Constructing synthetics from deep earth tomographic models
Recent studies of deep mantle structure indicate strong heterogeneity. To conduct high-resolution waveform modelling of these structures, we have developed a new method to construct 2-D synthetics directly from block-style tomographic models. Unlike the WKBJ approximation, which utilizes rays overshooting and undershooting receivers, our method (WKM approximation) uses rays that arrive at the receiver. First, the ray paths from the 1-D layered reference model are used to localize each ray segment, where the anomalous velocities are applied by overlay, as in tomography. Next, new p_i (t_i) (p_i ray parameter, ti traveltime) are computed to satisfy Snell's law along with their numerical derivative (δp/δt), which is used to construct a synthetic seismogram similar to the WKBJ method. As a demonstration of the usefulness of this method, we generated WKM synthetics for the D″ region of high velocities beneath Central America based on Grand's tomography model. Reasonable fits to broad-band data are obtained by condensing his distributed anomalies into his lowermost mantle layer; such a 2-D model predicts synthetics containing a laterally varying S_cd triplication similar to observations.
Additional Information© 2000 RAS. Issue published online: 29 July 2009; article first published online: 29 July 2009; in original form. This project was supported by the National Science Foundation grant number EAR97-2508. We thank the two anonymous reviewers for their comments, which helped to improve this paper.We also thank Mike Gurnis for his helpful suggestions. Contribution number 8631 of the Division of Geological and Planetary Sciences, California Institute of Technology.
Published - j.1365-246x.2000.00982.x.pdf