Magnitude 3.3 earthquake occurs eight miles east of Flagstaff, Arizona
The tremblor originated several miles north and east of the northeastern-most branch of the Quaternary Lake Mary Fault system. There are other suspected Quaternary faults in the vicinity. The M 3.3 event occurred at approximately 5 km depth, but this is a standard depth calculation for much of Arizona due to a generalized crustal model. The latitude/longitude estimate is more accurate, and greatly improves when there are stations nearby, such as BARN (AE, AZGS network) and WUAZ (USGS). The figure below portrays the seismic signal captured by broadband seismometers operated as part of the Arizona Broadband Seismic Network.
The Lake Mary fault system is located in the Northern Arizona Seismic Belt, an area riddled with dozens of Quaternary faults that extents from SE of Flagstaff NNW to Utah. Subsequently, northern Arizona experiences dozens of earthquakes annually, most of which fall below the threshold (~ M 2.5) of felt events. Lake Mary Fault bifurcates into several N-S and NW-SE splay faults near the city of Flagstaff (see the figure below, orange circles represent historic earthquake epicenters An M3.1 occurred near this same area on 11-04-2018, as well as several smaller events.
Historical Seismicity. Between 1906 and 1912, Flagstaff was rocked by three nearby M6.0+ earthquakes. Hundreds of smaller magnitude events have occurred in the Northern Arizona Seismic Zone, with scores of events each year. The Oak Creek Canyon fault system west-southwest of Flagstaff is another source of felt earthquakes; on 30 November 2014, a M 4.7 earthquake was felt widely throughout northern and central Arizona, including Sedona – Flagstaff, Arizona.
The AZGS-DEMA Natural Hazards in Arizona interactive viewer displays Quaternary Faults and more than 3,000 historic earthquake epicenters.
Posted by AZGS Staff 15 Oct 2020.