Coseismic Deformations of the 2011 Tohoku, Japan, Earthquake and Triggered Events Derived from ALOS/PALSAR

Abstract

The Tohoku earthquake on March 11, 2011, caused a remarkably large deformation on the island of Honshu, Japan. By analyzing ALOS/PALSAR data, a range increase of up to 3.6 m at the tip of the Oshika Peninsula, the closest point to the epicenter, was detected from ascending orbits. Combining ascending and descending interferograms, this peninsula was confirmed to have subsided and shifted eastward. This deformation may have been caused by a huge reverse slip on the plate interface near the trench axis.

This large deformation induced local earthquakes with magnitudes of 6 or larger and volcanic unrests. Among them, the April 11 M7.0 event in southern Fukushima Prefecture occurred on previously unrecognized active faults. More than nine fringes showing range increases were found in the vicinity of the epicenter of the Fukushima event. This observation is consistent with normal faulting on faults whose motion was previously not recognized. We also found slight range increases in volcanic regions in Northeast Japan. These observations imply that the March 11 shock induced large extensional stress in the crust of eastern Japan.