Geoscience Reference
In-Depth Information
Figure 13.27 The epicenter of the Sumatra-Andaman earthquake in
December 2004.
The initial earthquake (at red dot) measured 9.1 on the
Richter scale and was the second most powerful quake on record. As a
result of this earthquake, a massive tsunami was created that killed over
200,000 people along the coasts of the Indian Ocean. The yellow dots show
the location of aftershocks.
Andaman Islands
tsunami
, which is a kind of seismic wave that radiates out-
ward from the disturbance zone. Tsunamis form and radi-
ate outward in much the same way that water is displaced
when you flick your hand upward while holding it beneath
surface. Although tsunamis can develop due to a volcanic
eruption or landslide, they are most commonly associated
with earthquakes.
Once the water was displaced due to the Sumatra-Andaman
earthquake, a tsunami rapidly radiated outward in the ocean
(Figure 13.28c). The tsunami subsequently raced across the
Indian Ocean at speeds ranging from 500 km/h to 1000 km/h
(310 mi/h to 620 mi/h). It reached the northwest coast of
Sumatra to the east in about 15 minutes and the southern
Car Nicobar
Nicobar Islands
Great Nicobar
Sumatra
Tsunami
A destructive sea wave caused by a disturbance
within the ocean, such as an earthquake, volcanic eruption, or
landslide.
Indian Ocean
Sumatra
Burma plate
Stress gradually builds at
subduction zone along
India and Burma plate boundary.
India plate
(a) Before the earthquake
Burma plate
Earthquake causes Burma plate
to thrust up and over the India plate
several meters, causing massive
displacement of overlying water.
Figure 13.28 Evolution of
the 2004 tsunami in the
Indian Ocean.
(a) Tectonic
stress builds up where the
India plate subducts beneath
the Burma plate along the
Sumatra Fault. (
Source
: Geo-
science Australia.) (b) Pent-up
stress is suddenly released in
a massive earthquake. In ad-
dition to significant horizontal
movement, the Burma plate
is thrust up and over the India
plate. The vertical movement
displaces water in the over-
lying Indian Ocean. (c) After
the water is initially displaced,
seismic waves rapidly radiate
outward in the water.
India plate
(b) Earthquake strikes
Tsunami spreads
West
East
Tsunami spreads rapidly,
reaching the nearby coast of
Sumatra to the east in 15 minutes
and the more distant shore of
Somalia to the west in 7 hours.
Burma plate
India plate
(c) Tsunami radiates outward along the length of fault rupture
