HR: 1340h
AN: S23B-0235    [Abstracts]
TI: Analysis of Historic Seismicity in the Transition Zone of southeastern Arizona
AU: * Chang, J C
EM: chang@geo.utep.edu
AF: University of Texas El Paso, Department of Geological Sciences, 500 W. University Avenue, El Paso, TX 79968 United States
AU: Brumbaugh, D S
EM: David.Brumbaugh@NAU.edu
AF: Northern Arizona University, Department of Geology, P.O. Box 4099, Flagstaff, AZ 86011 United States
AB: The Colorado Plateau, southern Basin and Range, and Transition Zone divide Arizona into three physiographic and tectonic provinces (Figure 1). Little is known of the nature of seismicity in the Transition Zone of Arizona and neighboring New Mexico due to low rates of seismicity and poor historical instrumental coverage. The lack of historic instrumental coverage affects location and fault analysis of tremors. This is true for a swarm of events in 1938 that occurred in the Transition Zone of both Arizona and New Mexico. Locations are not well-constrained, relying largely on felt reports (Taggart and Baldwin, 1982). Earthquakes both large and recent enough that information about faulting may be obtained are rare in the Transition Zone. Details about faulting from seismic data exist from only one Transition Zone earthquake in Arizona. The epicenter is located far to the northwest of the area of this study in the Central Basin section of the Transition Zone (Eberhart-Phillips et al. 1981). Comparing information gained from this study will better elucidate Arizona Transition Zone faulting and seismicity. The Arizona Earthquake Information Center (AEIC) seismic stations recorded a swarm of eight earthquakes on 21 December 2003 that occurred in the Datil-Mogollon section of the Transition Zone. Six of the eight events were located, the epicenters forming a 25 km northwest trend, 62 km northwest of Clifton, Arizona. Information derived from the 2003 swarm events and earlier historic events are used to compare the seismicity and tectonic structures within the sections of the Transition Zone, as well as seismicity and tectonic structures of the adjacent Colorado Plateau and southern Basin and Range provinces, and help determine the role of the Arizona Transition Zone in the tectonics of the southwestern United States. The focal mechanism derived from this study of the 2003 swarm is similar to the 1976 Chino Valley earthquake, far to the northwest, in the Arizona Transition Zone. Similar focal mechanisms were derived by previous workers for the Colorado Plateau of Arizona (Wong and Humphrey, 1989). This study supports the role of the Arizona Transition Zone as being an intermediate tectonic Province between the Colorado Plateau and southern Basin and Range in Arizona.
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005