Arizona Regional Moment Tensor Catalog 1990-2015

Abstract:

Seismicity in Arizona is moderate compared to other parts of the U.S. Intermountain West region. However, large (M6+) damaging earthquakes have occurred in the past suggesting significant regional deformation and associated seismic hazard exist. Seismicity is concentrated in north-central Arizona near the western edge of the Colorado Plateau with scattered activity in the Arizona Transition Zone and the southern Basin and Range province extending towards the Rio Grande Rift. Sparse seismic station coverage had prevented a comprehensive analysis of earthquake source parameters so far. Permanent broadband seismic stations were installed starting in the 1990’s but coverage expanded significantly only in 2006 with the EarthScope Transportable Array and its legacy stations. Utilizing regional three-component broadband waveforms, we attempted seismic moment tensor inversion for all M4+ and M3.5+ earthquakes since 1990 and 2000, respectively. We obtained source parameters (faulting style, depth, seismic moment) for over 40 events in Arizona and vicinity ranging from M_w=3.2 to 5.3 roughly doubling the existing database. Mechanisms along a band extending from northwestern to southeastern Arizona show predominant normal faulting character. T-axes are usually E-W oriented but rotate towards N-S near 35N. Events near the Nevada-Utah border have strike-slip mechanisms with NW-SE oriented T-axes while to the south a few western Arizona strike-slip events have more northerly oriented T-axes. Centroid depths are mainly in the upper 10-15 km with a slight tendency of deeper sources proximal to the Colorado Plateau. The largest earthquake during the last 20 years, an M_w=5.2 event in June 2014, occurred in otherwise quiet southeastern Arizona underscoring the potential for significant earthquake sources throughout most of the state. The main shock at 9-12 km depth has an oblique normal faulting mechanism while the vivid aftershock sequence shows mechanisms that range from strike-slip to normal faulting.