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Chapter 5. Solid-Earth Sciences

Studies of Crustal Deformation

Investigations of crustal deformation on local and regional scales have been continued as an important part of the tectonophysics program, much of which is directly linked to understanding earthquake source processes and crustal movements associated with volcanoes. Starting with the pioneering work of Harrison, mentioned above, this effort has employed point measurements using strain and tilt meters, creep meters, gravity measurements, electronic distance measuring (EDM) devices in fault zones, and now, Synthetic Aperture Radar (SAR) and Global Positioning System (GPS) surveys. The EDM work, concentrated on the San Andreas fault, was the primary contribution of Larry Slater, a former CIRES fellow. William Farrell studied in detail the influence of ocean loading variations on crustal deformation observations, thus contributing to the interpretation of measurements of changes in surface elevation and ground tilt. John Wahr, CIRES fellow and professor of physics, contributed to theory and modeling of post-seismic deformation as one part of his analysis of surface elevation variations, described below.

In 1986, Roger Bilham and Randolph Ware created the nucleus of UNAVCO, a consortium of universities (now more than 100) applying GPS methods to the study of global tectonics. As of 2001, CIRES owned 22 GPS receivers that are operating in permanent or mobile arrays in the Himalayas, Tibet, China, Venezuela, Mexico, and Ethiopia. This work enhances understanding of regional or continental scale deformations, as well as local changes related to earthquake generation. Bilham and Kristine Larson lead this GPS work. Numerical modeling has been an important tool in the interpretation of the field data.

A recent innovative application of strain measurements is the monitoring of strains in the soft soil under Mexico City associated with strong motions following large subduction-zone earthquakes along Mexico's southern coast.

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