巻号一覧
48 巻 (1995 - 1996)
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前身誌
48 巻, 3 号
選択された号の論文の13件中1～13を表示しています
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羽鳥 徳太郎1995 年 48 巻 3 号 p. 307-314
発行日: 1995/11/25
公開日: 2010/03/11
ジャーナル フリーA large tsunami was generated off East Hokkaido at 22:23 (JST) on Oct. 4, 1994. According to JMA, the epicenter of the main shock was located at 43°22′N, 147°40′ E with a depth of 30km and earthquake magnitude, M=8.1. The tsunami hit Shikotan, Kunashiri Islands, and double-amplitude reached 342cm at Hanasaki. Wave-periods of about 40min were predominant on tide-gauge records at Hokkaido and Sanriku stations. The aftershock area which nearly corresponding to the tsunami source is 200×100km, extending along the Kurile trench. The tsunami source area was lapped over that due to the 1969 Shikotan earthquake (M=7.8). Tsunami magnitude on the Imamura-Iida scale was determined to be m=3 judging from the tsunami height-distance diagram. This value is normal compared to earthquake with similar size in other regions. On the relation between tsunami height and earthquake magnitude for the East Hokkaido tsunamis since 1918, the heights at Hanasaki are scattered, but about three times higher than those of the Etorofu-Urup tsunamis. The ratios of tsunami heights at the Sanriku coast to the initial semi-amplitude at Hanasaki were about 0.5, but those of the big bays (seiche period of 40-50min) reached 2.0. On the contrary, the amplitude ratios at the Hokkaido coast facing the Okhotsk Sea are 0.4 or less. Tsunami heights at Ogasawara-Chichijima Is. often deviated more than twice time higher than the average tsunami magnitude because of the refractive effect.抄録全体を表示PDF形式でダウンロード (994K) -
小泉 尚嗣, 北川 有一, 佃 為成, 矢部 征1995 年 48 巻 3 号 p. 315-329
発行日: 1995/11/25
公開日: 2010/03/11
ジャーナル フリーWe have observed precise groundwater temperature at Yudani hot spring in Tottori Prefecture, Japan since September 1991. The resolution of the temperature measurement is 0.001°C. The same observation was done from May 1983 to July 1984, with lower resolution of 0.01°C. The groundwater temperature has periodic fluctuations mainly induced by the earth tides. The temperature also changes due to atmospheric pressure and sometimes has clear coseismic rises. Such coseismic rise was observed 7 times with very similar patterns. Generally, the felt earthquakes at Yudani hot spring with JMA intensity 3 or greater coincides with the coseismic groundwater temperature changes and unfelt distant large earthquakes sometimes caused the same coseismic changes. These changes might have been caused by volumetric strain changes induced by tides, atmospheric pressure and earthquakes and we calculated respective strain sensitivity of the groundwater temperature. The sensitivity from the response to the atmospheric pressure is nearly equal to that from the tidal response (1.10m°C/10-8 strain). However, the sensitivities estimated from the coseismic temperature changes and the static strain steps which were calculated from the earthquake fault model in a homogeneous elastic half space are more than 1000 times larger than the sensitivity from the tidal response. Therefore, the coseismic static strain steps cannot explain these coseismic changes on the groundwater temperature. We propose that these changes are caused by local strain release induced by the seismic waves which have little effect on the seismic intensity.抄録全体を表示PDF形式でダウンロード (1562K) -
その1 岐阜測候所観測記録のシミュレーション野澤 貴, 武村 雅之, 池浦 友則, 山中 浩明1995 年 48 巻 3 号 p. 331-340
発行日: 1995/11/25
公開日: 2010/03/11
ジャーナル フリーRecords observed at Gifu observatory by an Imamura's type strong motion seismograph are one of the most useful records in Japan to investigate a source process of the 1923 Kanto earthquake (M=7.9). It is because amplitudes of the records are not saturated in EW and UD components, instrumental response of the seismograph has been clarified, and many records due to recent events occurred near the focal region of the Kanto earthquake have been obtained by more accurate seismographs at the same site. In the present study, a source process of the 1923 Kanto earthquake is elucidated through a simulation of the records using the normal mode theory in the period range from 2 to 20s. First, a crustal structure from the source to the station is estimated so as to explain dispersive characteristics of Love waves observed at Gifu observatory for the recent events, and their records are simulated to confirm a validity of the estimated crustal structure. Secondly, the records from the Kanto earthquake are simulated using the obtained crustal structure to deduce the source process of this event. According to KANAMORI (1971), a macroscopic faulting is a reverse right-lateral fault on a plane dipping 34° towards N20°E, whose slip has much strike component. If two big subevents with the same focal mechanism obtained by KANAMORI (1971) and with a time interval of about 12s are assumed on the fault plane, the observed records can be well explained. The first subevent is located under the Odawara city and the second one under the Miura Peninsula. The focal depth of the second event is 15 to 35km being deeper than that of the first event, which is 5 to 25km in depth. The seismic moments and the rise time are assumed 2.5×1027 dyne-cm and 5s for both the events respectively. On the other hand, if the focal mechanism of the second event is dip slip type, the observed records can be also explained well, even though the focal depth of the second subevent is the same as that of the first one. This model is consistent with a slip distribution on the fault plane obtained from geodetic data.抄録全体を表示PDF形式でダウンロード (1261K) -
山本 みどり, 岩田 知孝, 入倉 孝次郎1995 年 48 巻 3 号 p. 341-351
発行日: 1995/11/25
公開日: 2010/03/11
ジャーナル フリーWe propose a new method to estimate site amplification effects at specific sites, separating source and propagation-path effects. First, we calculate “specified spectra” from a given source and propagation-path effects, with a fixed site effect of 2.0. Then, we include effects of rupture process into the “specified spectra” using the empirical Green's function method. Site effects can be defined as a ratio of observed seismic spectra to the “specified spectra”. We applied this method to the ground motion data during the 1993 Kushiro-oki earthquake as strong motions and those of other small earthquakes as weak motions in the south-east area of Hokkaido. We found nonlinear site effects at the station KSR, in Kushiro city, where the maximum of horizontal amplitude was 711.4cm/s2 during the 1993 Kushiro-oki earthquake. The predominant frequency of the site effects became smaller and the amplification level of those at high frequencies became lower than those for the weak motions.抄録全体を表示PDF形式でダウンロード (1235K) -
長 郁夫, 中西 一郎, 今西 和俊, 佐藤 魂夫1995 年 48 巻 3 号 p. 353-364
発行日: 1995/11/25
公開日: 2010/03/11
ジャーナル フリーThe great Hokkaido Toho-Oki earthquake (MJMA=8.1) occurred at 13h 23m on October 4, 1994 (GMT), in the region off the Shikotan Island. Since all STS-1 seismographs in Eastern Japan were saturated by the earthquake, broad-band strong-motion seismographs (velocity response is flat from 0.015s to 600s) installed at two stations in the region of the northern end of the main land of Japan, where the seismic intensity of 4 was reported by JMA, were used to make a long-periods (≥70s) moment tensor inversion. Our solution in terms of best double couple is (strike, dip, slip)=(69°, 67°, 119°), Mc=1.8×1021 Nm (Mw=8.0), and centroid depth=42km. This depth of 42km and aftershock distribution determined by the Research Center for Earthquake Prediction of Hokkaido University may suggest that the earthquake occurred within the Pacific plate.
Since the data of this great Hokkaido Toho-Oki earthquake are recorded at epicentral distances of about 5 to 6°, the spatiotemporal source finiteness must affect our estimate of moment tensor even at long-periods (≥70s). Our numerical experiments using finite sources (e. g., unilateral moving line source) show that the source finiteness has a small influence on the source mechanism estimate, but causes the seismic moment to be underestimated. The moment reduction rate depends on the mode of moment release (moving source) and is about 50% in the case of the October 4 earthquake. This result may suggest that our estimation of the moment of the October 4 earthquake should be multiplied by a factor of about 2. The experiments also show that the source finiteness effect can be reduced by using data of longer periods when the station coverage is good.抄録全体を表示PDF形式でダウンロード (1453K) -
今西 和俊, 池田 岩音, 佐藤 魂夫1995 年 48 巻 3 号 p. 365-373
発行日: 1995/11/25
公開日: 2010/03/11
ジャーナル フリーWe investigated the rupture process of the 1993 Hokkaido-Nansei-Oki earthquake (MJMA=7.8) using the broad-band strong motion seismograms recorded at Tomari which is located about 260km distant from the epicenter. We determined the rupture model employing the empirical Green function method in which the waveform of a main shock is synthesized from the waveform of an aftershock. We used the aftershock (MJMA=6.0) that occurred near the main shock epicenter about three hours later. The observed waveforms are best fitted to the synthetics produced for the rupture model involving two major events which ruptured at a time interval of 31-34 seconds. The first event is located near the epicenter and the second event is located near the Okushiri island, about 70km south of the first event. The fault sizes of the two events are both 40×20km2, which are small as compared with the overall area of the aftershock distribution. The total rupture duration is 43-46 seconds. It appears likely that the seismic energy was not released uniformely from the entire aftershock area. The present rupture model is consistent with the previous results obtained from the waveform inversions of teleseismic and strong motion data, suggesting the validity of the empirical Green function method and its usefulness for investigating the rupture process of large earthquakes.抄録全体を表示PDF形式でダウンロード (936K) -
林 愛明, 宇田 進一1995 年 48 巻 3 号 p. 375-386
発行日: 1995/11/25
公開日: 2010/03/11
ジャーナル フリーThe Nojima Earthquake Fault 18km long appeared along the northwestern coastal line in Awaji Island in the 1995 Southern Hyogo Prefecture Earthquake. This fault can be divided into four segments based on the morphological characteristics, geological structures, gravity anomaly, and distributions of aftershocks. These segments are named here from north to south, Nojima segment (Awajicho to Nojima river), Ogura segment (Nojima river to Toshima river), Ikuha segment (Toshima river to Murotsu), and Kareki segment (Murotsu to Ozaki). These fault segments form a dextral strike-slip fault system showing an en echelon form and generally trend toward N30°-60°E. The Nojima and Ogura segments coinside with the Nojima geological fault. The Ikuha and Kareki segments appeared as new fault ruptures, the former following almostly along the axis of the Mitsukoshi flexure, and the latter parallel to and partly along the Shizuki geological fault.
The boundaries between two adjacent fault segments along the Nojima Earthquake Fault are geological and geomorphological boudaries between the basement of Pre-Neogene granitic rocks and the Kobe Group and Quaternary deposits, and between the basin and hill. These boundries show the characters of dilational jogs. Furthermore, it is clear that the aftershock distributions are concentrated in the areas around these dilational jogs. It seems that the main earthquake rupture propagated southwestward from the main epicenter along the Nojima geological fault and then jumped to the next en echelon segment at the dilational jog to the southwestern end area.
As stated above, it is clear that the morphological distributions of the four fault segments of the Nojima Earthquake Fault are controlled by the deep geological structures. The topography and morphology of the Nojima Earthquake Fault provides both useful information on the mechanics of faulting and predictions regarding the heterogeneity of earthquake.抄録全体を表示PDF形式でダウンロード (1411K) -
松本 聡, 津村 紀子, 開原 貴美, 岡田 知己, 堀内 茂木, 長谷川 昭, 伊東 明彦1995 年 48 巻 3 号 p. 387-399
発行日: 1995/11/25
公開日: 2010/03/11
ジャーナル フリーRecent studies made by several researchers show that most parts of P-coda are composed of wavelets incident from the direction of the source region for a frequency range lower than a few Helz. To study characteristics of P-coda wave in a region where strength of inhomogeneity is high, we carried out two seismic array observations in and around a volcanic region of northeastern Japan. One seismic array (Tone array), which is composed of 40 stations, was set up in a volcanic region. The other (GZD array) with 38 stations was set up in a region about 20km away from the former. Seismic data were recorded by personal computers at a sampling frequency of 200Hz. These data were band-pass filters at central frequencies of 2, 8 and 16Hz to be analyzed by using semblance coefficients. Analysis for the GZD array shows that the maximum semblance directions in the P-coda parts almost coincide with the hypocenter direction. On the other hands, the maximum semblance directions for 8 and 16Hz in the P-coda parts are much scattered for the Tone array. These results show that inhomogeneity in the volcanic region is relatively stronger than surrounding region at scale lengths shorter than a few hundreds meters. The mean free path beneath the Tone array, which is located in the volcanic region, estimated to be shorter than 10km based on a single scattering model.抄録全体を表示PDF形式でダウンロード (1521K) -
遠田 晋次, 井上 大栄, 久保内 明彦, 高瀬 信一, 二階堂 学1995 年 48 巻 3 号 p. 401-421
発行日: 1995/11/25
公開日: 2010/03/11
ジャーナル フリーThe Atera fault system is northwest striking left-lateral strike-slip fault that runs for approximately 70km in Central Japan. In this study, trech exposures across the Kowachi (Ogo site) and Atera faults (Aonohara and Dendahara site) identified the most recent faulting with the 1586 Tensho earthquake in historical records. Radiocarbon dates between 1400 A. D. and 1630 A. D. from in situ buried wood at Ogo probably imply sudden subsidence during the Tensho earthquake. The other 6 possible surface faulting events with average interval of 1800 years are also recognized in 11000 years. Furthermore, the timing of the most recent paleoliquefaction and severe deformation of sediments at Aonohara and Dendahara respectively is restricted between 1300 A. D. and 1630 A. D. as well as the Ogo results.
In some previous studies, the Atera fault system had been regarded as one of the precaution faults for the lack of the evidence for the most recent paleoseismicity. However, regarding for quasi-periodic behavior of seismic faulting intervals, geological evidences in this study and very low microseismicity for decades suggests that this fault system is in the period of dormancy during a seismic cycle.抄録全体を表示PDF形式でダウンロード (3944K) -
大堀 道広, 奥田 暁, 若松 邦夫, 安井 譲1995 年 48 巻 3 号 p. 423-427
発行日: 1995/11/25
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (6153K) -
近藤 恵子, 山田 功夫1995 年 48 巻 3 号 p. 429-431
発行日: 1995/11/25
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (2165K) -
佐藤 博樹, 長谷川 昭1995 年 48 巻 3 号 p. 433-434
発行日: 1995/11/25
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (265K) -
古川 信雄1995 年 48 巻 3 号 p. 435-437
発行日: 1995/11/25
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (301K)
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