1997 Fiscal Year Final Research Report Summary
MORPHOLOGY OF BEDROCK CHANNELS FLOWIN ACROSS ACTIVE FAULTS
| Project/Area Number |
07808016
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
自然地理学
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| Research Institution | CHUO UNIVERSITY |
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Principal Investigator |
OUCHI Shunji Chuo University, Faculty of Science and Engineering, Associate Professor, 理工学部, 助教授 (00185191)
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| Co-Investigator(Kenkyū-buntansha) |
YAMAZAKI Haruo Tokyo Metropolitan University, Faculty of Science, Professor, 理学部・地理学科, 教授 (70260784)
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| Project Period (FY) |
1995 – 1997
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| Keywords | ACTIVE FAULT / BEDROCK CHANNEL / OFFSET STREAM / LONGITUDINAL PROFILE / FLUME EXPERIMENT |
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| Research Abstract |
Longitudinal profiles of streams offset by faults usually show some discontinuities in or near the offset reaches. Relatively gentle steams (<0.5) offset by active faults in central Japan, the longitudinal profiles of which are measured in the field, have offset reaches steeper than adjacent reaches but with step-like features, while offset reaches of relatively steep (>0.1) streams have slopes gentler than adjacent reaches. The offset reaches of two creeks across the San Andreas Fault, California, show a little steeper gradient than adjacent reaches, while smaller gullies have gentler offset reaches.
The flume experiments indicate that the experimental streams do not respond to lateral deformation so much but they quickly adjust their longitudinal profiles by the incision in the downstream reach. The incision seems to be accelerated by the enhancement of flow turbulence downstream form the offset reaches.
Actual fault movements that have both lateral and vertical components can make the slope of displacement steeper or gentler than the channel. In the case of gentler displacement in the easily erodible bed material, accelerated incision in the downstream reach and the deposition in the upstream reach would keep the longitudinal profile relatively smooth. If the channel cannot incise the bed enough, gentler part would remain in the longitudinal profile. Where the displacement is steeper, deposition of sediments supplied from the fault scarp would enlarge the offset valley and succeeding incision would result in the formation of small terraces and/or steps in the longitudinal profile.
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