SURFACE MOTION DETECTION FROM A SMALL APERTURE GEODETIC NETWORK, SOUTHERN LOS ANGELES BASIN

Over the past 4 years, numerous students at Orange Coast College in Costa Mesa, CA have been engaged in measuring crustal motions through a geodetic network at numerous ground stations throughout the southern Los Angeles basin, including Orange, and portions of Los Angles, San Diego, Riverside, and San Bernardino counties of California. To reduce the potential error, the network is of small aperture (<20 km). The purpose of this invesitgation has been to search for and monitor the spatial and temporal nature of displacement across active and potentially active faults. Thus, we document pre-, co- and post-seismic displacement and aseismic creep, if any, especially where geologic evidence indicates current or recent activity of the faults in question. Data from this network serve to clarify how strain accumulated by crustal movement is distribute across this region. Preliminary results from these data indicate deformation in several areas. Surface motions have been detected astride several fault zones including the Newport-Inglewood, El Modena, Norwalk, Whittier, Elsinore, and Chino Hills faults, and potential blind-thrust faults in the Puente/Peralta Hills. Based on these data, there appears to be a discrepancy between the geodetic and inferred geologic rates of slip along the Whittier-Elsinore-Chino Hills fault system. Also, stations across a potential restraining bend along the south branch of the Newport-Inglewood fault zone appear to be converging at a high rate. Assuming that surface motions accruately depict subsurface conditions, this may possibly indicate that strain is accumulating at depth in these locations.