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Analysing the 1811-1812 New Madrid earthquakes with recent instrumentally recorded aftershocks

机译：使用最近仪器记录的余震分析1811-1812年新马德里地震

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Although dynamic stress changes associated with the passage of seismic waves are thought to trigger earthquakes at great distances, more than 60 per cent of all aftershocks appear to be triggered by static stress changes within two rupture lengths of a mainshock(1-5). The observed distribution of aftershocks may thus be used to infer details of mainshock rupture geometry(6). Aftershocks following large mid-continental earthquakes, where background stressing rates are low, are known to persist for centuries(7,8), and models based on rate-and-state friction laws provide theoretical support for this inference(9). Most past studies of the New Madrid earthquake sequence have indeed assumed ongoing microseismicity to be a continuing aftershock sequence(10-12). Here we use instrumentally recorded aftershock locations and models of elastic stress change to develop a kinematically consistent rupture scenario for three of the four largest earthquakes of the 1811-1812 New Madrid sequence. Our results suggest that these three events occurred on two contiguous faults, producing lobes of increased stress near fault intersections and end points, in areas where present-day microearthquakes have been hitherto interpreted as evidence of primary mainshock rupture. We infer that the remaining New Madrid mainshock may have occurred more than 200 km north of this region in the Wabash Valley of southern Indiana and Illinois-an area that contains abundant modern microseismicity, and where substantial liquefaction was documented by historic accounts. Our results suggest that future large mid-plate earthquake sequences may extend over a much broader region than previously suspected.
机译：尽管与地震波通过相关的动态应力变化被认为会在很远的距离触发地震，但所有余震中有60％以上似乎是由主震两个破裂长度内的静态应力变化触发的（1-5）。因此，所观察到的余震分布可用于推断主震破裂几何的细节（6）。众所周知，背景应力率较低的中部大陆大地震之后的余震会持续多个世纪（7,8），基于速率和状态摩擦定律的模型为这一推论提供了理论支持（9）。过去对新马德里地震序列的大多数研究确实都假设持续的微地震是持续的余震序列（10-12）。在这里，我们使用仪器记录的余震位置和弹性应力变化模型来为1811年至1812年新马德里序列的四次最大地震中的三个地震建立运动学上一致的破裂情景。我们的结果表明，这三个事件发生在两个连续的断层上，在迄今已被解释为主要主震破裂证据的地区，在断层相交处和终点附近产生了应力增加的波瓣。我们推断，剩余的新马德里大地震可能发生在该地区以北200多公里处，位于印第安纳州南部和伊利诺伊州的瓦巴什河谷，该地区蕴藏着丰富的现代微震性，历史记载大量液化。我们的结果表明，未来的大型中板地震序列可能会比以前怀疑的范围更广。

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