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Volume 68, Issue 2
Displaying 1-3 of 3 articles from this issue
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ARTICLES
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Tomoko EMOTO, Noriko TSUMURA, Hiroshi FURUYA, The Research Group for t ...2015 Volume 68 Issue 2 Pages 17-29
Published: July 10, 2015
Released on J-STAGE: October 06, 2015
JOURNAL FREE ACCESSTo determine crustal structure of the Neodani Fault zone, where the largest inland Nobi earthquake occurred in 1891, an active-source seismic experiment was carried out in the northern Mino region, central Japan. The shots were recorded by seismic array stations settled across the Neodani Fault Zone and we applied seismic reflection analysis to the data and obtained reflection profiles of the crust. Then we estimated crustal velocity by forward modeling using travel times of first break and reflected waves. We found significant reflections with duration of 2 s around 10 s two way travel time. Based on comparisons with other reflection profiles, we interpreted the events to come from the laminated lower crust within the overriding plate. The depth of the laminated crust varies across the Neodani Fault Zone, which is shallower in the southwest than in the northeast, implying that displacement along the Neodani faults extends to the deep crust. In the southwestern part of study area, the top of the Philippine Sea plate (PSP) estimated from travel time tomography is shallower than the lower limit of the laminated lower crust. We thus suggest that the subducting PSP may contact with the bottom of the overriding crust beneath the northern Mino district.View full abstractDownload PDF (8640K) -
Masayuki KANO, Hiromichi NAGAO, Shin’ichi SAKAI, Shigeki NAKAGAWA, Sad ...2015 Volume 68 Issue 2 Pages 31-44
Published: July 10, 2015
Released on J-STAGE: October 06, 2015
JOURNAL FREE ACCESSThe dense seismic array “MeSO-net” (Metropolitan Seismic Observation network), in which 296 accelerometers, at this moment, are installed with several kilometer intervals, was established in 2007 for the purpose of the disaster mitigation for forthcoming large earthquakes. Whether the actual azimuths of MeSO-net seismometers newly installed after 2009 were really in the magnetic north or not has not been verified yet, while the azimuths of three seismometers installed before 2008 were already confirmed to be in the opposite direction. Since such obvious errors in the azimuths badly affect subsequent data processing, we evaluate the azimuths of all seismometers based on cross-correlations with seismograms recorded at nearby Hi-net tiltmeters and F-net broadband seismometers. Our result suggests that the northward components at more than 80% of stations are determined to be within 10 degrees from the magnetic north, while those at the three stations are reconfirmed to rotate more than 90 degrees as the previous study pointed out. Correcting azimuths of all seismograms based on the result, the estimated coherence is clearly improved in the frequency band less than 0.10Hz.View full abstractDownload PDF (5869K) -
Mamoru KATO, Jun HIOKA2015 Volume 68 Issue 2 Pages 45-53
Published: July 10, 2015
Released on J-STAGE: October 06, 2015
JOURNAL FREE ACCESSKyoto City has experienced a number of large seismic ground motions since it was established approximately 1200 years ago. Descriptions of these shakings are recorded in written documents which have been used to investigate historic earthquake hazards. In those documents often appears that stone lanterns at major temples and shrines collapsed and suffered damages, and descriptions of such damages are used to determine that the shaking at that site was at least as severe as 5 in JMA Intensity Scale. When stone lanterns are heavily damaged during earthquakes, some of them would be removed from the site and replaced by new ones afterward, which implies that the age distribution of stone lanterns which we observe today is affected by the history of strong ground motions. We examine ages of stone lanterns at Kitano-Tenmangu Shrine, Kyoto and investigate whether the correlation between the ages of stone lanterns and historic earthquakes is evident at this site. Severe damages of stone lanterns caused by strong ground motions in 1830 and 1854 at this site are documented in the historic documents, and we are able to identify that high numbers of stone lanterns that were newly build within a few years of these earthquakes currently remain at this site. We statistically argue that ages of existing stone lanterns at Kitano-Tenmangu Shrine are affected by historical strong seismic ground motions in Kyoto, and that these stone lanterns as a group record occurrence of historic earthquakes in Kyoto.View full abstractDownload PDF (1424K)
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