But the Seattle and Tacoma faults are probably the most serious earthquake threat to the populous Seattle–Tacoma area. A 2002 study of bridge vulnerability estimated that a magnitude 7 earthquake on the Seattle Fault would damage approximately 80 bridges in the Seattle–Tacoma area, whereas a magnitude 9 subduction event would damage only around 87 bridges in all of Western Washington. The same study also found that with failure of just six bridges (the minimum damage for a Benioff M 6.5 event) there could be at least $3 billion lost in business revenue alone. Subsequent retrofitting by the Washington Department of Transportation and the City of Seattle would likely reduce damage to key bridges. But there is concern that such an earthquake on the Seattle Fault would devastate unreinforced masonry (URM) buildings, of which the City of Seattle is estimated to have around a thousand, concentrated in Capitol Hill, Pioneer Square, and the International District.