Study: Nearly 1,000 earthquakes shook Arizona in recent years

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By Mike Gertzman By Mike Gertzman

TEMPE, Ariz. -- Arizona isn't known for its earthquakes, but researchers at Arizona State University said Tuesday nearly 1,000 earthquakes were recorded in the state over the past three years.

Scientists 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 of Arizona.

EarthScope's USArray Transportable Array was deployed within Arizona from April 2006 to March 2009. It was the first time researchers could examine earthquake activity on a statewide scale. The equipment found almost 1,000 earthquakes during the three-year period.

The results of the study were the direct result of improved amount and quality of earthquake data by EarthScope.

"It is significant that we found events in areas where none had been detected before, but not necessarily surprising given the fact that many parts of the state had never been sampled by seismometers prior to the deployment of the EarthScope USArray," said Jeffrey Lockridge, a graduate student in ASU's School of Earth and Space Exploration and the project's lead researcher.

While nearly 1,000 earthquakes seem alarmingly high, 91 percent of of the earthquakes Lockridge detected in Arizona were "microquakes."  Those earthquakes have magnitude of 2.0 or smaller and aren't usually felt by humans. Geologists use small magnitude earthquakes to map otherwise hidden faults beneath the surface.

The largest earthquakes and the majority of seismicity recorded in Arizona have been in the north-central part of the state.

Lockridge published the results of the project in this year's August issue of the Bulletin of the Seismological Society of America.