Earth Planets Space, Vol. 64 (No. 12), pp. 1209-1221, 2012
Tomokazu Kobayashi, Mikio Tobita, Mamoru Koarai, Takaki Okatani, Akira Suzuki, Yuko Noguchi, Masayuki Yamanaka, and Basara Miyahara
Geospatial Information Authority of Japan, 1 Kitasato, Tsukuba, Ibaraki 305-0811, Japan
(Received December 27, 2011; Revised July 30, 2012; Accepted August 31, 2012; Online published January 28, 2013)
Applying interferometric SAR (InSAR) analysis using ALOS/PALSAR data to inland crustal earthquakes in the Fukushima-Hamadori area, we succeeded in mapping a ground displacement associated with the Mj 7.0 earthquake that occurred on 11 April, 2011. The most concentrated crustal deformation is located ∼20 km west of the city of Iwaki, showing displacements away from the satellite with ∼2.2 m at the maximum. Clear displacement discontinuities are recognized with an offset of ∼1.6 m at the maximum, which are just on the Shionohira, Idosawa and Yunotake faults. From field surveys, we found that earthquake surface faults appeared with a vertical offset of ∼1.9 m, consistent with the InSAR observation, and their locations correspond to the discontinuities in the interferogram. We inverted the InSAR data to construct slip distribution models, and our models show (1) nearly pure normal fault motions (2) on west-dipping planes (3) with moderate-dip-angles (50-65°). The inferred west-dipping normal fault motion on the Yunotake fault is correlated with the present-day topographic features, consistent with the idea that the historically-repeated normal faultings have developed the topography. On the other hand, for the Shionohira and Idosawa faults antithetical relationships are presented, maybe suggesting that large normal faultings have been infrequent historically.
Key words: Fukushima-Hamadori (Mj 7.0), InSAR, earthquake surface faults, normal fault, Shionohira fault, Idosawa fault, Yunotake fault.