Coseismic displacement due to the 2008 Iwate-Miyagi Nairiku earthquake detected by ALOS/PALSAR: preliminary results

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 similar to 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.