SIMULATION OF CODA WAVE ENVELOPE IN-DEPTH DEPENDENT SCATTERING AND ABSORPTION STRUCTURE

Coda waves are considered to be composed of scattered waves. For simpl icity, previous models of coda wave generation have often assumed spat ial uniformity of scattering and absorption. To account for possible d epth dependent attenuation, the energy density of coda waves are synth esized using the Monte Carlo simulation method with multiple isotropic scattering assumption. Uniform velocity structure is assumed and impu lsive point source is used. In depth dependent structures given in thi s paper, the synthesized envelopes give coda Q(-1) decreasing with inc reasing lapse time, which has been observationally known well but has not been adequately explained with uniform models. The energy density becomes asymptotically close to a common decay curve irrespective of e picentral distances as the lapse time increases. However, the amount o f the energy density from two sources is different at the same receive r at even the same lapse time for the same radiation energy when the f ocal depths are different. Theoretical basis of the conventional coda normalization method is examined in cases of the strong depth dependen t attenuation structure.