Banca de QUALIFICAÇÃO: GUILHERME WEBER SAMPAIO DE MELO

Uma banca de QUALIFICAÇÃO de MESTRADO foi cadastrada pelo programa.
DISCENTE : GUILHERME WEBER SAMPAIO DE MELO
DATA : 13/12/2018
HORA: 15:00
LOCAL: Auditório do DGEF
TÍTULO:

SISMOTECTONIC ANALYSIS OF THE SAINT PAUL TRANSFORM SYSTEM, ATLANTIC EQUATORIAL, ON 2013

PALAVRAS-CHAVES:

Mid-Atlantic Ridge; St. Paul Transform System; Seismotectonic; Fluid Percolation; Weakness Zone

PÁGINAS: 29
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Geociências
RESUMO:

Seismic activity studies in regions of the Mid-Atlantic Ridge have been a challenge for science due to the low coverage that seismology global networks offer in such regions. Despite the high cost and logistical issues, efforts using temporary or permanent deployments of equipment to better understand how these geologic faults behave, and their temporal evolution in those tectonic plate bourdary zones. In this work, we show the results obtained from a seismotectonic analysis performed from the earthquakes occurred during the 2013 year in the Saint Paul Transform System (SPTS). The study was carried using data recorded by a seismic station installed on the Saint Peter and Saint Paul Arquipelago (ASPSP) and a hydrophony array implanted during the COLMEIA project. The epicentral location of events with magnitude <3.3 was done using the Single Station Location (SSL) through of back-azimuth, yielding 52 events and with its hypocenters being estimated using polarizations analysis. Others 10 events of M> 3.3 were recorded also at regional stations located in NE Brazil, Cape Verde, Ascension Island and East coast of Africa, together with the ASPSP station. The HYPOCENTER software was used in this case to calculate the hypocenters, using the travel time correction. Next, we then located the same 10 events using only ASPSP station, but now together from the P wave records obtained by the hydrophones. The results show that the hypocenters obtained with the hydrophones has a smaller error values when compared with the obtained using of the regional stations. The hypocenter depths has values between 0.22 and 16.7 km below the ocean floor, it located in three different zones of the SPTS: Atobá Ridge Zone (ARZ), the Eastern Shear Zone (ESZ) and the Central Fracture Zone (CFZ). The seismic events on the ARZ presented a complex variation of depths, due to the thrust faults associated with the transpression along the transform fault, showing that the brittle-ductile zone is between 14-16 km of depth. Most hypocenters have been consistent with gravimetric data of thickness of a low density layer (serpentinized crust or mantle), so that in some cases the events is deeper than serpentinized zone, possibly due to the fluid percolation that allows the rocks break in deep faults. We identified that there is several earthquakes on the fracture zones located at the central segment of the SPTS. We believe that these events in the CFZ are caused by reactivation of a weakness zone, so that stresses originated on the ARZ or possible thermal changes in the stress field have reactivated these weaker zones.

MEMBROS DA BANCA:
Presidente - 1451214 - ADERSON FARIAS DO NASCIMENTO
Interno - 350640 - FRANCISCO HILARIO REGO BEZERRA
Interno - 2218779 - HELENICE VITAL