Chain reaction activated separate fault zone in second huge earthquake

Seismic experts believe a magnitude 7.3 quake that rocked southwestern Japan in the early hours of Saturday occurred on a separate fault zone from a massive temblor that struck barely a day earlier, and was triggered by a chain reaction involving a series of tremors.

The 1:25 am earthquake was about 16 times as large as a magnitude 6.5 temblor that hit Kumamoto Prefecture Thursday night, the Japan Meteorological Agency said, describing the latest jolt as the main quake and the initial one as a foreshock.

The governmental Earthquake Research Committee concluded Friday that the magnitude 6.5 quake happened on the 81-kilometre Hinagu fault zone running along the central part of the island of Kyushu.

Shinji Toda, professor of earthquake geology at Tohoku University, said the 64-kilometre Futagawa fault zone located north of the Hinagu zone could have moved to cause the fresh quake.

The village of Minamiaso, where a major landslide occurred, and the city of Uto in Kumamoto, where the city hall was half destroyed, are located at either end of the Futagawa fault zone.