Japan's second quake on Saturday ‘main’ shock
TOKYO (The Japan News/ANN) - The 6.5 magnitude quake on Thursday was a foreshock to the main 7.3 magnitude quake early Saturday.
The Japan Meteorological Agency announced that the magnitude-6.5 earthquake that struck Kumamoto prefecture on Thursday night (April 14) was likely a foreshock to the magnitude-7.3 main quake that struck the prefecture before dawn on Saturday.
The 2011 Great East Japan Earthquake was another case in which a large quake preceded a main quake. A magnitude-7 quake hit the Tohoku region on March 9, two days prior to the massive main quake. After a series of quakes that were then believed to be aftershocks, a major magnitude-9.0 quake hit the region on March 11.
In northern Miyagi Prefecture in July 2003, a magnitude-6.4 main quake hit seven hours after a magnitude-5.6 foreshock.
In both cases, the agency initially judged the foreshocks as main quakes and did not regard them as signs that a larger quake would strike.
“When an earthquake occurs, it’s difficult to predict that a larger quake will occur later in terms of seismology,” Gen Aoki, head of the agency’s earthquake and tsunami monitoring section, said at a press conference early Saturday.
He was responding to a reporter who asked whether the agency might have failed to recognise Thursday night’s quake as a foreshock.