The Physics of Low-Frequency Earthquakes with Doubling Recurrence Intervals near Parkfield

Abstract:

Recent advancements in seismic detection lit up low-frequency earthquakes (LFEs) below the seismogenic zone near Parkfield that cluster in tremor bursts with doubling of recurrence intervals. The striking recurrence pattern can be explained by the successive occurrence of slow and fast slip events that trigger LFEs, but the source characteristics of the LFEs are still poorly understood. In particular, the decadal seismic record indicates that tremor bursts containing more LFEs and lasting longer are also associated with lower-amplitude ground motion. Here, we use numerical models of rupture dynamics to investigate the physics of micro-asperities under rapid loading to explain the source characteristics of the Parkfield LFEs. We find that the peak velocity of the slip event controls the number of LFEs per burst. However, the duration of the underlying slip does not directly control the duration of the tremor burst. This implies that the LFEs are triggered and take place shortly after the slip events, in a manner similar to mainshock/aftershocks interactions. Our results bring a better understanding of the physics of triggered tectonic tremors associated with underlying slow-slip events.