Tracking mining-induced seismicity in Arizona

Our friends at Geology.comhttp://geology.com/news/2012/united-states-mining-seismicity.shtml reminded us that the USGS tracks mining-induced seismicity across the US, principally caused by blasting to break up the rocks.   The figure below shows a concentration around the Kayenta coal mine on the Navajo and Hopi reservations in the northeast and near the Morenci copper mine near Clifton.    It's not obvious why the Clifton area blasts extend to the southeast into New Mexico.  The USGS map does not show seismic events around Lake Mead that are supposedly quarry blasts.  [Right, mining-induced seismicity, Arizona-New Mexico, from 1997-2000.  Credit, USGS]