关键词: 依兰-伊通断裂, 地表破裂, 断层陡坎, 全新世

Abstract:

No earthquake greater than M6 has been documented on the Yilan-Yitong Fault,and no trace of activity since the late pleistocene has been seen either at the northeastern section of the famed Tanlu grand fault zone in eastern China.Thus this fault is recognized active in the early Quaternary and capable of generating moderate quakes.By analyzing high-resolution satellite images and field work,a 70km-long geomorphic scarp in Tonghe County of Heilongjiang Province and a 10km-long geomorphic scarp in Shulan County of Jilin Province were discovered.The scarps are 1～2m high and offset the young terraces.Subsequently,the trench at Tonghe County revealed fault displacement which almost reaches the surface.The uppermost stratum dislocated by the fault is dated to be 1730±40 years B.P.Analysis of geomorphic feature of the fault scarp and the trench profile suggests that an M≥7 paleoearthquake occurred along the fault since 1730±40 B.P.The trench at Shulan County reveals the faulted late Pleistocene stratum covered by stratum dated to be 2360±40 years B.P.All these data suggest that some segments of Yilan-Yitong Fault are active since Holocene and M7 earthquake occurred.So,further detailed research will be necessary to determine the range of the latest activity of this fault,the time of the rupture and recurrence intervals of major earthquakes.These data will be of great significance for earthquake zonation and assessment of seismic risk in this region.

Key words: Yilan-Yitong Fault, surface rupture, fault scarp, Holocene