Imaging widespread seismicity at midlower crustal depths beneath Long Beach, CA, with a dense seismic array: Evidence for a depth-dependent earthquake size distribution
Imaging widespread seismicity at midlower crustal depths beneath Long Beach, CA, with a dense seismic array: Evidence for a depth-dependent earthquake size distribution
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DOI：
10.1002/2015gl064942
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发表时间：
2015-08-16
影响因子：
5.2
通讯作者：
Ampuero, Jean-Paul
中科院分区：
文献类型：
--
作者：
Inbal, Asaf;Clayton, Robert W.;Ampuero, Jean-Paul
我们使用由 5200 个垂直地震检波器组成的密集地震阵列来监测加利福尼亚州长滩的微震活动。通过记录波场的向下延续可以减轻由于人为活动而导致的低信噪比。向下连续的数据被连续反向投影，以搜索来自阵列下方源的相干到达，这揭示了许多以前未检测到的事件。地震活动的空间分布与绘制的断层轨迹或附近油田的活动无关。许多事件发生的深度超过 20 公里，远低于该地区普遍接受的地震深度。地震活动表现出符合大森定律的时间聚集性，其大小分布在20公里以上遵循古腾堡-里希特关系，但在更深的深度呈指数下降。密集阵列可以检测到比该地区永久地震网络小两个震级单位的地震。由于 20 公里深度以上的事件规模分布遵循指数接近 1 的幂律，因此这一改进使有效表征长滩地震活动所需的时间减少了一百倍。
We use a dense seismic array composed of 5200 vertical geophones to monitor microseismicity in Long Beach, California. Poor signal-to-noise ratio due to anthropogenic activity is mitigated via downward-continuation of the recorded wavefield. The downward-continued data are continuously back projected to search for coherent arrivals from sources beneath the array, which reveals numerous, previously undetected events. The spatial distribution of seismicity is uncorrelated with the mapped fault traces, or with activity in the nearby oil-fields. Many events are located at depths larger than 20 km, well below the commonly accepted seismogenic depth for that area. The seismicity exhibits temporal clustering consistent with Omori's law, and its size distribution obeys the Gutenberg-Richter relation above 20km but falls off exponentially at larger depths. The dense array allows detection of earthquakes two magnitude units smaller than the permanent seismic network in the area. Because the event size distribution above 20km depth obeys a power law whose exponent is near one, this improvement yields a hundred-fold decrease in the time needed for effective characterization of seismicity in Long Beach.