著者
三井 雄太 柳谷 俊
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
巻号頁・発行日
vol.75, pp.109-115, 2012-03-19

We observed clear fractoluminescence in crystalline quartzite, quartz crystal and fused silica at uniaxial compressional loading tests by commercial digital cameras. These fractoluminescence are composed of blue and red colors. In particular, a blue color does not appear in fractures of fused silica but appear in crystalline quartzite and quartz crystal, which implies that the piezoelectric charge and discharge play a key role in the blue-color fractoluminescence via excitation of N2 molecules.
著者
吉澤 和範
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.71, pp.39-48, 2008-03-15

Seismic waves generated by a nuclear test carried out by North Korea on October 9, 2006 were observed throughout the Japanese islands. Clear arrivals of Pn waves, which traveled below the Moho discontinuity underneath the Japan Sea, were recorded by the Japanese broad-band seismic network, F-net, deployed by National Research Institute for Earth Science and Disaster Prevention (NIED). We analyzed the waveforms of the nuclear event observed at F-net stations as well as some global seismic stations in East Asia. Apparent path-average velocity of Pn waves and their maximum amplitudes are estimated from vertical component seismograms of the F-net stations. We found conspicuous regional variations of apparent path-average velocity and maximum amplitude. For example, fast apparent velocity and larger amplitude are observed in the paths across the Japan basin in the northern Japan Sea, whereas slow velocity as well as relatively smaller amplitudes are found in the path to stations in Kyushu. Such regional variability of Pn waves is likely to make it difficult to estimate source parameters for this small-scale explosive event in the Korean Peninsula, only using the Japanese seismic network. These results suggest the necessity of a precise three-dimensional seismic model of the Japan Sea to utilize Japanese seismic network data for analysis of regional seismic waves that propagate along a variety of paths in the Japan Sea.
著者
鈴木 建夫 新井田 清信 西田 泰典 大島 弘光 室伏 誠
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.70, pp.53-65, 2007-03-15

Many authors have discussed the eruption time sequence and the mechanism of volcanic eruptions by estimating the ejected velocity of the volcanic blocks, with the aid of other factors of eruptive phenomena. Equations of motion for the volcanic blocks have been proposed by considering the factors, such as the air resistance, the influence of the wind, the inclination of the explosion principal axis and so on. However, the equation of motion and its solution has not been considered that the air resistance power was vector quantity for the flight of volcanic blocks. In this paper a new equation of motion for the ejected volcanic blocks is proposed by considering the air resistance power as vector quantity.
著者
鈴木 建夫 新井田 清信 西田 泰典 大島 弘光 室伏 誠
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.70, pp.67-83, 2007-03-15

The present authors pointed out, in the last paper, a mistake in the equation of motion for volcanic blocks. Reliable assumption of the air resistance to the blocks is required for accurate estimation of initial velocity of volcanic blocks. However, little attention has been given to the point. This paper organizes the problems about the estimation of the air resistance and proposes a new method of the estimation. Also this paper organizes the effect of factors on the distribution of volcanic blocks. Model calculations revealed the effect of the atmospheric air density cannot be ignored. For the effect of explosion principal axis on the distribution of volcanic blocks, this paper proposes an extended equation which volcanic blocks eject to all the directions around the crater.
著者
蓬田 清
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.111-128, 2013-03-19

After the 2011 Tohoku-Oki earthquake, the immediate threat of megathrust earthquakes in and around Japan has been suddenly advocated by some researchers. One even points out the possibility of a larger event than ever, an event of Magnitude 10. In this study, we discuss whether an event of M10 will be realistic or not, from not only statistical aspects of earthquake occurrence or macroscopic scaling laws of seismic sources in a conventional manner(e.g., fault size, the amount of slips)but also the diversity of megathrust earthquakes that was revealed after the occurrence of the 2011 Tohoku-Oki earthquake. From a simple extrapolation of seismicity and macroscopic scaling laws, one event of M10 occurs every 500 years all over the world, with its fault length, width and average slip to be 1,200 km, 600 km and 50 m, respectively. The width may not exceed 200 km very much because of the limitation of an elastic region of a plate boundary in a subduction zone. We therefore need either of (1) average slip as large as 100 m or (2) fault length of more than 1,500 km for a possible M10 event. The average slip may be able to exceed 100 m, considering an area of very large shallow slips associated with the 2011 Tohoku-Oki earthquake, but we must take care that this is possible only for an event of the along-dip double segmentation. This type of events is, however, generally adjacent to segments of weak plate coupling with small coseismic slips. In contrast, an event of the conventional along-dip single segmentation may extend its fault into many adjacent segments. A drawback in this case is that the average slip may not exceed 50 m unless there are several segments of very strong plate coupling, resulting in co-seismic slips lager than those with usual events repeating in each segnent. Although a very large strong shallow segment of the double segmentation is a candidate of am M10 event, we cannot find any clear evidence of such a region from the present spatial seismic pattern in the world. The subduction zone in south Chile is the best candidate from its apparent strong plate coupling although it may not occur for a while due to the nearly complete strain release associated with the 1960 earthquake. We consider a very large event will be impossible even if a large portion of subduction zones breaks in the Aleutian trench because of the existence of several segments of weak plate coupling with slow events or aseismic slips in this trench.
著者
小山 順二 都筑 基博 蓬田 清 吉澤 和範
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.129-146, 2013-03-19

2011 年3 月11 日マグニチュード9.0 の超巨大地震が東北地方太平洋沿岸をおそった.この地震は過去千年以上にわたる日本付近で発生したどの地震よりも大きな津波を励起し,地震動災害ばかりではなく歴史に残る甚大な津波災害を発生させた.従来,このような超巨大地震が日本付近で発生することは,地震学的に想定されてこなかった.我々は,この超巨大地震の発生を考えるうえで,今まで見過ごされてきた超巨大地震の発生場には二つの異なった特徴があることに気が付いた.それはAlong-dip Double Segmentation(ADDS)とAlong-strike Single Segmentation(ASSS)という異なった地震活動である.我々はこの考えに基づき,世界中で発生した超巨大地震を調べなおし,超巨大地震の発生場を,地震活動の特徴(ADDS/ASSS),地震メカニズム,破壊様式,沈み込み帯の形状,上盤プレートの性質や背弧海盆の活動といった性質から,明らかにする.
著者
高橋 浩晃 宮村 淳一
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.177-190, 2009-03-15

We investigate the activity of deep low-frequency earthquakes (DLE) in Japanese Islands by JMA hypocenter catalogue during 1997 to 2008. It is confirmed that DLE cluster is distributed in every region. This implies that DLE phenomenon is common in Japanese subduction zone. Many active DLE clusters are identified in and around the quaternary volcanoes in whole area. There are also many non-volcanic clusters in Hokkaido and Tohoku regions, but very few in Kanto, Koushinetsu, Chubu, Hokuriku and Kyushu regions. High activity of non-volcanic clusters is observed in Kinki region. No clear correlation between DLE number and volcano activity index during 100 and 10,000 years is recognized. This fact implies the possibility that DLE activity is not precursor signal of shallow volcanic activities such as eruption at any time. Lower limit of DLE hypocenter depth generally coincides with depth of Moho discontinuity of each region. This may indicates that structure of upper mantle and lower crust and its boundary strongly control the occurrence of DLE's.
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

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.