The great earthquakes that have shaped Japan 日本に大きな影響を与えた地震

Transcription

1 The great earthquakes that have shaped Japan 日本に大きな影響を与えた地震 Brian Kennett, Research School of Earth Sciences, ANU Takashi Furumura Earthquake Research Institute, University of Tokyo

2 Japan tectonic plates 2 Japan has been created by the interaction of four tectonic plates 5 year energy release in earthquakes

3 Earthquake scale - magnitude 3 100km M7 M6 M 8 100km*50km M km*150 km Impact extends much further as the earthquake magnitude grows. Increasing M by 1 unit means the energy is larger by factor of 32 A collection of M7 events does not have anything like the impact of the largest earthquakes.

4 Earthquake Intensity 4 Magnitude Intensity Japanese 7-point scale Level of shaking depends on earthquake scale (M), distance and site conditions. - For 1 unit of seismic intensity the ground shaking grows by 3. -The shaking becomes smaller with distance from the source - Poor site condition (soft materials) increases intensity Soft sediment Hard rock

5 Seismic Activity 1 day 5 19 Nov 2013 Due to the collision of the plates, a large number of oceanic earthquakes and shallow inland earthquakes occur beneath Japan

6 Seismic Activity 1 month More than 10 % of earthquakes in the world occur in JAPAN. The Japan Meteorological Agency determines 320 earthquake hypocenters every day! 18 Oct Nov.,

7 Seismic Activity 5 years 7 M7 most years M8 about every 10 years

8 Earthquake Impact 8 Traditional wooden structures are vulnerable to collapse and subsequent fire Contemporary illustrations of the effect of the 1855 earthquake in Edo

9 Mw 7.3 Kobe Earthquake 1995 Destructive damage occurred within a narrow (<2km) and long (>20km) belt zone located 1-2km away from the active fault trace. Death toll 6770, Economic impact large e.g. PC chips Damage Belt JMA Intensity=7

10 10 Three great earthquakes 1891 Neodani (Nobi) M8.1 very large inland earthquake, demonstrated the vulnerability of Western style construction 2011 Offshore Tohoku M9.2 expected event size underestimated, recurrence time perhaps 1000 years major tsunami and subsidence 1707 Hoei Nankai M8.7 but perhaps M9.1 far more frequent events than in north economic impact much greater

11 1891 Neodani 11 Intensity The lines of tea bushes marking the edge of land plots were originally straight, but were offset in 1891

12 1891 Neodani Preserved fault cross-section at Midori - 6 m vertical throw 1991

13 1891 Traditional Structures 13 Almost total destruction in parts of Gifu followed by major fires

14 1891 Western Style Structures 14 Western style structures fared badly study by Milne set stage for earthquake resistant structures

15 2011 Tohoku-Oki Mw Earthquake ruptured to trench (59 m seafloor offset) Major impact from tsunami Sendai Airport

16 Subduction zone earthquakes in Japan 2010 view Hokkaido Kobe Tokyo Tohoku Ibaraki Tokachi Sanriku Miyagi Fukushima Kushiro Off Miyagi earthquake M7.5, 99% (30 years) In Miyagi, a M7.5 earthquake has occurred at intervals of about 40 years for hundreds of years

17 Subduction zone earthquakes in Japan Actual event was much larger than anticipated: M9 - which had been not experienced for hundreds of years. Tokyo Hokkaido Tohoku Ibaraki Tokachi Sanriku Kushiro Miyagi 2011 March 11 Off Tohoku Earthquake Fukushima Likely previous event 869 Jogan

18 Intense and long duration shaking in populated cities due to amplification of ground motions in soft sediments Visualized REAL wavefield using 1800 stations Shaking skyscrapers (NHK TV) 2 G 1 min Ground acceleration (cm/s/s) Miyagi Tokyo Fukushima

19 2011 Land Subsidence Crustal deformation after the earthquake Miyagi Horizontal Vertical 530 cm GEONET: Geological Survey of Japan 120 cm Due to crustal deformation by the earthquake NE Japan moved 5.3 m east, and subsided 1.2 m. Sea water does not return because of the land subsidence. 19

20 Upheaval of sea bottom caused by the earthquake produced tsunami. The large (> 5m) tsunami off Tohoku (80 km offshore) warned of the attack of huge (>30m) tsunami in 30 min. Tsunami produced by sea bottom deformation Tsunami height [m] 5 m 浸水高 [m] 2 m t/ 10 min 20 min TM2 TM1 Ocean bottom tsunami record Tsunami simulation

21 2011 Event Mechanism Triggered sequence of ordinary earthquakes linked to a tsunami earthquake Continental Plate Trench 1896 Meiji Sanriku (M8.4) 2011 Off Tohoku M Enpo Boso-oki (M8)

22 Re-evaluation of future Nankai-Trough earthquakes

23 Hoei Kowa (1) Thick tsunami deposit - x 2-5 thicker than that of Hoei - observed in Kyushu and Shikoku 3.11 Off Tohoku Tenmu AD B.C event Kaniga-ike Lake (2) Seismic slip? - friction-heat (seismic) slip 図 : JAMSTECによる near the trough? Kaniga Ike Lake Kochi Tokushima トラフ軸 Oita 海溝

24 - The 1707 Hoei earthquake (M8.7) which was the largest event in the past 300 years has been used for disaster prevention planning. - Recently an EXTREME model (M9.1) was presented based on recent knowledge of seismology/geology etc. Tokyo Earthquake Occurrence History (for past 300 years) 1707 Hoei 1854 Ansei 1944/ 1946 Showa

25 Tsunami Height [m] EXTREME Nankai-trough earthquake (1) Tsunami On coast Kochi 宝永地震 + 慶長地震 EXTREME model Hoei Earthquake EXTREME earthquake times higher tsunami (ex. >20 m in Kochi ) -No effect on tsunami in internal sea and bay Kyushu Shikoku Kii Tokai Boso Osaka Kochi

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28 Expected long-period ground motions from the earthquake 2-3 times larger and 2 times longer duration than that of the off Tohoku earthquake Expecting Nankai Trough Earthquake Tokyo Shaking table test (Steel 30 floor) Input 2011 Off Tohoku Earthquake E-defense at Kobe

29 Nankai Scenarios 30

30 1707 Mt Fuji eruption A few months after the great 1707 earthquake. Mt Fuji had its most recent eruption Ash fell across the Tokyo region at levels that would cause major disruption today

31 Future developments 32 Improved seismic warning systems integrating rapid computation of earthquake effects Calculations of scenario earthquakes to provide full range of information for disaster assessment Better coupling of the full range of seismological and geodetic results to get an integrated picture on both short and long time-scales Enhanced awareness of potential impact for generations in western Japan who have not felt a great earthquake since the 1940 s

32 Ground motion, crustal deformation, and tsunami from the 2011 Off Tohoku Earthquake Implemented on K Computer -24,576 node (196,608 cores) Sustain Performance: -0.5 PFLOPS (16-20 %) Temporary result Maeda and Furumura (2012)

33 Earthquake Early Warning from the Off Tohoku quake - Alarm started 5.4 s after the earthquake - Finally, at 110 s the estimated magnitude was set to M8.1

34 Prof. Takashi Furumura 古村孝志 & Earthquake Research Institute, University of Tokyo Earthquake Spokesman NHK