西北地区东部5级以上地震序列统计研究

Statistical Study of Earthquake Sequences of M_S≥5.0 in the East of Northwest China

对1970年1月至2012年12月西北地区东部51次5级以上地震序列进行统计研究,其中走滑型占58.8%,逆断和逆冲型占19.6%,正断型占11.8%。在相同破裂类型和序列类型下,主震与最大余震的震级关系线性较好,主震与最大余震时间间隔之间的线性关系较差。走滑型和逆断型地震的60%以上主震后1天内发生最大余震,正断型地震中16.7%主震后1天内发生最大余震。若序列不属双震多震类型,分析最大余震时,可利用经验公式ΔM=1.54×M-6.53。

In this study,we statistically analyzed 51 earthquake sequences with magnitudes≥5.0that occurred in eastern Northwest China from Jan.1970 to Dec.2012.Of these,the strike-slip type occurred 30 times,representing 58.8%of the total.The overlap and inverse-impulse type occurred ten times,representing 19.6%,and the normal fault type occurred six times,representing11.8%.With respect to earthquake rupture type,the mainshock-aftershock type represented more than 60%of the rupture types,followed by the isolated type,and lastly the double shock or multiple shock type.With respect to normal-fault-type earthquakes,the mainshock-aftershock type had the highest proportion at 50%.The next highest proportion was the double shock or multiple shock type at 33.3%.The isolated type was least frequent.For earthquakes of the same rupture and sequences types,a linear relation between the main shock magnitude and the greatest aftershock magnitude was most common.Also,the relation was weak between the main shock occurrence time and the greatest aftershock occurrence time.More than 60%of the strike-slip and inverse-impulse types experienced the greatest aftershocks one day after the main shock but only16.7% of the normal fault type experienced the greatest aftershocks one day after the main shock.If a sequence cannot be categorized as a double shock or multiple shock sequence,the empirical equationΔM =1.54×M-6.53 can be used to analyze the greatest aftershock.