Mapping Geodetic Strain Rates into Long and Intermediate Term Earthquake Potentials
Abstract
We modify our method of long and intermediate term earthquake forecast using geodetically derived crustal strain rates. The method is based on the assumptions that: (a) seismicity rate is steady and proportional to the horizontal maximum shear strain rate; and b) earthquake magnitude distribution is spatially invariant except for an amplitude constant which is proportional to the maximum horizontal shear strain rate. This method is relatively easy to implement if crustal deformation is steady, and not so if significant postseismic deformation is involved. The difficulty is two folds: First a populated continuous GPS network, not always available in most parts of the world, is needed to monitor postseismic deformation both in space and time. Second causal relationship between the transient strains and earthquake occurrence is not quite clear. We tackle the problem by (a) implementing a postseismic deformation model such that transient strain rates could be derived from limited observational data epochs of a geodetic network, and (b) treating the postseismic strain the same as the long term tectonic strain for earthquake forecast, since the former is imposed onto the brittle upper crust the same way as the latter to cause earthquakes. Data analysis in southern California reveals that postseismic deformation is best described by a logarithmic function, with a decay time constant of 10 days regardless of earthquake magnitudes and locations. Combining the postseismic and secular strain rates one could assess the long and intermediate earthquake potentials, which evolve with time. Application of the method to earthquake forecast in southern California and its retrospective test result will be presented at the meeting. We will also assess the possible gain for earthquake forecast using faultmodel aided strain rates rather than the strain rates derived directly from the geodetic data.
 Publication:

AGU Fall Meeting Abstracts
 Pub Date:
 December 2007
 Bibcode:
 2007AGUFM.G22A..08S
 Keywords:

 1207 Transient deformation (6924;
 7230;
 7240);
 1240 Satellite geodesy: results (6929;
 7215;
 7230;
 7240);
 1242 Seismic cycle related deformations (6924;
 7209;
 7223;
 7230);
 7223 Earthquake interaction;
 forecasting;
 and prediction (1217;
 1242);
 7230 Seismicity and tectonics (1207;
 1217;
 1240;
 1242)