SURFACE DEFORMATION ASSOCIATED WITH GROUND WATER PUMPING AND CONJUNCTIVE USE PROGRAMS IN THE SANTA ANA BASIN, SOUTHERN CALIFORNIA

Surface deformation mapping of the Santa Ana Basin, southeast of Los Angeles, California, between 1993 and 2000, using Satellite Interferometric Synthetic Aperture Radar (InSAR) and continuous Global Position System (GPS), indicates that >110 mm of seasonal uplift and subsidence and ~20 mm of annual subsidence occurred in the basin during this period. This deformation pattern began in 1995-96 corresponding to a widespread increase in ground-water pumping throughout the basin; this pattern has continued into 2002. The seasonal and annual deformation patterns are attributed to changes in the ground-water pumping and conjunctive-use programs. This basin-wide deformation is spread over a 20- by 40-km region and correlates with seasonal changes in ground-water levels that are as much as 30 m and annual water-level declines of about 1.5 m. The seasonal and annual deformation patterns show a steep deformation gradient across the Newport-Inglewood fault with as much as 60 mm of seasonal motion and 10 mm of annual subsidence concentrated in a narrow zone along the fault. Mapping the spatial and temporal deformation patterns in ground water basins will provide valuable information for resource managers who strive to mitigate subsidence by altering the magnitude, distribution, and timing of ground-water pumping.