Ariz. study sees thousands of earthquakes

Arizona, historically thought to experience low levels of recorded seismicity, had nearly 1,000 earthquakes in a three-year period, researchers said. A lack of seismic stations in most regions contributed to the perception that widespread earthquakes in Arizona are rare, seismologists at Arizona State University said, but their study from 2006 to 2009 found nearly 1,000 earthquakes rattling the state, a university release reported Tuesday. The study used new seismic data collected as part of the EarthScope project, intended 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 and provided the first opportunity to examine seismicity on a statewide scale, researchers said. "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," researcher Jeffrey Lockridge said. While the number of earthquakes recoded in the study may sound alarmingly high, researchers said, it is a direct result of the improved volume and quality of seismic data provided by EarthScope. Of the earthquakes detected by the study, 91 percent were "microquakes" with a magnitude of 2.0 or smaller, which are not usually felt by humans, the researchers said.