Moment Tensors of Induced Microearthquakes in The Geysers Geothermal Reservoir From Broadband Seismic Recordings: Implications for Faulting Regime, Stress Tensor, and Fluid Pressure
Moment Tensors of Induced Microearthquakes in The Geysers Geothermal Reservoir From Broadband Seismic Recordings: Implications for Faulting Regime, Stress Tensor, and Fluid Pressure
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DOI：
10.1029/2018jb016251
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发表时间：
2018-10
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通讯作者：
Changpeng Yu;V. Vavryčuk;P. Adamová;M. Bohnhoff
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作者：
Changpeng Yu;V. Vavryčuk;P. Adamová;M. Bohnhoff
使用来自现场宽带网络的波形数据和基于主成分分析的方法计算了间歇泉地热田1，421次微震的全矩张量。研究了断层活动的空间特征、应力张量和各向同性分量。所研究的事件形成不同的集群分别占主导地位的正断层（NF）和走滑（SS）故障。SS主导的集群与在油田西南侧观察到的SS应力状态有关，其中存在两个NW-SE走向的断层带。越来越多的比例的SS故障附近的NF主导的集群的浅部和深部观察。储层上部和下部之间的温差不会改变团簇的整体应力状态。应力比在北西部远小于在该领域的东南部。对于96%的事件，检索到的ISO范围在-5%至25%之间。正ISOs的平均百分比与各层组的平均注入速率相关，且在主注入层段以下随深度的增加而增加。只有10%的事件显示负ISO，并且主要限制在抽汽深度范围内。负ISO事件的比例表明抽汽的地震响应比注水弱得多。ISO百分比的空间变化不跟随地震活动性变化，因为ISO对与流体注入和迁移相关的压力变化更敏感。
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.