Two-Dimensional Magnetotelluric Data modeling of the Sabalan geothermal fieldusing REBOCC and MT۲DInvMatlab codes

In this paper the modelling of Magnetotelluric (MT) data of Sabalan geothermal was undertaken to evaluate the resistivity models at the shallow depth and in the upper layers of thermal reservoir. For this purpose, a profile with the length of approximately ۱۰ km include seven MT measuring stations selected and two-dimensional (۲D) modelling source codes named the reduced based Occam (REBOCC) and the MT۲DIinvMatlab inversion has been applied. The data points were carefully selected between frequency range ۰.۰۱- ۱۳۲ Hz. In order to explain the mechanism of the geothermal reservoirs, some global conceptual model is presented that each of these models is valid for the interpretation of geothermal phenomena in a particular area. MT۲DInvMatlab inversion source code prepared based on the finite elements (FEM) method for forward modelling. Inversion parameters as an Input file and appropriate mesh blocks design should prepared before starting the modelling and inversion. After setting up the model parameter, ۲D inversion of the Sabalan magnetotelluric data has been performed using smoothness-constrained least square methods with a spatially regularization parameter estimation. The ACB (Active Constraint Balancing) algorithm employed to stabilize the model. Both apparent resistivity and phase data has been used to have model with minimum misfit for TM mode data. REBOCC is the second inversion program using for ۲-D modeling. The resulting models reveal the presence of a resistive cover layer (Cap-rock) underlain by an anomalous conductive layer and other geological structures such as fluid-filled faults in about ۵۰۰-۱۰۰۰ m below the ground surface. A very low resistivity (۳-۵ ohm-m) feature at the depths below ۲۰۰۰ m, bounded by two more resistive (۱۰۰-۵۰۰ ohm-m) features that interpreted as the main reservoir of the geothermal system in the area. At shallow depths, the resistivity model obtained from the MT data is consistent with the general conceptual resistivity model proposed for high-temperature geothermal systems.