The clustering behavior of injection‐induced earthquakes is examined using one month of data recorded by the LArge‐n Seismic Survey in Oklahoma (LASSO) array. The 1829‐node seismic array was deployed in a 25 km×32 km area of active saltwater disposal in northern Oklahoma between 14 April and 10 May 2016. Injection rates in the study area are nearly constant around the time of the deployment. We develop a local magnitude (⁠ML⁠) equation for the region and estimate magnitudes for 1104 earthquakes recorded by the deployment. The determined earthquake magnitudes range from ML 0.01 to 3.0. The majority of earthquakes occurred between 1.5 and 5.5 km depth, and the shallowest earthquake depths overlap with the base of injection wells at depths between 1.5 and 2.5 km. We compute focal mechanisms of the largest events (⁠ML>2.0⁠), and find a mix of normal‐ and strike‐slip‐faulting types. Earthquakes occur regularly in time during the deployment, but are not evenly distributed in space across the study area, that is, they are spatially clustered. Analysis of the nearest‐neighbor distances in the space–time–magnitude domain shows the seismicity is dominated by single‐event clusters (i.e., independent events). This high proportion of single‐event clusters compared with multievent clusters has been previously noted for induced events at geothermal sites. When clustering occurs, the number of events in a cluster is typically small. We observe only four clusters with 10 or more events. For these larger clusters, we find equivalent numbers of foreshocks and aftershocks; however, the foreshock sequences are significantly longer in duration lasting days to tens of days, while aftershock sequences are observed only on the order of one day. The minimal clustering observed for events in the LASSO array suggests that the majority of events are being directly driven by stress changes due to local saltwater disposal.

中文翻译：

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大n地震阵列观测到的注入诱发地震的最小聚类

使用俄克拉荷马州拉格恩地震调查（LASSO）阵列记录的一个月数据，检查了注入诱发地震的聚集行为。在2016年4月14日至5月10日期间，在俄克拉荷马州北部的25 km×32 km活跃咸水处置区部署了1829个节点的地震阵列。研究区域的注入速率在部署期间几乎保持不变。我们为该区域开发了一个局部震级方程（⁠ML⁠），并估计了部署记录的1104次地震的震级。所确定的地震震级范围为ML 0.01至3.0。大部分地震发生在1.5至5.5 km深度之间，最浅的地震深度与注入井底部在1.5至2.5 km之间重叠。我们计算最大事件的焦点机制（⁠ML>2.0⁠），并找到正常和走滑断层类型的混合体。地震在部署过程中会定期发生，但在整个研究区域的空间分布不均匀，也就是说，它们在空间上是聚类的。对时空幅度域中最近邻距离的分析表明，地震活动主要由单事件簇（即独立事件）决定。以前已经注意到，与多事件聚类相比，单事件聚类的比例很高，这是地热场中诱发事件的原因。发生群集时，群集中的事件数通常很少。我们仅观察到具有10个或更多事件的四个群集。对于这些较大的星团，我们发现前震和余震的数量相等。但是，前震序列的持续时间从几天到数十天明显更长，而余震序列只能在一天左右的时间内观察到。在LASSO阵列中观察到的事件的最小聚类表明，大多数事件是由于局部盐水处理导致的应力变化直接驱动的。