Search

Some landslides around the world that have low-angle failure planes show exceptionally poor mechanical properties. In some cases, an extraordinarily pure clay layer has been detected on the rupture surface. In this work, a complex landslide, the so-called Diezma landslide, is investigated in a low-to moderate-relief region of Southeast Spain. In this landslide, movement was concentrated on several surfaces that developed on a centimeter-thick layer of smectite (montmorillonite-beidellite) clay-rich level. Since these clayey levels have a very low permeability, high plasticity, and low friction angle, they control the stability of the entire slide mass. Specifically, the triggering factor of this landslide seems to be linked to the infiltration of water from a karstic aquifer located in the head area. The circulation of water through old failure planes could have promoted the active hydrolysis of marly soils to produce new smectite clay minerals. Here, by using geophysical, mineralogical, and geochemical modelling methods, we reveal that the formation and dissolution of carbonates, sulfates, and clay minerals in the Diezma landslide could explain the elevated concentrations of highly plastic secondary clays in its slip surface. This study may help in the understanding of landslides that show secondary clay layers coinciding to their low-angle failure planes.

Landslides in reservoir contexts are a well-recognised hazard that may lead to dangerous situations regarding infrastructures and people’s safety. Satellite-based radar interferometry is proving to be a reliable method to monitor the activity of landslides in such contexts. Here, we present a DInSAR (Differential Interferometric Synthetic Aperture Radar) analysis of Sentinel-1 images that exemplifies the usefulness of the technique to recognize and monitor landslides in the Rules Reservoir (Southern Spain). The integration of DInSAR results with a comprehensive geomorphological study allowed us to understand the typology, evolution and triggering factors of three active landslides: Lorenzo-1, Rules Viaduct and El Arrecife. We could distinguish between rotational and translational landslides and, thus, we evaluated the potential hazards related to these typologies, i.e., retrogression (Lorenzo-1 and Rules Viaduct landslides) or catastrophic slope failure (El Arrecife Landslide), respectively. We also observed how changes in the water level of the reservoir influence the landslide’s behaviour. Additionally, we were able to monitor the stability of the Rules Dam as well as detect the deformation of a highway viaduct that crosses a branch of the reservoir. Overall, we consider that other techniques must be applied to continue monitoring the movements, especially in the El Arrecife Landslide, in order to avoid future structural damages and fatalities.

Active tectonics in North Africa are fundamentally driven by NW-SE directed slow convergence between the Nubia and Eurasia plates, leading to a region of thrust and strike-slip faulting. In this paper, we analyse the morphometric characteristics of the northern Tunisia sector. We aim to identify unknown active tectonic structures, and to further understand the mechanisms driving the drainage evolution in this region. The interpretation of morphometric data was ground-truthed with field data. Our analysis indicates that recent fluvial captures have been the main factor driving fluvial network reorganization in NE Tunisia. The Medjerda River has increased its drainage area during the Quaternary by capturing adjacent axial valleys to the north and south of its drainage divide. These captures are probably driven by the gradual uplift of adjacent axial valleys by reverse/oblique faults or associated folds like El Alia-Teboursouk and Dkhila faults. Our fieldwork found that these faults cut Holocene sediments thus showing recent fault activity. The growth and stabilization of the axial Medjerda River, contrary to the natural transverse drainage development of mature orogens, might be caused by a combination of crustal shortening structures and mantle dynamic processes. The Medjerda River flows SW-NE from the South Atlassic dextral transfer zone to the regional topographic low defined by the Gulf of Gabes and the Straits of Sicily, which in turn, may be influenced by the underlying Tunisian slab in the region

It has long been recognized that earthquakes change the stress in the upper crust around the fault rupture and can influence the behaviour of neighbouring faults and volcanoes. Rapid estimates of these stress changes can provide the authorities managing the post-disaster situation with valuable data to identify and monitor potential threads and to update the estimates of seismic and volcanic hazard in a region. Here we propose a methodology to evaluate the potential influence of an earthquake on nearby faults and volcanoes and create easy-to-understand maps for decision-making support after large earthquakes. We apply this methodology to the Mw 7.8, 2016 Ecuador earthquake. Using Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) and continuous GPS data, we measure the coseismic ground deformation and estimate the distribution of slip over the fault rupture. We also build an alternative source model using the Global Centroid Moment Tensor (CMT) solution. Then we use these models to evaluate changes of static stress on the surrounding faults and volcanoes and produce maps of potentially activated faults and volcanoes. We found, in general, good agreement between our maps and the seismic and volcanic events that occurred after the Pedernales earthquake. We discuss the potential and limitations of the methodology.

En este estudio proponemos una metodología para generar mapas de las fallas potencialmente activadas después de un terremoto. Estos mapas están dirigidos a usuarios no expertos encargados de gestionar la situación posterior al seísmo. La metodología consiste 1) en la estimación de la fuente sísmica a partir de datos de geodesia espacial (datos de interferometría radar y GNSS) y 2) cálculo del cambio de esfuerzos de Coulomb en las fallas activas cercanas a la fuente sísmica. Para el mapa final, que consiste en una versión simplificada de los resultados de este análisis, se ha utilizado un código semáforo con tres posibles valores que informan del nivel de verosimilitud (alta, media o baja) de que una falla haya sido activada por el terremoto. Hemos aplicado esta metodología en el terremoto de Ecuador de abril de 2016 (Mw 7.8). Discutimos los resultados preliminares de este análisis y el potencial y limitaciones de esta metodología. = In this study we propose a methodology to generate maps of faults potentially activated after an earthquake aimed at non-expert users in charge of managing the post-earthquake situation. The methodology consists of 1) estimation of the seismic source from spatial geodesy (radar interferometric and GNSS data) and 2) calculation of the Coulomb stress change in active faults in the vicinity of the earthquake. For the final map, consisting on a simplified version of the results of this analysis, a “traffic light code” has been used with three possible values (high, medium or low ) that represent the seismic activity likelihood of the fault activation. We apply this methodology to the April 2016, Mw 7.8 Ecuador earthquake. We discuss the preliminary results of this analysis and the potential and limitations of this methodology.

It has long been recognized that earthquakes change the stress in the upper crust around the fault rupture and can influence the behaviour of neighbouring faults and volcanoes. Rapid estimates of these stress changes can provide the authorities managing the post-disaster situation with valuable data to identify and monitor potential threads and to update the estimates of seismic and volcanic hazard in a region. Here we propose a methodology to evaluate the potential influence of an earthquake on nearby faults and volcanoes and create easy-to-understand maps for decision-making support after large earthquakes. We apply this methodology to the Mw 7.8, 2016 Ecuador earthquake. Using Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) and continuous GPS data, we measure the coseismic ground deformation and estimate the distribution of slip over the fault rupture. We also build an alternative source model using the Global Centroid Moment Tensor (CMT) solution. Then we use these models to evaluate changes of static stress on the surrounding faults and volcanoes and produce maps of potentially activated faults and volcanoes. We found, in general, good agreement between our maps and the seismic and volcanic events that occurred after the Pedernales earthquake. We discuss the potential and limitations of the methodology.

The analysis of remote sensing data to assess geohazards is being improved by web-based platforms and collaborative projects, such as the Geohazard Exploitation Platform (GEP) of the European Space Agency (ESA). This paper presents the evaluation of a surface velocity map that is generated by this platform. The map was produced through an unsupervised Multi-temporal InSAR (MTI) analysis applying the Parallel-SBAS (P-SBAS) algorithm to 25 ENVISAT satellite images from the South of Spain that were acquired between 2003 and 2008. This analysis was carried out using a service implemented in the GEP called “SBAS InSAR”. Thanks to the map that was generated by the SBAS InSAR service, we identified processes not documented so far; provided new monitoring data in places affected by known ground instabilities; defined the area affected by these instabilities; and, studied a case where GEP could have been able to help in the forecast of a slope movement reactivation. This amply demonstrates the reliability and usefulness of the GEP, and shows how web-based platforms may enhance the capacity to identify, monitor, and assess hazards that are associated to geological processes.

Deterministic methods are appropriate for analyzing specific slopes at site-scale where geotechnical parameters are better known. Probabilistic techniques provide better results than deterministic methods at regional scales (1:10,000–1:50,000). However, the performances of deterministic and probabilistic methods at large scales (e.g. 1:5000-scale) are not well-known. We applied GIS-based deterministic (WEDGEFAIL, SAFETYFACTOR, SHALSTAB) and probabilistic (Likelihood ratio) methods to a mountain road of 14 km in the Alpujarras region (S Spain) to investigate the behavior of these models at detailed scales. The studied road stretch was affected by 111 landslides (7–8 landslides/km) during the 2009–2010 winter in a period of high precipitation. These landslides cut off the road in several points and disconnected the central region of Alpujarras from the main transport infrastructures. We delimited a small study area with only 4 km2 restricted to the slopes that cross the road where we gathered as much data as possible. Our results show that deterministic methods have less prediction capability at ~1:5000-scale than probabilistic methods and it seems that the needed effort to improve their results is not worthwhile. However, it must take into account that probabilistic methods need an inventory and they could not have been applied before the analyzed landslide event. As our results indicate, the deterministic methods, such as the SHALSTAB model, are reliable tools to make an evaluation of the stability of cut slopes in a roadway at project-scale.

The analysis of remote sensing data to assess geohazards is being improved by web-based platforms and collaborative projects, such as the Geohazard Exploitation Platform (GEP) of the European Space Agency (ESA). This paper presents the evaluation of a surface velocity map that is generated by this platform. The map was produced through an unsupervised Multi-temporal InSAR (MTI) analysis applying the Parallel-SBAS (P-SBAS) algorithm to 25 ENVISAT satellite images from the South of Spain that were acquired between 2003 and 2008. This analysis was carried out using a service implemented in the GEP called “SBAS InSAR”. Thanks to the map that was generated by the SBAS InSAR service, we identified processes not documented so far; provided new monitoring data in places affected by known ground instabilities; defined the area affected by these instabilities; and, studied a case where GEP could have been able to help in the forecast of a slope movement reactivation. This amply demonstrates the reliability and usefulness of the GEP, and shows how web-based platforms may enhance the capacity to identify, monitor, and assess hazards that are associated to geological processes.

This work integrates detailed geological and hydrogeological information with PSI data to obtain a better understanding of subsidence processes detected in the detrital aquifer of the Vega de Granada (SE Spain) during the past 13 years. Ground motion was monitored by exploiting SAR images from the ENVISAT (2003–2009), Cosmo-SkyMed (2011–2014) and Sentinel-1A (2015–2016) satellites. PSInSAR results show an inelastic deformation in the aquifer and small land surface displacements (up to −55 mm). The most widespread land subsidence is detected during the ENVISAT period (2003–2009), which coincided with a long, dry period in the region. The highest displacement rates recorded during this period (up to 10 mm/yr) were detected in the central part of the aquifer, where many villages are located. For this period, there is a good correlation between groundwater level depletion and the augmentation of the average subsidence velocity and slight hydraulic head changes (<2 m) have a rapid ground motion response. The Cosmo-SkyMed period (2011–2014) coincided with a rainy period, and the land subsidence is only concentrated in some points. Rates of average subsidence up to 11.5 mm/yr are obtained for this period and are anthropogenic in origin, being related to earthmoving works. During the Sentinel-1A monitoring period (2015–2016) most of the region showed no deformation, except for some points of unknown origin in the NE sector. A general conclusion is that there is a clear lithological control in the spatial distribution of ground subsidence; all the subsiding areas detected are located where a higher clay content was identified. Although the SE sector of the aquifer had more intense groundwater exploitation, no land subsidence processes were detected, as coarse-grained sediments predominate in the substratum. This research will contribute to the drawing-up of a management plan for the sustainable use of this strategic aquifer, taking into account critical levels of groundwater

In this paper three different approaches for landslide susceptibility modeling—Shallow Landslide Stability model (SHALSTAB), Likelihood Ratio (LR) and Generalized Additive Model (GAM)—are compared. They are based on deterministic and statistical methods, respectively. These methods were tested in the Pogliaschina catchment (25 km2 wide; Northern Apennines, Eastern Liguria, Italy), heavily hit by an intense rainfall on 25 October 2011, that caused hundreds of shallow landslides, human losses and severe damage to infrastructure and buildings. The paper focuses on the assessment of the predictive performance of the three methods through a two-fold cross-validation technique and prediction rate curves (PRCs) analysis. The preliminary results have revealed that statistical methods have a higher predictive capability than the deterministic one.

In the present work, the case of the Cármenes del Mar resort (Granada, Spain) is shown. It can be considered one of the most extreme examples on the Mediterranean coast of severe pathologies associated with urban development on coastal landslides. The resort, with 416 dwellings, was partially built on a deep-seated landslide which affects a soft formation composed of dark graphite schists. In November 2015, the City Council officially declared a state of emergency in the resort and 24 dwellings have already been evacuated. We have used two remote sensing techniques to monitor the landslide with the aim of identifying and measuring a wide range of displacements rates (from mm/year to m/year): (1) PSInSAR, exploiting 25 ENVISAT SAR images acquired from May 2003 to December 2009, and (2) photogrammetry, considering the output from two Unmanned Aerial Vehicle (UAV) flights made in June 2015 and January 2016 and the outdated photos from a conventional flight in 2008. The relationship between the geology of the site, data from PS deformation measurements, building displacements, rainfall and damage observed and their temporal occurrence allows a better understanding of the landslide kinematics and both the spatial and temporal evolution of the instability. Results indicate building displacements of up to 1.92 m in 8 years, a clear lithological control in the spatial distribution of damage and a close relationship between the most damaging events and water recharge episodes (rainy events and leaks from swimming pools and the water supply network). This work emphasises the need to incorporate geohazards into urban planning, including policies to predict, prepare for and prevent this type of phenomenon.

The first complete volcano-structural map of El Hierro (Canary Islands, Spain) has been developed in order to provide a tool for volcano-tectonic analyses and volcanic hazard evaluation on the island. This map is a synthesis of collated and interpreted field data and bathymetric maps. We have integrated information obtained from: (1) high-resolution digital elevation models, (2) bathymetric information, (3) topographic, geologic and geomorphological maps, (4) aerial photographs and orthoimages, (5) previous reports and scientific publications, and (6) new detailed field surveys. The 1:100,000-scale map includes the main volcano-structural elements such as vents, eruptive fissures, dykes, faults, and landslides scars. This information has been used for analysing the volcano-tectonic evolution of El Hierro and for estimating the probability of new vent opening on the island (i.e. volcanic susceptibility). We expect that this map will underpin future geological studies and future volcanic risk assessment.

The first complete volcano-structural map of El Hierro (Canary Islands, Spain) has been developed in order to provide a tool for volcano-tectonic analyses and volcanic hazard evaluation on the island. This map is a synthesis of collated and interpreted field data and bathymetric maps. We have integrated information obtained from: (1) high-resolution digital elevation models, (2) bathymetric information, (3) topographic, geologic and geomorphological maps, (4) aerial photographs and orthoimages, (5) previous reports and scientific publications, and (6) new detailed field surveys. The 1:100,000-scale map includes the main volcano-structural elements such as vents, eruptive fissures, dykes, faults, and landslides scars. This information has been used for analysing the volcano-tectonic evolution of El Hierro and for estimating the probability of new vent opening on the island (i.e. volcanic susceptibility). We expect that this map will underpin future geological studies and future volcanic risk assessment.

In the present work, the case of the Cármenes del Mar resort (Granada, Spain) is shown. It can be considered one of the most extreme examples on the Mediterranean coast of severe pathologies associated with urban development on coastal landslides. The resort, with 416 dwellings, was partially built on a deep-seated landslide which affects a soft formation composed of dark graphite schists. In November 2015, the City Council officially declared a state of emergency in the resort and 24 dwellings have already been evacuated. We have used two remote sensing techniques to monitor the landslide with the aim of identifying and measuring a wide range of displacements rates (from mm/year to m/year): (1) PSInSAR, exploiting 25 ENVISAT SAR images acquired from May 2003 to December 2009, and (2) photogrammetry, considering the output from two Unmanned Aerial Vehicle (UAV) flights made in June 2015 and January 2016 and the outdated photos from a conventional flight in 2008. The relationship between the geology of the site, data from PS deformation measurements, building displacements, rainfall and damage observed and their temporal occurrence allows a better understanding of the landslide kinematics and both the spatial and temporal evolution of the instability. Results indicate building displacements of up to 1.92 m in 8 years, a clear lithological control in the spatial distribution of damage and a close relationship between the most damaging events and water recharge episodes (rainy events and leaks from swimming pools and the water supply network). This work emphasises the need to incorporate geohazards into urban planning, including policies to predict, prepare for and prevent this type of phenomenon.

The first complete volcano-structural map of El Hierro (Canary Islands, Spain) has been developed in order to provide a tool for volcano-tectonic analyses and volcanic hazard evaluation on the island. This map is a synthesis of collated and interpreted field data and bathymetric maps. We have integrated information obtained from: (1) high-resolution digital elevation models, (2) bathymetric information, (3) topographic, geologic and geomorphological maps, (4) aerial photographs and orthoimages, (5) previous reports and scientific publications, and (6) new detailed field surveys. The 1:100,000-scale map includes the main volcano-structural elements such as vents, eruptive fissures, dykes, faults, and landslides scars. This information has been used for analysing the volcano-tectonic evolution of El Hierro and for estimating the probability of new vent opening on the island (i.e. volcanic susceptibility). We expect that this map will underpin future geological studies and future volcanic risk assessment.

Previously not measured subsidence on railway tracks was detected using DInSAR displacement maps produced for the central sector of Ebro Valley (NE Spain). This area is affected by evaporite karst and the analyzed railway corridors traverse active sinkholes that produce deformations in these infrastructures. One of the railway tracks affected by slight settlements corresponds to the Madrid–Barcelona high-speed line, a transport infrastructure highly vulnerable to ground deformation processes. Our analysis based on DInSAR measurements and geomorphological surveys indicate that this line show dissolution-induced subsidence and compaction of anthropogenic deposits (infills and embankments). By using DInSAR techniques, it was also measured the significant subsidence related to the activity of sinkholes in the Castejón–Zaragoza conventional railway line. Thus, this study demonstrate that DInSAR velocity maps coupled with detailed geomorphological surveys may help in the identification of the sectors of railway tracks that may compromise the safety of travellers.

Sinkholes in karst areas may cause subsidence damage in transportation infrastructures, demolition of buildings and even the loss of human lives when they occur in a catastrophic way. Differential Interferometry (DInSAR) is a promising technology for detecting and characterizing sinkholes, as well as for reducing the associated risk when combined with other sources of data such as a sinkhole inventory. In this work, the usefulness of InSAR techniques and data for sinkhole risk management have been analyzed through the comparison of three DInSAR-derived velocity maps with a comprehensive sinkhole inventory in the Ebro Valley, NE Spain. The DInSAR maps have contributed to improve the sinkhole inventory in different ways: (1) detection of non-inventoried sinkholes; (2) revision of sinkhole areas previously classified as inactive as active; (3) refinement of underestimated sinkhole boundaries. The obtained results suggest that DInSAR products are suitable for analyzing active dissolution-induced subsidence. The application of these techniques may help in recognizing and better characterizing previously unknown karst subsidence problems and in preventing personal and property losses. However, the analysis reveals that the available DInSAR maps combined overlook about 70% of the previously mapped active sinkholes mainly due to decorrelation.

Morphometry is a discipline extensively applied in the landscape analysis of regions affected by active tectonics. Recently, the specific techniques of morphometry have been used for studying the surficial expression of other phenomena such as volcanism and mass movements. We are applying diverse landscape analysis techniques for analyzing the relief morphology in the central region of Costa Rica, a confluence of active tectonics, volcanism and landsliding. The objectives of our project are to better understand the reliability of the morphometry analysis techniques in the mentioned geographical setting, and to provide new information for improving the geological knowledge of the study area. Our preliminary results indicate that landscape analysis techniques have proven be useful in the study area for identifying active tectonic structures and large landslides; and for assisting in geological mapping and for volcanism analysis.

[EN] A 1:5000 scale geomorphological landslide inventory map of the glaciated headwaters of the Gállego River in the Spanish Pyrenees is presented. This map, covering an area of 57.6 km2 and mainly produced by direct mapping in the field, provides a more comprehensive and accurate picture of the distribution of slope movements than previous maps. Around 20% of the area is affected by large flow-dominated slope movements developed on Paleozoic slates. Our map shows that some of these post-glacial landslides have blocked the main drainage at several sites creating landslide-dammed lakes. The damage caused by landslides in the mapped area, with an estimated cost of greater 10 million euros, is mostly related to the activity of pre-existing slope movements, some of which have been reactivated or accelerated by adverse human alterations (e.g., excavation at the toe, overloading, higher water infiltration). This study illustrates that the incorporation of detailed cartographic landslide inventories in the planning and development process of alpine areas may contribute to reduce significant landslide-related damage in a cost-effective manner.

Differential Interferometric Synthetic Aperture Radar (DInSAR) has been applied to detect and measure ground deformation in a stretch of the Ebro River valley (Spain) excavated in salt-bearing evaporites. The capability of the Small Baseline Subset (SBAS) DInSAR technique to detect ground displacement is analyzed comparing the DInSAR results with the available geomorphological information. The deformation map derived from 27 European Remote Sensing (ERS) satellite images covering more than five years provides sub-centimeter displacement measurements in zones coinciding with known active sinkholes and landslides. Moreover the map provides the first account of mining subsidence in the area. The measured deformation rates reach 1·68 cm/y for the sinkholes, 0·80 cm/y for the landslides and 1·45 cm/y for the area affected by mining subsidence. The SBAS DInSAR technique provided deformation measurements in a small proportion (5-10%) of the known active sinkholes and landslides. This limitation is mainly due to the lack of coherence in agricultural areas, the spatial resolution of the deformation map (pixel size of 90 m), and the parallelism between the ERS satellite line of sight and the linear escarpment on which most of the landslides occur. Despite this, the interferometric technique provides valuable data that complement traditional geomorphological studies including the quantification of the deformation phenomena, the identification of mining subsidence otherwise only recognizable by geodetic methods, and the detection of creep deformation which might correspond to premonitory indicators of catastrophic sinkholes and landslides capable of causing the loss of lives. Detailed DInSAR studies combined with field data would be required to improve the analysis of each deformation area. © 2009 John Wiley & Sons, Ltd.