1. S52C-01
Outline of the 2016 Kumamoto, Japan, earthquakes and lessons learned for a large urban earthquake in Tokyo metropolitan area
Naoshi Hirata1, Aitaro Kato1, Kouji Nakamura2, Yohei Hiyama3
1 Earthquake Research Institute, the University of Tokyo 2 , Japan Metrological Agency
3 Geospatial Information Authority of Japan
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2. Tectonic setting
Gray circles are epicenters of earthquakes with a depth < 60 km
Blue star is the 2016 Kumamoto earthquake
MTL: Median Tectonic Line
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3. Two large earthquakes with JMA seismic intensity 7 at Mashiki town in Kumamoto
The April 14, 2016 earthquake with Mjma 6.5 (Mw5.2)
The April 16, 2016 earthquake with an Mjma=7.3 (Mw7.0)
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4. Foreshock（Mj6.5) Main shock（Mj7.3) 28 hrs later 2016/12/16
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5. Totally destroyed houses: 8,364
Fatalities: 154
Totally destroyed houses: 8,364
(as of Dec. 7, 2016)
2016, May 14th　Naoshi town
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6. 2016/12/16
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7. Cumulative number of earthquakes after each major inland event in japan (Mj≧3.5)
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8. Foreshocks and Mainshock
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9. Foreshocks and Mainshock
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10. Surface faulting and known active faults
Right-lateral surface slip
Along the Futagawa fault zone, about 30 km long, a series of surface faults are found.
The maximum faulting is 2.2 m right-lateral slip at Mashiki town, Dozon area.
2016, May 14th　Naoshi town
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11. Assessment of the Futagawa fault zone in February 2013 by ERC
Along the Futagawa segment of the Futagawa fault zone, an earthquake with M7.0 may occur with a 2 m right-lateral slip.
A chance of occurrence of the event is approximately 0 to 0.9% in 30 years.
The segment is classified to belong to a “fairly high possibility” group among about 100 prominent active faults.
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12. Probability of M6.8+ in 30 years
Entire Kyushu: 30-42％
North
Central
South
Central Kyushu:18-20％
Cumulative distribution
Probability (%)
© Earthquake Research Committee, Headquarters for Earthquake Research Promotion (HERP)
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13. 208 Mj ≧ 7 earthquakes for 148 years (1868-2016)
Cumulative number
M-T
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14. Probabilistic Seismic Hazard Assessment
A chance for Japanese Seismic Intensity 6- or larger in 30 years: as of Jan. 1, 2016
Probability of earthquake occurence＋ site amplification
Injury by traffic accidents: 24%
Suffering from fire: 1.9%
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© HERP, ERC

15. Probabilistic Seismic Hazard Assessment
Mashiki Town
28%
Kumamoto City 14%
Probabilistic Seismic Hazard Assessment
A chance for Japanese Seismic Intensity 6- or larger in 30 years: as of Jan. 1, 2016
Probability of earthquake occurence＋ site amplification
Injury by traffic accidents: 24%
Suffering from fire: 1.9%
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© HERP, ERC

16. New Guidelines for Seismic Forecast Information after Big Earthquakes
ERC guidelines from 1988:
JMA issues aftershock probabilities after any big earthquake.
New ERC guidelines after the Kumamoto experience:
JMA only warns about possible strong motion of similar level after a big earthquake (during about one week).
If seismicity continues after the first week, JMA issues aftershock probabilities as a factor compared to the pre-earthquake probabilities.
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17. Summary
The 2016 Kumamoto earthquakes, Mj6.5 and Mj7.3, generate JMA seismic intensity 7 twice. Note that M7+ events occur once or twice every year in and around Japan.
More than 200 foreshocks and aftershocks of Mj ≧ 3.5 occurred: the most active seismicity among in-land earthquakes in Japan.
More than 150 were killed and 80,000 houses were totally destroyed by the events.
The 2016 Kumamoto earthquakes occurred on assessed active fault segments in an area of a high probability.
However, local people and, to some extent, local government officials did not understand their earthquake risk. We need further efforts to communicate risk to the public and stakeholders.
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Basic comprehensive policy

18. End
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