Long-range triggering of earthquakes provides a window into
earthquake initiation processes. In this talk, I review the
observational facts about long-range triggering and discuss their
implications for the start of slip in general. We observe that
seismic shaking make earthquakes, long-range triggering is more
often observed in geothermal areas, seismicity persists and other
long-range triggered phenomena occur such as deformation and water
level change. The last observation motivates a detailed
investigation of the coupling between seismic waves and pore
pressures. Based on water well records in Grants Pass, OR, I
conclude that unclogging of fractures results in pore pressure
redistribution during earthquakes which can in turn trigger
earthquakes. This redistribution of pore pressure is consistent
with triggering thresholds in Long Valley Caldera. As further
evidence of the macroscopic effects of very small shaking, I also
discuss large permeability changes as a result of small seismic
stresses at Pinon Flat Geophysical Observatory.
To begin viewing slides, click on the first slide below. (Or, view as pdf.)