Tidal triggering of low frequency earthquakes near Parkfield, California: Implications for fault mechanics within the brittle‐ductile transition

摘要: [1] Studies of nonvolcanic tremor (NVT) have established the significant impact small stress perturbations on NVT generation. Here we analyze influence solid earth and ocean tides a catalog ∼550,000 low frequency earthquakes (LFEs) distributed along 150 km section San Andreas Fault centered at Parkfield. LFE families are identified in data basis waveform similarity thought to represent small, effectively co-located occurring brittle asperities an otherwise aseismic fault depths 16 30 km. We calculate sensitivity each these 88 tidally induced right-lateral shear (RLSS), fault-normal (FNS), their time derivatives use hypocentral locations family map spatial variability this sensitivity. occurrence is most strongly modulated by fluctuations stress, with majority demonstrating correlation RLSS 99% confidence level or above. Producing observed rate modulation response requires effective source region. There substantial lateral vertical variations tidal sensitivity, which interpret reflect variation region properties, such as friction pore fluid pressure. Additionally, find that highly episodic, shallow generally less correlated stresses than deeper, continuously active counterparts. The weaker insignificant positive (tensile) FNS. Two groups demonstrate stronger tension north compression south correlate clamping coincide releasing right bend surface trace locations, suggesting remains localized contiguous down near base crust. deep high both tensile normal may be indicative increase contact area depth. Synthesizing our observations those other LFE-hosting localities will help develop comprehensive understanding transient slip below “seismogenic zone” providing constraints parameters physical models slow LFEs.