Magnitude 9.0 - OFF THE WEST COAST OF NORTHERN SUMATRA
2004 December 26 00:58:53 UTC
Southeast of Saline Seismograph - Extracted Earthquake Off the West Coast of Sumatra
Southeast of Saline Seismograph - 24 Hour Seismic Graph for December 25th & 26th
 

Magnitude

9.0
Date-Time Sunday, December 26, 2004 at 00:58:53 (UTC) = Coordinated Universal Time
Sunday, December 26, 2004 at 7:58:53 AM = local time at epicenter
Location 3.316°N, 95.855°E
Depth 30 km (18.6 miles) set by location program
Region OFF THE WEST COAST OF NORTHERN SUMATRA
Reference 250 km (155 miles) SSE of Banda Aceh, Sumatra, Indonesia
310 km (195 miles) W of Medan, Sumatra, Indonesia
1260 km (780 miles) SSW of BANGKOK, Thailand
1605 km (990 miles) NW of JAKARTA, Java, Indonesia
Source USGS NEIC (WDCS-D)
Remarks At least 79,900 people were killed by the earthquake and tsunami in Indonesia. Tsunamis killed at least 41,000 people in Sri Lanka, 10,000 in India, 4,000 in Thailand, 120 in Somalia, 90 in Myanmar, 66 in Malaysia, 46 in Maldives, 10 in Tanzania, 2 in Bangladesh, 1 in Seychelles and 1 in Kenya. Tsunamis caused damage in Madagascar and Mauritius and also occurred on Cocos Island and Reunion. The tsunami crossed into the Pacific Ocean and was recorded in New Zealand and along the west coast of South and North America. The earthquake was felt (VIII) at Banda Aceh and (V) at Medan, Sumatra and (II-IV) in parts of Bangladesh, India, Malaysia, Maldives, Myanmar, Singapore, Sri Lanka and Thailand. A mud volcano near Baratang, Andaman Islands began erupting on December 28. This is the fourth largest earthquake in the world since 1900 and is the largest since the 1964 Prince William Sound, Alaska earthquake.
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Map of the Indian Ocean
Technical Information   The devastating megathrust earthquake of December 26, 2004, occurred on the interface of the India and Burma plates and was caused by the release of stresses that develop as the India plate subducts beneath the overriding Burma plate. The India plate begins its descent into the mantle at the Sunda trench, which lies to the west of the earthquake's epicenter. The trench is the surface expression of the plate interface between the Australia and India plates, situated to the southwest of the trench, and the Burma and Sunda plates, situated to the northeast.

In the region of the earthquake, the India plate moves toward the northeast at a rate of about 6 cm/year relative to the Burma plate. This results in oblique convergence at the Sunda trench. The oblique motion is partitioned into thrust-faulting, which occurs on the plate-interface and which involves slip directed perpendicular to the trench, and strike-slip faulting, which occurs several hundred kilometers to the east of the trench and involves slip directed parallel to the trench. The December 26 earthquake occurred as the result of thrust-faulting.

Preliminary locations of larger aftershocks following the megathrust earthquake show that approximately 1200 km of the plate boundary slipped as a result of the earthquake. By comparison with other large megathrust earthquakes, the width of the causative fault-rupture was likely over one-hundred km. From the size of the earthquake, it is likely that the average displacement on the fault plane was about fifteen meters. The sea floor overlying the thrust fault would have been uplifted by several meters as a result of the earthquake. The above estimates of fault-dimensions and displacement will be refined in the near future as the result of detailed analyses of the earthquake waves.

The world's largest recorded earthquakes have all been megathrust events, occurring where one tectonic plate subducts beneath another. These include:

the magnitude 9.5 1960 Chile earthquake, the magnitude 9.2 1964 Prince William Sound, Alaska, earthquake, the magnitude 9.1 1957 Andreanof Islands, Alaska, earthquake, and the magnitude 9.0 1952 Kamchatka earthquake. As with the recent event, megathrust earthquakes often generate large tsunamis that cause damage over a much wider area than is directly affected by ground shaking near the earthquake's rupture.