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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. - PowerPoint PPT Presentation
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DECEMBER 2004 INDIAN OCEAN EARTHQUAKE AND TSUNAMI
PrimaryGround shaking and surface ruptureLiquefactionLandslidesTsunami
SecondaryFiresFloods
EARTHQUAKE HAZARDS
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.
Earthquake Magnitude and Intensity
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 fault length (determined from aftershock zonelength) for various earthquakes.
Alaska, 1964
Denali, 2002
Landers, 1992
Sumatra, 2004
Magnitude versus fault length
Northridge, 1994
Loma Prieta, 1989
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
Geist, Titov and Synolakis, Tsunami: Wave of Change, Scientific American, January, 2006.
Tsunami-generating EQs and sources
India subducts beneath Burma microplateat 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
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
Sumatra earthquakes
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 yrLonger 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
Seismogram analysis shows most slip in southern 400 km
Aftershocks show slip extended almost 1200
km
C. JiERI
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 Sumatra-Andaman 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
One of the largest earthquakes since seismometer invented ~ 1900
Stein & Wysession after IRIS
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
http://staff.aist.go.jp/kenji.satake/animation.gif
Red - up motion, blue downHyndeman and Wang, 1993
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
QuickTime™ and aGIF decompressor
are needed to see this picture.
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
Tsunami generated along fault, where sea floor displaced, and spreads outward
Reached Sri Lanka in 2 hrs, India in 2-3
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
Normal tide variation
Tsunami (~1.2 m maximum wave height; note that waves are visible for over 2 days)
Geist, Titov and Synolakis, Tsunami: Wave of Change, Scientific American, January, 2006.
Wave Heights: Satellite observation vs calculated model
Tsunami wave propagation characteristics – note that as water depth becomes smaller, waves slow down, become shorter wavelength, and have larger amplitude
When the water is 10 m deep, what is the separation of the waves in minutes?
NOAA
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
Geist, Titov and Synolakis, Tsunami: Wave of Change, Scientific American, January, 2006.
Train and tracks destroyed, SW coast of Sri Lanka
Tsunami wave trough, Sri Lanka coast
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
TSUNAMI WARNING
Deep ocean buoys can measure wave heights, verify tsunami and reduce false alarms
HOWEVER, HARD TO PREDICT EARTHQUAKES recurrence is highly variable
M>7 mean 132 yr 105 yr Estimated probability in 30 yrs 7-
51%
Sieh et al., 1989Extend earthquake history
with geologic records -paleoseismology
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 Helens1980 eruption
USGS
1989 Loma Prieta earthquake
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
BUT PLATE TECTONICS IS ALSO
CRUCIAL FOR HUMAN LIFE
Press & Siever
“CIVILIZATION EXISTS BY
GEOLOGICAL CONSENT”
The same geologic processes that make our
planet habitable also make it dangerous