Chapter 15
2004: Indian Ocean Tsunami
177
THE REPORTED STORY
The New York Times Abstract:
World’s most powerful earthquake in 40 years erupts underwater off
Indonesian island of Sumatra, sending walls of water barreling thousands of
miles and killing more than 13,000 people in half dozen countries across South
and Southeast Asia; thousands more are missing or unreachable; earthquake,
measuring 9.0 in magnitude, sets off tsunamis with speeds of 500 miles an hour
and more, crashing into coastal areas of Sri Lanka, India, Thailand, Indonesia,
Maldives and Malaysia; 40-foot-high walls of water devour everything and
everyone in their paths; force is felt 3,000 miles away in Somalia, on eastern
coast of Africa, where nine people are reported killed; aid agencies rush staff
and equipment to region, warning that rotting bodies threaten health and water
supplies; none of most affected countries have warning systems in place to
detect coming onslaught and alert their citizens to move away from coastline;
seismologists with United States Geological Survey say ocean west of Sumatra
and island chains to its north are hot zone for earthquakes because of nonstop
collision occurring there between India plate beneath Indian Ocean seabed and
Burma plate under islands and that part of continent. (Waldman, 2004)
THE BACK STORY
T
HE SUMATRA-ANDAMAN EARTHQUAKE
When two oceanic plates collide, the younger tectonic plate rides over
the edge of the older plate. This occurs because the younger plate is less
dense. The older plate bends and plunges deeply into the Earth, creating a
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178 Engineering Ethics: An Industrial Perspective
Figure 15.1 Sumatra-Andaman Earthquake Map.
Courtesy of http://www.NPR.org, National Public Radio, Inc., all rights reserved.
trench at the plate interface. One example of this subduction zone is the
plunging of the Indo-Australian plate beneath the Eurasian plate.
On December 26, 2004, this fault ruptured, allowing the edge of the
Eurasian plate to spring back up. The fault slipped by as much as 50 feet in
places, averaging about 33 feet of displacement along the segment off the
northwestern tip of Sumatra, where the quake was centered. From the epi-
center, the rupture expanded along the fault at a speed of about 1.5 miles
per second toward the north-northwest, for about 720 to 780 miles.
Eventually, the northern part of the fault slipped about as much as the
southern part, uplifting and tilting the Andaman Islands (Figure 15.1).
Although most earthquakes last only a few seconds, this earthquake
lasted about 10 minutes. The seismic magnitude of the earthquake was
estimated as between 9.1 to 9.3 (NSF, 2005). The earthquake also caused
sustained vibrational free oscillations at periods greater than 1000 seconds.
These oscillations remained observable for weeks in broadband seismic
data from global networks. The frequencies and decay rates of earth’s free
oscillations offered strong constraints on our planet’s interior composition,
mineralogy, and dynamics. Upon analysis, these data are expected to
provide new perspectives on Earth’s structure (Park, 2005).
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