The investigators plan to address some fundamental issues behind non-volcanic tremor. Where does triggered tremors occur along the transform plate boundary in California, and elsewhere in the world? Are tremors preferentially triggered in a limited range of tectonic regimes? Why do the geothermal regions have many triggered earthquakes, but no apparent triggered tremors? Is there a stressing threshold for triggered tremors? Their initial survey has shown that only a few teleseismic earthquakes triggered tremors around the Parkfield section of the SAF, but the triggering threshold is still not clear. A systematic examination of surface waves of many earthquakes with different amplitudes and frequency content is needed. It is still not clear whether fluid flow induced by volumetric changes of Rayleigh waves, or transient shear stresses from Love waves is the most effective mechanism for tremor triggering. A systematic survey of tremors triggered by many teleseismic events will help to distinguish different triggering mechanisms. Are the triggered tremors the same phenomenon as the ambient (non-triggered) tremors and do they follow the new scaling relationship of slow earthquakes? Does slow slip and triggered earthquake accompany triggered tremors? Is there a constant background of tremor?
The work will provide better understanding of fault slip, and would have a transformative impact for seismology, geodesy, geology, friction and rock mechanics, and perhaps more. A better understanding of tremor occurrence along the SAF system in California and elsewhere and its relation to slow slip events and occurrence of large earthquakes is directly relevant to seismic hazard mitigation. The research will involve the education of graduate students in both participating institutions, and will also involve undergraduate students.
