Experts warn of more quakes in the region

‘‘What happened was not a surprise. Scientists have been talking about an increased likelihood of more earthquakes in this area because of the rupture that happened in December,’’ said Lori Dengler, a geologist at Humboldt State University in Arcata, California. ‘‘And it may not stop here.’’

Earthquakes occur along the boundaries between sections of Earth’s surface known as plates. The area where Monday’s quake occurred is particularly troublesome because of the speed at which plates there are converging, and their relative positions.

The region west of the island of Sumatra is a ‘‘subduction zone,’’ where plates are sliding over and under one another. ‘‘These are the places where we have most of the world’s earthquakes, and lots and lots of volcanoes,’’ an Dengler said.In December, a section of one plate about 700 miles long suddenly plunged about 30 feet beneath another, causing a magnitude 9.0 earthquake that created the devastating tsunami.

That event probably increased pressure on the next section of the plate boundary just to the south, causing Monday’s similar sudden thrust of one plate beneath the other, this time apparently involving a smaller section of perhaps 200 to 300 miles.

Scientists said it’s very likely that the extra stresses put on by the quake happening to the northwest triggered this earthquake. There is now an increased possibility that yet another massive quake could occur soon, farther along the same plate boundary, experts said.

‘‘Think of a crack in your windshield that propagates over time,’’ said Kate Hutton, a seismologist at the California Institute of Technology. ‘‘Once there’s a break, the two ends are the most highly stressed and it eventually keeps growing.’’ —Washington Post/Lat-WP