Large earthquakes may trigger more earthquakes

New Scientist : Several recent large earthquakes have prompted scientists to ask whether a large quake can provoke another one elsewhere in the world. Tom Parsons of the US Geological Survey in Menlo Park, California, conducted a survey of global seismic activity since 1979; he presented the results last week at the Seismological Society of America annual meeting in Salt Lake City, Utah. Although he found that at least seven quakes of magnitude 5 or larger may have been caused by other quakes, they always lagged at least 9 hours behind. For a week after the 2012 Indian Ocean earthquake, there were so many smaller quakes around the world that researchers are convinced they must be connected. But why one quake can provoke another and why there is such a long time delay between them remain a mystery. It may be that an earthquake in one area can affect subterranean water pressure in another area, or that geothermally or volcanically active areas may be particularly susceptible.