The ground along the Futagawa fault line zone in Mashiki, Kumamoto Prefecture, shifted sideways by around 1.8 meters, researchers investigating the aftermath of the April 16 magnitude-7.3 earthquake have confirmed.
According to researcher Takashi Nakata, a professor emeritus of geomorphology at Hiroshima University, the sideways shift was found running east to west, along with a vertical shift of around 70 centimeters. He says evidence of the shift can be observed running along the Futagawa fault line zone for at least 6 to 7 kilometers, cutting across paved roads and footpaths along rice fields.
Nakata says no such shift was found in an on-site investigation made on April 15, and he believes that the Futagawa fault line zone moved in the 7.3-magnitude "principal" quake that struck in the wee hours of April 16.
It is generally held that inland active-fault earthquakes of magnitudes larger than 6.8 sometimes leave evidence of tectonic movement on the earth's surface.
Meanwhile, University of Tsukuba associate professor of earthquake studies Yuji Yagi and other scientists examining the seismic waves produced by the 7.3-magnitude quake say that it may have originated with the Futagawa fault line zone. The fault surface, about 50 kilometers long and 20 kilometers wide, appears to have shifted 1.8 meters or more in a northeasterly direction for about 20 seconds, Yagi says.