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Paper in GRL on non-double-couple components at The Geysers geothermal field

Finally we published a paper related to investigation of seismic moment tensors of microseismic events at The Geysers geothermal field.

Reference

Martínez-Garzón, P., Kwiatek, G., Bohnhoff, M., and G. Dresen (2017). Volumetric components in the earthquake source related to fluid injection and stress state. Geophys. Res. Lett. 44, DOI: 10.1002/2016GL071963. [ Article Page ]

Abstract

We investigate source processes of fluid-induced seismicity from The Geysers geothermal
reservoir in California to determine their relation with hydraulic operations and improve the corresponding seismic hazard estimates. Analysis of 869 well-constrained full moment tensors (Mw 0.8–3.5) reveals significant non-double-couple components (>25%) for about 65% of the events. Volumetric deformation is governed by cumulative injection rates with larger non-double-couple components observed near the wells and during high injection periods. Source mechanisms are magnitude dependent and vary significantly between faulting regimes. Normal faulting events (Mw<2) reveal substantial volumetric components indicating dilatancy in contrast to strike-slip events that have a dominant double-couple source. Volumetric components indicating closure of cracks in the source region are mostly found for reverse faulting events with Mw>2.5. Our results imply that source processes and magnitudes of fluid-induced seismic events are strongly affected by the hydraulic operations, the reservoir stress state, and the faulting regime.

Paper on theoretical limits on detection and analysis of small earthquakes

Finally, the paper entitled “Theoretical limits on detection and analysis
of small earthquakes” has been published in Journal of Geophysical Research: Solid Earth. In this paper we investigate theoretical limits on detection and reliable estimates of source characteristics of small earthquakes using synthetic seismograms for shear/tensile dislocations on kinematic circular ruptures and observed seismic noise and properties of several acquisition systems (instrument response, sampling rate). The results presented in the manuscript provide guidelines on detection of small events in various geological environments, along with information relevant to reliable analyses of earthquake source properties.

Reference:

Kwiatek, G., and Y. Ben-Zion (2016), Theoretical limits on detection and analysis of small earthquakes, Journal of Geophysical Research-Solid Earth, 121, doi:10.1002/2016JB012908.

Radiation pattern of shear-tensile faults on Matlab File Exchange

While writing a paper to Journal of Geophysical Research on S-to-P radiated energy ratio from shear-tensile events I created a number of MATLAB functions related to the methodology presented inside. One of the routines, rpgen.m, I just uploaded to MATLAB file exchange. This function calculates P, S, SH and SV radiation pattern from shear-tensile fault at certain takeoff angle and azimuth of observation. The fault itself is parameterized by strike, dip, rake, tensile angle and Poisson’s ratio.

Link: RPGEN.M – Matlab File Exchange.