第6回極域科学シンポジウム[OG] 地圏11月16日（月）　国立極地研究所３階セミナー

Kanao Masaki

Takenaka Hiroshi

Tono Yoko

Toyokuni Genti

Tsuboi Seiji

坪井 誠司

東野 陽子

竹中 博士

豊国 源知

金尾 政紀

National Institute of Polar Research Repository

  グリーンランド氷床における広帯域連続地震波形記録を用いた地震波干渉法解析  豊国 源知 1、竹中 博士 2、金尾 政紀 3、坪井 誠司 4、東野 陽子 5 1東北大学大学院 理学研究科 地震・噴火予知研究観測センター 2岡山大学 大学院自然科学研究科 3国立極地研究所 4海洋研究開発機構 5文部科学省  Ambient noise cross-correlation analysis using broadband continuous seismic waveform data from the Greenland ice sheet  Genti Toyokuni1, Hiroshi Takenaka2, Masaki Kanao3, Seiji Tsuboi4, and Yoko Tono5 1RCPEVE, Graduate School of Science, Tohoku University, Sendai, Japan 2 Graduate School of Natural Science & Technology, Okayama University, Okayama, Japan 3NIPR, Tokyo, Japan 4JAMSTEC, Yokohama, Japan 5MEXT, Tokyo, Japan  The GLISN (GreenLand Ice Sheet monitoring Network) is an international project to seismologically monitor changes in the Greenland ice sheet, by deploying a large broadband seismograph network in and around Greenland. This project is currently managed through joint collaboration by 11 countries for operating 32 seismic stations, although only four of them are on the ice sheet. Japan is a partner country from when the project was launched, and has been sending a field team every year since 2011. A joint USA and Japanese GLISN team has ever serviced three stations on ice sheet (station code: ICESG, DY2G, and NEEM) and also three stations on bedrock at the coastal area (NUUK, SOEG, and DBG), which indicates a great effort of this team among the whole GLISN committee. Especially in 2015, the joint team succeeded in relocating a seismometer at ICESG station, by excavation from 5 m depth below the snow surface.  The GLISN broad-band seismic data (20 sps) is available in realtime via the Iridium satellite network. The data is also open to the public at the IRIS Data Management Center (http://www.iris.edu/ds/nodes/dmc/). In this work, we detected the Rayleigh wave by the ambient noise cross-correlation analysis of the GLISN data, to investigate shallow structure including both ice sheet and bedrock in Greenland.       We used the vertical-component records during Jan. 1, 2015 – Apr. 20, 2015 from four GLISN stations on ice sheet (ICESG, DY2G, NEEM, SUMG). Daily cross-correlation functions (CCFs) for all possible pairs of stations are computed by the following procedure. First, we divide the continuous records into 600-s-long segments with 450-s overlap. Second, we correct the instrument response, eliminate segments with event data or error values, and apply the whitening in frequency domain and banalization in time domain. After that we calculate the daily CCFs by stacking CCFs for each segment (e.g., Shapiro & Campillo, 2004; Takagi & Okada, 2012). The final CCFs can be obtained by stacking all daily CCFs for the whole analysis range.  We found, for example, nearly constant Rayleigh wave group velocity of 2.8 km/s, for the period range of 2-14 s, on the CCF of the NEEM-SUMG pair. We also found that the ambient-noise sources are well corresponded to ground strong wind areas. In the presentation, we will show results for the other station pairs.  References Shapiro, N.M. and M. Campillo, Emergence of broadband Rayleigh waves from correlations of the ambient seismic noise, Geophys. Res. Lett., 31, L07614, doi:10.1029/2004GL019491, 2004. Takagi, R. and T. Okada, Temporal change in shear velocity and polarization anisotropy related to the 2011 M9.0 Tohoku-Oki earthquake using KiK-net vertical array data, Geophys. Res. Lett., 39, L09310, doi:10.1029/2012GL051342, 2012.  

Ambient noise cross-correlation analysis using broadband continuous seismic waveform data from the Greenland ice sheet

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Ambient noise cross-correlation analysis using broadband continuous seismic waveform data from the Greenland ice sheet

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