We undertook the imaging of a section below the San Gabriel Mountains near LARSE line 1 from seismic network recordings of the June 28, 1991 M5.8 Sierra Madre event and its aftershocks in an attempt to reproduce the bright spot seen by Fuis et al. (1996). (Click here for a comparison of results.)
The 18 sections below show a 50 km long by 40 km deep image of crustal structure, with negative reflectivities yellow and positive reflectivities brown. The images show the successive pre-stack Kirchhoff-sum 3-d time migration of records from 18 events, starting with the Sierra Madre mainshock.
Among the usual near-vertical Kirchhoff migration artifacts, the final image clearly shows a strong north-dipping reflective zone at 15-20 km depth below the northern side of the San Gabriel Mountains, extending north below the San Andreas fault into the Mojave Desert.
The animation below, given in three formats, also shows the successive migration imaging of the bright spot as data from each event is added.
Animated GIF,
QuickTime, or
MPEG.