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The seismicity in the SE Iberian Peninsula is distributed parallel to the coast in a well-developed strike-slip fracture system known as the Eastern Betic Shear Zone (EBSZ). This work focuses on the characterization of the shallow subsurface structure of the Algezares-Casas Nuevas Fault, within the Carrascoy Fault System of the EBSZ. The Carrascoy Fault borders the Guadalentín Depression to the south, which is a densely populated area with extensive agricultural activity. Therefore, this faults system represents a seismic hazard with significant social and economic implications. We have constructed two velocity-depth models based on P-wave tomography and Multichannel Analysis of Surface Waves (MASW) acquired from seismic reflection data. The resulting velocity models have allowed us to interpret the first ~250m depth and have revealed: i) the thickness of the critical zone; ii) the geometry of the Algezares-Casas Nuevas Fault; iii) the depth of the Messinian/Tortonian contact and iv) the presence of blind thrusts and damage zones under the Guadalentín Depression. Our results have also helped us to estimate an apparent vertical slip rate of 0.66±0.06m/ky for the Algezares-Casas Nuevas Fault since 209.1±6.2ka. Our results provide a methodological and backflow protocol to study the shallow subsurface of active faults, complementing previous geological models based on paleoseismological trenches, and can be used to improve the seismic hazard assessment of tectonically active regions around the world., The authors would like to acknowledge the project INTERGEO (CGL2013-47412-C2-1-P) GEO3BCNCSIC for the data access. Data are public access through SeisDARE (DeFelipe et al., 2021), dataset Martí et al. (2015). The Ministry of Education and Culture of the Republic of Indonesia is thanked for the main author’s Ph.D. scholarship (D3.2/KD.02.01/2019). JA is funded by MICINN (IJC2018-026335-I). I.P. is funded by the Spanish Government and the Universidad de Salamanca (Beatriz Galindo grant BEGAL 18/00090). IDF is funded by a FEDER-Junta de Castilla y León Postdoctoral contract (SA0084P20). We thank the GIPP-GFZ, (Germany) and Lisbon University (Portugal) for the instrumentation provided. Generalitat de Catalunya (AGAUR) grant 2017SGR1022 (GREG); EU (H2020) 871121 (EPOSSP); and EIT-RawMaterias 17024 (SIT4ME).

[EN]: A seismic profile has been performed across the Algezares-Casas Nuevas fault zone, the SW section of the major Carrascoy Fault, a potential source of earthquakes in the region and hence an important threat to the nearby City of Murcia. The seismic data were processed to obtain a Vp model and provide insight into the depth structure of the fault zone. The Vp model was interpreted according to the local geology and surface data, enabling the location of the Messinian/Tortonian contact, and also the erosive contact of the Red Unit (Pliocene alluvial fan deposits) on the Messinian deposits. Both contacts are offset by two principal thrusts identified in the profile, by a similar amount ca. 135-140 m. Considering the age of the onset of the deformation, quoted in 209 ka in previous studies, a vertical slip rate around double that previously calculated can be estimated. We discuss the different causes for this disagreement and we conclude about the important impact that such a slip rate could have on seismic hazard studies., This research was funded by the Secretaría de Estado de Investigación, Desarrollo e Investigación (MINECO) projects INTERGEO (CGL2013-47412-C2-1-P) and QUAKESTEP (CGL2017-83931-C3-1-P). I.P. is funded by the Spanish Government and the Universidad de Salamanca (Beatriz Galindo grant BEGAL 18/00090). J.A. is funded by grant IJC2018-036074-I, by MCIN/AEI /10.13039/501100011033.

2021 International Symposium on Deep Earth Exploration and Practices DEEP-2021, 1 - 6 november 2021, Virtual Meeting & International Everywhere, A multidisciplinary study unsing a number of different geophysical methodologies forcharacterizing the nature and structure of the shallow subsurface was carried out in an area of activedeformation located in (SE Iberian Peninsula). An approximately 400 km long network of prominentactive faults oriented NE-SW near parallel to the coast line constitute a singular tectonic feature thatcharacterize the southeastern part of the Iberian Peninsula. This transpressive tectonic corridor, knownas the Eastern Betics Shear Zone (EBSZ) is considered one of the longest and most active fault systemin the Iberia Peninsula. The EBSZ system is a strike slip plate boundary, which is accommodating theconvergence within Iberia of the interaction between the Nubian and Eurasian plates. The fault networkfeatures a reverse and left-lateral strike-slip kinematics with a characteristic sigmoidal trend delineatedby a number of major individual faults as well as other less relevant faults. Within and along thislocalized deformation corridor many destructive earthquakes with relative high intensities have affectedthis region since historical times The interdisciplinary geophysical datasets acquired place strongconstraints on the high-resolution structure of the well defi ned fracture system. The datasets reveal thethickness and properties of the critical zone (CZ) layer. The study includs: Electrical ResistivityTomography (ERT), fi rst arrival time seismic tomography, and multichannel analysis of surface waves(MASW). The combination of these three methods yields complementary benchmarks for mappingshallow subsurface fault zones and the physical properties of the CZ layer. The resulting model andinterpretation reveal new information on the relationship between the topographical slope and thethickness of the CZ layer related to the transport process and the accumulation of regolith alteration.The distribution of the CZ layer is characterized by layers with low P-wave & S-wave velocity anomalies(Vp< 1300 m/s & Vs< 600 m/s) and high resistivity (¿ > 100 ¿m). The presence of a fault zone ischaracterized by vertically low velocity anomalies (P-wave and S-wave) with laterally marked contrastanomalies featuring higher velocity. Meanwhile, from ERT, the fault zone is characterized by a strikingvertical change in resistivity. The results of ERT data processing and P-wave & S-wave velocity inversionare able to provide good and consistent shallow subsurface images. However, the high-resolution S-wave profi le of the MASW method is very accurate in describing the thickness of the CZ layer. From NWto SE, the thickness of the CZ layer varies in thickness from 15 to 30 m in areas with gentle slopes andthickens up to thickness of about 50-60 m at locations with high topographical slopes. In addition, thepresence of the fault zone also has the effect of strengthening the CZ layer as a zone that producesrelatively thick regolith alteration. Keywords: critical zone CZ, ERT, Lorca, MASW, regolith

The deep structure of the Alhama de Murcia Fault (AMF) is characterized by means of the analysis of surface waves identified in shallow high resolution seismic reflection data. Multichannel analysis of surface waves (MASW) is used to unravel the 2-D S-wave velocity model and image the depth geometry of the fault system. The study area includes segments of the fault located in La Salud area. Two approaches have been used to achieve a well constrained velocity model in the AMF fault zone. Conventional seismic reflection processing work flow has been used to clean the seismic data and increase its S/N ratio. Occam’s approach has been used to invert the digitized surface wave dispersion curves. 1D shear wave velocity-depth profiles were estimated in shot and CDP domains. Relatively well resolved 2D velocity-depth models were obtained by com- posite of the 1D Velocity-depth functions. These composite 2D-velocity models are able to constrain the depth geometry of the fault zone up to 100 m depth. The fault zone is indicated by a relatively broad low velocity anomaly that correlates with the fault’s surface expression.

Two scientific boreholes, Almera-1 and Almera-2 were drilled in the Barcelona University campus area in 2011. The main purpose for this drilling was to create a new geophysical logging and downhole monitoring research facility and infrastructure. We present results obtained in the frame of multidisciplinary studies and experiments carried out since 2011 at the ICTJA “Borehole Geophysical Logging Lab - Scientific Boreholes Almera” downhole lab facilities. First results obtained from the scientific drilling, coring and logging allowed us to characterize the urban subsurface geology and hydrology adjacent to the Institute of Earth Sciences Jaume Almera (ICTJA-CSIC) in Barcelona. The subsurface geology and structural picture has been completed with recent geophysical studies and monitoring results. The upper section of Almera-1 214m deep hole was cased with PVC after drilling and after the logging operations. An open hole interval was left from 112m to TD (Paleozoic section). Almera-2 drilling reached 46m and was cased also with PVC to 44m. Since completion of the drilling in 2011, both Almera-1 and Almera-2 have been extensively used for research purposes, tests, training, hydrological and geophysical monitoring.

En 2011 junto al Instituto de Ciencias de la Tierra Jaume Almera-CSIC, en Barcelona, se perforó un sondeo científico con el objeto de disponer de una infraestructura destinada a la investigación con sondas de testificación geofísica, monitorización de sondeos, la formación especializada y también para la exploración del subsuelo urbano. La extracción de testigo continuo y un completo estudio mediante sondas de testificación geofísica del ICTJA-CSIC, permitieron caracterizar la sección geológica, estructuras atravesadas y características hidrogeológicas en el sondeo Almera-1. Se presentan aquí los resultados obtenidos en una exploración sísmica de la estructura en el entorno del sondeo y el reconocimiento de la estructura en la que está emplazado el mismo. En este contexto se planteó una tomografía sísmica vertical inversa pseudo-3D (o 2.5D), cuyo dispositivo experimental, metodología y resultados son objeto de este trabajo. Se define la estructura en el entorno del sondeo y se establece una correlación entre las respuestas geofísicas y los distintos tramos de materiales reconocidos en el subsuelo.

La falla de Alhama de Murcia (AMF) es una de las fallas más activas de la Península Ibérica y fue la causante del terremoto de Lorca de 2011 que significó numerosos daños materiales e incluso víctimas mortales. Esta falla oblicua en dirección NE-SO, que se extiende por más de 100 km, ha sido estudiada en superficie pero poco se sabe de su estructura en profundidad. Esto es especialmente importante para poder interpretar de forma correcta los numerosos datos paleosísmicos que se están obteniendo, ya que conocer la relación estructural en profundidad de las distintas ramas que forman la AMF es esencial. Por este motivo, y dentro del marco del proyecto InterGEO, se ha realizado una campaña de adquisición de datos sísmicos 2D a lo largo de la AMF, centrándose en los segmentos más interesantes en la zona de Lorca-Totana. Aquí se presentan los los resultados preliminares del procesado de algunos de los perfiles adquiridos en esta campaña que muestran la primera imagen estructural de la falla en profundidad y que permitirá entender el comportamiento de dicha falla, así como determinar su relevancia desde el punto de vista del riesgo sísmico., Este trabajo ha podido ser realizado gracias a la financiación de los proyectos CGL2014-56548-P, 2009-SGR-1595, 2009-SGR-1595.

Trabajo presentado en el 17th International Seismix Symposium, celebrado en Aviemore (Escocia), del 15 al 20 de mayo de 2016, The Alhama de Murcia fault (AMF) is one of the most active faults of the Iberian Peninsula and the source of the Lorca 2011 earthquake that caused significant demage including several casualties. This NE-SW oblique (strike slip-reverse movement) fault, extended up to 100 km, has been extensively mapped to characterize its surface structure but almost no information is available of the structure and geometry at depth. As a result of the Lorca 2011 earthquake and its devastating effects in the population a need for better knowledge of the AMF became mandatory. Accordingly, InterGEO project pursues to understand the seismic behaviour of the fault and determine its relevance in seismic hazard. In order to achieve this, a multidisciplinary approach is used including detailed geological mapping, paleoseismic trenches, borehole logging and geophysical characterization., The main aim is to characterize the AMF in the sorroundings of the Lorca city ,from surface to depth, in the most interesting fault segments., Research supports: CGL2014-56548-P, 2009-SGR-1595 , CGL2013-47412-C2-1-P

Trabajo presentado en la 9ª Asamblea Hispano Portuguesa de Geodesia y Geofísica, celebrada en Madrid (España), del 28 al 30 de junio de 2016, [ES] El sistema de fallas Alhama-Murcia (FAM) se halla en la cordillera Bética, al sur de la Península Ibérica. Con orientación NE-SW tiene una extensión de unos 100 km y ha sido ampliamente cartografiada para caracterizar su estructura superficial, pero hay poca informaciónsobre su estructra y geometría en profundidad. El terremoto destructivo de Lorca (Mw 5.2) ocurrido en 2011 se asocia a esta falla. En el marco del proyecto de investigación InterGEO que tiene por objetivo el desarrollo de Obsevatorios cercanos a fallas activas (NFO), se obtuvieron una serie de modelos geofísicos 2D en distintos transectos del sistema. En esta comunicación se presentan los modelos sísmicos (refracción, reflexión y MASW) y un perfil eléctrico (ERT) profundoobtenidos para el transecto de la Torrecilla, situados a 3 km al SW de Lorca donde la zona de falla está más concentrada. Los resultados de estos modelos se correlacionan con un sondeo de invetsigación de 175 m de profundidad perforado cerca de la rambla de La Torrecilla., [EN] The Alhama-Murcia system fault (AMF) is placed in Betic mountain range to the south of the Iberian Peninsula. This NE-SW oblique fault, extended up to 100 km, has been extensively mapped to characterize its surface structure but almost no information is available of the structure and geometry at depth. The destructive earthquake of Lorca (Mw 5.2) occurred on 2011 is associated with this fault. Within the InterGEO research project with the aim to be the seed for the development of a future Near Fault Observatories (NFO), 2D geophysical models were carried out cutting the AMF at several segments. In this communication we present the seismic models (refraction, reflection and MASW) and the 2D electrical resistivity profile (ERT) obtained in the Torrecilla transect, three km SW of Lorca where the fault zone shearing is more concentrated. The results of these 2D models are correlated with the results of the scientific borehole FAM-1 a 175 m depth drilled close to La Torrecilla rambla.

O presente trabalho pretende identificar estruturas arqueológicas enterradas no povoado de Outeiro do Circo (Mombeja, Beja), cruzando dois métodos de prospecção geofísica: georradar e magnetometria. Para concretizar o objectivo da missão realizaram-se ensaios dos dois métodos em áreas distintas. O processamento dos dados registados permitiu identificar estruturas enterradas, nomeadamente os vestígios da muralha que rodeava o povoado e edifícios que terão existido no seu interior. Os resultados de ambos os métodos permitem inferir a existência de estruturas arqueológicas no local, que em breve serão confirmadas pelas escavações arqueológicas em curso.

Monitoring seismic signal associated to active faults in SE Iberia was undertaken by the installation of 3-component geophone strings in boreholes and also on the surface, close to active faults located in Torreperogil-Sabiote area and Baza basin. Our instrumentation was installed in existing hydrogeological and geotechnical boreholes for continuous monitoring of low intensity seismic activity during 8 months. Borehole geophone strings consisting of 8 receivers of 3-component, with 15Hz of natural frequency, spaced 6 m at depth were used. The main purpose of continuous monitoring of the seismic signal in the subsurface was to record the high frequencies of the seismic data and to investigate and eventually characterize fault creep and seismic noise related to deformation and fault movements in seismically active areas. The dataset recorded included a series of low magnitude earthquakes and is being analyzed to identify and characterize seismic events. A 3G GSM module was used together with the acquisition system in order to guarantee remote access to check the acquired data quality and to control the acquisition parameters. Also, the remote access allowed us to pre-process the data 'in situ' and to perform only selective transmission of the most relevant files. Because of the isolated and remote locations of some of the monitoring stations, proprietary software was developed to avoid the possible losses of communication between the acquisition system and remote control computer. In this contribution we present the most relevant features of the acquisition and methodology implemented for this acquisition, first results of the field experiment and data processing and advantages of the on site pre-processing management and remote operation of the acquisition system. This system is being applied to other active fault zones in the area.

In the frame of the research conducted to develop efficient strategies for investigation of rock properties and fluids ahead of tunnel excavations the seismic interferometry method was applied to analyze the data acquired in boreholes instrumented with geophone strings. The results obtained confirmed that seismic interferometry provided an improved resolution of petrophysical properties to identify heterogeneities and geological structures ahead of the excavation. These features are beyond the resolution of other conventional geophysical methods but can be the cause severe problems in the excavation of tunnels. Geophone strings were used to record different types of seismic noise generated at the tunnel head during excavation with a tunnelling machine and also during the placement of the rings covering the tunnel excavation. In this study we show how tunnel construction activities have been characterized as source of seismic signal and used in our research as the seismic source signal for generating a 3D reflection seismic survey. The data was recorded in vertical water filled borehole with a borehole seismic string at a distance of 60 m from the tunnel trace. A reference pilot signal was obtained from seismograms acquired close the tunnel face excavation in order to obtain best signal-to-noise ratio to be used in the interferometry processing (Poletto et al., 2010). The seismic interferometry method (Claerbout 1968) was successfully applied to image the subsurface geological structure using the seismic wave field generated by tunneling (tunnelling machine and construction activities) recorded with geophone strings. This technique was applied simulating virtual shot records related to the number of receivers in the borehole with the seismic transmitted events, and processing the data as a reflection seismic survey. The pseudo reflective wave field was obtained by cross-correlation of the transmitted wave data. We applied the relationship between the transmission response and the reflection response for a 1D multilayer structure, and next 3D approach (Wapenaar 2004). As a result of this seismic interferometry experiment the 3D reflectivity model (frequencies and resolution ranges) was obtained. We proved also that the seismic interferometry approach can be applied in asynchronous seismic auscultation. The reflections detected in the virtual seismic sections are in agreement with the geological features encountered during the excavation of the tunnel and also with the petrophysical properties and parameters measured in previous geophysical borehole logging. References Claerbout J.F., 1968. Synthesis of a layered medium from its acoustic transmision response. Geophysics, 33, 264-269 Flavio Poletto, Piero Corubolo and Paolo Comeli.2010. Drill-bit seismic interferometry whith and whitout pilot signals. Geophysical Prospecting, 2010, 58, 257-265. Wapenaar, K., J. Thorbecke, and D. Draganov, 2004, Relations between reflection and transmission responses of three-dimensional inhomogeneous media: Geophysical Journal International, 156, 179-194.

The TOMO-ETNA experiment was planned in order to obtain a detailed geological and structural model of the continental and oceanic crust beneath Mt. Etna volcano and northeastern Sicily up to the Aeolian Islands (southern Italy), by integrating data from active and passive refraction and reflection seismic methodologies, magnetic and gravity surveys. This paper focuses on the marine activities performed within the experiment, which have been carried out in the Ionian and Tyrrhenian Seas, during three multidisciplinary oceanographic cruises, involving three research vessels (“Sarmiento de Gamboa”, “Galatea” and “Aegaeo”) belonging to different countries and institutions. During the offshore surveys about 9700 air-gun shots were produced to achieve a high-resolution seismic tomography through the wide-angle seismic refraction method, covering a total of nearly 2650 km of shooting tracks. To register ground motion, 27 ocean bottom seismometers were deployed, extending the inland seismic permanent network of the Istituto Nazionale di Geofisica e Vulcanologia and a temporary network installed for the experiment. A total of 1410 km of multi-channel seismic reflection profiles were acquired to image the subsurface of the area and to achieve a 2D velocity model for each profile. Multibeam sonar and sub bottom profiler data were also collected. Moreover, a total of 2020 km of magnetic and 680 km of gravity track lines were acquired to compile magnetic and gravity anomaly maps offshore Mt. Etna volcano. Here, high-resolution images of the seafloor, as well as sediment and rock samples, were also collected using a remotely operated vehicle.