Near‐surface weakening in Japan after the 2011 Tohoku‐Oki earthquake

one of the largest in recent history. Ground motion caused by the seismicity around the time of the main shock was recorded by KiK‐net, the strong‐motion network that covers most of Japan. By deconvolving waveforms generated by earthquakes that are recorded at the surface and in a borehole at KiK‐net station FKSH18, we detect a reduction of shear‐wave velocity in the upper 100 m of about 10%, and a subsequent healing that varies logarithmically with time. Using all available borehole and surface records of more than 300 earthquakes tha