A Japanese researcher says the powerful earthquake that hit the western prefecture of Osaka last week was caused by 2 faults moving almost simultaneously.
The magnitude-6.1 quake on June 18th left 5 people dead and many injured.
Associate professor of the University of Tokyo's Earthquake Research Institute, Aitaro Kato, analyzed data from the quake and tremors believed to be aftershocks.
He found that the aftershocks concentrate on the northern and southwestern sides of the quake's focus.
This led him to conclude that the quake was caused by 2 faults in the area moving almost concurrently.
Kato says the northern fault is probably a reverse fault, where one piece of the earth's crust is pushed up by another.
The southwest fault is believed to be a strike-slip fault, where 2 pieces of crust move against each other horizontally.
Both faults are 4 kilometers long. The researcher estimates that they moved at a depth of between 10 and 13 kilometers.
He says analysis suggests that the northern fault moved first, and was immediately followed by the southwest fault.
Kato says the region remains seismically active and is calling on people to stay alert.