Sendai Earthquake of March 2011
One of the unique attributes of satellite-based Synthetic Aperture Radar (SAR) is its ability to acquire data over large areas. The European Space Agency Envisat/ASAR sensor collected a significant amount of SAR data over Japan in the weeks and months prior to and following the Sendai (Tohoku) earthquake. The magnitude 9.0 quake occurred on March 11, 2011 and was responsible for moving portions of Japan's northeastern landmass by as much as 2.4 meters. We obtained a series of coseismic SAR acquisitions from the Envisat sensor corresponding to the dates February 19, and March 21, 2011. The seven standard frames comprise an along track swath equal to 700 km and extend over much of the earthquake zone. The figure shows the result of interferometric SAR (InSAR) processing of the coseismic pair. The measured displacement is shown in colored contours, each representing 25 cm of motion along the radar line-of-site (LOS). The measured motion here is toward the radar, representing a general expansion of the landmass in the easterly direction. The raw data used for this work was obtained through the GEO Geohazards Supersite.
Among the variety of geophysical measurements available for this site are GPS displacement data for the period encompassing the quake. We have employed these data, obtained courtesy of the ARIA team at JPL and Caltech, in order to make an initial comparison between these ground measurements and the InSAR displacement measurements. The figure shows a scatter plot representing the results of this comparison, for latitudes above 36 degrees north. The 90 GPS measurements show generally good agreement with the InSAR displacements at the corresponding positions. Note also that the provided 1-sigma uncertainties in the GPS data are smaller than the size of the data markers in the plot.