Cyclical slope instability and volcanism related to volcano-tectonism in resurgent calderas: The Ischia island (Italy) case study

Filling of Xiangjiaba Reservoir Lake in the Southwest China triggered and reactivated numerous landslides due to water fluctuation. In order to understand the relationship between reservoirs and slope instability, a typical reservoir landslide (Dasha landslide) at the right bank of Jinsha River was selected as a case study for in-depth investigations. The detailed field investigations were carried out to identify the landslide with respect to its surroundings and to find out the slip surface. Boreholes were drilled to find out the subsurface lithology and the depth of failure of Dasha landslide. The in situ geotechnical tests were performed, and the soil samples from exposed slip surface were retrieved for geotechnical laboratory analysis. Finally, stability analysis was done using the 3D strength reduction method under different conditions of reservoir water level fluctuations and rainfall conditions. The in-depth investigations show that the Dasha landslide is a bedding rockslide which was once activated in 1986. The topography of Dasha landslide is relatively flat, while the back scarp and local terrain is relatively steep. The total volume of landslides is about 580×104 m3 with an average thickness of 20 m. Bedrock in the landslide area is composed of Suining Formation of the Jurassic age. The main rock type is silty mudstone with sandstone, and the bedding orientation is 300~310° ∠ 7~22°. The factor of safety (FOS) of Dasha landslide obtained by 3D strength reduction cannot meet the minimum safety requirement under the working condition of reservoir level fluctuation as designed, with effect of rainfall and rapid drawdown.

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Mapping and monitoring urban landslides in New Zealand using Sentinel-1 InSAR data: A case study from Gisborne

10.5194/egusphere-egu21-13744 ◽

2021 ◽

Author(s):

Matt Cook ◽

Martin Brook ◽

Jon Tunnicliffe ◽

Murry Cave ◽

Ian Hamling ◽

...

Keyword(s):

New Zealand ◽

Urban Area ◽

Ground Deformation ◽

Slope Instability ◽

Interferometric Synthetic Aperture Radar ◽

Rainfall Events ◽

Slip Surfaces ◽

Slow Moving ◽

Steep Slopes

<p>Landslides are widespread natural hazards that are responsible for substantial economic and societal damage globally each year. In New Zealand, landslides frequently occur on soil and rock, triggered by high rainfall, seismic activity, and land-use change and/or disturbance. This study focuses on Gisborne, a city where ongoing slope instability issues occurring across the steep slopes within the urban area are affecting several properties. Failure commonly occurs along reactivated slip surfaces, when slow-moving retrogressive slides transition into fast-moving flows during intense rainfall events. However, the extent and rate of slope deformation in the Gisborne area are poorly known. Spaceborne Interferometric synthetic aperture radar (InSAR) is a convenient method for measuring ground deformation and over the past decade, SAR systems have significantly developed and provide consistent, reliable, high-resolution global data. In particular, the launch of Sentinel-1 in 2014 marked a significant milestone, being the first civilian satellite designed explicitly for InSAR analysis, and it produces free and open access data. In this study, we illustrate the potential of InSAR to detect the slow movement of landslide deposits in Gisborne before rapid acceleration, using Sentinel-1 data. The pre-failure deformation of several previous landslides in Gisborne is measured to determine possible deformation thresholds for rapid acceleration across the urban area.</p>

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