Title 西南日本合同地震観測データを用いたレシーバ関数解析 Author(s) 上野, 友岳 ; 澁谷, 拓郎 ; 伊藤, 潔 Citation 京都大学防災研究所年報. B = Disaster Preventio Institute annuals. B (2006), 49(B): Iss

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B (2006), 49(B): Issue Date 2006-04-01 URL http://hdl.handle.

1 Title 西南日本合同地震観測データを用いたレシーバ関数解析 Author(s) 上野, 友岳 ; 澁谷, 拓郎 ; 伊藤, 潔 Citation 京都大学防災研究所年報. B = Disaster Preventio Institute annuals. B (2006), 49(B): Issue Date URL Right Type Departmental Bulletin Paper Textversion publisher Kyoto University

2 京都大学防災研究所年報第 49 号 B 平成 18 年 4 月 Annuals of Disas. Prev. Res. Inst., Kyoto Univ., No. 49 B, 2006 (2004) 40 km ( Nakanishi, 1980) Shiomi et al. (2004) Yamauchi et al. (2003) 40 km Ohkura (2000) (2001) ISI Fig.1 Epicenter distribution of teleseismic events used in this study 2000 (Shibutani et al., 2005) (, 2002) Ps (2003) (2002) Ueno et al. (2004) 20 km 30 km () 60 km

60 km 2000 2002 2004 (, 2002) Fig.1 (USGS) M6.030 80300 km 79Fig.2 (20022004) (40) (Hi-net) 260 km (A-A)140 km (B-B) T2000 Fig.3A-A Fig.2 20022004 (M>0.5) Ps PS P Fig.

5) from 2002-2004. Open circles indicate DLF (Deep Low Frequency) events. Inverted triangles are seismic stations and thin solid lines show active faults.

3 60 km (, 2002) Fig.1 (USGS) M km 79Fig.2 ( ) (40) (Hi-net) 260 km (A-A)140 km (B-B) T2000 Fig.3A-A Fig (M>0.5) Ps PS P Fig.2 Distributions of seismic stations used in this study and hypocenters in Southwest Japan determined by JMA (Japan Meteorological Agency). Plus signs show hypocenters of earthquakes (M>0.5) from Open circles indicate DLF (Deep Low Frequency) events. Inverted triangles are seismic stations and thin solid lines show active faults. Boxes (A-A, B-B ) shows regions, earthquakes in which are plotted in the depth sections (A-A, B-B ). Fig.3 Record sections of the vertical (upper figure) and radial (lower figure) components of an earthquake recorded along the A-A profile in Fig.2. The earthquake occurred in Malaysia Islands on October 19, 2003.

4 PS (Ps) (Langston, 1979 Ammon, 1991) Ps FFT 0 (Helmberger and Wiggins, 1971) 0.01 (Fig.4W.L.=0.01) (Park and Levin, 2000) FFT (, 2001) FFT S/N Singular Value Decomposition SVD (Chevrot and Girardin, 2000) SVD (Fig.5a)Fig.5b ( ) iasp91 (Kennett and Engdahl, 1991) JMA2001 (, 2002) Ps Fig.4 An example of normalized power spectra of vertical component for an earthquake estimated by using multiple taper (solid line) and cosine taper (dashed line). Horizontal broken lines show water levels (W.L.). Tps 1 p p dz z z ( ) ( ) TpsP (s)z (km) (z)(z)ps (km/s) p (s/km) Fig.2 Fig.6 () (Fig.2) 2 A-A 2000 Ueno et al. (2004) Ps Fig.6 Ps 30 km Ps Fig.2 A-A B-B Fig.6a A-A Ps 2040 km

5 Fig.5 Record sections of receiver functions. (a) shows receiver functions stacked for stations along the A-A profile. The origin of the distance axis is taken at the epicenter of the 2000 Western Tottori Earthquake. (b) shows receiver functions at AYKH station against back azimuths km 30 km 40 km 60 km 30 km Fig.6b B-B Ps A-A 30 km A-A A-A B-B 1520 km ( 2000 ) 20 km 60 km Fig.2 Fig.6 (Ps ) Yamauchi et al. (2003) Shiomi et al. (2004) 51 A-A 2040 km

6 Fig.6 Cross sections of receiver function images. (a) and (b) show the images along the A-A and B-B profiles shown in Fig.2. Red and blue colors indicate the positive and negative amplitudes of receiver functions. Yamaucthi et al. (2003) Shiomi et al. (2004) Fig.7a (2002) (2001) Ohkura (2000) Fig.7 JMA (Katsumata and Kamaya, 2003) Yamaguchi et al. (1999) MT Katsumata and Kamaya (2003) Yamauchi et al. (2003) Shiomi et al. (2004)

Fig.7 Cross sections of receiver function images with seismic activity. Solid lines indicate clear discontinuities, mainly the Moho discontinuity.

7 Fig.7 Cross sections of receiver function images with seismic activity. Solid lines indicate clear discontinuities, mainly the Moho discontinuity. Dashed lines indicate other discontinuities in the crust and upper mantle. Pluses and open circles indicate earthquakes and DLF events, respectively km A-A B-B 40 km (Gravity Research Group in Southwest Japan, 2001) 60 km 2000 (Ueno et al., 2004) (, 2003) (, 2002) Ps 60km 8 s ( 65 km ) 53 Fig.7a A-A Fig.7b B-B 15 km A-A 15 km

8 30 km 30 km 40 km 60 km 15 km Hi-net USGSJMA GMT (Wessel and Smith, 1991) (2002):,, 65, pp (2002),,, 54, pp (2001):,, Vol. 23, No. 10, pp (2002):, 2002, P004. (2001):,, 54, pp (2003): 2000 S,, Vol. 25, No. 8, pp (2002):,, P62. (2004):,, 57, 2, pp Ammon, C. J. (1991): The isolation of receiver effects form teleseismic P waveforms, Bull. Seism. Soc. Am., 81, pp Chevrot, S. and N. Girardin (2000): On the detection and identification of converted and reflected phases from receiver functions, Geophys. J. Int., 141, pp Gravity Research Group in Southwest Japan (2001): Cravity database of southwest Japan [CD-ROM], Spec. Rep. 9, Nagoya Univ. Mus., Nagoya, Japan. Helmberger, D. V. and R. Wiggins (1971): Upper mantle structure of midwestern Unites States, J. Geophys. Res., 76 (14), Katsumata, A., and N. Kamaya (2003): Low-frequency continuous tremor around the Moho discontinuity away from volcanoes in the southwest Japan, Geophys. Res. Lett., Vol. 30 (1), doi: /2002GL Kennett, B. L. N. and E. R. Engdahl (1991): Traveltime for global earthquake location and phase identification, Geophys. J. Int., 105, pp Langston, C (1979): Structure under Mount Rainier, Washington, inferred from telesesimic body waves, J. Geophys. Res. Vol. 84, No. B9, pp Ohkura, T. (2000): Structure of the upper part of the

9 Philippine Sea plate estimated by later phases of upper mantle earthquakes in and around Shikoku, Japan, Tectonophysics, 321, pp Nakanishi, I. (1980): Precursors to ScS phases and dipping interface in the upper mantle beneath southwestern Japan, Tectonophysics, 69, pp Park, J. and V. Levin (2000): Receiver functions from multiple-taper spectral correlation estimates, Bull. Seism. Soc. Am., 90 (6), pp Shibutani, T., H. Katao, and Group for the dense aftershock observations of the 2000 Western Tottori Earthquake (2005): Very dense aftershock observations of the 2000 Western Tottori Earthquake (Mj=7.3) in southwestern Honshu, Japan: high resolution aftershock distribution, focal mechanisms and 3-D velocity structure in the source region, Earth Planets Space, 57, pp Shiomi, K., H. Sato, K. Obara.and M. Ohtake (2004): Configuration of subducting Philippine Sea plate beneath southwest Japan revealed from receiver function analysis based on the multivariate autoregressive model, J. Geophys. Res. Vol. 109, B04308, doi: /2003jb Ueno, T., T. Shibutani, I. Doi and K. Ito (2004): Lower crust and upper mantle structure in the region of the 2000 western tottori, japan earthquake estimated from receiver function analyses, Am. Geophys. Union fall meeting, S51A Wessel, P., and W. H. F. Smith (1991): Free software helps map and display data, Eos Trans. AGU, 72, 441, pp Yamaguchi, S., Y. Kobayashi, N Oshiman, K. Tanimoto, H. Murakami, I. Shiozaki, M. Uyeshima, H. Utada, and N. Sumitomo (1999): Preliminary report on regional resistivity variation inferred from the Network MT investigation in the Shikoku district, southwest Japan, Earth Planets Space, 51, pp Yamauchi, M., K. Hirahara and T. Shibutani (2003): High resolution receiver function imaging of the seismic velocity discontinuities in the crust and the uppermost mantle beneath southwest Japan, Earth Planets Space Lett., Vol. 55, pp Estimation of Underground Structures Beneath Southwest Japan Derived from Receiver Function analysis Tomotake UENO, Takuo SHIBUTANI and Kiyoshi ITO Synopsis We imaged S wave velocity discontinuities by analyzing Ps converted waves in receiver functions with data from the Joint Seismic Observation of Japan Universities in Southwest Japan. The source area of the 2000 Western Tottori Earthquake is located in the observation area. The Moho discontinuity is clearly imaged in the result. It is possibly deduced that the clear Moho discontinuity in the Shikoku district is the continental Moho discontinuity rather than the oceanic one. Furthermore, earthquakes may occur at the boundary of the Philippine Sea Plate (PHP) or in the oceanic crust rather than in the uppermost mantle of the oceanic plate. The Moho discontinuity is located at ~30 km deep in the northern Chugoku district. A discontinuity was also found at ~60 km in the region. This discontinuity may be an extension of the PHP. Discontinuities in the crust are intermittent and they seem to be located just below the seismogenic zone. Keywords: receiver function, Ps converted wave, Philippine Sea Plate, Moho discontinuity

１２－２プレート境界深部すべりに係る諸現象の全体像

１２－２プレート境界深部すべりに係る諸現象の全体像 - 452 - - 453 - - 454 - - 455 - - 456 - Table 1 Comparison of phenomena associated with slip event at deep portion along the plate interface. - 457 - ECMJMA LFE 3 8 29 31 3 2-16Hz ECM Fig.1 Comparison