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Temporal static stress drop variations due to injection activity at The Geysers geothermal field, California
Author(s) -
Staszek M.,
OrleckaSikora B.,
Leptokaropoulos K.,
Kwiatek G.,
MartínezGarzón P.
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2017gl073929
Subject(s) - geothermal gradient , drop (telecommunication) , geology , induced seismicity , seismic moment , stress (linguistics) , pore water pressure , geotechnical engineering , seismology , geophysics , telecommunications , linguistics , philosophy , fault (geology) , computer science
Abstract We use a high‐quality data set from the NW part of The Geysers geothermal field to determine statistical significance of temporal static stress drop variations and their relation to injection rate changes. We use a group of 322 seismic events which occurred in the proximity of Prati‐9 and Prati‐29 injection wells to examine the influence of parameters such as moment magnitude, focal mechanism, hypocentral depth, and normalized hypocentral distances from open‐hole sections of injection wells on static stress drop changes. Our results indicate that (1) static stress drop variations in time are statistically significant, (2) statistically significant static stress drop changes are inversely related to injection rate fluctuations. Therefore, it is highly expected that static stress drop of seismic events is influenced by pore pressure in underground fluid injection conditions and depends on the effective normal stress and strength of the medium.