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.
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 aftershocks in the 6-range.
Indonesia's seismological agency immediately issued a tsunami warning for local coastlines for both coastlines, but there were no immediate reports of major tsunamis. The Pacific Tsunami Warning Center did not issue a warning, but initially issued an Indian Ocean-wide tsunami watch. The tsunami watch was later canceled for all countries, although several countries have continued their national alerts.
"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.
At a joint press conference with British Prime Minister David Cameron following the first earthquake, Indonesian President Susilo Bambang Yudhoyono said he ordered a disaster relief team to fly to Aceh, where there were reports of some panic but no immediate reports of significant damage or casualties. He said there was no risk of a major tsunami following the first quake and said the situation is 'under control'.
Officials at the Malaysian Meteorological Department said they had no immediate reports of tsunami waves but a tsunami warning has been issued as a precaution for several states on the west coast of Peninsular Malaysia, where tremors during the first earthquake lasted for about 5 minutes. "We decided to order an evacuation along the coastal states of Penang, Perlis, Perak, Kedah and Langkawi," an official said.
The National Tsunami Early Warning Center at Sri Lanka's Department of Meteorology issued a tsunami warning for the island following the first earthquake. "As the earthquake near Sumatra island at 02:08 pm today has generated tsunami that will affect Sri Lanka, those living near and along the Eastern and Southern coastal regions are advised to evacuate to safe places immediately," the center said in a bulletin.
In the Thai capital of Bangkok, some people reported feeling light shaking as a result of the first earthquake. "I was sitting at my desk on the top floor of an 11-story building in Bangkok and suddenly felt my head slightly swaying left to right," said Mike Amy. "I had felt the previous earthquake in Myanmar (Burma) in a similar way."
The Thai National Department of Disaster Prevention and Mitigation issued a tsunami warning for six provinces along the country's western coast, including the popular tourist destinations of Phuket, Krabi and Phang-Nga. The warning was later downgraded to monitoring status only, indicating there is no significant tsunami threat to Thailand.
The Indian government immediately issued a tsunami warning for the Andaman and Nicobar Islands and the coastal areas of Andhra Pradesh and Tamil Nadu. But the warnings were later canceled after Indian experts determined the earthquakes are unlikely to generate a major tsunami because there was no vertical displacement of water.
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.