Earth Planets Space, Vol. 61 (No. 4), pp. e9-e12, 2009E-LETTER
Youichiro Takada1, Tomokazu Kobayashi2, Masato Furuya1, and Makoto Murakami2
1Department of Natural History Sciences, Hokkaido University, Sapporo, Japan
2Institute of Seismology and Volcanology, Hokkaido University, Sapporo, Japan
(Received October 9, 2008; Revised January 29, 2009; Accepted February 12, 2009; Online published March 12, 2009)
Applying interferometric SAR (InSAR) analysis to the 2008 Iwate-Miyagi Nairiku earthquake, we detected notable ground displacements of several tens of centimeters to about 1.2 m that extend further south of the epicentral area. We explained the InSAR data by constructing a fault model consisting of four WNW dipping and one ESE dipping reverse faults. The residuals between observed and modeled deformation are less than 6 cm in most of the area, which is comparable to the errors caused by atmospheric effect. To fill the lack of InSAR data in the hypocentral area, we applied a pixel matching technique to the intensity images, which shows a shortening in range offsets by as much as ∼2 m along a narrow zone stretching along the eastern foot of Mt. Kurikoma, indicating a localized uplift. We also found remarkable contrasts in the range offsets around the low coherence area equivalent to a very large displacement gradient to the WNW of the hypocentral area as well as ESE. We conclude that the main faulting occurred on the WNW dipping reverse faults, but that the overall geometry of the fault system is quite complex including at least one conjugate faulting, as also supported by the hypocentral distribution of aftershocks.
Key words: 2008 Iwate-Miyagi Nairiku earthquake, pixel offset field, stereoscopic effect, complex fault structure.