Magnetotelluric interpretation of the Sabalan geothermal field in thenorthwest of Iran

In this paper, fourteen mt stations along a profile perpendicular to the main geologicalstructure were used in order to identify the geology of sabalan geothermal field includingthe extension of the surface cap-rock and clay-cap layers. the mt data collected between1-8192 hz is of useful quality and provides good control on the surface layers in manyareas. it means that reliable modeling should be possible to a depth of 1000 m dependingon resistivity distribution. te and tm-mode data and skew parameter show that the earthdimensionality differs from site to site, so we examined the 1d and 2d modeling alongthe profile. to have the best possible interpretation we used determinant data for 1dmodeling and joint te and tm-mode data in 2d modeling. the data was processed andmodeled using an improved modeling method. one-dimensional modeling was performedusing a forward operator based on reflection coefficient of the layers (zhadanov andkeller 1998) and the two-dimensional inversion has been done by using a code fromsiripunvaraporn and egbert (2000).the resulting 1d and 2d models show a high–verylow–low resistivity sequence with depth. the high resistive layer at the surface wasassigned to basalt, andesitic and old trachyandesitic flows and other impermeable rocksthat have thermal conduction and act as the cap-rock of the system. the role of the caprockis very important in sustainability of the system, because it prevents the reservoirfrom cooling by mixing with surface water. the second layer is a very conductive layerand is interpreted as the reservoir that has thermal convection and hot fluids contained inits fractures and pores. the resistive basement is a hot and solid magmatic intrusion and isinterpreted as a heat source that produces a conductive heat flow towards the reservoir. asa result, the shallow resistivity model of the sabalan area is in a good correlation with thegeological features. it shows the common conceptual resistivity model which has beenpresented for the geothermal reservoirs.