1992年四川力马地震序列期间激发的孕震结构
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摘要
对小震序列的深入研究或许可以作为对大震序列震后趋势研究的替代，本文将地震模拟量已转化为数字记录的力马小震序列用来尝试这种替代。文中利用该地区的工业爆破和天然地震资料，计算了Ｐ波和Ｓ波分层速度模型；以此速度模型为基础，采用一种对于小型台网数值性能极为优越的定位方法和区域台网确定震源深度的一种新方法，重新修定了震源位置和震源深度；在此基础上，计算了地壳介质Ｑ值的变化。结果表明：力马地震序列震源位置分布的空间走向与地表活动断裂的地质特征相符合；震源深度由浅入深变化，直至接近下地壳为止；该序列的第二主震发生在另一条邻近的断裂带上；在序列持续期间，地壳介质Ｑ值由高到低降至平均值以下而趋于平静。由此建议：判断震后趋势可跟踪特征量的变化，并结合地区条件和结构特征。
In this paper, a test or alternative scheme researching small earthquake sequences for large earthquake sequences is suggested, a small earthquake sequence-Lima earthquake sequece of which modelling observed records have been turned into digital data is made use of this test. In order to provide the deep construction background and the spatial distribution of structure for generating earthquake, the p-wave and S-wave layered velocity models in this area are obtained by using mine explosion and earthquake observed records; then, the hypocenter locations and focal depths of Lima earthquake sequence are determined adopting the velocity models given above and using a location method with well numerical property for a microseismic monitoring network (Zhao, Z. , et al, 1994) and a new method for determining focal depth from data of a local seismographic network (Zhao, Z., 1992) ; finally, on this bases, the variation of quality factor Q of crustal medium during the period of the sequence is estimated.The obtained results show: the trend of spacial hypocenter distribution in Lima earthquake sequence as seen from the three-dimensional perspective graph is corresponding with the strikes of local active faulted zones; the focal depths of this sequence from shallow to deep until close to the lower crust; these condary mainshock appears at another faulted zone near by the faulted zone where the first mainshock occurred;during this sequence development, the quality factors reduce to a lower value than the average Q of this area. Thus, we suggest that when assessing the trend analysis of aftershock, we should trace the variances of some characteristic parameters, at the same time, we should take the regional conditions and tectonic characters into account.
In this paper, a test or alternative scheme researching small earthquake sequences for large earthquake sequences is suggested, a small earthquake sequence-Lima earthquake sequece of which modelling observed records have been turned into digital data is made use of this test. In order to provide the deep construction background and the spatial distribution of structure for generating earthquake, the p-wave and S-wave layered velocity models in this area are obtained by using mine explosion and earthquake observed records; then, the hypocenter locations and focal depths of Lima earthquake sequence are determined adopting the velocity models given above and using a location method with well numerical property for a microseismic monitoring network (Zhao, Z. , et al, 1994) and a new method for determining focal depth from data of a local seismographic network (Zhao, Z., 1992) ; finally, on this bases, the variation of quality factor Q of crustal medium during the period of the sequence is estimated.The obtained results show: the trend of spacial hypocenter distribution in Lima earthquake sequence as seen from the three-dimensional perspective graph is corresponding with the strikes of local active faulted zones; the focal depths of this sequence from shallow to deep until close to the lower crust; these condary mainshock appears at another faulted zone near by the faulted zone where the first mainshock occurred;during this sequence development, the quality factors reduce to a lower value than the average Q of this area. Thus, we suggest that when assessing the trend analysis of aftershock, we should trace the variances of some characteristic parameters, at the same time, we should take the regional conditions and tectonic characters into account.
引文
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