Engineering Ethics

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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