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Hokkaido University Collection of Scholarly and Academic Papers (135.711 recursos)

HUSCAP (Hokkaido University Collection of Scholarly and Academic Papers) contains peer-reviewed journal articles, proceedings, educational resources and any kind of scholarly works of Hokkaido University.

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Mostrando recursos 1 - 18 de 18

  1. 広帯域MT観測及び重力測定による北海道東部弟子屈地域の地殻構造

    市原, 寛; 茂木, 透; 山谷, 祐介; 神山, 裕幸; 小川, 康雄
    Wide-band magnetotelliric and gravity surveys were conducted at the Teshikaga area, located in eastern Hokkaido, Japan, where intra-plate earthquakes had teken place. We inferred shallower (<2-Km depth) crustal density structur using the gravity and borehole data, and then compared it with resistivity structure revealed by two-dimensional MT inversions. The results show that the density and resistivity structures are closely correlated with each other. The resistivity profiles and Bouguer anomaly map indicate that the high density and high resistivity zone, which presumably represents Miocene volcanic and sedimentary rocks is apparently cut by a major dextral strike slip fault. Location and strike...

  2. 2004年12月26日 Sumatra-Andaman 地震の理論歪地震波形の計算と観測波形の比較

    池上, 裕; 岡本, 大志; 中西, 一郎; 小久保, 一哉
    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...

  3. 北海道で発生した津波地震 ー1975年北海道東方沖地震:再訪ー

    高橋, 浩晃
    The 1975 Hokkiado-Oki earthquake (Ms7.0) was characterized as a tsunami earthquake which had anomalous long source process time and spectrum of seismic waves. Predominant period of seismic waves were situated in several tens to several hundreds seconds. This abnormal long-period seismic wave generated very weak intensity distribution compared to the seismic moment (Mo) and epicenter distance. Aftershock distribution and focal mechanismw indicated this event occurrde on very shallow plate boundary close to the trench axis, in where seismicity has been very low. If next tsunami earthquake will occur near Hokkaido, JMA will be likely to underestimate the M, because JMA...

  4. 浅部膨張・深部収縮源によるデイサイトマグマ貫入ー有珠山への適用ー

    OKADA, Jun
    Series of Mogi's single source model display characteristic family curves on the logarithmic graph of vertical displacement versus horizontal distance. The family curves on log-log plots are simply characterized by the flat part at short distances and constant decay at farther distances. The specific corner distances, which are defined by the bending corner of the curves, are mainly controlled by the source depth. The edifice scale deformation associated with the 2000 eruption of Mt. Usu is far from that predicted by Mogi's single source. The vertical displacement shows much more sharp decay with distance around 5-6 Km and uplift-to-subsidence reversal...

  5. 2003年十勝沖地震(Mw8.3)による周期約20秒の長周期地震動

    前田, 宜浩; 笹谷, 努
    A lot of strong ground motion data from the 2003 Tokachi-oki earthquake (Mw8.3) were obtained by a dense strong motion network including K-NET, KiK-net and so on. We examine the long-period ground motions with a period of about 20 seconds based on these data. First, we estimate propagation directions and phase velocities of long-period Rayleigh waves at 64 seismic array sites in Hokkaido arranged from the dense network; the radius of the array is about 15 Km. The semblance analysis is applied to band-pass filtered, verticalcomponent waveforms at each array; the central frequencies are 0.03 and 0.05 Hz. The propagation...

  6. 日高山脈トッタベツ深成岩体の重力異常と貫入形態

    神山, 裕幸; 山本, 明彦; 長谷川, 健; 梶原, 崇憲; 茂木, 透
    An exposed cross section of the tilted Tottabetsu plutonic complex allows direct observation of its 2-D cross-sectional shape and pretilting vertical variation in lithology and small-scale internal structures. Furthermore, the cross-sectional exposure allows directevaluation of pretilting vertical density variations in both the pluton and the country rocks, which serve as a strong constraint in gravity modeling that complements information on the‘missing’original horizontal dimension of this tilted pluton. The pluton is rectangular in cross-sectional shape, measuring ~10-Km thick by ~8-Km wide. It is stratified with the uppermost thin granitic unit (~1-Km thick) and the underlying thick gabbro-diorite units (~9-Km thick) that preserve...

  7. ScSp波による北海道周辺での太平洋プレートの形状の推定

    長田, 絹絵; 吉澤, 和範; 蓬田, 清
    Geometry of the upper boundary of the subducting Pacific plate or slab was estimated in the Hokkaido region, Japan, using the ScSp phase: the converted phase to P wave at the boundary from the S wave reflected at the core-mantle boundary and propagating nearly vertically (i.e., ScS phase). Taking the advantage of a dense seismic network named “Hi-net” recently deployed across the Japanese islands, we applied several seismic array analyses to the recorded waveform data for a large nearby deep earthquake, in order to enhance weak ScSp signals in record. At first, we set up five blocks for the region...

  8. スラブ内地震の震源特性

    笹谷, 努; 森川, 信之; 前田, 宜浩
    We examine source characteristics of intraslab earthqakes based on the eleven source models estimated by the empirical Green’sfunction method. This method provides strong motion generation areas that reproduce near-source ground motions in a broadband period range(0.1~10sec). The storong motion generation areas roughly coincide with the asperity areas where stresses are largely released. Fault parameters of the asperity source model are outer fault parameters (entire source area and total seismic moment) and inner fault prameters (area of asperities,stress drop on each asperity and short-period level of the S-wave acceleration source spectrum). We find self-similar scaling of total seismic moment to the...

  9. S波コーダ振幅から推測される北海道東部における2次元不均質構造

    TAIRA, Taka’aki; YOMOGIDA, Kiyoshi
    We examined 2-D heterogeneous structure in the eastern Hokkaido region, using the S-wave coda amplification factor (CAF) with seismic storong-motion date of Kyoshin Net(K-NET). CAF is defined as the spectral ratio of coda waves among different stations after corrections for source, site, and overall propagation.(i.e,cada-Q) effects. Confirming that code-Q values are nearly independent of both source and station, the site effect at each station was esetimated by the coda-normalization method. The source effect was removed by taking the spectral ratio of S-wave coda among stations for each earthquake. We evaluated the CAF value of each source-station pair for three components,using...

  10. 阿寒カルデラとその周辺の重力構造

    長谷川, 健; 山本, 明彦; 神山, 裕幸; 中川, 光弘
    We performed gravity surveys and compiled pre-existing gravity data to obtain gravity anomalies of the Akan Caldera, eastern Hokkaido, and a new gravity map around the caldera was produced. In particular, we conducted gravity surveys on the frozen lake surface in winter to reveal a fine gravity structure. A new Bouguer anomaly map shows that the Akan Caldera is characterized by three closed mimima and takes its minimum value(~70mgal)in the central area of the caldera. It is consistent with our geologic studies suggesting that the Akan Caldera is multiple caldera. Characteristic low anomalies in the Akan Caldera gradually increase towards...

  11. 強震観測におけるSTA/LTA トリガー方式の問題点

    吉田, 邦一; 笹谷, 努
    We point out that sometimes a STA/LTA trigger algorithm does not work appropriately for strong-motion observations. The STA/LTA trigger algorithm evaluates the ratio of short-time average(STA) to long-time average(LTA) and is adopted to recognize an earthquake for recording by an event recorder. We observed strong-motion records in the northern part of the Ishikari plain during the 2003 Tokachi-oki earthquake and its largest aftershock. Peak ground accelerations of the records are about 1 m/s^{2 } and peak ground velocities, about 0.3 m/s. However,two of the stations which adopted the STA/LTA trigger algorithm failed in recording during the main shock and the...

  12. 濃尾平野における地震動シミュレーション

    南雲, 秀樹
    Nagoya City, one of the largest cities in Japan,is located on the Nobi basin where the future occurrence of Tokai and /or Tonankai earthquake disasters is feared. The prediction of strong ground motions in this region is a pressing concern in order to mitigate these disasters. In this study,I constructed a subsurface velocity structure model for an area of 60 Km×40 Km in the Nobi basin on the basis of geophysical exploration data. Basement structure of the Nobi basin has the following features. Large vertical offsets of 2.0 to 2.5 Km exist between the mountain area and the sediment site...

  13. 鹿児島県奄美大島における重力測定

    宮町, 宏樹; 藤田, 大介; 山本, 明彦; 平野, 舟一郎; 八木原, 寛; 後藤, 和彦; 中尾, 茂; 角田, 寿喜
    A high dense gravity measurement composed of 323 sites was carried out in Amami-Oshima Island,Kagoshima,in order to reveal the detailed gravity anomaly distribution. The obtained distribution shows that Amami-Oshima Island has the positive anomalies ranging from +32~+66 mgal with a trend from NE to SW parallel to Ryukyu trench. The trend-reduced gravity anomaly distribution also indicates the northern and southern areas in the island with negative gravity anomalies.

  14. 大阪堆積盆地モデルに基づいた表面波の卓越周期に関する検討

    宮腰, 研; 大西, 良広; 赤澤, 隆士; 堀家, 正則
    We estimated the predominant period of surface waves from the dispersion curves of the Love and the Rayleigh fundamental mode, calculated from 1-D verlocity structure models extracted from the Osaka basin model.The estimated predominant period is from 1 to 10 s for the Love waves and 1 to 6 s for the Rayleigh waves in the Osaka plain. The linear relationships between the predominant period of surface waves and the bedrock depth are confirmed. Predominant period is proportionality to the bedrock depth. Coefficient proportionality approximately equals 5 s/Km for Love waves and 2 s/Km for Rayleigh waves. We compared the...

  15. The 29 November 2004 M7.1 Kushiro-oki earthquake:An event between the on-going seismic quiescence area and the asperity ruptured by the 1973 Nemuro-oki earthquake

    KATSUMATA, Kei; YAMANAKA, Yoshiko
    We have investigated the source process and the aftershock distribution of a large earthquake with M=7.1 occurred on 29 November 2004 off the coast of Kushiro (or Shiranuka) in the eastern Hokkaido,Japan. The source parameters are summarized as follows:the total seismic moment M_0=3.4×10^{19}Nm,thatis,M_w=7.0;(strike,dip,ship)=(238°,33°,117°);depth of the initial break point=48 km;and source duration time =10sec. The aftershocks were relocated using the three-dimensional velocity structures of P-and S-waves,and we found that the aftershocks concentrated on a plane with the area of 30×15㎞^{2}dipping 22°toward the landside whose orientation agrees closely with that of the northwest-dipping nodal plane of the focal mechanism. The stress drop...

  16. 2004年スマトラ島沖大地震で発生した地球周回表面波

    吉澤, 和範
    The great Sumatra earchquake on December 26, 2004, which devastated the coastal areas of the Indian Ocean by the subsequent tsunami, generated tremendous numbers of surface-wave trains which traveled around the globe for many times. We analyse vertical-component seismograms of the event recorded by the F-net broadband seismic network in Japan, which has been deployed and maintained by NIED (National Research Institute for Earth Science and Disaster Prevention, Japan). By applying a band-pass filter between 3 and 5 mHz, we extract the long-period Airy phase of the fundamental-mode Rayleigh wave. The long period records display a magnificent series of multi-orbit...

  17. 回転成分地震計の改良と観測された回転成分地震波の性質

    森谷, 武男; テイセイヤー, ローマン
    We have developed rotation seismometer using four translation seismic sensors (L22d), which have the same amplitude and phase characteristics. A negative input impedance amplifier and band-pass filter have eliminated mechanical deviations of individual sensor and adjusted to have suitable characteristics. Temporal earthquake observations have executed using translation and rotation sensors, at three places, which have different surface geology. They were Mitsuishi (MUJ), Obihiro (OBI), and Usu volcano (SWZ) in Hokkaido. We demonstrate some seismograms of rotation and translation components. Between maximum amplitudes of rotation (Ar) and translation (At), an emprical formula; Log Ar=p Log At (1) has been found, and...

  18. 森谷武男教授記念号の発刊に際して ; 森谷武男助教授の略歴および業績


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