Earthquake and fault interactions in Asia measured by SAR interferometry

Eric Fielding 
Solid Earth Group 
Jet Propulsion Laboratory, Caltech 
Pasadena, California

The classic elastic rebound concept of the earthquake cycle developed by Harry
Fielding Reid has been confirmed by geodetic observations over the last century
as applying to most major faults, including of course the San Andreas fault
where it was first measured. Synthetic Aperture Radar (SAR) interferometry (and
also image offset analysis) using repeated satellite images of faults before
and after earthquakes has extended coseismic elastic rebound measurements to
areas where there are few or no ground geodetic surveys. The active tectonic
belt across Europe and Asia, often called the Alpine- Himalayan belt, has major
fault zones with rapid focussed deformation similar to the San Andreas fault
but also has large areas of more distributed deformation where seismogenic
faults are not so easily identified. Interferometric SAR or InSAR allows us to
identify unequivocally the fault that ruptured in shallow earthquakes (greater
than a depth-dependent magnitude) and estimate the distribution of slip on the
fault in many cases. The 2003 Bam, Iran earthquake ruptured a buried
strike-slip fault that was previously unknown, and unfortunately located
directly beneath the city. The broad and dense spatial coverage of InSAR also
enables the study of interseismic elastic strain build-up, postseismic
deformation, and aseismic deformation. We can compute the stress change due to
the coseismic slip of an earthquake on nearby faults and adjacent crust and
mantle. Measuring the deformation caused by this stress change allows us to
estimate the rheology of the fault zones, crust, and sometimes the upper
mantle.