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On Sep. 5, 2022, an MS 6.8 earthquake struck Luding County. The earthquake triggered large amounts of co-seismic landslides, which blocked the Wandong River for nearly 24 hours. Field surveys, image interpretation, spatial statistics, and hydro-logical calculations were used to investigate the characteristics of co-seismic landslides and the risk of debris flow following the earthquake. According to the findings, co-seismic landslides are primarily found in areas of earthquake intensity IX, and their sizes are typically small and medium. They are distributed along both sides of the channel, particularly on both sides of the thin ridge facing the air. The distance from the fault and slope controls the distribution of co-seismic landslides. The volume of debris flow runout in the Wandong catchment may be twice that of the debris flow prior to the earthquake. On this basis, the following disaster prevention and mitigation suggestions were put forward. The risk of runout debris flow in the catchment should be strengthened; The value of triggering rainfall of debris flow should be obtained as soon as possible through comprehensive monitoring and early warning; The scale amplification factor of debris flow should be fully considered in the design of debris flow prevention and control projects. This research can be used as a scientific reference for disaster prevention and mitigation of post-earthquake debris flows.

Multi-period debris flows have been developed in the last glacial period of the late Pleistocene-Holocene near the Grand Bend of the Yarlung Zangbo River in southeast Tibet, which combined to form a modern large-scale fan-shaped accumulation. The debris flows in the Bangga gully, Pai Town, were explored by ground survey, borehole, and 14C dating methods to investigate the chronological sequence of formation, accumulation depth, and outrush range. The analysis results show that there are still small-scale debris flows in the tributaries of the Bengga gully, and they are widely accumulated in the channel, but no debris flow accumulation has been found in the existing accumulation fan area. The Holocene debris flows in the Bunga gully were active around 8500 years ago, and the cumulative accumulation depth of a single period is about 10.9 m. The two carbon samples in the light gray silt sand formed by the shallow lake facies (fluvial facies) show that the modern riverbed of the Yarlung Zangbo River was deposited at a depth of about 0.4 m in 40 to 100 years, and the annual average deposition rate was about 4~10 mm. The boreholes at 2906.1~2896.7 m and 2849.4~2848.2 m above sea level reveal a thickness of 9.4 m and 1.2 m cake-like bluish-gray clay in turn. It is assumed that two river-blocking events occurred. The above results could provide a reference for the study of the debris flow activity characteristics since the Holocene in this region.

The southwest mountainous region in China is the worst-hit area due to the most developed geohazard chains. In order to better understand the pattern of the geohazard chains in this region, we analyzed the main control factors and characteristics of the geohazard chains based on 19 typical geohazard events in history. Three classification patterns, namely landslide-type, collapse-type, debris flow-type, and five typical hazard-inducing processes, were summarized. A typical hazard-inducing chain process in each model was selected for analysis. On this basis, we discussed the mechanism of the geohazard chain, the construction of a database and technical standard system, and the measures for preventing and controlling transboundary basin chain-type geohazards, aiming to provide a reference for the regional geohazard prevention and mitigation plan, and the major engineering projects' construction and people's safety in town.

On September 5th, 2022, the Ms 6.8 earthquake in Luding County, Sichuan Province induced large numbers of geological hazards. In order to deeply understand the evolution, distribution, and characteristics of geological hazards caused by the earthquake, we obtained the distribution of geological hazards by the field investigation and remote sensing interpretation. The conditions for hazard control and the countermeasures for hazard prevention and reduction are also analyzed. The results show that as of 22:00 on September 14, 2022, the earthquake has induced 565 geological hazards with threat objects in Luding County and Shimian County (including 331 collapses and 234 landslides), and 81 existing geological hazards whose deformation increased. The geological hazards induced by the earthquake are mainly medium and small mass high-level collapses, which are mainly concentrated in the areas with Seismic intensity zone of Ⅸ near the epicenter. These areas include Moxi Town, Detuo Township, both banks of Dadu River between Detuo Township and Dewei town in Luding County, Caoke Township and Wanggangping Township in Shimian County. According to the experience of the Wenchuan earthquake, the debris flow will be active in the next five years, and its characteristics of high frequency and viscous debris flow should be considered in the design of debris flow prevention and control engineering. Under the rainfall condition, the landslide deposition remaining on the slopes of Dadu River banks in the section of Detuo Township—Dewei Town can easily transform into debris flow. The transformation forms of the two hazards’ types should be fully considered in the design of prevention and control projects. The study can provide a reference for earthquake geological hazard prevention and post hazard reconstruction planning in the earthquake area.

On December 18, 2023, an Ms 6.2earthquake occurred in Jishishan County, Linxia Prefecture, Gansu Province, causing a large number of geological disasters and threatening people's lives and the safety of infrastructure. After the earthquake, Gansu and Qinghai provincial governments quickly deployed hundreds of geology professionals to carried out the investigation and verification geological disasters in the earthquake area. Based on the results of the earthquake geohazard investigation and verification, this paper analyses the characteristics, control factors and development trend of the earthquake-induced geohazards, and puts forward suggestions on disaster prevention and risk mitigation measures. Till December 23, a total of 2044 geohazards have been checked, including 78 new geohazards, 88 existing geohazards with intensified deformation due to earthquake, and 1 878 existing geohazards without obvious different from before. Most of new and intensified deforming geohazards are collapse, accounting for 67.5%, followed by landslide, accounting for 31.9%. Most of new and intensified deforming geohazards are small in scale, accounting for 84.9%, followed by medium, accounting for 10.8%. Disaster mode of new and intensified deforming geohazards are mostly small collapse threatening houses and roads. The co-seismic geohazards are densely distributed along the seismic fault, and the spatial density increases with the enhancement of earthquake intensity. Data from 206 groups of accelerate-meters within 50 km from the epicenter of the National Geological Safety Monitoring Network showed that the peak acceleration of the earthquake area was 30.4-1969.7 mg. and decayed logarithm with the increase of the distance from the epicenter. In addition, the surface deformation monitoring equipment also recorded the co-seismic displacement curve of a typical landslide. Analysis shows, earthquake put a deteriorate effect to rock and soil, which decreased their integration and strength. There is a magnificent geohazard after-effect of earthquake; collapse, landslide and debris flow will be much often than before. So the authors suggest: (1) update earthquake geohazard database as soon as possible, (2) work out targeted prevention and control measures for the geohazards with large potential danger, (3) conduct comprehensive remote sensing monitoring and research of earthquake-induced geohazard mechanism, (4) improve the meteorological early warning model and threshold. By all this efforts the risk of geohazards after earthquake will be reduced and controlled. [ABSTRACT FROM AUTHOR]

Landslide disasters occur frequently in the western mountainous regions of China and are characterized by high concealment, suddenness, and strong destructiveness. Early identification of potential disaster hazards is the most effective disaster prevention and mitigation measure. The western mountainous areas are mostly in alpine-canyon terrain with a wide range, which is hard or even impossible to reach, where the traditional early identification methods of manual inspection are difficult to implement. Interferometric Synthetic Aperture Radar (InSAR), as an emerging radar remote-sensing method, can efficiently and accurately identify the hidden dangers of landslide disasters. In this study, based on the European Space Agency’s Sentinel-1 synthetic aperture radar data, the time series InSAR technology was used to identify the potential landslide hazards in alpine-canyon terrain along Yajiang County-Muli County of the Yalong River, detecting eight potential geohazards. Based on the historical data of landslide hazards and optical remote sensing interpretation, the early identification results were verified and analyzed, and the danger level of the disaster points was evaluated. The influence of geometric distortion in InSAR technology on the early identification of potential landslide disasters in alpine-canyon terrain is also discussed. This case can provide powerful data and technical support for local disaster prevention and mitigation and provide ideas and references for the early identification of the hidden dangers of landslide disasters in mountain-valley areas.

On Sep. 5, 2022, an Ms6.8 earthquake struck Luding County. The earthquake triggered large amounts of co-seismic landslides, which blocked the Wandong River for nearly 24 hours. Field surveys, image interpretation, spatial statistics, and hydro-logical calculations were used to investigate the characteristics of coseismic landslides and the risk of debris flow following the earthquake. According to the findings, co-seismic landslides are primarily found in areas of earthquake intensity IX, and their sizes are typically small and medium. They are distributed along both sides of the channel, particularly on both sides of the thin ridge facing the air. The distance from the fault and slope controls the distribution of co-seismic landslides. The volume of debris flow runout in the Wandong catchment may be twice that of the debris flow prior to the earthquake. On this basis, the following disaster prevention and mitigation suggestions were put forward. The risk of runout debris flow in the catchment should be strengthened; The value of triggering rainfall of debris flow should be obtained as soon as possible through comprehensive monitoring and early warning; The scale amplification factor of debris flow should be fully considered in the design of debris flow prevention and control projects. This research can be used as a scientific reference for disaster prevention and mitigation of post-earthquake debris flows. [ABSTRACT FROM AUTHOR]