Hi Kate,
You missed one - the earthquake of Feb. 1, 1929 was followed by a Ms 6.0 in
Vancouver on March 1, 1929. There is no specific distance relationship between
the Seattle region and Hindu Kush which might suggest earthquakes there would
be more common than at other times. Since the two larger events you mention
in 1949 and in 1965 occurred more than a month after the Hindu Kush earthquakes
there may have been some intervening triggering earthquakes, or it just takes
a while for the generation of earthquakes in NW Washington. Anyway, I think
based on the history that at least for the next several week, the danger of a strong
earthquake in NW Washington is limited.