Energy partition and attenuation of Lg waves by numerical simulations using screen propagators

Energy partition and attenuation of Lg waves in complex crustal waveguides with both large-scale structures and small-scale random heterogeneities are studied by numerical simulations. A newly developed screen propagator meth od (half-space generalized screen propagators) is tested and applied to thi s problem. The screen method is two to three orders of magnitude faster tha n finite difference (FD) method and uses much less internal memory. The met hod has no numerical dispersion and can easily incorporate various Q models into the codes. After analyzing different attenuation mechanisms, this pap er is concentrated in simulating the leakage attenuation of Lg waves caused by forward large-angle scattering from random heterogeneities, which scatt ers the guided waves out of the trapped modes and leaking into the mantle. In addition to energy attenuation curves, variations of angular spectra of Lg waves along the path are also shown to give insight on the energy partit ion and scattering effects. The curve of equivalent Q for leakage attenuati on as a function of normalized scale length (ka) of the random heterogeneit ies agrees well with the scattering theory. The comparisons of the method w ith wavenumber integration and FD method, and the results of the numerical simulations demonstrate the validity and capacity of the screen propagator method in studying Lg attenuation. (C) 2000 Elsevier Science B.V. All right s reserved.