An 8.6-magnitude earthquake off Sumatra was a painful reminder of the tsunami that ravaged the coastlines of 12 countries and killed 220,000 people in 2004. It was also a relief and a test of preparedness.
The temblor, which struck in the late afternoon yesterday and was followed by aftershocks, triggered widespread tsunami warnings and panic in countries including Malaysia, India, Sri Lanka and Thailand. The warnings started coming down about four hours later as tsunami waves were limited to 1 meter (3.3 feet).
As night settled on the region, the situation started to return to normal after no casualties were reported and structural damage was limited to some buildings and a collapsed bridge in Aceh Besar, at an estimated loss of 2 billion rupiah ($220,000), Indonesia’s disaster management agency reported. Attention has now turned to how early warning systems and evacuation plans put in place after 2004 worked.
“The warning system worked quite well,” Smith Dharmasaraja, who headed Thailand’s National Disaster Warning Center set up after the 2004 tsunami, said today by phone. “Officials know exactly what they are supposed to do.”
Mexico City buildings also shook yesterday during a magnitude-7 quake that struck the country’s western coast 42 miles (69 kilometers) northwest of Lazaro Cardenas, in Michoacan state, at 5:55 p.m. local time, according to the U.S. Geological Survey. No damage was reported immediately in Michoacan.
The Indian Ocean quake hit 431 kilometers off the coast of Aceh, followed by aftershocks, according to the U.S. Geological Survey. That triggered tsunami warnings by national authorities and the Pacific Tsunami Warning Center, which were subsequently canceled for all areas of the Indian Ocean.
The earthquake prompted people to flee to higher ground, the airport on the Thai resort island of Phuket to close and caused a power failure in Aceh, one of Indonesia’s poorest provinces where 170,000 people died or went missing in the tsunami of 2004. An earthquake measuring above magnitude-7 will automatically cut power in Aceh, according to a Metro TV report yesterday.
Indonesia’s disaster management agency deployed three teams to coastal areas, had aircraft on standby and sent a search and rescue agency helicopter to assess the situation, Sutopo Purwo Nugroho, head of the agency’s data and information center, said in a text-message statement late yesterday.
Four people were reported to have light injuries and most residents returned to their homes during the night as electricity was restored, he said.
Early Warning System
After the magnitude-9.1 quake off Sumatra in 2004 and the resulting tsunami, which hit with little warning and caught hundreds of thousands by surprise, nations came together to increase preparedness, speed up the delivery of warnings and formulate evacuation plans.
Resorts and beaches dotting the western coastlines of countries including Thailand, Malaysia and Indonesia all have evacuation points and signs with emergency instructions for residents and vacationers.
Thailand’s beach resorts of Phuket and Krabi were among the worst-hit tourist destinations in 2004, and about half of the 5,395 people confirmed killed by the tsunami in six Thai provinces were foreigners, according to government data.
“The evacuations in Phuket and most major tourist destinations were in line with our preparation and training,” Somsak Kaosuwan, director of the Thai National Disaster Warning Center, said by phone today. “All foreigners understood the situation and fully cooperated with the evacuation orders.”
Yesterday’s earthquake also demonstrated how well the tsunami warning system worked in the region, he said.
The Pacific Tsunami Warning Center started doing tsunami warnings for the Indian Ocean in 2005 because the region didn’t have its own version. Once the Indian Ocean system gets approved by other countries and the United Nations, the U.S. will stop offering the service from Hawaii.
“This event certainly generated a tsunami that went right across the Indian Ocean basin, so yes I would say that it’s the first time there’s been an event where tsunami signals were sent all the way to Africa,” said Dan Jaksa, co-director of the Joint Australia Tsunami Warning Center at GeoScience Australia. “It’s certainly a pretty good test, and frankly it looks like it has worked very well.”
Tsunami waves were detected in the Sabang and Meulaboh districts in Aceh, the Indonesian Meteorology, Climatology and Geophysics Agency said in an e-mailed statement yesterday. The water level was 6 centimeters (2.36 inch) high in Sabang and 80 centimeters high in Meulaboh, the agency said. Aid groups including World Vision said they had rescue workers on standby.
Horizontal Versus Vertical
The epicenter of yesterday’s quake was 963 kilometers west of Kuala Lumpur and 1,797 kilometers west northwest of Jakarta, the USGS said. Aftershocks included a magnitude-8.2 temblor, according to the USGS.
“The faulting was horizontal rather than vertical and so there was no uplift of the sea floor,” which is what causes tsunamis, Kevin McCue, adjunct professor at the Central Queensland University and director at the Australian Seismology Center, said yesterday. “I expect very little damage to Sumatra and certainly no Indian Ocean-wide tsunami.”
The quake was at a depth of 33 kilometers, compared with a depth of 30 kilometers when the 2004 tsunami struck. That wave took about three hours to reach the subcontinent and killed more than 10,000 in India, mostly in the Andaman & Nicobar Islands, as well as the southern state of Tamil Nadu. It also caused damage and deaths in the Indian coastal states of Kerala and Andhra Pradesh.
Great Seismological Interest
“While it is fortunate that this earthquake caused little to no human consequence, it is of great seismological interest,” risk modelers Eqecat Inc. said in a statement. “A crustal, strike-slip earthquake of this magnitude is very unusual and indicates a previously unknown fault of considerable length at this location.”
A magnitude-9.0 earthquake off northern Japan in March last year triggered a tsunami as high as 39 meters high that left almost 20,000 people dead or missing. That temblor struck at a depth of 30 kilometers, according to the USGS. In September 2007, an 8.2-magnitude earthquake near Indonesia, located 15 kilometers deep, caused no high waves or damage in Sri Lanka and South India.
Buildings in neighboring Singapore shook after yesterday’s quake, which was initially measured at a magnitude of 8.9. Tremors were felt as far as Ho Chi Minh City and in India. Malaysia lifted its tsunami alert for coastal regions yesterday evening after tremors were earlier felt across the country. Shopping malls closed early in Penang, while about 1,000 people in villages in Kedah were ordered to evacuate their homes, the Star newspaper reported today.
‘Ring of Fire’
Indonesia’s 18,000 islands are prone to temblors because the nation sits along the Pacific’s “ring of fire” zone of active volcanoes and tectonic faults.
Yesterday’s quake was about 10 times less energetic than the one that caused the 2004 Indian Ocean tsunami, David Rothery, a volcanologist and planetary scientist at The Open University in the U.K., said in a statement.
The earthquake magnitude scale is logarithmic, meaning a magnitude 8.7 earthquake is about 23,000 times stronger than a 5.8 magnitude quake, according to the USGS. This means it would take 23,000 quakes of magnitude 5.8 to release the same amount of energy as one 8.7 earthquake.
A magnitude-9 earthquake, or the size that hit Japan last year, is about three times stronger than an 8.7 quake, according to the USGS.