Report for passive data acquired in the 1998-1999 Los Angeles Region Seismic Experiment II: a transect from Santa Monica Bay to the Westernmost Mojave Desert

Abstract

Between October, 1998 and April, 1999, 83 seismic stations were installed in the greater western Los Angeles, California area to record teleseismic, regional, and local earthquakes. The near-linear 93-km long array extended between Santa Monica Bay and the western Mojave Desert, through the epicentral region of the Northridge earthquake. The goals of the experiment were to determine crustal thickness below the western Transverse Ranges, San Fernando Valley basin, and western Mojave Desert, measure anistropy along the line with special emphasis on the San Andreas fault region, evaluate the potential for future strong ground shaking at sites in the basins, and determine the kinematic relationship between crustal and uppermost mantle deformation by three-dimensional tomographic inversion using regional network data combined with the array data. The stations consisted of three-component, broadband and short-period seismometers, and timing was controlled by Global Positioning System (GPS) receivers. The array recorded 165 Gb of raw waveform data in continuous (25 sps) and triggered (50 sps) streams. Approximately 144 teleseismic earthquakes with magnitudes ≥ 5.5, and 2025 local earthquakes with magnitude ≥ 2.0 were recorded. Preliminary results from three-dimensional teleseismic traveltime inversion tomography indicate that uppermost mantle seismic anomalies strongly correlate with thickened crust in the Transverse Ranges suggesting that the width of the compressional region and convergence rate control the location of deformation more than the San Andreas shear zone does.

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