Imaging of the North Perth Basin by Magnetotelluric Methods

Abstract

The North Perth Basin is a large sedimentary basin that formed following the separation of the Greater India plate from the Western Australian Shield. The Darling Fault System forms the eastern boundary of this basin, dividing the Dandaragan Trough sub-basin from the Yilgarn craton. Seismic profiling, gravity surveys, and well logging have thus far been unable to accurately determine the depth to basement, which is believed to be on the order of ~ 10km. Due to the deeper penetration capabilities, magnetotelluric methods may be able to further constrain this depth. This method may also more accurately measure the dip angles of the faults in the Darling Fault Zone, using a comparison between the resolving power of the impedance variables and the tipper. Magnetotelluric data was obtained from 20 sites spanning a ~100km E-W transect of the Dandaragan Trough and Darling Fault Zone. These data were processed and used as inputs for two inversion algorithms in order to obtain resistivity distribution models with depth scales. The depth of the Dandaragan Trough and dip angle of major faults were measured from these models using the resistivity threshold determined from well logs, and the results compared to expected values from previous geophysical surveys. Values measured were consistent with predictions, with measured depths of 10:1 ±1:6km for the Dandaragan Trough, and dip angles of ~ 61° and ~ 75° for the Darling and Urella Faults.