Assessing Urban Landslide Dynamics through Multi-Temporal InSAR Techniques and Slope Numerical Modeling

Landslides threaten more than before the urbanized areas and are a worldwide growing problem for the already affected communities and the local authorities committed to landslide risk management and mitigation. For this reason, it is essential to analyze landslide dynamics and environmental conditioning factors. Various techniques and instruments exist for landslide investigation and monitoring. Out of these, Multi-temporal Synthetic Aperture Radar Interferometry (MT-InSAR) techniques have been widely used in the last decades. Their capabilities are enhanced by the availability of the active Sentinel-1 mission, whose 6-day revisiting time enables near real-time monitoring of landslides. Interferometric results, coupled with ground measurements or other approaches such as numerical modeling, significantly improve the knowledge of the investigated surface processes. In this work, we processed the C-band SAR images of the available European Space Agency (ESA) satellite missions, using MT-InSAR methods to identify the surface deformations related to landslides affecting the Iași Municipality (Eastern Romania). The results (i.e., velocity maps) point out the most active landslides with velocities of up to 20 mm/year measured along the satellite Line of Sight (LOS). Following, we focused on the most problematic landslide that affects the Țicău neighborhood and is well-known for its significant implications that it had. To better understand its behavior and the sensitivity of the displacements to the environmental factors (i.e., rainfall), we carried out 2D numerical modeling using a finite difference code. The simulated displacement field is consistent with the InSAR displacements and reveals the most active sectors of the landslide and insights about its mechanism.

The Motion and Range of Landslides According to Their Height

The frequency of catastrophic geological disasters has been increasing significantly, causing tremendous losses of life and property. The study of landslide motion remains incomplete. The variables H/L (ratio of landslide height to length) are often used to describe landslide motion; however, they may also be affected by the height of the landslide itself. To better understand landslide dynamics, this paper aimed to 1) identify the process of landslide motion in relation to height; 2) understand the range of influence of sliding bodies according to height; and 3) construct a formula of landslide disaster range based on the travel distance of the slide center and changes in the center and shape of the sliding body. In this paper, medium-fine quartz sand was used in experiments to observe the movement patterns and sliding body barycenter variations occurring during landslides. We describe the changes that occur during landslides and their deposits’ morphological characteristics and barycenter variations with height. Based on these observations, a landslide model is derived. This paper proposes a new method of estimating the effects of landslides, which can help to mitigate the effects of disasters.

GNSS and RPAS Integration Techniques for Studying Landslide Dynamics: Application to the Areas of Victoria and Colinas Lojanas, (Loja, Ecuador)

This research tests the application of GNSS and RPAS techniques to the spatiotemporal analysis of landslide dynamics. Our method began by establishing non-permanent GNSS networks on the slope surfaces to perform periodic measurements by differential GNSS. Similarly, RPAS flights were made to acquire high-resolution images, which were oriented and georeferenced using ground control points and structure-from-motion algorithms to ultimately obtain digital surface models and orthophotos. Based on GNSS measurements, the direction and velocity of displacements were accurately calculated, and orthophotos and DSMs were used to calculate horizontal and vertical displacements in a set of significant points throughout the study area, reaching accuracies higher than 0.035 m in the GNSS data and 0.10 m in the RPAS data. These values were within the accuracy required for such studies. Based on the field observations and the results from the photogrammetric studies, the two studied landslides were classified as very slow flows. These techniques are the basis for establishing early warning systems in areas of natural hazards based on the calculation of displacement speeds of the surface of slopes.

Landslide-tsunamis along the flanks of Mount Epomeo, Ischia: propagation patterns and coastal hazard for the Campania coasts, Italy

Ischia Island has been repeatedly affected by mass collapses, which are mainly caused by the steepness of the main peak (Mt. Epomeo) and by phenomena related to its volcanic activity.The most relevant cases of mass failure studied in the literature and postulated to be tsunamigenic cover a wide spectrum of sizes, from sector collapse to small-volume mass transports. Tsunamis generated by landslides in Ischia may affect the coast of the Campania mainland, including the Gulf of Naples.The focus of this work is the evaluation of the pattern of the maximum tsunami energy. To this purpose, we perform a series of numerical simulations by moving the same landslide source in different hypothetical positions around the island. The landslide dynamics is computed through the code UBO-BLOCK, and the tsunami propagation by employing the code UBO-TSUFD, both in-house developed. The final goal is to characterize the coastal areas of the Campania mainland most exposed to tsunami attack from Ischia sources.It is found that the position of the landslide influences deeply the distribution of the tsunami elevation in the coastal stretch north of the Procida Mount, while, remarkably, it is irrelevant inside the Gulf of Naples where the bathymetric effect prevails.

Submarine landslide tsunamis in SW Iberia Margin: Sensitivity of tsunamigenic potential and hazard extent to physical properties of marine sediments

<p>Slope instability is probably the most effective process shaping the seafloor of continental margins. This process often leads to the occurrence of submarine mass failures that, if large enough, can cause potential tsunamis. Yet, the dynamics of the landslide evacuated material and their induced tsunamigenic potential remain largely uncharacterized in most continental margins. This applies to the SW Iberia Margin, where large underwater landslide episodes have been evidenced.</p><p>In this work, we investigate the sensitivity of landslide-generated tsunami to the physical properties of marine sediments involved in the slope failures in the SW Iberia Margin. This includes the landslide dynamics, the tsunamigenic potential and the tsunami hazard extent. Based upon the MAGICLAND (Marine Geo-hazards Induced by Underwater Landslides in the SW Iberian Margin) project database, we select promising sizable submarine landslide scenarios. We then use an in-house developed two-layer numerical code (based on a Bingham visco-plastic model for the landslide and a non-linear shallow water model for the tsunami) to simulate both the landslide dynamics and the induced tsunami generation and propagation.</p><p>In a first stage, the numerical simulations are done considering uncertain sediments properties deduced from the literature. Next, we perform numerical simulations of the selected landslide scenarios using accurate geotechnical properties (mainly the in-situ shear strength obtained from undisturbed samples) determined by laboratory tests conducted on from the analysis of available marine gravity cores in the SW Iberian Margin. Results show that the geotechnical parameters significatively influence the simulation results of both the landslide dynamics and induced tsunami. Particularly, we noticed major effects on the landslide downslope deformation, failure speed, deposited thickness and run-out, which considerably control the momentum transferred to the generated tsunami wave. This demonstrates that the use of inappropriate material properties leads to a misquantification of landslide tsunamigenesis and hazard extent.</p><p>This work was financed by national funds through FCT—Portuguese Foundation for Science and Technology, I.P., under the framework of the project MAGICLAND – Marine Geo-hazards Induced by Underwater Landslides in the SW Iberian Margin (PTDC/ CTA-GEO/30381/2017).</p>

Landslide tsunamis, from origin to hazard, an overview from the SLATE project

<p>Landslide tsunamis, despite their importance for the overall tsunami hazard, is not as well understood as earthquake tsunamis. Several uncertain factors contribute to the lack of understanding, such as the variability in the source mechanisms, the dynamics of the landslide and the tsunami generation, as well as the temporal probability of occurrence of landslide events. Here, we present an overview of research activities on landslide tsunami analyses in the H2020 ITN-SLATE project. This research originates from two PhD student projects within SLATE, which have so far resulted in at least six publications with several more in the pipeline. In the SLATE project, we show that both translational and rotational dynamic attributes of the landslide are good indicators of the tsunamigenic potential of slumps using the visco-plastic landslide model BingClaw, by correlating the acceleration times mass and also angular momentum with the induced tsunami height. Moreover, we have employed Navier-Stokes simulations to hindcast model experiments of subaerial landslide tsunamis. By using the experience modelling this benchmark to model tsunamis in many other geometrical settings, the Navier-Stokes model is further employed to test generality and discuss several existing parametric relationships from literature so far available only empirically. New 3D formulations for granular landslide dynamics have further been established. Numerical models have also been set up to simulate real cases such as Anak Krakatoa. Finally, a broad parametric study that constrain the landslide dynamics for a landslide probabilistic hazard analysis is undertaken, to show how using past observations can effectively reduce uncertainties related to landslide dynamics. Combining an overview of the study with some highlights, we show how SLATE has contributed to increasing our understanding of landslide tsunamis and their hazard. We also discuss how the outcome of this project provides a platform for further research. This work has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 721403.</p>

GNSS and RPAS integration techniques for studying landslide dynamics: Application to the areas of Victoria and Colinas Lojanas, (Loja, Ecuador)

This research tests the application of GNSS and RPAS techniques to the spatiotemporal analysis of landslide dynamics. Our method began by establishing non-permanent GNSS networks on the slope surfaces to perform periodic measurements by differential GNSS. Similarly, RPAS flights were made to acquire high-resolution images, which were oriented and georeferenced using ground control points and structure-from-motion algorithms to obtain digital surface models and orthophotos ultimately. Based on GNSS measurements, the direction and velocity of displacements were accurately calculated, and orthophotos and DSMs were used to calculate horizontal and vertical displacements in a set of significant points throughout the study area, reaching accuracies higher than 0.035 m in the GNSS data and 0.10 m in the RPAS data. These values were within the accuracy required for such studies. Based on the field observations and the results from the photogrammetric studies, the two studied landslides were classified as very slow flows.

Analysis of the 2017 June Maoxian landslide processes with force histories from seismological inversion and terrain features

SUMMARY A devastating landslide occurred in Maoxian (China) on 2017 June 24, which generated strong signals that were recorded by a regional seismic network. We determined the landslide force history from long-period seismic waves and identified eight subevents. For each subevent, we obtained an independent force history and calculated its sliding path. The shape of the terrain before and after the landslide was found to play a critical role in the motion of the sliding mass. A combination of seismic and terrain data was used to discriminate between or relate the subevents to each other, and to locate the initiation point of each sliding path. We explain the Maoxian landslide dynamics as the combination of the rock collapse, centripetal acceleration of the sliding body, deceleration and acceleration once again after overcoming obstacles along the sliding path.

Landslide dynamics inferred from in-situ measurements and time series of terrestrial imagery: the Cliets rockslide (Savoie, French Alps)

<p>Several geodetic methods can be combined to better understand landslide dynamics and behavior. The obtained deformation/displacement fields can be analyzed to inverse the geometry of the moving mass and the mechanical behavior of the slope (kinematic regime, rheological properties of the media), and sometimes anticipate the time of failure. Among them, dense in-situ measurements (total station measurements, extensometer data and GNSS surveys) allow reaching accuracy close to the centimeter. These techniques can be combined to dense time series of passive terrestrial imagery in order to obtain distributed information. Actually, more and more passive optical sensors are used to provide both qualitative information (detection of surface change) and quantitative information using either a single camera (quantification of displacement by correlation techniques) or stereo-views (creation of Digital Surface Models, DSM).</p><p> </p><p>In this study, we analyze a unique dataset of the Cliets rockslide event that occurred on 9 February 2019. The pre-failure and failure stages were documented using the above mentioned methods. The performance of the methods are evaluated in terms of their possible contribution to a monitoring survey.</p><p> </p><p><span>The Cliets landslide is located in the French Alps (Savoie) and is affecting the high traffic road of Gorges de l’Arly. Located upstream of a tunnel, the unstable slope was instrumented by the SAGE Society during the crisis in the period July–February 2019. About 8000 m</span><sup><span>3</span></sup><span> collapsed closing the tunnel access for one year. Topographic measurements of a series of 41 benchmarks by automated total station were used to determined the time of rupture and the landslide mechanical behavior (tertiary creep vs stable regime). Additionally, a fixed CANON EOS 2000D with a lens with a focal length of 24 mm, was installed in front of the landslide. Images were acquired hourly and the time series was processed using the TSM processing toolbox (Desrues et al., 2019). Displacement fields were generated over time and compared to the topographic measurements. Photogrammetric surveys were carried out to generate several DSMs before and after the crisis. It allowed to estimate the volume of the collapsed masses. Finally, geophysical surveys were included in the study to determine the thickness of the potential unstable layer. </span></p><p>The results allow highlighting (1) different kind of behaviors which are identified and explained by a simple physical models, (2) the volumes of the displaced masses, and (3) the absence of a direct relation of the failure with the meterological forcing factors.</p><p> </p><p><span><strong>Acknowledgments</strong></span><span>: These works are part of a CIFRE / ANRT agreement between IPGS/CNRS UMR7516 and the SAGE Society.</span></p>

Urban growth changes the pulse of a large deep-seated landslide

<p>While the behaviour of slow-moving landslides – response to seasonal precipitation, seismic shaking, etc. – is well described in natural mountainous environments, little is known on the influence of urbanisation on their dynamics. Yet, gradual urbanisation of hillslopes is commonplace in the outskirts of many cities of the tropics. Typically anarchic, construction on previously undisturbed slopes often initiates or enhances landslide activity, rapidly increasing the number of people exposed to landslide hazard. Aiming at studying how landslides respond to their progressive urbanisation, we here present a detailed analysis of the dynamics of a large, thousand-year-old slow-moving landslide located in the rapidly expanding city of Bukavu (eastern DR Congo). This slope failure developed in highly weathered lava layers hosts today more than 80 000 inhabitants; for many affected by incessant destruction of infrastructures and housing.</p><p>We used 4 years of temporally dense 3D kinematic data from satellite interferometry (MSBAS 3D), pixel tracking on satellite and Unmanned Aerial System (UAS) orthomosaics and aerial photograph analysis to examine the relationships between urbanisation, landslide activity and rainfall and seismic patterns. We found a closely tied relationship between subsurface pore-water pressure changes and surface velocities. Seasonal rainfalls are driving the kinematics of the landslide at the weekly timescale, despite the large (~30-100 m) depth of the landslide. Analysing landslide dynamics over the last 60 years, we observed an increased activity over a zone of the landslide that will rapidly become the fastest landslide unit. This destabilisation occurred in the ‘90s, alongside an intensification of the (informal) urbanisation of the hillslope, at a time when region’s violent conflicts and insecurity drove important rural-urban migration. Still the most active today, this landslide unit moves at paces of 0.5-3 meters per year, causing significant and persistent damages to infrastructures. We here argue that changes in water runoff, concentration and infiltration due to the anarchic and poorly maintained urban extension is modifying the long-term behaviour of the landside, rather than overloading due to buildings (often light and wooden structures) and infrastructures. The very quick response to pore pressure changes could also be associated to the dense urban fabric, even though the tropical characteristics of this environment (wet-dry seasons, high rainfall, very high weathering) should not be ignored. Our analysis help improve the evaluation of landslide hazard and mitigation in the area, but also across the other many cities of the tropics where similar environmental and societal conditions are met. These findings also have implications for our understanding of landslide dynamics and how humans are interfering with landscape evolution.</p>