Fig. 4. RMS misfit maps show the misfit between the observed data and the calculated data of each site as a function of period. The calculated data are obtained (a) from the inverted model shown in Fig. 5; (b) by replacing the C1 conductor of Fig. 5 with a 300 m zone; and (c) by replacing the C2 conductor of Fig. 5 with a 300 m zone.
Conduct the dimensionality analysis (Siripunvaraporn, 2012). Since Zxx and Zyy are more severely distorted, only the off-diagonal data, Zxy and Zyx, were used for the 3-D inversion to reduce the risk of producing artifacts in the inverted model. The minimum error floor was set at 5% of the |ZxyZyx| 1/2. For the outliers, the error bars were increased to be large enough relative to the neighboring data. The area with topography was discretized into a 49 × 52 × 67 grid in north-south, east-west and depth, respectively. For the vertical mesh, the first layer is discretized at 30 m to provide high accuracy responses for all data. The thickness of the subsequent layers increases by 1.5–1.8 times of the previous layers. The horizontal grid sizes in the survey region are 200 m on both