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tensile faulting

Tensile faulting

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.

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.

JGR Paper: Assessment of S/P radiated energy ratio from shear-tensile picoearthquakes

Together with Yehuda Ben-Zion we published a paper in Journal of Geophysical Research. The paper is entitled “Assessment of P and S wave energy radiated from very small shear-tensile seismic events in a deep South African mine“. The publication is my come-back to the JAGUARS project that we worked on between 2007 and 2011 and analyzed nano- and picoseismicity recorded in Mponeng deep gold mine in South Africa.

In the study we discuss requirements for reliable estimates of radiated seismic energy in S and P phases and derive ratios of S-to-P radiated energy of over 500 extremely small seismic events with local magnitudes −5.23 ≤ ML ≤ −2.41 (subdecimeter size) recorded by high-frequency acoustic emission (AE) sensors of the JAGUARS seismic network in the Mponeng deep gold mine, South Africa. Please see the article page for details.

Reference: Kwiatek, G. and Y. Ben-Zion (2013). Assessment of P and S wave energy radiated from very small shear-tensile seismic events in a deep South African mine. J. Geophys. Res. 118, DOI: 10.1002/jgrb.50274.