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.