Geoacoustic propagation through random seafloor models

Abstract

Finite difference forward models of elastic wave propagation through laterally heterogeneous upper oceanic crust are presented. The finite difference formulation is a two‐dimensional solution to the elastic wave equation for heterogeneous media and implicitly calculates P and SV propagation, compressional to shear conversion, interference effects, and interface phenomena. Random velocity perturbations with Gaussian and self‐similar autocorrelation functions and different correlation lengths are presented that show different characteristics of secondary scattering. The presence of a water‐solid interface in the models allows for the existence of secondary Stoneley waves, which account for much of the seafloor noise seen in the synthetic seismograms for the laterally heterogeneous models. “Random” incoherent secondary scattering increases as the product of wavenumber and correlation distance (ka) approaches 1. Deterministic secondary scattering from larger heterogeneities is the dominant effect in the models as ka increases above 1. Secondary scattering also shows up as incoherence in the primary traces of the seismograms when compared to the laterally homogeneous case. Cross‐correlation analysis of thc initial P‐diving wave arrival shows that, in general, the correlation between traces decreases as ka approaches 1.