The great earthquakes that have shaped Japan Brian - - PowerPoint PPT Presentation

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

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Japan – tectonic plates

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

M 8

100km*50km

M7

M 9

300 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.

１００ｋｍ

M6

Earthquake scale - magnitude

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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

Hard rock Soft sediment

Magnitude  Intensity

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Earthquake Intensity

Japanese 7-point scale

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

www.hinet.bosai.go.jp

Seismic Activity – 1 day

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More than 10 % of earthquakes in the world occur in JAPAN. The Japan Meteorological Agency determines 320 earthquake hypocenters every day! 18 Oct. - 19 Nov., 2013

www.hinet.bosai.go.jp

Seismic Activity – 1 month

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7

2001-2006

Seismic Activity – 5 years

M7 most years M8 about every 10 years

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Earthquake Impact

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

Damage Belt JMA Intensity=7

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

Mw 7.3 Kobe Earthquake 1995

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• 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

Three great earthquakes

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1891 Neodani

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

Intensity

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1891 Neodani

1891 1991 Preserved fault cross-section at Midori

• 6 m vertical throw

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1891 – Traditional Structures

Almost total destruction in parts of Gifu – followed by major fires

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1891 – Western Style Structures

Western style structures fared badly – study by Milne set stage for earthquake resistant structures

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2011 Tohoku-Oki Mw 9.0

Sendai Airport

Earthquake ruptured to trench (59 m seafloor offset) Major impact from tsunami

Subduction zone earthquakes in Japan – 2010 view

Tohoku Hokkaido

Tokyo

Kushiro Tokachi Sanriku Miyagi Fukushima Ibaraki

Kobe

In Miyagi, a M7.5 earthquake has occurred at intervals of about 40 years for hundreds of years

Off Miyagi earthquake M7.5, 99% (30 years)

Subduction zone earthquakes in Japan - 2011

Tohoku Hokkaido

Tokyo

Kushiro Tokachi Sanriku Miyagi Fukushima Ibaraki 2011 March 11 Off Tohoku Earthquake

Actual event was much larger than anticipated: M9

• which had been not

experienced for hundreds of years. Likely previous event 869 Jogan

Miyagi

Tokyo

Visualized REAL wavefield using 1800 stations

Intense and long duration shaking in populated cities due to amplification of ground motions in soft sediments

Fukushima

1 min 2 G Ground acceleration (cm/s/s)

Shaking skyscrapers (NHK TV)

Crustal deformation after the earthquake

Vertical Horizontal

GEONET: Geological Survey of Japan 530 cm 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.

Miyagi

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2011 Land Subsidence

http://www.coastal.jp/ttj t/

Tsunami produced by sea bottom deformation

浸水高 [m]

ＴＭ２ ＴＭ１

5 m 2 m 10 min 20 min Tsunami height [m]

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 simulation

Ocean bottom tsunami record

1677 Enpo Boso-oki (M8) 1896 Meiji Sanriku （M8.4） 2011 Off Tohoku M9.0

Triggered sequence of ordinary earthquakes linked to a tsunami earthquake

Continental Plate Trench

2011 Event Mechanism

Re-evaluation of future Nankai-Trough earthquakes

海溝

図： JAMSTECによる AD 300-600 Hoei Tenmu Kowa

Kaniga Ike Lake Kochi Tokushima

トラフ軸

(2) Seismic slip?

• friction-heat (seismic) slip

near the trough ? (1) Thick tsunami deposit

• x 2-5 thicker than that of Hoei
• observed in Kyushu and Shikoku

B.C event

Oita

Kaniga-ike Lake 3.11 Off Tohoku

Tokyo

• 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.

Earthquake Occurrence History (for past 300 years)

1707 Hoei 1854 Ansei 1944/ 1946 Showa

宝永地震＋慶長地震

EXTREME Nankai-trough earthquake (1) Tsunami

Hoei Earthquake EXTREME model

Shikoku Kii Tokai Boso Kyushu

Tsunami Height [m]

★ EXTREME earthquake

• 1.5 -2 times higher tsunami

(ex. >20 m in Kochi )

• No effect on tsunami in

internal sea and bay

Kochi Kochi Osaka On coast

Tokyo

☆ Expected long-period ground motions from the earthquake

・2-3 times larger and 2 times longer duration than that of the off Tohoku earthquake

2011 Off Tohoku Earthquake Expecting Nankai Trough Earthquake

Input

Shaking table test (Steel 30 floor)

E-defense at Kobe

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Nankai Scenarios

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

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Future developments

• 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

Maeda and Furumura (2012）

Temporary result

Implemented on K Computer

• 24,576 node (196,608 cores)

Sustain Performance:

• 0.5 PFLOPS (16-20 %)

Ground motion, crustal deformation, and tsunami from the 2011 Off Tohoku Earthquake

★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

• Prof. Takashi Furumura

古村 孝志

& Earthquake Research Institute, University of Tokyo Earthquake Spokesman NHK