Wave - equation - based travel - time seismic tomography – Part 2 : Application to the 1992 Landers earthquake ( M w 7 . 3 ) area

High-resolution 3-D P and S wave crustal velocity and Poisson’s ratio models of the 1992 Landers earthquake (Mw 7.3) area are determined iteratively by a wave-equationbased travel-time seismic tomography (WETST) technique. The details of data selection, synthetic arrival-time determination, and trade-off analysis of damping and smoothing parameters are presented to show the performance of this new tomographic inversion method. A total of 78 523 P wave and 46 999 S wave high-quality arrival-time data from 2041 local earthquakes recorded by 275 stations during the period of 1992–2013 are used to obtain the final tomographic models, which cost around 10 000 CPU hours. Checkerboard resolution tests are conducted to verify the reliability of inversion results for the chosen seismic data and the wave-equationbased travel-time seismic tomography method. Significant structural heterogeneities are revealed in the crust of the 1992 Landers earthquake area which may be closely related to the local seismic activities. Strong variations of velocity and Poisson’s ratio exist in the source regions of the Landers and three other nearby strong earthquakes. Most seismicity occurs in areas with high-velocity and low Poisson’s ratio, which may be associated with the seismogenic layer. Pronounced low-velocity anomalies revealed in the lower crust along the Elsinore, the San Jacinto, and the San Andreas faults may reflect the existence of fluids in the lower crust. The recovery of these strong heterogeneous structures is facilitated by the use of full wave equation solvers and WETST and verifies their ability in generating high-resolution tomographic models.