著者

澁谷 拓郎

出版者

京都大学

雑誌

基盤研究(C)

巻号頁・発行日

2011-04-28

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本研究では、南海トラフ巨大地震の発生や強震動の予測を高度化するために、巨大地震の震源域であり、破壊開始点であり、強い地震波の経路である紀伊半島の3 次元地震波速度構造を正確に推定することを試みた。沈み込むスラブが深さ30~40 kmに達するあたりの深部低周波イベント発生域は、低速度異常を示した。和歌山県北部の地震活動が活発な地域の下部地殻にも強い低速度異常域が存在することがわかった。これらは、スラブ内の含水鉱物が深部低周波イベント発生域付近で脱水分解して、その結果放出された流体がマントルウェッジや下部地殻に移動して、低速度域を作り出し、地震発生に関与していることを示している。

著者

中尾 節郎 片尾 浩 澁谷 拓郎 渡辺 邦彦

出版者

京都大学防災研究所

雑誌

京都大学防災研究所年報 (ISSN:0386412X)

巻号頁・発行日

no.45, pp.561-569, 2001

被引用文献数

1

著者

飯尾 能久 松本 聡 松島 健 植平 賢司 片尾 浩 大見 士朗 澁谷 拓郎 竹内 文朗 西上 欽也 廣瀬 一聖 加納 靖之 儘田 豊 宮澤 理稔 辰己 賢一 和田 博夫 河野 裕希 是永 将宏 上野 友岳 行竹 洋平 Bogdan ENESCU

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.58, no.4, pp.463-475, 2006-03-31 (Released:2010-03-11)

参考文献数

44

被引用文献数

1 2

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The 2004 Mid Niigata Prefecture Earthquake (MJMA 6.8) occurred on 23 October 2004. The mainshock was followed by four aftershocks with MJMA≥6.0. This earthquake is located in the Niigata-Kobe Tectonic Zone in which large strain rates (>0.1ppm/y contraction) have been observed by GPS data. We deployed three temporary online seismic stations in the aftershock area. Combining data from the temporary stations and from permanent stations around the aftershock area, we determined aftershock locations, and estimated the structures and the stress change in and around the aftershock region. Based on these results, we suggested a generating process of the 2004 Mid Niigata Prefecture Earthquake supposing that a very weak region exists in the weak zone in the lower crust just beneath the seismogenic fault.

著者

澁谷拓郎

出版者

京都大学

雑誌

京都大学防災研究所年報

巻号頁・発行日

vol.43(B-1), 2000

著者

澁谷 拓郎 平原 和朗 上野 友岳

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.61, no.Supplement, pp.199-207, 2009-07-31 (Released:2013-11-21)

参考文献数

38

被引用文献数

2

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Receiver function analyses have been developed since the late 1970s. Receiver functions are calculated by deconvolving the vertical component from the horizontal components of teleseismic P waveforms in order to remove the complexities of the source time functions and to extract the structural information beneath seismic stations. The receiver functions are sensitive to impedance discontinuities of the earth’s interior, especially to the shear wave velocity discontinuities. Therefore, the receiver function analyses have advantages in estimating the shear wave velocity structure and imaging the shear wave velocity discontinuities. In this paper we introduce several basic topics of the receiver function analyses. Firstly, we discuss the method of the calculation of the receiver functions, pointing out weaknesses in the water level method and the multitaper method and introducing the extended-time multitaper method. Secondly, we describe the inversions of the receiver functions for the shear wave velocity structure. We show two examples with the genetic algorithm. Thirdly, we introduce the way and several examples to image the shear wave velocity discontinuities with the use of the receiver functions. Finally, we discuss issues in the receiver function analyses which have not been addressed yet but should be in the near future.

著者

北 佐枝子 Heidi Houston 田中 佐千子 浅野 陽一 澁谷 拓郎 須田 直樹

出版者

日本地球惑星科学連合

雑誌

日本地球惑星科学連合2019年大会

巻号頁・発行日

2019-03-14

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The slip on the plate interface has the potential to affect the stress field and seismicity within the subducting slab. Several studies have examined the interaction of slow slip phenomena with intraslab earthquakes [Nankai and Tokai regions, Han et al. 2014; Mexico, Radiguet et al. 2018, 2018 JpGU meeting; New Zealand, 2018, Warren-Smith, 2018 AGU meeting]. Kita et al. [2018, SSJ meeting] reported the stress change in the whole slab associated with ETS times based on stress tensor inversion results. However, we find a clear double seismic zone under Kii Peninsula, as also noted in a previous study [e.g. Miyoshi and Ishibashi, 2004]. Therefore, we here examine seismicity rate variations, stress changes, and b-value variations of seismicity separately for the upper plane events and oceanic mantle ones relative to ETS timings beneath the Kii Peninsula. We use the JMA earthquake catalog, the NIED tremor catalog, the upper surface of the Philippine sea plate estimated by Shibutani and Hirahara [2016], P-wave polarity data by NIED, and a stress tensor inversion code [Vavrycuk, 2014].We determined the timings of ~30 large ETS beneath the Kii Peninsula from 2001 to 2017, and categorized slab seismicity relative to the occurrence times of nearby the ETS (i.e., 60 days before or after). We then combined or stacked the slab seismicity based on these relative occurrence times. The rate of seismicity both in the upper plane events and in the oceanic mantle ones after the ETS timings clearly decreased, compared to the rate before the ETS timings. The peaks of b-values of seismicity both in the upper plane events and oceanic mantle ones were found to occur 1.5 months before ETS. A change in stress orientations before and after the ETS was seen in the oceanic mantle, and a relatively small change was seen for the upper plane events. The stress change in the upper plane events appears to be larger in the region updip of the ETS zone. The results of our study suggest that the aseismic slip on the plate boundary may affect the stress field and the occurrence of seismicity within the subducting slab beneath the Kii Peninsula. Fluid migration from the oceanic slab into the ETS zone on the plate boundary could be related to the interaction of slow slip phenomena with intraslab earthquakes.

著者

平原 和朗 澁谷 拓郎

出版者

日本自然災害学会

雑誌

自然災害科学 (ISSN:02866021)

巻号頁・発行日

vol.31, no.1, pp.3-22, 2012