Magnitude 9.0 COSTA OESTE A NORTE DE SUMATRA Domingo, 26 de Dezembro 2004 às 00:58:53 UTC

Eis algumas informações que reuni ao longo desta semana sobre o sismo de Sumatra. Não sou sismóloga nem geofísica apenas uma engenheira do Território que há já alguns anos se apaixonou pela área do risco sísmico. Infelizmente esta é uma área de pouco interesse para os nossos governantes e, consequentemente os investimentos realizados são escassos. Gosto de salvar vidas ou melhor, penso que o faço uma vez que os projectos quando acabados não são implementados com rigor e muitas vezes "não dá jeito" dar a conhecer a realidade em que vivemos.

"The Indonesian region is one of the most seismically active zones of the earth; at the same time it has a leading position from the point of view of active and potentially active volcanoes. It is a typical island-arc structure with its characteristic physiographic features, such as a deep oceanic trench, a geanticline belt, a volcanic inner arc and a marginal basin.
The earthquake of December, 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 earthquake was felt (VIII) at Banda Aceh and (V) at Medan, Sumatra. It was also felt in Bangladesh, India, Malaysia, Maldives, Myanmar, Singapore, Sri Lanka and Thailand.

EFFECTS:
In Sri Lanka, the southeastern coastline was the worst-hit. In this densely populated area many villages along the ocean were washed off the map. Galle was a scene of total catastrophe. Almost the entire seafront was obliterated, with no buildings within 100 meters of the waterfront escaping undamaged.

In India the Andaman Islands, Nicobar Islands, Kerala, Tamil Nadu, Chennai, Andhra Pradesh were all affected.
With half of the casualties being reported from Sumatra, Indonesia—the region nearest to the earthquake’s epicenter—international relief organization officials warn that the overall casualty figures could rise to over 100,000. The death toll in Indonesia's Aceh province from a quake and tsunami that struck on Sunday might reach between 50,000 and 80,000. There were about 10,000 deaths in Meulaboh, the south-coast town nearest to the epicenter. Surveillance from flights over the town indicated it had been “wiped out”, with up to 80 per cent of buildings destroyed, raising fears for the fate of the area's 100,000 residents.

In Thailand, this caused great loss of life and destruction to buildings and infrastructure in the popular resort areas of Phuket, Phi Phi Island, Krabi, and other smaller islands in that vicinity. Along the eastern coast of Phuket island, waves crashed over Rassada Pier as passengers were waiting to board ferries for Phi Phi Island. The Laguna Phuket was protected from a direct hit by the headland to its South and thus spared the serious damage reported from other areas of the island. Other areas affected included Bang Tao Beach, Kamala Beach, Patong Beach, Kata Beach, Karon Beach, Nai Harn Beach and Phuket Fantasea. There was total destruction of resort properties and infrastructure on the Phi Phi islands, and all operations had ceased. Phuket's Patong beach along the west of the island took the bulk of the damage, and two-thirds of Thailand's fatalities occurred there.

The Maldives’s only international airport on the tiny island of Hululle reopened early on 27 December, after workers pumped out water that had inundated the runway. The entire island of Dhiffushi, a prime tourist destination, was submerged and would have to be rebuilt.
In Myanmar damage was reported only in the southern archipelago, with minimal to no impact reported at Ngapali, Chauntha, and Ngwe Saung beaches.

Praslin Island in Seychelles was also hit."