Earth Planets Space, Vol. 64 (No. 11), pp. e25-e28, 2012
Department of Geophysics, Graduate School of Science, Tohoku University, 6-3 Aramaki-aza Aoba, Aoba-ku, Sendai 980-8578, Japan
(Received November 16, 2011; Revised October 1, 2012; Accepted October 5, 2012; Online published November 1, 2012)
Teleseismic P-waves are observed even in a transverse component, and the ratio of the peak energy of the transverse component to that of the sum of the three components (peak energy ratio) is a good indicator to represent the strength of the heterogeneity in the structure. We analyze the short-period teleseismic P-waves recorded at a dense seismic network in Japan (Hi-Net) and determine the spatial changes of the heterogeneity in the Japanese islands. The results show that east Japan is characterized mainly by large peak energy ratios that represent strong heterogeneity. On the other hand, west Japan shows small peak energy ratios. Comparison of the results with detailed geological maps further shows that large peak energy ratios are observed at regions located close to both quaternary volcanoes and active faults, and the active fault region is characterized by slightly smaller peak energy ratios. Non-active regions, located far from volcanoes or faults, indicate the smallest ratios, although the ratios are larger than those estimated on stable continents. Plains that consist mainly of sediments show the largest peak energy ratios. However, peak delay times observed at the plains are much longer than the others, which suggests a different mechanism for generating the amplitudes in the transverse component.
Key words: Teleseismic P-wave, transverse component, heterogeneity, volcano, active fault plain.