# Remotely triggered earthquakes

### Remotely Triggered Earthquakes: Observations, Interpretations

Remotely triggered earthquakes have now been observed commonly in geothermal and volcanic regions. Analysis of historic earthquake sequences reveals that remotely triggered earthquakes occur commonly in intraplate crust as well. Because neither abundant geothermal/volcanic fluids nor weak faults are expected to exist in intraplate crust, this provides evidence that at least some faults in intraplate regions are critically stressed.

A sequence of large earthquakes along the Aleutian arc and Kurile-Kamchatka trench from 1952 to 1965 released interplate stresses accumulated over a much longer period prior to the sequence. The subsequent evolution of postseismic deformation of the Pacific lithosphere has been predicted using a viscoelastic coupling model consisting of a purely elastic oceanic lithosphere overlying a viscoelastic asthenosphere with viscosity = 5 $\times$ 1017 Pa s. Southward propagation of both postseismic strain and velocity fronts is consistent with patterns of (apparently triggered) earthquake occurrence along western North America over the past 30 years, including accelerations in California seismicity from about 1979 to 1994. The model is consistent with observed anomalous velocity of broadly distributed Pacific geodetic sites and suggests that stress redistribution following earthquakes may produce tangible effects over a spatial scale of 1000's of km.