A study of the mechanism and processes of Chiufengershan landslide triggered by Chi-Chi earthquake

Immediately after the Chi-Chi earthquake, the sliding surface of the Chiu-fen-erh-shan landslide was covered by erratic materials, so were the potential clues for the landslide processes. Years later, bedrock began to expose along with the crucial geological evidence. Based on careful investigation and new bore hole data, a new theory concerning the landslide process and mechanism is proposed.he sliding slope is a triangular dip slope. Its formation is controlled by the geological structure and discontinuities, with surface massive sandstone underlain by clayey sandstone alternated with thin shale. Judged from the thickness of the sliding strata and the position of the sliding surface, there should be no free fall end before the sliding. Large rills developed along joints oblique to the strike of the rock strata. Stains of ferric oxide were observed on the joint surface in many places, signifies the infiltration of surface runoff into the sliding surface, which eventually induced the landslide.everal left-slip faults and splay faults , as well as some ruptures perpendicular to strike were observed during investigation. According to the phenomena and the information provided by local residents, it is postulated that the earthquake induced horizontal rupture first, and then the up-and-down thrusts which caused collision and compression of the rock mass, and eventually resulted in the back thrust-like fault landform. Based on the core data, the depth of rock affected by the earthquake could have reached 25 m under the main sliding surface.hree sliding surfaces are found on the slope below the Long-nan industrial road. They exhibited a rare situation with the depth of the sliding surfaces decreased down-slope. Another unusual phenomenon is the middle part slope above the Long-nan industrial road is convex outward. It is postulated that the massif slipped up by the earthquake and then slipped down with a momentum exceeding the frictional force of the rock and caused the upper thicker rock strata slip over the surface of the left-slip fault and push the lower thinner rock strata down-slope. The remaining sliding mass at the down-slope side of the back thrust fault testifies its occurrence.he process of the earthquake triggered landslide is postulated as below:. Earthquake induced rock glide which in turn triggered rock fall at Dar-ping-chou with thunder-like noise.. The sliding of the lower massif of the main landslide drew the left-flank rock mass to turn counterclockwise to the edges of the slope and induced rockfalls into Sezi-ken and Jiu-tsai-hu streams. The middle part formed into two folds and tilted the “earthquake house”. . The upper massif of the main landslide and the right-wing massif, losing their end support, eventually slide down, and cause rock collisions and compressions.