## 2aUW13. An elastic wave diffusion theory for ocean crustal phase coda development.

### Session: Tuesday Morning, December 3

### Time: 11:14

**Author: Robert I. Odom**

**Location: Appl. Phys. Lab., Univ. of Washington, 1013 NE 40th St., Seattle, WA 98105**

**Author: Valerie I. Peyton**

**Location: Appl. Phys. Lab., Univ. of Washington, 1013 NE 40th St., Seattle, WA 98105**

**Author: James A. Mercer**

**Location: Appl. Phys. Lab., Univ. of Washington, 1013 NE 40th St., Seattle, WA 98105**

**Abstract:**

The seismic signals designated P[inf o] and S[inf o] are oceanic crustal
phases that can be recorded by hydrophones and ocean bottom seismometers. They
are characterized by long high-frequency codas and by their efficiency of
propagation. Many features of their propagation can be accounted for by
considering water-sediment reverberation and fine random layering on the oceanic
lithosphere. However, it appears that some range-dependent mechanism, perhaps
forward scattering from rough surfaces, is necessary to completely describe the
observed signals. An energy diffusion theory based on the coupled mode
representation for the solution of the wave equation is described. The theory
treats the diffusion of energy in spectral space in the strongly forward
scattering limit, and may provide a realistic physical model for the development
of the long P[inf o]/S[inf o] coda. The energy diffusivity is derived directly
from the continuum limit of the mode coupling matrix; it is proportional to the
spatial autospectrum of the coupling matrix. The applicability of the theory
requires that the mean free path for multiple scattering must be large compared
to the size of the medium fluctuations, and the spatial scale of the
heterogeneities must be large compared to the wavelength. [Work supported by
ONR.]

ASA 132nd meeting - Hawaii, December 1996