Mentawai Tsunami Update

On October 25^th, 2010, a 7.7 magnitude undersea earthquake 150 miles west of Bengkulu, Indonesia, generated a tsunami that devastated the nearby Mentawai Islands. The tsunami most severely impacted the South Pagai, North Pagai, and Sipora islands in the Mentawai archipelago off the coast of Indonesia, claiming over 500 lives and injuring a few hundred more. 

It was widely reported that the tsunami reached only 3 meters (10 ft), but during a field survey of the event, it was discovered that the tsunami reached up to 16 m (~50 ft) in certain places and inundated as far as 600 m (~2000 feet) inland. The size of the tsunami is particularly surprising because it is much larger than a 7.7 quake would have suggested. As a result, it is believed that the tsunami may have been the product of a slow quake occurring over a longer duration, also known as a “tsunami earthquake”. 

In the months following, there have been several efforts from international agencies to provide aid and relief to the roughly 15,000 displaced Indonesians. Unfortunately, due to poor weather conditions and the remoteness of the islands, relief teams initially had difficulty reaching the Mentawais. After navigating the obstacles, relief teams were able to provide food, shelter, and medical attention for the thousands of newly homeless people.

ASR Scientist Jose Borrero, who was featured in the Jakarta Globe for his research of the tsunami, has released a preliminary field report of the tsunami effects in the Mentawai Islands. The report details the post-tsunami investigation of Pagai, Sipora and Southern Siberut Islands. Dr. Borrero worked in conjunction with researchers from Earth Observatory Singapore, the Indonesian Institute of Science, Georgia (USA) Institute of Technology and the University of Southern California to collect information on the tsunami and its effects. The data will be used to better understand this unusual event from a scientific point of view and to improve hazard mitigation strategies in the Mentawai Islands.

To view the complete report click here.

The Indonesian Government formally terminated the Emergency Response on November 22, 2010, ending the emergency relief program and marking the beginning of efforts to rebuild the communities in the Mentawais. SurfAid International, whose staff is comprised of 90% Indonesian nationals, has played an integral role in supporting relief efforts in the Mentawais. They raised substantial funds for aid and continue to provide assistance on site, helping to implement recovery programs to rehabilitate victims and their communities. To learn more about Surfaid’s involvement go here:

http://www.surfaidinternational.org/emergencyresponse

To read more, check out these articles:

http://observers.france24.com/content/20101102-surfers-mobilize-help-mentawai-tsunami-victims-indonesia

http://www.thejakartapost.com/news/2010/10/28/mentawai-tsunami-death-toll-triples.html

http://surf.transworld.net/1000119132/news/surfaid-mentawai-tsunami-update/

Indonesia Mentawai Tsunami Was 17 Meters High

ASR ltd. scientist Jose Borrero makes some startling discoveries after completing field work in Indonesia.

Jakarta Globe: The tsunami that devastated the Mentawai Islands off West Sumatra last month featured waves much larger than would normally have been expected from the magnitude 7.7 earthquake that spawned it, according to a tsunami expert. 

Jose Borrero, from ASR Ltd., a marine consulting firm, said on Friday that the finding was extraordinary.

“We were extremely surprised by the size of the waves on one of the small islands offshore of Pagai,” he said at a press conference at the office of the presidential advisory council. 

“We found evidence that the tsunami waves reached a height of 17 meters, which was much bigger than we had expected to find,” he said. 

Borrero, who is also a researcher at the University of Southern California’s Tsunami Research Center, said that while most residents of the islands were aware of the potential for a tsunami, the majority had been caught unawares by the relative weakness of the Oct. 25 quake. 

“They knew that earthquakes are associated with tsunami, and that they should be aware of evacuating if they felt a strong earthquake,” he said. 

“However, this earthquake didn’t feel that strong to them, especially when compared with previous earthquakes in the area. So some people didn’t evacuate immediately upon feeling the earthquake. It wasn’t until they actually heard the sound of the waves coming through the trees and tearing down the forest that they actually knew that they had to go.” 

He said that because Indonesia would always be prone to tsunamis, residents should learn to read the signs. 

“Basically, tsunamis and earthquakes are part of natural life,” Borrero said. 

“You can’t live in fear of them. It’s best to understand them and work with a national system. By understanding them, we have the chance for survival. This isn’t something to be afraid of, but to be aware of, to know what to look for,” he said. 

At least 461 deaths have been confirmed as a result of the tsunami, while 43 others remain missing and are feared dead. 

The waves also rendered nearly 8,000 people homeless. 

Hermann M. Fritz, a tsunami expert from the Georgia Institute of Technology in the United States, said the real measure of an earthquake’s potential for causing a tsunami in tectonic subduction zones such as the Mentawais, was not the perceived strength of the quake but rather its duration. 

“How long the quake lasts will indicate its potential for a tsunami,” he said. 

“If you feel the shaking for more than 30 seconds or a minute, it’s important to evacuate immediately.” 

Danny Hilman, a researcher at the Indonesian Institute of Sciences (LIPI), said the Mentawai quake lasted more than a minute. 

However, he said most local people interviewed by the experts had said that at the time of the quake they only felt a swaying motion, and thus did not feel the need to evacuate. 

He said that in the case of Mentawai, while the quake registered at a magnitude of 7.7, its long duration meant it was more like a magnitude 8 temblor.

West Sumatra Tsunami

I received an email last night from Dr. Jose Borrero, who is currently conducting field surveys and distributing supplies to people suffering from the damage of the West Sumatra tsunami. After considering the magnitude of the tsunami and other relevant factors, we suggested that it might have been the result of a slow quake.

The size and destruction of the tsunami that destroyed local indigenous communities, was far more devastating than the magnitude of the quake might have implied. The team currently collecting data in West Sumatra will use this information in an effort to determine if, in fact, a slow tsunami quake caused this massive natural disaster.