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The Japan Trench Fast Drilling Project (JFAST) was a rapid-response scientific expedition that drilled oceanfloor boreholes through the fault-zone of the 2011 Tohoku earthquake. JFAST gathered important data about the rupture mechanism and physical properties of the fault that caused the huge earthquake and tsuanmi which devastated much of northeast Japan.〔Smithsonian.com (Fault that Caused Japan's 2011 Earthquake is Thin and Slippery ), Dec. 5, 2013〕〔Christian Science Monitor (Japan's monster quake: Do scientists have key to decode future tremblors? ), Dec. 6, 2013〕 == Background == The 2011 Tohoku-oki earthquake (2011 Tohoku earthquake) on March 11 with moment magnitude 9.0, was the largest in Japan's long history of destructive seismic events and severely damaged regions of northeast Honshu, with many deaths (over 15,000) and great economic losses ($US 200 to 300 billion).〔(Zhang, Top 5 Most Expensive Natural Disasters in History, AccuWeather.com, Mar. 30, 2011 )〕 Because of the huge societal impact, there was an urgency among scientists to respond with information and research results to explain the disastrous event. Soon after the earthquake, researchers of the Integrated Ocean Drilling Program (IODP) began planning the Japan Trench Fast Drilling Project (JFAST) to investigate the earthquake with ocean floor boreholes to the plate boundary fault.〔Nature News, http://www.nature.com/news/2011/111031/full/479016a.html Drilling ship to probe Japanese quake zone, Oct. 31, 2011〕〔phys.org, (Chikyu to set sail for IODP expedition: Japan trench fast drilling project ), March 9, 2012〕 This ambitious project drilled boreholes thorugh the fault that slipped during the earthquake in order to understand the unprecedented huge slip (40 to 60 meters)〔(Fujiwara et al., The 2011 Tohoku-Oki earthquake: displacement reaching the trench axis, Science, 1240. doi: 10.1126/science.1211554, 2011 )〕 that occurred on the shallow portion of the megathrust fault and was the primary source of the large tsunami that devastated much of the coast of northeast Honshu. There was much public interest in this high-profile scientific project with considerable Japanese〔Nippon Broadcasting System TV News, Japan, news story on Apr. 14, 2012〕〔Tokyo Broadcasting System Television News 23, featured story on May 3, 2012 (in Japanese)〕 and English 〔Discovery Channel Daily Planet (TV series) feature story on Mar. 9, 2012〕 media coverage of the operations 〔〔phys.org, (New subseafloor observatory begins measurement of frictional heating by the 2011 Tohoku, Japan earthquake ), July 23, 2012.〕 and results 〔〔livescience, ( Slippery Clay at Fault in 2011 Japan earthquake ), Dec. 5, 2013〕〔redOrbit (New Report Highlights Stress Change During 2011 Tohoku-Oki Earthquake ), Feb. 8, 2013,〕〔liberty voice ( Slippery Clay Explains Mystery of Tohoku-Oki Earthquake and Tsunami ), Dec. 6, 2013〕 Specific science objectives〔(Mori et al., Investigation of the Huge Tsunami from the 2011 Tōhoku-Oki, Japan, Earthquake Using Ocean Floor Boreholes to the Fault Zone, Oceanography 27, 132–137, 2014 )〕 included, *Estimation of the stress (mechanics) state in the region of the shallow fault from borehole breakouts. *Retrieval of core sample from the plate boundary fault zone to see geologic structures and measure physical properties of the fault zone. Before this project, no one had directly seen a fault zone that recently moved tens of meters in an earthquake. *Measurement of the temperature across the fault zone to estimate the level of dynamic friction during the earthquake. These thermal observations needed to be done quickly after the earthquake and was the main reason for the rapid mobilization of JFAST. The site for the offshore drilling was located about 220 km east of Sendai in the region of very large fault slip during the earthquake near the Japan Trench. == Deep water drilling operations == The D/V Chikyu, operated by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) sailed on IODP Expedition 343 from the port of Shimizu, Shizuoka on April 1, 2012, within 13 months after the earthquake. Chikyu is the only research vessel with the capabilities for the necessary drilling in very deep water of over 6900 meters. Two months of operations from April 1 to 24 May 24, 2012 were scheduled for drilling several boreholes to carry out Logging while drilling (LWD), install temperature sensors and retrieve core samples. The extreme water depths caused many technical challenges that had to be considered, such as the strength of the long pipe string, onboard handling of the pipe sections, and instrument operations at very high water pressure. These aspects needed careful planning and new tools on the ship. Various equipment had not been previously used in such deep water and caused many problems and delays during the first month at sea.〔 Eventually difficult engineering problems were overcome enabling retrieval of borehole core and installation of a temperature observatory across the fault zone at a depth of about 820 meters below the sea floor. New records were set for scientific drilling including, longest drilling string (7740 m) from the ocean surface and deepest core from the ocean surface (7752 m).〔〔 Because of delays due to technical difficulties and bad weather, the temperature observatory could not be deployed during the main expedition. However, during the supplementary Expedition 343T from July 5 to 19 a new borehole was quickly drilled and the temperature sensors were installed〔 Retrieval of the temperature data was scheduled for cruise KR13-04 during February 11 to 20, 2013 using the JAMSTEC ship R/V Kairei and Remotely Operated Vehicle (ROV) Kaiko-7000II. Kaiko-7000II is one of the few vehicles that can operate at 7000 meters water depth. Because of inclement weather and navigation problems the instruments could not be retrieved at this time. However, during the subsequent cruise KR13-08 from April 21 to May 9, 2013 the temperature instruments were successfully recovered on April 26. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Japan Trench Fast Drilling Project」の詳細全文を読む スポンサード リンク
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