华北地区几次大震前的b值异常变化

研究了华北地区几次大震周围的较小区域内和较大区域内的b值变化.发现了较小区域内的b值随时间先升高后逐步降低,直至最低值,震前又有所回升才发震;较大区域内的b值随时间的变化,在大震前有个明显的峰值期,其峰值期的长短与大震震级有关. 另外,研究了b值从大震震中向外随区域扩展的变化,发现b值从震中向外有逐步增高的趋势.在大震震中附近有个低b值区域,其外围有个高b值区域.

VARIATIONS OF THE b-VALUES BEFORE SEVERAL LARGE EARTHQUAKES OCCURRED IN NORTH CHINA

Studies concerning the variation of the b-values within smaller and larger areas surrounding epicenters before several strong earthquakes occurred in North China, have been made. It was found that for smaller areas around the epicenters the b-values vary with time from higher to lower values until the outburst of the earthquakes, while for larger areas peak values of & appear immediately before the earthquakes. The time duration of the peak, values seems to be related to the magnitudes of the large earthquakes.Besides, it was also studied that as the areas involved in the computation of the b-values enlarged, the values of -b tend to increase and in the vicinity of the epicenters there exist areas of low b-values, outside of it are areas of high b-values. This pattern of the variation of the b-values conforms with the spatial distribution of the seismic activity before the strong earthquakes.