Slope-forming Material Research Articles

Rock-fall runout simulation using a QGIS plugin along north–west coast of Malta (Mediterranean Sea)

Coastal instability in the form of rock fall is widespread along the northern coasts of Malta and is strictly connected to structural controls, such as lithology and tectonics. The local geological and geomorphological setting combined with extreme weather events, whose spatial and temporal occurrence is enhanced by ongoing climate and land use change, determines rock-fall hazard along the north–west coast of Malta, a hotspot for Mediterranean tourism. The present research portrays the results of a pilot study aimed at analyzing rock-fall runout probability along this stretch of coast. Cliffs and downslope terrains were the object of detailed field surveys. This included the detection of persistent joints in the source areas and the identification of slope-forming materials like debris and boulders present along the downslope terrains. The outcomes of the field surveys and GIS-based processing of topographic information were used for identification of the input parameters for rock-fall runout simulation. The latter was performed using a QGIS based plugin (QPROTO) that allows to determine expected runout extents and assess the rock-fall susceptibility. The result is the characterization and mapping of rock-fall runout probability zones along six investigated sites. The outputs of the research and the replicability of the method can be of interest for authorities aiming at defining risk management actions and undertaking mitigation measures compliant with sustainable development of coastal areas.

Analisis Faktor Keamanan Dan Probabilitas Kelongsoran Lereng Di Jalan Batu Besaung Kelurahan Sempaja Utara Kecamatan Samarinda Utara Kota Samarinda Provinsi Kalimantan Timur

A slope is an area of ​​morphology that has a certain geometry, namely the highest and lowest parts and has the potential for landslides if it is in an unstable condition (Wesley & Pranyoto, 2010 in Khodijah, et al, 2022). A slope can be composed of soil, rock, or both. Slope stability is influenced by slope geometry, physical and mechanical characteristics of the slope-forming material, water (hydrology and hydrogeology), rock weak plane structure (location, direction, frequency, mechanical characteristics), natural stresses in the rock mass, local stress concentrations, vibrations ( natural: earthquakes; and human actions: effects of blasting, effects of heavy equipment passing by), climate, the results of mine workers' actions, and thermic effects (Moshab, 1997 in Arif, 2016).

Sustainable rural infrastructure: guidelines for roadside slope excavation

The construction of non-engineered, equipment-based rural roads in Nepal Himalaya is one of the predominant causes of landslides. The construction frequency of such roads has significantly increased over the past decade. However, the present guidelines governing slope excavation for these roads are not based on geotechnical characterizations of sites. The current study uses the limit equilibrium method with the Mohr–Coulomb constitutive model to determine safe cut heights and slopes for varying geometric and material parameters. GeoStudio Slope/W was used to model soil slopes with various gradients, and cuts with varying depths and slope angles were modeled to calculate the factor of safety (FoS) against shear failure for different geometric and material conditions. The results of the study were visualized in design charts with FoS as the dependent variable. The analysis highlights the importance of different parameters, i.e., excavation depth, excavation slope, and existing ground slope in the FoS, in addition to the slope-forming material. Furthermore, a field study was carried out to validate the model using the clustering approach. The results from the field are similar to those from the numerical model, although some additional site-specific parameters like vegetation cover and surface runoff conditions should be considered before selecting the cut slope. Finally, this study proposes that future road construction guidelines should consider terrain parameters, hydrology, and geotechnical site conditions to promote sustainable road infrastructure and reduce future disaster risks in the Himalayan region.

PERENCANAAN PENCEGAHAN TANAH LONGSOR DENGAN METODE DINDING PENAHAN TANAH

A landslide is the displacement of slope-forming material in the form of rock, material, soil, or mixed material moving down or out of the slope. The causes of landslides vary from one location to another. The purpose of this study is to determine the characteristics of soil mechanics in determining the carrying capacity of the soil in planning landslide handling with the method of building a retaining wall. The methods used in this study started from visual identification, field testing and laboratory testing. The results of this study obtained that the condition of the soil at the coordinate point S.02041'47.25" ; E.118052'48.97'' Mamuju of West Sulawesi Province in the form of limestone, loose and sandy chunks based on the test results of the core drilling soil laboratory so that a good type of construction is recommended is to use a semi-gravity type soil retaining wall.

IDENTIFIKASI TINGKAT KERAWANAN TANAH LONGSOR DI AJIBARANG BANYUMAS MENGGUNAKAN METODE SKORING

Landslide is a form of natural phenomenon that often occurs in mountainous and hilly regions with steep up to very steep slopes. Landslide is the movement of slope-forming materials in the form of rocks, debris, soil or materials down the slope. This study aimed to identify the distribution of landslide-prone areas in Ajibarang, Banyumas Regency. The research was conducted by survey method. The model used to determine landslide-prone areas was the Stories Index Model approach. Analysis of geophysical factors was based on SPOT-5 image data and the Indonesia Topographical Map (RBI Map). Identification of land geophysical factors for susceptibility level was determined according to geological map, slope map, soil type map and land use map. The results showed that the level of landslide susceptibility in the study area was divided into 4 classes, namely very low (3.733,41 ha), low (3.303,73 ha), moderate (123,49 ha) and high (150,37 ha).

Gambaran Tingkat Pengetahuan Tentang Mitigasi Bencana Tanah Longsor pada Remaja di Desa Jeruk Selo Boyolali

Landslides are the movement of slope-forming materials in the form of rocks, debris, soil, or mixed materials that move down or out of the slope. Lack of public knowledge on handling emergency response, mitigation, and disaster preparedness can cause a lot of losses. This problem has been recorded since 2020, 572 landslides have been found with landslide-prone locations in Indonesia totaling 6,664 areas. Anticipation of landslides can be overcome by providing education on disaster risk management by providing landslide disaster mitigation. The purpose of this study was to describe the level of knowledge about landslide disaster mitigation among adolescents in Dayu hamlet, Jeruk village, Selo sub-district, Boyolali district. This study uses quantitative descriptive with the number of respondents as many as 50 teenagers who were selected based on total sampling technique. The analytical method used is univariate analysis. The study showed that the level of knowledge of adolescents regarding landslide disaster mitigation was found to be 88% (44 respondents) with good knowledge. The level of knowledge of adolescents related to landslide disaster mitigation in Dayu hamlet, Jeruk village, Selo sub-district, Boyolali district, was mostly well-informed.

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.

Negligence of Geological Investigations Site Leading to Slope Failure Incidents: A Case Study From Saih Al Ahmar in Bidbid, Northern Oman

This paper describes and analyzes a recent slope failure alongside Saih Al Ahmar water storage tank in Bidbid, and identifies the natural and induced causes of the landslide. Our analysis demonstrates that the landslide in Bidbid was the result of several combined factors: slope-forming materials, distribution of geological discontinuities and disturbance by human activities. Moreover, field observations, satellite imagery and geology of the study area indicate that the major factors which caused the landslide are the steep slope excavation along the developed tensional faults, the material in the slide ranging from talus deposits to interlayered peridotite and gabbro, cutting perpendicular to slope talus and removal of the toe of the slope. The slope failure and other stability concerns in the subsurface threatening the structural integrity of water storage infrastructure would not have arisen if the geology of the area had been carefully taken into account before the excavation phase. Landslide hazard assessment in the water tank area and its surrounding is necessary to manage the landslide risk. Proper measures should also be adopted to mitigate the impact and to avoid further failure in the slope already on the verge of movement by rainfall.

VETIVER ROOT PLANTING FOR PREVENTION AND MITIGATION OF LANDSLIDES IN DISASTER-PRONE AREAS, NGANJUK, EAST JAVA

Landslide is the transfer of slope-forming material in the form of rocks, debris, soil moving down or out of the slope. Geolologically, landslides are a geological phenomenon with a movement of land such as falling rocks or large lumps of land (Nandi, 2007). The majority of Nganjuk Regency, East Java, is at high risk of landslides. Reporting from Tirto.id news on February 19, 2021, there was a landslide in Ngetos Subdistrict, Nganjuk which claimed many victims. Nineteen people died, 20 were injured and 10 houses were severely damaged. Ngetos village is the largest village with the most populous population in Nganjuk. Unit of Natural Disease Support from Faculty of Medicine, Community Service Team of the Department of Anesthesiology and Reanimation Faculty of Medicine Universitas Airlangga in collaboration with the Center of Environmental Health Engineering and Disease Control (BBTKLPP) Surabaya in efforts to overcome landslide disasters that occurred in Nganjuk. Assistance provided includes medical assistance and environmental development as one of the disaster mitigation efforts. One of the mitigation measures carried out through this activity is reforestation by planting vetiver roots. Vetiver Roots are known as landslide prevention plants because their roots can reach depths soil of down to 5 meters. One of the causes of landslides is the lack of vegetation on the ground so it is prone to movement, especially if it rains heavily because there is no anchoring. Therefore, this activity is considered important to prevent repeated landslides.

Identification of submarine landslides in the Colombian Caribbean Margin (Southern Sinú Fold Belt) using seismic investigations

Submarine landslides can be triggered by several processes and involve a variety of mechanisms. These phenomena are important sediment transport processes, but they also constitute a significant geohazard. Mapping of the southwestern Caribbean Sea using 3D seismic data has allowed identification of several submarine landslides in the Colombian Margin in the area dominated by the Southern Sinú Fold Belt (SSFB). A poststack depth-migrated seismic cube survey with a 12.5 by 12.5 m bin spacing was used to identify landslides in an area covering 5746 km2. Landslides were interpreted using a seafloor morphologic parameter identification process and the internal deformation of the slope-forming material, as seen from seismic data. A total of 93 landslides were identified and classified based on their movement styles as follows: 52 rotational, 29 translational, and 12 complex landslides. In addition, 12 distinct deformational zones and a zone of mass transport complex (MTC) were identified. Five different ground condition terrains were interpreted based on landslide type and distribution as well as in geologic structures and seismic reflection analysis. Two main processes seem to influence landslides in the study area. First is the folding and faulting involved in the SSFB evolution. This process results in oversteepened slopes that start as deformational zones and then fail as translational or rotational slides. Those individual landslides progressively become complex landslide zones that follow geologic structural orientation. Second is the continental shelf break erosion by debris flows, which fills in intraslope subbasins and continental rise with several MTCs. According to the results, risk of damage by landslides increases in distances shorter than 4 km along structural ridge foothills in the study zone.

GIS-Based Soft Computing Models for Landslide Susceptibility Mapping: A Case Study of Pithoragarh District, Uttarakhand State, India

The main objective of the study was to investigate performance of three soft computing models: Naïve Bayes (NB), Multilayer Perceptron (MLP) neural network classifier, and Alternating Decision Tree (ADT) in landslide susceptibility mapping of Pithoragarh District of Uttarakhand State, India. For this purpose, data of 91 past landslide locations and ten landslide influencing factors, namely, slope degree, curvature, aspect, land cover, slope forming materials (SFM), elevation, distance to rivers, geomorphology, overburden depth, and distance to roads were considered in the models study. Thematic maps of the Geological Survey of India (GSI), Google Earth images, and Aster Digital Elevation Model (DEM) were used for the development of landslide susceptibility maps in the Geographic Information System (GIS) environment. Landslide locations data was divided into a 70 : 30 ratio for the training (70%) and testing/validation (30%) of the three models. Standard statistical measures, namely, Positive Predicted Values (PPV), Negative Predicted Values (NPV), Sensitivity, Specificity, Mean Absolute Error (MAE), Root Mean Squire Error (RMSE), and Area under the ROC Curve (AUC) were used for the evaluation of the models. All the three soft computing models used in this study have shown good performance in the accurate development of landslide susceptibility maps, but performance of the ADT and MLP is better than NB. Therefore, these models can be used for the construction of accurate landslide susceptibility maps in other landslide-prone areas also.

Mineralogical and physico-chemical properties of halloysite-bearing slip surface material from a landslide during the 2018 Eastern Iburi earthquake, Hokkaido

Destructive landslides were triggered by the 6.7 Mw Eastern Iburi earthquake that struck southern Hokkaido, Japan, on 6 September 2018. Heavy rainfall on 4 September in addition to intermittent rainfall around the Iburi Tobu area saturated and weakened the slope-forming materials (mostly altered volcanoclastic soils), making them susceptible to failure because of the earthquake’s strong ground motion. Most of the shallow landslides exhibited long runouts along gentle hill slopes, with characteristic halloysite-bearing slip surface at the base of the volcanic soils. This study investigated the mineralogical and physico-chemical properties of the slip surface material with the aim of understanding weakening and post-failure behaviors during the landslides. Halloysite in the slip surface had irregular-to-hollow-spherical morphology with higher mesopore volumes than tubular halloysite, which is related to a high capacity for water retention after rainfall. To reproduce possible chemical changes in the slip surface during rainfall, the sample was immersed in varying amounts of rainwater; solution pH increased and ionic strength decreased with increasing water content. These findings, alongside electrophoretic analysis, suggest that rainwater infiltration could have increased the absolute zeta potential value of the slip surface material. It is suggested that rainfall before the earthquake enhanced the colloidal stability of halloysite particles within the slip surface, owing to an increase in electrostatic repulsion. This decreased the material’s cohesive strength, which might have led to destabilization of the slope during ground shaking generated by the earthquake, and subsequent high-mobility flow after failure.Irregular-to-hollow-spherical halloysite on the slip surface of a shallow landslide triggered by the 6.7 Mw Eastern Iburi earthquake. Rainfall before the earthquake enhanced electrostatic repulsion of halloysite particles (owing to solution pH increase and ionic strength decrease), which might have led to destabilization of the slope.

2-D Cross-Plot Model Analysis Using Integrated Geophysical Methods for Landslides Assessment

The large or small scale of a landslide is a natural, widespread process, resulting from the downward and outward movement of slope-forming materials, such as sculpting the landscape. Characterized landslide material and properties’ inhomogeneities conditions become a challenge as the process required the availability of a wide range of data, observations, and measurements with an evaluation of geological and hydrological conditions. Detailed investigations represent an essential component of the landslide risk mitigation process, relying on subsurface investigations, discrete subsurface sampling, and laboratory tests. To extend this approach, seismic refraction and two-dimensional (2-D) resistivity were utilized to study the landslides activities in Ulu Yam. The cross-plot analysis was introduced to integrate the geophysical results based on the criteria of the model. Velocity distributions from seismic refraction revealed the stiffness of the soil, where weak zones identified with values of Vp ≤ 1200 m/s, defined as threshold frequency for failure to occur. The 2-D resistivity shows that the weak zones were identified with resistivity values of <1200 Ωm. The 2-D cross-plot model gives a comprehensive interpretation where a low velocity and resistivity value represents the failure plane of materials to failure. The volume of mass sliding was calculated based on retrieved information from the model.

Application of geoelectrical methods for identification of soil layer

Landslide is a geological event caused by the movement of rock or land mass that can be defined as the displacement of slope-forming material, which is the original rock as well as the other material that is moving with the gravity. The factors that influence landslides are soil layer, slip surface and saturated soil. Mapping or determining the landslide area is done by identifying several parameters that can trigger landslide. The geophysical method that can be used to analyse soil layer is resistance type of geoelectrical. Variations of each rock or soil layer resistance below the measuring point can be obtained from the measurements of current and potential differences. The research site is located East Aceh district, Indonesia. Geoelectrical measurements using Wenner-Schlumberger electrode configuration. Based on geological information, field observation and geophysical measuring results, the area is dominated by clay, sand and gravel material. Lithology of clay dominates the underside of the surface (until the depth of ± 30 meters. water that is held in sand lithology causes saturation of the sand. this is because there is a layer of clay under the sand which has low permeability or even impermeable properties. Saturated sand lithology can lead to contact between particles and has the potential to weaken it, causing soil movement.

Investigasi Pendugaan Gerakan Tanah Menggunakan Metode Electrical Resistivity Tomography dan Self Potential di Daerah Pasanggrahan Baru, Sumedang Selatan

Land movement occur because of the movement of slope-forming material such as of soil, rock or a combination of material types to a place that is lower due to the influence of gravity. The movement of slope material can be identified by the Electrical Resistivity Tomography (ERT) Method, because this method has good lateral and vertical resolution based on rock resistivity data. The trigger factors for land movement in Anjung Village, Pasanggrahan Baru, South Sumedang, among others: an increase in water content on the slopes and the slip plane. Increased water content is influenced by infiltration of rainwater as one of the triggers of land movement, can be detected by the Self Potential method (SP), while the slip plane can be detected by the method of Electrical Resistivity Tomography (ERT). Based on the results of the ERT and SP measurements, the results are: debris flow as a landslide plane (resistivity values: 31 – 170 Ohm.m and SP values: 5 – 13 mV), water table/water saturated layer (resistivity values: 1 – 13 Ohm.m and SP values: 14 – 34 mV), and breccias (resistivity values: 400 - 900 Ohm.m and SP values: 1-3 mV).Slip plane are estimated to be at boundary between the breccia and the material on it.Keywords: Land movement, resistivity, self potential, South Sumedang

Landslide investigation using self potential method and electrical resistivity tomography (Pasanggrahan, South Sumedang, Indonesia)

Landslide is a geological event that occurs because the movement of slope-forming material in the form of soil, rock or combination of material type to a lower place due to the influence of gravity. The trigger factor of landslide in Pasanggrahan, South Sumedang, Indonesia is the increase of water content in the slope and the slip plane. The slip plane began to actively to turn on when the rainy season arrives. The infiltration of rainwater into slopes as an avalanche trigger can be detected by Self Potential (SP) method. SP measurements were performed to determine changes in subsurface water flow. SP data acquisition using fixed base technique and leap frog technique. The rocks in the research area that serve as the slip plane are clays associated with Volcanic Breccia. One of the geophysical methods that can identify the slip plane is the Electrical Resistivity Tomography Method. The ERT method can detect slip plane based on rock resistivity. Based on the local geology that has been correlated with the value of Self Potential and Electrical Resistivity Tomography, the following results are obtained: water table : (1 - 13) Ohm.m and SP value : (16 - 50) mV, clay : (72 - 100) Ohm.m and volcanic breccia: (171 - 550) Ohm.m.

A review on mechanism of rainwater in triggering landslide

Landslide could be evaluated as a very serious issue in tropical countries due to its hazardous impact on lives and properties. One of the factors influencing to the development of landslides is the rainfall infiltration which is considered as a major triggering factor. It decreases the matric suction, increases the pore-water pressure and causes the groundwater table to rise. This paper is reviewing the mechanism of rainfall induced slope failure, the effect of rainfall infiltration, soil suction and the rise of groundwater table on slope stability. The results show high rainfall intensity infiltrates initially in a higher rate than soil permeability and develops a perched water table which induces shallow landslide. While, low rainfall intensity for a longer period is more dangerous than heavy rain for a short period. It increases the saturation of the soil and causes the matric suction to dissipate and this triggers landslide. Moreover, the review reveals that the factor of safety increases when the initial soil suction at the ground surface is high. The rise of groundwater increases the pore-water pressure and soften the slope-forming material and leads to landslide.

MECHANISM AND CHARACTERISTICS OF THE LANDSLIDES IN BONE BOLANGO REGENCY, GORONTALO PROVINCE, INDONESIA

One of the regencies in Gorontalo Province, Indonesia, Bone Bolango is an area in which landslides occur frequently. This study was at identifying the mechanism and characteristics of landslides in Bone Bolango Regency. This study is important to minimize hazards caused by this disaster. Data were obtained from the results of site survey, surface geological survey and geotechnical investigation. Cohesion during the dry season ranged between 0-15kPa, and the angle of internal friction ranged between 30 o -44 o . The topography of this area indicates a steep slope (>40°), with weathered rock and discontinuity. These internal factors made the slopes prone to landslide. Meanwhile, external factors that trigger landslides are high precipitation (>100mm), the absence of vegetation covering the slopes, as well as land use on the slopes. In general, the types of the landslide in the study area were debris flows, rotational slides, and rock falls. At the period of high precipitation, the rate of infiltration of rainwater into the soil was slower than the rate of the increase in the volume of rainwater deposited and flowing into the slope surface, resulting in the debris flow. Slope-forming material became soft due to the rise of groundwater levels. This caused a decrease in shear strength and pore water pressure that turned into positive. In the rock slope, rainwater filled the crack of slope discontinuity area so that rock got loose and fell freely. Therefore, a further research is necessary to conduct in order to determine the most accurate and efficient method for slope stability.

A Multistage Technique to Minimize Overestimations of Slope Susceptibility at Large Spatial Scales

Rainfall induced landslides are one of the most frequent natural hazards on slanted terrains. They lead to significant economic losses and fatalities worldwide. Most factors inducing shallow landslides are local and can only be mapped with high levels of uncertainty at larger scales. This work presents an attempt to determine slope instability using buffer and threshold techniques to downscale large areas and minimize slope uncertainties at local scales, then in a second stage, logistic regression is used to determine susceptibility at large scales. ASTER GDEM V2 is used for topographical characterization of slope and buffer analysis. Four static parameters (slope angle, soil type, land cover and elevation) for 230 shallow rainfall-induced landslides listed in a comprehensive landslide inventory for the continental United States are examined. A delimiting buffer equivalent to 5, 25 or 50 km is created around each landslide event facilitating the statistical analysis of slope thresholds. Slope angle thresholds at the pixel points 50, 75, 95, 99 and maximum percentiles are compared to one another and tested for best fit in a logistic regression environment. It is determined that values lower than the 75-percentile threshold misrepresents susceptible slope angles by not including slopes higher than 35°. Best range of slope angles and regression fit can be achieved when utilizing the 99 percentile slope angle threshold. The resulting logistic regression model predicts the highest number of cases correctly with 97.2% accuracy. The logistic regression model is carried over to ArcGIS where all variables are processed based on their corresponding coefficients. A regional landslide probability map for the continental United States is created and analyzed against the available landslide records and their spatial distributions. It is expected that future inclusion of dynamic parameters like precipitation and other proxies like soil moisture into the model will further improve accuracy. Keywords: Shallow landslides; Slope instability; Threshold analysis; Logistic regression; Regional analysis; GIS; Remote sensing Introduction Rainfall induced landslides are one of the most frequent natural hazards on slanted terrains. They usually result in great economic losses and fatalities globally. Worldwide at least 32,322 deaths between 2004 and 2010 have been reported [1] and in the United States alone, landslides cause $1-2 billion in damages and more than 25 fatalities in average each year [2]. Understanding, mapping, modeling and preventing the aftermath of these devastating events represents an important scientific and operational endeavor [3]. The term “Landslide” describes the downward and outward movement of slope-forming materials that include rock, earth, and debris or a combination of these [4]. Although landslides are considered to be dependent on the complex interaction of several static and dynamic factors [5-7] slope angle has great influence on the susceptibility of a slope to sliding. Increased slope angle usually correlates to increased likelihood of failure even if the material distribution on the slope is uniform and isotropic [5]. Undeniably, many other parameters are essential to the analysis of landslide risk. For example, changes in land use and land cover such as deforestation, forest logging, road construction, cultivation and fire on steep slopes can have a significant effect on landslide activity [8]. In addition, forest vegetation

Rainfall intensity–duration thresholds for the initiation of landslides in Zhejiang Province, China

Zhejiang Province, located in the southeast coastal region of China, is highly prone to rainfall-triggered landslides because of its geologic, geomorphologic, and climatic settings. The rainfall–landslide relationship is critically important for predicting rainfall-induced landslides. This study defines landslide-triggering rainfall intensity–duration thresholds for the entire Zhejiang region; and the 62 individual areas that comprise the region, based on 1569 shallow landslides which occurred from 1990 to 2013 and their corresponding detail rainfall records from 2457 rain gauges in the region. The results indicate that the rainfall thresholds vary spatially over the region. For rainfall durations from 1 to 24h, the threshold tends to increase from the northwestern part of Zhejiang to its southeastern coastal region; and it is lower in the central and coastal hill–basin regions than that in the western and southern mountainous regions. Variability of the threshold in space is mainly affected by the slope-forming materials and terrain slope gradients. Different soil types have different thresholds, and the thresholds for weathered rock slides are generally higher than those for soil slides. For the soil–weathered rock on slopes, the slope gradient has no obvious influence on the thresholds when the slope angle is <30°; the thresholds have an obviously increasing trend with the increase of slope angles in the range of slope angles from 30 to about 40°; and when slope angle is larger than about 40°, the thresholds rapidly decrease with gradient on the whole. These findings will facilitate the improvement of warning systems for regional rainfall-triggered landslides.