Rare 'doublet' quakes may present a hazard

STATE COLLEGE, Pa., Jan. 31 (UPI) -- U.S. geoscientists have discovered earthquakes occurring at the edges of tectonic plates can trigger events at a distance and much later in time.

The Pennsylvania State University researchers said such doublet earthquakes might present an underestimated hazard but might also shed light on earthquake dynamics.

"The last great outer rise earthquakes that occurred were in the 1930s and 1970s," said Associate Professor Charles Ammon. "We did not then have the equipment to record the details of those events."

The outer rise is the region seaward of the deep-sea trench that marks the top of the plate boundary, the scientists said.

Working with Professor Emeritus Hiroo Kanamori of the California Institute of Technology and Professor Thorne Lay at the University of California-Santa Cruz, Ammon looked at the sequence of seismic activity that link two earthquakes into a doublet.

"Such large doublet earthquakes, though rare, could be an underestimated hazard," says Ammon. "We are also interested in what these events tell us about how earthquakes interact, how the stresses and interactions allow one earthquake to trigger another."

The study, funded by the National Science Foundation and the U.S. Geological Survey, appears in the journal Nature.