Browsing by Author "Obayashi, Masayuki"

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    Lg attenuation in northeast China using NECESSArray data
    (Oxford University Press on behalf of The Royal Astronomical Society, 2015) Ranasinghe, Nishath R.; Gallegos, Andrea C.; Trujillo, Andrea R.; Blanchette, Alexander R.; Sandvol, Eric A.; Ni, James; Hearn, Thomas M.; Tang, Youcai; Grand, Stephen P.; Niu, Fenglin; Chen, Yongshun J.; Ning, Jieyuan; Kawakatsu, Hitoshi; Tanaka, Satoru; Obayashi, Masayuki
    The 127 station NorthEast China Extended SeiSmic Array (NECESSArray) provides large quantities of high quality seismic data in northeast China that allow us to resolve lateral variations of Lg Q or crustal attenuation at 1 Hz (Qo) to 2.0° or greater. Using the reverse two-station/event method with 11 642 Lg path-amplitudes from 78 crustal earthquakes, we obtain a 2-D tomographic image of Lg Qo with values ranging from ∼50 to 1400. A high degree of detail in the lateral variation of Lg attenuation is revealed in our tomographic image. High Qo regions are found in the Great Xing'an, Lesser Xing'an and Songen-Zhangguangcai Ranges. Low Qo regions are observed in the Songliao, Sanjiang and Erlian Basins. The lowest Qo is found near the Wudalianchi volcanic field and other Quaternary volcanic fields, the southern Songliao Basin, the western edge of the Erlian Basin and the Sanjiang Basin. Low Qo values are measured for paths that cross sedimentary basins with thick, unconsolidated sediments. Most of the high Lg attenuation in the Songliao Basin correlates reasonably well with low crustal Rayleigh wave phase velocity anomalies. The highest attenuating regions also correlate well with regions of Holocene volcanism..
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    Upper mantle tomography in the northwestern Pacific region using triplicated P waves
    (Wiley, 2014) Takeuchi, Nozomu; Kawakatsu, Hitoshi; Tanaka, Satoru; Obayashi, Masayuki; Chen, Y. John; Ning, Jieyuan; Grand, Steve P.; Niu, Fenglin; Ni, James; Iritani, Rryohei; Idehara, Koki; Tonegawa, Takashi
    We conducted delay time tomography of the upper mantle beneath the northwestern Pacific using P data from NorthEast China Extended SeiSmic Array, F-net, and nearby available stations. To improve resolution and accuracy in the vicinity of mantle discontinuities, we extracted traveltimes of both initial and secondary phases observed at triplication distances by using a waveform fitting technique. Compared with the model obtained by using only the initial phase, the resolution just above the 410 km discontinuity is especially improved, and low-velocity anomalies beneath the Changbai Volcano are clearly observed down to the 410 km discontinuity. Compared with previous models, low-velocity anomalies atop the 410 are more pronounced. The results of this study together with the previous receiver function analysis provide further support that we have hot material beneath the Changbai Volcano