Broad Band Trajectory Mechanics

Date: 4/25/2019

Time: 02:45 PM

Room: Elliott Bay

We present a trajectory-based solution to the elasto-dynamic equations of motion that is valid across a wide range of seismic frequencies. That is, the derivation of the solution does not invoke a high frequency assumption or require that the medium have smoothly-varying properties. The approach, adopted from techniques used in quantum dynamics, produces a set of coupled ordinary differential equations for the trajectory, the slowness vector, and the elastic wave amplitude along the ray path. In the limit of large frequencies, the coupling term approaches zero and the trajectories converge to high-frequency raypaths. Synthetic tests with interfaces and layers containing increasingly narrow transition zones indicates that the conventional high-frequency trajectories bend too sharply into high velocity regions as the wavelength exceeds the transition zone width. Test models based upon velocity structures from the Geysers and an exploration geophysics salt model indicate that discrepancies between the high-frequency and broad band trajectories can exceed several hundred meters to several kilometers at wavelengths of 1 Hz.

Presenting Author: Donald W. Vasco

Authors