Banca de QUALIFICAÇÃO: ALESSANDRO JOSÉ SOARES DANTAS
Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.DISCENTE : ALESSANDRO JOSÉ SOARES DANTAS
DATA : 14/12/2017
HORA: 15:00
LOCAL: Auditório do DGEF
TÍTULO:
Estimating lithospheric thickness under Brazil from spectral analysis of EMAG2 data and S-wave receiver functions
PALAVRAS-CHAVES:
Curie isotherm, S-wave receiver function, lithospheric thickness
PÁGINAS: 35
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Geociências
RESUMO:
This study aims at mapping lithospheric thickness across the entire Brazilian territory, using both magnetic and seismological methods. Using a spectral analysis technique, it was possible to map the Depth to the Bottom of Magnetic Sources (DBMS), which can be interpreted as the Magnetite Curie Isotherm (MCI), which is defined by the 580oC temperature. Like the MCI, the Lithosphere-Asthenosphere Boundary (LAB) is also an isotherm, although defined by temperatures between 1100 and 1330oC, which is the range for which mantle rocks start to melt. This process results in a decrease in seismic velocity, so that the LAB can also be detected through seismological methods. The spectral analysis technique consists of an asymptotic analysis of the radially averaged power spectrum, as proposed by Spector and Grant (1970), through which the top and the thickness of the magnetic layer can be estimated. The magnetic dataset utilized was the Earth Magnetic Anomaly Grid version 2 (EMAG2). The S receiver function (SRF) technique allows the estimation of crustal and lithospheric thickness throughout Brazil. This technique makes use of the telesseismic S-wave that has part of its energy converted to P-wave upon entering the lithosphere, generating the so-called Sp phase, which arrives at the seismic station without interference with multiple reverberations. The SRFs were computed at 100 Brazilian seismic stations belonging to the BR, BL, and Y4 networks. For each seismic station, the depth to the Moho, the LAB, and the ICM were estimated, obtaining variations between 32 and 63 km for the Moho and between 171 and 232 km for the LAB. The MCI, estimated from magnetic data, displayed depths between 26 and 46 km. Those results revealed that regions of thick lithosphere correlate with regions of thin crust, perhaps due to isostatic compensation. A good correlation was also observed between Moho and MCI depths, suggesting that - although the Moho is not an isotherm - its variation might berelated to changes in thermal flow. Finally, although the LAB and the MCI are both isothermal surfaces, they do not show a clear correlation. Variations in thermal conductivity might explain that discrepancy.
MEMBROS DA BANCA:
Interno - 1451214 - ADERSON FARIAS DO NASCIMENTO
Presidente - 1863578 - JORDI JULIA CASAS
Externo ao Programa - 346468 - JOSE ANTONIO DE MORAIS MOREIRA
Interno - 349684 - WALTER EUGENIO DE MEDEIROS