JFAST gathered important data about the rupture mechanism and physical properties of the fault that caused the huge earthquake and tsunami which devastated much of northeast Japan.
[1][2] The 2011 Tohoku-oki earthquake, with a moment magnitude of 9.0, was the largest in Japan's history, and severely damaged regions of northeast Honshu, with over 15,000 deaths and economic losses of $US 200 to 300 billion.
There was much public interest in this high-profile scientific project with considerable Japanese[7][8] and English [9] media coverage of the operations [4][10] and results [1][11][12][13] Specific science objectives[14] included, 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.
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.
[14] 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.
From the core samples, geologic structure data and measurements of physical properties, a single plate-boundary fault zone was identified with a high level of confidence at a depth of about 820 meters below the seafloor.
The actual slip surface for the 2011 earthquake may not have been recovered, but it is assumed that the structures and physical properties of the core are representative of the entire fault zone.
The very low frictional strength for the material from the Japan Trench fault zone is much lower than typically observed for other types of rocks.
[17] Examination of the microstructures in the laboratory samples, suggests that fluids are important in the faulting process and contribute to the low friction properties, possibly through thermal pressurization.
The results of the scientific investigations show that the huge slip during the 2011 Tohoku earthquake occurred on a simple and thin fault zone composed of pelagic sediments with a high smectite content.