Spatial variability of the earthquake size distribution from laboratory to global scale 

Stefan Wiemer
Swiss Seismological Service, ETH-Hoenggerberg


Abstract:
Strong spatial variations of the earthquake-size distribution (or Gutenberg-Richter law, 
log N = a-bM)) can be found for a large variety of tectonic regimes. In volcanic systems, 
for example, spatial variations of the b-value over just a few hundred meters are common. 
High b-value anomalies underneath volcanoes correlate well with magma chambers. Asperities 
in the Earth crust, measuring several kilometers, can sometimes be mapped through their 
unusually low b, offering new possibilities for improving seismic hazard assessment. On the 
other end of the spectrum, high b-value anomalies measuring several thousands of kilometers 
correlate well with the stress pattern prescribed by the India-Asia collision. This talk 
summarizes results of high resolution spatial mapping of the obtained by our group over the 
past 10 years. I will explore the uses and limitations of mapping a- and b-values, and 
discuss possible physical mechanism that explain the observations.