Post-seismic Landslides Research Articles

Monitoring and Assessment for the Susceptibility of Landslide Changes After the 2017 Ms 7.0 Jiuzhaigou Earthquake Using the Remote Sensing Technology

Monitoring the change of post-seismic landslides could provide valuable information for geological disaster treatment. The 2017 Jiuzhaigou Ms 7.0 earthquake has triggered a large number of landslides in the Jiuzhaigou United Nations Educational, Scientific and Cultural Organization (UNESCO) Natural Heritage site, which provides a unique opportunity for monitoring the spatio-temporal characteristics and exploring the impact factors of post-seismic landslides change. In this study, the spatio-temporal characteristics of landslides and their post-seismic changes are analyzed using multi-source, multi-temporal, and multi-scale remote sensing data combining with the field study. The Support Vector Machine classification, visual interpretation, field investigation, and Geographic Information System technology are employed to extract landslides and analyze their spatial distribution patterns. Moreover, the Certainty Factor method is used to explore the susceptibility of landslides and to find key impact factors. Our results show that the net increase area of landslide is 1.2 km2 until September 27th, 2019, which are induced by the expansion of coseismic landslide, the post-seismic landslide, and the expansion of vegetation degradation. Moreover, the area expansion of the coseismic and post-seismic landslides is mainly related to the increase of debris flow induced by the post-seismic torrential rainfalls. The highest net increase rate of post-seismic landslide change does not distribute on the regions with the highest density of coseismic landslides. The susceptibility of post-seismic landslide change is greatly influenced by slope, altitude, aspect, peak ground acceleration fault, and strata. It is higher in the coseismic landslide area with low susceptibility. This study also suggests that the potential landslides will most likely occur in the unstable slope region affected by the additional driving force. Therefore, great attention should be paid to identify and prevent the potential landslides on unstable slopes in addition to treatments of the sliding slopes. This study provides a good example for the monitoring and assessment of post-seismic landslides in mountainous regions with a steep slope and deep valley.

Landslide characteristics and its impact on tourism for two roadside towns along the Kathmandu Kyirong Highway

Frequent landslide events affect the Kathmandu Kyirong Highway (KKH), one of the most strategic Sino-Nepal highways, with multiple social effects. Amongst them, the impacts on local tourism, although being substantial, have not been studied so far. The aim of this research is to analyze the characteristics of such landslides and their influence on road damages and/or blockages as well as on local tourism industry. We analyzed the co-seismic landslides triggered by the Gorkha Earthquake, 2015 (7.8 Mw), the post-seismic landslides that occurred during the monsoons following the earthquake, as well as landslides which occurred or reactivated in 2018, with relation to the damage that they caused to the highway. High resolution satellite images from 2015 to 2018, and field data were used for the analysis. The Langtang avalanche that locates off the highway was also mapped due to its high impacts on tourism. Between 2015 and 2018, the number of road damaging landslides in the Betrawati-Rasuwagadhi section of KKH (where Dhunche and Syafrubesi towns are located) was 101 in the main track (MT) and 103 in the new track (NT), with respective average density of 1.46/km and 3.63/km. The dominant observed landslide types were debris slides and rock falls. Landslides were mostly concentrated in the locations with the following characteristics: 1) having higher elevated area, 2) being located with the ‘main central thrust’ and other lineaments’ belts, 3) belonging to the Proterozoic lesser Himalayan rocks, 4) having a slope gradient of 25°–45°, 5) having northern, western and southern slope aspect, 6) being subjected to average annual rainfall of higher than 1,000 mm, and 7) having less than 4 km distance from the past earthquake epicenters. The results further indicated that 7 rain-induced and 4 co- and post-seismic landslides have great impact on tourist flows. An impact analysis was also assessed through a door to door questionnaire survey with local hotel operators from Dhunche and Syafrubesi towns (n = 29 + 31). The results reveal that out of six rigorously affected sectors by landslides leading to road blockage, tourism business is the most impacted livelihood sector in these towns. The reduction of visitors in different hotels ranged from 50%–100% in Dhunche and 70%–100% in Syafrubesi for the first year aftermath of the tremor. This is higher than the respective 5%–50% tourist reduction due to rain-induced landslides. Using as a reference the base year 2014, the income loss of hotels in both towns was found to be 50%–100% in 2015, 20%–100% in 2016, 5%–75% in 2017, and similar to 35% in 2018. These results provide insights on the synergic effect of contributing factors for cut slope as well as down slope instability along mountainous motorways and their impact on income sources for local communities.

The long-term evolution of landslide activity near the epicentral area of the 2008 Wenchuan earthquake in China

The Wenchuan earthquake triggered numerous landslides and damaged vast areas of vegetation. Strong mountain earthquakes have long-term impacts on the activities of subsequent landslides. It is crucial for long-term geohazard risk assessment to investigate the spatio-temporal evolution of post-earthquake landslides. We used multi-year images from 2008 to 2018 to track the reactivation of coseismic landslides and newly occurring landslides to evaluate the influence of the Wenchuan earthquake on subsequent rain-induced landslides. With the aid of a GIS platform combined with field investigations, we analyzed the temporal and spatial evolutions of landslide activities over the past ten years and the factors controlling these changes. In addition, the process of vegetation recovery at landslide sites in the epicentral area was detected based on multi-year Landsat TM data after the Wenchuan earthquake. We observed that the total area of active landslides decreased significantly with time. In the first 5 years (2008–2013), the vegetation recovered quickly but was not well rehabilitated, and post-seismic landslides generally maintained high activity levels. Due to progressive revegetation and consolidation, most of the coseismic deposits along the hillslopes gradually stabilized. Subsequently (2013–2018), landslide activity weakened and mainly occurred in high and steep areas with poor vegetation recovery, particularly in proximity to the drainage network. Decreasing occurrence of rain-induced landslides was closely related to vegetation recovery in both time and space, and vegetation recovery could promote the reduction in post-earthquake landslide activities. We also proposed a quantitative model for the landslide rate in the epicentral area of the Wenchuan earthquake, which shows that the enhanced landslide rate reached its peak after the earthquake and will decrease to the pre-earthquake level in 25 years. The evolution of the post-seismic landslide activity can be categorized into four stages: high active period (2008–2013), low active period (2013–2018), recovery period (2018–2033), and stable period (after 2033).

Event-based rainfall warning regression model for landslide and debris flow issuing

Debris flow and landslide warnings are currently based on real-time monitoring of rainfall according to predefined warning lines. Conventionally, the rainfall variables combinations cumulative rainfall–duration (Re–D) and mean rainfall intensity–cumulative rainfall (Im–Re) for setting rainfall thresholds are used separately for landslide warning. The variables used in the regression analysis are correlated and a physical relationship Im = Re/D is available. Two-dimensional warning lines lack spatial feature and may not sufficiently reflect the rainfall characteristics required to initiate debris flows. A technical procedure using 3D regression analysis of the rainfall parameters interaction analysis was proposed. The rainfall warning regression surface is set on the basis of rainfall variables such as average rainfall intensity, effective cumulative rainfall, and duration. Here, a three-parameter, paraboloid rainfall warning regression surface generated using the variables of Im, D, and Re to determine the rainfall characteristics necessary to initiate debris flows and landslides is proposed. The proposed rainfall warning regression model reflects the rainfall characterization using a 3D diagram than the conventional threshold line. The regression results are converted in a multiple Im–D rainfall warning regression diagram containing various Re quantities for issuing landslide and debris flow warnings. Results show that the types of rainfall required to initiate debris flows and landslides include high rainfall intensity within a short duration and high cumulative rainfall over a long duration; moreover, debris flows could be affected by postseismic effects. The regression surfaces vary for rainfall events associated with different typhoons, which suggest that the initiation of landslides and debris flows is affected by the event that causes rainfall. An inclined plane surface is commonly used for describing a rainfall-induced landslide and debris flow regression surface for issuing warnings. The regression surface has parabolic geometry in postseismic landslide areas. The interactions of rainfall parameters using a three-dimensional regression analysis were studied and it was applied to the case of a catastrophic landslide and debris flow at Xiaolin Village in Taiwan.

Decadal vegetation succession from MODIS reveals the spatio-temporal evolution of post-seismic landsliding after the 2008 Wenchuan earthquake

Strong earthquakes, especially in continental mountainous areas, can trigger extensive mass wasting, producing large amounts of debris that accumulates along the hillslopes or in drainage channels. The coseismic deposits and disturbed slopes are prone to be reactivated or remobilized by heavy rainfalls in the subsequent years after the earthquake. Predicting how long post-seismic landslide activity will return to the pre-earthquake level is a key to risk assessment and management. However, this is still poorly understood, and lacks quantitative prediction approach. The 2008 Wenchuan earthquake triggered an unprecedented number of landslides, creating an extraordinary natural laboratory to investigate the evolution of post-seismic landslides and their impacts on environment. Using the vegetation recovery rate as an indicator, we present the observational evidence of the post-seismic landslide evolution based on MODIS NDVI time series between 2000 and 2018. Using a simple vegetation recovery rate (VRR) function, we quantify the rate of vegetation regrowth in the Wenchuan earthquake affected area, and discuss the decaying trend of post-seismic landslide activities. Our findings show that 83% of the co-seismic landslides become inactive within a decade. The NDVI trend suggests that landslide activity may return to the pre-earthquake level within 18 years. The sensitivity of vegetation regrowth to post-seismic landsliding thus offers a great potential to improve our understanding of the spatio-temporal evolution of the post-seismic landslide activities.

An Experimental Study on the Hydromechanical Behaviours of the Evolution of Postearthquake Landslide Deposits

In this study, a series of experiments of the full-scale physical model was employed to investigate the hydromechanical behaviours of the postearthquake landslide evolution, in forms of rill erosion and shallow headward failure on the rill bank slopes under unsaturated conditions. Soil-water characteristic curves (SWCC) were established using the Brooks-Corey (BC) and van Genuchten (VG) models. The stability of the shallow failure was then analyzed via a one-dimensional and unsaturated stability analysis model of the infinite slope. This measurement revealed that the preferential flow and the matrix flow coexisted when infiltration occurred and the VG model performs better in fitting the SWCC than the BC model. Consistent feedback between stability calculations and experimental observations enables the analysis of mechanisms of rill erosion and slope failure of postseismic landslide under the impact of preferential flow. Furthermore, the seepage-induced internal erosion phenomenon was observed in the experiment. This work thus provides a new perspective on the triggering mechanisms of debris flow during the postseismic period.

The role of active faults and sliding mechanism analysis of the 2017 Maoxian postseismic landslide in Sichuan, China

A giant, high-position rockslide occurred in Xinmo village of Maoxian County, Sichuan, China, on June 24, 2017. It was the largest rockslide recorded since the 2008 Wenchuan earthquake, and caused great loss. We use field survey data and relevant information to describe the geometric and zoning of the Maoxian landslide, and we discuss its sliding mechanism and the role of active faults in its formation. The sliding mode of the Maoxian landslide involves a plane failure mechanism (sliding rupture), while the slipping process can be divided into two stages: a rock cracking and deterioration stage, and a high-speed sliding stage. The role of active faults (earthquake and fault movement) is probably the most important factor in the Maoxian landslide formation, while lithology played a catalytic role and rainfall acted as an inducing factor. The fault vertical combination model (“back thrust” dynamic model) proposed in this paper provides a reasonable explanation for the different distribution of the coseismic landslides caused by the 1933 M 7.5 Diexi earthquake. We consider that a steep slope near the active fault, especially where the active fault intersects, just like the “locked segment” of a fault, is the uppermost area to develop a large landslide.

Two multi-temporal datasets that track the enhanced landsliding after the 2008 Wenchuan earthquake

Abstract. We release two datasets that track the enhanced landsliding induced by the 2008 Mw 7.9 Wenchuan earthquake over a portion of the Longmen Mountains, at the eastern margin of the Tibetan Plateau (Sichuan, China). The first dataset is a geo-referenced multi-temporal polygon-based inventory of pre- and coseismic landslides, post-seismic remobilisations of coseismic landslide debris and post-seismic landslides (new failures). It covers 471 km2 in the earthquake's epicentral area, from 2005 to 2018. The second dataset records the debris flows that occurred from 2008 to 2017 in a larger area (∼17 000 km2), together with information on their triggering rainfall as recorded by a network of rain gauges. For some well-monitored events, we provide more detailed data on rainfall, discharge, flow depth and density. The datasets can be used to analyse, on various scales, the patterns of landsliding caused by the earthquake. They can be compared to inventories of landslides triggered by past or new earthquakes or by other triggers to reveal common or distinctive controlling factors. To our knowledge, no other inventories that track the temporal evolution of earthquake-induced mass wasting have been made freely available thus far. Our datasets can be accessed from https://doi.org/10.5281/zenodo.1405489. We also encourage other researchers to share their datasets to facilitate research on post-seismic geological hazards.

Analysing post-earthquake mass movement volume dynamics with multi-source DEMs

The 2008 Wenchuan earthquake in Sichuan, China, dramatically changed the terrain surface by inducing large numbers of landslides. Due to the lack of adequate pre- and post-earthquake Digital Elevation Models, the landslide volume estimation was done either using empirical area-volume relationships over large areas or by field surveys in a few catchments with debris flow threats. The trend of the change of volume of loose materials in the earthquake affected area over the decade since the earthquake remains largely unknown. In this study we were able to address this issue using nine DEMs taken at different years and from different sensors to study the change in loose material volume caused by co-seismic and post-seismic landslides over a period of 9 years. The area around the towns of Yingxiu and Longchi, for which also multi-temporal landslide inventories were available, was selected for this study. Methods to register the DEMs and minimize their vertically bias were applied. The quality of the DEMs was assessed through GCPs and terrain representation. As could be expected, high resolution DEMs showed more realistic volume estimates than the low resolution ones. The analysis showed that the frequency and magnitude of the landslide volume dynamics decreases significantly after the early post-seismic period, and in the last years human activities became a more dominate factor than mass movements. The post-seismic material loss from 2008 to 2014 was close to the gained volume of the co-seismic landslides, and the depletion of the materials was mostly at the toes of the co-seismic landslides. The analysis was done based on gain and loss calculated from the DEMs, and actual volumes could not be calculated due to unknown failure surface depths of the landslides.

Decreased post-seismic landslides linked to vegetation recovery after the 2008 Wenchuan earthquake

Major mountain earthquakes could have long-term impacts on post-seismic landslide activities. Yet, we have limited understanding of the duration of these impacts due to a lack of long-term consistent observation. This study combines multi-year high spatial resolution and high temporal resolution remote sensing images collected before and after the 12 May 2008 MW 7.9 Wenchuan earthquake to investigate post-seismic landslide changes and vegetation recovery processes at landslide sites in the epicentral area. We found that the earthquake caused significant vegetation damage by triggering co-seismic landslides. Since that time, vegetation at these landslide sites has been continuously recovering, and the total post-seismic landslide area is decreasing concurrently. Post-seismic vegetation recovery reflects and possibly promotes the decrease of post-seismic landslide activities. Our findings on post-seismic vegetation recovery at landslide sites indicate that the Wenchuan earthquake's impact on regional post-seismic landslide frequency may disappear within two decades after the major event.

Brief communication: Post-seismic landslides, the tough lesson of a catastrophe

Abstract. The rock avalanche that destroyed the village of Xinmo in Sichuan, China, on 24 June 2017, brought the issue of landslide risk and disaster chain management in highly seismic regions back into the spotlight. The long-term post-seismic behaviour of mountain slopes is complex and hardly predictable. Nevertheless, the integrated use of field monitoring, remote sensing and real-time predictive modelling can help to set up effective early warning systems, provide timely alarms, optimize rescue operations, and perform secondary hazard assessments. We believe that a comprehensive discussion on post-seismic slope stability and on its implications for policy makers can no longer be postponed.

Post-seismic landslide extraction by combining texture analysis and emissivity estimating

Post-seismic landslide extraction by combining texture analysis and emissivity estimating

A sociotechnical approach toward earthquake-induced landslides

Background: Many landslides occur as a direct or indirect result of earthquakes. Recent studies have thoroughly examined the connection between earthquakes and post-seismic landslides triggered by rainfalls considering earthquake source distance and magnitude as well as the temporal delay of landslide activation. Methodology: Some of the recent seismic events that generated damaging landslides are presented in this study with special focus on socio-technical aspects along with the effectiveness of slope stabilization, the interaction of earthquake and subsequent rainfalls and disintegration of slope material due to water infiltration. Discussion: The mechanisms of compound effects are classified together with the research needs and possible mitigation measures. It is anticipated that the increased understanding of such mechanisms in the study areas is likely to be a prerequisite for a meaningful disaster risk reduction. The emphasis is also made on the importance of urgent post-earthquake damage surveys and benefiting from local seismic culture in land-use planning.

Plant community composition and interspecific relationships among dominant species on a post-seismic landslide in Hongchun Gully, China

The 5.12 Earthquake in 2008 and 8.14 Debris Flow in 2010 resulted in large-scale landslides that disturbed vast areas of vegetation in the Hongchun Gully, Wenchuan County, China. To define the specific characteristics of vegetation restoration during natural recovery after catastrophic events, vegetation species composition and interspecific associations were investigated on this typical landslide. Field survey data selected from a total of 51 sample plots belonged to seven belt transects and were analysed by Schluter’s variance ratio, pearson's chi-squared test, Spearman’s correlation coefficients and ecological species groups. Plant communities on the landslide consisted of 78 species, 65 genera and 52 families. Of the total of 78 species, 25 are identified as dominant species, among which Camptotheca acuminate, Toxicodendron vernicifluum, Coriaria nepalensis, Robinia pseudoacacia, Buddleja alternifolia, Anemone vitifolia and Nephrolepis auriculata play a constructive role during the natural afforestation. Moreover, according to environmental and ecological factors, these 25 dominant species could be divided into four ecological species groups. This study found that even though the landslide had frequently suffered from interference due to heavy rain, the vegetation succession processes are ongoing, and it is now at a shrub–herb community succession stage, which indicates that vegetation can naturally recover in the denuded sites. This study provides a useful insight into the ecological interactions and interdependence between plant species during the natural recovery of vegetation and provides valuable information on vegetation recovery modelling in the landslide area.

Rapid post-seismic landslide evacuation boosted by dynamic river width

How rivers evacuate large landslide deposits is crucial for predicting post-seismic hazards. A 2D hydro-sedimentary model demonstrates that a narrowing river channel increases sediment transport, which reduces export time by orders of magnitude.

Performance of Models for Flash Flood Warning and Hazard Assessment: The 2015 Kali Gandaki Landslide Dam Breach in Nepal

The 2015 magnitude 7.8 Gorkha earthquake and its aftershocks weakened mountain slopes in Nepal. Co- and postseismic landsliding and the formation of landslide-dammed lakes along steeply dissected valleys were widespread, among them a landslide that dammed the Kali Gandaki River. Overtopping of the landslide dam resulted in a flash flood downstream, though casualties were prevented because of timely evacuation of low-lying areas. We hindcast the flood using the BREACH physically based dam-break model for upstream hydrograph generation, and compared the resulting maximum flow rate with those resulting from various empirical formulas and a simplified hydrograph based on published observations. Subsequent modeling of downstream flood propagation was compromised by a coarse-resolution digital elevation model with several artifacts. Thus, we used a digital-elevation-model preprocessing technique that combined carving and smoothing to derive topographic data. We then applied the 1-dimensional HEC-RAS model for downstream flood routing, and compared it to the 2-dimensional Delft-FLOW model. Simulations were validated using rectified frames of a video recorded by a resident during the flood in the village of Beni, allowing estimation of maximum flow depth and speed. Results show that hydrological smoothing is necessary when using coarse topographic data (such as SRTM or ASTER), as using raw topography underestimates flow depth and speed and overestimates flood wave arrival lag time. Results also show that the 2-dimensional model produces more accurate results than the 1-dimensional model but the 1-dimensional model generates a more conservative result and can be run in a much shorter time. Therefore, a 2-dimensional model is recommended for hazard assessment and planning, whereas a 1-dimensional model would facilitate real-time warning declaration.

Spatial and temporal analyses of post-seismic landslide changes near the epicentre of the Wenchuan earthquake

Major earthquakes in mountain regions have persistent and significant influences on post-seismic landslides but their details have not been well understood. This work uses multi-year high-resolution satellite images and terrain parameters, such as elevation, slope, and aspect, to examine the topographic changes of post-seismic landslides. Despite disturbances during rainy months, landslide areas decreased significantly from 2008 to 2013 in all terrain parameters, indicating that landslide activity near the epicentre has been recovering to the pre-seismic level. The emergence of an increasingly active landslide type shows that landslide debris has been moving from hillslopes to valleys, which could impact post-seismic debris flows. The findings of this work provide important information for post-seismic infrastructure re-construction and disaster prevention in future mountain earthquake events.

Geomorphic and geologic controls of geohazards induced by Nepal's 2015 Gorkha earthquake.

The Gorkha earthquake (magnitude 7.8) on 25 April 2015 and later aftershocks struck South Asia, killing ~9000 people and damaging a large region. Supported by a large campaign of responsive satellite data acquisitions over the earthquake disaster zone, our team undertook a satellite image survey of the earthquakes' induced geohazards in Nepal and China and an assessment of the geomorphic, tectonic, and lithologic controls on quake-induced landslides. Timely analysis and communication aided response and recovery and informed decision-makers. We mapped 4312 coseismic and postseismic landslides. We also surveyed 491 glacier lakes for earthquake damage but found only nine landslide-impacted lakes and no visible satellite evidence of outbursts. Landslide densities correlate with slope, peak ground acceleration, surface downdrop, and specific metamorphic lithologies and large plutonic intrusions.

A 2000 yr rupture history for the Alpine fault derived from Lake Ellery, South Island, New Zealand

Determining the earthquake segmentation of plate-boundary transform faults remains a scientific challenge because paleoseismic data sets rarely resolve the end points of past ruptures. In this study, we test whether lacustrine paleoseismology can be used to assess rupture end points and the earthquake segmentation of the Alpine fault, one of the longest and fastest-slipping plate-boundary transform faults on Earth. Sediment cores from Lake Ellery record eight episodes of high-intensity shaking (modified Mercalli intensity [MM] IX) from Alpine fault earthquakes as event sequences of a turbidite produced by coseismic subaqueous mass wasting, overlain by deposits representing sediment flux from co- and postseismic landsliding in the fluvial catchment. Age-depth modeling constrains the timing of shaking events at a decadal resolution, facilitating correlation with two previously published lake records to reconstruct the spatial distribution of MM IX shaking along ~150 km of the Alpine fault. When resolved with existing on- and near-fault paleoseismic records, the lake data set demonstrates that independent ruptures of the South Westland and Central segments occurred in A.D. 845–775 and A.D. 739–646, and A.D. 646–592 and A.D. 416–370, respectively. Lakes adjacent to the Alpine fault provide paleoseismic records with sufficient spatial and temporal resolution to define along-strike differences in the pattern of rupture capable of distinguishing rupture termination at a geometric segment boundary. This multilake study suggests that locating the end points of ruptures using lacustrine paleoseismology will be most applicable in midlatitude convergent plate-boundary settings where along-strike topography and Quaternary glaciation have resulted in the widespread distribution of suitable lakes.

Spatial distributions of earthquake-induced landslides and hillslope preconditioning in the northwest South Island, New Zealand

Abstract. Current models to explain regional-scale landslide events are not able to account for the possible effects of the legacy of previous earthquakes, which have triggered landslides in the past and are known to drive damage accumulation in brittle hillslope materials. This paper tests the hypothesis that spatial distributions of earthquake-induced landslides are determined by both the conditions at the time of the triggering earthquake (time-independent factors) and the legacy of past events (time-dependent factors). To explore this, we under\\-take an analysis of failures triggered by the 1929 Buller and 1968 Inangahua earthquakes, in the northwest South Island of New Zealand. The spatial extents of landslides triggered by these events were in part coincident. Spatial distributions of earthquake-triggered landslides are determined by a combination of earthquake and local characteristics, which influence the dynamic response of hillslopes. To identify the influence of a legacy from past events, we first use logistic regression to control for the effects of time-independent variables. Through this analysis we find that seismic ground motion, hillslope gradient, lithology, and the effects of topographic amplification caused by ridge- and slope-scale topography exhibit a consistent influence on the spatial distribution of landslides in both earthquakes. We then assess whether variability unexplained by these variables may be attributed to the legacy of past events. Our results suggest that hillslopes in regions that experienced strong ground motions in 1929 were more likely to fail in 1968 than would be expected on the basis of time-independent factors alone. This effect is consistent with our hypothesis that unfailed hillslopes in the 1929 earthquake were weakened by damage accumulated during this earthquake and its associated aftershock sequence, which influenced the behaviour of the landscape in the 1968 earthquake. While our results are tentative, they suggest that the damage legacy of large earthquakes may persist in parts of the landscape for much longer than observed sub-decadal periods of post-seismic landslide activity and sediment evacuation. Consequently, a lack of knowledge of the damage state of hillslopes in a landscape potentially represents an important source of uncertainty when assessing landslide susceptibility. Constraining the damage history of hillslopes, through analysis of historical events, therefore provides a potential means of reducing this uncertainty.