Professor Howard Zebker

Fall 2001-2002

Date: Wednesday, October 24, 2001
Time: 4:15 PM; Refreshments at 4:00 PM
Location: 460-334

Seeing Flow Inside the Earth with Spaceborne Interferometric Synthetic Aperture Radar

Prof. Howard Zebker
Stanford University 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.