The 2015 Fillmore Earthquake Swarm and Possible Crustal Deformation Mechanisms Near the Bottom of the eastern Ventura Basin, California

Egill Hauksson, Jennifer Andrews, Andreas Plesch, John H. Shaw, & David R. Shelly

Published March 11, 2016, SCEC Contribution #6208

The 2015 Fillmore swarm occurred about 6 km west of the City of Fillmore in Ventura, California, and was located beneath the eastern part of the actively subsiding Ventura basin at depths from 11.8 km to 13.8 km, similar to two previous swarms in the area. Template-matching event detection showed that it started on the 5th of July 2015 at 2:21 UTC with a ~M1.0 earthquake. The swarm exhibited unusual episodic spatial and temporal migrations, and diversity in nodal planes of focal mechanisms as compared to the simple hypocenter defined plane. It was also noteworthy because it consisted of >1,400 events of M≥0.0, with M2.8 being the largest event. We suggest that fluids released by metamorphic dehydration processes, migration of fluids along a detachment zone, and cascading asperity failures caused this prolific earthquake swarm, but other mechanisms such as simple mainshock-aftershock stress triggering or a regional aseismic creep event are less likely. Dilatant strengthening may be a mechanism that causes the temporal decay of the swarm as pore pressure drop increased the effective normal stress, and counteracted the instability driving the swarm.

Citation
Hauksson, E., Andrews, J., Plesch, A., Shaw, J. H., & Shelly, D. R. (2016). The 2015 Fillmore Earthquake Swarm and Possible Crustal Deformation Mechanisms Near the Bottom of the eastern Ventura Basin, California. Seismological Research Letters, 87(4), 807-815. doi: 10.1785/0220160020.

Related Projects & Working Groups
seismology