We have analyzed shear‐wave splitting (SWS) data from local earthquakes in the Permian basin in west Texas to understand crustal stress change and induced seismicity. Two SWS parameters, the fast polarization direction and the delay time, are computed using a semiautomatic algorithm. Most measurements are determined in the Delaware basin and the Snyder area. In both regions, SWS fast directions are mostly consistent with local SHmax at stations that are relatively far from the earthquake clusters. Varying fast directions at one station are related to different ray paths and are probably caused by heterogeneity. In the Snyder area, most northeast–southwest fast directions are from the events in the northern part of the cluster, whereas the northwest–southeast fast directions are mostly from the southern part. The northeast–southwest and northwest–southeast fast directions could be attributed to the northeast‐trending normal faults and the northwest‐trending strike‐slip faults, respectively. SWS results in the Delaware basin have two unique features. First, most shallow earthquakes less than 4 km deep produce relatively large delay times. This observation implies that the upper crust of the Delaware basin is highly fractured, as indicated by the increasing number of induced earthquakes. Second, diverse fast directions are observed at the stations in the high‐seismicity region, likely caused by the presence of multiple sets of cracks with different orientations. This situation is possible in the crust with high pore pressure, which is expected in the Delaware basin due to extensive wastewater injection and hydraulic fracturing. We propose that the diversity of SWS fast directions could be a typical phenomenon in regions with a high rate of induced seismicity.

中文翻译：

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西德克萨斯州诱发地震的复杂剪切波各向异性

我们分析了得克萨斯州西部二叠纪盆地局部地震的剪切波分裂（SWS）数据，以了解地壳应力变化和诱发地震活动。使用半自动算法计算两个SWS参数，快速极化方向和延迟时间。大多数测量是在特拉华盆地和斯奈德地区确定的。在这两个地区，SWS的快速方向大多与离地震群相对较远的站点的当地SHmax一致。一个站的快速方向变化与不同的射线路径有关，并且可能是由异质性引起的。在Snyder地区，大多数东北向西南的快速方向来自该集群北部的事件，而西北向东南的快速方向主要来自南部的事件。东北西南方向和西北东南方向分别可归因于东北向的正断层和西北向的走滑断层。SWS在特拉华盆地的结果具有两个独特的特征。首先，大多数深度小于4 km的浅层地震会产生相对较大的延迟时间。这一观察结果表明，特拉华盆地的上地壳高度断裂，如诱发地震次数的增加所表明。其次，在高地震区的台站观测到不同的快速方向，这可能是由于存在多组方向不同的裂缝所致。在高孔隙压力的地壳中可能会出现这种情况，由于大量的废水注入和水力压裂，预计在特拉华盆地会出现这种情况。