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Facultad de Astronomía y Geofísica, Universidad Nacional de La Plata, Argentina
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- PublicationOpen AccessSeismicity and Crustal Velocity Structure of the Southern Central Andes - Western Argentina(2012-04-04)
; ; ; ; ; ;Scarfì, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Raffaele, R.; Dipartimento di Scienze Geologiche, Università di Catania, Italy ;Badi, G.; Facultad de Ciencias Astronómicas y Geofisicas, Universidad Nacional de La Plata, La Plata, Argentina ;Ibanez, J. M.; Instituto Andaluz de Geofisica, Universidad de Granada, Granada, Spain ;Imposa, S.; Dipartimento di Scienze Geologiche, Università di Catania, Italy; ; ; ; ; EAGE - European association of geoscientists & engineersA local seismic network, operating in western Argentina from 28°S to 33 °S, between August 1995 and January 1999, recorded more than 450 earthquakes. In this region, the geodynamic is controlled by the subduction of the Nazca plate beneath the South American lithosphere, which is characterised here by a sub-horizontal path before reassuming its downward descent. As accurate earthquake locations are of primary importance when studying the seismicity of a given area, events recorded by the local seismic network enable in-depth investigations into seismotectonic patterns, allowing us to improve the earthquake source characterization and the knowledge on the ongoing seismo-tectonics of the region. With this aim, we performed a simultaneous inversion of both the velocity structure and the hypocentre location. The obtained velocity images highlight vertical and lateral heterogeneities which, together with the distribution of the relocated events, can be associated with the main tectonic structures in the crust of the western Sierra Pampeanas region. The study also provided new constraints on the geometry of the subducted slab. We noted a great concentration of shallower seismicity with respect to that of the surrounding areas at the expected position of the Juan Fernandez Ridge, which certainly influences the subduction style along its strike, leading to the formation of a bent in the slab geometry.168 134 - PublicationRestrictedVolcanic tremor and local earthquakes at Copahue volcanic complex, Southern Andes,(2008-03-06)
; ; ; ; ; ; ;Ibanez, J.; Instituto Andaluz de Geofísica, Universidad de Granada, Campus de Cartuja s/n. 18071 Granada, Spain ;Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Bengoa, C.; Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina ;Caselli, A.; Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina ;Badi, G.; Facultad de Astronomía y Geofísica, Universidad Nacional de La Plata, Argentina ;Almendros, J.; Instituto Andaluz de Geofísica, Universidad de Granada, Campus de Cartuja s/n. 18071 Granada, Spain; ; ; ; ; In the present paper we describe the results of a seismic field survey carried out at Copahue Volcano, Southern Andes, Argentina, using a small-aperture, dense seismic antenna. Copahue Volcano is an active volcano that exhibited a few phreatic eruptions in the last 20 years. The aim of this experiment was to record and classify the background seismic activity of this volcanic area, and locate the sources of local earthquakes and volcanic tremor. Data consist of several volcano-tectonic (VT) earthquakes, and many samples of back-ground seismic noise. We use both ordinary spectral, and multi-spectral techniques to measure the spectral content, and an array technique [Zero Lag Cross Correlation technique] to measure the back-azimuth and apparent slowness of the signals propagating across the array.We locate VT earthquakes using a procedure based on the estimate of slowness vector components and S–P time. VT events are located mainly along the border of the Caviahue caldera lake, positioned at the South-East of Copahue volcano, in a depth interval of 1–3 kmbelow the surface. The background noise shows the presence of many transients with high correlation among the array stations in the frequency band centered at 2.5 Hz. These transients are superimposed to an uncorrelated background seismic signal. Array solutions for these transients show a predominant slowness vector pointing to the exploited geothermal field of “Las Maquinitas” and “Copahue Village”, located about 6 km north of the array site. We interpret this coherent signal as a tremor generated by the activity of the geothermal field.217 34 - PublicationRestrictedDepth dependent seismic scattering attenuation in the Nuevo Cuyo region (southern central Andes)(2009-12-29)
; ; ; ; ; ; ;Badi, G.; Facultad de Ciencias Astronomicas y Geofısicas, Universidad Nacional de La Plata, La Plata, Argentina. ;Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Ibanez, J. M.; Instituto Andaluz de Geofısica, Universidad de Granada, Granada, Spain ;Bianco, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Sabbione, N.; Facultad de Ciencias Astronomicas y Geofısicas, Universidad Nacional de La Plata, La Plata, Argentina. ;Araujo, M.; Instituto Nacional de Prevencion Sısmica, San Juan, Argentina.; ; ; ; ; In the present work we separated intrinsic from scattering attenuation coefficients both for the crust and the upper mantle in the tectonically highly active areas of the Southern-Central Andes - Nuevo Cuyo region, analyzing two groups of earthquakes, well separated in depth. This region is characterized by the presence of flat subduction. We apply MLTWA (Multiple Lapse Time Window Analysis), coda normalization and Q-coda techniques to measure the scattering and intrinsic attenuation coefficient and the total Q for S waves. We find that intrinsic attenuation does not decrease with depth whereas scattering attenuation is higher in the crust than in the upper mantle, and that intrinsic attenuation predominates over scattering attenuation. We interpret this observation in terms of the release of water and other fluids into the overlying lithosphere due to the dynamics of the subduction process, in agreement with most of the prevalent geodynamic models.201 27 - PublicationRestrictedSeismotectonic features from accurate hypocentre locations in southern central Andes (western Argentina)(2012)
; ; ; ; ; ; ; ;Scarfì, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Raffaele, R.; Dipartimento di Scienze Geologiche, Università di Catania, Italy ;Badi, G.; Facultad de Ciencias Astronómicas y Geofisicas, Universidad Nacional de La Plata, La Plata, Argentina ;Ibanez, J. M.; Instituto Andaluz de Geofisica, Universidad de Granada, Granada, Spain ;Imposa, S.; Dipartimento di Scienze Geologiche, Università di Catania, Italy ;Araujo, M.; Instituto Nacional de Prevención Sısmica, San Juan, Argentina ;Sabbione, N.; Facultad de Ciencias Astronómicas y Geofisicas, Universidad Nacional de La Plata, La Plata, Argentina; ; ; ; ; ; A local seismic network, over a five-year period, recorded about 450 earthquakes in western Argentina. In this region, the geodynamics is controlled by the subduction of the Nazca plate beneath the South American lithosphere, which is characterised here by a sub-horizontal path before reassuming its downward descent. As accurate earthquake locations are of primary importance when studying the seismicity of a given area, events recorded by the local seismic network enable in-depth investigations into seismo-tectonic patterns, allowing to improve the earthquake source characterization and knowledge on the ongoing seismo-tectonics of the region. To this end, we performed a simultaneous 1-D inversion of both the velocity structure and the hypocentre location. The minimum 1-D model obtained is complemented by station corrections which lead to a first insight into the deeper 3-D structure. In addition, stability tests were performed to verify the robustness of our earthquake location results. They reveal a fairly stable hypocentre determination, demonstrating that the locations obtained by the inversion process are not systematically biased. The results show that Sierra Pie de Palo is characterised by a crustal seismogenic structure, dipping west and extending from its eastern boundary to about 30 km of depth. The study also provided new constraints on the geometry of the subducted slab. We noted a great concentration of shallower seismicity compared to that of the surrounding areas of the Wadati-Benioff zone, at the expected position of the Juan Fernandez Ridge (JFR). Our hypocentres indicate that JFR certainly influences the subduction style along its strike, leading to the formation of a bend in the slab geometry.157 25