Construction of 3-D Earth Models for Station Specific Path Corrections by Dynamic Ray Tracing

摘要

Three-dimensional models of the crust and mantle structure beneath Area 1 International Monitoring System stations in Eurasia are constructed for use with either asymptotic ray or numerical methods of waveform modeling. The models combine crustal and upper models of varying resolution specified on latitude and longitude grids having variable spacing. Model parameters are interpolated using Delaunay triangulation in 3-D (tetrahedra). Unless accurate narrow-angle crustal reflections and reverberations are required, ray bookkeeping is simplified by making all first-order crustal discontinuities narrow transition zones. Station-specific path corrections (SSPC's) for travel times are obtained in these models by dynamic ray tracing (DRT). DRT provides information on wavefront that can be used to accurately interpolate travel times by a paraxial approximation in the vicinity of end points of rays. By this method travel times are computed in 3-D models at dense grids specified around each IMS station. Each grid point will contain travel time and quantities needed to interpolate travel times spatially at finer intervals. These interpolating quantities can also be useful to event relocation. The grid of values is given as a binary, direct access file. The wavefront curvature information provided for each path includes information needed for path integrated attenuation (t*), geometric spreading, and ray-synthetic seismograms.