Moment tensors of induced microearthquakes in The Geysers geothermal reservoir from broadband seismic recordings: Implications for faulting regime, stress tensor, and fluid pressure.

0494895 - GFÚ 2019 RIV US eng J - Journal Article
Yu, C. - Vavryčuk, Václav - Adamová, Petra - Bohnhoff, M.
Moment tensors of induced microearthquakes in The Geysers geothermal reservoir from broadband seismic recordings: Implications for faulting regime, stress tensor, and fluid pressure.
Journal of Geophysical Research-Solid Earth. Roč. 123, č. 10 (2018), s. 8748-8766. ISSN 2169-9313. E-ISSN 2169-9356
R&D Projects: GA ČR GC16-19751J
Institutional support: RVO:67985530
Keywords : full moment tensor * induced seismicity * faulting regime * isotropic component
OECD category: Volcanology
Impact factor: 3.585, year: 2018

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.
Permanent Link: http://hdl.handle.net/11104/0287954