GEODETIC MEASUREMENT OF DEFORMATION IN THE VENTURA-BASIN-REGION, SOUTHERN CALIFORNIA

We have measured the deformation in the Ventura basin region, southern California, with Global Positioning System (GPS) measurements carried out over 4.6 years between 1987 and 1992. The deformation within our network is spatially variable on scales of tens of kilometers, with st rain rates reaching 0.6 +/- 1 murad/yr in the east-central basin. Bloc klike rotations are observed south and northwest of the basin where th e maximum shear strain rates are an order of magnitude lower (0.06 +/- 1 murad/yr to the south). We also observed clockwise rotations of 1-d egrees-7-degrees/m.y. Shear strain rates determined by comparing angle changes from historical triangulation spanning several decades and GP S measurements give consistent, though less precise, results. The geod etic rates of shortening across the basin and Western Transverse Range s are lower than those estimated from geological observations, but the patterns of deformation from the two methods agree qualitatively.