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Land subsidence associated with overexploitation of aquifers is a hazard that commonly affects large areas worldwide. The Lorca area, located in southeast Spain, has undergone one of the highest subsidence rates in Europe as a direct consequence of long-term aquifer exploitation. Previous studies carried out on the region assumed that the ground deformation retrieved from satellite radar interferometry corresponds only to vertical displacement. Here we report, for the first time, the two- and three-dimensional displacement field over the study area using synthetic aperture radar (SAR) data from Sentinel-1A images and Global Navigation Satellite System (GNSS) observations. By modeling this displacement, we provide new insights on the spatial and temporal evolution of the subsidence processes and on the main governing mechanisms. Additionally, we also demonstrate the importance of knowing both the vertical and horizontal components of the displacement to properly characterize similar hazards. Based on these results, we propose some general guidelines for the sustainable management and monitoring of land subsidence related to anthropogenic activities. Introduction

This paper presents an advanced 3D numerical methodology to reproduce the kinematics of slow active landslides, more precisely, to reproduce the nearly constant strain rate (secondary creep) and the acceleration/deceleration of the moving mass due to hydrological changes. For this purpose, finite element analyses are performed in a large area covering a long time-span (12 years), in order to exhibit different interacting slope movements. First, we perform a stability analysis using the shear strength reduction (SSR) technique with a Mohr-Coulomb failure criteria. It is done in order to compute factors of safety (FS) and to identify two different scenarios, the first one being stable (FS > 1) and the second one being unstable (FS < 1). In the studied test case, the Portalet landslide (Central Spanish Pyrenees), the first scenario corresponds to an initial stable configuration of the slope and the second one to an unstable excavated configuration. Second, taking the first scenario as an initial condition, a time-dependent analysis is performed using a coupled formulation to model solid skeleton and pore fluids interaction, and a simplified ground water model that takes into account daily rainfall intensity. In this case, a viscoplastic constitutive model based on Perzyna’s theory is applied to reproduce soil viscous behavior and the delayed creep deformation due to the excavation. The fluidity parameter is calibrated to reproduce displacements measured by the monitoring systems. Our results demonstrate that 3D analyses are preferable to 2D ones for reproducing in a more realistic way the slide behavior. After calibration, the proposed model is able to simulate successfully short- and medium-term predictions during stages of primary and secondary creep.

This paper presents a gravimetric study (based on 382 gravimetric stations in an area about 32 km2) of a nearly flat basin: the Low Andarax valley. This alluvial basin, close to its river mouth, is located in the extreme south of the province of Almería and coincides with one of the existing depressions in the Betic Cordillera. The paper presents new methodological work to adapt a published inversion approach (GROWTH method) to the case of an alluvial valley (sedimentary stratification, with density increase downward). The adjusted 3D density model reveals several features in the topography of the discontinuity layers between the calcareous basement (2,700 kg/m3) and two sedimentary layers (2,400 and 2,250 kg/m3). We interpret several low density alignments as corresponding to SE faults striking about N140–145°E. Some detected basement elevations (such as the one, previously known by boreholes, in Viator village) are apparently connected with the fault pattern. The outcomes of this work are: (1) new gravimetric data, (2) new methodological options, and (3) the resulting structural conclusions.

The Canary Islands are mostly characterized by diffuse and scattered volcanism affecting a large area, with only one active stratovolcano, the Teide–Pico Viejo complex (Tenerife). More than 2 million people live and work in the 7,447 km2 of the archipelago, resulting in an average population density three times greater than the rest of Spain. This fact, together with the growth of exposure during the past 40 years, increases volcanic risk with respect previous eruptions, as witnessed during the recent 2011–2012 El Hierro submarine eruption. Therefore, in addition to purely scientific reasons there are economic and population-security reasons for developing and maintaining an efficient volcano monitoring system. In this scenario geodetic monitoring represents an important part of the monitoring system. We describe volcano geodetic monitoring research carried out in the Canary Islands and the results obtained. We consider for each epoch the two main existing constraints: the level of volcanic activity in the archipelago, and the limitations of the techniques available at the time. Theoretical and observational aspects are considered, as well as the implications for operational volcano surveillance. Current challenges of and future perspectives in geodetic volcano monitoring in the Canaries are also presented.

Subsidence related to multiple natural and human-induced processes affects an increasing number of areas worldwide. Although this phenomenon may involve surface deformation with 3D displacement components, negative vertical movement, either progressive or episodic, tends to dominate. Over the last decades, differential SAR interferometry (DInSAR) has become a very useful remote sensing tool for accurately measuring the spatial and temporal evolution of surface displacements over broad areas. This work discusses the main advantages and limitations of addressing active subsidence phenomena by means of DInSAR techniques from an end-user point of view. Special attention is paid to the spatial and temporal resolution, the precision of the measurements, and the usefulness of the data. The presented analysis is focused on DInSAR results exploitation of various ground subsidence phenomena (groundwater withdrawal, soil compaction, mining subsidence, evaporite dissolution subsidence, and volcanic deformation) with different displacement patterns in a selection of subsidence areas in Spain. Finally, a cost comparative study is performed for the different techniques applied. © 2013 Springer-Verlag Berlin Heidelberg.

In weather forecasting, current and past observational data are routinely assimilated into numerical simulations to produce ensemble forecasts of future events in a process termed “model steering”. Here we describe a similar approach that is motivated by analyses of previous forecasts of the Working Group on California Earthquake Probabilities (WGCEP). Our approach is adapted to the problem of earthquake forecasting using topologically realistic numerical simulations for the strike-slip fault system in California. By systematically comparing simulation data to observed paleoseismic data, a series of spatial probability density functions (PDFs) can be computed that describe the probable locations of future large earthquakes. We develop this approach and show examples of PDFs associated with magnitude M > 6.5 and M > 7.0 earthquakes in California.

The workshop on Deformation and Gravity Change: Indicators of Isostasy, Tectonics, Volcanism and Climate Change took place at the Casa de los Volcanes on Lanzarote, Spain, during March 1–4, 2005 (see Fig. 1). It was jointly organized and supported by the International Association of Geodesy (IAG), the Spanish Ministry of Education and Science, the Spanish Council for Scientific Research and the Cabildo Insular de Lanzarote. From an organizational point of view, the workshop also served as the first meeting of the members the IAG Working Group ICCT2 on Dynamic Theories of Deformation and Gravity Fields existing since late 2003, but was open to all ‘‘external’’ colleagues interested in its topic.

We review the results of the geodetic and structural studies carried out on La Palma Island using geodetic and geophysical data during the period 1992–2007. InSAR and GPS observation techniques were applied to study the existence of deformation on the island and gravity observations were carried out for structural studies. Gravity data were inverted using a nonlinear three-dimensional gravity inversion approach to obtain the geometry of the anomalous bodies constructed in a random growth process with respect to an exponentially stratified background. The main structural feature is a large central body (under the Caldera de Taburiente) with high density, which was interpreted as the Pliocene-age uplifted seamount and a relatively dense intrusive plutonic complex/magma body. The Cumbre Vieja series is characterized by elongated minima distributed according to the rift structure. InSAR results show a clear subsidence located on the Teneguía volcano, where the last eruption took place in 1971. A thermal source is the most probable origin for this deformation. A GPS network composed of 26 stations covering the total island surface was set up. Vertical displacements determined comparing the GPS coordinates obtained in 2007 with coordinates determined in 1994 are consistent with the InSAR results obtained in the southern part of the island. This is not the case for the northern part. From the comparison of 2006 and 2007 coordinates it is clear that more time is needed to obtain significant displacements, but observed trends are also consistent with InSAR results. All the observed significant displacements are in stations located outside of the large high-density central body.

Here we present a new mathematical tool, the localized Hartley (HL) transform (Hartley, 1942; Bracewell, 1990), that allows for the filtering of 1-D time series through the identification of the power at various spatial and temporal wavelengths. Its application to and the associated results are presented from its application to continuous Global Positioning System (GPS) data from southern California for the time period 1994 through 2006. The HL transform filter removes the high-frequency components of the data and effectively isolates the longer period signal. This long-period signal is modeled as time-dependent postseismic deformation using the viscoelastic-gravitational model of Fernández and Rundle (2004) for six stations selected for their proximity to the Northridge earthquake. The x-, y-, and z-components of the postseismic deformation are compared to the filtered data. Results suggest that this long-period deformation is a result of postseismic relaxation and that the HL transform filter provides an important new technique for the filtering of geophysical data consisting of the superposition of the effects of numerous complex sources at a variety of spatial and temporal scales.

Differential interferometry is a very powerful tool for detecting changes in the Earth’s crust where coherence conditions are good, but is difficult to employ in some volcanic areas due to dense vegetation. We apply two differential InSAR methods using the time series associated with the interferograms to perform a phase analysis on a data set for La Palma island (Canary Islands) from the ERS-1 and ERS-2 European Space Agency (ESA) satellites for the time period 1992 to 2000. Both methods involve choosing a master image from the database and creating a series of interferograms with respect to this image. The “Coherent Pixel Time Series” (CPTS) technique chooses pixels with good average coherence, aligns the unwrapped interferograms with a stable area and then performs an inversion to calculate the linear velocity to quantify the deformation. The Coherent Target Modeling (CTM) method calculates the temporal coherence of each pixel to identify stable targets and then determines the best velocity for each pixel by using a linear fit that maximizes the temporal coherence. Using these two methods we have been able to detect deformation on La Palma Island that has been previously undetectable by conventional InSAR methods. There is a roughly circular region on the Southern part of the island that is actively deforming at ~ −4 to −8 mm/yr. This region is located near the Teneguia valcano, the host of the last known eruption on La Palma in 1971. A thorough investigation of the possible sources for this deformation revealed that it was most likely created by a subsurface thermal source.

Knowledge of the Earth’s structure and dynamics calls for a multi-disciplinary study that makes use of the most advanced methods of Physics, Chemistry, Geology, Mathematics and Information Technology, in the framework, or in close collaboration with, the different branches of Earth Sciences such as Geology, Geophysics and Geodesy. The research to be developed includes subjects ranging from data acquisition, both with traditional techniques and with the most advanced resources of our time; data treatment and processing; to the development of new modelling methodologies for the simulation and reproduction and prediction of the terrestrial processes on a local, regional and, by far the most ambitious, global scale.

Knowledge of the Earth’s structure and dynamics calls for a multi-disciplinary study that makes use of the most advanced methods of Physics, Chemistry, Mathematics and Information Technology, in the framework, or in a close collaboration with, the different branches of Earth Sciences such as Geology, Geophysics and Geodesy. The research to be developed includes subjects ranging from data acquisition, both with traditional techniques and with the most advanced resources of our time; data treatment and processing; to the development of new modelling methodologies for the simulation and reproduction and prediction of the terrestrial processes on a local, regional and, by far the most ambitious, global scale.

In the early eighties RUNDLE (1980, 1981a,b, 1982) developed the techniques needed for calculations of displacements and gravity changes due to internal sources of strain in layered linear elasticgravitational media. The approximation of the solution for the half space was obtained by using the propagator matrix technique. The Earth model considered is elastic-gravitational, composed of several homogeneous layers overlying a bottom half space. Two dislocation sources can be considered, representing magma intrusions and faults. In recent decades theoretical and computational extensions of that model have been developed by Rundle and co-workers (e.g., FERNA´ NDEZ and RUNDLE, 1994a,b; FERNA´ NDEZ et al., 1997, 2005a; TIAMPO et al., 2004; CHARCO et al., 2006, 2007a,b). The source can be located at any depth in the media. In this work we prove that the perturbed equations representing the elastic-gravitational deformation problem, with the natural boundary and transmission conditions, leads to a well-posed problem even for varied domains and general data. We present constructive proof of the existence and we show the uniqueness and the continuous dependence with respect to the data of weak solutions of the coupled elastic-gravitational field equations.

The workshop on Deformation and Gravity Change: Indicators of Isostasy, Tectonics, Volcanism and Climate Change took place at the Casa de los Volcanes on Lanzarote, Spain, during March 1–4, 2005 (see Fig. 1). It was jointly organized and supported by the International Association of Geodesy (IAG), the Spanish Ministry of Education and Science, the Spanish Council for Scientific Research and the Cabildo Insular de Lanzarote. From an organizational point of view, the workshop also served as the first meeting of the members the IAG Working Group ICCT2 on Dynamic Theories of Deformation and Gravity Fields existing since late 2003, but was open to all ‘‘external’’ colleagues interested in its topic

Three-dimensional displacements and gravity changes were measured at 20 points between 2000 and 2002 at Merapi volcano, Java, Indonesia. Former models focused on the modeling of a single magmatic source located in the summit region of the volcano. Such models do not fit to our measurements between 2000 and 2002. A new hybrid model approach is developed consisting of an elastic-gravitational source described by a mass and energy term as well as a combined dip-slip/strike-slip fault zone in the summit region. Both nonlinear optimization problems, given by the common inversion of three-dimensional displacements and gravity changes, are solved by applying a genetic algorithm. The hybrid model fits the measurements accurately, tested by Fisher test statistics. Furthermore, our model for Merapi volcano confirms previous structural models for this region so that the new model is statistically proven as well as physically reliable.

In this paper, we analyze the stress change associated with the inverted volcanic source models at Mayon volcano, Philippines, where there are gravity changes without significant deformation after the 1993 eruption. We detail the applicable data and the associated inversion techniques and models prior to calculating the appropriate stress changes. It is determined that the stress change associated with the central magmatic source produces compressional stress changes at a secondary source to the northwest, prompting a change in the local water storage in the underlying fractured rock.

Surface displacements and gravity changes due to volcanic sources are influenced by medium properties. We investigate topographic, elastic and self-gravitation interaction in order to outline the major factors that are significant in data modelling. While elastic-gravitational models can provide a suitable approximation to problems of volcanic loading in areas where topographic relief is negligible, for prominent volcanoes the rough topography could affect deformation and gravity changes to a greater extent than self-gravitation. This fact requires the selection, depending on local relief, of a suitable model for use in the interpretation of surface precursors of volcanic activity. We use the three-dimensional Indirect Boundary Element Method to examine the effects of topography on deformation and gravity changes in models of magma chamber inflation/deflation. Topography has a significant effect on predicted surface deformation and gravity changes. Both the magnitude and pattern of the geodetic signals are significantly different compared to half-space solutions. Thus, failure to account for topographic effects in areas of prominent relief can bias the estimate of volcanic source parameters, since the magnitude and pattern of deformation and gravity changes depend on such effects.