著者

一柳 昌義 笠原 稔 高橋 浩晃 岡崎 紀俊 高橋 良 大園 真子

出版者

北海道大学大学院理学研究院

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.77, pp.5-13, 2014-03-19

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An earthquake swarm begun at the end of January, 2012 and the activity reached a peak in middle February, then gradually decreased by the end of April, in the Nigorikawa caldera, Hokkaido. The largest earthquake was the MJMA3.6 event which occurred on 15 February 2012 with maximum intensity 3.Temporal seismic observation with two stations carried out from 20 February to 9 April in the caldera. Detailed hypocenter distribution estimated by using both data temporal and secular observations shows two clusters, one of them is aligned along the northern caldera wall and another is located at eastern outside of caldera. Strike of alignment epicenter of the north cluster shows NE-SW direction, which is in good agreement with one of the nodal plane of focal mechanism of the largest event.

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

阿部 勝征

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.39, pp.57-62, 1981-01-31

著者

宇津 徳治

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

no.21, pp.45-52, 1969-02

著者

一柳 昌義

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.65, pp.229-246, 2002-03-25

著者

孫野 長治 播磨屋 敏生 八木 鶴平

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.18, pp.83-98, 1967-08-10

著者

上垣 拓郎 池上 裕 中西 一郎 小久保 一哉 露木 貴裕 中村 浩二 原田 智史

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.379-382, 2009-03-15

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The long-period strain seismograms from the Sumatra-Andaman earthquake of December 26, 2004 and the Nias earthquake of March 28, 2005 are analyzed by comparing the observed seismograms with synthetic seismograms calculated by normal mode theory. The multiple CMT source (Tsai et al., 2005) and Harvard CMT solution explain the seismograms recorded by both extensometers and volumetric strainmeters from the 2004 and 2005 earthquakes, respectively. The long-period strain seismograms observed in Japan are consistent with about 9 min source duration and 1200 km fault length proposed by Tsai et al. (2005) and Velasco et al. (2006).

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

---

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

池上 裕 岡本 大志 中西 一郎 小久保 一哉

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.69, pp.221-231, 2006-03-15

---

The great Sumatra-Andaman earthquake of December 26, 2004 is studied by using extensometer (strain-meter) as very-broard-band seismograph. We analyze the strain seismograms obtained by 100 m extensometers installed at Matsushiro Seismological Observatory. Japan Meteorological Agency. We compare the observed strain seismograms with thouse calculated by normal mode theory and obtain fairly good agreement between the observed and calculated seismograms for a five-sourcse model with a moment magnitude of 9.3 and a source duration of about 600 sec. We find a peculiar strain change right after the passage of Rayleigh wave in the NS component of the strain seismograms. This strain change cannot be explained by the summation of normal modes and double-couple type sources.

著者

北海道大学理学部物理学教室

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.10, pp.1-15, 1963-03-25

著者

一柳 昌義 高橋 浩晃 山口 照寛 東 龍介 山田 卓司 大園 真子 眞城 亮成 笠原 稔 谷岡 勇市郎

出版者

北海道大学大学院理学研究院

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.78, pp.37-51, 2015-03-19

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An earthquake swarm begun at 15 July 2012 in Nakagawa town of northern Hokkaido. The largest earthquake with MJMA4.3 occurred on 16 July 2012. We carried out temporal seismic observation with seven stations from 18 July 2012 to the last October 2012. Hypocenters were calculated using the Double-Difference hypocenter determination procedure with a local one dimensional P-wave velocity structure. Precise hypocenter data indicated that epicenters were distributed in very narrow area of 2 km×2 km with shallow depth from 4 km to 7 km. Earthquakes after middle of August occurred only in southern part of the region and depth had got shallower with time. Hypocenters indicated no clear alignment in consistent with any nodal planes of major earthquakes. An independent hypocenter cluster with shallower than 2 km was observed above the main activity area. A slow slip event (SSE) with Mw 5.4 coincidentally detected by GNSS crustal deformation data during the swarm. This swarm was situated at the southeastern end of the fault of SSE. This fact suggested that seismic swarm might triggered SSE or was induced by SSE.

著者

播磨屋 敏生 菊地 勝弘 遠藤 辰雄 堀江 成人

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.113-126, 1981-11-30

著者

岡田 弘 本谷 義信

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.24, pp.141-165, 1970-09-18

著者

中島 徹

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.32, pp.25-41, 1974-12-14

著者

宇津 徳治

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.21, pp.45-52, 1969-02-15

著者

宇津 徳治

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.20, pp.51-75, 1968-09-20

著者

西田 泰典

出版者

北海道大学大学院理学研究院

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.76, pp.15-86, 2013-03-19

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The self-potential (SP) method is based on measuring the natural electric potential differences, which generally exist between any two points on the ground. The SP fields have their origins in different mechanisms which can be used to identify ore deposits, geological features, ground water flow, and hydrothermal systems. The amplitude has a very wide spectrum, from a few mV/km to a few V/km, and their spatial distribution is correlated with the size of sources that lie at a depth within several hundred meters depth. Despite the fact that SP studies have been carried out by many researchers in the past, especially in field of mine prospecting, the use of the method had been restricted because the sources of SP anomalies were not fully identified and the development of other geophysical methods, such as seismic, electromagnetic and gravimetric methods, was very fast. However, since 1970, the SP method has again risen as a modern prospecting method for delineating the thermal state of geothermal fields. These studies have encouraged the application of the SP method to volcanological, geothermal, hydrological, seismological studies and so on. Spatial and temporal measurements of the SP field may prove to have the advantage of sensing dynamic aspects of the tectonic activities. This article will focus on fundamentals of theoretical and experimental SP studies and will show many field examples to guid for beginners.

著者

大島 弘光 前川 徳光 岡田 弘 谷口 宏充

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.29-43, 1997-03-31

著者

前田 宜浩 笹谷 努 一柳 昌義 山口 照寛 高橋 浩晃 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.243-253, 2005-03-15

著者

高橋 浩晃 前田 宜浩 笠原 稔

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)

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.399-410, 2009-03-15

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We investigate the characteristics of great earthquakes occurring in the central Kuril Islands on 1915, 1918, 2006 and 2007. Comparisons of seismic intensity distributions, tsunami data and waveforms of above four events were made. Though magnitudes of these earthquakes were almost the same, only the 1915 event did not generate observable tsunami. This fact may be due to deep focal depth of this earthquake. Similarities of seismic intensity distributions between the 1915, 1971 and 2008 deep-focus earthquakes also imply that the 1915 event was the deep-focus event in the northeastern Okhotsk Sea. Waveform properties of the 1915 and 2008 events supports above hypothesis. We conclude, therefore, that the 1915 earthquake was not the event in the central Kuril Island but in the Okhotsk Sea with deep depth. Large tsunami and widespread felt area of the 1918 earthquake show that this event was a typical shallow-dipping thrust event on plate boundary as indicated by previous studies.