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

Abstract

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.