华北地区强震前的信号震及其预测意义

Signal shock prior to strong earthquakes in North China area and its significance in prediction

根据对华北地区1970年以来MS≥6地震以前中小地震活动空间图像变化特征的分析,研究了"信号震"发生的时空特征及其地震活动背景,由"场 源"关系特征对一般地震进行严格的筛选识别,从而得出信号震的有关预测指标。信号震一般发生在强震前的2年之内,多数发生在15个月内;信号震与强震的距离不超过200km,多数在100km之内;震级强度一般为ML4.0～5.3。信号震一般发生在局部的ML≥4.0地震平静区内,一般发生在中小地震条带上或条带附近,在其周围或附近存在中小地震空区。检验结果表明,信号震发生后的9个月之内,其预测概率Pt即超过0.5,Rt值达到0.27;预测区域半径在距信号震震中100km之内时,其发生概率Pd可以达到0.73;预测强震震级一般为MS≥6.0。研究表明,信号震的环境应力值τ0明显高于其他地震,显示了高应力背景的异常显著性,它所辐射的地震波中很可能含有未来强震孕震区的大量的本质性信息。

Based on the analysis on the characteristics of spatial image variation of medium and small seismicity prior to M_S 6 earthquakes occurred in North China area since 1970, the space-time characteristics and the background for the occurrence of 'signal shocks' are studied. According to the characteristics of 'field-source' relation, a strict selection and recognition is made for the earthquakes and the relevant prediction index for the signal shocks are obtained. Generally speaking, the signal shocks occur in 2 years prior to the strong earthquake and most of them occur within 15 months; the distance between the signal shock and the strong earthquakes is no larger than 200 km and most of them are within 100km; the magnitude of the signal shocks is usually about M_L4.0～5.3. The signal shocks generally occur in the M_L4.0 seismically quiet area of a certain region, which occur in or near the medium and small seismic stripes with the seismicity gap of medium and small earthquakes nearby. The testing results indicate that in 9 months after the signal shock, its predictive probability is 0.5 and its R value is 0.27; when the radius of the predicted region is within 100 km to the epicenter of signal shocks, the probability for the occurrence of the predicted earthquakes is 0.73 and the predicted magnitude is generally M_S 6.0. The study in the paper indicates that the environmental stress value τ_0 of the signal shock is obviously higher than that of other earthquakes, which shows the significant abnormal background of high stress. Its seismic waves might probably contain a great amount of essential information of the seismogenic zone for the coming strong earthquakes.