A SURVEY OF NORTHERN ARIZONA SEISMICITY

Historic seismicity within the state of Arizona has been concentrated principally in the northern part of the state within the physiographic boundaries of the Colorado Plateau.Much of this activity is centered in a north-south belt of epicenters termed the Northern Arizona Seismic Belt (NASB).This seismicity appears to be a branchlike continuation of the southern part of the Intermountain Seismic Belt. The seismicity can be characterized to consist mostly of isolated events some as large as Ms6.2 and therefore suggesting a degree of seimic hazard. The most recent event to cause minor damage was the Mw5.3 Cataract Creek earthquake(1993). Within the NASB there are four hotspots with higher rates of activity:Blue Ridge, Flagstaff,Grand Canyon, and Kanab-Fredonia. Analysis of these concentrations of seismicity indicate preferred directions of extension for the southern Colorado Plateau that can be related to directions of well defined fault trends and fracture patterns. The regional pattern of seismicity and faulting in northern Arizona suggests an expansion of Basin and Range tectonics into the southern Colorado Plateau with the eastern boundary marked by the location of the seismicity of the NASB and associated faulting.