Evidence for fluid‐injection‐induced seismicity is rare in California hydrocarbon basins, despite widespread injection close to seismically active faults. We investigate a potential case of injection‐induced earthquakes associated with San Ardo oilfield operations that began in the early 1950s. The largest potentially induced events occurred in 1955 (⁠ML 5.2) and 1985 (⁠Mw 4.5) within ∼6 km from the oilfield. We analyze Synthetic Aperture Radar interferometric images acquired by Sentinel‐1A/B satellites between 2016 and 2020 and find surface deformation of up to 1.5 cm/yr⁠, indicating pressure‐imbalance in parts of the oilfield. Fluid injection in San Ardo is concentrated within highly permeable rocks directly above the granitic basement at a depth of ∼800 m⁠. Seismicity predominantly occurs along basement faults at 6–13 km depths. Seismicity and wastewater disposal wells are spatially correlated to the north of the oilfield. Temporal correlations are observed over more than 40 yr with correlation coefficients of up to 0.71 for seismicity within a 24 km distance from the oilfield. Such large distances have not previously been observed in California but are similar to the large spatial footprint of injection in Oklahoma. The San Ardo seismicity shows anomalous clustering with earthquakes consistently occurring at close spatial proximity but long interevent times. Similar clustering has previously been reported in California geothermal fields and may be indicative of seismicity driven by long‐term, spatially persistent external forcing.The complexity of seismic behavior at San Ardo suggests that multiple processes, such as elastic stress transfer and aseismic slip transients, contribute to the potentially induced earthquakes. The present observations show that fluid‐injection operations occur close to seismically active faults in California. Yet, seismicity is predominantly observed on smaller unmapped faults with little observational evidence that large faults are sensitive to induced stress changes.

中文翻译：

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加利福尼亚中部圣阿多的圣安德烈亚斯断层附近超过40年的潜在诱发地震

尽管在邻近地震活动断层附近广泛注入，但在加利福尼亚油气盆地中很少有流体注入引起的地震活动的证据。我们调查了与1950年代初开始的圣Ardo油田作业相关的注入诱发地震的潜在案例。最大的潜在诱发事件发生在距油田约6公里以内的1955年（ML 5.2）和1985年（Mw 4.5）。我们分析了Sentinel-1A / B卫星在2016年至2020年之间获取的合成孔径雷达干涉图像，发现表面变形高达1.5 cm /yr⁠，表明该油田部分地区的压力不平衡。San Ardo的流体注入集中在花岗岩基底正上方的高渗透性岩石中，深度约为800m⁠。地震主要发生在6-13 km深度的地下断层处。地震井和废水处理井在空间上与油田北部相关。在距油田24 km的距离内，地震相关性的时间相关性超过40年，相关系数高达0.71。如此大的距离以前在加利福尼亚州尚未观察到，但与俄克拉荷马州的大型注射空间足迹相似。San Ardo地震活动显示异常聚类，地震在空间上接近且间隔时间长时持续发生。以前在加利福尼亚的地热田中也曾报道过类似的聚类现象，并且可能表明地震作用是由长期的，空间上持久的外部强迫驱动的。圣阿多地震活动的复杂性表明，多个过程，例如弹性应力传递和抗震滑动瞬变，导致潜在的地震。目前的观察结果表明，在加利福尼亚，流体注入操作发生在地震活动断层附近。但是，地震活动主要发生在较小的未映射断层上，几乎没有观察到证据表明大断层对感应应力变化敏感。