Take it from an earthquake veteran and Search & Rescue guy, DON"T stand in a doorway. They are the weakest part of a wall. Get down next to something very sturdy (e.g. couch, refrigerator). When things fall down it usually forms a triangular pocket in those places.
What I've been told in emergency training at my office is that the "triangle of life" advice is
not recommended; the current recommendation is to crouch under a desk or table and hold onto it as best you can.
If you dive under a table, make sure it is sturdy, many are not. The office desk is good as it will not usually collapse under normal debris. The idea of a safe pocket applies and falling debris usually forms triangle spaces. This is not the "triangle of life" that is so controversial. My point is don't stand in a doorway, they are not safer than cover.