Abstract:
At Beijing time 19:58 on April 9, 2000, a large landslide occurred in Yigong area, Bomi County, Linzhi City, southeastern Qinghai-Xizang Plateau, caused extensive damage to about 8 km
2 of forest, blocked the river and formed the Yigong lake. Seismic waves can remotely detect the occurrence process of landslide events, which helps to quantitatively analyze their dynamic parameters of different sliding stages. Because of the large size and strong energy of the event, the seismic waveform of the Yigong landslide can be clearly seen on the remote seismic stations. We analyzed the dynamic process of the 2000 Yigong landslide using broadband seismic waveforms of the China Earthquake Networks Center, and found that the event lasted about 215 s, including the pre-slip initialization (about 65 s), the main slip (about 90 s), and the post-slip adjustment (about 60 s) phases. The duration of the initialization phase is relatively long and the low-frequency signal is weak. However the high-frequency signal gradually increased, indicating that the landslide is started with broken collapse. The main sliding phase is further divided into accelerated and decelerated sliding stages. During the accelerated sliding stage, the amplitudes of both the high-frequency and low-frequency signals are large. The terrain slope is steep and the material accelerated to slide in the Zhamunong valley. About 35 s after the acceleration process, the maximum speed reached about 191 m/s and the horizontal displacement of the landslide movement is about 3.1 km. By comparison, during the deceleration sliding stage, both the high-frequency and low-frequency signals decreased. This observation is corresponding to the widening of the landslide bed and the slowing of the slope. Then the speed of landslide movement continuously decreased to zero. The maximum horizontal and vertical displacements reached about 6.0 km and 3.2 km after 90 s, respectively. In the post-sliding adjustment stage, the amplitude of both high-frequency and low-frequency signals gradually weakens, which mainly reflects the scattered deposition of landslide materials at the bottom of the Zhamunong valley. The volume and sliding speed of the 2000 Yigong landslide is obviously larger than other landslides that have recently occurred in the southeastern Qinghai-Xizang Plateau. These observations suggest that the sliding friction of sediments in the valley decreased due to melting water and precipitation in the source area and giant deposits are formed. It is the major reason for the blockage of the Yigong Zangbu river and the formation of the Yigong Lake.