DECEMBER 2004 INDIAN OCEAN EARTHQUAKE
AND TSUNAMI
EARTHQUAKE HAZARDS
 Primary
Ground shaking and surface rupture
Liquefaction
Landslides
Tsunami
 Secondary
Fires
Floods
Earthquake Magnitude and Intensity
Richter Magnitude is a measure
of the strength of an
earthquake, as determined by
seismographic observations.
An increase of one unit of
magnitude (M3 to M4)
represents a 10-fold increase in
wave amplitude on a
seismogram or approximately a
30-fold increase in the energy
released.
Intensity is a measure of the
effects of an earthquake at a
particular place on humans,
structures and (or) the land
itself.
The intensity at a point
depends not only upon the
strength of the earthquake
(magnitude) but also upon
the distance from the
earthquake to the point and
the local geology.
India Moving north - colliding with Eurasia
Worldwide earthquakes per year:
Frequency-magnitude relations suggests that magnitude 9+ events
occur about once per decade.
Statistically, since 1900, the actual number is ~once per 20 years.
Earthquake magnitude controlled
by fault length rupture
Magnitude
versus
Length
Magnitude
versus
faultFault
length
Fault Length (km)
10000
Magnitude versus
fault length
(determined from
aftershock zone
length) for various
earthquakes.
Alaska, 1964
Sumatra, 2004
1000
Denali, 2002
Landers, 1992
100
Loma Prieta, 1989
Northridge, 1994
10
6
7
8
Magnitude
9
10
COMPLEX PLATE
BOUNDARY ZONE
IN SOUTHEAST ASIA
Northward motion of
India deforms all of the
region
Many small plates
(microplates) and blocks
Molnar & Tapponier, 1977
Tsunami-generating
EQs and sources
Geist, Titov and Synolakis, Tsunami: Wave of Change, Scientific American, January, 2006.
India subducts
beneath Burma
microplate
at about 50 mm/yr
Earthquakes occur at
plate interface along
the Sumatra arc
(Sunda trench)
These are the
destructive results of
many years of
accumulated plate
motion
Sumatra earthquakes
What other great (M > 8) earthquakes have occurred in the region?
Since 1900 and prior to the December 26 earthquake, the largest
subduction EQs in southern Sumatra to the Andaman Islands
occurred in 2000 and had a magnitude of 7.9.
 M 8.4 earthquake occurred in 1797
 M 8.5 in 1861
 M 8.7 in 1833
All three ruptured sections of the subduction zone to the south
of the 2004 earthquake.
The 1797 and 1833 EQ’s 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
INTERSEISMIC:
Relative plate rate about
50 mm/yr
Fault interface is locked
EARTHQUAKE (coseismic):
Fault interface slips,
overriding plate rebounds,
releasing accumulated
motion
HOW OFTEN:
Fault slipped ~ 10 m = 10000 mm / 50 mm/yr
10000 mm / 50 mm/yr = 200 yr
Longer if some slip is aseismic
Faults aren’t exactly periodic for reasons we don’t understand
MODELING
SEISMOGRAMS shows
how slip varied on
fault plane
Maximum slip area
~400 km long
Maximum slip ~ 20 m
Seismograms
under estimate
slip patch
TWO VIEWS OF THE PART OF THE SUMATRA
SUBDUCTION ZONE THAT SLIPPED
ERI
Seismogram analysis shows
most slip in southern 400 km
C. Ji
Aftershocks show slip
extended almost 1200 km
Earthquakes rupture a patch
along fault's surface.
The larger the rupture
patch, the larger the
earthquake magnitude.
Initial estimates from the
aftershock distribution show
the magnitude 9.3 SumatraAndaman Islands EQ
ruptured a patch of fault
roughly the size of California
For comparison, a
magnitude 5 earthquake
would rupture a patch
roughly the size of New York
City's Central Park.
NORMAL MODES
(ULTRA-LONG PERIOD
WAVES) SHOW SEISMIC
MOMENT 3 TIMES THAT
INFERRED FROM
SURFACE WAVES
IMPLIES SLIP ON AREA 3
TIMES LARGER
Entire 1200-km long
aftershock zone likely
slipped
SEISMIC MOMENT Mo
1 x 1030 dyn-cm
2.5 TIMES BIGGER THAN
INFERRED FROM 300-s
SURFACE WAVES
CORRESPONDING MOMENT
MAGNITUDE Mw 9.3,
COMPARED TO 9.0 FROM
SURFACE WAVES
Comparison of fault areas,
moments, magnitudes,
amount of slip shows this was
a gigantic earthquake
“the big one”
IF ENTIRE ZONE
SLIPPED, STRAIN
BUILT UP HAS BEEN
RELEASED,
LEAVING LITTLE
DANGER OF
COMPARABLE
TSUNAMI
Risk of local tsunami
from large aftershocks
or oceanwide tsunami
from boundary
segments to south
remains
EARTHQUAKE MAGNITUDE 9.3
Stein & Wysession after IRIS
One of the largest earthquakes since seismometer
invented ~ 1900
TSUNAMI - water wave generated by earthquake
NY Times
What other significant tsunamis have occurred in the region?
The following destructive tsunamis (Tsunami Laboratory, Institute of
Computational Mathematics and Mathematical Geophysics)
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
TSUNAMI GENERATED ALONG FAULT, WHERE SEA FLOOR
DISPLACED, AND SPREADS OUTWARD
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Hyndeman and Wang, 1993
Red - up motion, blue down
http://staff.aist.go.jp/kenji.satake/animation.gif
TSUNAMI SPEED IN DEEP
WATER of depth d
c = (gd)1/2
g = 9.8 m/s2 d = 4000 m
c = 200 m/s = 720 km/hr =
450 m/hr
QuickTime™ and a
GIF decompressor
are needed to see this picture.
Tsunami generated along
fault, where sea floor
displaced, and spreads
outward
Reached Sri Lanka in 2 hrs,
India in 2-3
http://staff.aist.go.jp/kenji.satake/animation.gif
NOAA
IN DEEP OCEAN tsunami has long wavelength, travels fast,
small amplitude - doesn’t affect ships
AS IT APPROACHES SHORE, it slows. Since energy is conserved,
amplitude builds up - very damaging
Tsunami wave
height (2 hours
after earthquake)
measured from
satellite radar
altimetry
NOAA
Satellite radar altimetry
Tide gauge record, east coast of India
Tsunami (~1.2 m maximum wave
height; note that waves are visible
for over 2 days)
Normal tide
variation
Wave Heights:
Satellite observation vs calculated model
Geist, Titov and Synolakis, Tsunami: Wave of Change, Scientific American, January, 2006.
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?
Chedi Resort,
Phuket, Thailand,
wave height ~4+ m
(from estimates of
water level from
beach umbrellas
on grassy area
above the beach).
Damage in Banda Aceh
Earthquake and Tsunami Damage,
Banda Aceh, Sumatra
Earthquake and
Tsunami Damage,
Sri Lanka
Train and tracks destroyed, SW coast of Sri Lanka
Geist, Titov and Synolakis, Tsunami: Wave of Change, Scientific American, January, 2006.
Tsunami wave trough, Sri Lanka coast
TSUNAMI WARNING
Deep ocean buoys can
measure wave heights, verify
tsunami and reduce false
alarms
Because seismic waves travel much
faster (km/s) than tsunamis, rapid
analysis of seismograms can identify
earthquakes likely to cause major
tsunamis and predict when waves
will arrive
HOWEVER, HARD TO PREDICT EARTHQUAKES
recurrence is highly variable
Extend earthquake history
with geologic records paleoseismology
Sieh et al.,
1989
M>7 mean 132 yr s 105 yr
Estimated probability in 30 yrs 7-51%
EARTHQUAKE RECURRENCE AT
SUBDUCTION ZONES
IS COMPLICATED
In many subduction zones, thrust
earthquakes have patterns in
space and time. Large
earthquakes occurred in the
Nankai trough area of Japan
approximately every 125 years
since 1498 with similar fault areas
In some cases entire region seems
to have slipped at once; in others
slip was divided into several
events over a few years.
Repeatability suggests that a
segment that has not slipped for
some time is a gap due for an
earthquake, but it’s hard to use
this concept well because of
variability
GAP?
NOTHING YET
Ando, 1975
EARTHQUAKE PREDICTION?
Because little is known about the fundamental physics of faulting, many
attempts to predict earthquakes searched for precursors, observable
behavior that precedes earthquakes. To date, search has proved
generally unsuccessful
In one hypothesis, all earthquakes start off as tiny earthquakes, which
happen frequently, but only a few cascade via random failure process
into large earthquakes
This hypothesis draws on ideas from nonlinear dynamics or chaos theory,
in which small perturbations can grow to have unpredictable large
consequences. These ideas were posed in terms of the possibility that
minuscule disturbances do not affect the overall frequency of storms but
can modify when they occur
If so, there is nothing special about those tiny earthquakes that happen
to grow into large ones, the interval between large earthquakes is highly
variable and no observable precursors should occur before them. Thus
earthquake prediction is either impossible or nearly so.
“It’s hard to predict earthquakes, especially before they happen”
PLATE TECTONICS IS
DESTRUCTIVE TO HUMAN
SOCIETY
Mt Saint Helens
1980 eruption
USGS
1989 Loma
Prieta
earthquake
BUT PLATE TECTONICS IS
ALSO CRUCIAL FOR
HUMAN LIFE
Plate boundary volcanism produces
atmospheric gases (carbon dioxide
CO2 ; water H2O) needed to support
life and keep planet warm enough
for life ("greenhouse" )
May explain how life evolved on
earth (at midocean ridge hot
springs)
Plate tectonics raises continents
above sea level
Plate tectonics produces mineral
resources including fossil fuels
Press & Siever
“CIVILIZATION EXISTS
BY GEOLOGICAL
CONSENT”
The same geologic
processes that make our
planet habitable also
make it dangerous