PRELIMINARY RESULTS OF CRUSTAL STRUCTURE FROM THE LARSE-II PASSIVE RECORDING EXPERIMENT USING TELESEISMIC P-TO-S CONVERTED WAVES

The 1998-1999 Los Angeles Region Seismic Experiment (LARSE-II) contained a passive recording phase in which 83 three-component broadband and short-period instruments were deployed along a 100 km long profile. The profile started near the coast in Malibu and traversed the Santa Monica Mts., the San Fernando and the Santa Clarita Valleys, the Western San Gabriel Mts., the San Andreas Fault (SAF), and ended in the Antelope Valley of the Mojave Desert. In this study, we use teleseismic P-to-S converted waves to image subsurface sedimentary basins and deep crustal structures. We generated a 2-D crustal structure image along the profile by stacking and migrating the radial receiver functions using the Common Conversion Point (CCP) stacking technique. The San Fernando Basin and the Santa Clarita Basin are well imaged with the basin bottoming at 6 to 8 km depth. In addition, a low-velocity patch exists near the surface under the Antelope Valley which might be an old sedimentary basin or low-velocity rocks. The Moho is seen clearly as a continuous flat feature at a depth of 32 km under the Mojave Desert. It is terminated near the downward extension of the SAF. In contrast, the Moho in the western side of SAF is quite different from the one under the Mojave Block in terms of sharpness and continuity. We also compared the Bouguer gravity anomaly and teleseismic arrival time delays along the profile with the predictions from the inferred crustal model. The preliminary modeling shows that most of the anomalies can be explained by the model.