EE 350 RADIOSCIENCE SEMINAR
Professor Howard Zebker
Date: Wednesday, October 24, 2001
Time: 4:15 PM; Refreshments at 4:00 PM
Seeing Flow Inside the Earth with Spaceborne Interferometric Synthetic Aperture Radar
Prof. Howard Zebker
Depts. of Geophysics and Electrical Engineering
Many geologic processes consist of the movement of fluids underground.
Because we are generally restricted to observing the surface of the Earth, our knowledge of
subsurface motion is indirect and in many cases insufficient to characterize it usefully. Recent
advances in technology, especially in interferometric synthetic aperture radar (InSAR), now enable
us to observe surface deformation from satellites at unprecedented accuracies over wide areas, and
thereby better characterize the underlying driving processes. Spaceborne sensors now provide
cm-scale deformation observations, over areas 100 km in size, at spatial postings of 10's of m.
These detailed measurements, coupled with inverse modeling, yield a much clearer picture of
movement at depth. Today we will examine several applications of InSAR technology, related to
natural hazards and also to man-made changes. We will first describe some recent measurements of
the flow of magma beneath active volcanoes, which are modeled in some cases as dislocations at
depth and in others as changes in pressure in the magma reservoirs. Another area is subsidence in
urban areas due to overdrafting of aquifers, a particular problem in the Southwest US. Finally, we
look at the viscous fluid motion of salt diapirs in very arid regions, and infer properties of the
salt layers deep beneath the surface.