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Earthquakes shake Indonesia, Mexico along Ring of Fire

April 11, 2012 12:00:00 AM PDT
Large earthquakes shook up millions of people on Wednesday in Indonesia and Mexico, along the Ring of Fire that circles the Pacific. There also was a smaller quake in Oregon.

Indonesia, one the world's most seismically active places, got hit with a magnitude 8.6 earthquake followed by an 8.2 aftershock about 300 miles southwest of the city of Banda Ache. The first one spawned a wave around 30 inches high. Seismologists say both were strike-slip earthquakes, which have vertical faults.

"Previous to this time, we've never seen a strike-slip quake larger than a magnitude 8.1," said Tom Heaton, a seismologist at the California Institute of Technology.

Scientists say the biggest quakes tend to be in subduction zones, where one plate of the Earth's crust dives under another, such as in the Japan quake last year, which triggered a tsunami. But in a strike-slip quake, the plates usually slide by each other without radically altering the height of the sea floor.

"When we realized it was the biggest earthquake we've seen on a strike-slip fault, the one good piece of news is it wasn't able to generate a significant tsunami," said Dr. Lucy Jones, a seismologist at the U.S. Geological Survey.

The quakes in Indonesia were the first of a cluster of quakes around the world. In Oregon, a magnitude 5.9 temblor struck about 160 miles west of Coos Bay. There were no reports of injuries.

"This is an area that actually often has magnitude 5.0 to 6.0 earthquakes. Essentially, no one feels them because they're far enough off shore," said Jones.

The latest powerful quake, a magnitude 6.5, struck in a sparsely populated area in the mountains of western Mexico. It could be felt more than 200 miles away in Mexico City, causing tall buildings to sway and people to evacuate into the streets.

But seismologists say it was actually the quake in Indonesia that triggered two small magnitude 2.6 quakes in California Wednesday -- one near Bakersfield and the other north of San Francisco.

"That happened as the surface waves from Indonesia were traveling through here. We can see it on our records," said Jones.

Seismologists said the bottom line is that there is no pattern for earthquakes, so it's best to always be prepared.

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