Using GPS and InSAR to study tectonics, deformation, and earthquakes GPS displacements, velocities (and transients) 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 InSAR Displacements

McCaffrey et al., 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

GPS displacement field

GPS receiver at Albert Head, Vancouver Island Geological Survey of Canada GPS transients: time-varying velocity

My research: Use GPS displacements, velocities, and transients to figure out how fault zones work at depth. Information from seismology, geology, geochemistry and lab experiments is also needed to build and verify models. Method: numerical modeling.

GPS velocities in the eastern Mediterranean region

Fitting the GPS velocities with moving, rigid blocks

which ones are missing? It’s not as simple as a bunch of rigid blocks...

D D’ D

North Anatolian Fault Zone (NAFZ) has M ~7.5 earthquakes about every 300 years fault slip! 0 to 20 km depth Non-seismic creep: 20 km depth to asthenosphere This allows rigid translation of one plate past the other

coseismic // postseismic “interseismic” dates and earthquake size from paleoseismology: recent geological slip rates dates and earthquake size from paleoseismology: recent geological slip rates Snapshots: GPS slip rates Within an individual earthquake cycle Over many earthquake cycles Deformation around a plate boundary fault at different time scales

Here is how interseismic deformation around a fault looks with InSAR from Yuri Fialko’s Science paper of last summer Colors scale with surface velocity High strain rate means elastic stresses are building up fast Next earthquake will be soon (or big)

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

wrapped (arghh) interferogram InSAR: like having thousands of not-too- precise GPS sites, measuring just one direction

Green’s function for surface displacements due to slip on a subsurface dislocation

0 km 32 km Slip (meters) Slip along the NAFZ in the M = 7.5 Izmit, Turkey earthquake

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

Queen Charlotte Fault Figures: Geological Survey of Canada

Earth models must connect episodic earthquakes with steady relative plate motion ‘rigid’ down to asthenosphere with localized shear zones? creeping below mid-crust? This is done with creeping goo Distribution and properties of this goo control the Earth’s response (i.e., surface motions, stress evolution)

viscoelastic relaxation: lower crust (Newtonian) afterslip: viscous creep along shear zone (Newtonian) afterslip: velocity-strengthening friction

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

Model performance: decay of postseismic velocities linear viscoelastic lower crust linearly viscous shear zone velocity-strengthening shear zone

Total modeled afterslip after a year Distance along fault (km) Depth (km) About twice this slip would be required to fit the postseismic GPS displacements after 1 year.

Anatolia-Eurasia plate boundary (central NAFZ) Eurasia Anatolia Moho ? tricky rheology required?

Postseismic strain (and stressing) rates in the Marmara Sea coseismic 900 days

Active Tectonics of western North America western Washington is ramming into SW British Columbia rigid blocks of continental crust (Sierra Nevada block, western Oregon block) are rotating NW Washington is squishing N- S Basin and Range is stretching E-W (SE Oregon, Nevada) Wells et al., 1998

Southwest BC: Our local active faults Queen Charlotte Fault M 8 Cascadia Subduction Zone Fault M 9.? Faults in the subducting slab M < 7? Shallow crustal faults M < 8

Henton et al., 2001 GPS velocity field: Vancouver Island