Lack of Additional Triggered Tectonic Tremor around the Simi Valley and the San Gabriel Mountain in Southern California

Abstract

Abstract We conduct a systematic search of tectonic tremor triggered by distant large earthquakes around the Simi Valley (SV) and the San Gabriel Mountain (SGM) in southern California. Out of 59 large earthquakes between 2000 and 2013, only the 2002 M w 7.9 Denali fault earthquake triggered clear tremor in the region. The observed travel times of the triggered tremors are consistent with theoretical predictions from tremor sources that are spatially clustered in the SV, close to the rupture zone of the 1994 M w 6.7 Northridge earthquake. We also estimate the triggering stress threshold as ∼12 kPa from measuring the peak ground velocities near the tremor source. The lack of clear tremor beneath the SGM provides a “negative” example for a region where tremor is expected to occur because of clear evidence of fluid‐rich zones at the middle crust. The results imply that the necessary conditions for tremor to occur are more than fluid‐induced low effective normal stress. Online Material: Figures of additional tremor inspection, tables of earthquake catalogs, and tremor locations.