TECTONIC PROCESSES AND
HAZARDS CASE STUDIES
2004 Asian Tsunami
Hazard event
- Caused by an underwater earthquake with an epicentre off the west coast of Sumatra,
Indonesia. The 3rd largest ever recorded earthquake (9.1) was caused by a rupture along the
fault along the destructive plate margin where the Indo-Australian plate is sliding under the
Eurasian plate (megathrust event) and had the longest faulting duration ever at 8-10
minutes. An estimated 1,600km of fault surface slipped around 15m along the subduction
zone.
- The underwater seismic activity offshore triggered a series of massive tsunami waves up to
30m high, which devasted communities off the coastline of the Indian Ocean.
- The sudden vertical rise of the seabed displaced a huge volume of water and sent the
tsunami waves travelling at up to 500mph towards coastlines with an arrival time of
anywhere between 15 minutes and seven hours. The tsunami travelled as far as Africa and
arrived with enough force to damage property and endanger people’s lives (300 dead in
Africa)
PPP:
Hawaii Pacific Tsunami warning centre picked up the seismic signals from the earthquake and warned
of a tsunami, issuing a tsunami bulletin, but had no real idea when or whether the tsunami was
actually going to come, due to the lack of monitoring equipment for tsunamis. The lack of water level
sensors, warning systems and disaster plans contributed to the catastrophic impact of the tsunami.
There was a several hour delay between the earthquake and the tsunami waves arriving at coastlines
across Asia, but the lack of a tsunami detection system (as they do not present clearly in deep water)
meant that the arrival of the tsunami came as a surprise to almost all of the victims. On some
eastern coastlines, the sea temporarily withdrew from the coast, and this caused many to actually
visit the coast to witness the phenomenon. Some of the few areas to evacuate included: the
Indonesian island Simeulue where locals felt the shaking of the ground and fled to higher ground, a
beach in North Phuket City where a young British tourist recognised the signs of the receding water
and helped others to escape to higher ground, and in Kamala Bay north of Phuket the signs were also
identified by a Biologist who helped others evacuate.
Area involved
- While Thailand is today classified as an NEE, it was a lower income country in 2004 and had a
low GDP, with many people on a very low income.
- Thailand beaches filled with tourist accommodations that were flimsy beach huts that were
easily swept away.
- Lack of sea defences
Impacts of the event
SOCIAL
, - 227,898 estimated deaths (many being tourists on the beaches of Thailand), 1.7 million
people displaced
- 13 countries affected, with the worst being Indonesia
- Outbreak of diseases such as cholera due to mixing of seawater, freshwater and sewage
water
- Over 140,000 houses destroyed
ECONOMIC
- Estimated cost of the damage just under $10 billion
- Fishing industry devastated – Sri Lanka’s fishing fleet 60% destroyed
- Loss of earnings from tourism – Phuket’s numbers dropped 80% in 2005
ENVIRONMENTAL
- Some smaller islands in the Indian Ocean completely destroyed
- 8 million litres of oil escaped from oil plants in Indonesia
- Huge volumes of debris washed up across the countries affected meant a huge clean-up
operation
- Effects on agriculture in farming areas as soil fertility ruined by salinisation and dumped
debris, farmlands eroded
- Coral reefs and coastal wetlands damaged
INFLUENCING FACTORS
- The lack of a detection AND warning system across the Indian Ocean meant that most
countries had relatively no information on the arrival of the tsunami and therefore were
completely unaware when it struck.
- Mainly LICs so not strong infrastructure etc, meaning buildings easily washed away
- Large tourist numbers across Thailand (reliant on tourism for economy) and other countries
meant many flimsy buildings on beaches, 9000 tourists killed.
Ten years on, many communities and coastal villages had rebuilt their lives, although many migrated
from the area. New cities were built on top of the ruins and outside aid greatly helped in the short
term. New tsunami warning system to prevent events reoccurring.
2011 Tohoku Tsunami
Hazard event
Japan is situated on the Ring of Fire, one of the most tectonically active zones in the world.
On March 11th, 2011, it experienced one of its largest tectonic events, a magnitude 9.0
earthquake 70km off the coast of the island of Honshu, at a destructive plate margin where
the Pacific and Eurasian plate meet. The cause of the quake was a rupture in the subduction
zone associated with the Japanese trench: scientists drilled into the subduction zone soon
after the quake and discovered a thin, slippery layer of clay which they believed allowed the
two plates to slide such a large distance (50m). Hundreds of aftershocks followed in the
coming days and weeks, with 2 over magnitude 7.0.
The megathrust earthquake lasted 6 minutes and caused the island of Honshu to move east
by 2.4m. The seabed by the focus of the earthquake rose 7m, displacing a volume of water
