Numerical Simulation Research On Dynamical Characteristics Of The Mahu Ancient Seismic Landslide-dammed Events

Mahu is located in Huanglang trough valley, the middle of Mabian-Daguan earthquake fault zone. It’s overall general characteristics of regional tectonic environment is form a triangle block by southern Lianfeng NE trending fold fracture, western Ebian-Jinyang SN trending fold belt and eastern Mabian-Huangjingba NNW trending fault zone. Regional geophysical field studies show’s that the Mabian-Huangjingba NNW trending fracture which does not cut through to the earth’s surface is a large deep fracture. Seismic activities along this fault zone is occured mainly in the intersecting dislocation tectonic position of itself and other three NE trending fault zone, the Lianfeng fracture, the Leibo fracture and the Meigu-Shashuiba fracture.Field research results shows that Mahu-Huanglang trough valley have least occured three times seismic landslide-dammed events in prehistory. Respectively located in Miaoping which in the east of Huanglang town, Ganchitang of Huanglang town, Haikou in the south of Huanglang town. The three events all showing the high-speed debris flow characteristics, dynamics are expressed as "shock rock structural weakening-slip control with fragmentation-the lower" sliding block "suddenly cut disintegration-landslide blocked climbing".Adopted the UDEC program which is suited to deal with discontinuous media is used to simulate the dynamic response of discontinuous media under the ground motions loads, analysis dynamical characteristics on dynamic strength and high-speed remote migration of ancient seismic landslide-dammed events. Research shows that the basalt slope over limestone slide bed is whole under stable condition in the case of natural. The research on the seismic response of original slope which were analyzed under a=1.6g(Ⅹ degree) and a=2.4g(Ⅺ degree) seismic acceleration conditions shows that under a=1.6g condition the model just produced local damage and the whole slope is in the state of limit equilibrium while under a=2.4g condition the model produced whole disintegration damage and showed a typical high-speed remote debris flow characteristics.Comprehensive analysis shows that the paleoearthquake strength which causing Mahu earthquake landslide dammed events should above seismic intensity XI degrees. Numerical simulation results shows that sliding body produces the maximum slip distance of1988m in a debris flow state at30s. Around in the10s the sliding body starts and during the10-30s it’s mean sliding velocity is99.4m/s. Between10-20s in the case of earthquake, the sliding body is in a rapid acceleration phase. Between15-20s, the acceleration and speed of the landslide are increased dramatically, the average maximum acceleration of the landslide is equivalent1.456g. Between20-30s, landslide showing a clear trend of slowing down the acceleration and after25seconds the landslide entering the deceleration phase.