Discovery Lecture, Dept. of Earth and Atmospheric Sciences, Purdue University February 28, 2005 Prof. Larry Braile, (Despite the popularity of this image, tsunami waves do not normally look like this.) The M9.0 Andaman Islands- Sumatra Earthquake and Tsunami of 26 December 2004

Tectonic Setting USGS

Schematic plate tectonic setting for tsunami generation NOAA Commonly, in mega-thrust earthquakes, a very large area of the ocean floor is uplifted TRENCH

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.)

Question: What other great (M > 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 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 ( USGS Sumatra earthquakes FAQs

USGS Main shock and aftershocks ~1200 km of the plate boundary moved, max. displacement ~ 15 m (?, preliminary est.)

24-hour seismograph record ~135 degrees distance

Seismogram

DescriptorMagnitudeAverage Annually Great8 and higher1 ¹ Major ² Strong ² Moderate ² Light ,000 (est.) Minor ,000 (est.) Very Minor ,300,000 (est.) ¹ Based on observations since ² Based on observations since Worldwide earthquakes per year (from USGS):

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.

Magnitude of earthquake is controlled by fault length that ruptures (data for diagram generated using Seismic/Eruption program) Magnitude versus fault length (determined from aftershock zone length) for various earthquakes (Alaska, 1964; Denali, 2002; Landers, 1992; Loma Prieta, 1989; Northridge, 1994, etc.). Results were quickly obtained using Seismic/Eruption views. Alaska, 1964 Denali, 2002 Landers, 1992 Sumatra, 2004

Largest earthquakes, USGS

LocationDate UTCMagnitude Coordinates 1. Chile S73.05 W 2. Prince William Sound, Alaska N W 3. Andreanof Islands, Alaska N W 4. Kamchatka N E 5. Off the West Coast of Northern Sumatra N95.78 E 6. Off the Coast of Ecuador N81.5 W 7. Rat Islands, Alaska N E 8. Assam - Tibet N96.5 E 9. Kamchatka N161.0 E 10. Banda Sea, Indonesia S E 11. Kuril Islands N149.6 E Largest earthquakes, USGS

DateMagn.Max HtKilledLocationComments m170NicaraguaMeasured Pacific-wide m1000 Flores Island m200Hokkaido m220Java m11 Kuril Islands Measured Pacific-wide m70Mindoro m12Peru m2000 New Guinea m50PeruMeasured Pacific-wide Some recent Tsunamis NOAA

DateMagn. Max. Ht. KilledLocationComments m40000Taiwan ?10253Indonesia m36000Indonesia Krakatau Eruption ?15000Indonesia m173Aleutians Many deaths in Hilo, Hawaii m534Chile Largest historical earthquake m115Alaska ?22778Guatemala m ~217,000 (4/8/05 est.) N. Sumatra Greatest number of fatalities Some Notable Tsunamis

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 ( /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 than 300 fatalities /11/24 South coast of the western Sumatra, estimated rupture from 1 S to 6 S latitude. Huge wave flooded all southern part of the western Sumatra. Numerous victims /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 /02/16 Exceptionally strong earthquake affected all the western coast of Sumatra. Several thousand fatalities Krakatau explosion 36,000 fatalities USGS

Tsunami travel time (hours; simulation) NOAA

Tsunami wave height (cm; simulation) NOAA

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

Animation courtesy of Dr. Dan Russell, Kettering University Water waves animation Direction of propagation

Tsunami simulation

Show video segments of tsunami waves and damage Source:

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

Tsunami wave trough, Sri Lanka coast

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 or gather fish or shells at that time.

Tsunami wave, Sri Lanka; note strong current

Banda Aceh, Sumatra, before tsunami

Banda Aceh, Sumatra, after tsunami Also:

Factors that increased loss of life and damage 1. Magnitude of earthquake – largest event in 40 years; and location near highly populated coastlines. 2. Approximately north-south orientation of the plate boundary that focused energy to the west and east.

4. the lack of a tsunami warning system and adequate rapid communication systems

DART tsunami warning system NOAA DART: Deep ocean Assessment and Reporting of Tsunamis

5. the lack of adequate public awareness of tsunamis and tsunami hazards (Although the 26 December 2004 earthquake and tsunami was a tragic event, two benefits are: that countries are now committed to installing effective tsunami warning systems worldwide, and, there is greatly increased public awareness of tsunamis and tsunami hazards.)

Many people watched the waves approach and did not take action until too late, or went out to explore the beach during a wave trough

6. the common building construction characteristics in developing countries

Some significant observations and occurrences Tsunami warning system could have saved many lives (many deaths occurred as tsunami hit over two hours after the earthquake). In Sumatra, experiencing the strong earthquake caused some people to move to higher ground; however, many did not. Apparently, many animals sensed the seismic waves, the sound of the tsunami waves approaching, or the vibration of the ground caused by crashing ocean waves, and moved to higher ground. Many people watched the waves approach or went out to explore the beach during a wave trough (receding water). A 10-year old girl is credited with saving about 100 people on a beach in Thailand when she noticed the water receding suddenly and told her mother that it looked like a Tsunami was approaching – a lesson that she had recently learned in school.

Earthquake and Tsunami Safety Earthquake safety – “Duck and cover”. Tsunami safety (when in a coastal, near-sea-level area; two situations, local EQ or distant EQ): If you feel strong shaking for 15+ seconds, after shaking, move to higher ground. If there is a tsunami warning, or if you observe unusual waves (appear to be large and rapid tidal changes, or water recedes), move to higher ground. Do not return until event is over; a tsunami includes multiple waves sometimes separated by minutes and may last for hours.

7. the growth of population and building in hazardous, low-elevation coastal areas Global population map

Close-up of Global population map

Global seismic hazard map

Close-up of Global seismic hazard map

December 26, 2004 Great subduction thrust fault earthquake

Largest historical natural disasters The same geologic processes that make our planet habitable also make it dangerous Seth Stein, Northwestern Univ.