Powerful Tsumani Inevitably Followed Japan Earthquake

March 11, 2011 -- The earthquake that struck off the Japanese island of Honshu on Friday created classic conditions for a powerful and destructive tsuanmi, geological experts told ABC News.

"It's the largest earthquake we believe has taken place off western Honshu since good seismological recording began in the early 20th century," said Dr. John Ebel, director of the Weston Observatory of Earth and Environmental Sciences at Boston College.

He said the thrust quake occurred when one tectonic plate—the Pacific Ocean plate—slid under another, the Asian plate. That type of earthquake is called a subduction quake—the same kind of quake that hit Sumatra in 2004, causing a horrific tsunami, and that caused devastation in Chile last year.

The 8.9-magnitude quake on Friday met three conditions to create a killer tsunami, according to Eric Calais, professor of geophysics at Purdue University. It was a shallow earthquake, occurring not that far into the earth's crust. Its epicenter was offshore, and it created a motion that raised the sea floor.

"It's a giant wave-making machine," said Dr. Larry Brown, professor of earth and atmospheric sciences at Cornell University.

All of Japan—in the famous Ring of Fire, an arc of volcanoes and earthquakes zones in the Pacific--is highly vulnerable to earthquakes, experts said, because the islands are located on a major boundary between the two tectonic plates. "It is THE dangerous geologic setting because it's capable of producing monster earthquakes up to and beyond a magnitude of 9," Calais said.