A new report out from the USGS on hazardous faults in the Intermountain West region includes a section on Arizona by AZGS hazards chief, Phil Pearthree.
He summarizes:
The overall picture of hazardous faults in Arizona has not changed significantly since the first basic studies were conducted about 25 years ago. Most historical seismicity in Arizona is concentrated in the northern part of the state with a cluster of events in the Flagstaff area dating back to 1900. However, the 1887 earthquake, which occurred just across the southern border in northern Mexico, is the largest historical earthquake to affect Arizona and possibly the entire IMW.
Ref: Evaluation of Hazardous Faults in the Intermountain West Region— Summary and Recommendations of a Workshop,
By Anthony J. Crone, Kathleen M. Haller, and Joseph Z. Maharrey, Open-File Report 2009–1140, 75p.