Landslide Volume Research Articles

Study on the relationship between rainfall, topography and landslide volume in the recent debris flow disasters in Hiroshima, Japan

Three types of sediment volume estimation equations were developed by analyzing the relationship between rainfall, topography (e.g. slope gradient, relative height) and the volume of collapsed sediment in 1 km grid for heavy rainfall events (2014 and 2018 events) in Hiroshima Prefecture where intensive slope failures and debris flows occurred. All three equations showed a tendency for the volume of collapsed sediment per unit area to increase with increasing rainfall. However, some equations showed the rate of increase tends to gradually plateau.

Power laws for accurate determination of landslide volume based on high-resolution LiDAR data

Landslide volume is critical in landslide risk management due to its close association with the landslide mobility and damage to elements at risk. Limited by accessibility, site conditions and availability of equipment, directly measuring the landslide volume on site is challenging. Instead, many empirical area-volume power-law models have been developed to estimate the landslide volume. Yet the validity of these power-law models for small-scale shallow landslides is in question considering the substantial uncertainty of field-estimated landslide volume data for developing these empirical power laws. In this study, two high-resolution LiDAR-derived digital terrain models taken in 2010 and 2020 are leveraged to interpret the volumes of 1326 shallow landslides that occurred in Hong Kong during the same period. The high precision of the digital terrain models ensures the accurate interpretation of landslides and the identification of landslide source and transport areas. On the basis of the interpreted landslide characteristics, new power-law models and a multivariate distribution model are proposed to accurately estimate the volumes of small-scale shallow landslides based on easy-to-obtain landslide source features such as source area, length, width or maximum depth. The multivariate distribution model rigorously expresses the conditional probability distribution of the landslide volume and quantifies the uncertainty of volume estimation. The models therefore enhance the capability of landslide risk assessment and management.

Application of Empirical Approaches for Fast Landslide Hazard Management: The Case Study of Theilly (Italy)

Landslide hazard management usually requires time-consuming campaigns of data acquisition, elaboration, and modeling. However, in the post-emergency phase management, time is a factor, and simpler but faster methods of analysis are needed to support decisions even in the short-term. This paper analyzes the Theilly landslide (Western Italian Alps), which was recently affected by a series of reactivations. While some instrumental campaigns are being carried out to support the design of protection measures, simple tools are also needed to assess the hazard of future reactivations and to evaluate the possibility of damming the torrent at the footslope. Therefore, state-of-the-art empirical methods were used and customized for the specific case study: a set of intensity–duration rainfall thresholds depicting increasing hazard levels was defined to monitor and forecast possible reactivations, while a methodology based on hydro-morphometric indices was applied to the case of study, to assess the possible evolution scenarios (landslide that does not dam the river, formation of a stable dam, formation of an unstable dam), based on the landslide volume. The proposed empirical methodologies have the advantage of requiring only ready-available input data and quick elaborations, thus allowing the rapid set up of tools that could be used for hazard management.

Landslides triggered by the 2015 Mw 6.0 Sabah (Malaysia) earthquake: inventory and ESI-07 intensity assignment

Abstract. On 4 June 2015, a Mw 6.0 earthquake occurred in the Sabah region (Malaysia), triggering widespread landslides along the slopes of Mt. Kinabalu. Despite the moderate magnitude, the Sabah earthquake was very efficient in triggering landslides: here I provide an inventory containing 5198 slope movements, mapped in an 810 km2 wide area. I investigate earthquake intensity using the Environmental Seismic Intensity (ESI-07) scale, which is a macroseismic scale based exclusively on earthquake environmental effects. The epicentral ESI-07 intensity is assessed at IX, considering the dimension of the area affected by secondary effects; such figure agrees well with a dataset of global earthquakes. I estimate the volume of individual landslides using area–volume scaling laws; then, I assign an ESI-07 intensity to each mapped landslide. I document that the selection of a given area–volume relation has a minor influence on the ESI-07 assignment. Then, I compare ESI-07 values to landslide density and areal percentage on a 1 km2 grid; such parameters are widely adopted in the description of earthquake-triggered landslide inventories. I argue that their integration with the ESI-07 scale may provide an effective way to compare earthquake damage on a variety of spatial and temporal scales. The methodological workflow illustrated here is useful in joining the scientific communities dealing with the development of earthquake-triggered landslide inventories and with ESI-07 assignment; I believe this effort is beneficial for both communities.

Finite Difference Modelling of Deformable Geosynthetics-Reinforced Barriers (DGRB) under the dynamic impact of debris avalanches

The behaviour of Deformable Geosynthetics-Reinforced Barrier (DGRB) is investigated with reference to the dynamic impact of debris avalanches. The aim of these barriers is to protect life of inhabitants and reduce the threat for the exposed structures. A Finite Difference Method code (FLAC, Itasca) is used and the dynamic impact is simulated as an external pressure applied over time to the barrier. The peak lateral pressure exerted by a debris avalanche is evaluated by a literature formulation including a flow-height dependent static component and a flow-velocity dependent dynamic component. Real values of height and velocity of debris avalanches are taken from previous research works. The trend of the pressure during the impact is obtained from the landslide volume and the impulse theorem. The DGRBs are composed of: i) coarse-grained material, ii) bidirectional PET geogrids; iii) external formwork. The soil-geosynthetics contact is simulated through a frictional interface. The several components used in the wrap-around technique are simulated following two different schematizations and the differences between them are highlighted. The used mathematical formulation allows reproducing the impacted barrier both in small and large displacement cases. The local and global displacements of the barrier, its failure mechanisms and the soil-geogrid interaction inside the barrier are investigated. The results outline the differences between the two ways of modelling the wrap-around technique. In particular, the computed global displacements are comparable in the two computational schemes while the simulated stress-strain responses of the structural elements are somehow different.

Pre-landslide topographic reconstruction in Baetis Chaos, mars using a CaSSIS Digital Elevation Model

Planview detailed morphological analysis of martian landslides is usually performed using orbital imagery such as from the ConTeXt camera (CTX) at 6 ​m/pix, the Colour and Stereo Surface Imaging System (CaSSIS) at 4.5 ​m/pix or the High-Resolution Imaging Science Experiment (HiRISE) at 0.25–0.5 ​m/pix. However, topographic information is key to fully understand a landslide's formation mechanism and its mobility, by estimating the material volumes mobilised and the spatial distribution of erosion and deposition. Digital Elevation Models (DEM) are required to carry out these analyses; nevertheless, there is currently a gap in landslide-volume studies between those using Mars Orbiter Laser Altimeter (MOLA) dataset at ∼450 ​m/pix or HRSC at 50–200 m/pix and those using HiRISE data at 1–2 m/pix, which is only partially filled by CTX elevation data at ∼20 ​m/pix. The CaSSIS camera on board the ESA/Trace Gas Obiter (TGO) can be used to produce DEMs, but so far, such data have not yet been used to conduct a landslide volume analysis. Here, we use three reconstruction methods (semi-automatic, morphology-based and tilted) on a CaSSIS DEM to estimate the initial topography and hence the volume and the distribution of erosion and deposition of a 6 ​km long landslide in Baetis Chaos. Despite the complex topography of the surrounding area due to the presence of an ejecta deposit beneath the landslide, we were able to estimate the landslide's volume and mass distribution. Using a tilted plane as part of estimating the initial topography produced the best results. We evaluated the success by considering the quantifiable balance between erosion and deposition (given the uncertainties) and more subjectively by considering whether the volume distribution matched with what was expected based on the morphology in images alone. Therefore, we recommend the use of this method for individual landslide studies in complex topography where detailed knowledge of the deposit-thickness distribution is required. The semi-automatic reconstruction method produces satisfactory volume estimates and would be better suited to studies where hundreds of landslides are present. We found that CaSSIS data can be used to successfully conduct such analyses, providing additional DEM coverage to study martian medium-scale landslides or other landforms of similar scale (5–15 ​km) with the notable benefit that it provides single-pass stereo image acquisition. • Digital Elevation Model are needed to estimates landslide's material volumes and distribution in order to fully understand their mobility. • CaSSIS (Colour and Stereo Surface Imaging System) DEM have not yet been used to conduct such landslide analysis. • Three reconstruction on a CaSSIS DEM have been used to estimate the volume and the material distribution of a landslide in Baetis Chaos on Mars. • CaSSIS data can be used to conduct analysis and provide additional coverage to study medium-scale landslides or other landforms (scale 5–15 km).

Bulli Pass Landslide Risk Management Part 1 - Hazard Assessment

The Princes Highway along Bulli Pass is a narrow, heavily trafficked two lane section of the Princes Highway that traverses steep slopes on a grade of 9H:1V on the Illawarra Escarpment, about 11 km north of Wollongong, and 75 km south of Sydney in New South Wales (NSW), Australia. It is an important arterial road for the northern suburbs of Wollongong, connecting Mt Ousley Road (M1 Princes Motorway) at the crest of the escarpment to the suburb of Thirroul on the coastal plain at the base of the escarpment. Bulli Pass has a long history of landslide and rockfall events, some of which were reported as early as 1890. One of the most significant of these events occurred on 17 August 1998 during a 1 in 100 year rainfall event. The 1998 landslide event comprised approximately 38 debris flows and slides and numerous rockfalls which partially inundated a number of cars and trapped about 15 cars on the pass. More recently, in early 2015, a small rockfall penetrated the windscreen of a car travelling up the pass. Transport for New South Wales (TfNSW) commissioned an investigation into slope instability hazards affecting the road in late 2011. This was followed in 2015 by a Risk Mitigation Options study and the detailed design of risk mitigation works in 2016. This paper provides an overview of the methods used to investigate hazards and assess risk at the site over a five year period. This has included research into the landslide history, geomorphological mapping, acquisition and review of airborne laser scanning (ALS) data, review of rainfall data and the development of a landslide volume frequency model. The development of this model allowed hazards to be readily communicated and risks to be assessed. The actual design and construction of the Shallow Landslide Barriers and the Debris Flow Barriers that followed on from these assessments will be discussed in a subsequent companion paper.

Preservation and transportation of large landslide deposits under decadal and millennial timescales in the Taiwan orogenic belt

Landsliding is one of the primary surface processes shaping the landscapes of active mountain belts. The mobilization (or stabilization) of landslide deposits plays a crucial role in fluvial dynamics, carbon output, and topographic development of active orogens. Despite numerous previous efforts, the controls on erosion or storage of large landslide deposits remain yet to fully understand. Toward this end, we investigated eight large landslides at three locations in Taiwan. Our observations of the Jiufengershan and Tsaoling landslides, the two largest co-seismic landslides of the 1999 Chi-Chi earthquake, indicate that as high as 90 % of the original landslide volume is still preserved in Jiufengershan after two decades, whereas only less than half remains in Tsaoling. The striking difference illustrates the importance of fluvial connectivity in the preservation or removal of landslide deposits. In the longer timescale, our topographic reconstructions of six fan terrace systems along the Laonung River revealed that, even with direct connectivity with one of the largest rivers in Taiwan, approximately 10 % to 30 % of the landslide deposits are still preserved in-situ after millennia of erosion. Their preservation ratio is mainly controlled by their age, their original size, and the river/hillslope processes nearby. Wider riverbeds around these terraces imply the occurrence of large landslides and subsequent deposition on riverbeds as an important mechanism of river lateral erosion. Our results suggest that a substantial portion of large landslide deposits may persist in the hinterland over thousands of years, and such long-term preservation of landslide deposits would be important in the landscape evolution and the mass balance of active orogenic belts.

AN OPEN-SOURCE-BASED WORKFLOW FOR DEM GENERATION FROM SENTINEL-1 FOR LANDSLIDE VOLUME ESTIMATION

Abstract. Digital elevation models (DEMs) serve as a basis for various geomorphological applications, such as, landform mapping, natural hazard assessment, and landslide characterisation. The inter-comparison of DEMs can be used to provide estimates of topographic change, for example, volume changes. Sentinel-1 synthetic aperture radar (SAR) data can be used to generate multitemporal topographic datasets using interferometric SAR (InSAR). Such analyses are often conducted using commercial software; however, a well-structured workflow based on free and open-source software (FOSS) increases the applicability and transferability of the DEM generation method and can facilitate the use of multi-temporal topographic analysis within the Earth Sciences. In this study, we aim to develop an open-source-based workflow for the generation of multi-temporal DEMs from Sentinel-1 data, and to explore their potential for landslide volume estimation using FOSS. We implemented this semi-automated and transferable workflow bundled in the open-source Python package “SliDEM”, which relies on SNAP, SNAPHU, and several other open-source software for geospatial and geomorphological applications, all distributed within a Docker image. Two major landslides in Austria and Norway were selected to test, evaluate, and validate the workflow in terms of reliability, performance, reproducibility, and transferability. Even if the quality of the Sentinel-1-based DEMs varies among the study areas, the preliminary results are promising. However, there is a need for improvement and thorough analysis of the causes of elevation errors. A comprehensive evaluation of the influence of the perpendicular and temporal baselines, topography, land use/land cover, and other environmental conditions can be systematically assessed within the “SliDEM” workflow.

Terraced Landscapes as NBSs for Geo-Hydrological Hazard Mitigation: Towards a Methodology for Debris and Soil Volume Estimations through a LiDAR Survey

Terraced landscapes are widely applied in many mountainous regions around the world as a result of the necessity to practice subsistence agriculture. Hence, they can be regarded as one of the most diffused anthropogenic modifications of the Earth’s surface. Different techniques have been used for their implementation leading to the artificial immobilization of debris and soil along the slopes whose surface is interrupted by a sequence of sub-horizontal and sub-vertical areas often using stone walls. In some areas of the world, such interventions are thousands of years old and their resistance to the degradation caused by the morphogenetic system can be attributed to the permeability of the stone walls as well as to their regular maintenance. In some other areas, the lack of maintenance has been the main cause for degradation processes ending with their collapse. The effects of climate change manifested through higher intensities and higher frequencies of rainfall are likely to accelerate the degradation process further by causing terraces to act as a source of debris or hyperconcentrated flow. This will in turn increase the severity of geo-hydrological hazards. The measures concerning reduction of geo-hydrological hazards are sought through identification of abandoned terraces and assessment of the potential for their sudden collapse. The present paper describes a framework for identification of abandoned terraces and estimation of the potential volume of shallow landslides that can be generated. The research conducted aims to advance the existing hazard assessment practices by combining numerical modeling with processing of high-resolution LiDAR data. A new algorithm is developed to support localization of terraces. The catchment scale approach applied to eight smaller catchments enables estimation of the total volume of soil and debris trapped along the slopes. It also generated some important quantitative data which will be used in the future risk assessment work. The work has been carried out within the EU-funded H2020 project RECONECT.

SIMULASI PENGUKURAN LONGSOR PADA KEMIRINGAN LERENG DAN KETEBALAN SERESAH YANG BERBEDA

Most areas in Indonesia have a high risk of landslides due to geological and geographical conditions. Landslide is affected by natural factors (such as slope stability) and human-made factors (such as land use). Slope stability is influenced by morphological conditions and hydrological conditions. Land use or land cover may affect surface roughness, which determines the infiltration rate into the soil. This study was an attempt to explore the influence of slope gradient and litter thickness on time required for landslides and the volume of landslides. This research was carried out in two different locations, Agro Techno Park and the Experimental Garden of the Faculty of Agriculture. The study was conducted in eight treatments, combinations of three factors, i.e. soil texture, slope gradient, and litter thickness, using ten replications. The duration required for landslides and the volume of landslides were measured. The gradient of the slope has a significant effect on the volume of landslides. An increase in slope at any litter thickness resulted in up to three times more volume. The difference in slope also has a significant effect on the time required for landslides. The clayey texture needs two times the longer time required for landslides to occur. The slope gradient has a more dominant influence than the thickness of litter and soil texture. The effect of the thickness of the litter is getting bigger; on the other hand, the effect of soil texture is getting smaller with increasing slope.

SIMULASI PENGUKURAN LONGSOR PADA KELERENGAN DAN KEDALAMAN BIDANG GELINCIR YANG BERBEDA

Landslide is one of the geological disasters that often occurs in Indonesia. Landslides can be caused by several factors; there are human factors and natural factors. In principle, landslides occur when the resisting force is smaller than the driving force. Landslides on a small and large scale can occur over time and have a fairly severe impact. Therefore, this study simulated the effect of slope and depth of slip surface on the duration and volume of landslides, which are simulated on two soils with different texture classes. Landslide simulations were conducted at Agro Techno Park and The Experimental Gardens Faculty of Agriculture. The simulation used eight treatments and ten replications consisting of three factors there are soil texture, slope and depth of slickenside. Landslide simulation was conducted using an acrylic box with a size of 100 cm x 50 cm x 75 cm with rain intensity 70 mm hour-1. The variables measured are landslides duration, landslides volume, soil texture and bulk density. Data analysis used an independent sample t-test. The result showed slope and slickenside have a significant effect on landslides duration and landslides volume. The greater the slope, the landslide occurs faster on landslides duration and the greater the volume of the landslide. The deeper slickenside has a longer landslides duration, but the volume of the landslide is larger. It showed that the greater slope has a smaller influence on the depth of slickenside and soil texture on the landslides duration and landslides volume.

HUBUNGAN KEMIRINGAN LERENG DAN PERSENTASE BATUAN PERMUKAAN TERHADAP LONGSOR BERDASARKAN HASIL SIMULASI

Landslide is the process of moving slope-forming material that moves out of the slope. Landslides cause adverse impacts, such as damage to residences, public facilities, death tolls, and damage to agricultural land. Factors for landslides are influenced by disturbing slope stability due to steep slopes, high rainfall intensity, and movement of soil, rock, or a mixture of both. The research was conducted at Agro Techno Park of Brawijaya University (silt loam texture soil) and the experimental field of Faculty of Agriculture Brawijaya University (clay texture soil). The landslide simulation tool used acrylic (100 cm x 50 cm x 75 cm), with an aluminum plate as a base for adjusting the slope. Artificial rain was set to be stable at an intensity of 70 mm hour-1. This study used a combination of three factors, namely soil texture (C: silt loam and J: clay); slope (L1: 40° and L2: 50°); and surface rock (B1: 25% and B2: 50%), so that there were eight treatments with ten repetitions. The landslide duration and volume were measured. The data obtained were then statistically analyzed through the normality test and the unpaired t-test. The results show that increasing slope gradient from 40° to 50° on silty loam texture with similar rock content at the soil surface resulted in 6 times faster and two times larger landslide volume. At a very steep slope, the effect of soil texture and % rocks at the surface would be smaller on landslide duration but became more significant on landslide volume. Generally, the landslide factors can be ranked from the most significant effect as follows: slope gradient, soil texture, and rocks coverage at the surface.

PENGARUH BATUAN DAN SERESAH PADA PERMUKAAN TANAH TERHADAP PENDUGAAN LONGSOR HASIL SIMULASI

Landslide is a natural disaster that often occurs in Indonesia. The total of landslides from 2003 to 2018 is 363, which were caused by controlling factors and triggering factors or restraining factors. The relation between two factors (litter and rock) that cause landslide is still rarely researched. This research was carried out from September 2020 to March 2021, in Agro Techno Park Cangar and Jatimulyo Experimental Station. A simulation used an acrylic box (100 cm x 50 cm x 75 cm), with soil 20 cm thick on an aluminium plate adjusted at a slope of 50°. Rainfall intensity was set at 70 mm hour-1, using an Adjustable Water Gun (as a rainfall simulator) with a current of 2.6 amperes rotation sprayer A. There were eight combination treatments consisting of three factors. The variables measured were landslide duration and volume. Data obtained were then analyzed using an unpaired t-test. Apparently, the faster the landslide occurs, the larger the avalanche volume. Among the three factors observed (soil texture, litter and rocks at the surface), surface litter was the most determining factor for landslide duration and volume. Landslide duration and volume were far different between the two soil textural classes when there was no litter at the soil surface. In contrast, if there was 3 cm litter, landslide duration and volume were quite similar between the two soil textural classes. To a small extent, the occurrence of the rocks at the soil surface may fasten and increase landslide volume.

Geomorphology and initiation mechanisms of the 2020 Haines, Alaska landslide

In early December 2020, an atmospheric river (AR) and rain-on-snow (ROS) event impacted the Haines, Alaska area, resulting in record-breaking rainfall and snowmelt that caused flooding and dozens of mass movement events. We consider the AR—a one-in-500-year event—as the trigger for the devastating Beach Road Landslide (BRLS), which destroyed or damaged four residences and took the lives of two people. The BRLS started as a debris avalanche and transitioned into a debris flow, with a total approximate landslide volume of 187,100 m3. Geomorphic analysis using lidar data identified evidence of paleo-landslides and displaced masses of rock, one of which served as the source area for the BRLS. Significant structural features in the weak ultramafic bedrock defined the head scarp area and formed the failure plane. This study illustrates the importance of identifying pre-existing landslide features and source areas likely to produce future landslides. As an increase in ROS events is projected for Southeast Alaska with warmer and wetter winters, we recommend the development of an AR scale coupled with geological information for the region, to enhance warnings to residents in landslide-prone areas.

Spatiotemporal Evolution Pattern and Driving Mechanisms of Landslides in the Wenchuan Earthquake-Affected Region: A Case Study in the Bailong River Basin, China

Understanding the spatiotemporal evolution and driving mechanisms of landslides following a mega-earthquake at the catchment scale can lead to improved landslide hazard assessment and reduced related risk. However, little effort has been made to undertake such research in the Wenchuan earthquake-affected region, outside Sichuan Province, China. In this study, we used the Goulinping valley in the Bailong River basin in southern Gansu Province, China, as an example. By examining the multitemporal inventory, we revealed various characteristics of the spatiotemporal evolution of landslides over the past 13 years (2007–2020). We evaluated the activity of landslides using multisource remote-sensing technology, analyzed the driving mechanisms of landslides, and further quantified the contribution of landslide evolution to debris flow in the catchment. Our results indicate that the number of landslides increased by nearly six times from 2007 to 2020, and the total volume of landslides approximately doubled. The evolution of landslides in the catchment can be divided into three stages: the earthquake driving stage (2008), the coupled driving stage of earthquake and rainfall (2008–2017), and the rainfall driving stage (2017–present). Landslides in the upstream limestone area were responsive to earthquakes, while the middle–lower loess–phyllite-dominated reaches were mainly controlled by rainfall. Thus, the current landslides in the upstream region remain stable, and those in the mid-downstream are vigorous. Small landslides and mid-downstream slope erosion can rapidly provide abundant debris flow and reduce its threshold, leading to an increase in the frequency and scale of debris flow. This study lays the foundation for studying landslide mechanisms in the Bailong River basin or similar regions. It also aids in engineering management and landslide risk mitigation under seismic activity and climate change conditions.

Landslide Susceptibility Assessment Considering Landslide Volume: A Case Study of Yangou Watershed on the Loess Plateau (China)

Because of the special geological conditions on the Loess Plateau, Landslide erosion is not only the main goal of prevention and control of geological disasters, but also an important erosion mode of soil and water loss in the basin. Thus, landslide susceptibility assessment before only considering landslide frequency is not far enough for a decision-maker. The study aims to consider both frequency and scale of landslides for a better landslide susceptibility evaluation. Taking the Yangou small watershed as an example, this study used a VR model, RIRA method, and the GIS method to comprehensively consider frequency and scale to analyze landslide susceptibility of the small watershed. Based on the detailed analysis of the existing literature, slope, elevation, NDVI, land-use, lithology, amount distant to road, amount distant to river, profile curvature, and rainfall as landslide are selected as the conditioning factors (CFs) of the landslide, to draw the sensitivity map. The map of landslide susceptibility was classified into five zones: very low, low, medium, high, and very high, and the cover areas occupy 6.90, 12.81, 12.83, 9.42, and 5.87 km2, respectively. A total of 60% of the landslide occurred in the zones of high and very high susceptibility, accounting for 87% of the total volume in the study area. The very high susceptibility is the area with a larger relief and along the river and road. The findings will help decision makers to formulate scientific comprehensive policies that take into account disaster prevention and soil conservation measures in specific regions.

A geometry-modelling method to estimate landslide volume from source area

A geometry-modelling method to estimate landslide volume from source area

On the Inference of Tsunami Uncertainties From Landslide Run‐Out Observations

AbstractProbabilistic tsunami hazard analysis (PTHA) due to submarine landslides is much less developed than PTHA for earthquake sources. This is partly because of less constrained data available for quantifying source probability, and partly because of the lack of knowledge related to the tsunami generation process due to landslide dynamics. This study provides a basis for estimating the uncertainty related to landslide dynamics for PTHA from submarine landslides based on a new landslide database in the Gulf of Cadiz. The establishment of this new database is described herein. We use submarine landslide run‐out statistics from this database to calibrate landslide parameters and related uncertainties employing the cohesive landslide model BingClaw. In turn, coupling the landslide motion to tsunami genesis is performed in order to characterize the inferred tsunami uncertainties. Important parameters that can explain the large tsunami uncertainties are the initial water depth of the landslide, the slope, the landslide volume, and the initial yield strength of the landslide material. Kinematic properties such as the initial landslide acceleration or the Froude number are found to strongly correlate with the tsunami‐genesis. In this study, we show how matching numerical landslide models with observed run‐out from past events in the field can give information about the uncertainty in their tsunami‐genic strength. This can in turn be applied in future PTHA for spanning uncertainty ranges due to the landslide dynamics on tsunami‐genesis, constrained by landslide run‐out data.

Submarine landslide source modeling using the 3D slope stability analysis method for the 2018 Palu, Sulawesi, tsunami

Abstract. Studies have indicated that submarine landslides played an important role in the 2018 Sulawesi tsunami event, damaging the coast of Palu Bay in addition to the earthquake source. Most of these studies relied on observed coastal subaerial landslides to reproduce tsunamis but could still not fully explain the observational data. Recently, several numerical models included hypothesized submarine landslides that were taken into account to obtain a better explanation of the event. In this study, for the first time, submarine landslides were simulated by applying a numerical model based on Hovland's 3D slope stability analysis for cohesive–frictional soils. To specify landslide volume and location, the model assumed an elliptical slip surface on a vertical slope of 27 m of mesh-divided terrain and evaluated the minimum safety factor in each mesh area based on the surveyed soil property data extracted from the literature. The soil data were assumed as seabed conditions. The landslide output was then substituted into a two-layer numerical model based on a shallow-water equation to simulate tsunami propagation. The tsunamis induced by the submarine landslide that were modeled in this study were combined with the other tsunami components, i.e., coseismal deformation and tsunamis induced by previous literature's observed subaerial coastal collapse, and validated with various post-event field observational data, including tsunami run-up heights and flow depths around the bay, the inundation area around Palu city, waveforms recorded by the Pantoloan tide gauge, and video-inferred waveforms. The model generated several submarine landslides, with lengths of 0.2–2.0 km throughout Palu Bay. The results confirmed the existence of submarine landslide sources in the southern part of the bay and showed agreement with the observed tsunami data, including run-ups and flow depths. Furthermore, the simulated landslides also reproduced the video-inferred waveforms in three out of six locations. Although these calculated submarine landslides still cannot fully explain some of the observed tsunami data, they emphasize the possible submarine landslide locations in southern Palu Bay that should be studied and surveyed in the future.