Medium change monitoring using ambient seismic noise and coda wave interferometry: examples from intraplate NE Brazil and the Mid-Atlantic Ridge

This thesis presents and discusses the results of ambient seismic noise correlation for two different environments: intraplate and Mid-Atlantic Ridge. The coda wave interferometry method has also been tested for the intraplate data. Ambient noise correlation is a method that allows to retrieve the structural response between two receivers from ambient noise records, as if one of the station was a virtual source. It has been largely used in seismology to image the subsurface and to monitor structural changes associated mostly with volcanic eruptions and large earthquakes. In the intraplate study, we were able to detect localized structural changes related to a small earthquake swarm, which main event is mR 3.7, North-East of Brazil. We also showed that the 1-bit normalization and spectral whitening result on the loss of waveform details and that the phase auto-correlation, which is amplitude unbiased, seems to be more sensitive and robust for our analysis of a small earthquake swarm. The analysis of 6 months of data using cross-correlations detect clear medium changes soon after the main event while the auto-correlations detect changes essentially after 1 month. It could be explained by fluid pressure redistribution which can be initiated by hydromechanical changes and opened path ways to shallower depth levels due to later occurring earthquakes. In the Mid-Atlantic Ridge study, we investigate structural changes associated with a mb 4.9 earthquake in the region of the Saint Paul transform fault. The data have been recorded by a single broadband seismic station located at less than 200 km from the Mid-Atlantic ridge. The results of the phase auto-correlation for a 5-month period, show a strong co-seismic medium change followed by a relatively fast post-seismic recovery. This medium change is likely related to the damages caused by the earthquake’s ground shaking. The healing process (filling of the new cracks) that lasted 60 days can be decomposed in two phases, a fast recovery (70% in ~30 days) in the early post-seismic stage and a relatively slow recovery later (30% in ~30 days). In the coda wave interferometry study, we monitor temporal changes of the subsurface caused by the small intraplate earthquake swarm mentioned previously. The method was first validated with synthetics data. We were able to detect a change of 2.5% in the source position and a 15% decrease of the scatterers’ amount. Then, from the real data, we observed a rapid decorrelation of the seismic coda after the mR 3.7 seismic event. This indicates a rapid change of the subsurface in the fault’s region induced by the earthquake.

Medium change monitoring using ambient seismic noise and coda wave interferometry: examples from intraplate NE Brazil and the Mid-Atlantic Ridge

This thesis presents and discusses the results of ambient seismic noise correlation for two different environments: intraplate and Mid-Atlantic Ridge. The coda wave interferometry method has also been tested for the intraplate data. Ambient noise correlation is a method that allows to retrieve the structural response between two receivers from ambient noise records, as if one of the station was a virtual source. It has been largely used in seismology to image the subsurface and to monitor structural changes associated mostly with volcanic eruptions and large earthquakes. In the intraplate study, we were able to detect localized structural changes related to a small earthquake swarm, which main event is mR 3.7, North-East of Brazil. We also showed that the 1-bit normalization and spectral whitening result on the loss of waveform details and that the phase auto-correlation, which is amplitude unbiased, seems to be more sensitive and robust for our analysis of a small earthquake swarm. The analysis of 6 months of data using cross-correlations detect clear medium changes soon after the main event while the auto-correlations detect changes essentially after 1 month. It could be explained by fluid pressure redistribution which can be initiated by hydromechanical changes and opened path ways to shallower depth levels due to later occurring earthquakes. In the Mid-Atlantic Ridge study, we investigate structural changes associated with a mb 4.9 earthquake in the region of the Saint Paul transform fault. The data have been recorded by a single broadband seismic station located at less than 200 km from the Mid-Atlantic ridge. The results of the phase auto-correlation for a 5-month period, show a strong co-seismic medium change followed by a relatively fast post-seismic recovery. This medium change is likely related to the damages caused by the earthquake’s ground shaking. The healing process (filling of the new cracks) that lasted 60 days can be decomposed in two phases, a fast recovery (70% in ~30 days) in the early post-seismic stage and a relatively slow recovery later (30% in ~30 days). In the coda wave interferometry study, we monitor temporal changes of the subsurface caused by the small intraplate earthquake swarm mentioned previously. The method was first validated with synthetics data. We were able to detect a change of 2.5% in the source position and a 15% decrease of the scatterers’ amount. Then, from the real data, we observed a rapid decorrelation of the seismic coda after the mR 3.7 seismic event. This indicates a rapid change of the subsurface in the fault’s region induced by the earthquake.

Cartografias mito-poéticas do imaginário nelidiano: das visões do mundo arcaico ao contemporâneo no romance fundador

Esta tesis trata de cómo se desarrolla en la obra de la escritora contemporánea Nélida Piñon una especie de pensamiento cartográfico, presente desde su primer romance Guia-mapa de Gabriel Arcanjo, publicado en 1961. Para que se interprete el universo literario nelidiano, formulamos nuestro trabajo estableciendo un confronto con el texto del mito iluminado por las reflexiones de Eliade (2007; 2007b; 2008) y Meletínski (2002); con el discurso filosófico pos-estructuralista, representado principalmente por las contribuciones de Deleuze y Guattari (1995; 1996; 1997) a respecto de una geografía del nomadismo; y de Foucault (1996; 2006) sobre el orden del discurso, o nacimiento de la literatura y el ser del lenguaje. Examinadas por la lectura crítica y comparativista de esta investigación, las cartografías mito-póeticas de Piñon son presentadas al lector asociándose a una geografía de los sentimientos y al que Maffesoli (2001) denomina deseo de errância y de perdición, particularmente en las obras Tebas do Meu Coração, A República dos Sonhos, O Presumível Coração da América e Fundador. Esa última novela, publicada en 1969, por lo tanto anterior a los otros textos mencionados, servirá como corpus principal de nuestro análisis, que objetiva demostrar como la narrativa de Piñon se conecta a un linaje literario estructurado a partir de las acciones de un determinado tipo de personaje conocido como inaugurador de ciudades o héroe civilizador o cultural. En la reedición de ese arquetipo de personaje, la autora instaura el elemento de la seducción, en un juego que se establece entre los sujetos masculino y femenino y que pone de manifiesto cuestiones relacionadas al erotismo, a la transgresión y al sagrado, abordadas en nuestro discurso por las consideraciones de Baudrillard (2008) y Bataille (1987). Para que se explicite la constitución de esos puntos, realizaremos un viaje de las visiones del mundo arcaico al contemporáneo por las páginas de Fundador, apuntando de qué manera la escritora brasileña retoma las imágenes del mito cosmogónico, del mito del eterno retorno y del paraíso terreal, que se inscriben como fundamento do su texto literario