In May 2012, spatially dense high resolution wide-angle seismic reflection data, ALCUDIA, was acq... more In May 2012, spatially dense high resolution wide-angle seismic reflection data, ALCUDIA, was acquired across the Central Iberian Massif. The experiment consisted in three lines of receivers, having a total length of ~350 km. The main line of receivers, the ALCUDIA wide-angle seismic transect, is ~310 km long. The ALCUDIA transect goes across, from north to south, the Central Unit, the Central Iberian Zone and the Tajo Basin. A supplementary transect, ~40 km long, samples the crust beneath the Central System mountain range. Five explosive sources, ~70 km apart, each one consisting in 1TM of explosive, were placed in ~55 m deep single boreholes. The acoustic energy generated by the 5 shots was recorded by over 900 TEXANS (single component, digital recording stations) from the IRIS-PASSCAL Instrument Center. The processed shot records show high-amplitude and well-defined P- and S-wave arrivals from the boundary between the upper and middle-lower crust, the Moho and the upper mantle. T...
ABSTRACT We present here new images of the seismic velocity and anisotropy variations in the uppe... more 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 Two controlled-source wide angle seismic reflection experiments have been acquired recen... more ABSTRACT Two controlled-source wide angle seismic reflection experiments have been acquired recently (2010 and 2011) in northern Africa across Morocco. A lithospheric scale transect can be constructed by joining both data sets. Hence, an approximately 700 km-long seismic velocity cross section can be derived. From south-to-north the transect goes from the Sahara Platform, south of Merzouga, to Tanger in the north. The first experiment, SIMA, aimed to constrain the crustal structure across the Atlas Mountains. The Rif, the orogenic belt located just south of the coast of Alboran Sea, was the target of the second experiment, RIFSIS. In both cases 900 recording instruments (TEXANS) from the IRIS-PASSCAL instrument center were used to record the acoustic energy generated by explosion shots. In both experiments the shots consisted of 1 TM of explosives fired in ~30 m deep boreholes. Although the data quality varies from shot to shot, key seismic phases as Pg, PmP, Pn, and a few intra-crustal arrivals have been identified to constrain the velocity-depth structure along the whole transect. Forward modelling of the seismic reflection/refraction phases reveals a crust consisting of 3 layers in average. The Moho topography shows from south to north a relatively moderate crustal root beneath the High Atlas, which can reach 40-42 km depth. The crust is thicker beneath the Rif where the Moho is imaged as an asymmetric feature that locally defines a crustal root reaching depths of 50 km and suggesting a crustal imbrication. P wave velocities are rather low in the crust and upper mantle. First arrivals/reflections tomography supports the forward modelling results. Low fold wide-angle stacks obtained by using hyperbolic move-out reveals the geometry of the Moho along the entire transect. Beneath the Atlas, the moderate crustal root inferred is not isostatically consistent with the high surface elevations, hence supporting the idea of a 'mantle plume' as main contributor to the Atlas Mountains topography.
Geochemictry, Geophysics, Geosystems, Nov 11, 2014
The different geodynamic models proposed since the late 90's to account for the complex evolution... more The different geodynamic models proposed since the late 90's to account for the complex evolution of the Gibraltar Arc System lack definite constraints on the crustal structure of the Rif orogen. Here we present the first well resolved crustal models of the Rif cordillera and its southern continuation towards the Atlas made using controlled-source seismic data. Two 300+ km-long wide-angle reflection profiles crossed the Rif along NS and EW trends. The profiles recorded 5 land shots of 1Tn each using ~850 Texans instruments. The crustal structure revealed from 2D forward modeling delineates a complex, laterally-varying crustal structure below the Rif domains. The most surprising feature, seen on both profiles, is a ~50 km deep crustal root localized beneath the External Rif. To the east the crust thins rapidly by 20 km across the Nekkor fault, indicating that the fault is a crustal scale feature. On the NS profile the crust thins more gradually to 40 km thickness beneath Middle Atlas and 42 km beneath the Betics. These new seismic results are in overall agreement with regional trends of Bouguer gravity and are consistent with recent receiver function estimates of crustal thickness. The complex crustal structure of the Rif orogen in the Gibraltar Arc is a consequence of the Miocene collision between the Iberian and African plates. Both the abrupt change in crustal thickness at the Nekkor fault and the unexpectedly deep Rif crustal root can be attributed to interaction of the subducting Alboran slab with the North African passive margin.
In the last 10–15 years, the number of high quality seismic stations monitoring the Euro-Mediterr... more In the last 10–15 years, the number of high quality seismic stations monitoring the Euro-Mediterranean region has increased significantly, allowing a corresponding improvement in structural constraints. We present here new images of the seismic velocity and anisotropy variations in the uppermost mantle beneath this complex area, compiled from inversion of Pn and Sn phases sampling the whole region. The method of Hearn has been applied to the traveltime arrivals of the International Seismological Center catalogue for the time period 1990–2010. A total of 579 753 Pn arrivals coming from 12 377 events recorded at 1 408 stations with epicentral distances between 220 km and 1 400 km have been retained after applying standard quality criteria (maximum depth, minimum number of recordings, maximum residual values …). Our results show significant features well correlated with surface geology and evidence the heterogeneous character of the Euro-Mediterranean lithosphere. The station terms reflect the existence of marked variations in crustal thickness, consistent with available Moho depths inferred from active seismic experiments. The highest Pn velocities are observed along a continuous band from the Po Basin to the northern Ionian Sea. Other high velocity zones include the Ligurian Basin, the Valencia Trough, the southern Alboran Sea and central part of the Algerian margin. Most significant low-velocity values are associated to orogenic belts (Betics, Pyrenees, Alps, Apennines and Calabrian Arc, Dinarides-Hellenides), and low-velocity zones are also identified beneath Sardinia and the Balearic Islands. The introduction of an anisotropic term enhances significantly the lateral continuity of the anomalies, in particular in the most active tectonic areas. Pn anisotropy shows consistent orientations subparallel to major orogenic structures, such as Betics, Apennines, Calabrian Arc and Alps. The Sn tomographic image has lower resolution but confirms independently most of the features evidenced in the Pn tomography.
Se estudian fallas de la Cordillera Bética Oriental, entre 3º-0º O y 6º30'-38º30' N, una de las ... more Se estudian fallas de la Cordillera Bética Oriental, entre 3º-0º O y 6º30'-38º30' N, una de las zonas más activas de la Península Ibérica, debido a la convergencia entre las placas Africana y Eurasia que provoca el movimiento de la Zona de Cizalla Trans- Alborán, formada por las fallas de Bajo Segura, Carrascoy, Alhama de Murcia, Palomares y Carboneras. Por su proximidad y por ser límite entre las unidades tectónicas de la Cordillera Bética, también se han estudiado las fallas de Crevillente y la Norbética. La actividad de las fallas se ha estudiado a partir de los datos de terremotos registrados desde 1900. Su comportamiento cinemático se ha deducido de los mecanismos focales a partir del registro instrumental, pero la escasedad de terremotos de magnitud superior a 3.5 Mw impide caracterizar correctamente las fallas del Bajo Segura, Crevillente y Norbética. Se ha completado el estudio con datos de GPS de la red CuaTeNeo, pero esta red se circunscribe a las fallas de Carboneras, Palomares y Alhama de Murcia, hecho que impide que se pueda determinar el comportamiento sísmico de las fallas de Crevillente y Norbética. A partir de los datos se han determinado los comportamientos sísmicos para Carboneras, Palomares y Alhama de Murcia. Para todas ellas se han registrado movimientos extensivos (0.9, 0.8 y 0.3 mm/año respectivamente) y de desgarre siniestro para Palomares y Alhama de Murcia (0.6 y 0.2 mm/año) y diestro para Carboneras (1.5 mm/año), si bien los datos insuficientes para esta falla provocan errores muy elevados. Se ha determinado la magnitud máxima potencial para las tres fallas en aproximadamente 7.4 Mw, si bien debe considerarse orientativa al no haberse incluido los errores registrados por los GPS. Por esta razón se recomienda un estudio GPS más intenso en la zona de Carboneras y su extensión hasta Crevillente.
In May 2012, spatially dense high resolution wide-angle seismic reflection data, ALCUDIA, was acq... more In May 2012, spatially dense high resolution wide-angle seismic reflection data, ALCUDIA, was acquired across the Central Iberian Massif. The experiment consisted in three lines of receivers, having a total length of ~350 km. The main line of receivers, the ALCUDIA wide-angle seismic transect, is ~310 km long. The ALCUDIA transect goes across, from north to south, the Central Unit, the Central Iberian Zone and the Tajo Basin. A supplementary transect, ~40 km long, samples the crust beneath the Central System mountain range. Five explosive sources, ~70 km apart, each one consisting in 1TM of explosive, were placed in ~55 m deep single boreholes. The acoustic energy generated by the 5 shots was recorded by over 900 TEXANS (single component, digital recording stations) from the IRIS-PASSCAL Instrument Center. The processed shot records show high-amplitude and well-defined P- and S-wave arrivals from the boundary between the upper and middle-lower crust, the Moho and the upper mantle. T...
ABSTRACT We present here new images of the seismic velocity and anisotropy variations in the uppe... more 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 Two controlled-source wide angle seismic reflection experiments have been acquired recen... more ABSTRACT Two controlled-source wide angle seismic reflection experiments have been acquired recently (2010 and 2011) in northern Africa across Morocco. A lithospheric scale transect can be constructed by joining both data sets. Hence, an approximately 700 km-long seismic velocity cross section can be derived. From south-to-north the transect goes from the Sahara Platform, south of Merzouga, to Tanger in the north. The first experiment, SIMA, aimed to constrain the crustal structure across the Atlas Mountains. The Rif, the orogenic belt located just south of the coast of Alboran Sea, was the target of the second experiment, RIFSIS. In both cases 900 recording instruments (TEXANS) from the IRIS-PASSCAL instrument center were used to record the acoustic energy generated by explosion shots. In both experiments the shots consisted of 1 TM of explosives fired in ~30 m deep boreholes. Although the data quality varies from shot to shot, key seismic phases as Pg, PmP, Pn, and a few intra-crustal arrivals have been identified to constrain the velocity-depth structure along the whole transect. Forward modelling of the seismic reflection/refraction phases reveals a crust consisting of 3 layers in average. The Moho topography shows from south to north a relatively moderate crustal root beneath the High Atlas, which can reach 40-42 km depth. The crust is thicker beneath the Rif where the Moho is imaged as an asymmetric feature that locally defines a crustal root reaching depths of 50 km and suggesting a crustal imbrication. P wave velocities are rather low in the crust and upper mantle. First arrivals/reflections tomography supports the forward modelling results. Low fold wide-angle stacks obtained by using hyperbolic move-out reveals the geometry of the Moho along the entire transect. Beneath the Atlas, the moderate crustal root inferred is not isostatically consistent with the high surface elevations, hence supporting the idea of a 'mantle plume' as main contributor to the Atlas Mountains topography.
Geochemictry, Geophysics, Geosystems, Nov 11, 2014
The different geodynamic models proposed since the late 90's to account for the complex evolution... more The different geodynamic models proposed since the late 90's to account for the complex evolution of the Gibraltar Arc System lack definite constraints on the crustal structure of the Rif orogen. Here we present the first well resolved crustal models of the Rif cordillera and its southern continuation towards the Atlas made using controlled-source seismic data. Two 300+ km-long wide-angle reflection profiles crossed the Rif along NS and EW trends. The profiles recorded 5 land shots of 1Tn each using ~850 Texans instruments. The crustal structure revealed from 2D forward modeling delineates a complex, laterally-varying crustal structure below the Rif domains. The most surprising feature, seen on both profiles, is a ~50 km deep crustal root localized beneath the External Rif. To the east the crust thins rapidly by 20 km across the Nekkor fault, indicating that the fault is a crustal scale feature. On the NS profile the crust thins more gradually to 40 km thickness beneath Middle Atlas and 42 km beneath the Betics. These new seismic results are in overall agreement with regional trends of Bouguer gravity and are consistent with recent receiver function estimates of crustal thickness. The complex crustal structure of the Rif orogen in the Gibraltar Arc is a consequence of the Miocene collision between the Iberian and African plates. Both the abrupt change in crustal thickness at the Nekkor fault and the unexpectedly deep Rif crustal root can be attributed to interaction of the subducting Alboran slab with the North African passive margin.
In the last 10–15 years, the number of high quality seismic stations monitoring the Euro-Mediterr... more In the last 10–15 years, the number of high quality seismic stations monitoring the Euro-Mediterranean region has increased significantly, allowing a corresponding improvement in structural constraints. We present here new images of the seismic velocity and anisotropy variations in the uppermost mantle beneath this complex area, compiled from inversion of Pn and Sn phases sampling the whole region. The method of Hearn has been applied to the traveltime arrivals of the International Seismological Center catalogue for the time period 1990–2010. A total of 579 753 Pn arrivals coming from 12 377 events recorded at 1 408 stations with epicentral distances between 220 km and 1 400 km have been retained after applying standard quality criteria (maximum depth, minimum number of recordings, maximum residual values …). Our results show significant features well correlated with surface geology and evidence the heterogeneous character of the Euro-Mediterranean lithosphere. The station terms reflect the existence of marked variations in crustal thickness, consistent with available Moho depths inferred from active seismic experiments. The highest Pn velocities are observed along a continuous band from the Po Basin to the northern Ionian Sea. Other high velocity zones include the Ligurian Basin, the Valencia Trough, the southern Alboran Sea and central part of the Algerian margin. Most significant low-velocity values are associated to orogenic belts (Betics, Pyrenees, Alps, Apennines and Calabrian Arc, Dinarides-Hellenides), and low-velocity zones are also identified beneath Sardinia and the Balearic Islands. The introduction of an anisotropic term enhances significantly the lateral continuity of the anomalies, in particular in the most active tectonic areas. Pn anisotropy shows consistent orientations subparallel to major orogenic structures, such as Betics, Apennines, Calabrian Arc and Alps. The Sn tomographic image has lower resolution but confirms independently most of the features evidenced in the Pn tomography.
Se estudian fallas de la Cordillera Bética Oriental, entre 3º-0º O y 6º30'-38º30' N, una de las ... more Se estudian fallas de la Cordillera Bética Oriental, entre 3º-0º O y 6º30'-38º30' N, una de las zonas más activas de la Península Ibérica, debido a la convergencia entre las placas Africana y Eurasia que provoca el movimiento de la Zona de Cizalla Trans- Alborán, formada por las fallas de Bajo Segura, Carrascoy, Alhama de Murcia, Palomares y Carboneras. Por su proximidad y por ser límite entre las unidades tectónicas de la Cordillera Bética, también se han estudiado las fallas de Crevillente y la Norbética. La actividad de las fallas se ha estudiado a partir de los datos de terremotos registrados desde 1900. Su comportamiento cinemático se ha deducido de los mecanismos focales a partir del registro instrumental, pero la escasedad de terremotos de magnitud superior a 3.5 Mw impide caracterizar correctamente las fallas del Bajo Segura, Crevillente y Norbética. Se ha completado el estudio con datos de GPS de la red CuaTeNeo, pero esta red se circunscribe a las fallas de Carboneras, Palomares y Alhama de Murcia, hecho que impide que se pueda determinar el comportamiento sísmico de las fallas de Crevillente y Norbética. A partir de los datos se han determinado los comportamientos sísmicos para Carboneras, Palomares y Alhama de Murcia. Para todas ellas se han registrado movimientos extensivos (0.9, 0.8 y 0.3 mm/año respectivamente) y de desgarre siniestro para Palomares y Alhama de Murcia (0.6 y 0.2 mm/año) y diestro para Carboneras (1.5 mm/año), si bien los datos insuficientes para esta falla provocan errores muy elevados. Se ha determinado la magnitud máxima potencial para las tres fallas en aproximadamente 7.4 Mw, si bien debe considerarse orientativa al no haberse incluido los errores registrados por los GPS. Por esta razón se recomienda un estudio GPS más intenso en la zona de Carboneras y su extensión hasta Crevillente.
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