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.

Produção de narrativas escritas no ensino fundamental: estudo de casos

This paper focuses on the construction of the narrative for elementary school students, searching to identify strategies they employed in the production of narrative texts representative of miniconto genre. Therefore, we take a sample forty texts produced by students of 6 and 9 years of basic education, twenty in the 6th year students (ten public school and ten private school) and twenty students in 9th grade (distributed similarly between public education and private). In general, we aim to understand the mechanisms by which producers build their narratives, as well as providing input for analysis of textual production of this genre. This research is based on Functional-Linguistic assumptions of the American side, inspired by Givón (2001), Thompson (2005), Hopper (1987), Bybee (2010), Traugott (2003), Martelotta (2008), Furtado da Cunha (2011), among others. In addition, from the theoretical framework presented by Labov (1972) about the narrative, coupled with Batoréo contribution (1998), we observed the recurring elements in the structure of narratives under study: abstract, orientation, complication, resolution, evaluation and coda. Also approached, but that in a complementary way, the notion of gender presented in Marcuschi (2002). This is a research quantitative and qualitative, with descriptive and analytical-interpretive bias. In corpus analysis, we consider the following categories: gender discourse miniconto; compositional structure of the narrative; informativeness (discursive progression, thematic coherence and narrative, topical-referential distribution); informative relevance (figure / ground). At the end of the work, our initial hypothesis of the better performance of students in 9th grade, compared to 6, and the particular context of education in relation to the public context, not confirmed, since, in the comparative study revealed that the groups have similar performance as the construction of the narrative, making use of the same strategies in its construction.

Produção de narrativas escritas no ensino fundamental: estudo de casos

This paper focuses on the construction of the narrative for elementary school students, searching to identify strategies they employed in the production of narrative texts representative of miniconto genre. Therefore, we take a sample forty texts produced by students of 6 and 9 years of basic education, twenty in the 6th year students (ten public school and ten private school) and twenty students in 9th grade (distributed similarly between public education and private). In general, we aim to understand the mechanisms by which producers build their narratives, as well as providing input for analysis of textual production of this genre. This research is based on Functional-Linguistic assumptions of the American side, inspired by Givón (2001), Thompson (2005), Hopper (1987), Bybee (2010), Traugott (2003), Martelotta (2008), Furtado da Cunha (2011), among others. In addition, from the theoretical framework presented by Labov (1972) about the narrative, coupled with Batoréo contribution (1998), we observed the recurring elements in the structure of narratives under study: abstract, orientation, complication, resolution, evaluation and coda. Also approached, but that in a complementary way, the notion of gender presented in Marcuschi (2002). This is a research quantitative and qualitative, with descriptive and analytical-interpretive bias. In corpus analysis, we consider the following categories: gender discourse miniconto; compositional structure of the narrative; informativeness (discursive progression, thematic coherence and narrative, topical-referential distribution); informative relevance (figure / ground). At the end of the work, our initial hypothesis of the better performance of students in 9th grade, compared to 6, and the particular context of education in relation to the public context, not confirmed, since, in the comparative study revealed that the groups have similar performance as the construction of the narrative, making use of the same strategies in its construction.