M. Hoshiba, SIMULATION OF CODA WAVE ENVELOPE IN-DEPTH DEPENDENT SCATTERING AND ABSORPTION STRUCTURE, Geophysical research letters, 21(25), 1994, pp. 2853-2856
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.