Heat Flow and the Seismogenic Zone in Southern California Colin F. Williams USGS, Menlo Park, CA U.S. Department of the Interior U.S. Geological Survey

Depth of seismicity in Southern California (after Nazareth and Hauksson, 2004)

Heat Flow in California

Landers EQ, Heat Flow and Seismic-Aseismic Transition

Heat Flow in Ventura and LA Basins

SHLK RDS

Observations  Observed pattern of seismicity depth cut-off consistent with variations in heat flow  Imperial Valley – Hi HF and Shallow Seismicity  Landers – Consistent Variations in HF, Seismicity and Rupture depth along strike  Ventura Basin – Lo HF and Deep Seismicity  San Gregorio Pass – No HF Constraint  Temperature for the seismic-aseismic transition is ~350 to 400 o C for most of southern California but is lower (~ o C ??) in the Mojave, probably due to lithologic variations  Improved EQ catalogues key to quantitative evaluation