Statistical analysis of seismic data from north-western and western Argentina

Due to the process of subduction of the Nazca Plate, high seismic activity is observed near the Argentine Andean range between 21~ and 36~ The new version of the Argentine Seismic Catalogue, which includes well-defined events during the period 1964-I989, allows us to perform an analysis of seismic risk. Earthquakes with epicenters in the provinces included in the north-western and western regions were studied using Gumbel III extreme value distribution. Modal extreme magnitudes and return periods were calculated for both regions and the results were compard with the ones obtained through the entire process techniques (both analytical and graphical). As a first study, we analyzed each province separately, after which mean values for each region were obtained. Modal values around 5-5.5 have been found and times of recurrence for events with m b > 6 of approximately 25 years were obtained.Facultad de Ciencias Astronómicas y Geofísica

Localización de hipocentros y determinación de su magnitud en Tierra del Fuego y zonas aledañas

New hypocentre locations of earthquakes with low to medium magnitude have been calculated in order to study Tierra del Fuego seismicity. The region has a complex tectonic setting: the island is crossed by a transforming fault named Magallanes-Fagnano which divides Tierra del Fuego in two continental blocks. This fault system constitutes the major continental segment of the South America-Scotia plate’s border. The island has an important seismological history which includes an event of magnitude 7.8 occurred on December 1949.Reports of earthquakes occurred in 1929, 1930, 1944, 1949 and 1970 are known by a study of historical seismicity. In this paper hypocentre locations and error analysis have been carried out. Records at five seismological stations have been analyzed during January-December 2007. More than 180 events have beenidentified and some of them were compared to events of NEIC (National Earthquake Information Center) and ISC (International Seismological Centre). Magnitude determinations have been calculated with first arrival amplitude. The majority of earthquakes have magnitude mb between 2 and 4 degrees. With respect to hypocentral depths, more than 50% of located earthquakes have their depths in the first 10 km. The seismicity map obtained shows that beyond rather dispersed seismicity related to the Magallanes-Fagnano fault, a concentration of epicentres is found in the Darwin Cordillera area and in the Scotia plate surrounding, displaying evidence of a correlation with the geotectonic area of studyNuevos hipocentros de sismos de baja a mediana magnitud han sido calculados con el fin de estudiar la sismicidad en la Isla de Tierra del Fuego y zonas aledañas. La región presenta un complejo escenario tectónico: la isla es atravesada por una falla transformante conocida como Falla de Magallanes-Fagnano la cual divide a Tierra del Fuego en dos bloques continentales. Esta falla constituye el mayor segmento continental del borde de las placas de Scotia y Sudamericana. La isla tiene una importante historia sismológica que incluye un evento de carácter destructivo ocurrido en diciembre de 1949 el cual alcanzó una magnitud de 7.8 en la escala de Richter.De un análisis de sismicidad histórica, se conocen reportes de sismos en los años 1929, 1930, 1944, 1949 y 1970. En el presente trabajo se ha realizado la localización de los hipocentros y el análisis de los errores en la determinación. A tal efecto se analizaron los registros de 5 estaciones sismológicas para el período enero 2007 – diciembre 2007. Más de 180 sismos fueron localizados y algunos de ellos comparados con los cinco eventos registrados por el NEIC (National Earthquake Information Center) y el ISC (Internacional Seismological Centre) para el mismo período. El cálculo de magnitud fue realizado a partir de la amplitud del primer arribo. La mayoría de los sismos tienen un valor de magnitud mb que se concentra entre 2 y 4 grados. Con respecto a la profundidad hipocentral, más del 50% de los eventos localizados tienen profundidades en los primeros 10 km. El mapa de sismicidad obtenido muestra una distribución de sismos sobre y en las cercanías de la falla Magallanes-Fagnano, una concentración de epicentros en el área de la Cordillera de Darwin y en los alrededores de la placa de Scotia, manifestando indicios de una correlación con el ambiente geotectónico del área de estudio

Crystallization properties of melt-quenched Ge-rich GeSbTe thin films for phase change memory applications

The crystallization process of melt quenched Ge-rich GeSbTe films, with composition optimized for memory applications, has been studied by optical reflectance measurements. The optical properties have been related to the structure and composition by means of the effective medium approximation. The compositional variations have been investigated by transmission electron microscopy and electron energy loss spectroscopy. Amorphous materials prepared by melt-quenching with different laser energy densities have been studied. For the energy density of 1.5 J cm−2, a uniform amorphous layer, with embedded Ge crystalline grains, is obtained. The film exhibits a crystallization temperature of 275 °C and no relevant phase separation during crystallization. For a lower energy density of 1 J cm−2, only half of the film thickness is quenched to the amorphous phase, with Ge depletion. The crystallization temperature of the Ge depleted film is 245 °C, and a partial phase separation occurs

Descripción de la ocurrencia de sismos a través de una distribución asintótica de valores extremos

En este trabajo se estudia parcialmente el riesgo sísmico de las provincias de Salta, Jujuy, La Rioja y Catamarca. Para ello se utiliza un método estadístico que sólo tiene en cuenta los valores extremos, semestrales, del catálogo de terremotos de cada región. El modelo aplicado, conocido como Gumbce III, está basado en una función de tipo asintótica. Los resultados que se obtienen son los valores de tres parámetros: una magnitud que es una cota para cada región, una magnitud característica y un parámetro ligado a la curvatura de la función distribución. Con estos parámetros se pueden determinar otros valores de interés para la prevención sísmica: la magnitud asociada a la energía media liberada por año en cada zona, tiempo de recurrencia para una magnitud dada y magnitudes extremas modales para un tiempo dado.Facultad de Ciencias Astronómicas y Geofísica

Estudio de la estructura cortical en la Isla de Tierra del Fuego a partir de datos sismológicos

La Isla de Tierra del Fuego (TdF) se encuentra ubicada en el extremo sur de la Cuenca de Magallanes, donde el borde transformante entre la Placa de Scotia y la Sudamericana define el Sistema de Fallas Magallanes-Fagnano (MFS), cuya falla principal tiene un movimiento sinestral. Con el fin de obtener información de la corteza, se realizó un análisis de funciones receptoras (FR) a partir de datos registrados en cinco estaciones sismológicas instaladas en la Isla. Una FR es el resultado de un proceso matemático de deconvolución de la componente vertical de un sismograma con la componente radial, y permite obtener información acerca de las discontinuidades en la corteza y en el manto. Posteriormente estas FR son sumadas mediante un proceso de H-K stacking con el cual es posible estimar valores de H y Vp/Vs a partir de un modelo de referencia. Se obtuvieron valores de H y Vp/Vs comprendidos entre 26-34 km y 1.68-1.85 respectivamente. La presencia de diferentes unidades geológicas y de diversas fallas que componen el MFS serían los responsables del ambiente geotectónico complejo presente en la zona y de los distintos valores obtenidos dependiendo de la ubicación de la estación y de la dirección de los telesismos seleccionados para el análisis.Peer Reviewe

Statistical analysis of seismic data from north-western and western Argentina

Due to the process of subduction of the Nazca Plate, high seismic activity is observed near the Argentine Andean range between 21~ and 36~ The new version of the Argentine Seismic Catalogue, which includes well-defined events during the period 1964-I989, allows us to perform an analysis of seismic risk. Earthquakes with epicenters in the provinces included in the north-western and western regions were studied using Gumbel III extreme value distribution. Modal extreme magnitudes and return periods were calculated for both regions and the results were compard with the ones obtained through the entire process techniques (both analytical and graphical). As a first study, we analyzed each province separately, after which mean values for each region were obtained. Modal values around 5-5.5 have been found and times of recurrence for events with m b > 6 of approximately 25 years were obtained.Facultad de Ciencias Astronómicas y Geofísica

Descripción de la ocurrencia de sismos a través de una distribución asintótica de valores extremos

En este trabajo se estudia parcialmente el riesgo sísmico de las provincias de Salta, Jujuy, La Rioja y Catamarca. Para ello se utiliza un método estadístico que sólo tiene en cuenta los valores extremos, semestrales, del catálogo de terremotos de cada región. El modelo aplicado, conocido como Gumbce III, está basado en una función de tipo asintótica. Los resultados que se obtienen son los valores de tres parámetros: una magnitud que es una cota para cada región, una magnitud característica y un parámetro ligado a la curvatura de la función distribución. Con estos parámetros se pueden determinar otros valores de interés para la prevención sísmica: la magnitud asociada a la energía media liberada por año en cada zona, tiempo de recurrencia para una magnitud dada y magnitudes extremas modales para un tiempo dado.Facultad de Ciencias Astronómicas y Geofísica

Crustal structure beneath Tierra del Fuego, Argentina, inferred from seismic P-wave receiver functions and ambient noise autocorrelations

We investigate the structure of the crust beneath the main island of Tierra del Fuego through a teleseismic receiver function analysis and ambient seismic noise autocorrelation using data of four available broad-band stations. The area is situated in a remote region of southern Argentina where the interaction between the South American and Scotia plates define the Magallanes-Fagnano Fault System. Crustal thickness, Vp/Vs ratios and S-wave velocity models were estimated using the H-k stacking method and the inversion of receiver functions with the Neighbourhood Algorithm. Furthermore, we applied an ambient seismic noise autocorrelation procedure to identify PmP Moho reflections at all stations. The three methods provide consistent estimates for the crustal thickness which ranges from about 24.5 km in the northern part of the Island to about 39.2 km in the south. The lowest and highest values of S-wave velocity found, in the most superficial layers of the crust, correlate with the presence of Tertiary and upper Cretacic sediments in the north and with older geological units composed by more consolidated lithologies in the south, respectively. Despite the diverse geological and tectonic settings present, our results do not change significantly for different parameters or subsidiary data sets, i.e., showing the robustness of our models which likely represent closely the local structure beneath the Island. This area is considered a very seismically active one and its crustal structure has been little explored demonstrating the importance of having new models and the necessity to increase the station coverage to allow a more detailed study of the region. Furthermore, the models presented here provide better constraints on the crustal structure, and will facilitate studies of the regional seismicity that can improve our understanding of the seismic hazard posed by earthquakes such as the magnitude 7.5 and 7.8 events that occurred in 1949. © 2018The data used in this study was obtained from scientific projects funded by the National Agency for the Promotion of Science and Technology, Argentina (ANPCyT), the National University of La Plata, Argentina (UNLP) and the National Institute of Oceanography and Experimental Geophysics, Italy (OGS). We would like to thank the staff of the Astronomical Station of Rio Grande (EARG) for the installation and maintenance of seismic stations and Marcelo Moreno from the National Institute of Seismic Prevention (INPRES) for operational support in getting data. Furthermore we are grateful to Larminat and Henninger families for allowing us to install the stations DSPA and ELCA and for providing collaboration with EARG. This work was partially supported by a grant from the National Scientific and Technical Research Council (CONICET). MS acknowledges the Spanish Project MISTERIOS CGL2013-48601-C2-1-R.Peer reviewe