Identification of Surface Waves Generated in a Sedimentary Basin in Japan

Recent events have allowed the observation of the effects of long-period motions on large-scale structures in Japan, and their devastating consequences. In this work we investigate the generation of surface waves in the basin of Nagoya (Nobi plain) in Japan, from seismograms of the K-net network, including recordings of the Mw 9.0 2011 Tohoku earthquake. The sur-face waves are identified by their polarization characteristics when the seismogram is repre-sented in the time-frequency space via the S-Transform. We adopt the “Normalized Inner Product” (NIP) as criterion to quantify the polarization features of the different train waves, since the NIP can be considered as the time-frequency counterpart of correlation. We then ap-ply filters based on the NIP to the S-Transform to isolate and extract the identified surface waves. With this procedure we provide the direction of propagation of the identified wa-vetrains, and then evaluate their mechanisms of generation.