THREE-DIMENSIONAL INVERSION OF THE EARTHSCOPE MAGNETOTELLURIC DATA USING THE INTEGRAL EQUATION METHOD

In this paper we apply 3D inversion to the MT data collected for the EarthScope project. We use the integral equation method as a forward modeling engine. Quasi-analytical approximation with a variable background (QAVB) method of Fréchet derivative calculation is applied. This technique allows us to simplify the inversion algorithm and to use just one forward modeling on every iteration step. A receiver footprint approach considerably reduces computational resources needed to invert the large volumes of

data covering vast areas. The data set, which was used in the inversion, was obtained through the Incorporated Research Institutions for Seismology (IRIS). The long period MT data was collected in Oregon, Washington, Idaho and parts of Montana from 2006 to 2008. The inverted electrical conductivity distribution agrees reasonably well with geological features of the region as well as with 3D MT inversion results obtained by other researchers.