate is coming at us and colliding with us anytime you have two plates collide you are going to deform or smush that's the scientific word smoosh the front ends of those vehicles the front ends of those plates are going to get compressed and and smooshed and so I'm going to change this arrow based on this GPS that herb was the first guy to document herb driver in British Columbia we need to slightly change our arrow the one the Fuca plates not really truly coming east it's coming at us northeast and as a result I'll go ahead and put some GPS vectors on here we have our 15 millimeters a year to the northeast in up by Bellingham so this motion is a direct result of the Juan de Fuca plate coming at us and smashing the front end of us we okay there that's not the exciting thing of what he what he shot what he what he what he delivered in the summer of 1999 he saw this 15 millimeters of year to the Northeast 15 millimeters of year to the Northeast 15 millimeters a year to the Northeast and then suddenly smack-dab in the middle the summer of 1999 every one of those stations started going Southwest for our two-week period they all quit at the same time going northeast and they all started going Southwest just a few millimeters three I shouldn't do that too many arrows so here's the first major moment of tonight that leads us to this idea that something weird is happening this is not the weird part the 15 millimeters a year to the northeast makes sense to us because we have a complete collision that's okay but the part that got freaky is this two-week span in the summer of 1999 that actually said every station went the other way and after that two-week time went back to the business of going northeast so there was a two-week event a two-week happening didn't know what it meant but we have this sudden reversal now pause the story for just a second five years earlier in Japan there was a significant earthquake that killed a lot of Japanese the Kobe earthquake 1994 maybe 5 1995 and I think the economy in Japan was still strong at that time they had money to burn and so they started installing GPS receivers and all sorts of other geodetic type equipment in Japan to try to help predict or at least understand these earthquakes in Japan the Japanese were the first to see this GPS about-face this two-week going back the other way routine but herb was the first guy to see it in North America so we're up to summers where he published his paper in 2001 ok hey scientific community we've got this funky behavior don't understand that GPS stations doing what they shouldn't be for two weeks and then they go back to it and by the way this is cumulative I'm getting ahead of myself forget that okay great all right doing okay so far okay Megan Miller Central Washington University starts meeting with herb and says I think I can get a bunch of money from the National Science Foundation to install a more GPS receivers and I wonder if what you caught herb up on Vancouver Island happened throughout the northwest or at least further south in Washington so she started working on this with a guy named Tim Melbourne I'm going to write his name down because he's kind of the star of tonight's show you've probably seen him in Safeway you didn't even know it he lives here to Melbourne classically trained seismologists grew up and passed a Dean and went to Caltech all that stuff and here he is in Ellensburg and he started working with Meghan on this problem and Meghan has since moved on to greener pastures and Tim has now taken over and has a number of graduate students working on this issue and so all this work we're going to talk about tonight over the last decade the unifying thread between all of that is this guy Tim I'll show you a picture just in case you see him ven-ven's bakery next time ok great so Meghan and Tim Central Washington University humble little Central Washington University got this funding to install all this equipment and start receiving and we hired a few extra people they actually work in Hepler Hall some of you in the ice age group you coda talks at Hepler Hall right what do you do you go in the front door you take a right to go to the auditorium right well if you go in the front door and take a left that whole Hall is offices of folks that work on this including Tim and Marcelo and Rex etc etc ok what did they find Meghan and Tim Melbourne just about a year after herb yes they saw the next one of these bizarre events where the arrows started going the other way for a two-week period and it gets better than this there is a 14 month almost clockwork 14 months between these two week windows so I'll say that again I'm not being very clear with my arrows it's almost like peacetime and quake time again if you want but this time is not in the trench we're just talking about these vectors the involving GPS motion visualize this and I'll have some animations for you visualize 14 months of 15 millimeters a year motion to the northeast two weeks of back 14 months two weeks back 14 months two weeks back we've observed it now for more than a decade and it's 14 months every time that was the contribution of Miller and Melbourne let me give you some dates just because by the end of this you might be spooked a little bit and you might want to avoid going over to Seattle next time this on campus ok May of 97 two weeks to the southwest July of 98 September of 99 December of 2000 February of Oh 2 etc the most recent one August of 2010 just a couple months ago we had our two weeks none of us knew it I didn't even you know just the Hepler guys say hey got an event going the next one if we keep this 14 months cycle intact which we have every reason to believe yeah you can do the math October of 2011 October of 2011 October of 2011 is the next time we're going to have one of these events I'm being coy about what the event is I'll get there in just a second the real concern is I can't hold it I got to say a little bit about it why should we care about these little events we think these events might be a possible loader or trigger for the next magnitude 9 event that's the real concern and that's why we're paying a lot of attention to this we're not there yet to understand why that is but I just jumped to one of the conclusions of tonight these freaky little two-week windows might be coincident with releasing all that energy at the trench okay so October 2011 don't don't schedule a big party over there okay great ah what are we doing next both dragger in 1999 through 2001 and Megan Miller and Tim Melbourne called these events slow silent earthquakes okay they have the ability to understand this movement of crust and realize what kind of energy we're talking about and that's the geophysical part which I'm pretty weak on I must admit but the basic message is a magnitude six point seven earthquake have you experienced one of those or have a concept of that it's potentially deadly earthquake six point seven and earthquakes that are six point seven around the world happen at the snap of a finger take that energy from a six point seven earthquake and have it release over a two-week window and you've got a slow earthquake so the equivalent of a magnitude six point seven is released but over this weird two-week window so it's slow and it's silent we're not feeling it even many of the instruments the seismograph we're not really picking it up very well that the things that record ground shaking so I agree they're strange they're freaky flash-forward the next couple of years herb draggers at it again with some Japanese scientists mainly the folks in Japan and they have the ability to work with something called tremor which I don't have the background to explain very well but the discovery of tremor which is what was viewed up to that point is kind of background noise with these events was actually interpreted as a real thing so these are no longer called slow silent earthquakes because they're truly not silent we do have instrumentation picking them up and there are signals being produced during the two-week window still unclear what it means but we have instrumentation to pick it up so it's more than just the GPS going the wrong way and again if I put an red arrow as half as long or even less than that the red is what we're talking about with what's one of these events so these events are now called slow earthquakes or another way these are called ETS events episodic tremor and slip I'll write that out if you want to sound smart tomorrow that's what you're going to lay on your coworkers all right episodic tremor and slip maybe you're getting bored about right now because we haven't applied this to anything real we haven't talked about the subduction zone and we're going there in just a second to try to explain why these episodic tremor and slept events are taking place so slow earthquakes episodic or tremor and slip or ETS events every 14 months in western Washington one of Tim Mel burns graduate students Walter zaleka wonderful brilliant guy from Massachusetts who spent a couple years in Ellensburg worked on this and started going further south so then we started using GPS receivers that were in Oregon in California in other words involving this entire plate boundary that was doing its regular thing last week in our lecture right you might recall by the way last week in our lecture we decided from Goldfinger's work that every 500 years the entire trench fails great earthquake magnitude nine but do you remember that also from last week there were more frequent earthquakes in Southern Oregon and Northern California in other words smaller segments of the trench were failing and producing slightly smaller earthquakes not magnitude 9 so as we looked more carefully we realized there was a more complicated story same thing with these ETS events and this is Walter's work from 2008 just a couple of years ago when he published this he realized and figured out that our recurrence it I'll do this in a different color our recurrence interval or average number of years between ETS events or slow earthquakes in Washington was our 14 months that I just mentioned he crunched the numbers with the GPS stations in Oregon and California there's an 18-month window between ETS events in Oregon especially Southern Oregon and you get into Northern California and there's an 11 month window so that flushes it a little bit more this is not just the Northwest that receives these events it is all along the strike or the along the trend of this trench but it doesn't behave the same all the way across this stretch what do we do with that we're not sure we'll try our best before we quit tonight that gets us up to 2009 and a paper that just came out by Tim Melbourne and his graduate student Jim Chapman and I think that's the last diagram I'm going to draw I guess I'll do it over here and then we'll go to some slides to flesh this out a bit oh all right I'm out of my comfort zone I don't know if you can tell this is not the stuff that I normally teach about and Tim has been helpful to me over the last week answering dumb questions but it still feels a little odd it's good for me healthy for me try this you know especially since literally people here in Ellensburg at Central are the main players in this one of the main players across the world really with this kind of work and the Japanese are still at it and there's some other folks as well but but we are we're our major player okay so back to what we started with tonight we'll put Westport Washington a coastal community on our picture here one more time is the Juan de Fuca plate subducting and here's the North American plate and now we realize it's more complicated the front end here's where our GPS stations are the front end of Washington is actually being compressed going the other way going against the grain make sure to make sense to you now why we have these vectors going back towards the Northeast let's put our locked zone in and let's add to it now using the details of the GPS and the ETS events it's now pretty clear that the locked zone goes down 30 kilometers so from the surface of the ocean from from the bottom of the ocean the ocean floor you can travel 30 kilometers down this interface and that's the length of the lock zone that's bad news because the longer we have a lock zone on this interface the further inland we are having tremendous ground shaking that's the point of the recent paper that came out with all this mathematics and GPS worked on here this length of the lock zone appears to be longer than we thought we're hoping it was a short lock tone mainly out here in the water and we mainly have tsunami issue but now it's starting to look like we're talking about literally crushed beneath the Olympic Peninsula and maybe further approaching the metropolitan area of the Puget Sound that is approaching this locked zone but we still haven't gotten to the model of why we think the ETS events are happening what if we go way down on this interface this is what I'm calling this boundary an interface between the North American plate and the Juan de Fuca plate so locked for 500 years and then release the energy right down here we're so warm and the conditions are so plastic that we do visualize beautiful slip at this depth in other words we don't think it ever gets locked down there and the Juan de Fuca plate gracefully slides beneath the North American continent we are not sure but that's the visualization now here is the point that we really want to hammer between 30 and 50 kilometers depth on the interface right here and here we're going to call that a transitional zone if you started daydreaming you're ready to come back here it is we think the slow earthquakes are happening at the surface because of a periodic release of energy from this transitional zone let me say that again we know that the 500 years between big earthquakes all we're doing is locking this up and we know that the 500 years between big earthquakes we have beautiful slip this far south what we think is in the transitional zone we're locking it for 14 months and then releasing the energy and locking it for 14 months and releasing the energy and locking it for 14 months and releasing the energy and that is our explanation of why we have these GPS receivers doing the about face every 14 months in western Washington so the real question is what is this like down here these are temperature and pressure conditions that are hotter and higher pressure than the locked zone is the rock kind of plastic is it like silly putty what's the role of fluids are there hot fluids in here allowing the release of some of this energy but there's one particularly key animation that will show what we think is happening here it will also help us explain this regular 14 month interval that's kind of where we are in our understanding and before we quit and go to the slides I was in the pasta company last night for our weekly dinner my wife who teaches at the middle school and my two kids who are still living with us oldest boys off to college so we go out to eat once a week most moms turn we went to pasta company and the youngest guy actually said so what are you going to talk about in your lecture tomorrow night and first of all it was just like a question to me without any sort of money involved you're asking for things so that was odd enough and then I and then I said well we're going to talk about these things called slow earthquake so we don't really understand them and I describe them just a little bit and he said well why should we care about those we don't feel them why should we care about him it was a typical teenage response but it was also an important question why do we care about him I mean it's cool we didn't know about them before it's neat didn't know about it we've made advances to understand Washington better but why should we keep pumping funding into work understanding these slow earthquakes here's the concern so I'll go back to what I leaked about 20 minutes ago at first glance it seems like this would be a good thing for avoiding the next magnitude 9 we're releasing energy right we're releasing this pent-up energy on this interface that must be a good thing that must mean the next time we have a big earthquake it won't be quite as big but the folks who work on this problem and understand the physics way better than I view it as not a good thing they say we're releasing the energy from the transitional zone and where is that strain going it's being transferred to the lock zone each slow earthquake is ratcheting up the strain or the stress level in the locked zone each slow earthquake gets us closer to the next magnitude 9 event that's why we're thinking currently that the next magnitude 9 event is going to happen during one of our ETS events that the ETS is the final straw to break the camel's back and set this thing off and that's potentially scary what was the date October 2011 we're probably okay there right because it's an average of 500 years but remember the poor folks in Southern Oregon who also have ETS events they were over do remember their recurrence interval from last week it's been 310 years and it's the recurrence interval was something like 270 years so the next ets event in southern oregon has more drama than our next ets event so they are worth learning about if they are truly a potential trigger and the only good news I can spin on this is that it is a two-week window that we have our slow release of this energy and if we can somehow identify the ets event in the future that is the trigger I don't know how we would do that but let's say 50 years from now we can actually know enough about these ETS events to know ok this is the one that's going to do it then we can predict in a sense the next magnitude 9 event because we've got the 14 month window we can get to everybody out of the Puget Sound whatever that means and and we can somehow prepare this is essentially potentially a precursor event which is what we've been looking for since plate tectonics was discovered in nineteen XTS I actually used to show a film I should probably find that film shot in 1970 right after all the plate tectonic exciting discoveries were made and this young geologist this guy with shades on and everything looks right in the camera he's like 1970 he says by 1981 we're going to be able to predict every major earthquake on this planet and there was so many mysteries solved in the 1960s with plate tectonics I don't blame the guy for thinking that way so just you know just gravy to figure out how to predict the earthquakes well here we are 50 years later and we really don't still have it figured out this is a potential precursor for the next magnitude 9 event and that's why it's we're studying ok he looks for his pointer he finds his pointer he grabs it he picks it up and he goes to the board speaking in the third person now that's that's that's real modesty for you here's a map of the world and hot spots those stationary fixed plumes and these numbers are these centimeters per year of movement this is from geologic evidence now so we've got a good feeling for the motion of the plates long before GPS next one error here's another piece of geologic evidence to prove that plates move at varying speeds it's going to take you a while to figure this one out but it's pretty powerful so let's take a moment to try it here's North America here's South America Africa you got it here's the Pacific Ocean with all these colors and the Atlantic Ocean with all these colors the colors are different ages of the ocean floor and the red colors are young rock and the greens and eventually blues are hundreds of millions of years old the seafloor spreads at the mid-atlantic ridge and the East Pacific Rise which ocean is spreading faster this is the answer because we have wider bands of colors meaning it's spreading faster than the bands of the colors we have in the Atlantic Ocean floor so that by itself tells us that these plates are moving at different rates don't know if you got that one but I tried my best yep next one so we have plates and of course we're talking about the interaction between North American plate Pacific and Juan de Fuca let's go there Eric here is a little movie cutting away don't start it yet please here's the trench so we have Juan de Fuca coming at us to the Northeast technically right beneath Oregon and Washington go ahead Eric so let's slice this God in living color moving pictures the dramatic aspect of it here we have subduction yes we have volcanoes that's next week I guess and those green stars where the earthquakes generated now let's zoom in on the subduction zone itself notice all the deformation here notice the smooshing of the edge the GPS is going to help us understand that that's truly taking place and then our blobs of magma feeding the volcanoes okay that's cute next one please here's an old-school diagram we're talking about magnitude nine events happening out here please understand there are other earthquakes that happen regularly they have nothing to do with what we're talking about tonight the Nisqually Earthquake of 2001 the big Seattle fault earthquake of more than a thousand years ago we can revisit that at some point but probably enough earthquake stuff for this series this fall next one please so not the greatest quality but I think does a nice job of showing our locked zone our slip zone in our transition zone and this was done before Chapman's work that was published last year so I think we want to bring this locks on further down so what what depth yeah maybe fifty fifty kilometers maybe maybe even sixty kilometers depth from the surface next one please this is a movie just showing the crumpling or the smooshing of the front end let's try Derek I'm underwhelmed so far how about you okay we have an original grid and we're going to start deforming the grid notice we're going up as well as in so we're going to have both that gradual lifting that we talked about the beginning of tonight and our being pushed inland the GPS will show us that next one please here's what a GPS receiver looks like and let's how see how the GPS can help us understand this smooshing of the front end go ahead so here's the position of the GPS station at time zero we're going to start subducting the plate by the way this we're going to start pulling the edge of North America down at the same time so two things are happening we're pulling the edge we're lifting and we're getting the north easterly vector of the GPS this can't go on forever five hundred years of that and then and then and then okay next one please so here's just a quick primer on the GPS we have our satellites we need three of them we need to basically triangulate to get distances from satellites to receivers every day unbelievable next one here's what a GPS station looks like this is an elmo on the way to the coast Shelly who works for you nav Co David Yamaguchi the guy that did the tree-ring stuff from last week Kevin de white from Morgan middle school next one go ahead Erik so here's Nevada and GPS helping us understand that Nevada is actively spreading we knew this geologically but we want to proof with this technology so again we have the GPS receivers getting further and further away from each other why because the crust is being extended and again these daily solutions of GPS data can beautifully show all this let's advance let's not even wait for the end of this one Eric ok back to David and his Tostitos and a GPS receiver next one please so beautiful photo from the CW geology website this is the top of Mount Olympus and there is a beautiful GPS station there and again this is what you should visualize for each of those dots throughout the Northwest GPS stations anchored into the bedrock including one on the top of Lindh Hall come visit me I'll show it to you there's there's a Lind a Lind station that cranks out data pretty well next one please so can you see this the longer the arrow the faster the rate annually here's all of our northeaster so this longest guy here is about probably 15 millimetres annually the shorter length is less than 10 millimeters annually look at these rates in Northern California along the San Andreas so you've heard me talk about this clockwise rotation of the Pacific Northwest crust I kind of blew it when I told you that I've learned since then that that it's not all in Northern California driving the clockwise rotation it's the Pacific plate yanking on this part true but it's this northeasterly motion of the Juan de Fuca that's really driving much of this northern part of the clockwise rotation didn't quite have that figured out till now next one movie showing the last 40 million years and I want you to focus on us and how we do ultimately get the clockwise rotation because of changing plate boundaries go for it here we don't need to get into the details of this this is an old plate that Eustace abduct no longer does we now have our Juan de Fuca we haven't done it yet have we but we're about to check it out in the last 15 million years here we go and it's the northeasterly motion of the Juan de Fuca driving the north easterly motion of the GPS not to the slow earthquakes yet though have we next one we'll get there so these orange dots are where we put GPS stations in once upon a time probably 10 years ago and now go ahead 2002 keep going 3 4 2005 2000 keep keep loading them in get students out central students go out take the summer start loading them up live in hotels watch ESPN every night it's a beautiful life and you ultimately have the spectacular network each of these orange dots giving us daily information about what they're doing next that gets us to the slow earthquake story next so I think we're going to burn through this pretty quick go for Derek here's our 15 here's a scale so 50 maybe even approaching 20 millimeters of movement with some of these stations to the northeast normally go for it let's bust through that next one so at Neah Bay Washington here's the actual data using a North vector and an East vector and working those together and figuring out that there's this northeasterly motion of 13 millimeters a year next one you go down to Tillamook Oregon North part of the Oregon coast next one so that's here what does that vector look like next gosh that's here next one keep going not as much keep going now let's go to Eastern Washington what are we doing next one nothing next one so Olo Ellensburg take your favorite city in eastern washington it's doing nothing is it really doing nothing it's part of the north could you go back sorry we're part of the north american plate we are going over the hot spot three centimeters a year but we're ignoring that now we're just talking about this weird stuff out in the front end and in that respect we're stationary compared to this motion here so there is this of pivot point where all this rotation is taking place and we are kind of at the inland where as far east as you start experiencing a little bit of this effect of the Juan de Fuca plate coming northeast next one okay so right these numbers are millimetres annually we're hit this too hard now keep going Oh Lord keep going here's here's an animation showing that we actually have individual blocks that are doing this rotation I promise we're getting to the slow earthquake stuff next one it's a movie yeah that was worth it okay next one please aha so here's what the slow earthquake data looks like it's it's messy I'm going to do my best to show it to you here's years 1997 98 99 2000 etc here are individual GPS receivers and all I want you to notice is that they go to the upper right and then they jump down they go to the upper right and they jump down each of these blue lines is what a slow earthquake in ETS event and I've got a couple animations that are good that I promise that I'll show you that I'll be worth your while next one here's one of them so we're going to start this movie in just a second here's our GPS receiver it looks like a big gumdrop and we're going to show it moving this is cut off on the top I guess we're going to go from Southwest to Northeast and we're going to plot that on this graph 98 to 2000 - let's try it Erik going to take a second to start out okay good Southwest to Northeast so great wait 14 months and then two weeks of back without you visualized 14 months to the northeast and then we got two weeks of back we're releasing energy in the transition zone down at the interface this is what we've discovered it's been going on for thousands of years right but we've only observed it in the last 10 the net result then is this kind of sawtooth pattern the general trend is this so we're altom utley compressing to the northeast but we have these two weeks of jogging back to the southwest the net result though is continuing to the northeast keep going back to that you got it now next one okay this is the best animation tonight then there's like five things going on at the same time so let me see if I can keep your attention for just a couple more minutes do we have we have the one if you could play we have the North American play we have this abduction so first of all we want to notice the original location of the edge of the North American plate what's going to happen to it when we start this movie it's going to start to get pulled back right great these are little cells showing the crust before we start compressing it and you'll notice that we're going to do the most compressing out here close to the lock zone and we're not going to mess with this at all these are GPS stations at the coast in the Olympics and over here in Ellensburg now this is actually Puget Sound and Ellensburg so we're going to plot that up here and these graphs are going to look different for each of these three GPS stations plus we're going to see what's going on in the transitions on this if you only want to look at one place in the in the movie look right here because that's what we think is causing the slow earthquakes every 14 months play it Hal okay yeah we got a narrator we can't most of us can't hear transition zone slip zone down below okay I'm just will let you watch this first time we'll probably watch it a second time just for fun and slow earthquake and slow earthquake every 14 months so you see what's happening with the GPS station going northeast northeast northeast Southwest look what's happening to our guy here up and inland next one this is really busy but it's Walters work saying here's the blue bars and the red bars are ETS event slow earthquake events but we're plotting now GPS is from Southwest British Columbia through Washington Oregon and into Northern California and here's the last little twist on our plot notice that it's not happening the ETS is not happening at the same place at the same time throughout the Cascadia Trench here's our 14 month window in Washington we're fine with that right but we said the the recurrence interval was different in Oregon in Northern California and so Walter has plotted all this these are all just selected GPS stations and there are little time series squiggles we were looking at before next one please same thing from Walter he's now giving you actual dates of the ETS the slow earthquakes and again plotting them from north to south across the Cascadia trench across the length of the Cascadia trench so there's still some some some strangeness next one so this is pretty sweet I'm going to show it to you once this is a movie on the Left we have plain old earthquakes that are happening in the last four years 2006 to now and over here are our tremor and slip our slow earthquake our ETF earthquakes and you can even see what the plot is here so this is the northern part this is the southern part the black dots then are either earthquakes happening over here and ETS events happening over here let's take a look at it we're mainly looking here at our transition zone every once in a while releasing some energy no pattern except for every 14 months we get something in Washington for some reason this animation is jumping a little bit I don't understand that it's a little less dramatic than it was before sorry about that none of these are magnitude 9 right we got to wait 500 years between those guys thankfully oh here it's finally working a little better here comes another little blop here comes there's going to be another ETS right here in Washington why and what are you trying to visualize you're visualizing beneath this that well that was a good question beneath this is the transition zone right the transition zone is not here we got to dig beneath the transition zone which happens to be beneath where all the people living next a couple final photos this is the geology department at Central and I'm showing you this photo because there's Tim Melbourne Marcelo Andy Craig and Rex are the heavy hitters doing this research they're all humble quiet guys but they're really really good at what they do next one Tim Melbourne let's build a shrine to him this evening next one please final slide this is the depth of the interface so this is is it even worth getting into this the the man I don't want to finish stumbling like this but I'm going to try anyway basically this is peeling off the North American plate and looking at the interface itself looking at the boundary between the North American plate and the subducting Juan de Fuca plate and notice this this been why is that the one the Fuca plate is not flat it's bent it's got an arch to it as its abducts so if you want even more complications you're dealing with a three dimensional slab that's not a plane as its abducts it has an arch to it that's why there's this bow and what we're talking about is when we finally do get big events on the interface we're going to have very little slip here and much much more slip as we get closer to the actual trench this is trying to plot the amount of slip when we have a magnitude 9 event 20 meters 20 meters of sudden ground movement under water generating tsunami out here but the bad news is some slip directly beneath the Olympics which is neighboring where our friends and loved loved ones live that's enough for tonight thanks for your attention appreciate you

Channel: Central Washington University

Views: 72,385

Rating: 4.8898163 out of 5

Keywords: Central Washington University Organization, Geology Field Of Study, Ellensburg Citytownvillage, Central Washington University, Ice Age Floods, Zentner Geology Lectures Downtown Ellensburg, Cwu Geology, Central Washingtion University, Earthquake, Cwu Geological Sciences, Geology, History, Flood, Education, Cwu

Id: r9recENBhiU

Length: 62min 58sec (3778 seconds)

Published: Thu May 02 2013

Reddit Comments

[u/dumbluk01]

Professor Nick is awesome. Be sure to check out all his YouTube stuff. Especially if you are interested in geology of the Pacific Northwest.

[u/alllie]

CWU's Nick Zentner presents 'Slow Earthquakes' - the 3rd talk in his ongoing Downtown Geology Lecture Series. Recorded at Raw Space on October 27, 2010 in Ellensburg, Washington, USA.