Comparative analysis of Rayleigh and Love waves detected propagating in the Nobi and Kanto basins during the 2004-, 2007- Chuetsu and 2011 Tohoku earthquakes

Propagation of long-period ground motion in sedimentary basins has been a subject of great interest among seismologists and engineers. Intense long-period ground motions consist primarily of surface waves that get trapped or generated locally as seismic energy travels through sedimentary deposits. In the present work, we investigate the propagation of surface waves in the basins of Kanto and Nobi in Japan, during three relatively recent events: The Mw 6.6 2004 Niigata Chuetsu, the Mw 6.6 2007 Chuetsu-Oki and the Mw 9.0 2011 Tohoku earthquakes. We identify the surface waves using a signal processing technique that detects their polarization characteristics, in the time-frequency space, using orthogonality relations among phase vectors. Then, by applying the “Normalized Inner Product” (NIP), regions of a particular type of polarization are delineated and filters are applied to isolate the associated surface waves, along with their direction of propagation. With our investigation, we attempt to follow the ‘flow’ of seismic energy as it approaches just outside the basins, and then how it evolves once inside the basin. Our analysis shows that the long period (