Earthquake swarms driven by aseismic creep in the Salton Trough, California

TLDR

In late August 2005, a swarm of more than a thousand earthquakes (M 1–5.1) occurred at Obsidian Buttes near the southern San Andreas Fault. The swarm offers a unique opportunity to assess mechanisms driving seismic swarms along transform plate boundaries and to improve short‑term seismic hazard forecasts. The authors employ earthquake‑triggering models combined with dense geodetic data to model swarm behavior and forecast hazard. Seismicity explains only 20 % of the observed deformation, indicating shallow aseismic slip as the primary driver, and models of aseismic creep reproduce both the swarm’s time history and its ~1 km h⁻¹ migration.

Abstract

In late August 2005, a swarm of more than a thousand earthquakes between magnitudes 1 and 5.1 occurred at the Obsidian Buttes, near the southern San Andreas Fault. This swarm provides the best opportunity to date to assess the mechanisms driving seismic swarms along transform plate boundaries. The recorded seismicity can only explain 20% of the geodetically observed deformation, implying that shallow, aseismic fault slip was the primary process driving the Obsidian Buttes swarm. Models of earthquake triggering by aseismic creep can explain both the time history of seismic activity associated with the 2005 swarm and the ∼1 km/h migration velocity exhibited by this and several other Salton Trough earthquake swarms. A combination of earthquake triggering models and denser geodetic data should enable significant improvements in time‐dependent forecasts of seismic hazard in the key days to hours before significant earthquakes in the Salton Trough.