HR: 1340h
AN: S53B-1276    [Abstracts]
TI: Frequency Dependence of Regional Coda Q: Numerical Modeling and a PNE Example
AU: Zhang, C
EM: chaoying.zhang@usask.ca
AF: University of Saskatchewan, 114 Science Pl., Saskatoon, SK S7N5E2, Canada
AU: * Morozov, I
EM: igor.morozov@usask.ca
AF: University of Saskatchewan, 114 Science Pl., Saskatoon, SK S7N5E2, Canada
AU: Duenow, J
EM: jduenow@mines.edu
AF: Colorado School of Mines, 1500 Illinois St., Golden, CO 80401, United States
AU: Morozova, E
EM: lena@uwyo.edu
AF: University of Wyoming, 1001 University Ave., Laramie, WY 82070, United States
AU: Smithson, S
EM: sbs@uwyo.edu
AF: University of Wyoming, 1001 University Ave., Laramie, WY 82070, United States
AB: Mapping of coda properties requires the use of parameterization reflecting the fundamental physics and stable in respect to unconstrained factors. We use numerical modeling of nuclear-explosion coda at regional distances to compare two types of such parameterizations, namely the frequency-dependent coda attenuation (Q_1Hz,η) and frequency-independent attenuation with geometric spreading, (γ, Q_coda). The modeling shows that for a constant intrinsic Q of the crust, the resulting coda Q exhibits strong and positive frequency dependence η ~ 1. This spurious frequency dependence is not related to model rheology but is caused by disregard of geometrical propagation effects, such as bending of scattered ray paths. By contrast, in the geometric-spreading approach, coda amplitude inversion using the synthetic records results in spreading parameters, γ = (0.8-1.6) 10^-2 s^-1, and frequency-independent Q_coda uniquely related to the crustal S-wave Q. Peaceful Nuclear Explosion (PNE) data from two different areas in Russia were found to have similar values of γ = 0.75 10^-2 s^-1, which are remarkably close to numerical results, and strongly different Q_coda values of 850 (in the East European Platform) and 2500 (the Siberian Craton). Combined with literature results, this suggests that tectonically active zones in both North America and Northern Eurasia could differ from stable areas by their high values of γ, and not so much by η. Modeling also shows that γ could increase in areas where high-attenuation or scattering layers are present within the crust. We therefore suggest that parameters γ and Q_coda could provide high quality, stable, and transportable discriminants for differentiating between crustal tectonic types and for seismic regionalization used in nuclear-test monitoring.
DE: 7205 Continental crust (1219)
DE: 7218 Lithosphere (1236)
DE: 7219 Seismic monitoring and test-ban treaty verification
DE: 7290 Computational seismology
SC: Seismology [S]
MN: 2007 Fall Meeting