The effect of initial and prior models on phase tensor inversion of distorted magnetotelluric data

Magnetotelluric (MT) data are often distorted by near-surface small-scale lateral heterogeneities. Inverting distorted MT data may produce artifacts or false anomalies, leading to unreliable interpretation. This problem can be avoided by inverting the phase tensor (PT), which is known to be free of galvanic distortion. However, PT inversion is known to strongly depend on the initial or prior model, because the PT itself does not contain absolute resistivity information. To obtain a reliable inversion result from a set of PT data, a proper initial or prior model is crucial. In this study, a one-dimensional mean resistivity profile estimated from the average sum-of-squared-elements impedance was chosen as an initial model, because it was proven to be less sensitive to galvanic distortion. Examples with synthetic data showed that PT inversion using such an initial and prior model is a viable approach for inverting galvanically distorted MT data. In addition, the present paper considers a situation, where the distortion is not purely galvanic. A simple synthetic study indicated that the PT is affected by inductive distortion, and thus, such inversion results should be interpreted with caution. Graphic Abstract