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Ｏｕｔｌｉｎｅｓ

Ｌｏｗ－Ｆｒｅｑｕｅｎｃｙ　Ａｃｏｕｓｔｉｃ　Ｇｒａｖｉｔｙ Ｗａｖｅｓ　Ｏｂｓｅｒｖｅｄ　ａｆｔｅｒ　ｔｈｅ　２００４ Ｓｕｍａｔｒａ－Ａｎｄａｍａｎ　Ｅａｒｔｈｑｕａｋｅ Takeshi Mikumo （Ｋｙｏｔｏ　Ｕｎｉｖｅｒｓｉｔｙ，　Ｊａｐａｎ） Ｔａｋｕｒｏ　Ｓｈｉｂｕｔａｎｉ　（ＤＰＲＩ，Ｋｙｏｔｏ　Ｕｎｉｖｅｒｓｉｔｙ，　Ｊａｐａｎ）. Ｏｕｔｌｉｎｅｓ. １．２００４　 Sumatra －Ａｎｄａｍａｎ　Ｅａｒｔｈｑｕａｋ e (Mw= ９．２） ; Ｇｒｏｕｎｄ　 u ｐｌｉｆｔ　ａｎｄ　 s ｕｂｓｉｄｅｎｃｅ

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Ｏｕｔｌｉｎｅｓ

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  1. Ｌｏｗ－Ｆｒｅｑｕｅｎｃｙ　Ａｃｏｕｓｔｉｃ　ＧｒａｖｉｔｙＷａｖｅｓ　Ｏｂｓｅｒｖｅｄ　ａｆｔｅｒ　ｔｈｅ　２００４Ｓｕｍａｔｒａ－Ａｎｄａｍａｎ　ＥａｒｔｈｑｕａｋｅTakeshi Mikumo（Ｋｙｏｔｏ　Ｕｎｉｖｅｒｓｉｔｙ，　Ｊａｐａｎ）Ｔａｋｕｒｏ　Ｓｈｉｂｕｔａｎｉ　（ＤＰＲＩ，Ｋｙｏｔｏ　Ｕｎｉｖｅｒｓｉｔｙ，　Ｊａｐａｎ）

  2. Ｏｕｔｌｉｎｅｓ １．２００４　Sumatra－Ａｎｄａｍａｎ　Ｅａｒｔｈｑｕａｋe (Mw=９．２）; Ｇｒｏｕｎｄ　uｐｌｉｆｔ　ａｎｄ　sｕｂｓｉｄｅｎｃｅ ２．Ｍｉｃｒｏｂａｒｏｇｒａｐｈ　rｅｃｏｒｄｓ　observed after the earth- quake 3. Waveform modeling for synthetic barograms 4. Comparison between the recorded and synthetic barograms 5. Summary and Preliminary Conclusions

  3. 1 Source Region of the 2004 Sumatra-Andaman Earthquake 1U,2U,3U,4U: Uplifted Zones 1D,2D,3D,4D: Subsided Zones

  4. Provided by K. Satake

  5. Arranged by K. Satake

  6. Microbarograph stations that recorded infrasound waves from the 2004 Sumatra-Andaman earthquake

  7. Ａｃｋｎｏｗｌｅｄｇｍｅｎｔｓ • We thank the following colleagues for providing us with • the microbarograph data obtained at the respective stations. • MAT(Matsushiro, Japan) • T. Tsuyuki (Matsushiro Seismological Observatory, JAM, Japan) • KAM(Kamioka, Japan) • W. Morii (DPRI, Kyoto University, Japan) DGR (Diego Garcia) A. Le Pichon (CEA/DASE/LDG, France), M. Garces & D. Fee (University of Hawaii, USA) PAL (Palau) M. Garces & D. Fee (University of Hawaii, USA)

  8. 　　　　　Ｏｂｓｅｒｖｅｄ １０Ｐａ ＣＨ　１２ ０ ＣＨ　１９ ０５：５５　Ｄｅｃ．２６ Observed (de-trended) and Filtered Records at MAT(Matsushiro, Japan) Ｆｉｌｔｅｒｅｄ　

  9. Ｏｂｓｅｒｖｅｄ 5 Pa CH1 CH1 05:53 Dec.26 Observed (de-trended) and Filtered Records at KAM(kamioka, Japan) Ｆｉｌｔｅｒeｄ

  10. Observed 0.5 Pa I52H2 1 Pa I52H6 03:36 Dec.26 Original and Filtered Records at DGR (Diego Garcia) Filtered

  11. Original and Filtered Records at PAL (Palau) Ｏｒｉｇｉｎａｌ Ｆｉｌｔｅｒｅｄ 　２Pa IS39H2 2 Pa IS39H5 05:03 Dec.26

  12. Microbarograph Records at Alaska and California stationsafter the 1964 Alaskan earthquake (Mw=9.0) (Mikumo,1968)

  13. Waveform Modeling Procedures 1. Dynamic response of the lower atmosphere up to an altitude of 220 km ( the standard ARDC model) to a surface source and receiver: Spectral amplitude response Aj(ω) and phase velocity Cj(ω) for gravity and acoustic modes (j=1~4) 2. Earthquake source parameters: 1) Source locations and dimensions of the uplifted and subsided regions, Lj, Wj (j=1~8) 2) Source spreading velocity vr (rupture velocity on the fault) 3) Average displacements Dj of uplift and subsidence (j=1~8) 4) Rise time of the displacements τ

  14. Green’s functions for propagating gravity (GR0) and acoustic (S0 & S1) modes, from 2U with a point source and a step time function, to MAT ＧＲ０ Ｓ０ 　Ｓ１ ＳＵＭ

  15. Source Region of the 2004 Sumatra-Andaman Earthquake 1U,2U,3U,4U: Uplifted Zones 1D,2D,3D,4D: Subsided Zones

  16. Synthetic Waveforms for MAT from Uplifted and Subsided Zones Ｘ３.５ ４U ４D ３U ３D ２D 　２U １U １D

  17. D2u/Dju D2u/Dju 3 1 4 2 6 3 Synthetic barograms for MAT with various displacements at 2U + 2D Uplift Displacement Dju / Subsidence Displacement Djd = 2 (assumed)

  18. Synthetics Synthetics Vr (km/s) τ (sec) 2.5 60 2.0 18 3 1.7 Synthetic barograms for MAT with various rise times and rupture velocities

  19. １０　Ｐａ Ｏｂｓｅｒｖｅｄ ＣＨ１２ Ｓｙｎｔｈｅｔｉｃ41 Comparison between the recorded and synthetic barograms at MAT

  20. Ｏｂｓｅｒｖｅｄ Ｆｉｌｔｅｒｅｄ 5 Pa Ｓｙｎｔｈｅｔｉｃ 41 Ｓｙｎｔｈｅｔｉｃ 41 Comparison between the recorded and synthetic barograms (left), and between the filtered and synthetic barograms (right) at KAM

  21. Frequency response of the barographsused at IMS stations (provided by Le Pichon, 2007)

  22. Filtered Filtered I52H2 0.5 Pa I52H2 Synthetic 41 Synthetic 61 Comparison between the filtered record and two different synthetic barograms at DGR

  23. Filtered 1 Pa Synthetic 41 Comparison between the filtered record and synthetic barogram at PAL IS39H2

  24. Summary • Very low-frequency (~0.0016 Hz) acoustic-gravity waves with a group velocity around 305~315 m/s can be identified on the records at a few high-sensitivity microbarograph stations including Matsushiro, Kamioka,Diego Garcia (IS52) and possibly Palau (IS39), (up to a maximum distance of ~5.500 km). • We attempt to model synthetic barogram waveform to the stations, on the basis of dynamic response of the lower atmosphere with the ARDC standard thermal structure up to an altitude of 220 km,taking into account seismic information. For this modeling, we incorporate the spreading velocity of the source region, the source dimensions of subdivided zones, the vertical displacement ofground and sea-surface uplift and subsidence and their rise times.

  25. Preliminary Conclusions 1. Some combinations of these source parameters provide the synthetic waveforms well consistent with the general features of the observed low-frequency records. 2. The results suggest that the uplift in the south-central Nicobar region may be more than a few times larger than that in the other regions, and also that the northern half of the entire region appears to contribute only a small portion to the generation of the observed acoustic-gravity waves. 3. The time constant for generating these waves may be shorter than a few minutes, as in the case of the 1964 Alaskan earthquake (Mw=9.0)

  26. Estimated uplift and subsidence in two zones(Bilham et al., 2003)

  27. Uplift and subsidence measured from field surveys on the Andaman to Sumatra islands in the Indian Ocean (Metzler et al., 2005)

  28. 1964 Alaskan Earthquake

  29. Comparison between the recorded and synthetic barogramsat Berkeley, California (Mikumo,1968)

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