Jian Lin, a geophysicist with the Woods Hole Oceanographic Institution, said the quake occurred just north of the site of the 1960 earthquake, with very little overlap. “Most of the rupture today picked up where the 1960 rupture stopped,” said Mr. Lin, who has studied the 1960 event, which occurred along about 600 miles of the fault zone and was measured at magnitude 9.5.

Image HILO, HAWAII, 1960 The stresses added along the fault zone by the earthquake, helped lead to the rupture on Saturday, experts said.

Like many other large earthquakes, the 1960 quake increased stresses on adjacent parts of the fault zone, including the area where the quake occurred Saturday. Although there had been smaller quakes in the area in the ensuing 50 years, Mr. Lin said, none of them had been large enough to relieve the strain, which kept building up as the two plates converged. “This one should have released most of the stresses,” he said.

Experts said the earthquake appeared to have no connection to a magnitude 6.9 quake that struck off the southern coast of Japan late Friday evening. Nor was the Chilean event linked to the magnitude 7.0 quake that occurred in Haiti on Jan. 12.

That quake, which is believed to have killed more than 200,000 people, occurred along a strike-slip fault, in which most of the ground motion is lateral. The Chilean earthquake occurred along a thrust fault, in which most of the motion is vertical.

Mr. Lin said his calculations showed that the quake on Saturday was 250 to 350 times more powerful than the Haitian quake.