Abstract

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/Pcodapne-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.

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