Virgilio Perez; Velocity response envelope spectrum as a function of time, for the Pacoima Dam, San Fernando earthquake, February 9, 1971. Bulletin of the Seismological Society of America ; 63 (1): 299–313. doi:
The spectrum of the velocity response envelope as a function of time for 5 per cent and 2 per cent critical damping has been calculated for the horizontal and vertical components of the Pacoima Dam accelerogram of February 9, 1971. The duration in terms of time and the number of cycles for a particular period of the response envelope above different levels are examined. The effects of critical damping and of peak ground acceleration on the velocity response envelope are also examined.