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板块构造学说的最有力的特征之一,是已知的板块运动让我们对板块边界未来大地震的发震位置和平均复发间隔有更清晰的认识。然而,板块构造学说却不能预测板块内的地震何时何地发生,因为理想的板块内部是不会变形的。因此,板块内部的地震风险评估过于依靠如下假设:从有限的历史记录中得到的小地震发震位置能够反映出连续变形的地区,而变形将诱发未来大地震[1]。然而,本文将要说明的是,最近许多这样的小地震很可能是几百年前发生过的大地震的余震。文中将给出一个简单的模型,并由此模型得出:余震序列的长度和断层加载速率呈反比关系。发生在缓慢变形的大陆内部的余震序列,其持续时间与在快速加载的板块边界所观测到的典型的10年尺度余震序列相比要长得多。因为这些预测与观测结果相符,所以将大陆内部地震看作稳态地震活动的一般做法高估了目前地震活跃地区的地震危险性,而低估了其他地区的地震风险。
One of the most powerful features of slab tectonics is that the known plate movement gives us a clearer idea of the location and average recurrence interval of future earthquakes on the plate boundaries. However, plate tectonics does not predict when and where earthquakes occur in the plate because the interior of the ideal plate does not deform. Therefore, the assessment of seismic risk inside the slabs relies too heavily on the assumption that the location of small earthquakes obtained from a finite historical record can reflect areas of continuous deformation, and the deformation will induce future earthquakes [1]. However, what this article will illustrate is that many of these recent earthquakes are likely to be aftershocks of major earthquakes that took place hundreds of years ago. In this paper, a simple model will be given. From this model, the length of aftershock sequence is inversely proportional to the fault loading rate. The aftershock sequence occurring within a slowly contaminating continent is much longer in duration than the typical 10-year aftershock sequence observed at rapidly loaded plate boundaries. Because these predictions are consistent with observations, the general practice of treating intracontinental earthquakes as steady-state earthquakes overestimates the seismic risk of currently active seismic regions and underestimates the seismic risk in other regions.