I don't know about research as such, but acording to 'Get Thru' (a New Zealand Civil Defence website) doorways aren't the best bet, and it's better to get underneath a sturdy piece of furniture:
SAFE PLACES IN AN EARTHQUAKE Somewhere
close to you, no more than a few steps
or less than three metres away, to
avoid injury from flying debris.
Under a strong table. Hold on to the
table legs to keep it from moving away
Next to an interior wall, away from
windows that can shatter and cause
injury and tall furniture that can
fall on you. Protect your head and
neck with your arms.
Keep in mind that in modern homes,
doorways are no stronger than any
other part of the structure and
usually have doors that can swing and
EDIT since the question has changed a little. I don't know of any research directly in this area, but every expert earthquake saftey organisation I've seen explicitly says no to doorways and yes to "drop cover and hold on" (1,2,3,4[pdf],5)
With regards to the 'triangle of life', New Zealand Cival Defence says
'Drop, cover and hold' is the official
advice of the New Zealand Government
developed collaboratively with expert
agencies such as GNS Science, EQC and
the Society of Earthquake Engineers
and cites Petal (1999) [pdf] as a source for how wrong the triangle of life is.