Is the Aftershock Zone Area a Good Proxy for the Mainshock Rupture Area?
Is the Aftershock Zone Area a Good Proxy for the Mainshock Rupture Area?
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DOI：
10.31223/osf.io/cp9vn
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发表时间：
2020-04
影响因子：
3
通讯作者：
J. C. Neo;Yihe Huang;D. Yao;S. Wei
中科院分区：
文献类型：
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作者：
J. C. Neo;Yihe Huang;D. Yao;S. Wei
余震的位置经常被观察到与主震位于同一断层面上，并用作其破裂区域的代理。地震重定位技术的最新发展极大地提高了地震定位的准确性，为量化余震分布和主震破裂区域提供了前所未有的机会。在本研究中，我们设计了一种一致的方法来计算加利福尼亚州 12 Mw≥5.4 主震余震所包围的面积，并通过滑移等值线得出的主震破裂面积进行标准化。我们还研究了主震滑移引起的库仑应力变化，并将其与余震区进行比较。我们发现，总体而言，余震区面积与主震破裂面积的比值，以下简称“余震比”，范围在0.5~5.4之间，大部分值大于1。同一主震采用不同的滑移反演模型会对结果产生较大影响，但重定位目录和先进国家地震系统目录估算的比值具有相似的模式。根据南加州重新定位的目录，余震比率在 0.5 到 4.3 之间，而北加州的余震比率则表现出更大的范围，从 1 到 5.4。早期余震窗口（一天内）的余震比率显示出相似的范围，但比使用整个余震持续时间的值更小，我们认为持续的余滑可能有助于在几次主震之后扩大余震区面积。研究结果表明，库仑应力变化尺度为正值的区域与余震带区域一致，余震的空间分布代表主震破裂和持续震后滑移的应力释放。
The locations of aftershocks are often observed to be on the same fault plane as the mainshock and used as proxies for its rupture area. Recent developments in earthquake relocation techniques have led to great improvements in the accuracy of earthquake locations, offering an unprecedented opportunity to quantify both the aftershock distribution and the mainshock rupture area. In this study, we design a consistent approach to calculate the area enclosed by aftershocks of 12 Mw≥5.4 mainshocks in California, normalized by the mainshock rupture area derived from slip contours. We also investigate the Coulomb stress change from mainshock slip and compare it with the aftershock zone. We find that overall, the ratios of aftershock zone area to mainshock rupture area, hereinafter referred to as “aftershock ratio”, lie within a range of 0.5–5.4, with most values being larger than 1. Using different slip-inversion models for the same mainshock can have a large impact on the results, but the ratios estimated from both the relocated catalogs and Advanced National Seismic System catalog have similar patterns. The aftershock ratios based on relocated catalogs of southern California fall between 0.5 and 4.3, whereas they exhibit a wider range from 1 to 5.4 for northern California. Aftershock ratios for the early aftershock window (within one-day) show a similar range but of smaller values than using the entire aftershock duration, and we propose that continuing afterslip could contribute to the expanding aftershock zone area following several mainshocks. Our results show that areas with positive Coulomb stress change scale with aftershock zone areas, and spatial distribution of aftershocks represents stress release from mainshock rupture and continuing postseismic slip.