Two-Dimensional Inversion of Papua New Guinea Data Using 'Least-Blocked' Models.

Abstract

Magnetotelluric data obtained from a region of Papua New Guinea have been inverted with the aid of a two-dimensional scheme in which the simplest 'least-blocked' model compatible with the data is sought. The average strike direction for the entire region and for all periods is estimated to be approximately N60W. In the rotated frame skew is small everywhere, but ellipticity values remain quite large at some sites, which raises some uncertainty about the assumption of two-dimensionality. Since the data also indicate the presence of local galvanic distortion, a static shift correction has been applied; both the original (rotated) data and the static-shift corrected data have been used to generate 'least-blocked' models. The final models for the two data sets are found to resemble each other quite closely. Both reveal a descending conductive layer beneath a resistive limestone cover of thickness 0.6-0.8 km on southwestern side of the profile increasing to around 2.1-2.4 km on the northeastern side. The one notable difference is that the descending conductive layer divides into two parts separated by a resistive limestone layer in the model obtained from static-shift corrected data, but not in the other.

Multi‐site, multi‐frequency tensor decomposition of magnetotelluric data

“…However, the focus of the survey was the uppermost crust, and hence there was insufficient recording time for precise estimates at long periods. Conventional (Swift, 1967) strike direction estimation, which is based on the magnitudes of the impedance elements rather than their phase relationships, yields a large scatter with frequency and site (see Figure 2 of Agarwal and Weaver, 1997). Using a step-wise approach of rotating the data by 1 • increments, fitting frequency-independent shear and twist to each site, and summing the site misfits, Toh and Uyeshima (1997) derived a minimum-misfit global strike direction of N60 • W (N30 • E) for the whole frequency range of 384-0.01 Hz.…”

Resistivity structure of high-angle subduction zone in the southern Kyushu district, southwestern Japan

“…The χ 2 misfit values were found to be much larger than those calculated from the final model. We carried out the F-test Weaver and Agarwal, 1993;Agarwal and Weaver, 1997). The deterioration of fit, S 2 , is defined as…”