16:45 〜 17:00
[SSS07-18] Source processes of large landslides in the eastern Himalaya
キーワード：Eastern Himalaya, Landslides, Seismic records
The Himalayan orogenic belt is located at the Indian-Eurasian plate collision zone. Due to the combined influence of tectonic movements and environmental changes, large-scale landslides have occurred in the eastern Himalayas, including the 2000 Yigong, 2017 Maoxian, 2018 Baige, and 2021 Sedongpu landslides. These events have caused severe river blockages and other secondary disasters in the upstream river areas. Here, we investigate the source processes of these events by using seismological methods, such as spectrum analysis, high-frequency energy calculation, and low-frequency waveform inversion.
Landslide events have many common features. The sources of landslides can be explained by single force models. Their waveforms consist mainly of surface waves with a propagation speed of 3-3.5 km/s, a time duration of several minutes and no obvious P-wave or S-wave signals. High-frequency signals are mainly generated by friction between the landslide debris and the sliding bed, and decay rapidly with increasing distance. Local seismic observations can be used to estimate the energy and the corresponding mass of the landslide. In contrast, low-frequency signals are mainly generated by the loading and unloading effects of the landslide on the sliding bed. Regional waveforms can be used to invert the dynamic source process of different landslides.
Landslide events also have clear differences in terms of the specific circumstances. The 2018 Baige event started with clear high-frequency signals, reflecting its scattered detrital collapse in the pre-sliding stage. During the acceleration stage, the 2017 Maoxian and 2021 Sedongpu events showed lager low-frequency signals than the high-frequency signals, indicating that the landslide source tends to start moving as a whole without involving much debris in the sliding valley. For the post-sliding stage, there was a second phase for the 2021 Sedongpu event, suggesting an impact on the opposite bank and a blockage of the river. This study provides new information for the disaster mitigation under the coupling of the structural and environmental conditions.
Landslide events have many common features. The sources of landslides can be explained by single force models. Their waveforms consist mainly of surface waves with a propagation speed of 3-3.5 km/s, a time duration of several minutes and no obvious P-wave or S-wave signals. High-frequency signals are mainly generated by friction between the landslide debris and the sliding bed, and decay rapidly with increasing distance. Local seismic observations can be used to estimate the energy and the corresponding mass of the landslide. In contrast, low-frequency signals are mainly generated by the loading and unloading effects of the landslide on the sliding bed. Regional waveforms can be used to invert the dynamic source process of different landslides.
Landslide events also have clear differences in terms of the specific circumstances. The 2018 Baige event started with clear high-frequency signals, reflecting its scattered detrital collapse in the pre-sliding stage. During the acceleration stage, the 2017 Maoxian and 2021 Sedongpu events showed lager low-frequency signals than the high-frequency signals, indicating that the landslide source tends to start moving as a whole without involving much debris in the sliding valley. For the post-sliding stage, there was a second phase for the 2021 Sedongpu event, suggesting an impact on the opposite bank and a blockage of the river. This study provides new information for the disaster mitigation under the coupling of the structural and environmental conditions.