The M9.0 Andaman IslandsSumatra Earthquake and Tsunami of 26 December 2004

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The M9.0 Andaman Islands-Sumatra Earthquake and
Tsunami of 26 December 2004
L. Braile, Purdue Universitybraile_at_purdue.edu,
www.eas.purdue.edu/braile
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Tectonic Setting
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Schematic plate tectonic setting for tsunami
generation
NOAA
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Historical Seismicity
(Indonesia is one of the most seismically active
areas in the world, has a long subduction zone
plate boundary, and many 7 earthquakes have
occurred there in the past, so it should be no
surprise that an M9 tsunami-generating event
would occur there.)
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Sumatra earthquakes FAQs
Question What other great (M gt 8) earthquakes
have occurred in the region? Answer Since 1900
and prior to the December 26 earthquake, the
largest earthquake along the subduction zone from
southern Sumatra to the Andaman Islands occurred
in 2000 and had a magnitude of 7.9.  A magnitude
8.4 earthquake occurred in 1797, a magnitude 8.5
in 1861 and a magnitude 8.7 in 1833 . All three
ruptured sections of the subduction zone to the
south of the recent earthquake.  Interestingly,
the 1797 and 1833 quakes are believed to have
ruptured roughly the same area with only 36 years
separating the events. Paleoseismic evidence
shows that great earthquakes or earthquake
couplets occur about every 230 years
(http//www.gps.caltech.edu/sieh/publications/a10
.html).
USGS
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Main shock and aftershocks 1200 km of the plate
boundary moved, max. displacement 20 m (?,
preliminary est.)
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Question What other significant tsunamis have
occurred in the region? Answer The following
destructive tsunamis are listed on a data base
maintained by the Tsunami Laboratory, Institute
of Computational Mathematics and Mathematical
Geophysics (http//tsun.sscc.ru/tsulab/20041226tsu
n.htm) 1. 1797/02/10 Central part of the western
Sumatra. The quake was most felt near Padang and
in the area within /-2 deg of equator. Padang
was flooded by powerful waves. More then 300
fatalities. 2. 1833/11/24 South coast of the
western Sumatra, estimated rupture from 1 S to 6
S latitude. Huge tidal wave flooded all southern
part of the western Sumatra. Numerous victims.
3. 1843/01/05 Strong earthquake west of the
central Sumatra. Terrible wave came from the
south-east and flooded all the coast of the Nias
Island. Many fatalities. 4.  1861/02/16
Exceptionally strong earthquake affected all the
western coast of Sumatra. Several thousand
fatalities. 5. 1883 Krakatau explosion 36,000
fatalities
USGS
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24-hour seismograph record
135 degrees distance
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Seismogram
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Worldwide earthquakes per year (from USGS)
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Worldwide earthquakes per year
Frequency-magnitude relationship suggests that
magnitude 9 events will occur about once per
decade statistically, since 1900, the actual
number is once per 20 years.
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Largest earthquakes, 1900 - 2004
USGS
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Largest earthquakes, 1900 - 2004
USGS
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Some recent Tsunami
NOAA
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Tsunami travel time (hours simulation)
NOAA
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Tsunami wave height (cm simulation)
NOAA
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Tsunami wave propagation characteristics note
that as water depth becomes smaller, waves slow
down, become shorter wavelength, and have larger
amplitude
NOAA
When the water is 10 m deep, what is the
separation of the waves in minutes?
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Tsunami simulation
http//staff.aist.go.jp/kenji.satake/animation.gif
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Tsunami simulation
Open Quick Time simulation (see these
websites) http//www.pmel.noaa.gov/tsunami/ http
//www.pmel.noaa.gov/tsunami/Mov/TITOV-INDO2004.mov
Note distance of propagation and reflection of
waves
NOAA
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Double click on the file TITOV-INDO20041.mov T
o view Quick Time movie of Tsunami simulation
from NOAA
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DART tsunami warning system
NOAA
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Commonly, the water recedes (a wave trough)
significantly for a few minutes before the first
wave crest arrives. People often go out to
explore the beach at that time.