HR: 0830h
AN: S11E-0343    [PDF]
TI: Lg Phase Propagation Characteristics in Northern Eurasia from Peaceful Nuclear Explosion Data
AU: * Li, H
EM: snow@uwyo.edu
AF: Hongyan Li, Department of Geology & Geophysics, University of Wyoming, P.O.Box 3006, Laramie, WY 82071-3006 United States
AU: Morozov, I
EM: igor.morozov@usask.ca
AF: Igor Morozov, Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N5E2 Canada
AU: Smithson, S
EM: sbs@uwyo.edu
AF: Hongyan Li, Department of Geology & Geophysics, University of Wyoming, P.O.Box 3006, Laramie, WY 82071-3006 United States
AU: Solodilov, L
EM: nadjatim@dol.ru
AF: Leonid Solodilov, Centre for Regional Geophysical and Geoecological Research (GEON), Moscow, 119034 Russian Federation
AB: Regional phases (Pn, Pg, Sn and Lg) play a significant role in monitoring small events for Comprehensive Test-Ban Treaty (CTBT). In all the regional phases, the Lg phase is usually the strongest, which is usually used to identify nuclear explosions from earthquakes. However, the Lg is weak or disappears in some tectonic areas. Therefore, studying propagation characteristics of the Lg phase and the factors affecting Lg phase propagation is necessary for the use of the Lg in nuclear monitoring. In order to quantitatively describe the variations in crustal attenuation across Northern Eurasia, we measure amplitude ratios and the Lg coda Q values from 21 Peaceful Nuclear Explosions (PNEs) recorded along six linear, long-range three-component profiles. These historic data provide unique opportunities to study the regional phase propagation characteristics in Northern Eurasia. Lg/Sn and Lg/Pgcoda amplitude ratios are significant parameters to constrain the variations of crustal structures. These ratios are higher ($>1$) within the Siberian Craton and decrease at tectonic boundaries and thick sedimentary basins. In agreement with the previous studies, Lg(1-2Hz)/Lg(6-8Hz) ratios are about 10 times higher for the PNEs than for earthquakes. Frequency-domain Lg coda Q measurements show large scatter due to the noise and limited frequency band; however, the Lg coda Q computed from the time domain method shows that the variations of the crustal structure are the most important factors to affect the Lg coda attenuation. It appears that thick sediments can block the Lg phase propagation. From the seven PNE profiles, we map the Lg coda Q distribution in Northern Eurasia and demonstrate the frequency dependence of the Lg coda Q.
DE: 5144 Wave attenuation
DE: 7205 Continental crust (1242)
DE: 7219 Nuclear explosion seismology
SC: Seismology [S]
MN: 2003 Fall Meeting