Phase Tensor Analysis of Magnetotelluric Data over Dalma Volcanics

摘要

Magnetotellurics (MT) is a passive exploration technique which allows determination of the subsurface resistivity distribution on the depth scales ranging from few tens of meters to several hundreds of kilometres. Seven Remote Reference MT data were acquired over a frequency range from 320Hz-0.00055Hz over a part of Dalma Volcanics. Time series for all five components E_, E_, H_, H_ and H_ were acquired. These were used to estimate impedance tensor. The apparent resistivity data for some of the sites were severely affected by static shift. However, as phase data is unaffected we have used phase tensor analysis to recover the dimensionality and strike direction. For some sites we also removed the galvanic distortion. The three invariant parameters of phase tensor as ellipticity (λ), phase tensor skew angle (β) and Azimuth of Phase Tensor Maximum (α-β) are used to get the information of dimensionality as well as strike direction. The analysis shows that for shorter periods the structure is ID whereas for longer periods (0.5 Hz - 0.001 Hz) the structure is 2D. The strike direction in the frequency range 0.5 Hz to 0.001 Hz varies between 37-45°. However, for some sites the longer period exhibits three dimensional structures.