A DISCUSSION OF BIAS IN MAGNETOTELLURIC RESPONSES

POMPOSIELLO CRISTINA; BOOKER JOHN; FAVETTO ALICIA

GEOPHYSICS

Society of Exploration Geophysicists Foundation

Lugar: Yale, Tulsa, US; Año: 2009 vol. 74 p. 59 - 65

0016-8033

Magnetic field noise biases magnitudes of magnetotelluric (MT) responsefunctions such as resistivity, impedance and the induction vector (tipper). This isparticularly severe in the so-called dead band between about 1 to 10 s period.The standard approach to remove these biases is to use a magnetic remotereference. In cases where this is not available or does not work because thenoise is correlated at the local and remote sites, it is possible to extract un-biasedestimates using an inversion algorithm that predicts the magnitude from thephase. However, an important condition for this to be successful is that phaseestimates are un-biased. A brief review of the theory of MT response bias ispresented and it is shown that phase can be biased if parallel components of theelectric and magnetic fields are correlated. This arises when the structure isthree-dimensional or a two-dimensional response is estimated in coordinates notparallel to strike. These ideas are illustrated with field data. It is also shown thatimprovements in electric field measurements make electric field references aviable option for estimating low bias responses up to periods approaching 1,000s