Computation of Travel Times and Station Correction Surfaces in Eurasia Using Three Dimensional Velocity Models
Abstract
We have investigated the performance of a variety of travel time computation methods for application in highly heterogeneous three-dimensional (3-D) velocity structures, such as those found in Central Eurasia. Recent 3-D models of the crust and upper mantle beneath Central Eurasia contain sharp vertical and horizontal velocity contrasts and thin layers which complicate the accurate computation of travel times. Techniques based on ray-perturbation theory or the graph method do not appear to work well when the velocity anomalies are large relative to the reference model. In these cases the reference ray can be very different from the minimum-time ray, and the methods fail to converge rapidly and in some cases do not converge at all to the global minimum. Ray shooting and finite-difference algorithms are more computationally expensive, but provide accurate results in the presence of large velocity contrasts. In the ray-shooting method, the model is parameterized in terms of smooth polynomials in all directions. Ray-shooting methods are normally implemented only in 2-D, and do not consider propagation paths off the sagittal plane. The finite difference method computes travel times for first-arriving phases for the entire model. Rays are obtained afterward by back-tracing from any point inside the model (receiver) to the source. This method is 3-D and the model is parameterized in terms of constant-velocity cubic cells. The accuracy of the travel times is determined by the cell size. Computer memory effectively limits the minimum cell size for a given region but this constraint can be overcome by computing travel times in 2-D.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2000
- Accession Number
- ADA529897
Entities
People
- A. Villasefior
- A.l. Levshin
- E.r. Engdahl
- M.p. Barmin
- Michael H. Ritzwoller
Organizations
- University of Colorado Boulder