C. Loupasakis

Application of the revised universal soil loss equation model on landslide prevention. An example from N. Euboea (Evia) Island, Greece

This study aims to evaluate the application of the Revised Universal Soil Loss Equation (RUSLE) on predicting of sites susceptible to slope failures caused by the soil erosion. It was carried out at the northern part of Euboea Island presenting one of the highest frequencies of landslide occurrence in Greece. All required datasets for the application of the RUSLE model were engaged to compile a potential soil erosion map of the study area. In addition, historical slope failure data were used to evaluate the produced map. Moreover, the frequency ratio statistical analysis was applied for the verification of the soil erosion map. The results showed a satisfactory agreement between the soil erosion intensity zones and distribution of landslides events. Therefore, the RUSLE model can be applied for the localization of sites susceptible to landslides that were prepared or triggered by the soil erosion. Finally, taking under consideration the contribution of erosion mechanisms over the landslides manifestation, a combination of measures were proposed for preventing and supporting these catastrophic phenomena.

Landslide susceptibility mapping by comparing the WLC and WofE multi-criteria methods in the West Crete Island, Greece

In the current research, the weighted linear combination (WLC) and the weights of evidence (WofE) methods were applied for landslide susceptibility zonation mapping in the Chania Prefecture of Crete Island, Greece. Several thematic maps representing various landslide conditioning factors, such as geology formations, faults proximity, altitude, slope gradient, aspect, curvature, rivers proximity, precipitation, roads proximity and land use types have been generated in a GIS environment. Three landslide susceptibility maps were created, one for each method and a combined one by applying the logistic regression approach to the WLC and WofE susceptibility maps. The maps were evaluated and validated using the efficiency rate curve, the receiver-operator curve and the spatially agreed areas methods. The resulting landslide susceptibility maps have uncertainties introduced due to the subjective knowledge of experts in the case of WLC method and to the quality of the recorded landslides sample in the case of the WofE method. Nevertheless, the performance of the three approaches was found to be almost equal with all methods to produce quite satisfactory results. Besides the comparison of the applied methods, the current study contributes to the risk management of the area, providing the first landslide susceptibility maps for Chania Prefecture.

Advanced interpretation of interferometric SAR data to detect, monitor and model ground subsidence: outcomes from the ESA-GMES Terrafirma project

Land subsidence is a common natural hazard striking extensive areas worldwide, with severe impacts on economy and environment. Subsidence has been recognized as one of geohazards needing research efforts and knowledge transfer at international level, especially when urban fabrics and infrastructures are directly involved in the land settling. Policies and solutions for land subsidence management can be different. Despite this variability, where mitigation methods need to be adopted, mapping, monitoring and simulation of subsidence have to precede their design and implementation. In this framework, Earth Observation (EO) and remote sensing have a major role to play. Satellite Synthetic Aperture Radar Interferometry, thanks to its wide spatial coverage and its millimeter accuracy, provides a valuable contribution in the management of hazard posed by subsidence-related deformation. The ESA-GMES Terrafirma project (2003–2014) has worked for the promotion of the persistent scatterer interferometry, a family of techniques ideally suited for the assessment of magnitude of surface deformations associated with subsidence phenomena. Within the Terrafirma Project a series of products, based on the integration of EO technologies and in situ data, has been established and delivered to a wide community of end user. Three case studies, outcomes of the Terrafirma project, are presented: the wide area of Rome (Italy), the Anthemountas basin and the Kalochori village (Greece). These case studies have been selected with the purpose of showing the essential contribution of interferometric data during the main activities that must be covered when dealing with geohazard investigations (i.e., mapping, monitoring and modeling). These three case studies are meant to be representative of the suite of services delivered by the Terrafirma project to specific end users with the legal mandated to manage the geohazard.

Geo-Characterization at selected accelerometric stations in Crete (Greece) and comparison of earthquake data recordings with EC8 elastic spectra

To estimate the seismic response according to Eurocode (EC8) and almost all other national codes, site conditions have to be properly characterized so that soil amplification and the corresponding peak ground motion can be calculated.In this work, different geophysical and geotechnical methods are combined in order to define the detailed ground conditions in selected sites of the Hellenic Accelerometric Network (HAN) in Crete. For this purpose, the geological information of the sites and shear wave velocity, calculated from surface wave measurements, is used. Additionally, ground acceleration data recorded through HAN have been utilized from intermediate depth earthquakes in the broader area of South Aegean Sea.Using the recorded ground motion data and the procedure defined in EC8, the corresponding elastic response spectrum is calculated for the selected sites. The resulting information is compared to the values defined in the corresponding EC8 spectrum for the seismic zone that includes the island of Crete.The comparison shows that accurate definition of ground type through geological, geotechnical and geophysical investigations is important. However, our current comparison focuses on the distribution of values rather than the absolute values of EC8-prescribed spectra, and the results should be considered in this context.

InSAR time-series monitoring of ground displacement trends in an industrial area (Oreokastro???Thessaloniki, Greece): detection of natural surface rebound and new tectonic insights

The industrial area of Oreokastro, NW of the city of Thessaloniki, is monitored using radar interferometry to determine the spatial evolution of the underlying ground deformation trends. Previous studies, using SAR data acquired between 1992 and 1999, have revealed subsidence; however, the driving mechanism has not been, so far, solidly explained. Here, SAR satellite data from ERS 1, 2 and ENVISAT missions, acquired between 1992 and 2010, are analysed to enhance our understanding of the ground displacement trends and provide a thorough interpretation of the phenomena. The analysis confirms a subsiding displacement pattern from 1992 to 1999, whereas the recent data indicate that after 2003 the motion direction has changed to uplift. This whole monitoring of subsidence and the subsequent uplift is a rarely documented phenomenon, and in the case of Oreokastro is not reflecting a natural process; on the contrary, the driver is anthropogenic, related to the regional aquifer activity. Our study also highlights the fact that the local faults act as groundwater barriers and captures the existence of a possible previously unknown tectonic structure.

Mining geohazards susceptibility and risk mapping: The case of the Amyntaio open-pit coal mine, West Macedonia, Greece

During the last decades, numerous methodologies for the construction of both susceptibility and risk maps have been developed in order to identify and mitigate geohazards such as landslides and secondarily land subsidence phenomena caused by the collapse of natural or man-made underground cavities. According to literature review, the conducted research concerning the assessment of land subsidence risk due to the overexploitation of the aquifer is still at an early stage. This study focuses οn the land subsidence phenomenon due to the overexploitation of the aquifer occurring in the Amyntaio basin in West Macedonia, hosting the active Amyntaio open-pit coal mine. This phenomenon has caused significant damage to settlements, farmlands and infrastructure. In order to construct susceptibility and risk maps knowledge of the geological, geotechnical, hydrogeological and tectonic settings of the study area is required. The proposed methodology for the production of a susceptibility and a risk map of land subsidence was based on the semi-quantitative method Weighted Linear Combination (WLC). The results were evaluated with an extensive field survey action recording, besides the above-mentioned settings, the spatial distribution of surface ruptures. The excellent agreement between the produced maps and the findings of the field survey, proved the added value of the maps, assigning them as crucial tools for the management of land subsidence phenomena.

Land subsidence phenomena investigated by spatiotemporal analysis of groundwater resources, remote sensing techniques, and random forest method: the case of Western Thessaly, Greece

The main objective of the present study was to investigate land subsidence phenomena and the spatiotemporal pattern of groundwater resources in an area located in western Thessaly, Greece, by using remote sensing techniques and data mining methods. Specifically, the nonparametric Mann–Kendall test and the Sen’s slope estimator were used to estimate the trend concerning the groundwater table, whereas a set of Synthetic Aperture Radar images, processed with the Persistent Scatterer Interferometry technique, were used investigate the spatial and temporal patterns of ground deformation. Random forest (RF) method was utilized to predict the subsidence deformation rate based on three related variables, namely: thickness of loose deposits, the Sen’s slope value of groundwater-level trend, and the Compression Index of the formation covering the area of interest. The outcomes of the study suggest a strong correlation among the thickness of the loose deposits and the deformation rate and also show that a clear trend between the deformation rate and the fluctuation of the groundwater table exists. For the RF model and based on the validation dataset, the r square value was calculated to be 0.7503. In the present study, the potential deformation rate assuming different water pumping scenarios was also estimated. It was observed that with a mean decrease in the Sen’s slope value of groundwater-level trend of 20%, there would be a mean decrease of 9.01% in the deformation rate, while with a mean increase in the Sen’s slope value of groundwater-level trend of 20%, there would be a mean increase of 12.12% in the deformation rate. The ability of identifying surface deformations allows the local authorities and government agencies to take measures before the evolution of severe subsidence phenomena and to prepare for timely protection of the affected areas.

Developing a landslide susceptibility map based on remote sensing, fuzzy logic and expert knowledge of the Island of Lefkada, Greece

The main objective of the study was to develop a novel expert-based approach in order to construct a landslide susceptibility map for the Island of Lefkada, Greece. The developed methodology was separated into two actions. The first action involved the construction of a landslide inventory map and the second the exploitation of expert knowledge and the use of fuzzy logic to produce a landslide susceptibility map. Two types of movements were analyzed: rapid moving slides that involve rock falls and rock slides and slow to very slow moving slides. The landslide inventory map was constructed through an evaluation procedure that involved the use of a group of experts, who analyzed data acquired from remote sensing techniques supplemented by landslide records and fieldwork data. During the second action an expert-driven model was developed for identifying the tendency of landslide occurrences concerning both types of movements. A set of casual variables was selected, namely: lithological units, slope angle, slope orientation, distance from tectonic features, distance from hydrographic network and distance from road network. The performance and validation of the developed model were compared with models that are constructed on the bases of each expert’s judgment. The results proved that the most accurate and reliable outcomes are obtained from the aggregated values assigned by the group of experts and not from the individual values assigned by each expert. The area under the receiver operating characteristic curves for the models constructed by the expert’s group was 0.873 for prediction curves of rapid moving slides and 0.812 for prediction rate curves of slow to very slow moving slides, respectively. These values were much higher than those obtained by each expert. From the outcomes of the study it is clear that the produced landslide susceptibility maps could provide valuable information during landslide risk assessments at the Island of Lefkada.

Land subsidence susceptibility and hazard mapping: the case of Amyntaio Basin, Greece

Landslide susceptibility and hazard mapping has been applying for more than 20 years succeeding the assessment of the landslide risk and the mitigation the phenomena. On the contrary, equivalent maps aiming to study and mitigate land subsidence phenomena caused by the overexploitation of the aquifers are absent from the international literature. The current study focuses at the Amyntaio basin, located in West Macedonia at Florina prefecture. As proved by numerous studies the wider area has been severely affected by the overexploitation of the aquifers, caused by the mining and the agricultural activities. The intensive ground water level drop has triggered extensive land subsidence phenomena, especially at the perimeter of the open pit coal mine operating at the site, causing damages to settlements and infrastructure. The land subsidence susceptibility and risk maps were produced by applying the semi-quantitative WLC (Weighted Linear Combination) method, especially calibrated for this particular catastrophic event. The results were evaluated by using detailed field mapping data referring to the spatial distribution of the surface ruptures caused by the subsidence. The high correlation between the produced maps and the field mapping data, have proved the great value of the maps and of the applied technique on the management and the mitigation of the phenomena. Obviously, these maps can be safely used by decision-making authorities for the future urban safety development.

Ground subsidence phenomena in Frakadona, West Thessaly, Greece

Ground subsidence is considered among the most frequent geological hazard that usually occurs as a consequence of a number of phenomena, namely: natural compaction of unconsolidated fine - grained deposits, groundwater over - exploitation, peat - oxidation and collapse of underground cavities. The main objective of the present study was to investigate the spatio - temporal patterns of ground deformation in the wider area of Farkadona Municipality in the north-eastern Trikala regional unit, Thessaly, Greece. A set of Synthetic Aperture Radar images, acquired in 1992–2003 by the European Space Agency satellites ERS1 and ERS2 and processed with the Persistent Scatterer Interferometry technique, along with geotechnical data from nearby exploratory boreholes, were used in order to explain the observed deformation. Increasing subsidence rates are observed at almost the entire area within the city complex of Farkadona, which is covered by loose Quaternary sediments of considerable depth. In most cases, the increased deformation rates have caused damages in the form of tensile cracks, mainly along the road network and adjacent buildings. The results of the performed analysis concluded that the geotechnical conditions of the loose deposits occupying the site and also the intensive exploitation of the aquifers are the two main causal factors of the land subsidence phenomena. Additionally, a clear correlation between the subsidence deformation rate and the thickness of the loose deposits has been detected. Besides the geological information, this study made clear that Persistent Scatterer Interferometry could be considered as a valuable tool and cost-efficient method for validating subsidence mechanisms and could serve as an alternative to ground-based measurements.