ACTIVE FAULTING AND BLOCK MOVEMENT ASSOCIATED WITH LARGE EARTHQUAKES IN THE MIN-SHAN AND LONGMEN MOUNTAINS, NORTHEASTERN TIBETAN PLATEAU

The Min Shan and central and southern parts of the Longmen Mountains f orm the middle segment of the north trending earthquake zone at the ea stern edge of the Tibetan Plateau. The Min Shan Mountains are a Cenozo ic to Quaternary uplift zone that has undergone south directed block m ovements to produce the 1933 Diexi earthquake (M = 7.5) on the Min Jia ng Fault and the 1976 Songpan earthquake swarm (M = 7.2, 6.7, 7.2) on the Huya Fault. The Min Jiang Fault on the western boundary of the upl ift zone is dominated by reverse movement with a right-lateral compone nt. The Huya Fault on the eastern margin of the Min Shan Uplift Zone i s also dominated by reverse movement but is associated with a left-lat eral component. The uplift and block movement of the Min Shan Mountain s are probably related to the compression at the eastern end of the Ku nlun Fault which is a major northwest trending strike-slip fault withi n the Tibetan Plateau. Quaternary deformation in the Longmen Mountains is characterized by relatively continuous thrusting on major faults a nd Himalayan folding events in foreland basin deposits, and no earthqu akes of M greater than or equal to 7 have been recorded there.