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.
2 0 0 0 OA CMT解と震源時間関数の迅速な自動決定とその結果の評価
- 著者
- 堀 貞喜 堀内 茂木 石田 瑞穂 大井 昌弘
- 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.52, no.3, pp.395-405, 1999-12-25 (Released:2010-03-11)
- 参考文献数
- 26
- 被引用文献数
- 1 1
Recent advances in broadband seismic observation enable us to analyze high quality waveform data just after the earthquake occurrence. An automated system for rapid determination of earthquake mechanisms for local events occurring beneath central Japan is developed with this point as background. When an earthquake occurs, its hypocentral parameters are determined automatically in several tens of seconds. In a case when an event occurring in a given area has a magnitude larger than a certain value, its source process is automatically analyzed by the use of a broadband waveform inversion technique. Considering the importance to shorten the computer process time to obtain the result, we calculate the Green's functions immediately after hypocentral parameters are calculated and when waveform data to be used in the inversion are being retrieved. The data of the Earth's response parameters, which are used in the calculation of the Green's functions, are stored on the hard disk so as to reduce the total lapse time. As a result, the CMT solution and source time function can be obtained in a few minutes after the earthquake occurrence. Inadequacy of theoretical waveform calculated by the 1-D Earth's model is corrected by introduction of station corrections to the observed arrival time and overparameterization to the source time function, where a number of double couple small sub-events are located in a certain time range. The CMT solution is represented by superimpose of moment tensors of small sub-events with very short duration. All the sub-events are assumed to occur at the same location (i. e., at the hypocenter) but to have different onset times. The source time function is also estimated from the temporal distribution of the sub-events. To evaluate the reliability of the results obtained from the present study, we compare them with the following two data sets: i) focal mechanism solutions determined by P first motion analysis, and ii) CMT solutions obtained from the other method for the same events. Our results are basically consistent with these two sets of mechanism solutions. However the agreement of the solutions is obviously better among the CMT solutions. Possible explanation for the difference between CMT and focal mechanism solutions is that the latter may be inaccurate because of insufficient push and pull first motion data, or that the total rupture may occur along the fault different from the initial rupture.
- 著者
- 堀 貞喜
- 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.39, no.3, pp.457-468, 1986-09-25 (Released:2010-03-11)
- 参考文献数
- 10
- 被引用文献数
- 5 5
The upper mantle earthquake of MJMA=6.1 which occurred beneath the Kanto district on October 4, 1985 was investigated in detail for analyzing its difference from other earthquakes around this event. Most of the upper mantle earthquakes at depths of 60-80km beneath this region has been explained that they are the interplate earthquakes with the thrust type focal mechanisms caused by the subducting motion of the Pacific plate relative to the overriding plate. But the present event was not categorized into such a type of earthquakes; the focal mechanisms of the main- and the aftershocks were the strike slip types rather than the dip slip ones. Redetermination of the hypocenters of the main- and aftershocks by using selected stations and station corrections revealed that the focal are a of the present earthquake was not smoothly connected with other groups of the upper mantle earthquakes. The present event obviously occurred below the upper surface of the Pacific plate. Namely, it is concluded to be an intraplate earthquake. The Pacific plate seems to be Λ-shape structure in the vicinity of the focal area of the M 6.1 event, where the plate is considered to be strongly coupled with the overriding plate. It is likely that the local difference in the subducting rate of the Pacific plate between the northern and southern limbs of the plate caused the intraplate fructure along the hinge plane of the plate. It is suggested that the temporal variation of the pattern of seismic activity around the focal region of the present event is related to an occurrence of the M 6.1 event.
1 0 0 0 OA 首都圏直下とその付近でのフィリピン海プレートスラブの形態
- 著者
- 江口 孝雄 堀 貞喜
- 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.3-4, pp.325-369, 2007-08-25 (Released:2009-11-12)
- 参考文献数
- 142
- 被引用文献数
- 1
We present a new view of the morphology of slab (s) subducted just beneath the Tokyo Metropolitan Area in Japan. Previously, several different models of the surface geometry of the subducted Philippine sea plate slab (PH slab) have been published mainly using seismicity data (e.g., Nakamura and Shimazaki, 1981; Maki, 1984; Kasahara, 1985; Ishida, 1992; Noguchi, 1998; Hori, 2006).In this study, first we discriminate a previously unknown seismic slab (called slab SG, or seismic slab SG) above the downgoing Pacific plate slab (PC slab), second identify the possible internal structure of slab SG, and third demonstrate tectonic evolution models. It is clear that the currently known surface contours of PH slab indicate the shallowest part of slab SG as well.Most previous studies assumed a PH slab with a constant thickness, and paid little attention to the tectonic characteristics of the vertical extent and/or the bottom geometry of slab SG with variable thickness. The bottom extent of the seismic slab SG beneath the Metropolitan area reaches 36.5N at least. The horizontal extent of seismic slab SG covers most of the lowland Kanto Plain. The bottom depth of slab SG is approximately 120 km near 36.5N and 139.0E, being the same as the surface depth of the PC slab there. Below the Sagami Trough axis near 34.5N and 140.0E, the lowest portion of slab SG is located at a depth of 80 to 90 km. The western bottom end zone of slab SG generally strikes in the NNW-SSE direction, being approximately parallel to the volcanic front.We suggest four basic morphology models of slab SG as follows. (1) Slab SG consists of both the PH slab at a shallower depth and a deeper underlain slab (slab SL). (2) A bookshelf-like configuration of northwardly inclined multi-slabs on the PC slab due to the intermittent southward shift of accumulation sites of short slab tips with episodic subduction at just south of the previously active paleo-Sagami Trough (s). We emphasize that the above evolutional bookshelf model is, to some extent, similar to the sediment layer accretion process near the deep trench system, but the dynamic situation is not the same. (3) A structure combining models (1) and (2). (4) Slab SG is merely the eastern part, having been cooled by the downgoing PC slab, of 65-70 km thick lithosphere of the Izu Outer Block (JOB) without any other slab components.To clarify the structure of the SG slab in more detail, we should incorporate high-gain seismic data from the on-line operating dense seismic observation network deployed at both marine and land areas covering the metropolitan area. In addition, we must study the effects of 3D mantle wedge circulation with dehydration process due to the subduction of both PC and PH slabs from different directions, as well as the space-time evolution history of accretion tectonics at the northern end zone of the Philippine sea plate.
1 0 0 0 OA 関東地方下のフィリピン海プレート内地震の発生機構
- 著者
- 堀 貞喜
- 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.50, no.2, pp.203-213, 1997-08-28 (Released:2010-03-09)
- 参考文献数
- 36
- 被引用文献数
- 2
The upper mantle earthquakes occurring within the Philippine Sea plate subducting beneath the Kanto district, Japan, were investigated for their hypocentral distribution and focal mechanisms. Earthquakes located above the double seismic plane, which is formed in conjunction with the subducting motion of the Pacific plate, were picked up on a graphic display with an “on-map selection” method. Hypocentral parameters were re-determined with removing stations far from the epicenter and with introducing station corrections to the observed arrival time data. Based on the relocated hypocenters, the focal mechanism solutions were also re-determined. Examining the hypocentral distribution in detail, we found that the earthquakes occurring within the Philippine Sea plate are classified into three groups and that their focal regions form a triple-layered structure. The earthquakes in Group I, which are located at the uppermost part of the slab, were found to occur in the oceanic crust of the Philippine Sea plate from their waveform analysis. The focal mechanism analysis showed remarkable difference between the earthquakes in Groups II and III. The down-dip compression type events are predominant for the earthquakes in Group II, while most of the focal mechanisms in Group III showed the earthquakes are occurring under the down-dip extension. We proposed a model to explain the earthquake mechanism within the Philippine Sea plate, where the “forced unbending” by the underlying Pacific plate causes compressional and extensional stress fields in the upper and lower portion of the slab, respectively.
- 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。
