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EGU General Assembly 2019, in Viena, Austria, 7–12 April 2019, Horizontal-to-Vertical Spectral Ratios (H/V) and Rayleigh group velocity dispersion curves can be used to estimate the shallow S-wave velocity (Vs) structure. Knowing the Vs structure is important for geophysical data interpretation either in order to better constrain data inversions for P-wave velocity (Vp) structures such as travel time tomography or full waveform inversions, or to directly study the Vs structure for geo-engineering purposes (e.g. ground motion prediction). The main purpose of this study is to investigate the potential and performance of the combination of H/V and surface wave dispersion data for a dense passive seismic array. The joint inversion of H/V and dispersion data for 1D Vs structure allows to characterize the uppermost crust and near surface, where the H/V data (0.03 to 10 s) is most sensitive while the dispersion data (1 to 30 s) constrains the deeper model which would, otherwise, add complexity to the H/V data inversion and impede its convergence. During this large-scale experiment, 197 three-component short-period stations were continuously operated for 6 months (April to October 2017) covering an area of approximately 1500 km2 with a site spacing of approximately 3 km. The recovered 1D models reach to a depth of 500 to 1000 m. Due to the wide site spacing compared to the model depth, combining these 1D models to a 3D model by interpolation is computationally more economic than attempting a real 3D inversion with this data. The illustrated 3D model can be used to constrain the fine structure of the upper crust for subsequent inversions that attempt to recover deeper models with inherently less resolution such as travel time tomography, or full waveform inversion that requires a very good starting model. Due to the sensitivity of H/V data to density, we also show a preliminary 3D density model of the area that could (and, in the future, will) be used in combination with available gravity measurements.

EGU General Assembly 2019, in Viena, Austria, 7–12 April 2019, Many ambient noise tomography applications are based on measuring surface wave group velocities from timedomain cross-correlations. This approach has several downsides, among them being: (A) reliable group velocity measurements require at least an inter-station distance of 3 wavelengths, (B) usually, only the fundamental mode of Rayleigh wave propagation is considered, disregarding the possible contribution to the observed group/phase velocity of higher modes, and (C) surface wave dispersion measurements only offer weak constraints for the very shallow and the very deep shear-wave velocity structure at the periods used in most regional studies. To overcome these limitations, we propose an inversion scheme based on Aki’s spectral formulation. First, we measured Rayleigh wave phase velocities by fitting Bessel functions to the observed cross-correlation spectra, and used these measurements in a tomographic inversion to produce a set of phase velocity maps. Then, we defined a grid of regularly spaced nodes on the phase velocity maps, and used the dispersion information on a non-linear inversion to obtain a 1D shear-wave velocity profile at each node. Our inversion scheme considers the influence of higher modes in the observed phase velocities. The same noise recordings used for measuring surface wave dispersion can be used to determine the H/V spectral ratios at the receivers. The fundamental frequency and the shape of the peaks in the H/V ratios can be related to the thickness of the sediment layers and the impedance contrasts between the sediments and the basement, thus providing additional constraints for the deep shear-wave velocity structure in the vicinity of the receivers. Therefore, for the nodes closer to the receivers, we performed a joint inversion of the Rayleigh wave phase velocities and the H/V spectral ratios. We applied this methodology to the data provided by the SISCAN-MISTERIOS network, a regularlyspaced grid of 40 broad-band stations with inter-station distances ranging from 27 to 440 km, deployed in the Basque-Cantabrian basin (N Spain) during the period 2014-2018. The Basque-Cantabrian basin (N Spain) is one of the major Mesozoic extensional basins developed during the opening of the Bay of Biscay. In Cenozoic times, the Alpine collision between the European plate and Iberian sub-plate caused the inversion of the normal faults, the reactivation of older (Variscan) thrusts and the creation of new structures. As a consequence, both the depth to the Paleozoic basement and the velocity structure vary greatly across the area, providing a challenging scenario to test the proposed methodology. In spite of some difficulties (i.e. weak impedance contrasts between the Mesozoic sediments and the Paleozoic basement in parts of the basin, problems to retrieve accurate spectral ratios for some stations at the considered frequencies, etc), the application of the methodology described above provided good results in areas where the structure was known in detail, and allowed us to achieve a better constrained image of the 3D shear-wave velocity structure across the whole basin.

EGU General Assembly 2019, in Viena, Austria, 7–12 April 2019, The presence of a crustal root beneath the central part of the Pyrenees has been extensivelly documented by seismic and gravity data and is related to the building of the Pyrenees Chain during the Alpine orogeny. The Eastern termination of the chain is affected by a second major orogenic process, the Neogene extension associated to the rotation of the Sardinia-Corsica block and the opening of the Valencia Trough. This extensional feature has resulted in a rather abrupt thinning of the crust, from 40-45 km about 80 km to the west of the Mediterranean coastline to less than 25 km beneath the eastern termination of the chain. The details of the transition between the central and eastern Pyrenees domains needs still to be fixed into detail. With this objective in mind, two passive seismic profiles have been acquired from mid 2015 to late 2016 within the OROGEN and Pyrope projects. Up to 38 broad-band stations were deployed along two orthogonal lines, with an interstation spacing close to 10 km. The NNE-SSW profile, oriented orthogonally to the Pyrenees trend, shows a well defined Moho beneath Iberia, slightly deepening from 32 to 35 km northwards. Beneath the Axial zone the Moho is located between 30 and 35 km and appears to be segmented in a couple of convertors. Further North, underneath the North Pyrenean Front Thrust , the Moho appears again as a clear and continuous convertor located at 28-30 km. This image clearly differs from the sections obtained in Central and Western Pyrenees, where the imbrication between the Iberian and Eurasian crusts is more conspicuous. Results of receiver function migration on the E-W profile suggest a smooth Moho thinning from a 40 km depth beneath the western termination of the line to 23 km close to the coastline, confirming the picture retrieved from previous, lower resolution experiments and evidencing the crustal thinning due to the Neogene extensional processes. Moderate magnitude earthquakes with epicenters located in the Gulf of Roses and near the intersecting point of the profiles have been recorded along the seismic lines during the experiment, hence providing additional constraints on the geometry of the crust/mantle boundary in the Eastern Pyrenees. In particular, the recordings of the Gulf of Roses event along the NNE-SSW line resulted in a fan profile proving than minor crustal thickness differences between Iberian and Eurasian crusts can still be recognized at longitudes around 2.7ºE, about 30km away from the Mediterranean coast. We are now progressing in the integration of these results with the available geologic transects in order to provide a more accurate geodynamical interpretation of this region., This work has been partially funded by the MISTERIOS Project (CGL2013-48601-C2-1-R).

SeisDARE (Seismic DAta REpository) is an open access database that stores Deep Seismic Sounding and high-resolution seismic data. The collected data are used to study the structure of the lithosphere and for exploration of natural resources, characterization of seismogenic zones and hazard assessment. SeisDARE stores normal incidenve and wide-angle reflection data that cover a wide variety of geological settings, both offshore and onshore. By following the FAIR (Findable, Accessible, Interoperable and Reusable) principles of data management and having regular updates, it brings endless research and teaching opportunities to the scientific, industrial and educational communities. Datasets in Digital.CSIC https://digital.csic.es/handle/10261/101879, Seismic reflection data (normal incidence and wide angle) are unique assets for solid Earth sciences as they provide critical information about the physical properties and structure of the lithosphere as well as about the shallow subsurface for exploration purposes. The resolution of these seismic data is highly appreciated; however they are logistically complex and expensive to acquire, and their geographical coverage is limited. Therefore, it is essential to make the most of the data that have already been acquired. The collation and dissemination of seismic open-access data are then key to promote accurate and innovative research and to enhance new interpretations of legacy data. This work presents the Seismic DAta REpository (SeisDARE), which is, to our knowledge, one of the first comprehensive open-access online databases that stores seismic data registered with a permanent identifier (DOI). The datasets included here are openly accessible online and guarantee the FAIR (findable, accessible, interoperable, reusable) principles of data management, granting the inclusion of each dataset in a statistics referencing database so its impact can be measured. SeisDARE includes seismic data acquired in the last 4 decades in the Iberian Peninsula and Morocco. These areas have attracted the attention of international researchers in the fields of geology and geophysics due to the exceptional outcrops of the Variscan and Alpine orogens and wide foreland basins, the crustal structure of the offshore margins that resulted from a complex plate kinematic evolution, and the vast quantities of natural resources contained within. This database has been built thanks to a network of national and international institutions, promoting a multidisciplinary research and is open for international data exchange and collaborations. As part of this international collaboration, and as a model for inclusion of other global seismic datasets, SeisDARE also hosts seismic data acquired in Hardeman County, Texas (USA), within the COCORP project (Consortium for Continental Reflection Profiling). SeisDARE aims to make easily accessible old and recently acquired seismic data and to establish a framework for future seismic data management plans. SeisDARE is freely available at https://digital.csic.es/handle/10261/101879 (a detailed list of the datasets can be found in Table 1), bringing endless research and teaching opportunities to the scientific, industrial, and educational communities., This research has been supported by the European Plate Observation System (grant nos. EPOS IP 676564 and EPOS SP 871121), EIT Raw Materials (grant no. 17024 SIT4ME), the Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe (grant no. SERA 730900), and the Ministerio de Ciencia e Innovación (Juan de la Cierva fellowship – IJC2018-036074-I).

In this study we analyse three wide-angle seismic profiles in the Pyrenees to provide new insights into their crustal structure. Several earthquakes with magnitudes greater than 2.5 that occurred in the vicinity of the analysed profiles have been used as the seismic source. We demonstrate the feasibility of using natural seismicity as the seismic source, which would allow using deployments of seismic stations designed for other objectives. We have analysed a total of three profiles in this study, two of them being located in the eastern Pyrenees (Cataluña) with N-S and E-O directions, and the third in the western Pyrenees (Navarra) with NE-SO orientation. All of them were originally deployed to record teleseisms for receiver function analysis. Profiles in the eastern Pyrenean edge constrain the top of the lower crust at a depth of 20 km. In the easternmost sector of the E-W profile, Moho has been imaged as an eastward rising ramp, with a depth decreasing from 35- 40 km in the middle of the profile to a depth of 25 km in the eastern edge. The Navarra profile allowed us to constrain the crustal structure of the western Pyrenean edge in detail. The obtained model allowed the imaging of the mid-lower crustal indentation between the Iberian and European plates. The European Moho has been constrained at a depth of 30 km in a small region of the central part of the model, whereas the Iberian Moho has been imaged in its northernmost edge dipping northwards to a depth of 45-50 km., En este trabajo se analizan tres perfiles sísmicos de refracción y reflexión de gran ángulo registrados en los Pirineos con el fin de aportar nuevos conocimientos sobre su estructura cortical. Se emplearon como fuente sísmica varios terremotos de magnitud superior a 2.5 ocurridos en las proximidades de las líneas a estudiar. Se demuestra la viabilidad de utilizar sismicidad natural como fuente sísmica para la realización de perfiles de gran ángulo, lo que permite aprovechar despliegues dispuestos con otros objetivos. Se analizarán dos perfiles localizados en el Pirineo oriental (Cataluña) con direcciones N-S y E-O, y un tercero en el Pirineo occidental (Navarra) con dirección NE-SO, desplegados inicialmente para el registro de telesísmos y el análisis de funciones receptoras. Los perfiles adquiridos en el sector oriental del Pirineo permitieron acotar el techo de la corteza inferior a 20 km de profundidad. El perfil E-O muestra, en su extremo más oriental, el Moho como una rampa ascendente hacia el este, pasando de los 35-40 km de profundidad en la zona central del perfil a 25 km en su extremo oriental. El perfil de Navarra permitió acotar con gran detalle la estructura cortical del extremo occidental del Pirineo. El modelo obtenido muestra la indentación de la corteza inferior y media Europea en la corteza Ibérica. El Moho Europeo aparece a 30 km de profundidad en la zona central, mientras que el Moho Ibérico muestra una rampa buzante hacia el norte, llegando hasta a los 45-50 km de profundidad en su extremo más septentrional., Este trabajo ha sido financiado por el Ministerio de Economía y Competividad, Proyecto MISTERIOS (CGL2013-48601-C2-R) y por el Grupo de Calidad de la Generalitat (2017 SGR1022). El proyecto PYROPE fue financiado por la Agencia Francesa de Investigación ANR blanc Programme (ANR-09-BLAN-0229).

16 pages, 8 figures, 4 tables.-- Data used in this work can be obtained by contacting labsis@geo3bcn.csic.es (for ICJA) or agarcia-jerez@ual.es (for EJDN)., The Horizontal-to-Vertical Spectral Ratio (HVSR) of ambient vibration measurements is a common tool to explore near surface shear wave velocity (Vs) structure. HVSR is often applied for earthquake risk assessments and civil engineering projects. Ambient vibration signal originates from the combination of a multitude of natural and man-made sources. Ambient vibration sources can be any ground motion inducing phenomena, e.g., ocean waves, wind, industrial activity or road traffic, where each source does not need to be strictly stationary even during short times. Typically, the Fast Fourier Transform (FFT) is applied to obtain spectral information from the measured time series in order to estimate the HVSR, even though possible non-stationarity may bias the spectra and HVSR estimates. This problem can be alleviated by employing the Hilbert–Huang Transform (HHT) instead of FFT. Comparing 1D inversion results for FFT and HHT-based HVSR estimates from data measured at a well studied, urban, permanent station, we find that HHT-based inversion models may yield a lower data misfit χ2 by up to a factor of 25, a more appropriate Vs model according to available well-log lithology, and higher confidence in the achieved model. © 2021 by the authors. Licensee MDPI, Basel, Switzerland., This work was funded by TOTAL under the framework of the Orogen project, with funding from the Spanish government through the ?Severo Ochoa Centre of Excellence? accreditation (CEX2019-000928-S) and the research team RNM-194 of Junta de Andaluc?a (Spain). Data from station EJDN were obtained in the context of the CGL2014?59908-JIN project, founded by the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund.

During the COVID-19 pandemic lockdown, the city of Barcelona was covered by a dense seismic network consisting of up to 19 seismic sensors. This network has provided an excellent tool to investigate in detail the background seismic-noise variations associated with the lockdown measures. Permanent stations facilitate comparing the seismic noise recorded during the lockdown quieting with long-term variations due to holiday periods. On the other hand, the data acquired by the dense network show the differences between sites located near industrial areas, transportation hubs or residential areas. The results confirm that the quieting of human activity during lockdown has resulted in a reduction in seismic vibrations in the 2–20 Hz band that is clearly higher than during holiday seasons. This effect is observed throughout the city, but only those stations not affected by very proximal sources of vibration (construction sites, industries) are clearly correlated with the level of activity denoted by other indicators. Our contribution demonstrates that seismic amplitude variations can be used as a proxy for human activity in urban environments, providing details similar to those offered by other mobility indicators., This research has been supported by the Ministerio de Ciencia, Innovación y Universidades (grant no. RTI2018-095594-B-I00), and the Generalitat de Catalunya (grant no. 2017SGR1022). We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

An optimal strategy for building realistic geological models must combine different geophysical techniques, each with its advantages and limitations. However, dealing with multiple geophysical datasets to derive a geological interpretation is not straightforward since geophysical parameters are not always functionally related. In this work, we propose an innovative approach consisting of using machine learning techniques to jointly interpret three geophysical datasets (a pseudo-3D resistivity model, a 3D velocity model, and 4 well-logs). These datasets, among others, were acquired to characterize the suitability of an evaporitic sequence for hosting a temporary storage facility of hazardous radioactive waste, which was planned in Villar de Cañas (Spain). Our strategy consisted of integrating both models in a single 3D bi-parametric grid that nested the velocity and resistivity values in each node. We then used a supervised learning algorithm to lithologically classify each node according to a training set based on the borehole data, which acts as ground truth. The training set is composed of classifiers that lithologically label resistivity-velocity pairs. However, the very shallow nodes lack classifiers due to the poor well-log coverage at the top part of the evaporitic sequence. To fill this gap, we computed an unsupervised cluster analysis that provided new classes to complete the training set. Finally, the supervised classification was applied, providing a new 3D lithology model that is far more consistent with the geology than the models derived from each parameter independently. The 3D model also revealed geological features previously unknown, notably the existence of an inactive fault. The proposed method can be applied to integrate and jointly interpret any kind of multidisciplinary datasets in a wide range of geoscientific problems, including natural resource exploration, geological storage, environmental monitoring, civil engineering practice, and hazard assessment., This work has been supported by projects ref: CGL2014-56548-P, CGL2016-81964-REDE supported by the Spanish Ministry of Science and Innovation, 2017 SGR 1022 Generalitat de Catalunya and, by ENRESA, the latter also facilitated access to log and resistivity data acquired and processed by industry partners (thanks and acknowledgments to INYPSA, EPTISA, ByA-Peñarrolla, and AGS). The instrumentation for the seismic acquisition was provided by different sources: the seismic data recording system consisted of 10 GEODE (Geometrics) and was provided by the GIPP-GFZ Potsdam (Germany). The acoustic energy used as a source was generated by a 250 kg accelerated weight drop provided by the Instituto Tecnico Superior, Univ. Lisbon, (Portugal) and a 90 kg accelerated weight drop provided by the Univ. of Oviedo, (Spain). JA is funded by MICINN (Juan de la Cierva fellowship - IJC2018-036074-I).

The dimensions, the geographical position and the complex geological history of the Iberian Peninsula makes it a unique and singular target to study its crustal and upper mantle structure and geodynamical evolution using geophysical methods. The lithospheric structure beneath Iberia has been investigated since the 1970’s using deep multichannel seismic reflection and refraction/wide-angle reflection profiling. Gravimetric and magnetic data were acquired following the deployment of permanent and temporary stations, mostly during the 1990’s. Beginning in the late 1990’s, the progressive use of Global Navigation Satellite Systems (GNSS) instruments contributed to monitor the present-day motions. During the last decades, numerous geological and geophysical surveys have investigated the Iberian lithosphere and upper mantle in the onshore and offshore regions, the most recent ones related to the TopoIberia project. The approach developed in this contribution is twofold. Firstly, we summarize the available geophysical information over Iberia, from focusing on the upper crust to the lithosphere-asthenosphere boundary and the transition zone marking the bottom of the upper mantle. Results of GNSS data, potential fields, controlled source seismic profiles, magnetotelluric data, body and surface wave tomography, receiver functions and 2D and 3D lithospheric modeling are reviewed and compared. Secondly, we focus on the areas of greater geodynamic interest and the regions where inconsistencies within the geophysical results, or contradictions in their tectonic interpretation exist, identifying the major questions that are still under debate. Besides shedding light to the state of knowledge and pointing out present-day research challenges, this review provides a tool for the integration of the diverse geophysical datasets with the surface geology and geodynamical processes that are interpreted to have built the complex geology of the Iberian Peninsula., The authors acknowledge funding from the Generalitat de Catalunya, grant/awards number AGAUR 2017SGR1022, and AGAUR 2017SGR847, the Spanish Ministry of Science, Innovation, and Universities grant numbers RTI2018-095594-B-I00, PGC2018-095154-B-100 and PGC2018-094227-B-I00 and the Spanish Ministry of Economy and Competitiveness grant numbers CGL2017-84901-C2 and PIE-CSIC-201830E039. IP is funded by the Spanish Ministry of Science, Innovation, and Universities and University of Salamanca grant BEAGAL18/00090. AV acknowledges funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S).

The Iberian Central System, formed after the Alpine reactivation of the Variscan Iberian Massif, features maximum altitudes of 2500 m. It is surrounded by two foreland basins with contrasting elevation: the Duero Basin to the north, located at 750-800m, and the Tajo Basin to the south, lying at 450-500 m. The deep crustal structure of this mountain range seems to be characterized by the existence of a moderate crustal root that provides isostatic support for its topography. New seismic data are able to constrain the geometry of this crustal root, which appears to be defined by a northward lower-crustal imbrication of the southern Central Iberian crust underneath this range. Contrarily to what was expected, this imbrication also affects the upper crust, as the existing orogen-scale mid-crustal Variscan detachment was probably assimilated during the Carboniferous crustal melting that gave rise to the Central System batholith. In addition, the lower crust might have thinned, allowing coupled deformation at both crustal levels. This implies that the reactivated upper-crustal fractures can reach lower-crustal depths, thus allowing the entire crust to sink. This new model can explain the differences in topography between the Central System foreland basins. Also, it provides further constraints on the crustal geometry of this mountain range, as it seems to be that of an asymmetric Alpine-type orogen, thus hindering the existence of buckling processes as the sole origin of the deformation. The results presented here have been achieved after autocorrelation of seismic noise along the CIMDEF (Central Iberian Massif DEFormation Mechanisms) profile. Although the resolution of the dataset features limited resolution (0.5-4 Hz, stations placed at similar to 5 km), this methodology has allowed us to pinpoint some key structures that helped to constraint the deformation mechanisms that affected Central Iberia during the Alpine orogeny., This research has been supported by the Ministerio de Ciencia e Innovacion (grant nos. CGL2014-56548-P and CGL2016-81964-REDE), the Consejeria de Educacion, Junta de Castilla y Leon (grant no. SA065P17), and the Generalitat de Catalunya (grant no. 2017-SGR-1022).

The Spanish Central System is an intraplate mountain range that divides the Iberian Inner Plateau in two sectors - the northern Duero Basin and the Tajo Basin to the south. The topography of the area is highly variable with the Tajo Basin having an average altitude of 450-500 m and the Duero Basin having a higher average altitude of 750-800 m. The Spanish Central System is characterized by a thick-skin pop-up and pop-down configuration formed by the reactivation of Variscan structures during the Alpine orogeny. The high topography is, most probably, the response of a tectonically thickened crust that should be the response to (1) the geometry of the Moho discontinuity, (2) an imbricated crustal architecture, and/or (3) the rheological properties of the lithosphere. Shedding some light on these features is the main target of the current investigation. In this work, we present the lithospheric-scale model across this part of the Iberian Massif. We have used data from the Central Iberian Massif Deformation (CIMDEF) project, which consists of recordings of an almost-linear array of 69 short-period seismic stations, which define a 320 km long transect. We have applied the so-called global-phase seismic interferometry. The technique uses continuous recordings of global earthquakes (>120ĝ' epicentral distance) to extract global phases and their reverberations within the lithosphere. The processing provides an approximation of the zero-offset reflection response of a single station to a vertical source, sending (near)-vertical seismic energy. Results indeed reveal a clear thickening of the crust below the Central System, resulting, most probably, from an imbrication of the lower crust. Accordingly, the crust-mantle boundary is mapped as a relatively flat interface at approximately 10 s two-way travel time except in the Central System, where this feature deepens towards the NW reaching more than 12 s. The boundary between the upper and lower crust is well defined and is found at 5 s two-way travel time. The upper crust has a very distinctive signature depending on the region. Reflectivity at upper-mantle depths is scattered throughout the profile, located between 13 and 18 s, and probably related to the Hales discontinuity. © Author(s) 2019., This research has been supported by the Spanish National Research Program (grant nos. CGL2014-56548-P and CGL2016-81964-REDE), the regional government of Castilla and León (project SA065P17), and the Generalitat de Catalunya (grant no. 2017-SGR-1022); Juvenal Andrés is supported by FPI (Formación de Personal Investigador) from the Spanish Ministry of Science, Innovation and Universities (grant no. BES-2015-071683).

In recent years the analysis of the variations of seismic background signal recorded in temporal deployments of seismic stations near river channels has proved to be a useful tool to monitor river flow, even for modest discharges. The objective of this work is to apply seismic methods to the characterization of the snowmelt process in the Pyrenees, by developing an innovative approach based on the hierarchical classification of the daily spectrograms. The CANF seismic broad-band station, part of the Geodyn facility in the Laboratorio Subterráneo de Canfranc (LSC), is located in an underground tunnel in the Central Pyrenees, at about 400 m of the Aragón River channel, hence providing an excellent opportunity to explore the possibilities of the seismic monitoring of hydrological events at long term scale. We focus here on the identification and analysis of seismic signals generated by variations in river discharge due to snow melting during a period of six years (2011-2016). During snowmelt episodes, the temporal variations of the discharge at the drainage river result in seismic signals with specific characteristics allowing their discrimination from other sources of background vibrations. We have developed a methodology that use seismic data to monitor the time occurrence and properties of the thawing stages. The proposed method is based on the use of hierarchical clustering techniques to classify the daily seismic spectra according to their similarity. This allows us to discriminate up to four different types of episodes, evidencing changes in the duration and intensity of the melting process which in turn depends on variations in the meteorological and hydrological conditions. The analysis of six years of continuous seismic data from this innovative procedure shows that seismic data can be used to monitor snowmelt on long-term time scale and hence contribute to climate change studies., This is a contribution of the MISTERIOS project [CGL2013-48601-C2-1-R] funded by the Spanish Ministry of Economy, Industry and Competitiveness. P.S. has been awarded by the Ministry of Economy, Industry and Competitiveness grant BES-2014-069419. Additional support from the Generalitat de Catalunya grant 2017SGR1022 and from the SANIMS project (RTI2018-095594-B-I00), funded by the Spanish Ministry of Science, Innovation and Universities. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

In November 2014, a temporary land and marine seismic network was deployed to monitor the drilling of an exploratory well in the Canary Channel (eastern Canary Islands). This region is characterized by low-seismic activity; however, because of the increased awareness of the potential seismic hazard caused by hydrocarbon exploitation activities, the drilling operations were monitored with an unprecedented level of detail for an activity of this kind. According to the reported earthquakes, there was not a measurable increase in seismicity in the vicinity of the well. Overall seismic activity was low, which is consistent with the historical seismicity records. Harmonic tremor, explained here as resonances of the instrument-seafloor system generated by bottom water currents in the area, was commonly detected on the ocean-bottom seismometer (OBS) recordings. The marine network data also revealed dozens of nonseismic short-duration signals per day that appear similar to other events on OBS recordings throughout the world. We suggest that they may be caused by direct perturbations on the OBS, mostly induced by ocean currents in the Canary Channel., This research was funded by Repsol Project GEOMARGEN‐3.

Two passive seismic profiles have been acquired in the eastern Pyrenees as part of the Pyrope and Orogen projects to investigate the crustal structure differences between this area and the central and western Pyrenees. Up to 28 broad-band stations were deployed along two orthogonal lines, with an interstation spacing close to 10 km. High frequency receiver functions allowed us to obtain the main lithospheric interfaces along those lines. The NNE-SSW profile shows a well-defined Moho beneath Iberia, slightly deepening northwards. Beneath the Axial zone the Moho appears to be segmented but does not show evidence of crustal imbrication. Further North, the Moho appears again as a continuous interface located around 30 km depth. This image clearly differs from the conspicuous imbrication between the Iberian and Eurasian crusts observed westward. The E-W profile shows a smooth Moho thinning from a 40 km depth to the west of the profile to 23 km close to the coastline, evidencing the crustal thinning related to the Neogene extensional processes. Additional constraints on the geometry of the crust/mantle boundary in the Eastern Pyrenees are obtained from local moderate magnitude earthquakes recorded along the seismic lines during the experiment. In particular, a fan profile built from an event located near the Mediterranean coast suggests that crustal thickness differences between Iberian and Eurasian crusts can still be recognized 30 km westward of the Mediterranean coast, in an area that seems to mark the limit between regions dominated by compressive and extensive processes. We propose a model in which the observed dissimilar Moho structure beneath the Eastern Pyrenees is interpreted as the result of a different Mesozoic pre-shortening margin configuration. Seismic results are consistent with recently proposed tectonic models including an intermediate continental block separating Iberia and Europe by two basins with extremely thin crust or exhumed mantle., This work was funded by the Spanish Ministry of Economy and Competitiveness Project MISTERIOS (CGL2013-48601-C2-2-R), with additional support from the Generalitat de Catalunya grant 2017SGR1022 and projects ALPIMED (PIE-CSIC-201530E082) and SUBTETIS (PIE-CSIC-201830E039). The PYROPE experiment was supported by the French Research Agency ANR blanc programme (project PYROPE, ANR-09-BLAN-0229).