Jordi Diaz

Abstract Evidence for an upper mantle discontinuity located between 60 and 70 km depth have been provided by different seismic data sets acquired in the Southern Iberian peninsula. First indications of such a discontinuity were obtained by the very long offsets ...

Extensive seismic and seismological research carried out recently in northern Spain reveals the existence of crustal thickening and wedging, evidencing an indentation between European and Iberian crusts throughout the Northern part of the Iberian plate affected by the Alpine compressional tectonics. Vertical and wide-angle seismic profiling at the Cantabrian Mountains (CM) and continental margin provided first evidences of a crustal

The velocity structure of the crust and the topography of the Moho across Morocco has been the main target of two recently acquired wide-angle seismic reflections transects. One is the SIMA experiment which provided seismic constraints beneath the Atlas Mountains and the second has been the RIFSEIS experiment which sampled the RIF orogen. Jointly this controlled source wide-angle seismic reflection data results in an almost 700 km, seismic profile going from the Sahara craton across the High and Middle Atlas and Rif Mountain till the Alboran. Current work on the interpretation of the seismic data-set is based on forward modeling, ray-tracing, as well as low fold wide-angle stacking. The data has resulted in a detailed crustal structure and velocity model for the Atlas Mountains and a 700 km transect revealing the irregular topography of the Moho beneath these two mountain orogens. Results indicate that the High Atlas features a moderate crustal thickness and that shortening is resol...

The Mohorovicic discontinuity (Moho) was defined by Andrija Mohorovicic in 1910 on the basis of an interpretation of regional earthquake records in Eastern Europe as a relatively abrupt increase in P-wave seismic velocities. The Moho is observed/detected world wide. It is the most important boundary within the Earth's lithosphere. The high resolution subsurface geophysical images have demonstrated that the crust-mantle boundary is a far more complex structure that the initial seismological definition established. The purpose of this contribution is to bring together some of the findings related to the crust-mantle transition beneath the Iberian peninsula and to synthesize these results into a perspective that has global implications. For the last three decades an extensive acquisition of varieties of geophysical and geological data has been carried out. These data include controlled-source seismic (refraction and reflection), natural source seismic, and regional geology. In NW I...

The Mohorovicic discontinuity (Moho) was defined by Andrija Mohorovicic in 1910 on the basis of an interpretation of regional earthquake records in Eastern Europe as a relatively abrupt increase in P-wave seismic velocities. The Moho is observed/detected world wide. It is the most important boundary within the Earth's lithosphere. The high resolution subsurface geophysical images have demonstrated that the crust-mantle boundary is a far more complex structure that the initial seismological definition established. The purpose of this contribution is to bring together some of the findings related to the crust-mantle transition beneath the Iberian peninsula and to synthesize these results into a perspective that has global implications. For the last three decades an extensive acquisition of varieties of geophysical and geological data has been carried out. These data include controlled-source seismic (refraction and reflection), natural source seismic, and regional geology. In NW I...

The knowledge of the anisotropic properties beneath the Iberian Peninsula and Northern Morocco has been dramatically improved since late 2007 with the analysis of the data provided by the dense IberArray broad-band seismic network deployed in the Topo-Iberia project, the increasing number of permanent stations operating in Morocco, Portugal and Spain, and the contribution of smaller scale/higher resolution experiments. The first Topo-Iberia deployment in the Betics-Alboran zone has evidenced a spectacular rotation of the fast polarization direction (FPD) along the Gibraltar arc following the curvature of the Rif-Betic chain. This result has been interpreted as an evidence of mantle flow deflected around the high velocity slab beneath the Alboran Sea Arc. Data from the second Topo-Iberia deployment and from additional deployments in the Moroccan Meseta and the western High Atlas have shown a rather uniform N100ºE FPD beneath the Variscan Central Iberian Massif, consistent with global...

In the frame of the European Union "THALES WAS RIGHT" project on seismogenic zones in European subductions and of the European Union "SALVADOR" programme of IfM-GEOMAR for the access to OBS, ocean bottom seismometers, we have deployed in early June 2006 and for 5 months an onshore-offshore array in the SW part of the Hellenic subduction, the area between the south west tip of Peloponissos and Crete. The array consisted of 5, three component OBS and of up to 15 land seismometers. This provided for the first time a constraint on the hypocentral locations of local earthquakes offshore, that up to then were poorly located because of an insufficient azimuthal coverage, since all the permanent stations are on land on one side. Comparison of the routinely located hypocenters by the permanent array with those located by the special local onshore/offshore local array shows that some background seismicity may be mislocated by several tens of kilometers with for instance sm...

ABSTRACT Systematic quality control of the seismic recordings acquired by the IBERARRAY broad-band seismic network is carried out. As part of the standard quality control procedure of the raw seismic data, the background noise power spectral density (PSD) is regularly estimated for all the stations of the IberArray portable seismic network and is statistically analyzed to compute probability density functions (PDFs) using the PQLX software package. These PDFs provide a useful tool for managing the network, as they allow to identify stations with unacceptable high noise levels in the frequency band of interest as well as temporal changes of the noise level that may indicate the convenience of changing the location of some sites. At long periods (20-120s), the vertical components usually lie 15db above the NLNM of Peterson (1993). The horizontal components are much noisier in this frequency range, often depassing the NHNM for the longest periods. At microseismic frequencies (0.05 - 0.3 Hz), the noise level is very similar between all the stations, while at high frequencies (> 1 Hz), the main contribution seems to arise from the cultural noise and therefore produces significant variations between the stations. Among the different features observed in the PDF curves, we can highlight the day/night differences in the mean noise level, specially significant for high frequencies, the importance of the local site effects, illustrated by two stations located less than 100 km away but lying in very different terrains and the observation of noise variations related to weather conditions in the microseismic band.

ABSTRACT The characteristics of the background seismic noise recorded at the IberArray broadband seismic network have been analyzed using power spectral density (PSD) estimates and their corresponding probability density functions (PDFs) for the whole data set (up to 55 stations continuously recording since summer 2007). These PDFs provide a useful tool for managing the network as they allow identifying stations with anomalous high noise levels, but also allow investigating the major sources of noise at different frequency bands and the seismic background noise variations related to time of day, season, weather, location and type of installation. At high frequencies (> 1 Hz), the main contribution seems to arise from the cultural noise, and therefore significant variations are observed between noise levels at different stations. At microseismic frequencies (0.05 - 0.3 Hz), the noise level is more uniform among stations, even if the sites along the Gulf of Cadiz show a slightly increased level. At long periods, the vertical components usually lay 15db above the NLNM and the horizontal components are much noisier, often exceeding the NHNM for the longest periods. Infragravity waves can be identified along the network for periods close to 100s, even for stations located inland. The map of the median noise levels across the Iberarray network shows a clear correlation with major geological features, as the Guadalquivir and Gharb sedimentary basins and the Central Iberian Massif. Among the main temporal variations observed we can highlight the day/night differences in the mean noise level, particularly significant for high frequencies, and the noise level variations correlated to the significant wave heights in the surrounding waters. Those latter variations are clearly observed in the microseismic band, but also at periods close to 100s, dominated by the infragravity waves.

During the last years, the deep crustal configuration of the Northern part of the Iberian Peninsula has been explored using teleseismic receiver function (RF) analysis of P to S conversions at main crustal interfaces. This area has been previously investigated by seismic reflection and refraction experiments and therefore provides an excellent opportunity to compare the results from independent approaches. In

In this study we present some results concerning the central Lesser Antilles Subduction Zone by using the data recorded by a temporary combined on- and o4shore seismic network. A data-set of !55 well located earthquakes, with a total of 4054 and 26!7 pickings for P- S-waves respectively, has been used to study the relationship between tectonic structures and seismicity. In particular, to obtain precise hypocentre locations, we applied the concept of minimum !D model, which incorporates the iterative simultaneous inversion of velocity and hypocenter parameters. The minimum !D model is complemented by station corrections that take into account the 3D velocity heterogeneity of the central Lesser Antilles Subduction Zone. Relocated hypocentres after the !D inversion improve our knowledge on the Subduction Zone with respect to those derived from the permanent arrays only.

ABSTRACT We present here new images of the seismic velocity and anisotropy variations in the uppermost mantle beneath the Mediterranean region, compiled from inversion of Pn and Sn phases. The method of Hearn (1996) has been applied to Pn and Sn lectures from the catalogs of the International Seismological Center and the Spanish Instituto Geografico Nacional. A total of 1,172,293 Pn arrivals coming from 16,527 earthquakes recorded at 1,657 stations with epicentral distances between 220 km and 1400 km have been retained (331,567 arrivals from 15,487events at 961 stations for Sn). Our results, grossly consistent with available 3D tomography images, show significant features well correlated with surface geology. The Pn velocities are high (>8.2 km/s) beneath major sedimentary basins (western Alboran Sea, Valencia Trough, Adriatic Sea, Aquitaine, Guadalquivir, Rharb, Aquitaine and Po basins), and low (<7.8 km/s) in orogenic areas (Betics, Pyrenees, Alps, Apennines, Dinarides, Helenides and Calabrian Arc), confirming the existence of marked variations in crustal thicknesses already documented in some active seismic experiments. The lowest velocity values are found under the Betics and the eastern and western Alps. Another low velocity anomaly is located below the south of Balearic Islands, probably related to a thermal anomaly associated to the westward displacement of the Alboran block along the Emile Baudot escarpment 16 Ma ago. The Pn anisotropic image shows consistent orientations sub-parallel to major orogenic structures, such as Betics, Apennines, Calabrian Arc and Alps. The station delays beneath Betic and Rif ranges are strongly negative, suggesting the presence of crustal thickening all along the Gibraltar Arc. However, only the Betics have a very strong low-velocity anomaly and a pronounced anisotropy pattern. The Sn tomographic image correlates well with the Pn image, even if some relevant differences can be observed beneath particular regions.

ABSTRACT The evolution of the Western Mediterranean is strongly affected by the collision of the African and Eurasian plates. The plate boundary as seen from earthquakes is diffuse over a wide area extending north and south of Gibraltar strait. The Western end of the Mediterranean is delineated by the Gibraltar Arc System, comprising the arcuate Spanish Betic and Moroccan Rif Mountain Belts, together with the Alboran-Sea Basin in-between. The extension of the Alboran Basin which started from Late Eocene and which coexisted with the Africa -Europe conversion is still under debate and is one of the key points to constrain the evolution of the Western Mediterranean. This motivated our interest to map the still unknown crustal transition from the Betic-Rif chain into the Alboran Sea, taking advantage of the coincidence in time (October 2011) of two seismic experiments in the area, on land (Rifsis project) and at sea (Gassis-WestMed project). For this purpose we deployed several tens of seismic stations, both in Morocco and Spain, to record the air-gun shooting (every 50 m) of the Sarmiento de Gamboa Spanish vessel performing multichannel reflection profiles at the Alboran sea, and hence to extend these marine lines to wide-angle distances in-land. The airguns were calibrated for the near zero-offset marine reflection study and it turns out to be difficult to observe clear signals on the records in-land at offsets larger than about 70 km. The data has therefore been processed with a frequency-dependent lateral coherence filter to enhance coherent reflection/refraction signals through the frequency-dependent attenuation of incoherent noise and signals. This processing has permitted to track signals (seismic energy) up to more than 200 km on some profiles. Hence, a classical procedure of forward modeling (ray tracing approach) to fit the travel times of the identified wide-angle phases is now underway, taking advantage of the sedimentary/basement sequences inferred from the multichannel sections to constrain the upper part of the velocity-depth model. The first structural results delineate significant lateral variations in crustal depths, particularly at the Rif-Alboran transition. In our presentation we will show and discuss data processing examples which enabled signal detection to large offsets, the signal identification and their interpretation, and the different 2-D cross sections which image the crustal transition to the Alboran Basin.

In Greece, receiver-function processing of teleseismic P-waves in the standard frequency band results in the image of a low-velocity layer at the top of the Hellenic slab twice thicker than expected for an oceanic crust. The objective of this work is to assess if this result could be due to a lack of resolution of the standard processing. A multiscale

TOPOIBERIA, is a multidisciplinary large scale research project which aims to study the links between the deep and superficial processes within the Iberian Peninsula.One of its main experimental components is the deployment of the IBERARRAY seismic network. This is a dense array (60x60 km) of new generation dataloggers equipped with broad-band seismometers which will cover Iberia and North Morocco in

Data recorded during a temporary deployment of ocean bottom seismometers (OBSs) are used in this study to monitor the presence of fin whales around the array. In the summer of 2003, ten OBSs were placed 250 km from the NW coast of Iberia in the Galicia Margin, NE Atlantic Ocean for a period of one month. The recorded data set provided a large variety of signals, including fin whale vocalizations identified by their specific acoustic signature. The use of a dense array of seafloor receivers allowed investigation into the locations and tracks of the signal-generating whales using a seismological hypocentral location code. Individual pulses of different sequences have been chosen to study such tracks. Problems related to the correct identification of pulses, discrimination between direct and multiple arrivals, and the presence of more than one individual have been considered prior to location. Fin calls were concentrated in the last two weeks of the deployment and the locations were spread around the area covered by the array. These results illustrate that, besides its classical seismological aim, deployment of semipermanent seafloor seismic arrays can also provide valuable data for marine mammal behavior studies.

... Issue. J Gallart, J Guimerá and C Olivera, Neogene paleostresses and present seismotectonic results of the Valencia Trough and ... WF Haxby, Geotectonic Imagery from SEASAT, Lamont-Doherty Geological Observatory of Columbia University, Yearbook 1982–1983 (1983), p. 12 ...