HR: 0800h
AN: S51A-0977    [Abstracts]
TI: Attenuation Properties of Regional Phases from Peaceful Nuclear Explosions in Northern Eurasia
AU: Li, H
EM: snow@uwyo.edu
AF: University of Wyoming, 1000 University Ave., Laramie, WY 82071 United States
AU: * Morozov, I B
EM: igor.morozov@usask.ca
AF: University of Wyoming, 1000 University Ave., Laramie, WY 82071 United States
AU: * Morozov, I B
EM: igor.morozov@usask.ca
AF: University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N5E2 Canada
AU: Smithson, S B
EM: sbs@uwyo.edu
AF: University of Wyoming, 1000 University Ave., Laramie, WY 82071 United States
AU: Morozova, E A
EM: lena@uwyo.edu
AF: University of Wyoming, 1000 University Ave., Laramie, WY 82071 United States
AB: In this study, we analyze the data from Peaceful Nuclear Explosion (PNE) profiles in Russia for amplitude ratios and coda properties, with an objective to provide a detailed characterization of regional phase propagation in northern Eurasia. Logarithms of Lg/Sn and Lg/Pcoda amplitude ratios at frequencies of 0.5-3 Hz show a consistent decay with the source-receiver distance, with regionally-dependent decay rates. These decay rates appear to correlate best with the variations of two crustal parameters: 1) Moho depth gradient measured away from the source and 2) the travel-time within the sediments (product of the slowness and thickness of the sedimentary cover). The variation of the crustal thickness is the more significant factor affecting Lg propagation and is interpreted as causing defocusing of Lg energy. Moreover, crustal thinning affects Lg propagation stronger than thickening, apparently causing the energy to leak into the mantle or become backscattered). The correlation of the Lg decay rates with the travel times within the sedimentary layers could be explained by seismic attenuation within the sediments. Another striking observation from comparative analysis of the PNEs is the difference of Lg coda decay characters across the study area. Within the East European Platform and south-west West Siberian Basin, Lg coda amplitude decays exhibit a relatively low frequency dependence of about power 0.13 of the frequency. By contrast, within the Siberian Craton, the coda exhibits a nearly constant decay rate for all frequencies, corresponding to the Q vs. frequency exponent of 0.8-1.0. However, such a strong frequency dependence of Q could actually be due to frequency-independent attenuation caused by geometric spreading and leakage of the seismic energy from the crust. Using this model, the geometric spreading parameter was found to be constant for the entire region, and crustal quality Q=470 west of the Urals and an infinite Q within the Sibarian Craton. Such low attenuation within the Siberian Craton is also supported by the observed Pg propagating to the distances of 1600-1700 km in this area.
DE: 7203 Body waves
DE: 7205 Continental crust (1219)
DE: 8103 Continental cratons
SC: Seismology [S]
MN: Fall Meeting 2005