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Volume 40 (1999 - 200･･･
- Issue 6 Pages 333-
- Issue 5 Pages 260-
- Issue 4 Pages 196-
- Issue 3 Pages 124-
- Issue 2 Pages 60-
- Issue 1 Pages 2-
Volume 40, Issue 2
Displaying 1-4 of 4 articles from this issue
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Taku KOMATSUBARA1999 Volume 40 Issue 2 Pages 60-69
Published: June 10, 1999
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSThis paper summarizes the characteristics of crustal movements associated with concealed faults, and discusses the application of some methods for seismic hazard assessments of concealed faults.
Many active concealed faults occur under active folding in the thick Neogene distributed area, especially Inner zone of Northeast Japan Arc, and they are significant sources of medium to large earthquakes.
An activity of concealed fault (fold earthquake) makes an uplifting with assynmmetrical folding. The width of uplifted area is roughly same to depth of the bottom of fault, and anticline have steep limb on the fault tip side. An faulting on a bending fault makes a complex anticlinorium which have short wave- length fold axes and/or structural terraces and steep dipping zone.
Such activities of concealed faults shall be recorded in the surface (Holocene) sediments and terraces crossing active anticlines. Thus clino- unconformities in the Holocene layers and differentiated terraces shall provide quantitative and essential data for restoring the paleo- seismicities on the concealed faults. But these methods are not applicable to the faults that lies under thick layers (fault tip located about 1km or more deep part of upper crust), or locates in the mountainous region where initial gradient of alluvial plain is steeper than the gradient of tilting accompanied with one faulting. In this case, the other pale- seismic records such as secondary faults, fossils indicating pale- sea level, emerged benches, pale-liquefaction, and the like. Each method, however, is not of wide application, thus synthetic judgments on some methods are needed to seismic hazard assessments.
The 3- dimensional features and slip distribution on the concealed (reverse) faults can be estimated from the surface and underground geologic structures and terrace deformations, so we may be able to provide effective information for estimation of strong ground motion on the basis of geologic and geomorphologic studies of active folding.View full abstractDownload PDF (2202K) -
Mitsuyoshi IKEDA, Kinya MIURA, Hiroshi KURIKAMI1999 Volume 40 Issue 2 Pages 70-85
Published: June 10, 1999
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSGroundwater temperature is one of the most effective environmental tracers. Groundwater temperatures are lower than average in recharge areas, and higher than average in discharge areas. Using this principle, groundwater flow around the Bibi River in Hokkaido was clarified as follows: (a) The upper Toasa River basin except for the Umaoi Hills belongs to the Bibi River groundwater basin. (b) The groundwater divide between the Bibi River and the Toasa River runs across the middle of the Toasa River Basin. (c) The western boundary of the Bibi groundwater basin locates at the 90m volcanic ash plateau, and there is very little leakage from Lake Shikotsu into the Bibi River groundwater basin. (d) The divide in the groundwater found from groundwater temperature is consistent with that estimated from the thermal advection-dispersion analyses by means of the finite element method, the groundwater table and the water balance.
Recently, groundwater temperature has found use as an index of global warming. Such an increase was found in the study area, owing to urbanization. Additionally, further development projects will require assessments on the groundwater flow system, and this study suggests that the change in groundwater temperature is an effective tool for these assessments.View full abstractDownload PDF (4311K) -
Takeshi KAMEI, Mitsugu KANDA, Hirokazu ISHIHARA1999 Volume 40 Issue 2 Pages 86-98
Published: June 10, 1999
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSThis paper integrates geological histories, geochemistry (sulfur, nitrogen and organic carbon concentration) and geotechnical characteristics of Holocene deposits in the Izumo Plain, southwest Japan. Sulfur, nitrogen and organic carbon relationships in Holocene sediments have been used to characterize depositional environments, namely normal marine, brackish water, freshwater and euxinic sediments. The weight ratio of organic carbon to pyrite sulfur (C/S ratio) is useful for evaluating sedimentary environments. The geomorphological processes of Izumo Plain during the Holocene is also described. In addition, data regarding calcite (CaCo3) content within natural silt and clay sediments with depth and its effect on strength-deformation characteristics is presented.
We have attempted in this paper to demonstrate the importance of integrated studies of sedimentary environments and the usefulness of CNS elemental analysis. This study offers the designer a better understanding of mechanical behaviour of Holocene deposits, leading to refinement of existing construction technology.View full abstractDownload PDF (2396K) -
Earthquake-induced Hydrological Changes: an Example from Kobe EarthquakeTomochika TOKUNAGA1999 Volume 40 Issue 2 Pages 99-106
Published: June 10, 1999
Released on J-STAGE: February 23, 2010
JOURNAL FREE ACCESSThe Dupuit-Ghyben-Herzberg model was applied to the Awajishima Island to explain hydrologic changes associated with the 1995 Hyogo-ken Nanbu (Kobe) Earthquake, and hydraulic properties (hydraulic conductivity, specific yield) were estimated using the available quantitative data. Results indicate that the hydraulic conductivity has increase at least 5 times over the pre-seismic value, and that the specific yield of the unconfined aquifer is at around 0.3 to 1.7% depending on the assumed recharge rate but regardless of the depth to the impermeable basement. Upward migration of deeper water due to salt-water intrusion may explain the change of chemical composition of discharged water. This analysis suggests the necessity of measuring the increase of the discharged water just after an earthquake to properly estimate the change in the hydraulic conductivity of the aquifer.View full abstractDownload PDF (1394K)
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