Earthquakes happened in region in 1975, 1993
Keith Brugger, a Professor of Geology at the University of Minnesota, Morris, said he hadn't yet reviewed any information regarding Friday's quake, but added that it probably was an event on the Great Lakes Tectonic Zone.
Keith Brugger, a Professor of Geology at the University of Minnesota, Morris, said he hadn't yet reviewed any information regarding Friday's quake, but added that it probably was an event on the Great Lakes Tectonic Zone.
West Central Minnesota sits on a "suture," or boundary, of the GLTZ. About 2.5 billion years ago, rocks of the Minnesota River Valley, which are 3.5 billion years old, collided with the slightly younger volcanic mass represented by granites and "greenstones," Brugger said.
"That event happened so long ago and we're still living with its legacy," Brugger said.
The greenstones were volcanic island arcs -- such as Japan and the Philippines -- that previously collided and contributed to the formation of North America, Brugger stated.
The GLTZ tectonic zone "suture" is a weakness and that any stress transmitted into, or generated within, the interior of present-day North America can cause the crust to fracture slightly.
"Hence the history of earthquake activity here in Minnesota," Brugger stated, recalling earthquakes in 1975 and 1993 in areas around Alexandria, Sauk Centre, Long Prairie and Staples.
(Information provided through the Morris Sun Tribune)
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