Application of Seismic Array Processing to Earthquake Early Warning
Application of Seismic Array Processing to Earthquake Early Warning
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DOI：
10.1785/0120130277
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发表时间：
2014-10-01
影响因子：
3
通讯作者：
Ampuero, J. -P.
中科院分区：
文献类型：
--
作者：
Meng, L.;Allen, R. M.;Ampuero, J. -P.
地震预警系统是在强震到来之前发出警告的系统，是减轻地震灾害的重要手段。目前运行的EEW系统基于点源假设，对大型事件的有效性有限，忽略有限源效应会导致震级低估。在这里，我们探讨的概念，表征破裂尺寸在真实的时间EEW使用小孔径地震台阵位于活动断层附近。反向追踪阵列波形允许估计破裂前缘的范围（作为破裂大小的代理）和真实的方向性，为现有EEW系统提供M> 7地震的补充EEW能力。我们在一个模拟的实时环境中实现了它，并分析了2004年美国地震局记录的加州帕克菲尔德6级地震。S.地质调查局帕克菲尔德密集地震仪阵列（UPSAR）阵列和2010年在加州圣地亚哥的强震传感器记录的7.2级El Mayor-Cucapah地震。我们发现，重要的是要纠正的偏差，在后方位角引起的倾斜结构下的UPSAR阵列，从较小的事件的数据的基础上。我们估计的破裂长度比其他研究推断的短30%，但对于EEW目的仍然合理。我们将这种差异归因于破裂方向性效应和单个阵列的有限视场。该方法的精度可以通过具有重叠视场的阵列网络来提高。我们通过使用九州和北方北海道的两个Hi-net站群跟踪2011年东北地震破裂来证明这一点。得到的结果是一致的反投影结果和合理的估计破裂长度和方向性。与其他提出的有限故障EEW方法相比，阵列方法受全球定位系统或地震网络粗糙度的影响较小，并提供了断裂的高频表征，从而为某些结构提供更合适的地面震动预测因子。
Earthquake early warning (EEW) systems that issue warnings prior to the arrival of strong shaking are essential in mitigating earthquake hazard. Currently operating EEW systems work on point-source assumptions and are of limited effectiveness for large events, for which ignoring finite-source effects result in magnitude underestimation. Here, we explore the concept of characterizing rupture dimensions in real time for EEW using small-aperture seismic arrays located near active faults. Back tracing array waveforms allow estimation of the extent of the rupture front (as a proxy of the rupture size) and directivity in real time, providing complementary EEW capabilities for M > 7 earthquakes to existing EEW systems. We implement it in a simulated real-time environment and analyze the 2004 M 6 Parkfield, California, earthquake recordings by the U. S. Geological Survey Parkfield dense Seismograph ARray (UPSAR) array and the 2010 M 7.2 El Mayor-Cucapah earthquake recordings by strong-motion sensors in San Diego, California. We find it important to correct for the bias in back azimuth induced by dipping structures beneath the UPSAR array, based on data from smaller events. Our estimated rupture length is 30% shorter than those inferred from other studies but still reasonable for EEW purposes. We attribute this difference to rupture directivity effects and the limited field of view of a single array. The accuracy of the approach may be improved with a network of arrays with overlapping fields of view. We demonstrate this by tracking the 2011 Tohoku earthquake rupture with two clusters of Hi-net stations in Kyushu and northern Hokkaido. The obtained results are consistent with teleseismic back-projection results and yield reasonable estimates of rupture length and directivity. Compared with other proposed finite-fault EEW approaches, the array method is less affected by the coarseness of a Global Positioning System or seismic network and provides a high-frequency characterization of the rupture that yields more suitable predictors of ground shaking for certain structures.