Characteristics and dynamic runout analyses of 1983 Saleshan landslide

1983洒勒山滑坡特征及动态全过程分析

Engineering Geology, Volume 243, 4 September 2018, Pages 181-195

Chao Kang, Fanyu Zhang, Fazhen Pan, Jianbing Peng, Weijiang Wu

摘要：In 1983, a catastrophic landslide occurred in Saleshan, Dongxiang, Gansu, China, which resulted in the death of 237 people and the destruction of 585 houses. Saleshan landslide was a rapid moving landslide in loess area, China, which moved with long run-out distance on a gentle sliding surface. This paper reviews the characteristics of the landslide and its consequence, analyzes the possible triggers and the processes of development, and back-calculates the kinematic characteristics of the landslide. The digital elevation models (DEMs) of the study area before and after the event were used to analyze the geomorphological characteristics before and after the event. The authors inferred the possible deformation and failure processes of the landslide based on available observations. Direct shear tests were carried out to obtain the parameters of the soil involved in the failure and post-failure process, which was adopted in the following simulation using an energy-based runout model. The velocities of moving materials at a different time stage together with the variation of runout distance and maximum flow height are presented. The authors also compared the calculated results with field observations and previous simulation results. Sensitivity analysis was conducted to understand the effect of internal and basal friction angles on the kinematic characteristics. This study indicates that the Saleshan landslide was a fast-moving landslide with long traveling distance. The landslide lasted more than one minute with a maximum velocity of approximately 25 m/s according to the calculation using the energy-based runout model, which was consistent with the estimations based on the observation of eyewitness. This study also gives an insight on the progressive failure mechanism and explains the high mobility of Saleshan landslide in details, which provides a reference for hazard zonation for areas along loess platforms.

Use of Sentinel-2 images for the detection of precursory motions before landslide failures

应用Sentinel-2卫星图探测滑坡灾害之前的先兆运动

Remote Sensing of Environment, Volume 215, 15 September 2018, Pages 507-516

Pascal Lacroix, Grégory Bièvre, Erwan Pathier, Ulrich Kniess, Denis Jongmans

摘要：The Sentinel-2 optical satellites provide a global coverage of land surfaces with a 5-day revisit time at the Equator. We investigate the ability of these freely available optical images to detect precursory motions before rapid landslides. A 9-month time-series of displacement is derived from Sentinel-2 data over a major landslide in the French Alps, which exhibited a sudden reactivation in June 2016. This analysis reveals a 7-month period of low activity (≤1 m), followed by a sudden acceleration of 3.2 ± 1.2 m in 3 days, before the failure of a mass of about 2 to 3.6 106 m3. The location of this precursory motion is consistent with that of the slow motions occurring since 2001 (about 1 m/year), as revealed by aerial photographs and LiDAR analysis. This change in activity over a very short period of time (days) emphasizes the value of the frequent revisit time of Sentinel-2, despite its medium resolution of 10 m. We finally simulate the ability of Sentinel-2 for detecting these precursory patterns before a rapid landslide occurs, based on typical Voight's laws for creeping materials, characterized by a power law exponent α. Based on this analysis and on global cloud cover maps, we compute the probability to detect pre-failure motions of landslides using the Sentinel-2 constellation. This probability is highly heterogeneous at the global scale, affected by the revisit time of the satellite and the cloud cover. However the main factors controlling this detection ability are the properties of the landslide itself (its size and the α parameter), with almost 100% of detection probability for α = 1.3 and 0% for α = 1.8. Despite all these limitations, probability to detect a motion before a landslide failure often reaches 50% for classical landslide parameters. These results open new perspectives for the early warning of large landslide motion from global and open source remote sensing data.

Analyzing successive landslide dam formation by different triggering mechanisms: The case of the Tangjiawan landslide, Sichuan, China  

不同诱发机理形成的连续堰塞坝分析：四川唐家湾滑坡实例研究

Engineering Geology, Volume 243, 4 September 2018, Pages 128-144

Xuanmei Fan, Weiwei Zhan, Xiujun Dong, Cees van Westen, Hans-Balder Havenith

摘要：The catastrophic Tangjiawan landslide, triggered by the 2008 Wenchuan earthquake, blocked the Duba River, impounding one of the most dangerous coseismic barrier lakes in Beichuan, China. The lake was drained by an artificial spillway within one month after the earthquake to minimize the potential dam-breach flooding risk. However, on September 5, 2016, this landslide was reactivated and dammed the river again, creating a 20-m high dam at the same location and resulting in the formation of a barrier lake with a volume of 0.6 million m3. The day after the event we carried out a field investigation of the landslide and obtained a high-resolution image and DEM using UAV. The satellite images from 2005, 2008, 2010 and 2015 were also collected to analyze the evolution of the landslide. Together with multi-temporal DEMs, the geometry and volumes of the displaced mass and the landslide dams and barrier lakes were calculated using image interpretation and 3D spatial analysis with GIS. This landslide is of great scientific interest, as it presents a good example of multiple reactivation of a pre-historical giant landslide under different triggering conditions: a reactivation of an older landslide during the Wenchuan earthquake, and a second reactivation during a rainfall event several years later. Meanwhile from the hazard assessment and prevention perspective, it is also representative as it dammed the river twice in 2008 and 2016, posing threats to both upstream and downstream areas. We infer that the successive landslides in this region could be caused by the strong tectonic activities: including earthquakes and high average uplifting rate. The results of landslide volume analysis using multi-temporal DEMs, contribute to the landslide mechanism analysis, and suggest that the landslide volume estimation is effected by the landslide type, landslide rupture surface location, and resolution of DEM. We also compare the performance of different empirical models of landslide stability and dam-breach flood parameters and discuss their application during the quick assessment of the potential hazard of the landslide dams. Generally, the successive landslide dams at the Tangjiawan site are caused by the successive landslide reactivations on an anti-dip slope controlled by strong tectonic activity and river erosion, involve with a mass of loose materials of previous landslide deposition, and possess high flood risk to the downstream area. The experience gained in this work can be used to assist the hazard assessment and the planning of the emergency measures for similar landslide dams in the future.

Electrical resistivity imaging for the characterization of the Montaguto landslide (southern Italy)  

意大利南部Montaguto滑坡特征的电阻率法成像

Engineering Geology, Volume 243, 4 September 2018, Pages 272-281

Jessica Bellanova, Giuseppe Calamita, Alessandro Giocoli, Raffaele Luongo, Sabatino Piscitelli

摘要：Electrical Resistivity Tomography surveys were carried out for the characterization of the Montaguto earth-flow, located in the southern Apennines chain (Campania Region, southern Italy). The earth-flow investigated is one of the largest and most complex landslides in Europe with a length of 3.1 × 103 m, a width ranging between 45 and 420 m and an area of about 6.6 × 105 m2. In the spring of 2010, a large reactivation of the earth-flow heavily damaged some strategic infrastructures. In order to mitigate the effects of the mass movement, considerable efforts were carried out by the Italian National Civil Protection Department (DPC) to tackle the emergency. The aim of the study was to contribute to a more accurate geometric reconstruction of the landslide body and to improve the knowledge of the geological setting. Due to the lithological characteristic of the outcropping lithotypes, i.e. Faeto Flysch (calcarenite, clay and marl) and Villamaina Unit (sand and silty clay), the electrical resistivity contrasts were not very pronounced. However, the high-resolution of the electrical tomographies was the key to observe the presence of both lateral and vertical discontinuities that were associated with lithological boundaries, structural features and sliding surfaces. The results of the geoelectrical surveys could be considered for planning additional and more appropriate actions aimed at the stabilization of different portions of the Montaguto landslide.