Geologists had expected the portion of the Pacific "Ring of Fire" that produced this quake to yield a temblor on the order of magnitude 8 or perhaps 8.5, she said. "Something as big as an 8.9 is a bit of a surprise," she said.
Photos: Scenes from the earthquake
Scientists did not expect such a big quake in the area because the plate boundary is not straight, but is fairly irregular. According to Lucile Jones of the U.S. Geological Survey, a quake of that size would require rupturing a zone at least 300 miles long.
The region had a magnitude 7.2 temblor Wednesday in almost exactly the same area. Typically, with any large earthquake, there is about a 5% chance that such a quake is a precursor of a larger quake. This appears to have been that 1-in-20 chance.
There have been at least two aftershocks of magnitude 7 or greater, and researchers expect more.
The quake was a "perfect storm for tsunami generation," Hough said — it was large in magnitude and very shallow. The quake was so close to land, about 80 miles offshore, that people on the shore really had no warning that a 15-foot wave was imminent.
The Indonesian earthquake that produced the Indian Ocean tsunami on Dec. 26, 2004, was a magnitude 9.1. The largest quake on record was the 9.5 temblor that struck Valdivia, Chile, in 1960.
Photos: Scenes from the earthquake
thomas.maugh@latimes.com