15:30 〜 16:30
[J02-P-06] New Guidelines for the Seismic Forecast Information after Big Earthquakes in Japan
A big earthquake of M6.5 occurred at 21:26 on 14 April, 2016 (JST) in Kumamoto Prefecture. That was the beginning of “The 2016 Kumamoto Earthquake". Japan Meteorological Agency (JMA) issued information about aftershock probability after 18 hours of this earthquake. However, after 28 hours of the M6.5 earthquake, a bigger earthquake of M7.3 occurred in the same region and triggered distant earthquakes. The seismically active area was finally spread up to about 150km long. As this seismic activity was revealed that it was not a simple mainshock - aftershock patterns, JMA stopped issuance of the following information about aftershock probability. With lessons learned from this, seismologists and JMA discussed under a framework of the Headquarters of Earthquake Research Promotion (HERP), and new guidelines were published in August 2016. The points of the guidelines are followings.
(1)JMA calls attention to strong motion which is similar level to the first big earthquake for about one week after big earthquakes.
(2)If there were prior cases of foreshock - mainshock - aftershock series or earthquakes with similar magnitude which occurred in the short term near the big earthquakes, JMA calls attention to such cases.
(3)If active faults and assumed source regions of big thrust-type subduction-zone earthquakes existed near the big earthquakes, JMA explains the characteristics and calls attention to them.
(4)After one week, if the active seismic activity continues, JMA issues aftershock probability. The probability is shown by magnification ratio which compares to the probability just after the biggest earthquake and before the big earthquakes.
(5)JMA uses a word “earthquake" instead of “aftershock" when JMA calls to attention to strong motion by aftershocks, because the word of “aftershock" gave some impression to people that bigger earthquakes would not occur.
We will introduce new Japanese policy and actual examples about Seismic Forecast Information after big earthquakes.
(1)JMA calls attention to strong motion which is similar level to the first big earthquake for about one week after big earthquakes.
(2)If there were prior cases of foreshock - mainshock - aftershock series or earthquakes with similar magnitude which occurred in the short term near the big earthquakes, JMA calls attention to such cases.
(3)If active faults and assumed source regions of big thrust-type subduction-zone earthquakes existed near the big earthquakes, JMA explains the characteristics and calls attention to them.
(4)After one week, if the active seismic activity continues, JMA issues aftershock probability. The probability is shown by magnification ratio which compares to the probability just after the biggest earthquake and before the big earthquakes.
(5)JMA uses a word “earthquake" instead of “aftershock" when JMA calls to attention to strong motion by aftershocks, because the word of “aftershock" gave some impression to people that bigger earthquakes would not occur.
We will introduce new Japanese policy and actual examples about Seismic Forecast Information after big earthquakes.