TY  - JOUR
A1  - Bentz, Stephan
A1  - Martinez-Garzon, Patricia
A1  - Kwiatek, Grzegorz
A1  - Dresen, Georg
A1  - Bohnhoff, Marco
T1  - Analysis of Microseismicity Framing M-L > 2.5 Earthquakes at The Geysers Geothermal Field, California
T2  - Journal of geophysical research : Solid earth
N2  - Preparatory mechanisms accompanying or leading to nucleation of larger earthquakes have been observed at both laboratory and field scales, but conditions favoring the occurrence of observable preparatory processes are still largely unknown. In particular, it remains a matter of debate why some earthquakes occur spontaneously without noticeable precursors as opposed to events that are preceded by an extended failure process. In this study, we have generated new high-resolution seismicity catalogs framing the occurrence of 20 M-L > 2.5 earthquakes at The Geysers geothermal field in California. To this end, a seismicity catalog of the 11 days framing each large event was created. We selected 20 sequences sampling different hypocentral depths and hydraulic conditions within the field. Seismic activity and magnitude frequency distributions displayed by the different earthquake sequences are correlated with their location within the reservoir. Sequences located in the northwestern part of the reservoir show overall increased seismic activity and low b values, while the southeastern part is dominated by decreased seismic activity and higher b values. Periods of high injection coincide with high b values and vice versa. These observations potentially reflect varying differential and mean stresses and damage of the reservoir rocks across the field. About 50% of analyzed sequences exhibit no change in seismicity rate in response to the large main event. However, we find complex waveforms at the onset of the main earthquake, suggesting that small ruptures spontaneously grow into or trigger larger events.
KW  - induced seismicity
KW  - earthquake nucleation
KW  - The Geysers
KW  - earthquake sequences
Y1  - 2019
UR  - https://publishup.uni-potsdam.de/frontdoor/index/index/docId/48504
SN  - 2169-9313
SN  - 2169-9356
VL  - 124
IS  - 8
SP  - 8823
EP  - 8843
PB  - American Geophysical Union
CY  - Washington
ER  -