Abstract
Abstract. 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-equation-based 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-equation-based 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.
Highlights
1 Introduction In Tong et al (2014b), we introduced a new tomographic method, the so called waveequation-based travel-time seismic tomography (WETST) which is a “2-D–3-D” adjoint tomography technique based upon a high-order finite-difference solver
Comparing with the “3-D–3-D” wave-equation travel-time inversion (Luo and Schuster, 1992) or the “3D–3-D” adjoint tomography based on spectral-element numerical solvers (e.g., Tromp et al, 2005; Fichtner et al, 2006; Tape et al, 2009), the theoretical disadvantage of this “2-D–3-D” tomographic method is that it ignores the influence of the off-plane structures on seismic arrivals
This indicates the necessity of solving full wave equations in complex structure imaging
Summary
In Tong et al (2014b) (hereinafter referred to as paper I), we introduced a new tomographic method, the so called waveequation-based travel-time seismic tomography (WETST) which is a “2-D–3-D” adjoint tomography technique based upon a high-order finite-difference solver. Tian et al (2007a) simultaneously determined P and S wave velocity and Poisson’s ratio models for the Landers earthquake area They showed a correlation between the seismic activity and crustal heterogeneities and suggested that the existence of crustal fluids may have weakened the fault zone and triggered the Landers earthquake. Taking these previous tomographic results as references, we test the performance of WETST in imaging crustal structures of the Landers earthquake source area. The tomographic images inverted by WETST may help shed some new lights on local heterogeneous structures and the nucleation of large crustal earthquakes
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