The seismograms collected during the passive phase of LARSE are complemented by the acquisition of deep-crustal multichannel seismic-reflection and refraction profiles using onshore and offshore sensors, and airgun and explosion sources (LARSE94, active phase; Brocher et al., 1995; ten Brink, et al., 1996; Okaya et al., 1996ab; Murphy et al., 1996). The reflection and refraction data are especially useful in resolving upper crustal structure in order to better understand and constrain lower crustal and mantle structures.
LARSE93 was a joint effort involving scientists from the University of California at Los Angeles (UCLA), the U.S. Geological Survey (USGS), the California Institute of Technology (Caltech), and the University of Southern California (USC). It took place between November 11, 1993 and December 16, 1993 and involved the installation and maintenance of approximately 88 digital seismometers along a southwest-northeast array in Southern California. The stations were deployed in a 175-km-long, linear array across the Los Angeles basin, San Gabriel Mountains, and Mojave Desert. For this survey, energy sources were local, regional, and teleseismic earthquakes. The seismometers were placed an average of 1 or 2 km apart along the part of the line from Azusa, in the southern foothills of the San Gabriel Mountains, to the northeastern Mojave Desert (Fig. 1; Table 1). Four stations were placed in the Los Angeles basin (two near Seal Beach and two near Whittier); the signals recorded at these stations contain relatively high noise levels. The denser part of the array was located in the San Gabriel Mountains with 1 km spacing; the sparser part, in the Mojave Desert, had 2 km spacing. A few stations were added to the array during the course of the experiment and, except for the first few and last few days of the experiment, most stations recorded data continuously during the four weeks. One station (#331) was located in the San Andreas fault.
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