Interpretation of high-frequency coda at large distances: stochastic modelling and method of inversion

Based on previous work, a stochastic convolution model is proposed for the Lg coda observed at large epicentral distances (Δ > 200 km). Coda at these distances differ from local coda in several respects. Effects of various physical processes, such as dispersion, scattering, and mode conversion on coda at large distances are discussed in detail. A spectral ratio method is developed for inversion of Lg coda Q, in which the large variance associated with inversion is greatly reduced. The method is also extended to the inversion of seismic source parameters by jointly using Lg and its coda. We have tested the model and method exhaustively using data from two GDSN stations and found the results to be superior to other methods when those methods used only a small number of stations.