用累积地震矩法研究全球地震活动性

本文基于Lomnitz提出的MRI理论,用累积地震矩(CSM)算法对全球1900—1999年7级以上的地震进行了处理,试图通过分析大震前CSM图像的变化,来判断地震发生的可能性。对不同地区的6个地震震前CSM图像的分析表明:7级以上地震的CSM图像在震前5到10年内会改变,大部分地震发生在CSM的高值区或次高值区。通过实际运算发现:在不同的地区应使用不同的值可获得较好的结果,用于计算的地震数越多,获得的结果越好。有些大地震前CSM异常区域不是唯一的,往往会出现几个,这可能与研究区域的地震活动性有关。因此,笔者认为:若要获得可靠的CSM图像,除应当考虑不同地区的小震活动水平外,还应考虑地震断层对震后能量分布影响。统计结果表明:在目标地震发生后,下一次地震在空间上发生在原地及2度距离范围内的概率较大,在3度以外区域发生的概率相差不大;在时间上,发生在原地区震后1年内的概率最高,这可能与余震活动有关;在5年的时间里,下一次地震发生的次数占到全部地震的70%以上。因此,要注意大地震后,目标地震附近有地震能量进一步释放的危险性。

Studying global seismicity with cumulative seismic moment

Based on the MRI theory by Lomnitz, global earthquakes of M≥7.0 from 1900 to 2003 were analyzed with cumulative seismic moment （CSM） method. The possibility of future earthquake occurrence was estimated through analysis of the change in CSM images before large earthquakes. The result from analyzing the CSM images of 6 earthquakes in different regions showed that the CSM images would change in 5 to 10 years before the earthquakes occurred, and most earthquakes occurred in high-value areas of CSM or second high- value areas. It was found by actual calculations that better results could be obtained by using different r values in different regions, and the more the number of earthquakes used to calcu- late, the better results could be obtained. There are generally more than one CSM anomalous areas before some large earthquakes, i. e. , several CSM anomalous areas often appear. This may be related to the seismicities in the study areas. Therefore, the authors thought that the impacts of seismic faults on the energy distribution after an earthquake should also be consid- ered besides considering the seismicities of small earthquakes in different regions in order to obtain reliable CSM images. Statistical results showed that the high probability of next earthquake occurrence would appear in original regions and 2 degree distance in space after the target earthquake occurred. The probability of next earthquake occurrence beyond 3 degree distance only showed little difference. In terms of time, the probability of the next earthquake is the highest within 1 year. This may be related to the aftershock activities. In 5 years, the number of the next earthquakes accounted for more than 70% of all earthquakes. Thus, it should be noticed that seismic energy near the target earthquake would be further released after large earthquakes.