1303年山西洪洞8级地震震源断层研究

Seismogenic Fault of the 1303 Hongtong M8 Earthquake in Shanxi Province

1303年在山西洪洞附近发生的8级巨大地震,是中国根据现存较为详细的文献记载史料所确定的最早的一次8级地震。这次地震距今已有700多年的历史,而地震所在区域至今仍有持续不断的小地震活动。本文根据地震破裂区1981年至2013年的中小地震精定位地震目录,采用震源断层面拟合方法,反演得到了1303年山西洪洞地震的震源断层面参数:走向19.3°、倾角88.5°、滑动角-170.0°。断层面长75.5km,宽26.2km,深度为地下11.12~37.35km。将地震破裂区的地震精确定位资料以近东西向的洪洞断裂为界划分为地震北段和地震南段,分段进行地震震源断层拟合,反演得到洪洞地震北段震源断层面参数:走向13.7°、倾角76.6°、滑动角-157.6°。断层面长32.7km,宽21.7km,深度为地下11.97~32.86km;南段震源断层面参数:走向20.3°、倾角87.1°、滑动角-154.6°。断层面长45.9km,宽16.6km,深度为地下9.32km^25.50km。无论是分段还是不分段,反演得到的洪洞地震震源断层均是右倾的近直立断层,属于右旋走向滑动性质。分段计算得到的地震北段震源断层深度比南段更深,将反演得到的震源断层与临汾盆地深部构造最新研究成果进行了分析对比,北段震源断层深度及倾角大小与深地震剖面推测得到的深大断裂几乎相同。震源断层在地表的投影与洪洞地震的高烈度区能够较好地对应。

The great Hongtong M8 earthquake occurred in 1303 in Shanxi Province,was the earliest M8 earthquake in China, according to historical records. Though the earthquake has a history of more than 700 years, small earthquakes have been continually occurring till now. This study determines the fault geometry of this earthquake by inverting seismological data of present-day moderate-small earthquakes in the focal area. We select a stripshaped zone from the relocated earthquake catalog in the period from 1981 to 2013 to invert fault plane parameters of this earthquake. The inversion results of the Hongtong M8 earthquake are as follows, the strike is 19. 3°, the dip angle is 88. 5°, the slip angle is -170.0°, the fault length is about 75.5 kin, the fault width is about 26.2 km, the lower- boundary depth is about 37.35 km and the buried depth of upper boundary is about 11.12 km. The relocated earthquakes are divided into two parts by the Hongtong fault. The earthquakes which located in the north of Hongtong fault are named as the north part, and the earthquakes which located in the south of Hongtong fault are named as the south part. We invert fault plane parameters for the two parts, the inversion results of the north part are as follows; the strike is 13.7°, the dip angle is 76.6°, the slip angle is -157.6°, the fault length is about 32.7 km, the fault width is about 21.7 km, the lower-boundary depth is about 32.86 km and the buried depth of upper boundary is about 11.97 km; the inver- sion results of the south part are as follows, the strike is 20.3°, the dip angle is 87.1°, the slip angle is --154.6~, the fault length is about 45.9 km, the fault width is about 16.6km, the lower-boundary depth is about 25. 50 km and the buried depth of upper boundary is about 9.32 km. It shows that the seismogenic fault is a right lateral strike-slip fault. The seismogenic fault depth of the north part is deeper than the south one. The seismogenic fault depth and its dip of the north part are similar to the results of the speculative conclusion by deep seismic exploration. The projection of the seismogenic fault on the ground corresponds well with the high intensity region of the Hongtong earthquake.