Smalley R, Ellis M A, Paul J, Van Arsdale R B
[1] Center for Earthquake Research and Information, [2] Department of Earth Sciences, The University of Memphis, Memphis, Tennessee 38152, USA.
Nature. 2005 Jun 23;435(7045):1088-90. doi: 10.1038/nature03642.
In the winter of 1811-1812, near the town of New Madrid in the central United States and more than 2,000 km from the nearest plate boundary, three earthquakes within three months shook the entire eastern half of the country and liquefied the ground over distances far greater than any historic earthquake in North America. The origin and modern significance of these earthquakes, however, is highly contentious. Geological evidence demonstrates that liquefaction due to strong ground shaking, similar in scale to that generated by the New Madrid earthquakes, has occurred at least three and possibly four times in the past 2,000 years (refs 4-6), consistent with recurrence statistics derived from regional seismicity. Here we show direct evidence for rapid strain rates in the area determined from a continuously operated global positioning system (GPS) network. Rates of strain are of the order of 10(-7) per year, comparable in magnitude to those across active plate boundaries, and are consistent with known active faults within the region. These results have significant implications for the definition of seismic hazard and for processes that drive intraplate seismicity.
1811年至1812年冬，在美国中部靠近新马德里镇的地方，距离最近的板块边界超过2000公里，三个月内发生的三次地震震动了美国整个东半部地区，使大片土地液化，其影响范围远远超过北美任何一次历史地震。然而，这些地震的成因及现代意义极具争议性。地质证据表明，过去2000年里，因强烈地面震动导致的液化现象（其规模与新马德里地震所产生的类似）至少发生过三次，甚至可能是四次（参考文献4 - 6），这与从区域地震活动性得出的复发统计数据相符。在此，我们展示了通过连续运行的全球定位系统（GPS）网络确定的该地区快速应变率的直接证据。应变率约为每年10^(-7)，与活跃板块边界处的应变率量级相当，并且与该区域内已知的活动断层相符。这些结果对于地震危险性的定义以及驱动板内地震活动的过程具有重要意义。
