Distinct spatial patterns of tidal and dynamic triggering at the Coso geothermal field

Abstract:

Observations of the triggering response of seismic fault systems to short- to medium-term stress fluctuations improve our understanding of earthquake nucleation, rupture failure processes, and local stress states. We examine earthquake triggering at and around the Coso, eastern California, geothermal field caused by periodic loading at two different frequencies, due to Earth tides (~10^-5 Hz) and seismic waves (~0.1-1 Hz). We observe strong tidal triggering but no remote seismic triggering within the Coso field, indicating a frequency-dependent triggering mechanism. The tidal triggering signal is strongest near the edges of the zone of production wells, suggesting fluid pressure gradients may encourage triggering at tidal periods, while the absence of aftershocks following the recent M7.1 Ridgecrest earthquake indicates that even relatively large dynamic stress changes do not trigger earthquakes in the Coso geothermal field.