Triggering Intensity Changes over Time and Space as Measured by
Continuous Waveforms in Southern California
Abstract
Dynamic triggering of earthquakes is when seismic waves from earthquakes
induce seismic activity at a distance. The observability of the seismic
wave stresses and their results presents a unique opportunity to
understand earthquake interactions and associated hazard implications.
The extent and timing of dynamic triggering at given specific stress
changes still remain inadequately predicted due to limited studies and
datasets. In particular, the requirement for complete,
well-characterized catalogs to detect triggering systematically
seriously limits the types of studies possible. To address this, we
utilized 7-year continuous waveform data from 239 stations in southern
California and used PhaseNet for phase picking to identify local
earthquakes and measure triggering without constructing any earthquake
catalog. We map the triggering intensity over the region and find that
overall, the Mojave segment of the San Andreas is the most easily
triggered region. However, the spatial pattern changes after the
Ridgecrest earthquake and the area becomes much less prone to
triggering, likely due to an exhaustion of the faults near failure in
the immediate aftermath of the Ridgecrest sequence. We further observe a
slow decay rate of dynamic triggering and conclude that low-frequency
waves (0.04-0.1 Hz) may be more effective in dynamic triggering than
high-frequency waves (1-3 Hz) which is consistent with a rate-state
assisted aseismic creep or hydrological triggering mechanism.