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本文对1988年9月18日福建长汀3.9级地震的前震序列的时、空分布、日频度衰减、能量释放、震源错动特征作了研究。结果表明,与该地震余震序列及福建地区的非前兆性小震群相比,长汀前震序列最主要的特征是:地震随时间分布具有明显成丛性;日频度随时间不断增加;震级随时间逐渐增强。用指标加以定量描述,即(1)前震序列的归一化熵Q~t明显低于余震,最大前震及主震发生前,Q~t明显降低;(2)各前震子序列的极大地震发生后日频度衰减系数h<1.0;(3)序列极大地震发生的时间比τ>0.5;(4)(?)~2E~(1/2)/(?)t~2≥0。在地震危险性分析中,Q~t、h、τ及(?)~2E~(1/2)/(?)~2可能是一些效能较高的指标。本文的例子还表明,在实际应用中,平均震级可能比b值更实用,而震源错动方式的一致性作为一种地震危险性指标,效能较差。
In this paper, the temporal and spatial distribution, daily frequency attenuation, energy release and source dislocation characteristics of the foreshock sequence of the Changting 3.9 Earthquake in Fujian Province on September 18, 1988 were studied. The results show that the main features of the Changting foreshock sequence are as follows: the distribution of earthquakes with time is significantly constricted compared with that of the aftershock sequence in this area and the non-precursor small earthquakes in Fujian; the daily frequency increases with time; Gradually enhanced over time. (1) The normalized entropy Q ~ t of the foreshock sequence is obviously lower than that of aftershocks, the largest foreshock and the main shock, Q ~ t obviously decreases; (2) The great earthquake of each foreshock sequence (4) (?) ~ 2E ~ (1/2) / (?) T ~ 2≥0. In the seismic hazard analysis, Q ~ t, h, τ and ~ 2E ~ (1/2) / (~) ~ 2 may be some indicators of high performance. The example in this paper also shows that in practical applications, the average magnitude may be more practical than the b value. However, the consistency of the source dislocation mode is less effective as a seismic hazard index.