Ph.D., Earth Sciences, University of California, San Diego, 1968.
Geomagnetic induction, magnetotellurics, inverse theory, geophysical fluid dynamics.
My main current interest is geomagnetic induction in the Earth. I was the prime mover behind the international EMSLAB project in the 1980's to study the electrical structure of the Juan de Fuca Plate and adjacent continent. EMSLAB imaged electrical structure which appears to be associated with injection of water into the lower continental crust during subduction. However, probably the most important result was a dramatic increase in the visibility and credibility of electromagnetic methods, particularly magnetotellurics (MT), in the wider Earth Science community.
In subsequent years, I have been involved in a series of large scale MT projects including in Tibet (INDEPTH) and along the San Andreas Fault. I have recently returned from Argentina, where we collected long period MT data along three transects in the Sierra Pampeanas. These are basement block ranges east of a volcanically quite segement of the Andes and overlying a nearly flat-lying portion of the subducted Nazca Plate. The range faults extend at high angle into the deep crust and maybe even to the mantle. The goal of the project is to understand the deformation properties of the lower crust and the mantle between the crust and the subducted slab.
My students and I have also been leaders in the revolution in MT methodology. We have developed a method for inverting induction data for multi-dimensional conductivity structure that is orders of magnitude faster than competing techniques. It is presently the only viable scheme for directly inverting large 3-D data sets. We have also been leaders in introducing robust statistical methods to geomagnetic time series analysis and we have introduced such methods into inversions too. Our work on time series analysis resulted in approximately an order of magnitude improvement in the reliability of MT data without new instrumentation.