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

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

Earthquake scale - magnitude Impact extends much further as the earthquake magnitude grows. Increasing M by 1 unit means the energy is larger M6 by factor of 32 M7 M 8 A collection of M7 events 100km*50km does not have anything like the impact of the M 9 largest earthquakes. 300 km*150 km １００ｋｍ 3

Earthquake Intensity Level of shaking depends on Magnitude  Intensity earthquake scale (M), distance and site conditions. Japanese 7-point scale - 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 4

Seismic Activity – 1 day 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 5

Seismic Activity – 1 month 18 Oct. - 19 Nov., More than 10 % of 2013 earthquakes in the world occur in JAPAN. The Japan Meteorological Agency determines 320 earthquake hypocenters every day! www.hinet.bosai.go.jp 6

Seismic Activity – 5 years M7 most 2001-2006 years M8 about every 10 years 7

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

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

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 10

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

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

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

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

2011 Tohoku-Oki Mw 9.0 Earthquake ruptured to trench (59 m seafloor offset) Major impact from tsunami Sendai Airport 15

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

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

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

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

Tsunami produced by sea bottom deformation Tsunami 5 m height [m] 浸水高 [m] http://www.coastal.jp/ttj 2 m t/ 10 min 20 min Ocean bottom tsunami record ＴＭ２ ＴＭ１ Tsunami simulation 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.

2011 Event Mechanism Triggered sequence of ordinary earthquakes linked to a tsunami earthquake 1896 Meiji Trench Sanriku （ M8.4 ） Continental Plate 1677 Enpo 2011 Off Boso-oki (M8) Tohoku M9.0

Re-evaluation of future Nankai-Trough earthquakes

(1) Thick tsunami deposit Hoei - x 2-5 thicker than that of Hoei 3.11 Off Tohoku - observed in Kyushu and Shikoku Kowa Tenmu (2) Seismic slip? AD - friction-heat (seismic) slip 300-600 図： JAMSTEC による near the trough ? Kaniga-ike Lake B.C event Kaniga Tokushima Ike Lake Kochi トラフ軸 海溝 Oita

Earthquake Occurrence - The 1707 Hoei earthquake (M8.7) which was the largest History (for past 300 years) 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. 1707 Hoei Tokyo 1854 Ansei 1944/ 1946 Showa

EXTREME Nankai-trough earthquake (1) Tsunami On coast 宝永地震＋慶長地震 Kochi ★ EXTREME earthquake EXTREME - 1.5 -2 times higher tsunami model Tsunami Height [m] (ex. >20 m in Kochi ) -No effect on tsunami in Hoei internal sea and bay Earthquake Kyushu Shikoku Kii Tokai Boso Osaka Kochi

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

Nankai Scenarios 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

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 32

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

★ 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