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Moment Tensors of Induced Microearthquakes in The Geysers Geothermal Reservoir From Broadband Seismic Recordings: Implications for Faulting Regime, Stress Tensor, and Fluid Pressure
Author(s) -
Yu Changpeng,
Vavryčuk Václav,
Adamová Petra,
Bohnhoff Marco
Publication year - 2018
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2018jb016251
Subject(s) - geothermal gradient , geology , seismology , induced seismicity , cauchy stress tensor , stress field , microseism , fault (geology) , stress (linguistics) , pore water pressure , isotropy , geophysics , geotechnical engineering , finite element method , thermodynamics , linguistics , philosophy , physics , classical mechanics , quantum mechanics
Full moment tensors of 1,421 microearthquakes in The Geysers geothermal field were calculated using waveform data from a field‐wide broadband network and the approach based on the principal component analysis. Spatial characteristics of faulting regime, stress tensor and the isotropic component (ISO) of moment tensors were investigated. The studied events form different clusters dominated by normal faults (NF) and strike‐slip (SS) faults, respectively. The SS‐dominated clusters are related to the SS stress state observed in the southwestern side of the field where two NW‐SE trending fault zones exist. Increasing proportions of SS faults were observed near the shallow and deep parts of the NF‐dominated clusters. Temperature differences between the upper and lower parts of the reservoir do not change the overall stress states of clusters. The stress ratios in the NW part are much smaller than in the SE part of the field. The retrieved ISOs range between −5% and 25% for 96% of events. The average percentages of positive ISOs are correlated with the average injection rates in different clusters, and keep an increasing trend with depth below the main injection interval. Only 10% of events show negative ISO and are mainly constrained within the depth range of steam extraction. The proportion of events with negative ISO suggests much weaker seismic responses of the steam extraction than the water injection. The spatial variations of the ISO percentage do not follow the seismicity variations as the ISO is more sensitive to the pressure changes related to the fluid injection and migration.