The M9.0 Tohoku Earthquake, Japan

Transcription

1 Geol 344 Lecture 22 The M9.0 Tohoku Earthquake, Japan Tuesday, March 22, 2011

2 This earthquake occurred 130 km (80 miles) east of Sendai, Honshu, Japan and 373 km (231 miles) northeast of Tokyo, Japan. Images courtesy of the US Geological Survey

3 Tohoku, Japan Earthquake: Tectonic Summary The magnitude 9.0 Tohoku earthquake on March 11, 2011, which occurred near the northeast coast of Honshu, Japan, resulted from thrust fauling on or near the subducion zone plate boundary between the Pacific and North America plates. At the laitude of this earthquake, the Pacific plate moves approximately westwards with respect to the North America plate at a rate of 83 mm/yr, and begins its westward descent beneath Japan at the Japan Trench. The locaion, depth, and focal mechanism of the March 11 earthquake are consistent with the event having occurred on the subducion zone plate boundary. Modeling of the rupture of this earthquake (red shading, approx.) indicate that the fault moved upwards of m, and slipped over an area approximately 300 km long (along- strike) by 150 km wide (in the down- dip direcion). The rupture zone is roughly centered on the earthquake epicenter along- strike, while peak slips were up- dip of the hypocenter, towards the Japan Trench axis. The March 11 earthquake was preceded by a series of large foreshocks over the previous two days, beginning on March 9th with a M 7.2 event approximately 40 km from the epicenter of the March 11 earthquake, and coninuing with another three earthquakes greater than M 6 on the same day.

4 Regional Seismicity of Japan

5 Zone of earthquakes marks top of slab. Called WadaI- Benioff zone. From Davidson et al., Chap 9

6 Japan Regional Seismicity, USGS Poster/Open File Report D

7 Tohoku, Japan Earthquake: Moment Tensor SoluIons (FaulIng Mechanisms) USGS Research Centroid Moment Tensor Mw 8.9 Distributed ~34 minutes acer OT (Jascha Polet, Cal Poly Pomona) global Centroid Moment Tensor V1 Mw 9.1 Released 7 hrs acer OT USGS W- Phase V1 Mw 8.9 Released 1 hr acer OT global Centroid Moment Tensor V2 Mw 9.1 Released ~ 3 days acer OT USGS W- Phase V2 Mw 9.0 Released 6 hrs acer OT Earthquake Research InsItute, Japan, CMT V1 Mw 9.0

8 11/03/11 5:46:23 Epicenter: MW 9.0 USGS/WPHASE CENTROID MOMENT TENSOR 11/03/11 05:46:23.00 Centroid: Depth 24 No. of sta:256 Moment Tensor; Scale 10**22 Nm Best Double Couple:Mo=3.9*10**22 NP1:Strike=193 Dip=14 Slip= 81 NP2:

9 Tohoku, Japan Earthquake: Finite Fault Model USGS V2-2011/03/18 Updated modeling shows peak slips of 30+ m, depending on the parameterizaion of rupture velocity. This updated model shows peak slip of ~32 m, using a range of rupture velocity from km/s. Models with constant rupture velocity show slips of m, all at shallow depths. This may imply that the up- dip nature of rupture is well resolved, but peak slips are not. Low slip regions near the fault edges, and fault base, are also poorly resolved.

10 Tohoku, Japan Earthquake: GPS Displacements GeospaIal InformaIon Authority of Japan

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13 The USGS PAGER map shows the populaion exposed to different Modified Mercalli Intensity (MMI) levels. MMI describes the severity of an earthquake in terms of its effect on humans and structures and is a rough measure of the amount of shaking at a given locaion. USGS PAGER Popula;on Exposed to Earthquake Shaking Overall, the populaion in this region resides in structures that are resistant to earthquake shaking. The color coded contour lines outline regions of MMI intensity. The total populaion exposure to a given MMI value is obtained by summing the populaion between the contour lines. The esimated populaion exposure to each MMI Intensity is shown in the table below. Image courtesy of the US Geological Survey

14 Tohoku, Japan Earthquake: Shaking DuraIon in Tokyo, Ground Velocity 6 minutes

15 Tohoku, Japan Earthquake: Acershock (and Foreshock) Sequence, 03/08/11-03/16/11 Note that the magnitudes of the 2011/03/11 06:15 (Mw 7.9) and 2011/03/11 06:25 (Mw 7.7) acershocks were updated from earlier, lower esimates. Updates occurred on 03/16 and 03/18, respecively.

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17 Tohoku, Japan Earthquake: Acershock (and Foreshock) Sequence, M:Time History

18 Tohoku, Japan Earthquake: Summary Poster USGS Current Version

19 Data: USGS PAGERCAT , USGS- NEIC & gcmt present Figure courtesy of Charles Ammon, acer Ammon et al., SRL, 2010

20 Shallow great earthquakes in subducion zones ocen cause tsunamis when they offset the ocean floor. This offset generates tsunami waves. This earthquake did produce a tsunami, which was measured on a nearby buoy and triggered the warning system. The water column height change that triggered the system. Flash anima;on of how the DART system detects ocean waves

21 Friday March 11 PACIFIC warning system MulIple alarms on a daily basis

22 Tsunami heights in meters. Maximum height was 7.3 m (~23 c). From HQ for Earthquake Research (Japan).

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24 Figure courtesy of NOAA

25 Tsunami waves swept away houses and cars in northern Japan and pushed ships aground. The tsunami waves traveled far inland, the wave of debris racing across the farmland, carrying boats and houses with it. The tsunami, seen crashing into homes in Natori, Miyagi prefecture. AP Houses were washed away by tsunami in Sendai, Miyagi Prefecture in eastern Japan, acer Japan was struck by a magnitude 9.0 earthquake off the northeastern coast. New York Times

26 Tohoku Earthquake Summary (updated March 20 th, 2011) M w : 9.0 FataliIes (official): 9079 (3/22/11) FataliIes (unofficial): >21,000 Injured:??? EsImated cost of damage: $248 billion Tsunami height (max): 730 cm Slip patch size: 300 km x 150 km Maximum slip: m Past earthquakes in region: 1994 M7.8 3 deaths 1978 M deaths 1933 M8.6 (29 m high tsunami) 3000 deaths 1896 M7.6 (38 m high tsunami) 27,000 deaths 1611 M? (tsunami produced) 869 M>8.0

27 See: htp:// japan- earthquake- map/index.html

28 Before and acer images of tsunami damage htp://

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36 YouTube videos of tsunami: htp://