Magnitude 8.9 (9.0) earthquake near Sendai,

east coast of Honshu, JapanFriday, March 11, 2011 at 05:46:23 UTC

Japan was struck by a magnitude 8.9 (9.0) earthquake off its northeastern coast last Friday. This the largest earthquake that Japan has experienced since measurements began.

Part of houses swallowed by tsunami

burn in Sendai, Miyagi Prefecture (state) after Japan

was struck by a strong earthquake off its

northeastern coast Friday, March 11,

2011.

New York Times

Chile 1960

Alaska 1964Sumatra 2004

Chile 2010Japan 2011

Russia 1952

Ecuador 1906

Alaska 1965

year1900 1920 1940 1960 1980 2000 2020

9.69.49.29.08.88.68.48.28.0

mag

nitu

deThis is about the 5th largest earthquake since 1900

Japan is one of the most seismically active areas in the world

Japan Trench

USGS

The event occurred where the Pacific and North American plates converge at a rate of 8.3 cm/year

Images courtesy of the US Geological Survey

Seismicity Cross Section across the subduction zone showing the relationship between color and earthquake depth.

The seismicity of the plate boundary outlines a subduction zone

ERI, Univ. Tokyo

371 aftershocks, M > 5, in the first two days after the event outline the fault area

ERI first motion sense of motion USGS centroid (average) sense of motion

10 - 15Looking from the side

Looking from below

The focal mechanism was a thrust fault

The maximum slip was about18 m

The vertical movement of the ocean bottom was up to 2 m and distributed over a 450 km x 150 km fault

A slip model

ERI, Univ. Tokyo

The rupture took about 30 seconds in each point but took 150 seconds to propagate from the focus to other parts of the fault.

Mom

ent r

elea

se ra

te

(

dyne

cm

/s)

time (seconds)

USGS centroid solution

The event was complete in 2.5 minutes

We model the vertical movement of the ocean bottom due to the event (2 m).

The water mass is lifted up by 2 m in 2-3 minutes over an area of 500x150 km and does not have time to flow down the slopes on the sides

Initiation of tsunami

The initial water bulge expands. The sea level depression on the landward side draws water from the coast.

The surface deflection propagates as a gravity surface wave .The wave speed is: H = water depth, g = gravity

The shallower the water, the lower the speed. Therefore, as the tsunami enters shallow waters the wave “piles up”.

The non-linear effects of shallow water magnification are difficult to model. Also, complex focussing effects occur in sounds and bays.

Initial propagation of tsunami

Hgv

Japan Pacific

NOAA

Calculated tsunami timing and maximum amplitude

In the deep ocean we can model the timing and amplitude distribution of the tsunami with precision.