The section of vertical-component spectra at stations in the Taiwan region after the 2004 December 26 Sumatra earthquake. (a) Amplitudes are small in the band of 3.3-3.4 mHz (within the red lines). (b) The magnification of spectra in the band 3.1-3.4 mHz displays significant coupled modes 0S25-0T25. Hanning-tapered Fourier transform is applied to 18-hr time-series, which start at 1000 s after the origin time. Dot lines indicate the theoretical frequencies of normal modes from the PREM model. Labels denote observing site codes.