Open AccessRotational properties of the magnetotelluric impedance tensor: the example of the Araguainha impact crater, Brazil
Author(s) -
Fischer Gaston,
Masero Wilhelm
Publication year - 1994
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.1994.tb00141.x
Subject(s) - ellipse , principal axis theorem , eccentricity (behavior) , geometry , anisotropy , geology , orientation (vector space) , tensor (intrinsic definition) , skew , magnetotellurics , plane (geometry) , geodesy , mathematical analysis , mathematics , optics , physics , quantum mechanics , astronomy , political science , law , electrical resistivity and conductivity
SUMMARY The rotational properties of the elements of the magnetotelluric impedance tensor are reviewed in terms of the three identical ellipses that these elements describe in the complex plane. It is shown that graphical representations of these ellipses provide a powerful and simple tool to evaluate MT sounding results. This study required clarification of the characteristics of 2‐D structures, where the ellipses reduce to line segments, and of the meanings of such concepts as skew S and anisotropy A . As should be well known, a vanishing skew is not a sufficient condition to guarantee a 2‐D structure; all it does is place the middle ellipse over the origin of the complex plane. The additional constraint is to close the ellipses into line segments. It is shown that the orientation of the ellipses in the complex plane is strongly related to the directional properties of the structure. Structures with strong directionality yield ellipses whose major axes point toward the origin. The principal coordinates then are essentially parallel to the directions of maximum anisotropy. For ellipses with their minor axes pointing to the origin, the structure is not very directional and is rather oriented at 45° from the principal coordinates. A given structure can show these two kinds of behaviour simultaneously, though in different period ranges, i.e. in different depths ranges, as is shown with data from the Brazilian Araguainha impact crater. The question of static‐shift removal from field data is also addressed.