Abstract: Having checked catalogs of historical and recent seismic events, posted by regional monitoring stations of Argentina, Bolivia, Brazil and the seismic records of the Seismological Station at FaCEN - UNA (CPUP) of those earthquakes with epicenters in the paraguayan territory, an inventory of earthquakes occurred in Paraguay is reported and its seismic zones are proposed.

Resumen: Habiendo recurrido a una revisión de catálogos de eventos sísmicos históricos y recientes, publicados por instituciones de monitoreo regionales de Argentina, Bolivia, Brasil y los registros de la Estación Sismológica de FaCEN - UNA (CPUP) de aquellos sismos con epicentros dentro del territorio paraguayo, se reporta un inventario de sismos ocurridos en Paraguay y se proponen sus zonas sísmicas.

ABSTRACT: The occurrence of earthquakes associated with the opening of groundwater wells is a very rare phenomenon. We present the results from a magnetotelluric profile of about 4 km-long that crosses a seismic zone near the town of Bebedouro, in the Northeastern part of the intra-cratonic Paraná basin, in Brazil. The seismic activity is thought to be caused by a raise in pore-pressure within a fractured basalt aquifer due to the natural injection of water from the shallow aquifer into the basalt. Regularized 2D inversions of the magnetotelluric data show that the basalt layer presents both electric resistivity (60-300 ohm-m) and thickness (400-600 m) within the expected ranges for the study area. However, an unforeseen abrupt change (~200 m) in the basalt thickness has been observed. This variation occurs close to the Western limit of the seismic zone and it nearly coincides with a geoelectric basement deepening of about 600 m. We interpret these lateral contrasts as a fault system that probably controlled the deposition of the Permian to Jurassic volcano-sedimentary sequence under the study area. Our study suggests that a preexisting structure affecting the basement and the basaltic layer is determinant in favoring seismicity associated with the opening of water wells.

ABSTRACT The main goal of this paper is to characterize the Coxim earthquake occurred in June 15th, 2009 in the Pantanal Basin and to discuss the relationship between its faulting mechanism with the Transbrasiliano Lineament. The earthquake had maximum intensity MM V causing damage in farm houses and was felt in several cities located around, including Campo Grande and Goiânia. The event had an mb 4.8 magnitude and depth was 6 km, i.e., it occurred in the upper crust, within the basement and 5 km below the Cenozoic sedimentary cover. The mechanism, a thrust fault mechanism with lateral motion, was obtained by P-wave first-motion polarities and confirmed by regional waveform modelling. The two nodal planes have orientations (strike/dip) of 300°/55° and 180°/55° and the orientation of the P-axis is approximately NE-SW. The results are similar to the Pantanal earthquake of 1964 with mb 5.4 and NE-SW compressional axis. Both events show that Pantanal Basin is a seismically active area, under compressional stress. The focal mechanism of the 1964 and 2009 events have no nodal plane that could be directly associated with the main SW-NE trending Transbrasiliano system indicating that a direct link of the Transbrasiliano with the seismicity in the Pantanal Basin is improbable.

We present the results of a study of surface-wave group velocity tomography, for the Chaco-Parana basin region. Previous surface waves analysis (e.g., Snokes and James; 1997, Feng et al., 2004, 2007) estimated Moho depth in the central Chaco basin and a low-velocity anomaly in the lithospheric mantle. However the seismic structure of the crust and upper mantle remains little characterized across the region due to the rather poor resolution, especially for the south region. The aim of this work is to improve the resolution for the Chaco-Paraná basin region using dispersion curves from regional earthquakes recorded at permanent and portable stations and inter-station dispersion curves derived from correlation of ambient noise, for a dataset of seismic noise recordings from permanent and local networks (BRASIS, INPRES) stations, achieving a better path coverage and a more uniform azimuthally distribution. A 2D group velocity tomographic inversion was performed obtaining maps that display improved resolution in northern Argentina and southern Brazil. A grid-search method was applied to estimate a crustal thickness model for the Chaco-Paraná basin. Estimates of the crustal thickness agree with the ~34 km found for CPUP station, the observed thin crust (less than 35 km) suggested by Assumpção et al., 2013 and the average crustal thickness (32-35 km) suggested by Snoke and James, 1997, Prezzi et al., 2009 and Dragone et al., 2012. Large crustal thickness variation is also observed between the Andean region and the Chaco-Parana basin and a deeper crust is found in the Paraná basin region compared with the Chaco-Paraná basin.

En este trabajo se presentan los resultados de la tomografía de velocidad de grupo de las ondas superficiales, para la región de la cuenca Chaco-Paraná. Estudios previos mediante ondas superficiales en la región de la cuenca de Chaco (e.g., Snokes and James, 1997; Feng et al., 2004, 2007) estimaron la profundidad del Moho y obtuvieron una anomalía de baja velocidad en el manto litosférico. Sin embargo la estructura sísmica de la corteza y el manto superior está poco caracterizada en toda la región debido a la resolución bastante limitada, especialmente en la zona sur. El objetivo de este análisis es mejorar la resolución para la región de la cuenca Chaco-Paraná utilizando curvas de dispersión de terremotos regionales registrados en estaciones portátiles y permanentes, y curvas de dispersión inter-estación obtenidas mediante la correlación de ruido ambiente para registros de ruidos sísmicos de estaciones permanentes y de redes locales (BRASIS, INPRES), logrando una mejor cobertura de las trayectorias y una distribución acimutal más uniforme. Se realizó una inversión tomográfica 2D de la velocidad de grupo obteniéndose mapas que presentan mejor resolución en la región norte de Argentina y sur de Brasil. Se aplicó un programa de inversión basado en el método de búsqueda de grilla que produjo un modelo del espesor de la corteza para la cuenca Chaco-Paraná. El espesor estimado es congruente con los 34 km encontrados para la estación CPUP, con la corteza delgada (menor a 35 km) sugerida por Assumpção et al., 2013 y con el espesor cortical promedio (32-35 km) sugerido por Snoke and James, 1997, Prezzi et al., 2009 y Dragone et al., 2012. Se observa además, una gran variación del espesor cortical entre la región andina y la cuenca Chaco-Paraná y la presencia de corteza más profunda en la cuenca de Paraná, comparada con la cuenca Chaco-Paraná.

Este trabalho apresenta a interpretação da função do receptor determinada para os eventos registrados na Estação Sismológica de Rio Claro, em operação desde outubro de 2002. As profundidades calculadas para a Moho variaram de 36 a 44 km. A análise da variação dos valores de profundidade mostra que eles estão associados aos azimutes dos eventos. Portanto decidiu-se fazer uma análise azimutal dos resultados obtidos. Os maiores valores foram calculados para eventos que se localizam à norte da estação e os valores de 36 km foram calculados para telessismos do quadrante SW. Estes resultados mostram que existe uma elevação da Moho na direção da estrutura ''Domo de Pitanga''. Estes resultados indicam que esta estrutura é provavelmente de origem tectônica e causada por eventos profundos do manto superior.

This paper presents an analysis of receiver functions to estimate crustal structure beneath the Rio Claro Seismological Station, which has been in operation since October 2002. The depths obtained for the Moho discontinuity range from 36 to 44 km. A systematic variation of Moho depths with azimuth was observed. Larger values were obtained with events arriving from the North and the values of 36 km were observed with teleseisms arriving from the SW. This result shows that in the region there is an elevation of the Moho discontinuity near the Domo de Pitanga structural high. This result probably indicates a tectonic origin for this structure caused by deep deformation processes involving the whole lithosphere.