The recent discovery of non-volcanic tremor has led to great excitement and research activity in the earth-science community. To date, tremor has almost exclusively been found in subduction zones. The only observation outside a subduction-dominated region is on the strike-slip San Andreas Fault in Parkfield, California. In Japan and Cascadia non-volcanic tremor lasting days to months occurs coincident with aseismic slip along the plate interface, and recent studies have identified short bursts of tremor triggered by the seismic waves of distant earthquakes. Since non-volcanic tremor is mostly observed in subduction zones, nearly all causative mechanisms proposed appeal to conditions expected in the subduction zones. We show that the conditions required for non-volcanic tremor generation must exist in a variety of tectonic environments, by presenting observations of non-volcanic tremor at seven sites along the transform plate boundary in California triggered by the 2002 Mw 7.8 Denali Fault, Alaska earthquake. These observations come from recordings of the Denali earthquake waves from broadband and short period seismometers archived at the Northern and the Southern California Earthquake Data Centers. Some models of non-volcanic tremor in subduction zones invoke frictional behaviors expected in regions transitional between where the fault is locked and slipping freely (creeping). Such transition zones likely occur in California at shallow depths below and adjacent to documented creeping fault segments. We find no clear correlation of tremor locations with creeping, locked, or transitional fault behavior. Other explanatory models relate non-volcanic tremor to the release of fluids from dehydration of the subducting plate. We find numerous triggered earthquakes in two geothermal fields but no tremor, implying that high fluid pressure and/or temperatures may be necessary for tremor generation, but they are not alone sufficient.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 8118 Dynamics and mechanics of faulting (8004);
- 8123 Dynamics: seismotectonics;
- 8163 Rheology and friction of fault zones (8034)