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On January 18, 2021, a moderate earthquake (Mw 6.5) occurred ~ 45 km southwest of San Juan, a city in Central-Western Argentina, at a relatively shallow depth of ~ 20 km. The earthquake caused damage to the environment and infrastructure in the affected area, which is home to ~ 600,000 residents. To assess ground deformation, identify the seismogenic source, and evaluate the extent of secondary effects, we utilized Differential Synthetic Aperture Radar Interferometry (DInSAR) techniques in combination with Sentinel-2 visible and infrared imagery, as well as field data. DInSAR results suggested centimeter-scale ground deformation around the epicenter, off-fault deformation linked to regional structures, and site effects, such as liquefaction and landslides. By combining the values extracted from a 3-year-long PSI and SBAS time series, we estimated a vertical displacement of approximately 4.5 cm near the epicenter. Off-fault deformation involves some degree of ground settling on top of a blind or buried section of the Papagallos fault system, the reactivation of a section of the Rinconada fault system, and liquefaction and ground settling processes in the Tulum Valley. Rockfalls were distributed throughout a geologically diverse terrain and along a NW swath, with their occurrence controlled by the shaking intensity. The total area affected by secondary effects was ~ 3800 km2. Based on the available focal mechanism solutions and the distribution of environmental damage, we propose a left-lateral strike-slip displacement in a blind NW-striking fault, although different interpretations are discussed. Finally, we estimated the epicentral depth from SBAS time series Bayesian Inversion and from differential travel times pP-P, obtaining a depth of 20–25 km. [ABSTRACT FROM AUTHOR]

On June 10, 2022, an earthquake swarm including three major earthquakes with magnitudes of Ms5.8, Ms6.0, and Ms5.2 occurred in Maerkang, Sichuan, China. According to statistics, at least 650 landslides have been triggered by this earthquake, with a total area of 1.2 km2. In this study, the spatial distribution of these landslides and their correlation with seismic, topographic, and geological factors were analyzed based on the coseismic landslide inventory. The results show that landslides are mainly distributed on the northeast side of the Songgang-Fubianhe fault (SG-FBHF), which is a VII intensity area. The closer to the epicenter, the more concentrated the landslide distribution. The landslide density increases significantly with increasing slope. The strata of the Upper Triassic Zhuwo Formation are more prone to coseismic landslide occurrence. Our results, when combined with the focal mechanism solution, precise location of aftershocks, and geological characteristics of the SG-FBHF, suggest that this earthquake is a left-lateral strike-slip earthquake along the SG-FBHF, and the seismogenic fault is slightly tilted to the northeast. In addition, nearly 70% of coseismic landslides are concentrated in the extreme seismic area of ~ 225km2, indicating that the seismic energy release is highly concentrated. This work analyzed the distribution of landslides triggered by a moderately strong earthquake swarm, providing a typical case for researchers to understand the spatial distribution pattern of earthquake-triggered landslides and a scientific support for disaster prevention of coseismic landslides in southwestern Sichuan, China. [ABSTRACT FROM AUTHOR]

A major earthquake (6.9 Moment magnitude) occurred in the Sikkim and Darjeeling areas of the Indian Himalaya as well as in the adjacent Nepal on 18th September 2011, triggering a large number of landslides. A total of 188 landslide locations were extracted in order to create the landslide inventory map (LIM). The earthquake-induced landslide susceptibility maps (LSMs) were created using an Artificial Neural Network (ANN) model and three novel deep learning approaches (DLAs), namely Deep Boosting (DB), Deep Learning Neural Network (DLNN), and Deep Learning Tree (DLT), as well as training points and 22 conditioning factors. The earthquake-induced LSMs validated using several statistical indices and the results showed optimal accuracy for all models, where DB yielding the highest prediction rate curve (PRC) of 98.5%. This is followed by DLT (97%), DLNN (96%), and ANN (91%). The results demonstrate maximum efficacy of the proposed earthquake-induced LSM. [ABSTRACT FROM AUTHOR]

During an earthquake sequence, there are often multiple recurring landslides. Understanding the spatial distribution of the landslides triggered by the first earthquake can help us predict the landslide susceptibility for subsequent shakes over a short term. This study used two landslide inventories from the Lombok earthquake sequence in Indonesia in 2018 to construct a short-term secondary disaster prediction model and an overall spatial prediction model using four machine learning algorithms. The average accuracy of the positive samples predicted by the prediction model was 7.1% lower than that of the short-term model. The highest accuracy of the overall prediction model was 14.9% higher, on average, and the area under the ROC curve (AUC) score was 8.1% higher, on average, but the corresponding probability thresholds were lower. The reason for this difference is that, in the short-term prediction model, since most of the landslides in the first landslide inventory were prone to fail two or more times due to the effect of multiple earthquakes, the prediction results have a high positive rate. This feature of the short-term prediction model makes it suitable for landslide rescue guidance in a sequence of earthquakes. In contrast, the overall prediction model can better represent the spatial distribution of the earthquake-triggered landslides in the area. [ABSTRACT FROM AUTHOR]

Quantifying the magnitude of an earthquake is very important for long-term and medium-term earthquake prediction, post-earthquake emergency rescue and seismic hazard assessment. Paleo-seismology is the investigation of past earthquakes in the geological record, in particular their location, timing and size. Uncertainties remain in the paleo-earthquake magnitudes determined by traditional surface rupture parameters, especially because most seismic events do not result in surface ruptures or are of less than 0.3 m (M = ~ 6–6.8). To address the problem of magnitude evaluation of earthquakes that did not reveal major dislocations, this paper deals with the methods used to determine the seismic shaking intensity based on the types and forms of soft-sediment deformation structures, including maximum liquefaction distance, thickness of disturbed layer, empirical formulae, and thickness of rapidly deposited sand layer. Then we discuss and analyze these methods in terms of their theoretical basis, advantages and disadvantages, accuracy, applicability and problems. We chose two case studies: first, a typical seismics-related deposit (liquefied layer and disrupted layer) represented by a seismite in the late-Pleistocene Lake Lisan section near Masada in the Dead Sea Basin; and second, the liquefied diapir triggered by an earthquake in the late-Quaternary lacustrine sediments at Luobozhai in the upper reaches of the Minjiang River, East Tibet. The five methods listed above are employed to determine earthquake magnitudes associated with the seismics-related deposit and liquefied diapir, yielding magnitudes of 5.5–6.5 and 6.0–7.0, respectively. The combination of the five methods, provided a new and relatively convenient method for determining seismic shaking, especially in lacustrine sediments. This study can serve as a valid reference for comparing methods of calculating the magnitude of a paleo-earthquake based on surface rupture parameters, and provides a better understanding of the long-term seismic activity and risk in tectonically active regions. [ABSTRACT FROM AUTHOR]

Landslides are the main secondary effects of earthquakes in mountainous areas. The spatial distribution of these landslides is controlled by the local seismic ground motion and the local slope stability. While gravitational instabilities in arid and semi-arid environments are understudied, we document the landslides triggered by the Sarpol Zahab earthquake (November 12, 2017, Mw7.3, Iran/Iraq border), the largest event ever recorded in the semi-arid Zagros Mountains. An original earthquake-induced landslide inventory was derived, encompassing landslides of various sizes and velocities (from rapid disrupted rockfalls to slow-moving coherent landslides). This inventory confirms the low level of triggered landslides in semi-arid environments. It also displays clear differences in the spatial and volumetric distributions of earthquake-induced landslides, having 386 rockfalls of limited size triggered around the epicenter, and 9 giant (areas of ca. 106 m2) active and ancient deep-seated landslides coseismically accelerated at locations up to 180 km from the epicenter. This unusual distant triggering is discussed and interpreted as an interaction between the earthquake source properties and the local geological conditions, emphasizing the key role of seismic ground motion variability at short spatial scales in triggering landslides. Finally, the study documents the kinematics of slow-moving ancient landslides accelerated by earthquakes, and opens up new perspectives for studying landslide triggering over short (~ 1–10 years) and long-time (~ 1000–10,000 years) periods. [ABSTRACT FROM AUTHOR]

On August 16th, 2018, a Mw 5.1 earthquake struck the Molise region (central Italy), inducing 84 earthquake-triggered landslides that predominantly involved soil covers of clayey materials and flysch on gently dipping slopes. To quantify the spatiotemporal landslide activity in the months immediately after the earthquake, a differential SAR interferometry (DInSAR) analysis was performed for a time span from 2 years before to one year after the earthquake, recognising both first-time and reactivated landslides. The results showed a clear increase in landslide activity following the low-magnitude earthquake with respect to the activities recorded in the same months of the previous years. Several coherent landslides (earth slides and earth flows) were observed following seasonally recurrent rainfall events. Such increases were observed for both reactivated and first-time landslides, showing decreases in inactive periods and activity over longer periods. Furthermore, the spatial density distribution of the landslides was investigated in the postseismic time interval along transects perpendicular and parallel to the direction of the tectonic element responsible for the seismic event. An asymmetrical distribution was deduced parallel to the fault strike with a higher number of landslides located inside the compressional sector according to a strike-slip faulting mechanism. [ABSTRACT FROM AUTHOR]

On 7th of August 2020, a Mw = 4.9 earthquake occurred in Mila province (Northeast Algeria). Consequently, more than 2000 houses were indirectly affected (partially damaged or collapsed) within 10 km from the earthquake's epicenter, in the locality of El Kherba. According to field surveys conducted 3 days after the earthquake, damages and casualties were directly linked to an earthquake-induced landslide that occurred after the main shock. This was evidenced by numerous cracks in the site's soil mainly perpendicular to the landslide direction. Local characteristics (i.e., geology, geomorphology) and anthropogenic activities expose this area to landslide hazard. This study shows the reliability of the ambient noise horizontal to vertical spectral ratio (HVSR) method in the characterization of an active landslide. Ambient noise records were processed through spectral ratio techniques to identify the landslide's geometry based on spectral responses analysis. The obtained results allowed the landslide's slip surface mapping and boundary delineation, which correlates well with the field observations. After the rotation of the signal's horizontal components, large variations in the experimental spectral ratios, in both amplitude and direction, revealed site effects (soil remoulding, crack network) on the soil dynamic behavior. [ABSTRACT FROM AUTHOR]

Earthquake-triggered landslides are common disasters of active mountain belts. Due to the lack of earthquake-triggered landslide inventory in Taiwan, it is not intuitive to observe spatial relationships and discover unique patterns between landslides and essential triggers. We examined strong earthquake events in Taiwan after the 1999 Mw7.6 Chi-Chi earthquake and targeted the 2013 ML6.5 Nantou earthquake to create the landslide inventory. We adopted two Landsat-8 satellite images before and after the event to detect landslides, and incorporated a 20-m DEM and rock type data of Taiwan to represent key factors triggering earthquake-induced landslides such as peak ground acceleration (PGA), lithology, slope roughness, slope, and aspect. Based on the analysis of the density of landslides, there are strong correlations between the landslide occurrence and seismic and geomorphic factors. Furthermore, we noticed that the landslide aspects have a systematic tendency towards the northeast, which is not correlated with the dip directions and wave propagation directions. Instead, we found that the northeastward landslide aspect is more associated with the westward–southwestward surface movement at the landslides. We found that the included angles between the landslide aspects and the displacement directions for all the landslides are ~ 100°–180°. The relationship indicated that the coseismic deformation of the Nantou earthquake may play a role in the landslide distribution. [ABSTRACT FROM AUTHOR]

The correlation of coseismic landslides with the seismic and morphological parameters has been investigated in detail by many researchers, mainly after the devastating 2008 M8.0 Wenchuan, China earthquake. One of the goals of such studies is to examine the spatial distribution of the earthquake-induced landslides in order to establish a pattern depending on the type of the seismic fault. This research focusses on the island of Lefkada, Ionian Sea, Greece, that is considered one of the most prone to earthquakes regions in Europe due to its proximity to the Cephalonia Transform fault. Landslide data from the two shallow strike-slip faulting earthquakes that occurred on 2003 and 2015 are statistically analyzed in order to evaluate the landslide magnitude and area of slope failures and their frequency-area size distributions. Furthermore, the spatial distribution of failures was investigated in detail regarding its correlation to topography (slope angle, aspect, local relief, elevation), geology, and the characteristics of fault rupture. We conclude that the landslide pattern is not controlled by a single parameter and that it results from a combination and interaction of seismic, morphological, and geological factors. In particular, the parameters of slope angle, geology, and fault rupture/asperities are the ones that are clearly related to the highest landslide densities. [ABSTRACT FROM AUTHOR]

This study is a revised inventory of landslides triggered by the Rudbar-Manjil earthquake (Mw = 7.3), 1990, obtained through the study of Komak Panah and Hafezi Moghadas (1993), interpretations of the stereoscopic aerial photos, and field data. We mapped the 223 coherent landslides with a total area of 11.3 km2 and a calculated volume of 3.8 × 108 m3 using a digital elevation model (DEM, 12.5 m) within the geographical information system (GIS) software. The correlation between landslide occurrence (size and distribution) and the controlling factors was analyzed using the bivariate model and the linear automated modeling (LINEAR) procedure in the SPSS software. Both LINEAR models of landslide volume (LV, m3) and landslide area (LA, m2) indicate the distance from the fault surface rupture is the most influencing factor on size prediction of coseismic landslides. The LA is more dependent on seismic factors, whereas the LV is on the lithology and topographic factors. The result of principal component analysis (PCA) model, using the GIS, showed that most landslides occurred in the red band (including 95% of the variance of controlling factors). Thus, the selected factors to investigate the landslide occurrence are valid and the PCA can be used to identify regions prone to coseismic landslides. The curves of landslide number density (LND, landslides/km2), landslide area percentage (LAP, landslide area/total area%), LA, and LV have a multimodal distribution (several patterns of response) by the topographic and seismic factors. It is recommended that other models be applied to better investigate the local effects of factors on the coseismic landslides. [ABSTRACT FROM AUTHOR]

Charosa and Dehdasht is a part of folded Zagros that is located in the Kohgiluyeh and Boyer-Ahmad Province in southwestern Iran. This area is covered with several Zagros anticlines such as the Kuh-e-Sefid, Sartal, Nil, and Siah. From the geological perspective, the Ilam–Sarvak formation makes the major and high altitudes of the region. Numerous landslides have occurred in the highlands of this area, with the largest known landslides being the Mundan rock avalanche in the Nil anticline with an approximate volume of more than one billion cubic meters and the Almor rock avalanche in the Sartal anticline. This study explores the probable triggering factors of these landslides based on geological studies, seismotectonic studies, and numerical modeling methods. According to the results of this research, between earthquake and groundwater (as the two major landslide-triggering factors), the earthquake was able to cause instability and slip onset. Based on seismic investigations, the Mountain front fault in the vicinity of these anticlines has high seismic potential. So, the occurrence of earthquakes with a 1000-year return period and a minimum 7.3 momentum magnitude is likely triggered by these rock avalanches. The results show that due to favorable geological and topographic conditions of the study area, the earthquake has been able to cause large and catastrophic landslides in the region's history. [ABSTRACT FROM AUTHOR]

We address the modeling of spatial distribution of coseismic landslides, based on an empirical approach applied to both recent and historical well-documented events. We analyze a dataset of 11 historical and recent normal faulting earthquakes in the Italian Central Apennines. Firstly, making use of a kernel density estimator approach, we calculated the regression between the extent of the maximum area affected by landslides (A; km2) and Mw, on the combined dataset of recent and historic earthquakes: Log A = (1.0397 Mw)–3.9288. Then, for recent earthquakes only, we analyzed the attenuation regression of landslide density (Dens; no. of landslides/km2) with distance from surface fault trace (Dfault; meters): Dens = 0.3661 × exp (− 5.053 Dfault). Historical events, still presenting systematically lower values of landslide densities, can be regressed on the same functional form resulting in a similar factor of attenuation with distance but with a different scaling factor. We thus argue that empirical regressions on historical earthquake-triggered landslides can be successfully exported elsewhere if a well-documented catalog is present and a calibration with several recent events can be done. [ABSTRACT FROM AUTHOR]

Geotechnical studies are carried out to investigate the location and magnitude of a prehistoric earthquake in eastern Canada. Previous studies identified 12 sensitive clay landslides of about 1020 cal BP in the Ottawa-Gatineau region, including one of the most disastrous slope failures in eastern Canada. The landslides were hypothesized to have been triggered by an earthquake. In the current study, three of those landslides are investigated to understand their failure mechanisms. The study sites form a triangle of lateral distances of about 38, 38 and 35 km. Micro-seismic surveys, cone penetrometer tests, vane shear tests, soil sampling and laboratory testing are conducted to collect geotechnical data. Slope stability models are constructed to calculate threshold ground accelerations required to trigger the landslides. The ground accelerations are used with Ground-Motion Prediction Equations to triangulate the earthquake. The results indicate an earthquake of a minimum moment magnitude of 5.9 near Eardley, Quebec. [ABSTRACT FROM AUTHOR]

In this study, we present a newly developed, comprehensive dataset of 196 historical earthquakes, including 127 events with known landslide fatality counts, which we use to examine the impact of earthquake-induced landslides. Using this dataset, we assess the potential impact of seismically induced landslides on affected populations, based on the exposure of population to expected landslide occurrence. We calculate predicted landslide probabilities out of a global statistical landslide model in the area surrounding each earthquake using USGS's ShakeMap model of strong ground motion. We identify estimated population exposure by comparing the predicted probability grid with a time-corrected global population dataset to determine a predicted landslide exposure index. We compare these values to the number of actual fatalities for 91 training events and use these comparisons, together with the United Nations Human Development Index as a vulnerability proxy, to develop a multiple regression model that can potentially be used to provide order-of-magnitude estimates of human impact of earthquake-induced landslides. We observe a significant positive correlation between predicted and observed fatalities, but with very high variability in fatality rates for similar exposure levels, suggesting that other factors (e.g., landslide type and density, the effect of urbanization on population exposure) should be used to improve this estimate. We also demonstrate that these estimates of landslide impacts can be used in a deterministic mode, in collaboration with use of scenario earthquakes, to assess the potential impacts of anticipated future events. With further development, these landslide scenarios can be used by vulnerable communities to improve land use planning, structural design, and emergency response in landslide-prone areas. [ABSTRACT FROM AUTHOR]

Seismically triggered landslides can cause great damage to the road construction in mountainous areas. The permanent displacement analysis based on Newmark sliding-block model can evaluate risk of these landslides from the perspective of deformation damage and overall failure probability of slopes. However, the sliding-block model does not consider the attenuation effect of the shear strength on the sliding surface during earthquake, causing the calculated value of Jibson method to be less than the actual value. Therefore, the Newmark model was modified by adding attenuation coefficients to the effective internal friction angle and the effective cohesion of geologic units. The landslide areal density was proposed for hazard zoning with the Wenchuan earthquake data. The results showed that the predicted values agreed well with the real distribution of the landslides triggered by the Lushan earthquake. The proposed hazard zoning method in this paper can predict the severity of seismic landslides in consideration of the environmental changes in mountainous regions after the earthquake and provide support for the site selection in highly seismic areas. [ABSTRACT FROM AUTHOR]

Earthquake-triggered landslides significantly contribute to worsening the impact of seismic events; thus, comprehensive landslide inventories are essential for improving seismic hazard assessment. During complex seismic sequences, landslides are triggered by more than one event and the final inventory reflects the spatial and temporal evolution of the sequence. Here, I analyze the landslides triggered by the 2018 Lombok (Indonesia) seismic sequence. I use high-resolution satellite imagery to map 4823 landslides triggered after the 05/08/2018 event (Mw 6.9) and 9319 landslides after the 19/08/2018 event (Mw 6.9). I analyze the distribution and evolution over time of landslide density and landslide area percentage. Despite the significant increase in number and cumulative area of the landslides, the 05/08 and 19/08 events share the maximum dimension of individual landslides; this suggests that the maximum intensity is equal for the two events, i.e., X on the Environmental Scale Intensity scale. I compare the distribution of landslides with macroseismic information provided by eyewitnesses through online questionnaires. Finally, I investigate the role of earthquake environmental effects within seismic sequences, showing that effects on the natural environment provide complementary information with respect to traditional intensity and felt reports. [ABSTRACT FROM AUTHOR]

Rockfall hazard is a very common phenomenon mainly occurring in mountainous slopes, coastal cliffs, volcanoes, riverside, and trenches. In the present research, a model is developed for hazard analysis of seismic rockfalls on a regional scale. For this purpose, three models including Adaptive Neuro-Fuzzy Inference System (ANFIS), multilayer perceptron artificial neural network (MLP), and radial basis function artificial neural network (RBF) were utilized. Firooz Abad-Kojour earthquake of 2004 was used as the benchmark and the model base. The rockfall-susceptible zones predicted by ANFIS, MLP, and RBF methods were compared with the database (distribution map) of seismic rockfalls. The results showed a good overlap between MLP-predicted rockfall hazard zones and database (distribution map) of seismic rockfalls. To evaluate the statistical results of ANFIS, MLP, and RBF models, the verification parameters with high accuracy such as density ratio, quality sum (Qs), and Receiver Operating Characteristic Curve were employed. By analyzing the hazard maps and considering the Qs index obtained by ANFIS (26.76) and MLP (49.19), and RBF (13.84), it could be observed that the calculated Qs of MLP were higher than those of ANFIS and RBF. Moreover, based on the obtained value of the area under the curve from ANFIS (0.984), MLP (0.986), and RBF methods (0.884), it is seen that the MLP network, compared to ANFIS and RBF models, provided a higher accuracy in hazard analysis of rockfalls caused by the earthquake of Firooz Abad-Kojour of 2004. [ABSTRACT FROM AUTHOR]

Rockfalls pose serious threats to human beings, structures, and lifelines. In the present research, a model was developed to predict the possibility of seismic rockfalls on a regional scale. For this purpose, three models including logistic regression (LR), a multilayer perceptron artificial neural network (MLP), and a radial basis function artificial neural network (RBF) were employed. Bivariate logistic regression is a multivariable statistical method that provides a mathematical model using independent variables to predict the occurrence probability of a given phenomenon at a certain location. Although artificial networks of RBF and MLP are pretty similar, there are some structural differences in the components between these two neural networks. The earthquake of Changureh-Avaj in 2002 was used as a basis and benchmark for the model presented in this work. The sustainable zones predicted by LR, MLP, and RBF methods were compared with a database (distribution map) of seismic rockfalls. The results showed good overlap between RBF-predicted rockfall susceptibility zones and database (distribution map) of seismic rockfalls. Besides, in order to evaluate the statistical results of LR, MLP, and RBF models, the verification parameters with high accuracy such as density ratio (Dr), quality sum (Qs), and Receiver Operating Characteristic Curve (ROC) were used. By analyzing the susceptibility maps and considering the Qs index obtained by LR (2.94) and MLP (3.482), and RBF (4.344), it could be observed that the Qs of RBF were higher than that of LR and MLP. Moreover, based on the obtained value of AUC from LR (0.859), MLP (0.910), and RBF methods (0.956), it is seen that the RBF method provided a higher accuracy in predicting the probability of rockfalls occurrence caused by the earthquake of Changureh-Avaj in 2002 compared to LR and MLP methods. [ABSTRACT FROM AUTHOR]

Hundreds of landslides were triggered by the mainshocks (up to Mw 6.5) that occurred in 2016 in Central Italy during the seismic sequence that originated in the Apennine and ended in January 2017. These landslides were studied via field-based investigation and remote sensing techniques during the weeks immediately after the mainshocks occurred. EarthQuake-triggered Landslides (EQtLs) mostly consisted of rockfalls and rockslides. The spatial distribution of the examined EQtLs with respect to the epicentres of the main shocks resulted in very good agreement with the available empirical curves of maximum distance vs. magnitude. Based on the collected dataset, approximately 70% of the landslides impacted transportation routes (national, provincial and secondary roads linking towns and mountain villages) since they principally detached from road cuts. The landslides caused traffic interruption, and some delayed rescue vehicles from reaching the zones most damaged by earthquakes; moreover, some landslides caused the temporary isolation of several localities in the epicentre area. Even if it seems obvious that road cuts favour slope failure under shaking conditions, the dataset reported here is the first one for Italy where such an effect is quantified. Moreover, a statistical analysis was conducted to explore the relationships between the spatial distribution of EQtLs and some selected causative factors, including both natural (i.e., earthquake and terrain) and anthropogenic factors (i.e., presence of roads and trackways). Among the considered combinations of causative factors (both natural and anthropogenic), this study demonstrates that the occurrence of the uphill road cuts at the bottom of deep incised V-shaped valleys strongly influenced the spatial clustering of the EQtL triggered in 2016 in Central Italy. [ABSTRACT FROM AUTHOR]

The 2010 Mw = 8.8 Maule earthquake, which occurred in the subduction contact between the Nazca and the South American tectonic plates off the coast of Chile, represents an important opportunity to improve understanding of the distribution and controls for the generation of landslides triggered by large megathrust earthquakes in subduction zones. This paper provides the analysis of the comprehensive landslide inventory for the Maule earthquake between 32.5° S and 38.5° S. In total, 1226 landslides were mapped over a total area of c. 120,500 km2, dominantly disrupted slides. The total landslide volume is c. 10.6 Mm3. The events are unevenly distributed in the study area, the majority of landslides located in the Principal Andean Cordillera and a very constrained region near the coast on the Arauco Peninsula, forming landslide clusters. Statistical analysis of our database suggests that relief and lithology are the main geological factors controlling coseismic landslides, whilst the seismic factor with higher correlation with landslide occurrence is the ratio between peak horizontal and peak vertical ground accelerations. The results and comparison with other seismic events elsewhere suggest that the number of landslides generated by megathrust earthquakes is lower than events triggered by shallow crustal earthquakes by at least one or two orders of magnitude, which is very important to consider in future seismic landslide hazard analysis. [ABSTRACT FROM AUTHOR]

This paper presents a new methodology to systematically quantify the shape of landslides by their ellipticity (eL) and length‐to‐width ratio (ΛL), along with variability in these measures over different geomorphic settings. Two large substantially complete triggered‐event landslide inventories (source area and runout) are used: (i) 11 111 earthquake‐triggered landslides (1994 Northridge, USA); and (ii) 9594 rainfall‐triggered landslides (1998, Guatemala). Three methods are trialled to abstract landslide shapes to ellipses. The best method fits a convex hull to each landslide shape, approximates an ellipse with the equivalent convex hull area and perimeter, and scales this ellipse to match the original landslide area. An ellipticity index (eL) is used based on the intersection of the original landslide shape and the elliptical approximation. We consider an ellipse a reasonable approximation of landslide shape if eL ≥ 0.5 (>80% of landslides in each of the two landslide inventories). Landslides with eL < 0.5 reflect processes such as coalescence. We calculate for each landslide an ellipse length‐to‐width ratio (ΛE), finding 1.2 ≤ ΛE ≤ 15.1. The statistical distributions of ΛE are examined for ten categories of landslide area (AL). An inverse‐Gamma probability density function is found to be a good statistical model for landslide ΛE, with model parameters dependent on landslide area category. As landslide area AL increases, ΛE tends to decrease for the Northridge (earthquake‐triggered) inventory and increase for Guatemala (rainfall‐triggered). In three additional (rainfall‐triggered) landslide inventories, ΛE trends are similar to Guatemala. Our findings show that (i) an ellipse is a reasonable model for >80% of landslide shapes across different geomorphic settings, (ii) those landslides significantly deviating from an ellipse can be related to landscape processes, (iii) the length‐to‐width ratios of ellipses are non‐normally distributed, with implications for modelling landslide hazard and risk. Supporting information includes code so that the new methodology may be applied more widely. © 2018 John Wiley & Sons, Ltd. We present a methodology to systematically quantify the shape of landslides by their ellipticity (eL) and length‐to‐width ratio (ΛE). An ellipse is a reasonable model for >80% of landslides. Landslides that deviate from an ellipse are related to landscape processes. ΛE ranges 1.2–15.1 and is non‐normally distributed. [ABSTRACT FROM AUTHOR]

Evaluating the failure probability of a slope under the seismic condition during a given exposure time is important for performance-based assessment of slope stability. In this paper, a two-stage method is suggested to study the seismic stability of a slope during a given exposure time. In the first stage, the exceedance probability of the horizontal pseudo-static acceleration is evaluated. In the second stage, the vulnerability curve of the slope, which shows the relationship between the horizontal pseudo-static acceleration and the failure probability of the slope, is established. The failure probability of the slope during a given exposure time is then assessed by combining the exceedance probability curve of the horizontal pseudo-static acceleration and the vulnerability curve of the slope. Examples investigated show that the reliability of a slope under the seismic condition is controlled by multiple slip surfaces. A slope may have different failure probabilities during the same exposure time when it is at different locations because of different levels of ground shaking. Event at the same site, different slopes may have different failure probability because of the difference in factors like slope geometries and geological conditions. The method suggested in this paper can be used to quantify the effect of the above factors on the reliability of a slope. [ABSTRACT FROM AUTHOR]

We develop a database containing 95 historical natural slope and 37 tailing dam failures triggered by earthquake. The database analyses show that earthquake-triggered failures in natural slopes are mostly initiated in the narrow ridges. We also collect published data on 177 open pit mines struck by earthquakes of which 85 mines are located in the seismically active areas. The database indicates no reportable failures triggered by earthquakes in the affected mines. We employ a finite element code to investigate the geometrical and stiffness contrast effects distinguishing the behavior of natural slopes and tailing dams from open pit slopes experiencing earthquake dynamic loading. It is concluded that narrow ridge and the top soil layer in natural slopes and the hill-shaped geometry and unconsolidated top later of tailing dams amplifies the horizontal peak ground velocity by factor of 8 compared to open pit mine slopes. Our numerical modeling of the rock slopes suggests that the typical pit geometry and the competent material in open pit mines boost the slope stability through decreasing the topographical amplification effects. [ABSTRACT FROM AUTHOR]

Landslides along active fault zones are important hazards during and after earthquakes. They can also cause secondary disasters such as surges, creation of landslide dams, and flooding, especially in reservoir areas. This study analyzed landslide susceptibility of the Xiangjiaba Reservoir area associated with the Yaziba Fault. Analysis of permanent displacement and failure probabilities were used for the regional assessment. Ground motion attenuation relations were selected and compared to produce a peak acceleration map using the Yaziba Fault as the seismic source. Geotechnical parameters were determined by classification of rock groups and geomorphic data were calculated using GIS tools. A distribution of the permanent displacements and a failure probability map was generated. According to the peak ground acceleration (PGA) map, the C-B model was adopted to present the actual conditions of PGA in greater detail while local specific models are more appropriate if there is little measured data. Results indicated larger displacement values and failures are distributed on both sides of the fault, especially in the hanging wall. The feasibility of the research approach was verified using historic earthquake-induced landslides. [ABSTRACT FROM AUTHOR]

Landslides as secondary seismic effects are causing some patterns of soil failure that are often considered among the most destructive ones. In fact, the impact from triggered landslides has sometimes exceeded damage directly related to strong shaking and fault rupture. The objective of this research study is landslide hazard and risk assessment considering different water saturation and earthquake scenarios, for a selected area in a sub-urban hilly part of Skopje-the capital of Macedonia. The final product is represented by digital maps of expected permanent displacements for a defined earthquake scenario, in different water saturation conditions of the instable soil layer. Qualitative landslide risk assessment is performed taking into consideration the exposure map of the habitants and local road of the area. As to the target area, it can be concluded that it has the potential for instability that, under certain scenarios, could result in economic and social damage (vulnerability of individual houses, vulnerability of infrastructure and alike). The results from this study referring to potentially affected population and infrastructure present solid base for preventive mitigation activities for reducing the consequences of geotechnical hazards in Skopje City associated with earthquakes. [ABSTRACT FROM AUTHOR]

A geodatabase of landslides and other geomorphologic and hydrologic phenomena, triggered by earthquakes in Portugal, was built based on the analysis of historical records. As a result, 28 earthquake-triggered landslides were identified; the landslides were associated with 10 earthquakes that occurred between 382 and 1969. However, the landslide recognition and the definition of its precise location were difficult due to the time elapsed since the occurrence of most of the landslides and to the changes in the morphologic features of the affected slopes. Despite these limitations, it was possible to establish that most landslides were disrupted landslides that affected jointed rocks. The earthquake-triggered landslides are concentrated in the southern and central areas of Portugal, close to the main seismic sources, as opposed to the recurrent landslides induced by precipitation in the northern and central parts of the country. Other identified geomorphologic and hydrologic phenomena induced by earthquakes in mainland Portugal include: ground cracks (48 cases), liquefaction (75 cases) and water spring and fountains anomalies (262 cases). These secondary earthquake effects were reported for 5 earthquakes, but these may be considered representative only in two cases: the earthquakes of 1 November 1755 and of 23 April 1909. The distance between the site of the above-mentioned phenomena and the corresponding earthquake epicentre varies according to the earthquake magnitude and the type of phenomena. The 1755 earthquake (M 8.7) induced geomorphologic and hydrologic effects farther from the epicentre (maximum distance of 658 km) than the 1909 earthquake (M 6), whereas the effects associated with the latter were felt much closer to the earthquake epicentre (maximum distance of 172 km). The hydrologic effects brought about by the 1755 earthquake probably occurred throughout the country (distance of at least 658 km from epicentre) in contrast to ground cracks (526 km) and liquefaction (504 km). [ABSTRACT FROM AUTHOR]

A high steep rock hill with two-side slopes near National Road 213 is used as a prototype in this paper. The full process from initial deformation to sliding of the slope during ground shaking is simulated by a new discrete element method-continuum-based discrete element method. Then, the seismic responses of a high steep rock hill with two-side slopes are researched from the base of time, frequency and joint time-frequency domain using Hilbert-Huang transform and Fourier Transform. The findings are: first, the stress concentration phenomenon occurs at the top of the sliding mass, and then some tension and shear failure points appear, which expand from the top toward the toe of the sliding mass along the structural plane. At the same time, the number of tension failure points gradually increases. Then the toe of the sliding mass fails, and shears out from its toe which results in the landslide. If the material parameters are under the same conditions, the landslide in the middle of the slope occurs before that at the foot of slope, and the starting time of landslide and the arrival time of the peak ground acceleration are synchronous or the former slightly lags behind the latter. The difference of distribution and dissipation of earthquake energy in the sliding body and sliding bed is the major influence factor to induce the landslide. When the accelerations are small, the instantaneous frequency of accelerations between sliding bed and sliding body is generally consistent, the energy transmittance coefficients of the sliding structural plane and the controlled frequency band of the energy all range in a limitation; with the increase of the seismic intensity, the instantaneous frequency and the energy transmittance coefficients gradually decrease, and then they are steady within the lower limitation. At the same time, the controlled frequency band also shifts gradually from high frequency band to the lower one. Based on the input seismic wave, the peak acceleration amplifies as the increase of elevation, regardless of the monitoring points on the steep slope, gentle slope side or inside of the slope. Generally speaking, amplification of the vertical peak acceleration is stronger than that of the horizontal peak acceleration, and amplification of the peak acceleration on a steep slope is stronger than that on a gentle slope, and that of inside of the slope is the weakest amplification. [ABSTRACT FROM AUTHOR]

A 12 million of m translational rockslide developed on a dip slope underlain by limestone with interlayered marls, and responsible for the destruction of the Montclús village in the fourteenth century, has been investigated by means of geomorphological and geophysical surveys. The combination of historical-geoarcheological, geomorphological, seismic refraction and electrical resistivity imaging datasets allowed the (1) reconstruction of the late Quaternary episodic evolution of the landslide, (2) characterization of the geometry and internal structure of the slid mass and (3) identification of preferential groundwater flow paths that favoured slope instability. The development of the landslide involved at least two different displacement episodes controlled by sliding surfaces at successively deeper stratigraphic positions. The first landsliding event, recorded by highly weathered landslide deposits situated above a perched failure plane, occurred approximately during the global Last Glacial Maximum (23-19 ka BP). The most recent event, which destroyed the Montclús village built on already slid rocks, is placed in the fourteenth century. Most probably, this reactivation event was triggered by the 1373 Ribagorza earthquake, with an estimated moment magnitude of M 6.2. This work illustrates the benefits of combining geomorphological data with complementary geophysical technics in landslide investigation. [ABSTRACT FROM AUTHOR]

Due to the increased need of storage, larger and higher structures are being built all over the world, thus requiring a more careful evaluation of the mechanical performance of their foundation deposits both in terms of bearing capacity and compressibility behaviour. The design of such structures and their serviceability and stability is largely governed by the effects of the dynamic loading conditions principally because of their significantly elevated risk in seismic prone zones. In this paper, numerical analyses using an advanced constitutive model, able to account for the initial soil structure and its progressive degradation, have been performed to investigate the seismic response of a silo foundation built on structured clays. The proposed analyses involve the use of a fully-coupled finite element approach. For the dynamic simulations, three different input motions have been selected form earthquake databases according to the seismic hazard study of the specific site. The results of the silo dynamic response are illustrated in terms of signal amplification, permanent excess pore water pressures, accumulated displacements and structure induced degradation during and after the seismic loading. The dynamic behaviour of the footing indicates that extreme earthquake events can induce large destructuration in natural clays, leading to ground settlements up to twice the observed ones under static loads, which need to be properly accounted for in the design. This suggests that there are significant advantages in using advanced models which recognise the existence of initial soil structure and its subsequent damage due to the applied dynamic loads. [ABSTRACT FROM AUTHOR]

Large-scale landslides along the Kubusu and Besso rivers in Toyama Prefecture are developed in the Miocene Iwaine Formation, which is composed of andesitic lava, tuff, and tuff breccia. In the middle member of this formation, the tuff is easily altered to montmorillonite-bearing rock, and subsequently plays an important role in the development of landslides events, which tend to be large-scale events, as the massive lava of the upper member forms a cap rock over the tuff. The Kiritani and Koinami basins, which are flat intermontane basins located along the Kubusu and Besso rivers, respectively, are interpreted as landslide-dammed lakes, later filled with sediment. Accelerator mass spectrometry C ages show that the landslides forming each dam occurred simultaneously, at approximately 2500 BP. These ages were measured from wood fragments embedded in the landslide material of Kiritani, and from an in situ stump drowned during the impoundment of Koinami. If the trigger of these landslides was an earthquake, it is most likely to have been the penultimate event along the Atotsugawa fault zone. [ABSTRACT FROM AUTHOR]

Although earthquakes are thought to be one of the factors responsible for the occurrence of landslides in Hokkaido, there exist no enough records which can allow correlating many of the old slope failures in the island with earthquakes. In the absence of these records, an attempt was done in this study to use the abundance, frequency, magnitude, depth, and distribution of historical earthquakes to deduce that many of the slope failures in the region were triggered by strong and continuous seismicity. The determination of the zones of influences of selected earthquakes using an existing empirical function has also supported this conclusion. Moreover, the use of a 10% probability of exceedance of earthquake intensity in 50 years, and the geological and slope maps has allowed preparing a landslide hazard map which explains the role of future earthquakes in the formation of slope failures. The result indicates a high probability of occurrences of landslides in the hilly regions of the southeastern part of Hokkaido due to expected strong seismicity and earthquake intensities in these areas. On the other hand, the low level of intensity in the north has given rise to low probability of landslide hazard. There are also places in the center of the island and high intensity regions in the east where the probability of landslide hazard was influenced by the contribution of the geological and slope maps. [ABSTRACT FROM AUTHOR]

This study examined the frequency-size distribution of 6117 landslides spread over 440 km2 in Iburi Subprefecture, Hokkaido, Japan, induced by the Hokkaido Eastern Iburi Earthquake (Mw 6.6) on September 6, 2018. The study area is characterized by gently undulating terrain that is finely dissected by shallow streams and covered predominantly by layers of volcanic products with high water content. Most of the landslides were shallow landslides, and their slip surfaces often formed in a layer of volcanic soil called the "Ta-d," deposited at 9000 ybp. Low ridges separating small catchments allowed individual landslides to coalesce in many locations. The average size of landslides was 7160 m2. Landslide size tended to increase with slope angle up to 20° to 25° and then decrease with further increase of slope angle. About half of the landslides occurred in a feature with both concave planform and profile curvature, and their average size was 8720 m2. In contrast, 17% of the total landslides occurred in the case of both curvatures being convex, and their average size was 5190 m2. The results indicated that the accumulation of saturated soil in concave features provided more opportunities for landslides of large sizes. The frequency-size distribution of the landslides presented high rollover, 5.0 × 10−3 km2, but the exponent of power law decay for medium to large landslides, − 2.46, was not largely different from those of studies in other locations. Compared with other seismically caused examples, the landslides triggered by the Hokkaido Eastern Iburi Earthquake can be characterized as more clustered, more numerous, and larger in size for the moment magnitude of the earthquake. Conversely, the magnitude scale for the landslide event estimated from the total landslide area was equivalent to that of a region struck by an earthquake of Mw = 7.0 to 7.4. This study demonstrated that gently undulating regions can produce unexpectedly large and frequent landslides when struck by an intense earthquake, and when soil layers vulnerable to ground shaking cover the ground. [ABSTRACT FROM AUTHOR]

This study examined the frequency-size distribution of 6117 landslides spread over 440 km2 in Iburi Subprefecture, Hokkaido, Japan, induced by the Hokkaido Eastern Iburi Earthquake (Mw 6.6) on September 6, 2018. The study area is characterized by gently undulating terrain that is finely dissected by shallow streams and covered predominantly by layers of volcanic products with high water content. Most of the landslides were shallow landslides, and their slip surfaces often formed in a layer of volcanic soil called the "Ta-d," deposited at 9000 ybp. Low ridges separating small catchments allowed individual landslides to coalesce in many locations. The average size of landslides was 7160 m2. Landslide size tended to increase with slope angle up to 20° to 25° and then decrease with further increase of slope angle. About half of the landslides occurred in a feature with both concave planform and profile curvature, and their average size was 8720 m2. In contrast, 17% of the total landslides occurred in the case of both curvatures being convex, and their average size was 5190 m2. The results indicated that the accumulation of saturated soil in concave features provided more opportunities for landslides of large sizes. The frequency-size distribution of the landslides presented high rollover, 5.0 × 10−3 km2, but the exponent of power law decay for medium to large landslides, − 2.46, was not largely different from those of studies in other locations. Compared with other seismically caused examples, the landslides triggered by the Hokkaido Eastern Iburi Earthquake can be characterized as more clustered, more numerous, and larger in size for the moment magnitude of the earthquake. Conversely, the magnitude scale for the landslide event estimated from the total landslide area was equivalent to that of a region struck by an earthquake of Mw = 7.0 to 7.4. This study demonstrated that gently undulating regions can produce unexpectedly large and frequent landslides when struck by an intense earthquake, and when soil layers vulnerable to ground shaking cover the ground. [ABSTRACT FROM AUTHOR]

Seismic rockfall is one of the prevalent geohazards that cause huge losses in the earthquake-stricken areas. In the present research, a model is developed to map susceptibility (occurrence probability) of seismic rockfalls in a regional scale using Logistic Regression (LR) and Adaptive Neuro-Fuzzy Inference System (ANFIS) techniques. In this research, Firooz Abad-Kojour earthquake of 2004 was introduced as the benchmark and the model base. The susceptible zones predicted by LR and ANFIS methods were compared with the database (distribution map) of seismic rockfalls, by which the results revealed a good overlapping between the susceptible zones predicted by the ANFIS and the field observation of rockfalls triggered by this earthquake. Besides, for the statistical evaluation of results obtained by LR and ANFIS models, the verification parameters with high accuracy such as density ratio (Dr), quality sum (Qs), and receiver-operating characteristic curve (ROC) were used. By analyzing the susceptibility maps and considering the Qs index obtained by LR (21.04184) and ANFIS (26.75592), it could be found that the Qs of ANFIS is higher than that of LR. Moreover, based on the obtained value of the area under the curve (AUC) from LR (0.972) and ANFIS (0.984) methods, ANFIS provided a higher accuracy in zonation and susceptibility mapping of rockfalls triggered by Firooz Abad-Kojour earthquake of 2004 compared to the LR method. [ABSTRACT FROM AUTHOR]