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At 12:52 pm on September 5, 2022, an Ms 6.8 earthquake occurred in Luding County, Sichuan Province, China. Based on high-resolution aerial photographs and satellite imageries obtained after the earthquake, as well as field investigation, a total of 8685 earthquake-triggered landslides (EQTLs) were interpreted. The landslides covered an area of 30.7 km2, with a source area of 9.4 km2. These EQTLs were mainly distributed in areas with a seismic intensity of VIII and IX. Most of the landslides were small and medium in size, and their types included landslide, rockfall, and rock slump. Characteristic landslide distributions were found, EQTLs were distributed along the Xianshuihe fault, landslide area decreased gradually with an increased distance to the fault; EQTLs were distributed along the Daduhe River and roads; besides, landslide distribution was associated with ground deformation caused by the earthquake. EQTLs' characteristics indicated that, a large number of EQTLs were located near the foot of the slope; the full area of EQTLs and their source area followed a power function. This study concluded that Luding EQTLs were greater in number and area but relatively smaller in terms of affected area. Investigations on geo-hazards post-earthquake and risk assessment were proposed in the earthquake-stricken area to support the rehabilitation and reconstruction. [ABSTRACT FROM AUTHOR]

The "9.5" Luding earthquake (Ms 6.8), which occurred on September 5, 2022, has triggered thousands of landslides, and caused coseismic landslide sediment in the mountain basin to increase significantly. After the Luding earthquake, landslide sediment may continue to divert to channels, and increase the activity of debris flows. Importantly, the formation of debris flows can pose a major threat to infrastructure, lives and property. To better understand the landslide sediment that increased by the "9.5" Luding earthquake and its impact on the activity of debris flows, we mapped the coseismic landslide database using satellite images. A total of 9142 landslides with an area of 49.51 km2, covering 4.81% of the whole basin, were triggered by the Luding earthquake. The coseismic landslides induced by this earthquake are dominated by shallow landslides and are densely distributed in the combined zone of the Xianshuihe fault and the Dadu fault. Approximately 333.31×106 m3 (error: 111.43×106 m3/−70.73×106 m3) of coseismic landslide sediments were induced by the earthquake in the epicenter, and the landslide materials were concentrated downstream of the basins. In addition, more than 13986.45×104 m3 (error: 4675.67×104 m3/−2967.92×104 m3) of landslide sediment may supply for debris flow occurrence. Simultaneously, the small basins that are distributed near Moxi, Detuo and the junction of the Xianshuihe fault and Daduhe fault are more susceptible to debris flows when rainstorms hit these regions. Therefore, prevention and mitigation measures, early warning, and land use planning should be adopted in advance in these regions. However, from the perspectives of landslide scale and the degree of landslide-channel coupling, the activity or active intensity of debris flows in the Luding earthquake area may be lower than that in the epicenter area of the 2008 Wenchuan earthquake. [ABSTRACT FROM AUTHOR]

On Monday, May 12, 2008, a devastating mega-earthquake of magnitude 8.0 struck the Wenchuan area, northwestern Sichuan Province, China. The focal mechanism of the earthquake was successive massive rock fracturing 15 km in depth at Yingxiu. Seismic analysis confirms that the major shock occurred on the Beichuan-Yingxiu Fault and that aftershocks rapidly extended in a straight northeast-southeast direction along the Longmenshan Fault zone. Fatalities approaching a total of 15,000 occurred, with a significant number resulting from four types of seismically triggered geohazards-rock avalanches and landslides, landslide-dammed lakes ('earthquake lakes'), and debris flows. China Geological Survey has identified 4,970 potentially risky sites, 1,701 landslides, 1,844 rock avalanches, 515 debris flows, and 1,093 unstable slopes. Rock avalanches and landslides caused many fatalities directly and disrupted the transportation system, extensively disrupting rescue efforts and thereby causing additional fatalities. Landslide-dammed lakes not only flooded human habitats in upstream areas but also posed threats to potentially inundated downstream areas with large populations. Debris flows become the most remarkable geohazards featured by increasing number, high frequency, and low triggering rainfall. Earthquake-triggered geohazards sequentially induced and transformed to additional hazards. For example, debris flows occurred on rock avalanches and landslides, followed by landslide-dammed lakes, and then by additional debris flows and breakouts of the landslide-dammed lakes and downstream flooding. Earthquake-induced geohazards occurred mainly along the fault zone and decreased sharply with distance from the fault. It can be anticipated that post-earthquake geohazards, particularly for debris flows, will continue for 5-10 years and even for as long as 20 years. An integrated strategy of continuing emergency response and economic reconstruction is required. The lesson from Wenchuan Earthquake is that the resulted geohazards may appear in large number in active fault regions. A plan for geohazard prevention in the earthquake-active mountainous areas is needed in advance. [ABSTRACT FROM AUTHOR]