著者

八木 勇治 菊地 正幸 吉田 真吾 山中 佳子

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.51, no.1, pp.139-148, 1998-07-03 (Released:2010-03-11)

参考文献数

26

被引用文献数

16 23

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We investigate the rupture process of Hyuga-nada earthquake of April 1, 1968 (MJMA 7.5). Applying a multiple-time window inversion scheme to teleseismic body wave data, we obtained a detailed spatio-temporal distribution of moment release. The main source parameters are: the seismic moment=2.5×1020[Nm]; the rupture area=64×48[km2]; the stress drop=3.4[MPa]; the focal depth=15[km]. The rupture consists of three major asperities: the first asperity centring about 10km south and 20km west from the hypocenter and having a maximum slip of 4.0m, the second one centring about 8km north and 5km east from the hypocenter and having a maximum slip of 3.0m, and the third one centring about 50km west from the hypocenter and having a maximum slip of 3.2m. We compared the rupture area with that of a few large events (M>6.5) subsequent to the 1968 event. Then we found that the above three asperities of 1968 event coincide with the low seismicity area in the Hyuga-nada region, and do not overlap with the source area of the subsequent large events (M>6.5). This rupture pattern and the seismicity suggest that an area of slab bending as well as fracture of the slab can behave as barriers during earthquake rupture. These barriers may control the maximum size of earthquake source in this region.

著者

永井 理子 菊地 正幸 山中 佳子

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.54, no.2, pp.267-280, 2001-09-20 (Released:2010-03-11)

参考文献数

25

被引用文献数

29 54

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In an attempt to examine the characteristic behavior of fault asperities (large slip areas), we comparatively studied two large earthquakes: the Tokachi-oki earthquake (M 7.9) of May 16, 1968 and the Sanriku-oki earthquake (M 7.5) of December 28, 1994, which have a partially common source area. Both the strong motion records at a regional network and the teleseismic body waves at global networks were analyzed to determine the detailed spatio-temporal distribution of moment release. The aftershock distribution, which may provide us with a more reliable location of asperity, was also re-examined using the same underground structure and the same algorithm for both events.The total seismic moment, Mo, and the source duration, T are obtained as: Mo=3.5×1021Nm; T=90s for the 1968 event, and Mo=4.4×1020Nm; T=60s for the 1994 event. It is also shown that the 1968 event consists of more than two asperities, one of which took a role of asperity again for the 1994 event. The distribution of relocated aftershocks, which fringe the major asperities, strongly supports this fact. A simple calculation indicates that the seismic coupling is almost perfect (100%) in this common asperity. We thus propose that there exist characteristic sites for asperities where fault slip occurs only as a seismic event, and that the individual asperities usually manifest M 7 class earthquakes but sometimes synchronize to cause M 8 class earthquakes.

著者

菊地 正幸 山中 佳子 纐纈 一起

出版者

学術雑誌目次速報データベース由来

雑誌

地學雜誌 (ISSN:0022135X)

巻号頁・発行日

vol.110, no.2, pp.204-216, 2001

参考文献数

12

被引用文献数

1 21

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A sudden collapse of the summit of Miyake-jima occurred on July 8, 2000, together with intermittent eruptions. This collapse generated long-period seismic waves with a dominant period of about 10s. Following this event, very long-period seismic pulses (VLP pulses) with a duration of about 50s were observed a few times a day until they ceased at the largest summit eruption on August 18. We analyzed these seismic pulses using waveform data recorded at several domestic stations for broadband seismographs and strong motion seismometers on Miyake-jima. The July 8 event is well characterized by a single-force directed initially upward and later downward during 12 sec. The single-force is interpreted as an abrupt collapse of massive rock. The total mass is estimated to be about 5 × 10<SUP>10</SUP> kg with fall of about 300 m. On the other hand, VLP pulses are modeled by moment-tensors with an isotropic component. They are located about 1 km southwest from the summit and 2 to 3 km deep. All three principal values are positive. The largest one is horizontal and the smallest one is near vertical. The total volume change due to 39 VLP pulses is 2.6× 10<SUP>8</SUP>m<SUP>3</SUP>, amounting to nearly one half of the total volume of the summit collapse. Based on theresults, we propose a buried geyser model. A large reservoir of hot water was formed just after the summit collapse on July 8. The ground water poured into the reservoir, being rapidly heated by hot rock underneath, and evaporated to form a highly pressurized steam, which pushed a lower conduit piston into the magma reservoir to generate VLP pulses. Non-isotropic expansion of the VLP pulses may be ascribed to the shape of the magma reservoir.

著者

古村 孝志 纐纈 一起 坂上 実 山中 佳子 高橋 正義

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.54, no.2, pp.299-308, 2001-09-20 (Released:2010-03-11)

参考文献数

12

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Seismic intensity at Shikine-jima during the earthquake swarm of Izu-Islands in 2000 is usually one or two ranks higher than that at neighbor island, though epicentral distances to these islands are almost similar. In order to investigate the cause of anomalous large seismic intensity, three portable strong motion instruments have been installed at the island.The spectral ratios of observed S waveforms at sedimentary stations at Shikine-jima demonstrate severe site amplification of 2 to 10 within a wide frequency range between 1 to 10Hz relative to rock site. The experiments based on a GA inversion indicate unusual subsurface structure with very low (VS=31-427m/s) and high attenuation (QS=15-148) superficial layer overlying a bedrock (VS=1000m/s, QS=200) with large contrast at the interface is a main cause of high seismic intensities.The influence of nonlinearity was also found near a coast of Shikine-jima when the ground acceleration level exceeds 300cm/s2. The nonlinear ground response yielded a considerable reduction of the ground motions, so that the observed peak accelerations during the severe earthquakes were only about 50% of that predicted by linear ground response.

著者

前田 裕太 寺川 寿子 加藤 愛太郎 山中 佳子 古本 宗充 山岡 耕春 堀川 信一郎 松廣 健二郎 奥田 隆

出版者

特定非営利活動法人日本火山学会

雑誌

日本火山学会講演予稿集

巻号頁・発行日

vol.2014, 2014-11-02

著者

篠原 雅尚 村井 芳夫 藤本 博己 日野 亮太 佐藤 利典 平田 直 小原 一成 塩原 肇 飯尾 能久 植平 賢司 宮町 宏樹 金田 義行 小平 秀一 松澤 暢 岡田 知己 八木 勇治 纐纈 一起 山中 佳子 平原 和朗 谷岡 勇市郎 今村 文彦 佐竹 健治 田中 淳 高橋 智幸 岡村 眞 安田 進 壁谷澤 寿海 堀 宗朗 平田 賢治 都司 嘉宣 高橋 良和 後藤 浩之 盛川 仁

出版者

東京大学

巻号頁・発行日

2010

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2011年3月11日、東北地方太平洋沖でM9.0の巨大地震が発生し、地震動・津波被害をもたらした。この地震の詳細を明らかにするために、各種観測研究を行った。海底地震観測と陸域地震観測により、余震活動の時空間変化を明らかにした。海底地殻変動観測及び地震波反射法構造調査から、震源断層の位置・形状を求めた。さらに、各種データを用いて、断層面滑り分布を明らかにした。現地調査により、津波の実態を明らかにし、津波発生様式を解明した。構造物被害や地盤災害の状況を明らかにするとともに、防災対策に資するデータを収集した。

著者

山中 佳子 山中 佳子

出版者

名古屋大学大学文書資料室

雑誌

名古屋大学大学文書資料室紀要 (ISSN:13493868)

巻号頁・発行日

no.21, pp.221-237, 2013-03

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シンポジウム記録「東海大地震からアーカイブズをどう守るべきか : 震災への保存と地域連携を考える」(名古屋大学シンポジオンホール, 2013年2月7日)

著者

勝俣 啓 山中 佳子

出版者

北海道大学大学院理学研究科地球惑星科学専攻(地球物理学)

雑誌

北海道大学地球物理学研究報告 (ISSN:04393503)

巻号頁・発行日

no.69, pp.23-39, 2006-03

被引用文献数

3

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We have investigated the source process and the aftershock distribution of a large earthquake with M=7.1 occurred on 29 November 2004 off the coast of Kushiro (or Shiranuka) in the eastern Hokkaido,Japan. The source parameters are summarized as follows:the total seismic moment M_0=3.4×10^{19}Nm,thatis,M_w=7.0;(strike,dip,ship)=(238°,33°,117°);depth of the initial break point=48 km;and source duration time =10sec. The aftershocks were relocated using the three-dimensional velocity structures of P-and S-waves,and we found that the aftershocks concentrated on a plane with the area of 30×15㎞^{2}dipping 22°toward the landside whose orientation agrees closely with that of the northwest-dipping nodal plane of the focal mechanism. The stress drop was estimated to be 89 bars. The aftershock area does not overlap with the asperity ruptured by the main shock,but outlined the asperity. These observations strongly suggest that the main shock itself is a very usual interplate event at depth of around 50 km in the Japan subduction zone. However,taking the tectonic circumstance into account,thisi is an outstanding event since the focal area was located between the five-years-lasting seismic quiescence area and the asperity ruptured by the 1973 Nemuro- Oki earthquake.