3-D modeling of the deep electrical conductivity of Merapi volcano (Central Java): integrating magnetotellurics, induction vectors and the effects of steep topography

We derive a 3-D model of the electrical conductivity structure of Merapi volcano in Central Java from magnetotelluric (MT) sounding curves and geomagnetic induction vectors. Topography has been considered explicitly in the model. The overall magnitude of the conductivities is constrained by MT measurements, while lateral variations are mainly derived from geomagnetic induction vectors. The resulting model is consistent with both the MT transfer functions (apparent resistivities and phases) and the magnetic transfer functions (induction vectors). The final model consists of two 3-D structures, i.e. a central conductor and a second conductor lying to the southwest of the summit. The high conductivity material is probably hot saline water as suggested by position and lateral extent of the high conductivity material.