I am preparing a seismic hazard map of Seattle and I was curious about the great 7.4 magnitude earthquake that occurred in the Seattle area during 900-930 A.D. On a second note, is it possible to infer the epicenters of paleoearthquakes (earthquakes that happened more than 800 years back)? And to what confidence level?
If the quake you describe was on the Seattle Fault, you can probably guess the start point and the end point of the fault movement based just on the magnitude of the quake. (Quakes that "snap" longer portions of the fault release more energy.) The start point will give you the epicenter location.