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

• Published in: Geophysical Journal International
• Main Authors: Gusev, A. A., Abubakirov, I. R.
• Format: Text
• Language: English
• Published: Oxford University Press 1999
• Subjects: Articles; Kamchatka
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/136/2/309; https://doi.org/10.1046/j.1365-246X.1999.00741.x

The vertical profile of effective turbidity under Kamchatka is reconstructed from observations of distance-dependent broadening of the inchoherent pulse of high-frequency body waves from small earthquakes, by means of a new approach and data processing scheme developed in Paper I. The key ‘effective turbidity’ parameter, g e , used is an immediate generalization of the common isotropic turbidity/scattering coefficient g . Measurements of 200–600 onset-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 2–4Hz frequency band. The inversion of data is performed in terms of the parameters 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 results, but also reveal rather limited resolution, not permitting the recovery of detailed profiles or a comparison of results among individual stations. The inversions indicate that the values of effective turbidity decay from the surface down: within the depth interval h = 0–50km, the decay is gradual; 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 are very close for P and S waves: 50–60km (±20 per cent) for the 0–20km layer; 250–300km (±30 per cent) for the 20–80km layer; and at h > 60–80km, l e ≈ 100( h /40)−2–4 for both P and S waves. The value of both the P - and the S -wave optical thickness (total scattering loss) of the upper 200km is about 0.75 (±25 per cent), and the lithospheric-scattering contribution to t*P is estimated as 0.2s at 1Hz. The expected S -wave scattering loss agrees reasonably with the standard regional amplitude attenuation curve, probably reflecting the secondary role of intrinsic loss at 3Hz. The S -wave scattering Q in the lithosphere of Kamchatka is estimated for f = 1 Hz as 125, 205 and 255 for ...