These traveltimes are saved in simple binary float files with known byte order, which is the same for every station. Due to seismic reciprocity, this is equivalent to computing a traveltime from an event at each grid node in the volume to the receiver. spherical coordinates allow use on local, regional, or global scalesĪfter parameterizing a velocity model (or more than one) on a regular structured grid, traveltimes are computed for each station by placing a source at the station location.includes topography for accurate station elevations and topographic effects on the wavefield.can include known (or assumed) interfaces such as the moho.is stable even for extremely heterogeneous media.computes traveltimes at every grid point in a single simulation.In principle, any traveltime solver can be used for this step, but the FMM has the following advantages: The FMM solves the eikonal traveltime equation using finite differences on a regular grid in spherical coordinates cut by interfaces (e.g., topography, moho).
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Traveltimes are computed using the Fast Marching Method (FMM) software written by N. Regular-grid binary files also facilitate the grid search in step 2. Computation of sub-grid location using least squares and location derivatives calculated by trilinear interpolationīecause nearly all of the significant computation occurs in step 1, steps 2 and 3 can occur in real time.A 2-stage grid search to locate the grid node with the lowest residual arrival time.This occurs only once for each station unless the velocity model is updated.