P-Wave Train Synthetic Seismograms Calculated by Quantized Ray Theory

• Published in: Geophysical Journal International
• Main Author: McMechan, George A.
• Format: Text
• Language: English
• Published: Oxford University Press 1974
• Subjects: Articles; Arctic
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/37/3/407; https://doi.org/10.1111/j.1365-246X.1974.tb04093.x

The quantized ray theory formulation is used to construct synthetic body wave seismograms from a ray parameter-distance curve. The synthetic seismograms calculated by this new technique compare favourably with the exact Cagniard-de Hoop solutions, but require far less time to produce. The ease and rapidity with which the calculations can be done allow the routine use of synthetic seismograms in body wave inversions. Inclusion of amplitude constraints greatly reduces the range of valid Earth models. As an example, a P -wave velocity-depth model is found for the upper mantle beneath the Canadian Arctic. The model is constrained by ray parameter and travel time data as well as the observed amplitude behaviour in the first 10-15 s of real vertical component seismograms recorded between 10 and 40 degrees. As each arrival observed on each record provides a number of constraints for the ray parameter curve, a relatively few wave trains provide a great amount of information on the velocity structure. Even when individual arrivals cannot be separated on a record, because of interference with each other, synthetic seismograms can be used. The interference pattern itself can be reproduced, and by tracing back through the calculations, one can define the number, amplitudes and travel times of the interfering arrivals.