I have a old house ( built in 1909) and I'm curious about re-enforcing the roof. It is made of 2X4 rafters with a single 2X4 cross beam crossing every third or so rafter. The rafters meet in a "V" and are simply nailed together. Obviously it's been without issue's for 100 years, and typically I am a big fan of not fixing what isn't broke. I am concerned about earthquakes (live in Portland, OR). Would adding nail plates and cross beams to every rafter be wise? Should I just leave it be?