Abstract: An Overview of Southern California Crustal Deformation Studies and Their Tectonic Interpretation

Kenneth W. Hudnut

Geodetic studies, particularly the high-accuracy results obtained from Global Positioning System (GPS) data, have helped to define the active tectonics of the western Transverse Ranges. Recent results of the Transverse Ranges Experiments (TREX) and related work have documented revisions to earlier published reports on crustal deformation in the region. A review of the earliest to the most recent geodetic results will be followed by a summary of the currently documented rates and styles of deformation. Also, the latest findings from work in the Los Angeles region, a focus of intensive recent GPS studies, will be discussed. A challenging aspect of geodetic work is to convert the displacement vectors obtained into, for example, slip rates that are useful as inputs to tectonic or seismic azard models. Because the faults under study are generally locked to depths of 10 to 20 km, modeling is required to interpret the observed displacement field. The related problems and limitations inherent in obtaining equivalent fault slip rates from a displacement field map will be discussed, and a range of plausible models investigated for the Los Angeles region. Without accurate information on the geometry of faulting at depths >10 km, where interseismic slip occurs, many fault slip models are tenable. Because of this, the interpretation of geodetic data in terms of slip rates on active faults will continue to rely in turn on interpretations of deep structures that are based on seismic images, borehole, and surface geological data. It is hoped that resolution of controversies over he nature of deep structure in the western Transverse Ranges will coincide with the development of a more complete geodetic picture of ongoing deformation, and that cooperative work can then lead to a greatly improved seismic hazard model for the region. In the meantime, geodetic information can provide among the strongest constraints on expected moment rate, for computing seismic hazard in areas of "blind" or widely distributed faulting.

AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994