Abstract:“La Sorbella” is a deep-seated existing landslide in a Miocene clayey formation located in central Italy. Given the interaction with a national road, this landslide has been monitored for a long time with inclinometers and hydraulic piezometers. Recently, the monitoring system was implemented by adding pressure transducers in the Casagrande cells and by equipping the old inclinometers with in-place probes, to allow a remote reading of the instruments and data recording. This system allowed to identify that the… Show more
“…To infer the complex mechanics of post-seismic landslide movements, multi-parameter monitoring of slow-moving landslides 9 dynamics in seismic environments has been undertaken 5 , 10 , 11 . These studies show a co- and a post-seismic acceleration of the landslides over several weeks, and material damage (i.e.…”
Section: Introductionmentioning
confidence: 99%
“… Figure 1 Time-series of slow-moving landslide displacements in the days around several earthquakes. ( A ) GNSS time-series on the Maca landslide (Peru) during 2 local earthquakes (adapted from 5 and 11 ), ( B ) InSAR time-series on the Mela-Kabod landslide (Iran) during a Mw 7.3 earthquake (adapted from 13 , represents a co-seismic motion of about 34 m calculated with a satellite image correlation), ( C ) Inclinometer time-series on La Sorbella landslide (Italy) during 2 distant earthquakes (adapted from 10 ). No rainfalls were recorded in the time-periods shown.…”
Section: Introductionmentioning
confidence: 99%
“…1 B). The ratio between co- and post-seismic motions varies a lot from one case study to the other, from no post-seismic motion 10 to post-seismic motions three times larger than co-seismic ones 5 . Furthermore, two earthquakes do not produce similar co- and post-seismic motion ratios on the same landslide.…”
Section: Introductionmentioning
confidence: 99%
“…Other hypothesis related to effects of fluid migration during the shaking 16 , or variations of the material permeability 17 must also be investigated. However, the observation of transient post-seismic motions of landslides is still limited to a few number of case-studies 5 , 10 , 11 , 13 in the intermediate and far field of earthquakes (distance at least 2-3 times the fault length), where seismic shaking has limited groundwater effects 18 . All these uncertain conclusions show the need for more observations of post-seismic landslide motions to better infer the underpinning mechanisms.…”
In the days to weeks following an earthquake, landslides can display specific post-seismic motions, including delayed initiations and post-seismic relaxations. These motions have an uncertain origin, sometimes attributed to specificities of the landslide basal interface or to fluid transports in the landslide basal shear zone. Here we address this question, by documenting the co- and post-seismic motions of slow-moving landslides accelerated by the Gorkha earthquake (Mw 7.8, 25/04/2015, Nepal). We detect 11 slow-moving landslides over an area of 750 km$$^2$$
2
in the near field of the earthquake, and monitor their motions thanks to a time-series of Pléiades optical satellite images and SAR Sentinel-1 images. The post-seismic landslide motions are much larger than the co-seismic ones, reaching up to $$34 \,\pm\, 0.6$$
34
±
0.6
m accommodated over 2 months. A delayed initiation of several days (> 4 days) is also measured for at least two of the landslides. We analyze our findings in regards with all the previous observations on slow-moving landslides accelerated by earthquakes, and propose that the post-seismic motions are caused by diffusion of groundwater from co-seismic material contraction up to the landslide basal shear zone or from internal landslide reconfiguration. Our observations strongly suggest the main control of the hydrology in the landslide processes under seismic forcings.
“…To infer the complex mechanics of post-seismic landslide movements, multi-parameter monitoring of slow-moving landslides 9 dynamics in seismic environments has been undertaken 5 , 10 , 11 . These studies show a co- and a post-seismic acceleration of the landslides over several weeks, and material damage (i.e.…”
Section: Introductionmentioning
confidence: 99%
“… Figure 1 Time-series of slow-moving landslide displacements in the days around several earthquakes. ( A ) GNSS time-series on the Maca landslide (Peru) during 2 local earthquakes (adapted from 5 and 11 ), ( B ) InSAR time-series on the Mela-Kabod landslide (Iran) during a Mw 7.3 earthquake (adapted from 13 , represents a co-seismic motion of about 34 m calculated with a satellite image correlation), ( C ) Inclinometer time-series on La Sorbella landslide (Italy) during 2 distant earthquakes (adapted from 10 ). No rainfalls were recorded in the time-periods shown.…”
Section: Introductionmentioning
confidence: 99%
“…1 B). The ratio between co- and post-seismic motions varies a lot from one case study to the other, from no post-seismic motion 10 to post-seismic motions three times larger than co-seismic ones 5 . Furthermore, two earthquakes do not produce similar co- and post-seismic motion ratios on the same landslide.…”
Section: Introductionmentioning
confidence: 99%
“…Other hypothesis related to effects of fluid migration during the shaking 16 , or variations of the material permeability 17 must also be investigated. However, the observation of transient post-seismic motions of landslides is still limited to a few number of case-studies 5 , 10 , 11 , 13 in the intermediate and far field of earthquakes (distance at least 2-3 times the fault length), where seismic shaking has limited groundwater effects 18 . All these uncertain conclusions show the need for more observations of post-seismic landslide motions to better infer the underpinning mechanisms.…”
In the days to weeks following an earthquake, landslides can display specific post-seismic motions, including delayed initiations and post-seismic relaxations. These motions have an uncertain origin, sometimes attributed to specificities of the landslide basal interface or to fluid transports in the landslide basal shear zone. Here we address this question, by documenting the co- and post-seismic motions of slow-moving landslides accelerated by the Gorkha earthquake (Mw 7.8, 25/04/2015, Nepal). We detect 11 slow-moving landslides over an area of 750 km$$^2$$
2
in the near field of the earthquake, and monitor their motions thanks to a time-series of Pléiades optical satellite images and SAR Sentinel-1 images. The post-seismic landslide motions are much larger than the co-seismic ones, reaching up to $$34 \,\pm\, 0.6$$
34
±
0.6
m accommodated over 2 months. A delayed initiation of several days (> 4 days) is also measured for at least two of the landslides. We analyze our findings in regards with all the previous observations on slow-moving landslides accelerated by earthquakes, and propose that the post-seismic motions are caused by diffusion of groundwater from co-seismic material contraction up to the landslide basal shear zone or from internal landslide reconfiguration. Our observations strongly suggest the main control of the hydrology in the landslide processes under seismic forcings.
“…Recently, Tagarelli and Cotecchia [14] carried out a coupled hydro-mechanical numerical analysis on the influence of discontinuities on the behavior of landslides in intensely tectonized clay formations. Ruggeri et al [15] and Ruggeri et al [16] also considered the role of discontinuities on the overall behavior of landslides.…”
To analyze the response to hydrological conditions of an instable slope in a structurally complex clay formation, the hydraulic conductivity of the subsoil was estimated and pore water pressures were monitored. Two types of field tests were carried out: falling head tests in the Casagrande piezometers and localized seepage measurements in test boreholes. The experimental data show that in a narrow band around the slip surface, the hydraulic conductivity is higher—more than two orders of magnitude—than that of the landslide body and of the stable formation. Furthermore, the data of a long-term monitoring by Casagrande piezometers and vibrating wire cells show that the response of pore water pressures to the site hydrological conditions along the shear band is far faster than in the landslide body and in the stable formation. The slip band seems largely connected to the atmosphere, and the water pressures in the band are correlated with the deep displacement rates of all the inclinometers crossing the active slip surface.
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