Earthquake and Tsunami:
Maps, charts and sequence of events
Collected by George Weber
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Table of contents
1. The cause: moving geological plates 2. The first disaster: the earthquake |
1. The cause: moving geological plates
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On Average the Indo-Australian plate moves below the Eurasian plate at around 70 mm per year. Often, however, the plates get locked and move very little for many years and pressure builds up. When the accumulated pressure is suddenly released, a major earthquake results. This is what happened on 26th December 2004 below Sumatra.
2. The first disaster: the earthquake of 26th December 2004
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(left)
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3. The second disaster: a Tsunami is set off
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Chart from |
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The red lines show the tsunami front at half-hourly intervals. The background shows the sea depth contours and is from Manfred Leier, World Atlas of the Oceans, 2000, Firefly Books, Buffalo NY, USA. From the epicenter of the primary earthquake (1), the tsunami spreads out at, initially, around 700 km/h and with a starting height of 37 m. By the time the wavefront has reached Banda Aceh (3), its height has already been reduced to "only" 12 m, when reaching the island of Sabang (4) it is 6 m and when reaching the coast near Sigli (5) east of Bandar Aceh it is 5 m in height. The estimates of the tunami's early height are based on the extent and distance from the sea of damage caused. After clearing the northern tip of Sumatra, the tsunami does not lose significant hight anymore but instead slows down in the shallower waters. When the Tsunami reaches the Thai island of Phuket (6) it still produces heights of 4.5 m (Karon beach) and 5.5 m (Patong beach). Because the power of the tsunami was deflected by Simeulue island (2) immediately to the south of the epicentre and by the west coast of Sumatra, much of the wave energy was deflected to the west and the north. The short time delay between initial and deflected wave energy also caused two tsunamis to move closely together northwards to the Nicobar (7) and Andaman (8) islands. Coastlines and islands with significant loss of life and serious coastal damage are coloured red.
For photographs of the damage caused by the tsunami, see Pictures |
The map below shows just how far and how quickly the tsunami travelled and how far. Human casualties were reported from East African beaches 7-8 hours after the main earthquake near Sumatra. The height of the tsunami had reduced to around 0.5 m by the time it reached the African coast. This may not sound much but if someone is taken completely by surprise, even such a relatively small wave can still be deadly.
The red lines show the progress of the tsunami across the Indian Ocean in half-hourly intervals. It is noticeable that the speed of the tsunami's advance is not significantly slowed down as long as the wave moves in deep waters.
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1. Sri Lanka 2. Andaman islands 3. Nicobar islands 4. Simeulue island 5. Nias island 6. Mentawai islands 7. Maldive islands 8. Seychelle islands |
The wave hight in meters (m) at any time during the tsunami
(modelled)
(adapted and simplified from Quirin Schiermeier, "On the Trail of
Destruction", Nature 433:350-353, 27th January 2005.
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1 m = 3.28 ft. |
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Arrival time (local) 26th December 2004, and max. height of the tsunami Kata beach: 10:05 hours, max. height 4 m (13.1 ft) Patong beach: 10:06 hours, max height 5.5 m (18 ft) Kamala beach: 10:07 hours, max. height 5.3 m (17.5 ft) Khao Lak resort: 10:11 hours, max. height 10.6 m (34.7 ft)
Sea levels: 1. light blue: undisturbed, normal 2. darker blue: drop of sea level ahead of the tsunami (the "false ebb") 3. red: tsunami (in several waves) 4. violet: weakening of the tsunami, violently disturbed sea 5. darker blue: lower to almost normal sea level, sea still very disturbed |
The Sequence of events on 26th December 2004
26 December 2004
07:58 (local time at Aceh, northwest Sumatra, Indonesia). 60 km off the west coast of northern Sumatra, at 10 km depth, the Indo-Australian plate slides further under the Eurasian plate which is instantly lifted by about 10 m. The energy released is equivalent to around 10,000 atomic bombs. A gigantic volume of water is set in motion in the form of a monstrous wave that moves off in all directions. Initially the speed of this wave is 700 km/h and its height 37 m.
07:59. The official geophysicist on duty at Padang, Indonesia, notes that his seismopraph has recorded an earthquake ofintensity 8 on the Richter scale. He tries to notify the National Earthquake Centre in Jakarta but cannot get through.
08:14. The Pacific Tsunami Warning Centre registers an earthquake. "I know at once that this was no puny thing, perhaps a 7", said someone at the Center. Together with a colleague, he does some detailed calculations and reaches the conclusion that the quake must have been an 8.0 on the Richter scale. This news is distributed in a Bulletin that goes to many countries, among them Indonesia and Thailand. Other coastal regions of the Indian Ocean do not get the news since they are not connected to the warning system for the Pacific Ocean. In Thailand there are discussions if perhaps the quake had started a Tsunami. On the interest of tourism it is decided not to give out a warning. "Five years ago we gave such a warning after an earthquake in Papua-Newguinea, but the tourism authority complained and told us that this was damaging the tourist industry," a seismologist said in Bangkok.
08:20. The Tsunami breaks over the Sumatran city of Banda Aceh.
08:31. In Australia, an alarmed official sends a Tsunami warning to all Australian embassies. Endangered countries are not warned, apparently out of fear that diplomatic protocol could be broken. Worldwide the most highly equipped earthquake observation center with 300 monitoring stations is the organsiation to monitor observation of the trreaty prohibiting nuclear test explosions, based in Vienna/Austria. This organisation, which ould be best qualified to evaluate the incoming signals and issue warnings, remains quiet. The organisation's computers note the situation without human help. It is a public holiday and no staff are present.
08:45. The two scientists at the Pacific Tsunami Warnuing Centre refine their analyses. They now find that the quake had a force of 8.5. Now seriously worried, they call their boss. He sugggests that a new warning is issued but he does not think that a quake of this magnitude could cause a destructive Tsunami posing a threat.
08:54. The meteorological service of India sends a warning per fax - unfortunately not to the responsible minister of science but to his predecessor who has been out of office since the change of government in May 2004. One hour later, he sends another fax, this time to the responsible control centre at the Ministry of the Interior. Another hour passes before the cabinet is informed - at that time many thousands are already dead. The country "leading worldwide in call centres, did not manage to use telephones in such a case", one commentator said.
08:59. Agence France Press reports the earthquake but not the tsunami.
09:04. The Pacific Tsunami Warning Center on Hawaii corrects the strength of the earthquake in its bulletin to 8.5 and mentions the possibility of a local tsunami. The connection between the strength of an earthquake and the tsunami is not clear-cut: not every earthquake lifts the sea floor and causes a tsunami.
09:50. The tsunami reaches the Thai holiday resort of Phuket. A little later it reaches the coastsof southern India and Sri Lanka.
10:31. The Pacific Tsunami Warning Centre first sees news bulletins of a news agency on the internet where deaths in Sri Lanka are reported. For them, this is the first hint at the power of the tsunami. They cocnluded that "more will die." They try to send more warnings to the region but find that they "do not have the telephone number of a single person in that area".
10:40. News agencies report firth deaths in Phuket.
11:00. The British BBC reports 150 dead in Sri Lanka. Thai officials confirm 4 dead in Phuket.
11:05. The tsunami reaches Male, the capital of the Maldive islands. "The islands are only about 1 m above sea level and a wave of 1.5 m went right over us," says a government official.
12:25. The Tsunami spreads further in the Indian Ocean. Scientists from the American Harvard University send out an E-mail in which they state that they have calculated a force 8.9 on the Richterscale for the earthquake. That means that the quake was ten times as strong as originally assumed. Now it becomes clear why the quake could cause such a monstrous tsunami. The last quake with comparable strength took place 40 years ago in Alaska.
13:01. The Pacific Tsunami Warning Centre issues a warning that tsunamis could form in the western parts of the Indian Ocean.
14:00-15:00. The tsunami reaches the coasts of Somalia and Kenya in eastern Africa.
15:00. The news agencies now report at least 150 along the coast of southern India, 400 dead in Sri Lanka and 21 dead in Phuket, among them some tourists.
Evening. There is talk of 11,000 dead.
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For casualty figures etc, see |
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Last changed: 15 Feb 2005
Epicenter
35 to 12 m
12 to 4 m
4 to 2 m
2 to 1 m
1 to 0.6 m
0.6 to 0.4 m
0.4 to 0.2 m
0.2 to 0.1 m
not significantly affected