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Since the 1980s a number of active and passive seismic experiments have revealed significant information about the Earth’s crust in the broader European Alpine region. In this paper, we use seismic waveform data from the AlpArray Seismic Network and three other temporary seismic networks, to perform receiver function (RF) calculations and time−to−depth migration to update the knowledge of the Moho discontinuity beneath the broader European Alps. In particular, we set up a 5 homogeneous processing scheme to compute RFs using the time-domain iterative deconvolution method, and apply consistent quality control to yield 107,633 high-quality RFs. We then perform time−to−depth migration in a newly implemented 3D spherical coordinate system and using a European-scale reference P and S wave velocity model. This approach, together with the dense data coverage, provide us with a 3D migrated volume, from which we present migrated profiles that reflect the first-order crustal thickness structure. We create a detailed Moho map by manually picking the discontinuity in a set of orthogonal 10 profiles covering the entire area. We make the RF dataset, the software for the full processing workflow, as well as the Moho map, openly available; these open-access datasets and results will allow other researchers to build on the current study.

Within the framework of the European collaborative research initiative AlpArray (http://www.alparray.ethz.ch), the Istituto Nazionale di Geofisica e Vulcanolgia (INGV) deployed overall 20 broad-band seismic stations in Northern Italy and on two islands in the Tyrrhenian Sea (Capraia and Montecristo) during Fall-Winter 2015. The temporary deployment (16 stations) will run for two to three years and 4 INGV National Seismic Network accelerometric sites are now equipped with additional permanent broad-band sensors. The 16 temporary stations are equipped with REF TEK 130 digitizers and Nanometrics Trillium Compact 120 s sensors, a couple have Nanometrics Trillium 120P sensors and one a Streckeisen STS2. For each site we describe the settings and discuss the noise levels, the site effects and the preliminary sensitivity analysis.

The IberArray instrumental platform, part of the TopoIberia project, has provided a huge increase on the geophysical datasets available to constrain the structure and dynamics of the mantle beneath the Iberian Peninsula. Receiver Functions have allowed to map accurately large crustal thickness variations. Volume and surface wave tomographies have been obtained for the crust and the upper mantle, allowing to define the geometry of the highvelocity slab beneath Alboran. The 410-km and 660-km discontinuities have been investigated using novel crosscorrelation/stacking techniques. Finally, the measurement and interpretation of the anisotropic parameters has provided a new insight on the asthenospheric flow., Este trabajo ha recibido financiación procedente proviene del Ministerio de Economía y Competitividad (MINECO) mediante los proyectos CSD 2006-00041 (TopoIberia), Red TopoIberia-Iberarray CGL2014-54582-REDC] y de la subvención de la Generalitat de Catalunya 2009SGR996.

Topo-Iberia has been a large-scale Spanish project running from 2007 to 2013 that integrated more than 150 researchers on Earth Sciences. One of its key assets was the management of an observatory platform, named IberArray, aimed to provide new geophysical datasets (seismic, GPS, MT) to constrain the structure of Iberia with unprecedented resolution. The IberArray seismic pool was composed by 70+ BB stations, covering the study area in 3 deployments with a site-density of 60km x 60km. The data base holds ~300 sites, including the permanent networks in the area. Hence it forms a unique seismic database in Europe that allows for multiple analyses to constrain the complex geodinamics of the Western Mediterranean. A summary of new results coming from different techniques is presented here. The SKS splitting analysis has provided a spectacular image of the rotation of the fast velocity direction along the Gibraltar Arc. In central and northern Iberia, the fast polarization directions are close to EW, consistently with global mantle flow models considering contributions of surface plate motion, density variations and net lithosphere rotation. Those results suggest an asthenospheric origin of the observed anisotropy related to present-day mantle flow. Receiver functions have revealed the crustal thickness variations beneath the Atlas, Rif and southern Iberia, evidencing a relevant crustal root beneath the Rif, in agreement with recent, high- density active seismic experiments. The Variscan Iberian massif shows a flat Moho discontinuity, while the areas reworked in the Alpine orogeny show a slightly thicker crust. Beneath N Iberia, the imbrication of the Iberian and Eurasian crusts results in complex receiver functions. Depths exceeding 45 km are observed along the Pyrenean range, while the crust thins to values of 26-28 km close to the Atlantic coasts. The geometry of the 410-km and 660-km discontinuities has been investigated using novel cross-correlation/stacking techniques. Ambient noise tomography allows to identify the main sedimentary basins and to discriminate between the Variscan and the Alpine reworked areas. Local body-wave tomography in North Morocco has improved the location of the small magnitude events on the area and the details of the crustal structure. Teleseismic tomography has confirmed, using an independent data set, the presence of a high-velocity slab beneath the Gibraltar Arc.

Se han aplicado técnicas de correlación cruzada y de stacking para detectar señales por la coherencia entre su forma de onda y la de una señal piloto. Se extrae una ondícula piloto de la componente vertical, que contiene la fase P y parte de su coda, y se aplican la correlación cruzada de fase y la correlación cruzada geométricamente normalizada entre la ondícula piloto y las componentes radial y vertical de cada evento. Con este procedimiento se detectan las fases convertidas de P a s y las reflexiones en las diferentes discontinuidades del manto superior. El stacking se usa para realzar las señales que llegan de forma consistente (conversiones y reflexiones cercanas al receptor) y para atenuar fases profundas aisladas y también llegadas espurias. Hemos usado más de 40 estaciones seleccionadas de la red sísmica IberArray ubicada en el S de España y N de Marruecos. Se han detectado conversiones de P a s y reflexiones de onda P en las discontinuidades de 410-km y 660-km de profundidad (límites de la Zona de Transición) debajo de la zona de estudio. Se presentaran mapas del espesor de la Zona de Transición y su interpretación utilizando todos los datos disponibles., Este trabajo es una contribución de los proyectos: CSD2006-00041, CGL2008-03474-E/BTE, CGL2008-01830 y P09-RNM-5100.

Upper mantle discontinuities are commonly studied through the detection of waves which have been converted/reflected at these discontinuities. In this work a novel processing approach which is leaned on receiver functions and which is based on cross-correlation and stacking techniques was implemented to search for weak amplitude upper mantle phases that arrive in the P-wave coda, such as P-to-s conversions. To add consistency and robustness to the detections, the new approach has been used together with receiver functions. This, also permits to bridge observation gaps due to break down of one of the techniques inherent to data characteristics. The aim of this work is to map the limits of the Transition Zone, which are the 410-km and 660-km depth discontinuities, beneath the Iberian Peninsula and north Africa. The new processing approach uses two independent cross-correlations (phase cross-correlation and cross-correlation geometrically normalized) and stacking techniques (phase weighted stack) in order to eliminate the source influence and to enhance coherent signals detected for the different events at individual stations. A pilot wavelet is selected from the vertical component, this wavelet contains the P phase and part of its coda with the later arriving depth phases. Converted and reflected phases are then detected by the cross-correlation of this pilot with the vertical and radial component of each recorded event, and the stacking of cross-correlograms for common conversion point areas. Cross-correlation provides relative travel times with respect to the P phase through its correlation maxima, and stacking enhances the signals which arrive consistently (near receiver conversions and reflections) and attenuates isolated depth phases such as near source reverberations and spurious arrivals. Slant stacks are used to correctly identify these coda signals. The described process was performed for teleseismic earthquakes registered in the seismic network of TopoIberia project. A total of 260 broad band seismic stations have been used which were deployed in Spain, Portugal and north Africa. We focus on the converted phases P410s and P660s, and map the corresponding discontinuities beneath Spain and north Africa. Clear P-to-s conversions at the 660 km depth discontinuity were detected beneath the studied region. The P410s phase is less well observed. Both discontinuities show topography which are within the expected depth variations observed in global studies. We will present maps of the Transition zone thickness and their interpretation using all available data.

A novel technique was implemented to search for weak amplitude upper mantle phases that arrive in the P wave coda. Phase cross correlation (pcc) and different stacking techniques, linear stack (ls) and phase weighted stack (pws), were applied in order to eliminate the source influence and spurious arrivals from the vertical and radial component of records from single stations. A pilot wave was selected from the vertical component, this wavelet contains the P wave and part of its coda. PCC was performed between this pilot and the vertical, and the radial component of each recorded event. This was done for several earthquakes from the same station, and the process was also repeated for other stations. As pcc is a measure of waveform similarity, the result is a cross correlogram with amplitudes between -1 and 1, with high amplitude values at lag times where the pilot and the recorded component have similar waveforms. Thus, it is expected that this procedure detects P to s conversions, and reflections at different mantle discontinuities (Moho, 410, 660). Other undesired phases, such as reverberations near the source due to the source depth were canceled stacking (LS, PWS) cross correlograms from a single station and different hypocentral depths. Stacking will enhance signals which arrive consistently (near receiver conversions and reflections) and attenuate isolated depth phases and also spurious arrivals. In other words, stacking over different sources will enhance signals due to the discontinuities beneath the receiver. Besides the source equalization, pcc provides relative travel times with respect to the P phase through its correlation maxima. Slant stacks using different values of slowness were performed in order to identify the different reflected and converted waves. The data set used in this study was selected from the first phase of the IberArray seismic network deployment of the Topo-Iberia project. More than 50 broad band stations were deployed in south Iberia and north Africa. Due to the amount of data provided by this project we selected some stations to make a first analysis. We aim to find P wave reflexions and P to s conversions from the upper mantle discontinuities beneath south Spain. Our final goal is to map and to characterize the different upper mantle discontinuities.