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foreign

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the earthquake that rocked southern

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california last january caught many by

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surprise but dr andrea donnellan a

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geophysicist from nasa's jet propulsion

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laboratory in pasadena actually saw it

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coming

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we knew that there was a likelihood of

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an earthquake here on a fault similar to

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the one that we saw and we had estimated

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the potential of there being about a

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magnitude 6.4 earthquake so we weren't

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surprised this earthquake occurred

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dr donald and her colleagues track

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changes in the earth's crust throughout

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the la area they do it with antennas

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like this receiving signals from a

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series of satellites called the global

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positioning system or gps

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it's a navigational system but we use it

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to very precisely measure motion of the

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ground

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being squeezed and pushed and we can

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assess earthquake hazard from that

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her research prior to the january quake

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indicated a buildup of stress along a

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fault running through the northridge

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california area exactly where disaster

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ultimately struck

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one of her goals now is to assess the

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impact of this northridge quake on

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future events

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studies indicate that the stress

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increased along the ventura basin which

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is being squeezed close so we want to

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monitor that region very carefully try

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and understand if the earthquake hazard

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has increased there

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although they can't predict precisely

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where and when an earthquake will occur

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dr donald and her colleagues

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identification of potential hot spots

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should help focus efforts to shore up

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buildings and homes so that when the

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so

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still play here

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the seismologist can measure an

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earthquake and see what happened after

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the fact but for the first time with gps

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and other techniques like it we can

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actually measure how the earth is moving

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and try and assess earthquake hazard

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oh mountain we found out went up 15

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inches

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and that means it went up and stayed up

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15 inches so the mountain actually grew

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the ultimate goal is to help quantify

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the earthquake hazard in the la area and

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we would like to help prioritize things

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like building code retrofits right now

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there's just a blanket if you find a

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building that needs fixed you fix it

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there's no priority on one area being

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we don't do prediction we do forecasting

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so we're looking on 10 or 20 or 50 year

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probabilities of earthquake occurrence

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and i do want to point out that we do

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this work in conjunction with the

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geologists and the seismologists that

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this is one more component to the puzzle

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but we don't do

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you can't just lean back a little bit

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and they used to

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shine lights across mountains and

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measure angles between mountain peaks

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that was a very imprecise technique

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what we're looking for now is the post

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seismic relaxation we call it to

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understand how this fault has affected

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we're doing that by putting in a network

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of continuous gps receivers so when

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there's an earthquake like we had in

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northridge we don't have to drive a

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truck up here and deploy the receiver we

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instantly have data as soon as the

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so we'd like to see these techniques

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used in northern california and they are

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to some extent we'd also like to see

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them in the pacific northwest and all

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over the world japan is setting up a

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now the blind thrust fault obviously it

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has a tip right about in here right

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roughly

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the coast of the proxy but it extends

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well back

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where depending where you want to put it

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it stands back at least back that this

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thing is locked or not and that's that's

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the main concern that i have well we can

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certainly put sides down here we see

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these rotations we also see then the

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displacements are a lot higher on this

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side okay much smaller here we have a

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lot higher strength okay so it is so the

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polar rotation is somewhere up in here

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it's actually here oh really it's really

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tight okay extremely tight what i'd

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really like to know is a is this ramp

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locked in which case we shouldn't see

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any strand accumulating across it which

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it sounds like we'll also see what's

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happening both seismically from here

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because the

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largest post seismic motion should be

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about a fault dimension away from the

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one way that i use andrea's data is to

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try to understand whether these faults

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are

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slipping

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very slowly but inexorably at depth and

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relieving strain that way or whether

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they're locked and accumulating strain

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over over hundreds and thousands of

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years and eventually that snaps loose as

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there are

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several faults within the metropolitan

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los angeles region that we're

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particularly concerned about five or six

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in particular that potentially could

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produce very large earthquakes by very

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large i mean

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well in excess of magnitude 7

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much much larger than the recent

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we're learning a lot from every new

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earthquake and all of these data

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eventually do come out in new building

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codes new building specifications that

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hopefully will present prevent you know