Earth Planets Space, Vol. 63 (No. 7), pp. 621-625, 2011
Tomokazu Kobayashi, Mikio Tobita, Takuya Nishimura, Akira Suzuki, Yuko Noguchi, and Masayuki Yamanaka
Geospatial Information Authority of Japan, Kitasato-1, Tsukuba, Ibaraki 305-0811, Japan
(Received April 7, 2011; Revised June 21, 2011; Accepted June 23, 2011; Online published September 27, 2011)
Applying interferometric SAR (InSAR) analysis using ALOS/PALSAR data to a megathrust earthquake (Mw 9.0) that ruptured off-shore of Tohoku, Japan, on 11 March, 2011, we succeeded in mapping a ground displacement distributed over ∼600 km range in the north-south orientation and ∼200 km range in the east-west orientation. A relative slant range lengthening of ∼4 m that is the largest displacement ever observed in Japan on InSAR records was detected at the tip of Oshika peninsula, consistent with GPS observations. The interferograms, calculated using quick but less accurate orbit data, are contaminated by long-wavelength noise, preventing us from measuring the correct ground displacement. We demonstrate that an InSAR analysis incorporating GEONET data effectively reduces noise and enables the prompt and accurate mapping of the ground displacement. Additionally, a clear coseismic signal due to an inland earthquake in northern Ibaraki on 19 March, 2011 (Mj 6.1) was also detected. Our preferred fault model assuming two segments shows a nearly pure normal fault motion with a west-dipping fault plane. The ΔCFF calculation suggests that the Mw 9.0 main shock promoted the Mj 6.1 event.
Key words: The 2011 Tohoku earthquake (Mw 9.0), InSAR, crustal deformation, northern Ibaraki earthquake (Mj 6.1).