A series of mining explosions, occurring from April 1972 to May 1975, have been analyzed for evidence of travel time variations and hence intrinsic P velocity variations in the Puget Sound region. Since the area is seismically active, it is important to establish observational bounds on velocity changes that might occur due to phenomena such as stress changes or dilatancy effects. From 475 explosions well recorded on 10 stations, relative P wave arrival times are calculated using one station as a reference. After major source migration effects are identified and removed, stations receiving sharp P arrival onsets show stability within 0.2 sec and median values for each month of data show less than 0.1 sec variation. Although time-dependent velocity changes may contribute to the remaining unexplained residual variations, minor source migration, signal variability, and related reading error account for most of them. Detailed source position data are necessary to properly identify the source of time-dependent, residual anomalies from explosion records.