The strong increase of seismicity rates in the contiguous USA over the last 10 years is linked to the injection of huge amounts of wastewater from oil and gas production in unconventional hydrocarbon reservoirs. We calculated 549 moment tensors of induced earthquakes (M_W ≤ 4.9) in southern Kansas to study their source mechanisms and their relation to injection activity. Seventeen percent of the events analyzed contained significant volumetric (ISO%) components, and these events mostly occurred near the two largest local earthquakes during the 4 months of largest active wastewater disposal. Mapping the local stress field, we determined that most of the region lies within a transtensional stress regime, with a maximum horizontal stress σ_Hmax trending N75°E. In the epicentral area of the M_W 4.9 Milan earthquake, the σ_Hmax trend is rotated to about S80°E. Locally, two areas display a change in the stress field orientation with depth, from transtensional above 5.5 km depth to strike slip deeper in the basement. Relating the resolved fault geometries to the obtained local stress field orientation, we find that most of the activated fault planes were optimally oriented to the current stress field and thus small stress perturbations caused by the water injection could lead to failure.

中文翻译：

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美国堪萨斯州南部与废水诱发地震相关的震源机制和应力场变化

在过去的 10 年里，美国本土地震活动率的大幅上升与非常规油气藏中石油和天然气生产中大量废水的注入有关。我们计算了诱发地震的549矩张量（中号_W¯¯  ≤4.9）在堪萨斯州南部以研究它们的来源机制及其注射活动的关系。17% 的分析事件包含显着的体积 (ISO%) 分量，并且这些事件大多发生在 4 个月最大的活跃废水处理期间的两次最大的当地地震附近。绘制局部应力场，我们确定大部分区域位于张应力范围内，最大水平应力σ _Hmax趋势 N75°E。在M _W 4.9 米兰地震的震中区，σ _Hmax趋势旋转到大约 S80°E。在局部，两个区域显示应力场方向随深度的变化，从超过 5.5 公里深度的横张到基底更深的走滑。将解析出的断层几何形状与获得的局部应力场方向联系起来，我们发现大多数激活的断层平面都以当前的应力场为最佳方向，因此注水引起的小应力扰动可能导致故障。