Factors influencing seismic wave attenuation in the lithosphere in continental rift zones

International audienc

How tumour-induced vascular changes alter angiogenesis: Insights from a computational model

International audienc

Analysis of the Mw 4.3 Lorient earthquake sequence: a multidisciplinary approach to the geodynamics of the Armorican Massif, westernmost France

A Mw 4.3 earthquake occurred on 2002 September 30, in the Armorican Massif, NW France. Since it was one of the largest events ever recorded in this region, this was the opportunity to improve our seismotectonic knowledge of the Armorican Massif. We performed a post-seismic survey (SISBREIZH), which allowed us to locate accurately 62 aftershocks within 14 days. An analysis of the main shock using broadband records provided a normal fault mechanism with a dextral strike-slip component located at 12-km depth. The aftershock sequence exhibits: (1) a combination of almost pure right-lateral strike-slip and dominant normal faulting similar to the main shock; (2) magnitudes ranging from 0.4 to 1.9 and (3) depths ranging from 11.5 to 13.5 km, that is, close to the main shock hypocenter. The distribution of the aftershocks defines a rupture plane dipping 60° to the south with a fault length of ≈2 km consistent with the source parameters of the main shock. Beside the SISBREIZH survey, a morpho-structural analysis has been conducted: we found fault plane solutions with southward-dipping N120-150 normal fault planes. The stress tensor computed after the aftershock focal mechanisms is a strike-slip regime with a NE-SW extensional direction. The Lorient earthquake appears to reactivate Late Hercynian structures and the whole sequence is reflecting the regional-scale tectonic stress field expressed by a combination of strike-slip and normal faulting

How tumour-induced vascular changes alter angiogenesis: Insights from a computational model

International audienc

Quand la Terre tremble. Séismes, éruptions volcaniques et glissements de terrain en France

International audienc

Lithospheric modification by extension and magmatism at the craton-orogenic boundary: North Tanzania Divergence, East Africa

We present a joint analysis of newly acquired gravity and teleseismic data in the North Tanzanian Divergence, where the lithospheric break-up is at its earliest stage. The impact of a mantle upwelling in more mature branches of the East African Rift has been extensively studied at a lithospheric scale. However, few studies have been completed that relate the deep-seated mantle anomaly detected in broad regional seismic tomography with the surface deformation observed in the thick Archaean Pan-African suture zone located in North Tanzania. Our joint inversion closes the gap between local and regional geophysical studies, providing velocity and density structures from the surface down to ca. 250 km depth with new details. Our results support the idea of a broad mantle upwelling rising up to the lithosphere and creating a thermal modification along its path. However, our study clearly presents an increasing amplitude of the associated anomaly both in velocity and density above 200 km depth, which cannot be solely explained by a temperature rise. We infer from our images the combined impact of melt (2-3 per cent), composition and hydration that accompany the modification of a thick heterogenous cratonic lithosphere are a response to the hot mantle rising. The detailed images we obtained in density and velocity assert that Archaean and Proterozoic units interact with the mantle upwelling to restrict the lithosphere modifications within the Magadi-Natron-Manyara rift arm. The composition and hydration variations associated with those units equilibrate the thermal erosion of the craton root and allow for its stability between 100 and 200 km depth. Above 80 km depth, the crustal part is strongly affected by intruding bodies (melt and gas) which produces large negative anomalies in both velocity and density beneath the main magmatic centres. In addition to the global impact of a superplume, the velocity and density anomaly pattern suggests a 3-D distribution of the crust and mantle lithospheric stretching, which is likely to be controlled by inherited fabrics and enhanced by lateral compositional and hydration variations at the Tanzanian craton-orogenic belt boundary