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A study of regional phases from earthquakes and explosions in Western Russia

TELEDYNE GEOTECH, 314 MONTGOMERY STREET, ALEXANDRIA, VIRGINIA 22314

Abstract

The propagation of seismic phases P_n, P_g, S_n, and L_g from earthquake and explosion sources, as recorded at regional distances, is studied by using short-period records from the WWSSN stations. The time-distance plots from explosions, shallow earthquakes, and intermediate depth-of-focus earthquakes show that the depth or nature of the seismic source has no significant effect on the velocity of propagation of any of the regional phases. The phases P_n, S_n, and L_g travel with velocities about the same as in the Eastern United States but P_g has a velocity considerably lower than that reported for the Western or the Eastern United States. Propagation paths of L_g and S_n from earthquakes in Western Russia, as recorded on the three-component, short-period records from Kabul (KBL) and Meshed (MSH), have been mapped. Paths within the region approximately bounded by azimuths N30°W to N60°E of KBL and northeast to east of MSH have been found to be consistently efficient for L_g and mostly efficient for S_n. This efficiency of propagation appears to be due to relatively thick crust and a relatively flat moho rather than the absence of large topographic features or geological faults. Data from the short-period vertical component records indicate that for transmission paths lying within the region of efficient propagation of L_g, the maximum L_g amplitude is generally large than the maximum P-wave amplitude for earthquakes but generally smaller than that for explosions. This difference in the level of L_g excitation appears to be a useful discriminant for events in Western Russia.

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