Diretrizes para aquisição e processamento de dados geofísicos magnetotelúricos: o caso do fragmento cratônico São Luís/MA

Abstract

Since the 1950s, the magnetotellurics method (MT) has been widely used in mineral and oil prospecting (sedimentary basins), cratonic regions and recognitions of crustal-scale geological discontinuities. MT geophysical method consists of a passive technique that aims to investigate geoelectric characteristics of subsoil through the interaction between telluric currents and subsurface materials. The objective of the work is show a guide for an MT campaign through the acquisition of 15 MT stations in an area where it covers the São Luís cratonic fragment with the purpose of scientific dissemination and formation of specialized teams. The working method comprises the following steps based on the principles of MT method: MT instrumentation, data acquisition, data processing, and geophysical products (forward modeling and pseudo-sections). 15 MT stations were acquired with an equidistance of 12 km and an NNW-SSE profile length of 180 km. All frequencies for each MT sounding were subjected to the Notch FIR filter to subtract the contribution from the powerline. The 15 calculated impedance tensors are displayed in apparent resistivity (ρ) and phase (Ф). The resistivity values varied from 0.027 (MT-08) to 10.530 (MT-12) ohm-m. For the prognosis of the subsurface geoelectric characteristics, three geophysical products were created: initial geophysical model, TE and TM mode pseudo-sections. The manuscript presented an explanatory guide for the acquisition of magnetotellurics geophysical data in northeastern Brazil, with the purpose of contributing to the formation of new teams in MT surveys serving as a reference for students and/or professionals from geosciences in the initiation to MT method.