Most of Arizona has experienced low levels of recorded seismicity, but a comprehensive analyses of seismic activity revealed that nearly 1,000 earthquakes have rattled the stated over the past three years.
Researchers at ASU's School of Earth and Science Exploration used new seismic data collected as part of the EarthScope project to develop methods to detect and locate small magnitude earthquakes across the entire state.
EarthScope's USArray Transportable Array was deployed in Arizona and provided the first opportunity to examine seismicity on a statewide scale. Its increased sensitivity allowed researchers to find almost 1,000 earthquakes during a three-year period, including many in regions of Arizona that were previously thought to be seismically inactive.
One-thousand earthquakes over three years may sound alarmingly high, but ninety-one percent of the quakes detected were "microquakes" with a magnitude of 2.0 or smaller. These quakes are typically not felt by humans.
The largest earthquakes and the majority of seismic activity recorded in Arizona have been located in the north-central portion of Arizona. Recently, a pair of magnitude 4.9 and 5.3 earthquakes occurred in the Cataract Creek area outside of Flagstaff. Earthquakes of magnitude 4.0 or larger also have occurred in other areas of the state, including a magnitude 4.2 earthquake in December 2003 in eastern Arizona and a magnitude 4.9 earthquake near Chino Valley in 1976.
The results of the study appear in a paper titled, "Seismicity within Arizona during the Deployment of the EarthScope USArray Transportable Array," published in the August 2012 issue of the Bulletin of the Seismological Society of America.