Magnetotelluric Characterization of the Alhama de Murcia Fault (Eastern Betics) - Preliminary Results

The Lorca Earthquake (11/5/2011, Mw 5.2) stands as the most destructive in Spain over the last 50 years. It was interpreted as having occurred in an intersegment zone of the strike-slip Alhama de Murcia Fault (AMF). Within the research project “Intergeosima”, a multi parametric characterization and monitoring of the fault structure is ongoing, with the aim of developing a future Near Fault Observatory (NFO) to improve the understanding of the seismic behaviour of the fault in the short and medium term. In this work we present the preliminary results of a magnetotelluric (MT) survey carried out along the rambla de la Torrecilla (SW of Lorca). A more resistivity area might correspond to the Quaternary units, whereas the conductive areas might delineate the extent of the fault gauge materials. Further analysis and inversion of the data are necessary to obtain a more detailed picture of the extension and geometry below the fault zone

Architectural characterization of a delta-front reservoir analogue combining Ground Penetrating Radar and Electrical Resistivity Tomography : Roda Sandstone (Lower Eocene, Graus-Tremp basin, Spain)

Three-dimensional reconstruction of reservoir analogues can be improved combining data from different geophysical methods. Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) data are valuable tools, since they provide subsurface information from internal architecture and facies distribution of sedimentary rock bodies, enabling the upgrading of depositional models and heterogeneity reconstruction. The Lower Eocene Roda Sandstone is a well-known deltaic complex widely studied as a reservoir analogue that displays a series of sandstone wedges with a general NE to SW progradational trend. To provide a better understanding of internal heterogeneity of a 10m-thick progradational delta-front sandstone unit, 3D GPR data were acquired. In addition, common midpoints (CMP) to measure the sandstone subsoil velocity, test profiles with different frequency antennas (25, 50 and 100MHz) and topographic data for subsequent correction in the geophysical data were also obtained. Three ERT profiles were also acquired to further constrain GPR analysis. These geophysical results illustrate the geometry of reservoir analogue heterogeneities both depositional and diagenetic in nature, improving and complementing previous outcrop-derived data. GPR interpretation using radar stratigraphy principles and attributes analysis provided: 1) tridimensional geometry of major stratigraphic surfaces that define four units in the GPR Prism, 2) image the internal architecture of the units and their statistical study of azimuth and dips, useful for a quick determination of paleocurrent directions. These results were used to define the depositional architecture of the progradational sandbody that shows an arrangement in very-high-frequency sequences characterized by clockwise paleocurrent variations and decrease of the sedimentary flow, similar to those observed at a greater scale in the same system. This high-frequency sequential arrangement has been attributed to the autocyclic dynamics of a supply-dominated delta-front where fluvial and tidal currents are in competition. The resistivity models enhanced the viewing of reservoir quality associated with cement distribution caused by depositional and early diagenetic processes related to the development of transgressive and regressive systems tracts in high-frequency sequences

Social Enterprise in Spain: A Diversity of Roots and a Proposal of Models

The term “social enterprise” was first used, at the end of the 1980s, by organisations that promoted the social and labour integration of persons at risk of social and labour exclusion and other similar social activities. The social economy sector has since slowly introduced this term to describe its entities in order to gain recognition by society, and it is working to promote a generally accepted definition of social enterprise’s behaviour based on the principles and values of the social economy (participation, general interest...). According to Article 5 of Spanish Law 5/2011 on the Social Economy, work integration social enterprises and so-called “special employment centres” are part of the social economy, and so are all firms and entities carrying out activities following the values and principles of the social economy sector. In this context, organisations of the social economy sector also are beginning to use the “social enterprise” concept. In Spain, a debate still exists regarding its exact definition. A mix of perspectives on this concept, with different nuances, can be observed. Besides, the current context of reduced governmental budgets and social services in Spain causes social organisations to adopt new approaches to this term of social enterprise, as this type of organisation is more likely to receive funds from the European Union. This paper’s objective is to analyse all perspectives on the concept of social enterprise as well as the various social enterprise models existing in Spain. The document structure is organized as follow. In the first section, we present the context and the main concepts related to social enterprises in this country. In the second section, we provide an analysis of changes in the evolution of social enterprise criteria to identify established models and emerging patterns. In the third section, we put forward another typology, based on institutionalisation stages. Finally, we conclude by recommending an approach to future work and provide a basic bibliography on the subject

Time-lapse cross-hole electrical resistivity tomography (CHERT) for monitoring seawater intrusion dynamics in a Mediterranean aquifer

Surface electrical resistivity tomography (ERT) is a widely used tool to study seawater intrusion (SWI). It is noninvasive and offers a high spatial coverage at a low cost, but its imaging capabilities are strongly affected by decreasing resolution with depth. We conjecture that the use of CHERT (cross-hole ERT) can partly overcome these resolution limitations since the electrodes are placed at depth, which implies that the model resolution does not decrease at the depths of interest. The objective of this study is to test the CHERT for imaging the SWI and monitoring its dynamics at the Argentona site, a well-instrumented field site of a coastal alluvial aquifer located 40¿km NE of Barcelona. To do so, we installed permanent electrodes around boreholes attached to the PVC pipes to perform time-lapse monitoring of the SWI on a transect perpendicular to the coastline. After 2 years of monitoring, we observe variability of SWI at different timescales: (1) natural seasonal variations and aquifer salinization that we attribute to long-term drought and (2) short-term fluctuations due to sea storms or flooding in the nearby stream during heavy rain events. The spatial imaging of bulk electrical conductivity allows us to explain non-monotonic salinity profiles in open boreholes (step-wise profiles really reflect the presence of freshwater at depth). By comparing CHERT results with traditional in situ measurements such as electrical conductivity of water samples and bulk electrical conductivity from induction logs, we conclude that CHERT is a reliable and cost-effective imaging tool for monitoring SWI dynamics.This work was funded by the project CGL2016-77122-C2-1-R/2-R of the Spanish Government. This project also received funding from the European Commission, Horizon 2020 research and innovation programme (Marie Sklodowska-Curie (grant no. 722028)). The author Albert Folch is a Serra Húnter Fellow.Peer ReviewedPostprint (published version

Imaging leachate runoff from a landfill using magnetotellurics: The Garraf karst case

Electrical and active source electromagnetic geophysical methods have been traditionally employed to approach and tackle environmental problems, such as those caused by landfills. However, since these problems are more consequential and cover broader areas, it is necessary to use deeper penetration methods, such as magnetotellurics. In the Garraf Massif (Catalan Coastal Ranges, NE Spain), an urban waste disposal landfill had been in operation from 1974 to 2006, during which more than 26 million metric tons of garbage had been deposited. This landfill overlies karstic terrain, thus principally impacting groundwater circulation. Previous electrical resistivity tomography profiles had partially imaged the infill but were not able to penetrate below the base of the original landfill. During 2019 and 2020 we performed a magnetotelluric study over the landfill and its surrounding with the goals of characterizing the electrical resistivity of the infill and below it. The 2D and 3D resistivity models confirmed the highly conductive nature of the leachate and allowed us to identify its presence below the landfill base, which we quantified with maximum thicknesses of 90 m. This proved that landfill leachate had filtered through the original impermeable layer, enhanced by the karstic drainage structure

High-resolution scan of the Pyrenean crustal structure combining magnetotelluric and gravity data

The Pyrenees have undergone complex geodynamic evolution starting with experiencing significant tectonic events during the Variscan Orogeny, followed by the intrusion of large granitic complexes during the late Variscan stage, then the collision between the Iberian and European plates during the Alpine Orogeny, and finally, Mesozoic extension. Despite extensive studies and the application of various geophysical methods (two-dimensional seismic reflection data, gravity, and long period magnetotellurics) to investigate the Pyrenean structure, there are still fundamental questions regarding its basement and cover architecture. Specifically, the geometry at depth of significant bodies such as the Late Variscan intrusive granites and Triassic evaporitic accumulations, remains unclear. To better understand these issues, we have conducted joint magnetotelluric and gravity surveys along a 60-kilometer-long transect, spanning the boundary between the Axial and South Pyrenean Zones. Our final geological interpretation shows that the La Maladeta batholith consists of two distinct granitic bodies related to different intrusive pulses. In addition, we identify important Triassic evaporitic accumulations at depth. This work shows the high potential of integrating two geophysical models for understanding the geological evolution of structurally complex areas. The magnetotelluric and gravity data are complementary, with each dataset providing a different resolution for investigating the basement and cover architecture of the Pyrenees. These resolutions depend on the varied petrophysical properties of the rocks involved, including water content and deformation grade

Structure of the mantle beneath the Alboran basin from magnetotelluric soundings

We present results of marine MT acquisition in the Alboran sea that also incorporates previously acquired land MT from southern Spain into our analysis. The marine data show complex MT response functions with strong distortion due to seafloor topography and the coastline, but inclusion of high resolution topography and bathymetry and a seismically defined sediment unit into a 3D inversion model has allowed us to image the structure in the underlying mantle. The resulting resistivity model is broadly consistent with a geodynamic scenario that includes subduction of an eastward trending plate beneath Gibraltar, which plunges nearly vertically beneath the Alboran. Our model contains three primary features of interest: a resistive body beneath the central Alboran, which extends to a depth of ~150 km. At this depth, the mantle resistivity decreases to values of ~100 Ohm-m, slightly higher than those seen in typical asthenosphere at the same depth. This transition suggests a change in slab properties with depth, perhaps reflecting a change in the nature of the seafloor subducted in the past. Two conductive features in our model suggest the presence of fluids released by the subducting slab or a small amount of partial melt in the upper mantle (or both). Of these, the one in the center of the Alboran basin, in the uppermost-mantle (20-30km depth) beneath Neogene volcanics and west of the termination of the Nekkor Fault, is consistent with geochemical models, which infer highly thinned lithosphere and shallow melting in order to explain the petrology of seafloor volcanics