ConocoPhillips School of Geology and Geophysics, the University of Oklahoma, Norman, OK, USA.
Oklahoma Geological Survey, the University of Oklahoma, Norman, OK, USA.
Sci Rep. 2017 Jul 10;7(1):4945. doi: 10.1038/s41598-017-04992-z.
The Pawnee M5.8 earthquake is the largest event in Oklahoma instrument recorded history. It occurred near the edge of active seismic zones, similar to other M5+ earthquakes since 2011. It ruptured a previously unmapped fault and triggered aftershocks along a complex conjugate fault system. With a high-resolution earthquake catalog, we observe propagating foreshocks leading to the mainshock within 0.5 km distance, suggesting existence of precursory aseismic slip. At approximately 100 days before the mainshock, two M ≥ 3.5 earthquakes occurred along a mapped fault that is conjugate to the mainshock fault. At about 40 days before, two earthquakes clusters started, with one M3 earthquake occurred two days before the mainshock. The three M ≥ 3 foreshocks all produced positive Coulomb stress at the mainshock hypocenter. These foreshock activities within the conjugate fault system are near-instantaneously responding to variations in injection rates at 95% confidence. The short time delay between injection and seismicity differs from both the hypothetical expected time scale of diffusion process and the long time delay observed in this region prior to 2016, suggesting a possible role of elastic stress transfer and critical stress state of the fault. Our results suggest that the Pawnee earthquake is a result of interplay among injection, tectonic faults, and foreshocks.
波尼 5.8 级地震是俄克拉荷马州有仪器记录以来最大的一次地震。它发生在活动地震带的边缘，与 2011 年以来其他 5 级以上地震类似。它沿着一个以前未绘制地图的断层破裂，并在一个复杂的共轭断层系统中引发余震。通过高分辨率地震目录，我们观察到在距主震 0.5 公里范围内，存在向主震传播的前震，表明存在前兆非地震滑动。大约在主震前 100 天，两次 M≥3.5 的地震沿着一条与主震断层共轭的已绘制地图的断层发生。大约 40 天前，两个地震群开始发生，其中一次 M3 地震发生在主震前两天。三次 M≥3 的前震都在主震震源处产生了正库仑应力。这些共轭断层系统中的前震活动几乎立即对注入率的变化做出响应，置信度为 95%。注入和地震之间的短时间延迟与扩散过程的假设预期时间尺度以及 2016 年之前该地区观察到的长时间延迟都不同，这表明弹性应力传递和断层临界应力状态可能起到了一定作用。我们的研究结果表明，波尼地震是注入、构造断层和前震相互作用的结果。
