Vertical profile of effective turbidity reconstructed from broadening of incoherent body-wave pulses - II. Application to Kamchatka data

The Vertical profile of effective turbidity under Kamchatka is reconstructe d from observations of distance-dependent broadening of the inchoherent pul se of high-frequency body waves from small earthquakes, by means of a new a pproach and data processing scheme developed in Paper I. The key 'effective turbidity' parameter, g(e), used is an immediate generalization of the com mon isotropic turbidity/scattering coefficient g. Measurements of 200-600 o nset-to-peak delays for P and S waves for five Kamchatka stations are used for interpretation. The estimates based on these data correspond to the 2-4 Hz frequency band. The inversion of data is performed in terms of the para meters of two generic vertical effective turbidity structures: a piecewise- constant profile (PCP) and truncated-inverse-power-law profile (TPLP), both used in several variants. The variants of the inversions give consistent r esults, but also reveal rather limited resolution, not permitting the recov ery of detailed profiles or a comparison of results among individual statio ns. The inversions indicate that the values of effective turbidity decay fr om the surface down: within the depth interval h = 0-50 km, the decay is gr adual; at greater depths it is much steeper, roughly following the inverse cube law. The estimates of average effective mean free path l(e) = 1/g(e) a re very close for P and S waves: 50-60 km (+/- 20 per cent) for the 0-20 km layer; 250-300 km (+/- 30 per cent) for the 20-80 km layer; and at h > 60- 80 km, l(e) approximate to 100(h/40)(-2-4) for both P and S waves. The valu e of both the P- and the S-wave optical thickness (total scattering loss) o f the upper 200 km is about 0.75 (+/- 25 per cent), and the lithospheric-sc attering contribution to t(p)* is estimated as 0.2 s at 1 Hz. The expected S-wave scattering loss agrees reasonably with the standard regional amplitu de attenuation curve, probably reflecting the secondary role of intrinsic l oss at 3 Hz. The S-wave scattering Q in the lithosphere of Kamchatka is est imated for f =1 Hz as 125, 205 and 255 for hypocentral distances of shallow events of 30, 100 and 300 km, respectively.