18 0 0 0 OA 特集号「地殻からマントルまで―モホ(面)とは何か?―」はじめに
12 0 0 0 OA 高精度即時震源パラメータ解析システム (AQUA)の開発
- 著者
- 松村 稔 伊藤 喜宏 木村 尚紀 小原 一成 関口 渉次 堀 貞喜 笠原 敬司
- 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.59, no.2, pp.167-184, 2006-12-15 (Released:2013-08-05)
- 参考文献数
- 27
- 被引用文献数
- 7 10
We have developed an automatic system called the Accurate and QUick Analysis System for source parameters (AQUA System) that provides rapid estimates of hypocenter location, magnitude, and moment tensor for medium to large-scale earthquakes that occur near or underneath Japan. The AQUA System monitors high-sensitive real-time seismic waveform output from the Hi-net operated by the National Research Institute for Earth Science and Disaster Prevention (NIED). Upon detecting an earthquake, the AQUA System provides an estimate of the event’s hypocenter and magnitude within 15-30 seconds. Within a further 2-10 minutes, the system provides centroid moment tensor (CMT) solution by inversion technique using broadband seismic waveform of NIED F-net. To assess the accuracy of the new system, we compared hypocenter and magnitude data derived from the AQUA System over the period from September 2004 to August 2005 with catalog data from the Japan Meteorological Agency (JMA). We also compared CMT solutions derived from the AQUA System with corresponding values from the NIED F-net and catalog data of Harvard University’s CMT Project. A total of 339 seismic events were detected during the period of analysis. The AQUA System determined hypocenters for 324 of these events and CMT solutions for 224 events. The estimated hypocenters are within 10km horizontally and 20km vertically of the hypocenters calculated by the JMA in 80% of cases, and the CMT solutions were approximately the same as those obtained from other systems. The results of analyses by the AQUA System are published on the website of NIED Hi-net.
- 著者
- 栗原 亮 小原 一成
- 出版者
- 日本地球惑星科学連合
- 雑誌
- JpGU-AGU Joint Meeting 2020
- 巻号頁・発行日
- 2020-03-13
3 0 0 0 西南日本における超低周波地震の網羅的検出
- 著者
- 馬場 慧 武村 俊介 小原 一成
- 出版者
- 日本地震学会
- 雑誌
- 日本地震学会2019年度秋季大会
- 巻号頁・発行日
- 2019-08-15
2 0 0 0 OA スロー地震と水
- 著者
- 小原 一成
- 出版者
- 公益社団法人 東京地学協会
- 雑誌
- 地学雑誌 (ISSN:0022135X)
- 巻号頁・発行日
- vol.116, no.1, pp.114-132, 2007-02-25 (Released:2009-11-12)
- 参考文献数
- 60
- 被引用文献数
- 3 2
Water affects many geological and geophysical phenomena, for example, earthquake generation. Recently, anomalous earthquakes, which are strongly related to fluid have been detected in a subduction zone by densely distributed geodetic and seismic observation networks. These are called slow earthquakes and are divided into many categories of earthquakes. The long-term slow slip in Tokai or Bungo Channel, which occurs at the subducting plate interface, is a phenomenon with a very long time-constant ranging from months to years. At the deeper part of the long-term slow slip, the short-term slow slip occurs with a period of several days associated with the non-volcanic deep low-frequency tremor in the transition zone on the plate interface in southwest Japan. These slow earthquakes might be related to fluid liberated from the down-going slab by dehydration process. At the shallower part of the subducting plate interface, the very low-frequency earthquakes occur in the accretionary prism near the Nankai trough. These slow earthquakes indicate a weakening of frictional strength at the plate interface and low stress drop due to the existence of fluid.
2 0 0 0 OA フィリピン海プレート沈み込みに伴う浅部および深部スロー地震群
- 著者
- 小原 一成
- 出版者
- 一般社団法人 日本地質学会
- 雑誌
- 地質学雑誌 (ISSN:00167630)
- 巻号頁・発行日
- vol.115, no.9, pp.437-447, 2009 (Released:2010-03-10)
- 参考文献数
- 55
- 被引用文献数
- 3 1
近年の高密度地震観測網整備に伴い,南海トラフから西南日本に沈み込むフィリピン海プレートの境界付近で,様々なスロー地震が検出されている.巨大地震発生域の深部では,数日間継続するプレート境界固着すべりとしての短期的スロースリップイベント,周期20秒に卓越する深部超低周波地震,2 Hzに卓越する深部低周波微動が,全長約600 kmの帯状領域に沿って複数のセグメントに分かれ,半年あるいは3ヶ月など周期的に発生する.また,南海トラフ陸側の付加体内部では周期約10秒に卓越する浅部超低周波地震が発生している.これらのスロー地震は,浅部では付加体変形過程,深部では沈み込むフィリピン海プレートの海洋地殻あるいは付加体堆積物での脱水分解反応や変成作用と関わっている可能性があり,プレート沈み込み帯における地質体形成や流体循環の現場を反映するものとして注目される.
2 0 0 0 OA 1983年日本海中部地震の前震と余震の震源分布
- 著者
- 海野 徳仁 長谷川 昭 小原 一成 松沢 暢 清水 洋 高木 章雄 田中 和夫 小菅 正裕
- 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.38, no.3, pp.399-410, 1985-09-25 (Released:2010-03-11)
- 参考文献数
- 13
- 被引用文献数
- 1 6
Hypocenter determination for aftershocks of the 1983 Japan Sea Earthquake (M7.7) is made by using the seismic networks of Tohoku University and of Hirosaki University. The obtained aftershock area is 160km long in north-south direction with a width of 40km, distributing itself along the eastern margin of the Japan Basin. Most of the aftershocks are located within the area bordered by the 2000m and 3000m isobaths, northern and southern ends being surrounded by the Sado Ridge and the Oshima Plateau, respectively. Precise hypocenter distribution deliniates an eastward dipping fault plane with a shallow dip angle. Almost all the aftershocks are located in the crust, which is consistent with the fact that the PMP phase is clearly observed from most of the aftershocks.A remarkable later phase is observed at many stations 4-7 sec after the P arrival. This later phase is interpreted as the reflected wave both at the sea surface and at the Moho discontinuity (pwPMP). Focal depth distribution estimated from arrival time differences between PMP and pwPMP phases also shows the eastward dipping fault plane with a shallow dip angle.Foreshock activity started 12 days before the occurrence of the main shock within a concentrated area in the vicinity of the main shock hypocenter. All the foreshocks are classified into two groups: one with high peak-frequency and the other with low peak-frequency, each having very similar wave forms. Hypocenters of low peak-frequency events are located at shallower depths than those of the main shock and high peak-frequency events.
2 0 0 0 OA 地震学的探査によるモホ不連続面の検出
- 著者
- 汐見 勝彦 松原 誠 小原 一成
- 出版者
- 公益社団法人 東京地学協会
- 雑誌
- 地学雑誌 (ISSN:0022135X)
- 巻号頁・発行日
- vol.117, no.1, pp.45-58, 2008-02-25 (Released:2010-02-10)
- 参考文献数
- 35
- 被引用文献数
- 2 2
By the end of the last century, the rough configuration of the Moho discontinuity beneath the Japan Islands had been revealed based on explosion surveys and natural earthquake observations. Recently, however, some researchers have pointed out that local roughness of the Moho geometry or relative location between continental and oceanic Moho might provide important knowledge about the source regions of large earthquakes. Within the southern portion of the Kinki district, the Philippine Sea plate subducts beneath the continental plate at the Nankai Trough. We detect P-to-S converted wave energy from the Moho velocity discontinuity beneath the Kinki district with receiver function analysis, and compare the results of other recent investigations of the depth of Moho. Both oceanic and continental Moho discontinuities are detected in not only our receiver function analysis but also active-source seismic exploration survey and travel-time tomography analysis. The inferred depths of the subducting oceanic Moho beneath the Kii Peninsula, the southern Kinki district, and the continental Moho beneath the northern Kinki correspond well with each other. However, beneath the central Kinki district, no significant converted phases are observed corresponding to the Moho depth inferred from the travel-time analyses. We interpret that no sharp velocity discontinuity exists around the Moho in the central Kinki district.
2 0 0 0 OA スロー地震学
- 著者
- 小原 一成
- 雑誌
- 新学術領域研究(研究領域提案型)
- 巻号頁・発行日
- 2016-06-30
- 著者
- 小原 一成
- 出版者
- 公益社団法人 東京地学協会
- 雑誌
- 地學雜誌 (ISSN:0022135X)
- 巻号頁・発行日
- vol.112, no.6, pp.837-849, 2003
- 被引用文献数
- 5 14
Non-volcanic deep low-frequency tremors detected in southwest Japan are distributed in the forearc side along the strike of the descending Philippine Sea plate. The source depth of the tremor corresponds to the slab interface or the Moho discontinuity. The time sequence of the tremor activity is characterized by long durations from hours to weeks. The mobility and the successive occurrence of the tremor are thought to be related to the existence of fluid liberated from the slab by a dehydration process. The spatial distribution of the tremors is not homogeneous in a narrow belt but is spatially clustered. The major activity of the tremors with relatively long time durations is also clustered periodically, with a period of 2-3 months in the east and middle of Shikoku area and about 6 months in the west of Shikoku. On the other hand, tremors are sometimes triggered by local earthquakes or teleseismic waves. The periodicity of the tremor activity may represent a stable accumulation of fluid with a stable subduction process and the triggering phenomenon implies the unstable condition of the occurrence of tremors.
1 0 0 0 OA 深部低周波微動の時系列的特徴
- 著者
- 小原 一成
- 出版者
- Tokyo Geographical Society
- 雑誌
- 地学雑誌 (ISSN:0022135X)
- 巻号頁・発行日
- vol.112, no.6, pp.837-849, 2003-12-25 (Released:2009-11-12)
- 参考文献数
- 20
- 被引用文献数
- 12 14
Non-volcanic deep low-frequency tremors detected in southwest Japan are distributed in the forearc side along the strike of the descending Philippine Sea plate. The source depth of the tremor corresponds to the slab interface or the Moho discontinuity. The time sequence of the tremor activity is characterized by long durations from hours to weeks. The mobility and the successive occurrence of the tremor are thought to be related to the existence of fluid liberated from the slab by a dehydration process. The spatial distribution of the tremors is not homogeneous in a narrow belt but is spatially clustered. The major activity of the tremors with relatively long time durations is also clustered periodically, with a period of 2-3 months in the east and middle of Shikoku area and about 6 months in the west of Shikoku. On the other hand, tremors are sometimes triggered by local earthquakes or teleseismic waves. The periodicity of the tremor activity may represent a stable accumulation of fluid with a stable subduction process and the triggering phenomenon implies the unstable condition of the occurrence of tremors.
1 0 0 0 OA 首都圏地震観測網(MeSO-net)の展開
- 著者
- 笠原 敬司 酒井 慎一 森田 裕一 平田 直 鶴岡 弘 中川 茂樹 楠城 一嘉 小原 一成
- 出版者
- 東京大学
- 雑誌
- 東京大學地震研究所彙報 (ISSN:00408972)
- 巻号頁・発行日
- vol.84, no.2, pp.71-88, 2010-01-28
To better assess the seismic hazards produced by a magnitude 7 or greater (M 7+) earthquake in the Tokyo metropolitan area, we have launched the Special Project for Earthquake Disaster Mitigation in Tokyo Metropolitan area (2007−2011). This requires establishing a highly dense seismic-array observation network in and around Tokyo to monitor ongoing micro-earthquakes with relatively high precision even if noise levels are generally high. We have started developing the Metropolitan Seismic Observation network (MeSO-net). Deployment of MeSO-net seismic stations is currently underway. The number of observatories at project termination will be 400 with a 2−5km interval in space. In this paper, we summarize how we solved technically difficult and practical problems involved in MeSO-net construction. We start with a review of related work to better understand the technical difficulties involved in deploying stations in metropolitan areas such as Tokyo. Next, we explain our approach to verifying a meaningful design of an observatory and its deployment at local sites. We further describe our decision-making process in practice for implementing station deployment. We hope that establishing the MeSO-net will support a new assessment of the seismic hazards produced by M 7+ earthquakes in the Tokyo metropolitan area.
1 0 0 0 OA 定常観測網から得られた首都直下の三次元地震波速度構造
- 著者
- 松原 誠 小原 一成
- 出版者
- 東京大学地震研究所
- 雑誌
- 東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo (ISSN:00408972)
- 巻号頁・発行日
- vol.84, no.4, pp.331-344, 2009
Many researchers have studied the three-dimensinal seismic velocity structure beneath the Kanto region, central Japan using seismic tomography, because the structure is very complicated due to subducting of the Pacific and the Philippine Sea plates beneath the Eurasian plate. The Tokyo metropolitan area is located in the Kanto region. Initially, the subducting Pacific and Philippine Sea plates are imaged with high-velocity zones. With many data, the oceanic crust at the uppermost part of the subducting Philippine Sea plate was imaged clearly. After construction of the NIED Hi-net, the oceanic ocrust of the Pacific plate subducting to depths over 100km was also imaged. A large low-velocity region at depths of 30-50km beneath the central Kanto region in the east-west direction was found by many researchers. The reason for the low-velocity is considered to be the existence of a serpentinied mantle wedge, curling Eurasian crust, and thick oceanic crust of the Philippine Sea plate. A low-velocity zone at depths of 40-70km beneath the eastern Kanto region with north-south direction was also found. The reason for this low-velocity is considered to be the existence of serpentinied mantle wedge and curling Philippine Sea plate. A high-density seismograph network, called MeSO-net, is under construction in this metropolitan region. The results with these data are expected to reveal a more detailed structure beneath the metropolitan area. We review former studies on the velocity structures beneath the Kanto region and note some characteristic structures beneath the Kanto region with results along arrays of MeSO-net.
1 0 0 0 OA 2011年東北地方太平洋沖地震に関する総合調査
- 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
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。
1 0 0 0 OA 定常観測網から得られた首都直下の三次元地震波速度構造
- 著者
- 松原 誠 小原 一成
- 出版者
- 東京大学地震研究所
- 雑誌
- 地震研究所彙報 (ISSN:00408972)
- 巻号頁・発行日
- vol.84, no.4, pp.331-344, 2009
Many researchers have studied the three-dimensinal seismic velocity structure beneath the Kanto region, central Japan using seismic tomography, because the structure is very complicated due to subducting of the Pacific and the Philippine Sea plates beneath the Eurasian plate. The Tokyo metropolitan area is located in the Kanto region. Initially, the subducting Pacific and Philippine Sea plates are imaged with high-velocity zones. With many data, the oceanic crust at the uppermost part of the subducting Philippine Sea plate was imaged clearly. After construction of the NIED Hi-net, the oceanic ocrust of the Pacific plate subducting to depths over 100km was also imaged. A large low-velocity region at depths of 30-50km beneath the central Kanto region in the east-west direction was found by many researchers. The reason for the low-velocity is considered to be the existence of a serpentinied mantle wedge, curling Eurasian crust, and thick oceanic crust of the Philippine Sea plate. A low-velocity zone at depths of 40-70km beneath the eastern Kanto region with north-south direction was also found. The reason for this low-velocity is considered to be the existence of serpentinied mantle wedge and curling Philippine Sea plate. A high-density seismograph network, called MeSO-net, is under construction in this metropolitan region. The results with these data are expected to reveal a more detailed structure beneath the metropolitan area. We review former studies on the velocity structures beneath the Kanto region and note some characteristic structures beneath the Kanto region with results along arrays of MeSO-net.
- 著者
- 堀 貞喜 石田 瑞穂 青井 真 井上 公 大久保 正 岡田 義光 小原 一成 笠原 敬司 木村 尚紀 熊谷 博之 汐見 勝彦 関口 渉次 根岸 弘明 野口 伸一 松本 拓己 山水 史生 藤原 広行 功刀 卓 浅野 陽一 関根 秀太郎 廣瀬 仁 松原 誠 安逹 繁樹 伊藤 喜宏 針生 義勝 松林 弘智 松村 稔 宮川 幸治 山品 匡史 坂無 雅子 雷 楓 伊東 明彦 岩田 知孝 ト部 卓 川勝 均 木下 繁夫 工藤 一嘉 纐纈 一起 佐藤 春夫 佐藤 比呂志 武井 恵雄 中尾 茂 平田 直 平原 和朗 堀家 正則 松澤 暢 山北 聡 綿田 辰吾 山野 誠
- 出版者
- 独立行政法人防災科学技術研究所
- 雑誌
- 防災科学技術研究所年報 (ISSN:09186441)
- 巻号頁・発行日
- vol.15, pp."I-12"-"I-16", 2004-09-06
地震調査研究推進本部の総合基本施策(「地震に関する観測、測量、調査及び研究の推進についての総合的かつ基本的な施策(平成11年4月23日)」)、及び調査観測計画(「地震に関する基盤的調査観測計画(平成9年8月29日)」、「地震に関する基盤的調査観測計画の見直しと重点的な調査観測体制の整備(平成13年8月28日)」、「地震に関する基盤的調査観測等の結果の流通・公開について(平成14年8月26日)」)等に基づき、高感度・広帯域地震観測施設と強震観測施設を整備し、観測網の維持・管理・運用を行う。これら基盤的観測網と防災科研の在来地震観測網から得られるデータの収集・処理を行い、気象庁、大学等のデータと合わせて蓄積・流通・公開を行う。また、防災科研が海外に整備した観測施設についても、円滑な維持・管理とともに、観測方式の高度化を行いつつ、データの収集・処理・蓄積・公開を行う。さらに、各観測網から得られるデータを用いて、高度な地殻活動のモニタリングを実施し、地震活動状況の推移を判断するための研究成果を創出する。
