Zisin (Journal of the Seismological Society of Japan. 2nd ser.)
Online ISSN : 1883-9029
Print ISSN : 0037-1114
ISSN-L : 0037-1114
Volume 53, Issue 2
Displaying 1-8 of 8 articles from this issue
  • Subsurface Structure between the Konan Terrace and the Menuma Lowland
    Kazuo YAMAGUCHI, Naomi KANO, Takanobu YOKOKURA, Tsutomu KIGUCHI, Toshi ...
    2000 Volume 53 Issue 2 Pages 115-125
    Published: December 25, 2000
    Released on J-STAGE: March 11, 2010
    JOURNAL FREE ACCESS
    Several active faults have been recognized based on displacement of geomorphic surfaces around the Konan terrace and Menuma lowland, Saitama Prefecture, northwestern Kanto Plain. In this area, a shallow damaging earthquake occurred (1931 Nishi Saitama earthquake, M=6.9) and the Median Tectonic Line (MTL) probably extends southeastward. However, the relationship between the active faults and the MTL is not well known, because the subsurface structure of them has not been investigated enough. We therefore conducted seismic reflection surveys and interpreted the seismic sections together with previously published geological and geophysical data. The following conclusions are reached:
    (1) A similar deformation pattern of sedimentary layers is detected at 100m to 1km depth under both the flexure scarp of the Fukaya fault and its extension. This supports the southeast extension of the fault. The Fukaya fault has been active at least to the Kumagaya Ohashi of the Ara River based on the estimated ages of the deformed layers.
    (2) Discontinuous reflectors are recognized at 100m to 1km depth near the Naranashi fault that has been inferred from surface geology. They are the material boundary MTL, which juxtaposes the Sanbagawa metamorphic rocks against the Neogene strata. But the material boundary MTL is not clear to the northeast of the Naranashi fault.
    (3) The Fukaya fault and Konan fault are considered as a listric master fault dipping southwest and a secondary fault dipping northeast, respectively, and they have formed a popup. This is based on reflector dips, directions of fault displacement, stress field and fault lengths.
    (4) The dip and strike of the Naranashi fault are similar to those of the source fault of the Nishi Saitama earthquake. This implies that the two faults correspond.
    (5) A schematic model is proposed in which the Naranashi fault branches off northeastward at depths and continues upward to the Fukaya fault.
    Download PDF (5488K)
  • Satoshi FUJIWARA, Shinzaburo OZAWA, Makoto MURAKAMI, Mikio TOBITA
    2000 Volume 53 Issue 2 Pages 127-136
    Published: December 25, 2000
    Released on J-STAGE: March 11, 2010
    JOURNAL FREE ACCESS
    The 1995 Hyogo-ken Nanbu earthquake in Japan caused large crustal deformation, however, only a few exposed faults have been identified by ground survey and detailed positions of the earthquake faults have not been mapped. The displacement field on the surface associated with the earthquake was mapped by a satellite radar interferometry image. The Synthetic Aperture Radar (SAR) interferogram generally shows elastic motion caused by the main earthquake but many discontinuities of the fault displacements are found, the latter of which can be most easily visualized in the surface displacement gradient. During the earthquake a concentration of damage, so-called damage belt, was observed. Though we found displacements probably caused by hidden faults just under the damage belt, the hidden faults were shorter in length and their displacements were smaller than those of the known faults running along the northern edge of the damage belt. However, strong seismic vibration was observed just on the small faults found in surrounding area of the main faults. Accordingly there is some possibility that the hidden small faults accelerated the main seismic vibration.
    Download PDF (4285K)
  • Shoji SEKIGUCHI
    2000 Volume 53 Issue 2 Pages 137-151
    Published: December 25, 2000
    Released on J-STAGE: March 11, 2010
    JOURNAL FREE ACCESS
    We obtained three-dimensional P and S velocity structures of the uppermost mantle beneath the Kanto, Tokai and Chubu districts, Japan, by means of travel time tomography. We used 18 years travel time data recorded by the National Research Institute for Earth Science and Disaster Prevention. High velocity subducted Philippine Sea plate is revealed below the Kanto and Tokai district. Low velocity oceanic crust of the Philippine Sea plate is also revealed below the Kanto and Tokai district. The oceanic crust below the Kanto area is found to be a complex shape, which shows the deformation of the Philippine Sea plate. High velocity area, ahead of the leading edge of the Philippine Sea plate associated with seismic activity, suggests the existence of the aseismic plate. Some high Poisson's ratio areas are found in the low velocity areas.
    Download PDF (18752K)
  • Mitsuhisa WATANABE, Yoko OTA, Ikuo SUZUKI, Hiroshi SAWA, Yasuhiro SUZU ...
    2000 Volume 53 Issue 2 Pages 153-164
    Published: December 25, 2000
    Released on J-STAGE: March 11, 2010
    JOURNAL FREE ACCESS
    The western margin of the Echigo Plain, central Japan, is marked by a set of reverse faults trending NNE-SSW. These faults are assumed to be very active ones. However, it is difficult to know the recent rupture history of the faults because of thick pile of unconsolidated sediment. The Torigoe Fault vertically dislocates the late Pleistocene fluvial terrace surfaces over several meters, west of Nagaoka City, southern part of the Echigo Plain. We identified a gentle, broad slope on Holocene lowland as the distinct faulted topography on the basis of interpretation of large-scale aerial photographs and leveling of topographic profiles. The fault displays the evidence for its recent reactivation about 2m high. Trenching and drilling surveys across the deformed zone reveal the vertical displacement associated with faulting, the timing of latest faulting event and average recurrence interval of the Torigoe Fault. The most recent faulting on the Torigoe Fault probably occurred since 12th-13th century. The ground surface was vertically dislocated about 2m by reverse slip. The net-slip on fault plane should be over 2m. Although great shaking might attack the area around the fault, there is no historical record of heavy damage since 17th century. The fault vertically offsets the gravel layer dated at ca. 5, 600-5, 700 BC by 10-12m. The amount of displacement represents the accumulative result of five to six faulting events. The younger sediment (1, 300-2, 400 BC) may be offset by 5-6m. If there have been five to six faulting events since ca. 5, 600-5, 700 BC, the average recurrence interval of faulting is estimated to be 1, 100-1, 900yrs.
    Download PDF (1816K)
  • Yasunori MORI, Ruka YAMASHITA, Iwao KAWABE, Takamori ITO, Koichiro NAG ...
    2000 Volume 53 Issue 2 Pages 165-176
    Published: December 25, 2000
    Released on J-STAGE: March 11, 2010
    JOURNAL FREE ACCESS
    Gas bubbles separating from ground water has been monitored continually by a gas chromatograph and an α scintillation Rn detector at a well of Nagashima spa, a southern suburb of Nagoya, central Japan since October 1997. The Nagashima well is 1500m deep and located at a distance of 5km from the Yoro active fault. Concentrations of He, H2, Ar, N2 and CH4 and Rn in the gas bubbles are analyzed. H2/Ar anomalies have been recorded in relation to some earthquakes (M<3.1) occurred in and near the northern part of Ise Bay between June and August 1999. The accumulated data support the idea that H2 is generated through the mechano-chemical reaction between groundwater and fresh silicate surfaces of slip planes presumably induced by preseismic slips. The H2/Ar anomalies can be classified into “spike-like change” and “ramp function-like change” based on the variation patterns of the observed H2/Ar anomalies. The two types of anomalous changes of H2/Ar ratio can be interpreted by using two models for the preseismic deformation on a slip plane as groundwater conduit. One is the aseismic stick-slip model for local contact areas on the slip planes, and the other is the crack growth model by stress corrosion. If mechano-chemical reaction of fresh silicate surfaces created by the stick-slip or the crack growth with water can produce H2 gas, the observed temporal variation of H2/Ar ratio possibly corresponds to the rate of stick-slip or crack growth and increase of newly produced rock surfaces. The ramp function-like increases of H2/Ar suggest increasing rates of stick-slip or crack growth for a prolonged period preceding earthquakes along the active fault zone.
    Download PDF (1633K)
  • Aftershock Distribution soon after the 1993 Hokkaido Nansei-oki Earthquake
    Yasuhira AOYAGI, Shintaro ABE
    2000 Volume 53 Issue 2 Pages 177-180
    Published: December 25, 2000
    Released on J-STAGE: March 11, 2010
    JOURNAL FREE ACCESS
    Download PDF (5536K)
  • Kenji UEHIRA, Takeshi MATSUSHIMA, Hiroshi SHIMIZU, Shigeki ADACHI, Kou ...
    2000 Volume 53 Issue 2 Pages 181-184
    Published: December 25, 2000
    Released on J-STAGE: March 11, 2010
    JOURNAL FREE ACCESS
    Download PDF (6539K)
  • Atsushi WATANABE, Hiroshi TAKENAKA, Yushiro FUJII, Hiroyuki FUJIWARA
    2000 Volume 53 Issue 2 Pages 185-192
    Published: December 25, 2000
    Released on J-STAGE: March 11, 2010
    JOURNAL FREE ACCESS
    Download PDF (1084K)
feedback
Top