UPDATE 4 -- Huge earthquakes strike off Indonesia, generate small tsunamis

[News_Editor]

UPDATE 4 -- Huge earthquakes strike off Indonesia, generate small tsunamis

2012-04-12 06:59:29 GMT+7 (ICT)

JAKARTA, INDONESIA (BNO NEWS) -- Two major earthquakes struck off the west coast of northern Sumatra in Indonesia on Wednesday afternoon, generating small tsunamis and shaking buildings as far away as Singapore, Thailand, Sri Lanka, Malaysia, Bangladesh and India, but causing little actual damage.

The first earthquake at 2:38 p.m. local time (0838 GMT) had a preliminary magnitude of 8.6 and was centered about 434 kilometers (269 miles) southwest of Banda Aceh, the capital of Aceh province on the northern tip of Sumatra. It struck about 22.9 kilometers (14.2 miles) deep, making it a shallow earthquake, according to the United States Geological Survey (USGS).

Several hours later, at 4.43 p.m. local time (1047 GMT), a large aftershock with a preliminary magnitude of 8.2 struck about 618 kilometers (384 miles) south-southwest of Banda Aceh at a depth of approximately 16.4 kilometers (10.2 miles), according to the USGS. Seismologists also reported a series of other aftershocks in the 6-range.

Indonesia's seismological agency immediately issued a tsunami warning after both earthquakes, while the Pacific Tsunami Warning Center issued an Indian Ocean-wide tsunami watch. Both the tsunami warnings and watches were later canceled after only small tsunamis were generated.

"Sea level readings now indicate that the threat has diminished or is over for most areas. Therefore the tsunami watch issued by this center is now canceled," the Pacific Tsunami Warning Center said in a bulletin. It said monitoring gauges mounted on buoys recorded a tsunami of 1.06 meter (3.5 feet) relative to normal sea levels near the Indonesian city of Meulaboh in Aceh. Smaller tsunamis were recorded at Australia's Cocos Island, the Sri Lankan port city of Trincomalee, and in Thailand.

Fears of a repeat of the earthquake and tsunami disaster in the Indian Ocean in 2004 failed to materialize due to the nature of the earthquake. The earthquake in December 2004 was a magnitude 9.1, significantly stronger than Wednesday's earthquakes, but struck the same region. The first earthquake on Wednesday struck about 328 kilometers (204 miles) southwest of the earthquake in 2004, much further away from the coast.

Most importantly, Wednesday's earthquakes occurred in the middle of an oceanic plate, causing the faults in the crust to move side to side instead of up and down. An earthquake at a plate boundary along a subduction zone, where one tectonic plate is diving beneath another, has a much greater potential to generate a tsunami because it displaces the ocean floor, causing a displacement of water.

Wednesday's main earthquake lasted approximately five minutes and was felt across the region, prompting hundreds of thousands of people to run out of buildings. Electricity and mobile phone networks were briefly interrupted in Banda Aceh but, despite widespread panic, there were no reports of major damage or casualties as a direct result of the earthquake.

The Jakarta Globe reported that a 70-year-old man in Banda Aceh died from a heart attack as evacuating people screamed in panic.

Indonesia is on the so-called 'Pacific Ring of Fire', an arc of fault lines circling the Pacific Basin that is prone to frequent and large earthquakes. On December 26, 2004, one of the most powerful earthquakes ever recorded struck off the west coast of Sumatra in Indonesia. The 9.1-magnitude earthquake unleashed a deadly tsunami, striking scores of countries in the region, killing at least 227,898 people.

Most recently, on January 11, a powerful 7.1-magnitude earthquake struck about 423 kilometers (262 miles) southwest of Banda Aceh at a depth of about 10 kilometers (6.2 miles). Tremors could be felt in Banda Aceh where residents fled from buildings and rushed to higher ground, but no tsunami was generated.

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