Episodic growth of fault‐related fold in northern Japan observed by SAR interferometry

The interferometric analysis using ALOS SAR data allows us to map the detailed spatial pattern of the deformation associated with the 2007 M6.8 Niigataken Chuetsu‐oki earthquake. The interferograms reveal not only a large deformation near the source area of the earthquake but also a local uplift in the region of active folding, 15 km east of the earthquake epicenter. The 1.5‐km‐wide and 15‐km‐long band of uplift is located along the anticline axis of an active fold and cannot be explained by the elastic deformation resulting from the mainshock of the earthquake. This uplift suggests the episodic growth of active folds. The analysis of the range changes along two directions and the vertical displacement by leveling reveals that episodic creep on an east‐dipping reverse fault just beneath the uplift band has caused the growth of the fault‐related fold. The acceleration of this creep has been probably triggered by an increase in static stress due to the earthquake