عنوان مقاله [English]
نویسندگان [English]چکیده [English]
There are various examples of the use of the magnetotelluric method in the investigation of groundwater potential and detection of aquifers and their contamination in the literature (Alies & Rodriguez, 2015; Asaue et al., 2012; Falgàs et al., 2005; Mejiʹas et al., 2008; MeliʹI et al., 2011; Pedersen et al., 2005; Steuer et al., 2008). Considering that the study area is located at a proper distance from the Caspian Sea, it has the potential for geological storage of iodine reserves. The groundwater resources in the study area are most likely to contain salts with a high percentage of iodine as a rare mineral. In the previous investigation of the data, a different data-set was used; no strike angle was estimated, and resistivity models derived from one- and two-dimensional inversion of the determinant of the impedance tensor were presented (Oskooi et al, 2014). In this paper, the results of strike estimation and distortion analysis, as well as inversion of joint TE-TM mode data and three-dimensional inversion have been discussed. We estimated the strike and dimensionality of the data based on the phase tensor method (Caldwell et al, 2004). The phase tensor is defined by the ratio of the real and imaginary parts of the impedance tensor, and its prominent feature is that it is not affected by distortion. The skew angle or the tensor’s asymmetry can be used as an indication of dimensionality. The azimuth of strike is determined based on the orientation of tensor’s principal axes. Figure 2 displays a map of phase tensor ellipses for the whole frequency range and the characteristic profile I. The color bar shows the skew angle values. As it can be seen, data show mainly one-dimensional behavior (low values of the skew angle) with some local two- and three-dimensional effects, especially at long periods. The regional magnetotelluric response can be distorted due to the presence of the small-scale near-surface structures. The level of distortion was examined using WAL rotational invariants (Weaver et al, 2000) implemented in WALDIM code (Mart'i et al, 2009). Based on the values of a set of eight rotational invariants-including seven independent and one dependent parameter and considering threshold values for each of them regarding the level of present noise- dimensionality, strike direction and values of shear and twist angles as part of distortion parameters along with their errors are estimated. Figure 5 shows histogram of estimated twist and shear angles for the characteristic profile I. Low values of these two parameters indicate that the data have not been severely affected by distortion.