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EOSC_212.ppt - Earth and Ocean Sciences

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					    Using GPS and InSAR to study
     tectonics, deformation, and
             earthquakes
•   GPS displacements, velocities (and transients)
•   InSAR displacements
                          InSAR Displacements
Position to within about 1 cm
Great spatial coverage
Sensitive to vertical motion
Bad for high slopes or treed
regions
Satellite not always looking at
what you want when you want
Not so good for very large
earthquakes
                     GPS displacements and velocities

                                                  CGPS has sub-mm precision
                                                  Can detect rate and direction
                                                  changes
                                                  Good for rates and transients
                                                  Not so precise at poles
                                                  Vertical less precise than
                                                  horizontal
                                                  Only point measurements




 McCaffrey et al., 2004
http://ees2.geo.rpi.edu/rob/www/gps/gps2004.htm
        My research: Use GPS
    displacements, velocities, and
   transients to figure out how fault
         zones work at depth.

    Method: numerical modeling.


 Information from seismology, geology,
geochemistry and lab experiments is also
   needed to build and verify models.
GPS velocities in the eastern
  Mediterranean region
Fitting the GPS velocities with
      moving, rigid blocks
    D




    D’



D        D’
North Anatolian Fault Zone (NAFZ) has M
                  ~7.5
  earthquakes about every 300 years




fault slip!        Non-seismic creep: 20 km   This allows rigid translation
0 to 20 km depth   depth to asthenosphere     of one plate past the other
     Deformation around a plate boundary
         fault at different time scales
Within an individual earthquake cycle

    postseismic      “interseismic”
    //
coseismic                      Snapshots: GPS slip rates

Over many earthquake cycles


 dates and earthquake size from paleoseismology:
            recent geological slip rates
Here is how interseismic deformation around a
            fault looks with InSAR

                                                      Colors scale with
                                                      surface velocity

                                                      High strain rate
                                                      means
                                                      elastic stresses are
                                                      building up fast


                                                      Next earthquake will
                                                      be soon (or big)
    from Yuri Fialko’s Science paper of last summer
               Of course, last year’s EOSC 352
                students knew this already....


                                        Shear strain rate and strain rate
                                               axis orientations
                                        From EOSC 352 Homework #5




SCEC GPS velocity field version 3
Lots can be learned from modeling interseismic deformation
                  (beyond today’s scope)
The 1999 Izmit, Turkey earthquake:
  InSAR and GPS displacements
   InSAR: like having
 thousands of not-too-
   precise GPS sites,
  measuring just one
        direction
wrapped (arghh) interferogram
 Green’s function for surface
displacements due to slip on a
    subsurface dislocation
        Slip along the NAFZ in the M = 7.5
             Izmit, Turkey earthquake

0 km



32 km
                    Slip (meters)
When the Izmit earthquake happened it
   built up stresses in some areas




We can actually calculate this stress change and
•   model the Earth’s response to it
•   calculate changes in earthquake probability
    on local faults
Test the hypotheses using finite-
        element models
Models must reproduce the pattern and decay
                    of
        “postseismic” deformation




  postseismic velocities one year after the Izmit earthquake
Model misfit to data after one year
Three years after the 1999 earthquake
Earth is still responding to the earthquake
              stress perturbation
Anatolia-Eurasia plate boundary (central
                NAFZ)
       Eurasia


        Anatolia
                   ?



                                            Moho

                          tricky rheology
                              required?
Postseismic strain (and stressing) rates in the
                Marmara Sea


                               coseismic




                                900 days
    Southwest BC: Our local active faults
Queen Charlotte
Fault M 8

                                Shallow crustal
                                faults M < 8


       Cascadia
       Subduction Zone
       Fault M 9.?


                     Faults in the
                     subducting slab M <
                     7?
             GPS velocity field: Vancouver Island




Henton et al., 2001

				
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