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U.S. Geological Survey (USGS) scientists were in Jakarta, Indonesia, on March 28, 2005, when a magnitude 8.7 earthquake occurred off the northwest coast of Indonesia's island of Sumatra, less than 200 km southeast of the epicenter of the magnitude 9.0 earthquake that shook the region on December 26, 2004. The scientists were preparing for followup studies of the devastating tsunami generated by the December 26 earthquake, and they quickly revised their plans to include investigation of the smaller tsunami generated by the March 28 earthquake. (See "Why Wasn't There a Larger Tsunami?", this issue.) Throughout the month of April, USGS scientists measuring the impacts of both tsunamis in Indonesia have been posting photographs and accounts of their work on the Notes From the Field...USGS Scientists in Sumatra Studying Recent Tsunamis Web site.
The USGS scientists are part of the West Sumatra International Tsunami Survey Team, formed in cooperation with the Indonesian government to conduct indepth studies of the impacts of the December 26, 2004, tsunami. This effort, funded in part by the U.S. Agency for International Development (USAID)'s Office of Foreign Disaster Assistance, will complement and expand on the findings of a survey conducted earlier this year (see "Astonishing Wave Heights Among the Findings of an International Tsunami Survey Team on Sumatra," Sound Waves, March 2005.
Although the March 28 earthquake did not generate a tsunami as large as the one that lashed countries around the Indian Ocean on December 26, the survey team soon learned that a local tsunami with reported wave heights of 2 to 4 m had hit coastal areas near the epicenter of the March earthquakeincluding Simeulue Island, Nias Island, and the Singkil district on mainland Sumatra. Computer models indicated that even larger waves might have struck the Banyak Islands. The team added all these areas to their itinerary of field stops along Sumatra's west coast.
Nias Island was the first of these areas to be visited by the scientists. Their report dated April 2, 2005, notes: "The 28 March tsunami was large and destructive at Lagundri Bay in southwest Nias Island. The team measured tsunami runup of 3 to 4 m and inundation distances of 400 to 500 m. Although there were few buildings in this location because it is a surf camp, more than 12 buildings were destroyed by the 28 March tsunami." People ran inland and uphill as soon as the earthquake shaking stopped; they were out of harm's way when the tsunami came ashore as one loud wave 5 to 15 minutes after the earthquake. The March 28 tsunami was larger at Lagundri Bay than the December 26 tsunami, which did no damage at this site.
The survey team consists of 5 Indonesian scientists and 12 U.S. scientists, including 6 from the USGS: Bruce Jaffe and Bob Peters (both stationed in Santa Cruz, CA), Guy Gelfenbaum and Peter Ruggiero (both stationed in Menlo Park, CA), Bob Morton (St. Petersburg, FL), and Etienne Kingsley (contractor stationed in Olympia, WA). The team conducted fieldwork from March 30 to April 26 in order to:
Because the December tsunami had washed out many coastal roads, the survey team chartered a boatthe 61-ft-long merchant vessel Seimoa, which ordinarily runs surfing chartersto transport them to field sites along the coast. The team departed from Padang at about 9:30 a.m. on March 30 (Western Indonesia Standard Time), and at the time of this writing they had visited the Batu Islands, Simuk Island, Nias Island, and Sarangbaung Island.
Visit Notes From the Field...USGS Scientists in Sumatra Studying Recent Tsunamis to read updated and archived accounts of the West Sumatra International Tsunami Survey Team's fieldwork, find information about the survey and survey-team members, view photographs from the field, and see maps of study-site locations.
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