From devastation in Japan,vital data

The slip,or the ground movement along the fault that caused the earthquake,exceeded 30 yards. Yet the rupture area was significantly smaller than the rupture area of the less severe Sumatra earthquake of 2004. Generally,there is a strong relationship between slip and area,but this is an outlier, said Jean-Philippe Avouac,a geologist at the California Institute of Technology who was not involved in the study. In a way,you could have guessed the rupture area. But because of the amount of slip,you would have a hard time to guess the magnitude.

In addition,the slip along the fault appears to have occurred at the relatively shallow depth of about six miles,resulting in a major tsunami.

For the same slip at a greater depth,there would be far less disturbance of the ocean, Dr Avouac said.

The researchers used GPS data that has continuously recorded ground movement on the Japanese islands for about 15 years.

The undersea earthquake that erupted off Japans eastern coast on March 11 was magnitude 9.0,the fourth largest on record.

By studying the data,it may be possible to better predict and prepare for future events,in Japan and elsewhere.