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Geology
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Radar Image for the Study of Landslide Structures in HK
3. The relationship between land slides and subordinate structures
3.1 The structure controlled micro-geography
Study area has many valleys and steep slops, so the outcrops are comparable rich. The changes
of micro geography are exactly reflecting the distribution of subordinate shear plans. On the
northern slop of Needle Hill, a serials P shear plans regularly distributed in NNE, formed the
land surface as shape of rhombus and formed the Duplex Structure locally. It is a typical feature
of high strain area. The sharp end of the land slopes are the record of former weathering and
erosion, the positions of S shaped image texture and the brightness quick change are the possible
positions of produce land slides. Fig.4(left) clearly show that the transtension structure is the
control factor of producing landslide, especially when the subordinate shear planes change dip
angle at depth(right). There are no brittle bent deformations in study area, so the plan
deformations are well recorded by radar image. Because radar wave has strong capacity of
detect lineation, the possibility of recording the R, P, R’ shear plans is largely increased. By
selecting the weak information of lineations in radar image, we can recognize rich subordinate
joints. Almost all of these joints are of structure significance, so the error can be largely avoided
during the structure analyze.
Fig.4 Map of landslide and its structural backgound (See text for detailes)
3.2 Search landslide in radar image
The image procession not enhanced the feature of subordinate structures, and also reserved the
main regional faults. This increased the systemic interpretation of radar image, and is favorable
to apply the broken theory. By field examination, the most of lineation image are subordinate
shear plans, which have significant feature of structure deformation.
3.3 Field data of landslide
The subordinate transtension structures in Jubilee Reservoir was also based on the field data.
The granite there is strongly weathered, and the base rock is regular exposed. The NE dextral
shear plans are: 30 / 120 < 80.20 / 110 < 78, represented by the heavy joints belt. The NW
tension plan is 346 / 256 < 88, where existed a deep valley. On the north edge of the valley,
there is a newly formed land slide. So, under the movement of N45E strike-slip fault, we can
figure out that N60E dextral shear plans located at the direction of P shear plan, N30E dextral
shear plans located at the direction of R shear plan, and the NW faults located at the direction of
R’ direction. This composition controlled the different scale of boulder falls land slide in NW
extension fault direction, and the alluvium gravity land slide in N60E shear direction.
3.4 Acknowledgement
This project support from Hong Kong Research Grand Committee (CUHK 4334/98E) and Hong
Kong Industry Supporting Fund (AF/169/98). The 308 subject of 863 Project made the Radar
image of Hong Kong.
References
- Armin Gruen and Haihong Li, 1997,Semi-Automatic Linear Feacher Extraction by Dynamic
Programming and LSB-Snakes, Photogrammetric Engineering & Remote
Sensing,Vol.63,No.8,August ,pp985-995
- Batlett, W.L., Friedman, M. and Logan, J.M., 1981, Experimental folding and faulting of
rocks under confining pressure, Tectonophysics, vol.79, pp.255-277
- Bennet, J.D., 1984, Review of tectonic history, structure and metamorphism of Hong Kong,
Geotechnical Control Office, 6/84
- C.F.Lee, Chen Hong, 1997, Landslides in Hong Kong: Causes and Prevention, Acta Geo-Graphica
Sinica, Vol.52, Supplement, pp.114-121 (in Chinese with English Abstract)
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