Detection and mapping of soil liquefaction in the 2011 Tohoku earthquake using SAR interferometry

We have identified areas of soil liquefaction by the analysis of surface changes caused by the 2011 Tohoku earthquake, using synthetic aperture radar (SAR) interferometry in the Kanto region of Japan. Changes in surface scattering properties were evaluated using phase-corrected coherence, computed from the reflective intensity (amplitude) of SAR data. Often, the loss of coherence (decorrelation) is simply considered to represent areas damaged from the disaster. However, temporal decorrelation could also be induced by ordinal surface cover change in addition to disaster damage. Therefore, we use a coherence change threshold to discriminate significant decorrelation caused by soil liquefaction from that produced by ordinal surface cover changes. Moreover, local surface displacements are estimated using phase information from the SAR data. Our results compare favorably with those from surveys of sand boils and aerial photography, showing that surface changes derived from SAR data are associated with soil liquefaction. Our results demonstrate that soil liquefaction occurred mainly near the waterfront along Tokyo Bay and the Tone River, and ground subsidence was widely distributed.