Irregular focal mechanisms observed at Salton Sea Geothermal Field: Possible influences of anthropogenic stress perturbations

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Edited by: Martin Schoenball

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Abstract

At the Salton Sea Geothermal Field (SSGF), strain accumulation is released through seismic slip and aseismic deformation. Earthquake activity at the SSGF often occurs in swarm-like clusters, some with clear migration patterns. We have identified an earthquake sequence composed entirely of focal mechanisms representing an ambiguous style of faulting, where strikes are similar but deformation occurs due to steeply-dipping normal faults with varied stress states. In order to more accurately determine the style of faulting for these events, we revisit the original waveforms and refine estimates of P and S wave arrival times and displacement amplitudes. We calculate the acceptable focal plane solutions using P-wave polarities and S/P amplitude ratios, and determine the preferred fault plane. Without constraints on local variations in stress, found by inverting the full earthquake catalog, it is difficult to explain the occurrence of such events using standard fault-mechanics and friction. Comparing these variations with the expected poroelastic effects from local production and injection of geothermal fluids suggests that anthropogenic activity could affect the style of faulting.

Additional publication details

Publication type Conference Paper
Publication Subtype Conference Paper
Title Irregular focal mechanisms observed at Salton Sea Geothermal Field: Possible influences of anthropogenic stress perturbations
Year Published 2018
Language English
Publisher Stanford University
Contributing office(s) Earthquake Science Center
Description 11 p.
Larger Work Type Book
Larger Work Subtype Conference publication
Larger Work Title Proceedings, 43rd Workshop on Geothermal Reservoir Engineering
Conference Title 43rd Workshop on Geothermal Reservoir Engineering
Conference Location Stanford, CA
Conference Date February 12-14, 2018