Researchers say rapidly spreading fault ruptures may have amplified the intensity of the earthquake that jolted Japan's Noto Peninsula and surrounding areas on January 1 one year ago.

The government's Earthquake Research Committee says the magnitude 7.6 quake may have occurred as faults slipped in a 150-kilometer zone just north of the peninsula.

Scientists analyzed data from hundreds of seismometers to examine how fault ruptures expanded in the area.

They say tears initiated slowly off Suzu City at the peninsula's northeastern edge.

But they estimate that some 20 seconds later, ruptures started to propagate at a velocity of roughly 2 to 3 kilometers per second.

The seismologists say the phenomenon may have helped intensify sliding of faults near Wajima City, a western neighbor of Suzu.

They say those movements triggered shaking that emanated toward Wajima and eventually caused considerable damage.

The scientists included researchers from the University of Tokyo's Earthquake Research Institute and the University of California, Los Angeles. The institute's Associate Professor Aoki Yosuke is among those on the team.

Aoki notes that bedrock layers north of the peninsula are strongly stuck together over a 10-kilometer wide area. He says breaks in the layers nearby suggest that fault ruptures accelerated in the zone.

Aoki says he has hardly ever observed a quake in which fault ruptures begin slowly and progress as quickly as the one in Noto. He adds that simulating various seismic patterns can help predict quake damage.