• ISSN 2097-1893
  • CN 10-1855/P

2000年易贡高速滑坡的动力学过程

Dynamic process of the 2000 Yigong high-speed landslide

  • 摘要: 北京时间2000年4月9日19时58分,青藏高原东南缘林芝市波密县易贡地区发生大规模滑坡,造成约8 km2的森林大范围受损,阻塞河道形成易贡湖. 地震波形可以远程探测大规模滑坡事件的发生过程,有助于对滑坡事件的阶段性动力学参数进行定量分析. 由于该事件规格大、能量强,使得易贡滑坡地震波形在远距离地震站上仍然有清晰的记录. 本文利用中国地震台网宽频带地震台站波形数据对2000年易贡滑坡的动力学过程进行了分析,发现该事件持续时长约215 s,包括滑前启动阶段(约65 s)、主要滑动阶段(约90 s)和滑后调整阶段(约60 s). 滑前调整阶段持续时间相对较长,低频信号较弱,而高频信号由弱逐渐增强,指示滑坡起始阶段主要以碎屑崩塌为主. 主要滑动阶段进一步分为加速滑动和减速滑动过程,加速滑动过程高频信号和低频信号振幅较大,地形坡度较陡,物质在扎木弄沟中加速下滑,加速约35 s后达到最大速度约191 m/s,此时滑坡运动水平位移约3.1 km;相比而言,减速滑动过程高频和低频振动信号由强转弱,对应滑坡滑床变宽、坡度变缓,滑坡速度不断减小至0,约 90 s后水平位移和垂直位移分别达到最大值约6.0 km和3.2 km. 滑后调整阶段高低频信号振幅逐渐变弱,主要反映滑坡物质在扎木弄沟谷底部沉积. 2000年易贡滑坡的体积和滑动速度明显大于青藏高原东南缘近期发生的其他滑坡事件,反映源区冰雪融水和降水导致沟谷沉积物下滑摩擦力减小,形成巨型堆积体,是易贡藏布河堵塞形成易贡湖的主要原因.

     

    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 km2 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.

     

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