利用余震频度分布进行宏观震中快速判定

微观震中和宏观震中的偏离是现阶段震后烈度快速判定亟待解决的问题。 本文旨在通过研究中国西部1970年以来7个M_S≥6.5破坏性大地震后24小时内的余震频度N值的空间变化, 分析和判定主震破裂的大致范围, 从中得出可能的宏观震中位置, 为大地震的应急救援提供参考。 本文将主要以2008年汶川地震为例说明最小完整性震级确定的步骤和结果, N值计算方法和N值分布图的绘制以及宏观震中的确定, 最后将7次大地震每个时段估计震中和实际的宏观震中进行比较和分析。 研究结果显示: ① 破坏性大地震24小时内不同时段由余震频度N值分布得到的宏观震中, 可有效缩小由微观震中评估烈度产生的偏差; ② 震后2、 4、 12、 24小时四个时段的估计震中能够作为烈度快速判定的修正因子, 满足震后快速响应的时效性要求。 并且震后24小时的估计震中效果最好。

Rapid Determination of Macro-epicenter by the Spatial Distribution of Aftershock Frequency

The deviation of micro-epicenter and macro-epicenter is an urgent task in the rapid assessment of earthquake intensity. This paper aims at studying the main area of earthquake rupture and marking the possible position of macro-epicenter through the research of spatial distribution of aftershock frequency N-value within 24 hours after seven greater than M_S6.5 earthquakes, so as to provide reference for emergency rescue. We illustrated the steps and results of determining the minimum completeness magnitude base on the case of the 2008 Wenchuan earthquake, in order to get calculation method and distribution chart of N-value, and determine the macro-epicenter. And finally, we compare and analyze the estimated epicenters with the actual epicenters at each period of the five earthquakes. We concluded that ① at each period of the 24 hours after the catastrophy, the macro-epicenter calculated from aftershock frequency N-value distribution could reduce the deviation referred from the estimated epicenters of micro-epicenter; ② that estimated epicenters at the periods of 2 hours, 4 hours, 12 hours and 24 hours after the earthquake can be used as the correction factor of fast judgement of earthquake intensity, which can meet the timeliness of earthquake quick reponse, and best estimate the epicenter at the period of 24 hours after erathquakes.