Seismotectonic and stress distribution in the central Chile subduction zone

Journal of South American Earth Sciences, v. 15, n. 1, p. 11-22, 2002. http://dx.doi.org/10.1016/S0895-9811(02)00003-2International audienc

Andean geodynamics : main issues and contributions from the 4th ISAG, Gottingen

Tectonophysics, v. 345, n. 1-4, p. 1-15 [507], 2002. http://dx.doi.org/10.1016/S0040-1951(01)00203-7International audienc

The Mw 7.7 Tocopilla Earthquake of 14 November 2007 at the Southern Edge of the Northern Chile Seismic Gap: Rupture in the Deep Part of the Coupled Plate Interface

Bulletin of the Seismological Society of America, v. 99, p. 87-94, 2009. http://dx.doi.org/10.1785/0120080192International audienc

The October 15, 1997 Punitaqui earthquake (Mw=7,1) : a destructive event within the subducting Nazca plate in Central Chile

Tectonophysics, v. 345, n. 1-4, p. 199-210, 2002. http://dx.doi.org/10.1016/S0040-1951(01)00213-XInternational audienc

A double seismic zone in the subducting Juan Fernandez Ridge of the Nazca Plate (32°S), central Chile,

International audienceThe region of central Chile offers a unique opportunity to study the links between the subducting Juan Fernandez Ridge, the flat slab, the double seismic zone (DSZ), and the absence of modern volcanism. Here we report the presence and characteristics of the first observed DSZ within the intermediate-depth Nazca slab using two temporary seismic catalogs (Ovalle 1999 and Chile Argentina Seismological Measurement Experiment). The lower plane of seismicity (LP) is located 20-25 km below the upper plane, begins at 50 km depth, and merges with the lower plane at 120 km depth, where the slab becomes horizontal. Focal mechanism analysis and stress tensor calculations indicate that the slab's state of stress is dominantly controlled by plate convergence and overriding crust thickness: Above 60-70 km depth, the slab is in horizontal compression, and below, it is in horizontal extension, parallel to plate convergence, which can be accounted for by vertical loading of the overriding lithosphere. Focal mechanisms below 60-70 km depth are strongly correlated with offshore outer rise bend faults, suggesting the reactivation of preexisting faults below this depth. The large interplane distances for all Nazca DSZs can be related to the slab's unusually cold thermal structure with respect to its age. Since LPs globally seem to mimic mantle mineral dehydration paths, we suggest that fluid migration and dehydration embrittlement provide the mechanism necessary to weaken the rock and that the stress field determines the direction of rupture

Seismic time reversal experiment in the Low Noise Underground Laboratory, LSBB (France)

International audienc

Seismicity and hydromechanical behavior of a fractured porous rock under a high pressure fluid injection

International audienceWe performed high-pressure water injections in boreholes set in a fractured porous limestone at 250 m-depth in the LSBB URL in order to investigate the coupling relationships between induced seismicity and the rock permeability changes. The seismic events and tilts of the free wall of the gallery were monitored at different locations by two 3-component accelerometers and two 2D tiltmeters located from 1.5 to 2 m from the injection chamber. Changes in fluid pressure and flow rate were simultaneously monitored in the chamber. A damage-induced permeability increase of a factor of 2.2 occurred after a 10 seconds long swarm of complex seismic events caused by a pressure peak injection of 3.5 × 106 Pa and a sudden increase in the injected flow rate from 0 to to 5.3 × 10−5 m3 ⋅ s−1. The various angular directions observed on both tiltmeters and 3D accelerometric components indicate that the source of the deformation remains complex and evolves over the time of fluid pressure diffusion in the fractures. At the beginning, signals appear dominated by the source geometry, the rock mass boundary and stress conditions. After the damage and during the pressure decay, tangential slipping of the fracture behavior dominates stress relaxation in the medium. Finally, tilt monitoring coupled with seismo-acoustic measurements present a promising way to quantitatively estimate the relationships between the changes in fractured rocks permeability and seismicity induced by fluid pressurization

A new seismic tomography of Aigion area (Gulf of Corinth, Greece) from the 1991 data set.

International audienceA new three-dimensional delay traveltime tomography is performed to image the intermediate structure of the western Gulf of Corinth. A large data set, collected in 1991 during a two-month passive tomographic experiment, has been reanalysed for the reconstruction of detailed Vp and Vs images. An improved tomography method, based on an accurate traveltime computation, is applied to invert simultaneously delayed P and S first-arrival traveltimes for both velocity and hypocentre parameters. We perform different synthetic tests to analyse the sensitivity of tomography results to the model parametrization and to the starting 1-D model selection. The analysis of the retrieved Vp and Vs models as well as deduced Vp/Vs and Vp·Vs images allows us to interpret and delineate the distribution of lithological variation, porosity/crack content and fluid saturation in the upper 9–11 km of the crust beneath the gulf. The tomographic models image a rather complex crustal structure, which is characterized by a vertical change in both velocity features and seismicity distribution. We identify a shallower zone of the crust (0–5 km depth), in which velocity distributions seem to be controlled by the still active N–S extensional regime and a deeper zone (7–11 km depth), which matches the seismogenic zone. The correlation between this latter and a specific unit of the Hellenic mountain structure (the Pyllite–Quartzite series) allows us to suggest a possible explanation for seismicity concentration in a narrow band at 7–9 km depth. Finally, the occurrence of clusters showing low-angle normal fault mechanisms in areas characterized by high Vp/Vs values indicates a possible role of fluids in triggering brittle creep along the identified low-angle normal faults