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很多地震会伴有前震(Jones and Molnar,1976,1979)。但是,对产生前震的机制和为什么有些地震有前震而其他却没有的原因,目前尚不清楚(Abercrombie and Mori,1996;Reasenberg,1999;Jones,1984;Doser,1990;Maeda,1999;McGuireetal,2005)。这里我们利用在北太平洋区域有最佳仪器记录地区的地震目录,来分析1999年到2011年间所有震级大于6.5、震源深度小于50km的地震的前震序列。所用数据包括了31例发生在板块边界的地震和31例板内地震。我们发现,与板内地震相比,板间地震的前震序列有显著不同的特点。北太平洋地区,发生在板块边界的最大地震在之前数月到数天时间内,会出现地震活动加速现象,并最终导致主震发生。相反,板内环境下前震出现的机会就非常少。我们认为,在板块边界地区大地震的破裂前,两个板块的分界面便开始了缓慢的滑动。这种相对长期的前兆性变化可能有助于减缓板块边界的地震灾害。
Many earthquakes are accompanied by foreshocks (Jones and Molnar, 1976, 1979). However, it is unclear what the mechanism is for the foreshock and why some of the earthquakes have foreshocks but none of them (Abercrombie and Mori 1996; Reasenberg 1999; Jones 1984; Doser 1990; Maeda 1999; McGuire et al 2005 ). Here we use the catalog of earthquakes with the best instrumental record in the North Pacific region to analyze the foreshock sequences for all earthquakes with magnitudes greater than 6.5 and focal depths less than 50 km from 1999 to 2011. The data used include 31 earthquakes that occurred at the plate boundary and 31 intraplate earthquakes. We find that the foreshock sequences of interplate earthquakes have significantly different characteristics compared to the intraplate earthquakes. In the North Pacific, the largest earthquakes that occurred at the plate boundaries accelerated seismicity over the months and days before and eventually led to mainshocks. In contrast, there is very little chance of a foreshock occurring in an intraplate environment. In our opinion, the interface between the two plates began to slide slowly before the great earthquake ruptured in the plate boundary area. This relatively long-term precursor change may help reduce the seismic disasters on the plate boundaries.