Refração Sísmica Profunda no Setor Sudeste da Província Tocantins / Deep Seismic Refraction on Southestearn Sector of the Tocantins Province

AUTOR(ES)
DATA DE PUBLICAÇÃO

2000

RESUMO

This work to fulfil the degree of Master of Sciences is inserted among the deep seismic refraction studies of the Thematic Project Geophysical Studies and Tectonic Model of the Tocantins Province Central and Southeast Sectors, Central Brazil . Three refraction lines, of around 300 km long each, were deployed, two of them in the Central sector and the other in the SE sector, that is subject of the present work. The equipment used in this experiment was composed by 111 SGR digital seismographs belonging to the PASSCAL Program. Complemented with auxiliary instruments from USGS and 13 seismographs belonging to IAG/USP. The space among the recording points was 2.5 km, which were located along main and secondary roads. Every 50 km was fired an explosion with 1000 kg of emulsion in each extreme and 500 kg in the central point. The geographical co-ordinates were determined by using the GPS differential method. The main objective of this work is to obtain as a final product a seismic velocity model with the physical characteristics of the main discontinuities in the crust and upper mantle. The packages SAC, SU and SEIS were used to perform the data analysis and processing. To carry on the modelling were used the ray theory and the synthetic seismograms construction, belonging to the SEIS package Data from the extreme and middle points of the seismic line were used to elaborate the final model, considering that due to technical problems signals from the other four explosions were not recorded. Apart from that, the recorded explosions did not present clear signals all along the extension of the line. Due to these facts, and considering also the geological units present in the studied region, are suggested three seismic velocity models. The first model is referred to the direct shot (EX31), which is localised in the Southwest extreme of the line on the Parana Basin province. In this model we obtained the P wave velocity (VP) of 2 km/sec at the surface, corresponding to the unconsolidated sediments and soil on the top of that basin. At a depth of 86 m we found VP of 5,15 km/sec and at a depth of 350 m the velocity VP of 4,6 km/sec, corresponding to the basalt and sand layers of the Parana Basin. Underlying them, at 650 m of depth we found the basement with VP of 5,75 km/sec and finally at a depth of 4 km there is a layer with VP of 6,07 km/sec, corresponding to a typical upper crust P wave velocity. The second model corresponds to the reverse shot (EX34) that is localised in the middle point of the line on the granitoides of the Araxa Group. For this model we obtained VP of 2 km/sec for the superficial layers, then at a depth of 60 m was obtained V P of 5,69 km/sec and for a depth of 860 m the value of V P is 6,25 km/sec. Finally, the third model belongs to the whole line section (300 km) from the direct shot (EX31). This model was obtained by using the arrivals of secondary phases and the results of models proposed in other works. From the surface down to 4 km of depth this model is similar to the first one. At 20 km of depth there is a layer with VP of 6,70 km/sec, corresponding to the lower crust, with Moho at a depth of 40 km with VP of 8,00 km/sec.

ASSUNTO(S)

província tocantins tocantins province refração sísmica profunda modelo de velocidades sísmicas deep seismic refraction deep seismic sounding seismic velocities model

ACESSO AO ARTIGO

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