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Two-Dimensional Crustal and Upper-Mantle Velocity Models from Profile 'Quartz', Russia,

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We develop two-dimensional 2-D P-wave velocity models for the crust and for the upper mantle along the ultra-long Deep Seismic Sounding profile DSS Quartz. Two-dimensional effects play a principal role in Lg propagation and are directly related to the problem of quantitative modeling of Lg and its use as a seismic discriminant. The use of DSS profiles provides us with unique opportunities to study large-scale propagation effects of various seismic phases, and especially Lg, across geological and tectonic boundaries. The results of this study have a direct relevance to the calibration of seismic discriminants. To develop our 2-D crustal model, we use the data obtained using 28 chemical explosions along the north-western half of the profile. It is the first attempt of using these data after they have been digitized and obtained in the West. Applying a travel-time tomographic inversion method, we develop a velocity model and estimates of its resolution. Two important resolved features of the model are 1 high velocity block at the base of the crust under the Baltic Shield, 2 crustal roots under the Ural Mountains. Using the data from 2 nuclear explosions in the same part of the profile we develop a preliminary 2-D upper mantle P-wave velocity model. The model supports the conclusion of the roots under the Urals, and suggests a south-east dipping low-velocity zone in the upper mantle. The latter, however, is to be supported by the analysis of the data from the third nuclear shot, which is now in the processing stage. As a result of this work, we will obtain a comprehensive 2-D model of the crust and of the uppermost mantle, will obtain better estimates of obtained resolution of geological features. This knowledge would provide better means of calibration of the amplitudes of Lg and other phases for their use in CTBT applications.

Subject Categories:

  • Government and Political Science
  • Geology, Geochemistry and Mineralogy
  • Seismology
  • Seismic Detection and Detectors
  • Nuclear Weapons

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