青藏高原北部地区弱震空间图像特征与中短期地震预测方法
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摘要
通过对青藏高原北部地区 31次地震的研究 ,确定了震前地震活动图像的中短期预测指标以及中期向短期过渡的异常判据及预测方法。研究结果表明 ,中强地震前普遍存在地震空区、弱震条带、前兆地震或震群、地震活动增强和平静等异常图像 ,所表现出的异常时间存在很大的差异。具有中短期特征的弱震空区 (段 )和条带一般出现在震前 1～ 3a,平均持续时间 1a,在空区解体后 1～ 6个月发生地震。大多数前兆地震或震群活动属于短临异常 ,一般出现在震前几天至 6个月 ,震级差为 1 0～ 2 3,距离震中 5～ 6 0km ,空间上主要集中在祁连山地震带。地震活动增强以应力集中为主 ,属于短期异常特征。异常图像在时间上表现为中期阶段以孕震空区、弱震条带、地震活动增强和平静等异常 ,异常比较显著且不同步 ;短临阶段出现前兆地震和地震空区停止活动而形成的临震前的相对平静。异常图像在空间上具有较明显的分区性 ,与区域活动构造有一定的关系。
In this paper, the criterion of the mid-short term forecast is determined by the seismicity pattern before the mainshock. At the same time, the anomaly indexes and prediction method which transfer from mid term to short term are determined according to the study of 31 earthquakes occurred in the north of Qinghai-Tibet Plateau. The results show that before the mid-strong earthquakes there generally exist the anomalous patterns including seismic gap, belt of weak earthquake, precursory shock or swarms, anomalies of active seismicity or quiescence. There are large differences in the time order of anomalous patterns. The gap and belt of weak earthquake always appeared in the period which extends from one year to three years before mainshock. The average of continual time is one year. The mainshock occurred within 6 months after the disappearance of gap of weak earthquake. Most precursory events and seismic swarms belong to the short-impending term anomalies, which appeared from several days to six months before mainshock. The magnitude difference is 1.0-2.3 between the mainshock and the precursory events. The precursory events are mainly distributed along the Qilianshan seismic belt. The pattern of activation and quiescence appeared half a year to two years before mainshock and occurred in half a year during the quiescence time. The anomalous pattern of mid-term is the seismogenic gap, belt of weak earthquake, seismic activation and quiescence. Also those anomalies are obvious and synchronous. The precursory earthquake appeared and the seismic gap stopped during the short and imminent stage and formed a relative quiescence before the earthquake. The anomalous pattern shows an obvious sub-area feature, which has a certain relation with the regional structure.
In this paper, the criterion of the mid-short term forecast is determined by the seismicity pattern before the mainshock. At the same time, the anomaly indexes and prediction method which transfer from mid term to short term are determined according to the study of 31 earthquakes occurred in the north of Qinghai-Tibet Plateau. The results show that before the mid-strong earthquakes there generally exist the anomalous patterns including seismic gap, belt of weak earthquake, precursory shock or swarms, anomalies of active seismicity or quiescence. There are large differences in the time order of anomalous patterns. The gap and belt of weak earthquake always appeared in the period which extends from one year to three years before mainshock. The average of continual time is one year. The mainshock occurred within 6 months after the disappearance of gap of weak earthquake. Most precursory events and seismic swarms belong to the short-impending term anomalies, which appeared from several days to six months before mainshock. The magnitude difference is 1.0-2.3 between the mainshock and the precursory events. The precursory events are mainly distributed along the Qilianshan seismic belt. The pattern of activation and quiescence appeared half a year to two years before mainshock and occurred in half a year during the quiescence time. The anomalous pattern of mid-term is the seismogenic gap, belt of weak earthquake, seismic activation and quiescence. Also those anomalies are obvious and synchronous. The precursory earthquake appeared and the seismic gap stopped during the short and imminent stage and formed a relative quiescence before the earthquake. The anomalous pattern shows an obvious sub-area feature, which has a certain relation with the regional structure.
引文
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[4]国家地震局科技监测司.地震监测与预报方法清理成果汇编(测震学分册)[M].北京:地震出版社,1989.
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