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Volume 53, Issue 3
Displaying 1-13 of 13 articles from this issue
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Fujio AKITA, Norio MATSUMOTO2001 Volume 53 Issue 3 Pages 193-204
Published: March 25, 2001
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSM7.6 Kushiro-Oki, M7.8 Hokkaido-Nansei-Oki, M8.1 Hokkaido-Toho-Oki and M7.5 Sanriku-Haruka-Oki earthquakes occurred around Hokkaido, northern Japan during the period from January, 1993 to December, 1994. We have collected groundwater-level records in 12 wells observed by local governments in Hokkaido to investigate the relationship between coseismic changes in water levels and volumetric strain induced by the four large earthquakes. Coseismic water level changes are found in many wells. The maximum coseismic change in water level was 2.5m, induced by the Hokkaido-Nansei-Oki earthquake. The volumetric strain fields induced by the four earthquakes have been calculated by using published parameters of dislocation models, and compared with the coseismic water level changes. Generally, the volumetric strain changes at wells where water level fell coseismically are dilatation, and those at wells where water level rose are contraction. As far as the relationship between water level changes and volumetric strain induced by the earthquakes in seven wells where water level data are available for at least three earthquakes, coseismic water level changes at all the seven wells are found to be proportional to the calculated volumetric strain. Furthermore, the coseismic water level changes are found to be proportional to not only the volumetric strain but also an amplitude of ground motion caused by the earthquakes in four wells where water level are available for all the four earthquakes by applying AIC (The Akaike Information Criterion) method. The strain sensitivities of the water level at the four wells, which are between 1.6 and 19.6mm/10-8 strain when the contribution of both the volumetric strain and the ground motion are taken into account, are as large as strain sensitivities inferred from the earth tides in 17 wells observed worldwide.View full abstractDownload PDF (1647K) -
Hideaki GOTO, Takashi NAKATA, Hiroyuki TSUTSUMI, Koji OKUMURA, Toshifu ...2001 Volume 53 Issue 3 Pages 205-219
Published: March 25, 2001
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe Median Tectonic Line active fault system (MTL) is one of the most active and longest active faults on land in Japan, and has a potential source of destructive large earthquakes. However, paleoseismological data along the MTL are sparse in Shikoku. The history of surface-rupturing earthquakes, particularly the timing of the latest events, on each segments is key data for examining the interaction of neighboring faults and evaluating the long-term seismic risk.
To date the latest surface-faulting events on the MTL active fault system in Shikoku, we excavated mini-trenches on the Iyo fault and extracted vertical thin sections of unconsolidated soil layers by the Geoslicer on the Okamura and Ikeda faults. In this paper, we discuss the characteristics of active faulting along the MTL based on the results at the three sites and previously published data.
The latest event occurred after the 14th century at Ichiba on the Iyo fault. The slip associated with the event was 2.1-2.3m based on a series of right-laterally offset rice paddy dikes. Geoslicer studies at Kishinoshita on the Okamura fault and at Iyo-Mishima on the Ikeda fault suggest that the latest event occured after the 16th century and after the 13th century, respectively.
The youngest age of the latest event is not well defined by the geological studies. Since historical documents during the 18th century do not record any activity of the MTL on land, the timing of the most recent events on the fault is confined to between the 13th and 17th centuries. Therefore, timing of the latest events in Shikoku is concentrated within the past several hundred years. This suggests a temporal clustering of active faulting on the MTL, similar to that observed from other major fault worldwide.View full abstractDownload PDF (2399K) -
Takayuki KANESO, Junji KOYAMA, Takeo MORIYA, Hiroaki TAKAHASHI2001 Volume 53 Issue 3 Pages 221-229
Published: March 25, 2001
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSWe seek the way of high-speed sampling GPS observation as a broad-band displacementseismomete. For this purpose it is necessary to evaluate the noise level inherent to the GPS observation due to ionospheric and tropospheric effects, multi-path and satellite configuration. In this study, we develop a stand-alone data acquisition system for the continuous high-speed sampling GPS observation after overcoming the troubles in automatic handling the large volume of GPS data. Four GPS stations are establised in Hokkaido area and the period of each observation is half year to year and half. Telemetry of the GPS data using the public telephone line is tested and completed. GPS station coordinates are calculated every second by the GPS kinematic method. Noise reduction for each noise source has been made, and noise levels of horizontal and vertical components after the reduction are about ±4mm, ±7mm, respectively in the case of 150km baseline length. Noise levels of various baseline lengths are also evaluated in different period ranges. These estimates of noises prove that the earthquake larger than JMA magnitude 5.9 can be detected at a GPS station 60km away from the epicenter.View full abstractDownload PDF (3397K) -
Wataru MORII2001 Volume 53 Issue 3 Pages 231-240
Published: March 25, 2001
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSEarth's free oscillations excited independently of earthquakes were detected by the vertical strain seismograph being in operation at the Amagase Observatory, Kyoto University, Japan. Though weak, diurnal variation in Earth's background free oscillations was evident. The maximum and the minimum of diurnal variations were found in intervals from 14 to 16 o'clock (JST) and from 6 to 8 o'clock (JST), respectively. It was also found that the feature of the diurnal variation above mentioned was evident in the summer of the northern hemisphere and disturbed in the winter.View full abstractDownload PDF (1214K) -
Tamotsu OKUSAWA, Hiroaki TSUKAHARA2001 Volume 53 Issue 3 Pages 241-253
Published: March 25, 2001
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSMany small earthquakes occurred in the Matsushiro area in a period from 1965 to 1967. This is called “Matsushiro Earthquake Swarm”. The swarm earthquakes are interpreted as a result of deep ground water intrusion into the focal area. At the hardest time of the crustal movement, water flow from pre-existing springs increased, and many new springs appeared along a hidden fault zone formed by the swarm earthquakes. Some of springs are still alive and have peculiar chemical compositions. The deep ground water must have caused the earthquake swarm. We show the characteristics of the deep ground water through analyzing chemical composition. Our measured data and many published data show that the deep ground water obtains Ca2+ from rocks and loses Na+ during its upwelling migration through the fault zone of Matsushiro Swarm Earthquakes. The data also show that the major components of Cl- and (Na++Ca2+) have a liner relation in concentrations, although every spring water has different concentrations of Cl- and (Na++Ca2+). It is interpreted in terms of mixing deep ground water with shallow ground water at defferent ratios. The concentrations of the major ions of the deep ground water are estimated from both of our measured data and compiled data using the liner relation, e. g., Na+: 310meq/l, Cl-: 330meq/l. Analysis of our measured data also reveals that the small temporal variation in the concentration of Ca2+ in a short period such as several months is attributable to the reaction between the ground water with CO2 and surrounding rocks.View full abstractDownload PDF (4150K) -
Taka'aki TAIRA, Kenshiro Tsumura2001 Volume 53 Issue 3 Pages 255-258
Published: March 25, 2001
Released on J-STAGE: March 11, 2010
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Isao YAMADA2001 Volume 53 Issue 3 Pages 259-262
Published: March 25, 2001
Released on J-STAGE: March 11, 2010
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Norihito UMINO, Yoshihiro ITO, Toshihiro IGARASHI, Akira HASEGAWA2001 Volume 53 Issue 3 Pages 263-268
Published: March 25, 2001
Released on J-STAGE: March 11, 2010
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Ikuei MURAMATSU2001 Volume 53 Issue 3 Pages 269-272
Published: March 25, 2001
Released on J-STAGE: March 11, 2010
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Shin'ya TSUKADA, Kazuo OHTAKE2001 Volume 53 Issue 3 Pages 273-280
Published: March 25, 2001
Released on J-STAGE: March 11, 2010
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Mamoru NAKAMURA2001 Volume 53 Issue 3 Pages 281-284
Published: March 25, 2001
Released on J-STAGE: March 11, 2010
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Masayuki TAKEMURA, Takafumi MOROI2001 Volume 53 Issue 3 Pages 285-302
Published: March 25, 2001
Released on J-STAGE: March 11, 2010
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Junichi YAMAZAKI2001 Volume 53 Issue 3 Pages 303-312
Published: March 25, 2001
Released on J-STAGE: March 11, 2010
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