Dynamic triggering

Abstract

A growing body of evidence demonstrates that dynamic stresses propagating as seismic waves from large earthquakes are capable of triggering additional earthquakes ranging from aftershocks in the near-field (within one or two source dimensions of the mainshock epicenter) to remotely triggered earthquakes at distances exceeding 10 000 km. Most of the triggered earthquakes are small (generally M ≤ 3) except within the near field, where dynamic stresses may trigger slip on subadjacent fault segments leading to complex rupture comprising of several large earthquakes of comparable magnitude. Crustal surface waves with periods of 15–30 s and peak dynamic stresses greater than ∼0.01 MPa seem to be most efficient in triggering remote seismicity. Current models for dynamic triggering fall under two broad groups: one appealing to Coulomb failure with various friction laws, and the other appealing to the activation of crustal fluids either hydrous or magmatic. No single model appears capable of accounting for the wide variation observed in the nature of triggered activity. Spatial sampling of dynamic triggering on a global scale is still woefully inadequate because of the limited distribution of adequate seismic networks. From the limited data currently available, it appears that extensional stress regimes hosting geothermal and volcanic activity are more susceptible to remote dynamic triggering than compressional stress regimes, although remote triggering is not limited to extensional regimes. Instances of remote triggering in the few areas with continuous, high-resolution deformation instrumentation (all volcanic or geothermal areas) include distinctive deformation transients, suggesting that the locally triggered seismicity in these areas may be a secondary response to a more fundamental aseismic process that likely involves some form of fluid transport or phase change. Recent evidence for triggering by solid Earth tides and ocean loading in convergent plate margins provides a low-frequency, low-amplitude reference point for the spectrum of stresses capable of dynamic triggering. Remaining challenges include establishing better sampling of the distribution of triggered seismicity and better constraints on physical models for the triggering process.