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The M9.0 Andaman Islands-Sumatra Earthquake and Tsunami of 26 December 2004 L. Braile, Purdue University email@example.com , www.eas.purdue.edu/~braile Tectonic Setting Schematic plate tectonic setting for tsunami generation NOAA Historical Seismicity
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L. Braile, Purdue Universitybraile@purdue.edu,
(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 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).
~1200 km of the plate boundary moved, max. displacement ~ 20 m (?, preliminary est.)
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/20041226tsun.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
~135 degrees distance
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.
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?
Open Quick Time simulation (see these websites)
Note distance of propagation and reflection of waves
To view Quick Time movie of Tsunami simulation from NOAA
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.