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Correlation of Lg Amplitude Ratios from Peaceful Nuclear Explosions to Crustal Structure in Northern Eurasia

¹ Department of Geology and Geophysics
University of Wyoming
Laramie, Wyoming 82071-3006
snow{at}uwyo.edu
lhysnow{at}yahoo.com
sbs{at}uwyo.edu
 (H.L., I.B.M., S.B.S.)

² University of Saskatchewan
114 Science Place
Saskatoon, Saskatchewan S7N5E2, Canada
igor.morozov{at}usask.ca
 (I.B.M.)

^* Present address: 10053 Westpark Drive, #296, Houston, Texas 77042, lhysnow{at}yahoo.com.

Because the Lg phase is strongly affected by the variations of crustal structure in some areas, understanding these factors is important for nuclear test monitoring. This study examines the effects of regional tectonic structure on Lg propagation by using the Peaceful Nuclear Explosion (PNE) profiles in Russia. The logarithms of Lg/Sn and Lg/Pcoda PNE-amplitude ratios within the 0.5- to 3-Hz frequency band are measured and correlated with the regional crustal structures. Both ratios are found to decrease within the areas with thick, low-velocity sedimentary cover and across tectonic boundaries with abrupt variations of crustal thickness. For the offset derivatives of both the logarithmic ratios, a linear relationship to the slopes of the Moho and the vertical travel times within the sedimentary cover is determined. A strong negative slope is observed along both crustal thinning and crustal thickening segments, and a positive slope follows the negative slope across a crustal thickening segment. Therefore, crustal thinning appears to affect the Lg propagation stronger than crustal thickening, which could be due to focusing Lg energy within the crustal wave guide. The log-amplitude regression provided in this article could be useful for predicting Lg behavior in areas where amplitude measurements are not available.