Fig. 4.
From: Detection of seismic events triggered by P-waves from the 2011 Tohoku-Oki earthquake
Fourier spectra of horizontal components of the 2011 Tohoku-Oki earthquake. The spectra of the background, P-waves, and surface waves that include triggered NVT, are obtained using the time windows 1, 2, and 3 at KWBH shown in Fig. 2(d). Also shown are the surface wave spectrum for the same time window at SYTH and the spectrum of P-waves at KWBH from the Mw 6.1 reference earthquake. The station SYTH is shown by a cross in Fig. 1.