Inversion of moment tensor focal mechanisms for active stresses around the microcontinent Iberia: Tectonic implications

Previous studies about the strength of the lithosphere in the center of Iberia fail to resolve the depth of earthquakes because of the rheological uncertainties. Therefore, new contributions are considered (the crustal structure from a density model) and several parameters (tectonic regime, mantle rheology, strain rate) are checked in this paper to properly examine the role of lithospheric strength in the intraplate seismicity and the Cenozoic evolution. The strength distribution with depth, the integrated strength, the effective elastic thickness and the seismogenic thickness have been calculated by a finite element modelling of the lithosphere across the Central System mountain range and the bordering Duero and Madrid sedimentary basins. Only a dry mantle under strike-slip/extension and a strain rate of 10 -15 s , causes a strong lithosphere. The integrated strength and the elastic thickness are lower in the mountain chain than in the basins. This heterogeneity has been maintained since the Cenozoic and determine the mountain uplift and the biharmonic folding of the Iberian lithosphere during the Alpine deformations. The seismogenic thickness bounds the seismic activity in the upper-middle crust, and the decreasing crustal strength from the Duero Basin towards the Madrid Basin is related to a parallel increase in Plio-Quaternary deformations and seismicity. However, elasto-plastic modelling shows that current African-Eurasian convergence is resolved elastically or ductilely, which accounts for the low seismicity recorded in this region.Keywords: lithospheric strength, effective elastic thickness, seismogenic thickness, Iberia, finite element modelling ResumenLos estudios previos sobre resistencia de la litosfera en el centro de Iberia no logran resolver la profundidad de los terremotos debido a las incertidumbres reológicas. Por eso, en este trabajo se han considerado nuevas contribuciones (estructura cortical obtenida de un modelo de densidad) y se han comprobado varios parámetros (régimen tectónico, reología del manto, tasa de deformación) para examinar adecuadamente el papel de la resistencia de la litosfera en la sismicidad intraplaca y en la evolución Cenozoica. Mediante una modelización de elementos finitos, se ha calculado la distribución de la resistencia con la profundidad, la resistencia integrada, el espesor elástico efectivo y el espesor sismogénico en una sección litosférica que atraviesa la cadena montañosa del Sistema Central y las cuencas sedimentarias del Duero y Madrid. Sólo un manto seco en desgarre/extensión y una tasa de deformación de 10 -15 s -1, o bajo extensión y 10 -16 s -1 , origina una litosfera resistente. La resistencia integrada y el espesor elástico son más bajos en el sistema montañoso que en las cuencas. Estas anisotropías se han mantenido desde el Cenozoico y determinan el levantamiento de la cadena y el plegamiento biarmónico de la litosfera Ibérica durante las deformaciones alpinas. El espesor sismogénico limita la actividad sísmica en la corteza superior-media, y l...

Section: The Iberian Intraplate Rheological Model: Strong Vs Soft Masupporting

confidence: 71%

Section: Boundary Conditionsmentioning

confidence: 99%

Strength of the Iberian intraplate lithosphere: Cenozoic deformations and seismicity

Martín-Velázquez

Muñoz

Gómez-Ortíz

et al. 2016

“…seismicity in this area indicates a local N-S oriented of Shmax (Antón et al, 2010a), while regional data show a more NW-SE oriented Shmax (De Vicente et al, 2008). The whole study area was deformed by extensional and strike-slip brittle faulting during post-Variscan and Alpine times (Arthaud and Matte, 1975;Vegas, 2005;Martín-González et al 2011).…”

Section: Geological and Tectonic Settingmentioning

confidence: 99%

Seismicity and potencially active faults in the Northwest and Central-West Iberian Peninsula

Martín-González

Antón

Arévalo

et al. 2012

Self Cite

The Northwest and Central-West Iberian Peninsula configure an intraplate area far from the active plate boundaries, where the Variscan basement crops out extensively (Iberian Massif). This area of the Iberian Peninsula has been traditionally considered a seismically stable region; however, it presents a moderate intraplate seismicity which indicates the presence of active structures and the occurrence of potentially damaging earthquakes. The scarcity of Mesozoic and Cenozoic deposits makes very difficult to track the record of the more recent tectonic activity and the characterization of active tectonic structures within the Iberian Massif. Nevertheless the seismic sequences of 1995-1997 in Lugo (5.1 mb; IV) and 2003 in Zamora (4.2 Mw) provided important information about the orientation of the present stress tensor, and the distribution of the hypocenters informed about the rupture geometry of the fault planes. The present work integrates geological, geomorphological, structural, and seismological data in order to define the main potentially active faults in the region. Faults trending NE-SW to N-S are potentially active as strike-slip, in some cases with a reverse component, under a NW-SE to N-S compression.

“…The models have distinct orientations (Fig. 7B) in order to test possible lateral changes in the lithospheric structure and considering the distinct orientations of the NW−SE-to WNW−ESE-trending Variscan and NE−SW-trending Alpine structures (e.g., De Vicente et al, 2008;Simancas et al, 2013). All models are built using the ALCUDIA Model as the template for the crustal structure (Fig.…”

Section: Gravity Models In the Calatrava Volcanic Provincementioning

confidence: 99%

Gravity modeling of the lithosphere in the Calatrava Volcanic Province (Spain): geodynamic implications.

Granja-Bruña

Vegas²,

Domingo

et al. 2015

Self Cite

(M.A.S.D.); amunoz@ucm.es (A.M.M.); ssainz-maza@fomento.es (S.S.M.A)Received: 12 January 2015 / Accepted: 5 July 2015 / Available online: 20 July 2015 AbstractThe origin of the intraplate volcanism in the Calatrava Volcanic Province (CVP) is controversial. On the basis of its geochemical signature, it has been ascribed to an "aborted" rift, implying lithospheric thinning. However, the volcanism occurred during the generalized Cenozoic NW−SE-oriented compressive tectonic regime. On the other hand, on the basis of evidence for its deep-seated origin, it has been linked to the existence of a baby-plume detached from an active megaplume below the Canary-Azores Islands and the western Mediterranean. In order to understand better the aforementioned geodynamic scenarios for the origin of the CVP, we address here the study of the lithosphere in the CVP and its vicinity by means of gravity analysis and 2+1/2D modeling. Gravity modeling results do not support the rifting model adopted for the intraplate volcanism occurred in the CVP because the crust shows a quasi-constant thickness. Density models suggest the existence of a sub-crustal, anomalous low-density block that could be underplated magmatic material at the base of the crust, suggesting that only a minor part of it intruded up into the crust and erupted. The localized magmatism of the CVP can be related to the combination of two factors: active, the gentle folding of the Iberian lithosphere and associated uplifting of the Variscan basement due to the NW-directed transmission of compressive stresses in the upper plate yielded by the subduction/collision in the south Iberian margin. The formation of the lithospheric folding in the Calatrava region results in a decrease of the pressure beneath the swell of the antiform that is likely to bring about basaltic magmatism below the swell; and one passive, the existence of a Variscan right-lateral shear band, which yields a weakened crust that facilitates the ascent of the magmatic materials. The relatively small volume, but large extension, of the volcanic outcrops could be associated with the preferential ascent of the magmas along the weakened crust of this NW−SE-trending Variscan shear band.Keywords: Calatrava, intraplate volcanism, gravity modeling, lithosphere structure, upward continuation Resumen El origen del volcanismo intraplaca en la Provincia Volcánica de Calatrava (CVP) es controvertido. En base a su signatura geoquímica se ha atribuido a la formación de un rift "abortado", implicando un adelgazamiento litosférico. Sin embargo, el volcanismo se desarrolló durante un régimen tectónico compresivo orientado NW-SE que fue generalizado en la región de Calatrava durante el Cenozoico. Por otro lado, en base a las evidencias de su origen profundo, se le ha relacionado con la existencia de una mini-pluma desconectada de una mega-pluma activa debajo de los archipiélagos de Canarias y Azores, y en el Mediterráneo occidental. Con el propósito de contribuir a la discriminación entre los escenarios geodinámicos mencionados...