Estudio de los movimientos de compensación isostática en una zona del Levante español

En base a los datos geológicos y gravimétricos existentes en la región de Valencia, se comprueba que los jóvenes y recientes movimientos tectónicos cumplen las leyes de compensación isostática y se avanzan hipótesis de evolución geodinámica

Results and experiences of application of the Refraction Microtremor method for the geophysical investigation of the new subway lines in Madrid (Spain)

Geophysical exploration with seismic methods in urban zones presents several disadvantages: the presence of numerous sources of seismic noise, the scanty penetration when the seismic source is a hammer and the disability to detect buried low-velocity beds. Recently (Louie, 2001) a new method of seismic investigation has been developed, which allows vertical modeling of Raleygh waves from spectral analysis (Vphase/frequency) using the seismic signal registered with conventional seismographs and geophones. This method allows to detect low-velocity buried beds of great interest in tunneling, and to reach depths below 50 meters. In this work we discuss the conditions of application and experiences obtained during the 2005 geophysical surveys carried out in Madrid before the excavation of the new subway tunnel

Precise OBS location at the sea bottom in active seismic profiles using the air gun shot records

The Norcaribe campaign, in November – December 2013, funded by Spanish Ministry of Innovation and Science (Norcaribe Project CGL2010-17715), was performed on board of the Spanish research vessel “Sarmiento de Gamboa” around the Hispaniola island, also with the participation of the Dominic Republic Navy patrol vessels and several Haiti and Dominic Republic institutions. During the campaign, a 200 km long, wide-amgle refraction seismic profile was carried out crossing the Beata ridge. The air gun signal (5100 ci) was recorded by 15 OBSs deployed along the seismic line in water depths between 2.300 meters and 4.320 meters. To obtain the section records, the OBS position is needed, usually the deployment location is used, but the OBS can drift while is sinking due to the deep oceanic currents. The recovery locations at surface could provide information about the drift, assuming a constant sea current since the deployment to the recovery, but it is imprecise. In this work we show a method to obtain a precise location of the OBS at the sea bottom using a high-resolution bathymetry and the OBS record of the closest air gun shots of the profile. Also, the preliminary results for the Norcaribe campaign (Beata ridge profile) are shown.Peer Reviewe

Morphostructure at the junction between the Beata ridge and the Greater Antilles island arc (offshore Hispaniola southern slope)

Oblique convergence between the Caribbean plate's interior and the inactive Greater Antilles island arc has resultedin the collision and impingement of the thickened crust of theBeata ridge into southern Hispaniola Island. Deformation resulting from this convergence changes from a low-angle southward-verging thrust south of easternHispaniola, to collision and uplift in south-central Hispaniola, and to left-lateral transpression along theSouthern peninsula of Haiti in western Hispaniola. Using new swath bathymetry and a dense seismic reflectiongrid, we mapped the morphological, structural and sedimentological Elements of offshore southern Hispaniola.We have identified four morphotectonic provinces: the Dominican sub-basin, the Muertos margin, the Beataridge and the Haiti sub-basin. The lower slope of the Muertos margin is occupied by the active Muertos thrustbelt, which includes several active out-of-sequence thrust faults that, were they to rupture along their entirelength, could generate large-magnitude earthquakes. The interaction of the thrust beltwith the Beata ridge yieldsa huge recess and the imbricate system disappears. The upper slope of the Muertos margin shows hick slopedepositswhere the extensional tectonics and slumping processes predominate. The northern Beata ridge consistsof an asymmetrically uplifted and faulted block of oceanic crust. Our results suggest that the shallower structureand morphology of the northern Beata ridge can be mainly explained by a mechanism of extensional unloadingfrom the Upper Cretaceous onward that is still active residually along the summit of the ridge. The tectonicmodels for the northern Beata ridge involving active reverse strike–slip faults and transpression caused by theoblique convergence between the Beata ridge and the island arc are not supported by the structural interpretation.The eastern Bahoruco slope an old normal fault that acts as a passive tear fault accommodating the sharpalong-strike transition from low-angle thrusting to collision and uplifting.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEGeological Survey Coastal and Marine Geology ProgramDirección General de Minería of the Dominican Republicpu

Comparación entre las técnicas AEOS, Re-Mi y PS-logging aplicadas en un terreno de estructura profunda conocida

En este estudio se contrastan los resultados que ofrecen dos técnicas de uso habitual en el Laboratorio de Geotecnia del CEDEX, el AEOS y el PS-logging, con los de una técnica relativamente novedosa, el Re-Mi (o sísmica pasiva). Para ello se emplean los resultados obtenidos por las tres técnicas en un emplazamiento común de estructura profunda conocida: un tramo de terraplén ferroviario recién construido. La técnica más precisa en la identificación de las diferentes partes de la estructura de tierras (terraplén, cimiento y contacto con el terreno natural) es el PS-logging, seguido por el AEOS y Re-Mi. Los valores de Vs promedio proporcionados por cada técnica presentan importantes diferencias, obteniéndose los más altos con el PS-logging, seguido por AEOS y Re-Mi. La desviación de los valores Vs promedio obtenidos por una técnica en particular, en comparación con las otras, es similar. Respecto a la técnica Re-Mi, cabe destacar que, si bien no se ha mostrado muy precisa en este estudio, presenta un alto grado de operatividad en cuanto a implantación, ejecución y procesado de datos

Crustal structure and continent‐ocean boundary along the Galicia continental margin (NW Iberia): insights from combined gravity and seismic interpretation

The magma‐poor rifted continental margin of Galicia has an extremely complex structure. Its formation involved several rifting episodes that occurred ultimately during the early Cretaceous near a ridge triple junction, which produced a change in the orientation of the main structures in its transition to the north Iberia margin. In addition, there is a superimposed partial tectonic inversion along its northwest and northern border which developed from the Late Cretaceous to at least Oligocene times. The present study integrates a large volume of new geophysical information (mainly marine gravity data and 2D seismic reflection profiles) to provide insights on the formation of this rift system and on the development of its later inversion. The combined interpretation and modeling of this data enable the presentation of a new crustal and structural domains map for the whole Galicia margin. This includes the rift domains related to the extreme thinning of the crust and the lithospheric mantle (stretched, necking, and hyperextension and mantle exhumation (HME) domains), as well as a domain of intense compressional deformation. New constraints arise on the origin, the deep structure, and the characterization of the along‐ and across‐strike variation of the continent‐ocean transition of the margin, where a progressive change from hyperextension to partial inversion is observed. The development of both rifting and later partial tectonic inversion is influenced by the existence of former first‐order tectonic features. Most of the tectonic inversion is focused on the HME domain, which in some areas of the northwestern margin is completely overprinted by compressional deformation

Bouguer anomalies of the NW Iberian continental margin and the adjacent abyssal plains

The NW Iberian continental margin has a complex structure, resulting from the succession of several rifting episodes close to a ridge triple junction, and a superimposed partial tectonic inversion stage. The wide-ranging physiography matches the diverse tectonic deformation domains related to its evolution. Each deformation domain has a distinctive gravity signal, so the detailed Bouguer anomaly map presented here is a good first approach to the regional study of the whole margin. Moreover, as the presented chart is a complete Bouguer anomaly map (including terrain corrections), its analysis and interpretation can be done in terms of density, geometry and depth variations below the seafloor. This map is mainly based on the dataset obtained during seven one-month surveys carried out in the frame of the Spanish Economic Exclusive Zone project, and also includes two 2 + 3/4D density models illustrating the deep structure of the marginThe marine surveys are supported by the Spanish Defense Ministry, as this is the managing body of the Spanish Exclusive Economic Zone Project (SEEZ). Additionally, the Universidad Complutense de Madrid funds travel expenses of its personnel embarking on the surveys, as does the Instituto Geológico y Minero de España in the frame of the internal project entitled ‘Plan de Investigaciones Geológicas y Geofísicas de la Zona Económica Exclusiva Española (ZEEE)