地理学評論
Online ISSN : 2185-1727
Print ISSN : 1347-9555
ISSN-L : 1347-9555
Characteristics of Small Offset Streams Crossing Strike-Slip Faults in Japan
Shunji OUCHI
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ジャーナル フリー

2006 年 79 巻 5 号 p. 179-197

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Seven small offset streams crossing strike-slip faults in central to south-western Japan, longitudinal profiles and channel course geometry of which were measured in the field, show no correlation between the amount of channel offset (offset length) and drainage area or channel length above the fault. The method to estimate fault slip rates from the relationship between offset length and channel length above the fault seems not valid for these offset streams. The angle of deflection, which is the angle between the fault line and the reach connecting reaches divided by fault displacement (offset reach), shows a negative correlation wi offset length for the streams of long offset, while no correlation is clear for the streams of short offset. When the channel offset is short and significant channel shift towards the steepest possible course does not occur yet, fault zone width probably controls the deflection angle. The negative correlation for the streams of long offset may reflect the easier channel shift of the streams with shorter offset among them. The deformation types of these offset streams are judged as Type A (offset slope of fault displacement is smaller than channel gradient) except for one as Type C with larger offset slope. Some configurations characteristic to the deformation types still remain in their longitudinal profiles with various degrees of fluvial adjustment. Offset streams seem to be in the repeated process of tectonic deformation and fluvial adjustment as long as the fault actity continues.

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