9628974 Zumberge This grant provides $53,209 as partial support of investigator salaries and the costs of computing equipment to be used in an absolute gravity resurvey of sites in California together with testing of a new fringe-signal processing technique. Specifically, surveys and instrument calibrations will be made at 7 sites using a new Micro-g solutions Model FG5 absolute gravity meter together with an older IGPP-AGM-1 instrument which was used at these sites six years ago. The newer instrument provides approximately five times greater sensitivity in the measurement of local acceleration of gravity. The comparison between measurements using both instruments is important for calibration of the newer instrument in order to monitor secular changes in vertical tectonic displacements at these sites. Without such a calibration study, the older measurements would be lost as a baseline with the retirement of the IGPP- AGM-1. Resurvey of these sites is timely as sufficient time has passed so that the centimeter scale vertical resolution possible with absolute gravimetry will allow significant determination of rates of vertical crustal deformation in this tectonically active region of the world. Of particular interest, these measurements, when made in conjunction with GPS or satellite laser ranging (SLR) as independent measures of vertical displacement, should yield insight into the mechanisms responsible for deformation. Historical SLR measurements exist for two of the proposed resurvey sites, namely, Quincy and Monument Peak. ***
