The magnitude 8.9 earthquake that struck Friday off the coast of Japan “is going to be among the top 10 earthquakes recorded since we have had seismographs,” said seismologist Susan Hough of the U.S. Geological Survey in Pasadena. “It’s bigger than any known historic earthquake in Japan, and bigger than expectations for that area.”

Geologists had expected the portion of the 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.”

A quake that big usually requires a long, relatively straight fault line that can rupture, such as those found in Peru and along the eastern coast of South America. Thursday’s quake occurred in the Japan Trench, where the Pacific tectonic plate slides under the Japan plate. . .