著者

森谷 武男 茂木 透 高田 真秀 笠原 稔

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

vol.68, pp.161-178, 2005-03-15

著者

杉本 芳博 森谷 武男

出版者

北海道大学理学部地球物理学教室

雑誌

北海道大学地球物理学研究報告 (ISSN:04393503)

巻号頁・発行日

vol.42, pp.155-167, 1983-10-25

著者

今西 伸行 西村 浩一 森谷 武男 山田 知充

出版者

The Japanese Society of Snow and Ice

雑誌

雪氷 (ISSN:03731006)

巻号頁・発行日

vol.66, no.1, pp.3-10, 2004-01-15 (Released:2009-08-07)

参考文献数

16

被引用文献数

1 1

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雪崩発生に伴う地震動の特徴を把握するとともに,雪崩の発生地点と規模を推定する手法を確立するため,4台の地震計を用いて,2001年1月から4月までの80日間,北海道大学天塩研究林内で観測を行った.期間中に,対象域で確認された雪崩の86%にあたる50例の震動波形を得ることができ,地震計によって高い確率で雪崩発生のモニタリングが可能であることが判った.ほぼ同地点で発生した雪崩による震動は類似した波形を示すこと,震動の卓越周波数と地震計から雪崩発生点までの距離との間には負の相関があり,これから発生点の推定が可能であること,また雪崩の運動エネルギーと位置エネルギーとの関係を用いて,雪崩質量の推定が可能であることが示された.

著者

田村 慎 笠原 稔 森谷 武男

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.55, no.4, pp.337-350, 2003-03-15 (Released:2010-03-09)

参考文献数

27

被引用文献数

4 4

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We have studied micro-seismicity in the northern part of Hokkaido (north above 44°N) from June to November in 1998 combining eleven temporal seismic stations with seven and five routine ones operated by Institute of Seismology and Volcanology (ISV) in Hokkaido University and Sapporo Meteorological Observatory, Japan Meteorological Agency (SMO), respectively.Firstly we determined 91 hypocenters of local earthquakes in this period using the dense network. These hypocenters are about three times of the number of those from the routine network alone. One-dimensional P-wave velocity structure assuming four-layer model (assumed thickness of 2, 8, 10km and infinite) and station corrections were estimated using a P-wave travel time inversion method with 735 P-wave arrival time records of 81 events. The velocity of each layer was determined to be 2.83km/sec for the first layer, 5.32km/sec for the second one, 6.32km/sec for the third one and 6.69km/sec for the bottom half space. From the P-wave station corrections we obtained, this region can be classified into three zones parallel in the north-south direction; the western islands region in the Sea of Japan, the western part of mainland, and the eastern part of mainland. Each zone shows the value of less than-0.5sec, +0.1-+0.4sec, and-0.1--0.5sec, respectively.Next, the hypocenters with the inverted velocity structure and the station corrections are relocated. As the results show, some hypocenters in the anomalous delayed station correction zone, i. e. the western part of mainland, are clearly located at the depth range from 20 to 25 km. Focal mechanism solutions of these deep events show normal fault type, while shallower events less than 20 km depth show strike-slip and reverse fault types. We also relocated 381 earthquake hypocenters which were routinely determined by ISV from October 1996 to December 2000. According to the relocated hypocenter distribution, a high seismic zone is shown in the western part of mainland with about 50km wide along a north-south direction. On the other hand, the eastern part of mainland is strongly characterized as aseismic zone. The boundary between the seismic and aseismic zones corresponds to the geological boundary between Kamuikotan metamorphic belt and Hidaka belt.

著者

杉本 芳博 藤井 智史 森谷 武男 笹谷 努

出版者

北海道大学理学部地球物理学教室

雑誌

北海道大学地球物理学研究報告 (ISSN:04393503)

巻号頁・発行日

vol.40, pp.79-91, 1981-11-30

著者

森谷 武男 茂木 透 高田 真秀 山本 勲

出版者

北海道大学大学院理学研究院自然史科学部門(地球物理学) = Department of Natural History Sciences (Geophysics), Graduate School of Science, Hokkaido University

雑誌

北海道大学地球物理学研究報告 (ISSN:04393503)

巻号頁・発行日

vol.72, pp.269-285, 2009-03-15

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A new observation system established in Hokkaido, northern Japan to confirm a suspected relationship between anomalous radio-wave propagation and impending earthquakes has been documenting anomalous VHF-band radiowave propagation beyond the line of sight prior to earthquakes since December, 2002. During such events, radio waves transmitted from an FM radio station were scattered, such that they could be received by an observation station beyond the transmitting station's line of sight. A linear relationship was established between the logarithm of the total duration time of the anomalous transmissions (Te) and the magnitude (M) or maximum seismic intensity (I) of the impending earthquake for M4- to M5-class earthquakes that occurred at depths of about 50 km beneath the Hidaka Mountains in Hokkaido, Japan in June 2004 and March 2008 as reported in the previous paper (Moriya et al., 2005). Similar linear relationships are also valid for earthquakes that occurred at other depths. Te is longer for shallower earthquakes and shorter for deeper ones. Numerous parameters seem to affect Te, including hypocenter depths and epicentral surface conditions (i.e., sea versus land). This relationship is important because it means that pre-seismic, anomalous transmission of VHF-band waves may be useful in predicting the size of an impending earthquake. To avoid misidentification of FM stations that have identical frequencies, three 64 MHz band transmitters were established, each with a unique frequency. Earthquakes that occurred in and around eastern Hokkaido scattered waves from FM-band and 64 MHz-band stations and provided quantitative relationships between Te and M, and between Te and I. Using the interferometer at the TES observation site, the incident azimuth of the scattering waves from the Hiroo station was measured. Prior to two earthquakes that occurred beneath almost the same part of the Tokachi region at depths of 86 km and magnitudes of M 4.9 and 4.0, the interferometer yielded incident azimuths of S18W and S34W. The true azimuths from TES to the hypocenters of the two earthquakes were S35W and S38W, respectively. These two measurements, therefore, suggest that anomalous transmission of VHF waves is caused by scattering at the epicenters of impending earthquakes.

著者

島村英紀 森谷武男著

出版者

北海道大学図書刊行会

巻号頁・発行日

1994

著者

花籠 靖 中西 一郎 森谷 武男 笠原 稔

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.43, no.2, pp.213-225, 1990-06-24 (Released:2010-03-11)

参考文献数

19

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The rapid determination of seismic moment and source mechanism for near earthquakes is attempted by a moment tensor inversion of long-period seismic waves. The inversion method is based on a normal mode theory. The data for the inversion are recorded at three stations in Hokkaido, Japan. Each station is equipped with a three-components very-broad-band seismograph. Source parameters of six earthquakes (mb_??_5.5) in and around the Japan region (epicentral distances of 200 to 1500km) for the period from January to April 1989 are determind by applying the moment tensor inversion to the long-period waveform data. Changing the components (UD, NS, EW) and record length used in the inversion the stability in the moment tensor solution is examined. A good S/N ratio is required to obtain a stable solution in the inversion of three-components data from a single station. Data length of 4-8min after the earthquake origin time is enough to attain stable source mechanism determination by using the three-stations data.

著者

森谷 武男

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

vol.60, pp.61-75, 1997-03-31