Seismic calibration of northern Eurasia using regional phases from nuclear explosions and three-dimensional Moho configuration of accreted terranes in western British Columbia

The Lg phase is usually the strongest among the regional phases (Pn, Pg, Sn, and Lg), and is widely used for nuclear test monitoring. However, the Lg phase is strongly affected by variations of crustal structure. This study examines the effects of regional tectonic structure on Lg propagation using Peaceful Nuclear Explosion (PNE) profiles in Russia. Firstly, Lg/Sn and Lg/Pcoda amplitude ratios at 0.5-3 Hz are measured and correlated with the regional crustal structure. Both ratios are found to decrease within the areas with thick sedimentary cover and across tectonic boundaries with abrupt variations of crustal thickness. Secondly, frequency-independent Lg Q is determined by a two-station spectral ratio method for different tectonic areas. The slope of the logarithms of both Lg/Sn and Lg/Pcoda amplitude ratios and Lg 1/Q are correlated with the thickness of the sedimentary cover divided by shear velocity and the Moho slope.; Yield-mb linear relationship is commonly used to estimate source yield. The relationship is affected by the source conditions including source medium and source depth. From the available information of the PNEs in northern Eurasia, I determined the yield-mb relationship for clay, salt, sandstone/shale, and limestone/dolomite with shot depth <2485 m, and then a general linear relationship is determined for all the "hard" rocks except clay.; P/Lg spectral ratio at frequencies above the P corner frequency (fc) is determined as a promising parameter for nuclear discrimination. I determined fc for both P- and S-phases through Pn- and Sn-spectra after Q compensation, and then a linear relationship between m b and fc for both P and S phases is determined respectively. With the known mb, fc can be estimated through the equation. The fc-mb relationship also provides better constraint on mb by determining fc from regional phases.; The accreted terranes and the continental arc in southeastern Alaska and western British Columbia represent one of the best areas to study the processes for continental crustal growth. In particular, studies of the structures and formation of the Coast Shear Zone (CSZ) and the Coast Mountains Batholith (CMB) by the multidisciplinary ACCRETE project in 1994 yielded important information for understanding these processes. The observed 3-D variations of the crustal structure in this study are in agreement with those derived along the Portland Canal fjord, and particularly show a ∼15-km long Moho ramp (from ∼24-26 km depth to the west and ∼31 km to the east of the CSZ), which extends along the strike of the CSZ. This extends the earlier interpretation and shows that ramp is indeed likely associated with transpressional tectonics and magmatic crustal addition east of the CSZ.