﻿I would be interested to find some information or discussion about the use of seismic coefficient in the pseudo static stability analysis of dam and embankment. Given that a horizontal peak ground acceleration(pga) and a vertical pga are given, based on the location where the structure is to be built, how do you come up with a seismic coefficient in the stability analysis. If only one of the two pga’s are known (pgah or pgav), how to estimate the value of the other ? Do you only use the pgah, pgav or should you use a combination of the two. What combination is used ? Some suggestions include pgav = 2/3 pgah. Seismic coefficient in combination, horizontal = 2/3 pgah, vertical = 1/3 pgav or 4/9 pgah. Seed 1979, Marcuson 1992 recommended to use seismic coefficient as roughly 1/3 to 2/3 of pgah. Looking at the whole spectrum of what people discussed, you can practically pick up any number and it can be justified ! Any comments ? Others look at the dam safety guidelines, and usually they find very vague statements. To throw more confusion, the values provided for the pgah or pgav are even in doubt with introduction of “Continental Plates theory”, versus “historical data used to determine the pga. Which is correct ? Which is the recommended practice ?