Instituto Nacional Of Prevencion Sismica

Argentina

Instituto Nacional Of Prevencion Sismica

Argentina

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Havskov J.,University of Bergen | Sorensen M.B.,University of Bergen | Vales D.,Instituto Portugues do Mar e da Atmosfera | Ozyazcoglu M.,Atatürk University | And 3 more authors.
Bulletin of the Seismological Society of America | Year: 2016

Published results of coda Q show a large variation in values. These variations are often claimed to be related to different tectonics, whereas they might just be related to using different assumptions in the processing, leading to different input parameters for the analysis. In this study, the effect of using different processing parameters is investigated and significant differences, particularly at low frequencies, are observed. We find a new set of optimal parameters, which we recommend using in future studies. Using a short lapse time of 30 s and optimal parameters, data from both similar and very different tectonic regions are used to calculate coda Q using the same program and the same parameters. The regions considered are eastern Anatolia, the Azores, Jan Mayen, northwestern and central Argentina, the Shanxi rift system in China, and southwestern Norway. We obtain the following relations: eastern Anatolia (Q =88 f0.66), Azores (Q =86 f0.70), Jan Mayen (Q =90 f0.72), northwestern and central Argentina (Q =89 f0.94), Shanxi rift system (Q 99 f0.89), and southwestern Norway (Q =124 f0.91). The results show that coda Q is very similar for regions of similar tectonics and significantly different for regions with varying tectonics. Using alternative, more common parameters gives different Q, but the regional differences remain, so which parameters to use to get correct coda Q values is still uncertain. However, coda Q can clearly distinguish different tectonic areas provided identical processing parameters are used, even if they are not optimal. © 2016, Seismological Society of America. All rights reserved.


Scarfi L.,Italian National Institute of Geophysics and Volcanology | Raffaele R.,University of Catania | Badi G.,National University of La Plata | Ibanez J.M.,University of Granada | And 3 more authors.
Tectonophysics | Year: 2012

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 characterized 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 characterized 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. © 2011 Elsevier B.V.


Perucca L.P.,National University of San Juan | Perucca L.P.,CONICET | Rothis M.,CONICET | Rothis M.,Instituto Nacional Of Prevencion Sismica | Vargas H.N.,CHISNANCO SRL
Geomorphology | Year: 2014

The drainage pattern on the western piedmont of the Sierra de La Cantera is divergent, typical of alluvial fans and showing anomalies that are directly related to the trace of La Cantera thrust. In previous studies, two types of anomalies were identified: upstream of the fault scarp, rivers have a broom-shaped pattern, while downstream - in the hanging block - streams become denser, more sinuous and incised. In this contribution, these morphotectonic aspects were analyzed in detail, making direct and indirect analysis to quantify the relationship between these anomalies and the faults affecting alluvial fans. In addition, the influence of neotectonic activity on smaller water course patterns in the alluvial fan areas was investigated in order to find indicators of on-going vertical movements, since the spatial arrangements of these piedmont channels are determined by slope and structure, where active faults cause diversions or anomalies. Topographic profiles in two selected channels cutting across the trace of the fault were performed using a differential GPS in order to establish the relationship between the sinuosity and slope of these rivers. The results obtained allow us to state that the most sinuous channels have lower slopes and are located in the hanging wall of the fault. Morphometric analysis of scarps stated that active tectonics have played an essential role in controlling the drainage pattern in the piedmont, leading the rivers to adjust to these slope variations.Finally, based on the geomorphologic, stratigraphic, structural and seismological characteristics and parameters analyzed, La Cantera Thrust is considered a seismogenic source of significance to the nearby towns (>. 700,000 inhabitants) and also to the large-scale dams built downstream along the San Juan River. © 2013.

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