ANALYSIS OF SHORT-PERIOD REGIONAL PHASE PATH EFFECTS ASSOCIATED WITH TOPOGRAPHY IN EURASIA

Propagation of regional seismic phases is highly dependent on path eff ects, but we have a limited understanding of these effects and no gene ral procedure for accounting for path variation influence on regional waveforms. Thus, there is strong regional variability in the effective ness of regional wave discriminants used to identify small earthquakes and nuclear explosions. Motivated by many observations of correlation between surface geology and regional phase behavior, we empirically e xplore the relationship between short-period regional and upper mantle distance signal energy and statistics of topography along different t ravel paths using data for underground nuclear explosions at Semipalat insk, Kazakhstan. We find strong linear correlations of the logarithmi c rms amplitude ratio S(n)/L(g) (and to a lesser extent, P/L(g)) with mean altitude, rms roughness, rms slope, and skewness of topography al ong the paths to receivers in Eurasia. This indicates that energy part itioning in the regional wave field is controlled by wave-guide struct ure and attenuation variations that are manifested in surface topograp hy. This suggests that it is feasible in many cases to directly calibr ate regional discriminants for path effects in terms of observable sur face topography, as a surrogate for overall path properties. The relat ionships also help to understand the nature of regional phase propagat ion.