Fig. 1

a Map showing the cluster of 19 MT stations from the western part of Thailand (see Boonchaisuk et al. 2013). They are plotted on the geological map of this area (after Department of Mineral Resources 2006). b Example of rotational invariant, det (gray diamonds) and ssq (brown squares), impedances from an individual station (KAN-120C). The det impedances have magnitudes smaller than the ssq impedances, which is as predicted (Rung-Arunwan et al. 2016) because the det impedance is biased downward by geometric distortion