SEISMO-LINEAMENT ANALYSIS OF THE KANAB-FREDONIA AREA OF THE SOUTHERN COLORADO PLATEAU

The Northern Arizona Seismic Belt (NASB) extends southeast from the Arizona-Utah border to the Mogollon Plateau of central Arizona and defines the seismic boundary between the Colorado Plateau and the Basin and Range Province. The NASB is the source of seismic activity in the Kanab-Fredonia area and has produced earthquakes with magnitudes as large as M5.75 (Brumbaugh, 2008, J. Geophys. Res., v. 113, B05309, doi:10.1029/2007/JB005278). Earthquakes of this size have caused damage to unreinforced masonry structures in Fredonia AZ and Kanab UT and have triggered rockslides in the Grand Canyon area (Stover, C.W., Coffman, J.L., 1993, Seismicity of the United States, 1568-1989 (revised): U.S.G.S. Profession United State Government Printing Office, Washington).

The seismo-lineament analysis method (SLAM) is used to investigate the possible correlation between the nodal planes of an earthquake focal-mechanism solution and the surface trace of faults in the epicentral area (Cronin et al., 2008, Environmental and Engineering Geoscience, v. 14, p. 199-219). The purpose of this study is to apply the SLAM procedure to four moderate-sized earthquakes in the Kanab-Fredonia area to identify which seismogenic fault generated each of the earthquakes. Focal mechanism solutions for these events have been computed by David Brumbaugh (2008, J. Geophys. Res., v. 113, B05309, doi:10.1029/2007/JB005278).

Preliminary results indicate that the four earthquakes are located in the area of the Toroweap and West Kaibab faults; however, information from published geologic maps along these faults appears inconsistent with the nodal-plane or slip-vector orientations. The projections of the nodal planes to the ground surface do appear to correlate with geomorphic features that might indicate that there are previously unmapped seismogenic faults in the region.