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因为前震被看作是后续地震最可靠的前兆事件之一,它们在准确测定即将到来地震的时间和地点方面都很有用。但最具挑战性的问题还没有令人满意的答案。这些问题包括:为什么有些地震可以作为其他地震的前震,而有些则不行?哪些关键性因素控制着它们?在本项研究中,根据地震破裂形态,一组发生在中国和美国西部的走滑破裂型地震(MS≥6.0)被分成三种类型:1类,2类和3类。它们分别指的是包含张性岩桥、压性岩桥,以及张性与压性混合型岩桥的破裂的地震。前震更可能在1类和3类地震之前出现,而不大可能出现在2类地震之前。这些现象可能表明,对走滑型地震来说,张性连接的结构使得前震易于发生。与先前发表的一些成果不一致的是,前震的发生与本研究所涉及的主震震源深度(小于30km)似乎并不相关;这意味着,对于不同震源机制和位置的地震,正应力增加可能对前震发生有不同的影响。在本研究的数据集中,未发现前震与主震震级之间的确定性联系。
Because foreshocks are considered as one of the most reliable precursors of subsequent earthquakes, they are useful in accurately determining the timing and location of upcoming earthquakes. But the most challenging issue still does not have a satisfactory answer. These questions include: Why some earthquakes can be used as precursors to other earthquakes while others are not? What key factors control them? In this study, a series of strike-slip ruptures occurred in China and the western United States Earthquakes (MS≥6.0) are divided into three types: Category 1, Category 2 and Category 3. They refer to the ruptured earthquakes that include the tensile rock bridge, the pressure rock bridge, and the tension and compression rock bridge, respectively. Foreshocks are more likely to occur before Class 1 and 3 earthquakes and are less likely to precede Class 2 earthquakes. These phenomena may indicate that for the strike-slip earthquakes, the structure of the tension connection makes the foreshock prone to occur. In contradistinction to some previous published results, it seems that the occurrence of foreshocks does not seem to be related to the focal depth (less than 30 km) of the main shocks involved in this study; this means that the normal stress increases for different focal mechanisms and locations Pre-earthquake occurrence have different effects. In the data set of this study, no definite connection between foreshocks and mainshock magnitude was found.