2.2 Digital Cross Section
The Digital Cross Section Profile is based on the 3-D graphics of Shing Mun Country Park
produced by the 3-D geo-referenced visualization system, Geo3Dvision, developed by our
research group, we can get the digital cross section profile A-B by using the function of cross
section analysis of Geo3D vision ( Figure 2, A,B are marked on Fig.1). The digital cross section
profile then can be used as a basic map to support the interpretation of all geological layers and
faults with the integration of other geological material and our observing and analyzing results.
In this phase, all interpretation outcomes are described on papers. ArcView is finally employed
to digitize the paper-based cross section A-B, and edit symbols of varied geological layers,
blocks and faults. As a result, a 2-D data file including the cross section profile, geological
layers, and faults, as well as a 2-D map could be obtained. Moreover, the 2-D data of the cross
section A-B can be incorporated into the web based virtual environment for 3-D display and
analysis after the coordinate transformation from 2-D coordinate system to 3-D system. From
the digital cross section, we can easily get the land surface information and the geology
information. The faults showed in the cross section mainly depend on the subordinate shear
plans. The other abbreviations represent crystal tuff with biotite(JTM), vitric tuff with
fiamme(JAC), siltstone and mudstone(SL), crystal tuff and tuff breccia(JSM), granodiorite(GD),
fine-grained granite(GF).
Fig. 2 Digital Cross Section A-B
2.3 Structure composition
The movement of strike slip fault can produce a subordinate stress field and form a set of
subordinate structural surfaces(Fig.3). Based on the results of image procession, we recognized
the subordinate structures surfaces of R-shear plan. R’-shear plan. P-shear plan in study area,
and the micro pull-apart structure in the direction of R shear plan has structure records in Jubilee
Reservoir region. R-shear plans are with a smaller acute angle a 1 to the main shear plan Y
(doted line in Fig.3). The angle a 1 is equal to half of angle . , the inner friction angle of rock.
The value of a 1 is about 8
°~20
°,
and the angle direction represent the move direction of inside
block. R plan can be a fault or joint of shear plan, it has same movement as the main fault. R
plan exhibits the distribution of sinistral shear set in main fault zone of dextral movement, and
exhibits the distribution of dextral shear set in main fault zone of sinistral movement. R’ shear
plan is with a larger acute angle
a2
to the main shear plan Y. The angle
°2 is equal to
90
° minus
j/2, the angle direction represent the move direction of inside block. The shear direction of
plan R’ is against the move direction of main shear plan, called anti-movement shear plan, and
exhibits itself as a fault or shear joint. R ’ plan exhibits the distribution of sinistral shear set in
main fault zone of dextral movement, and exhibits the distribution of dextral shear set in main
fault zone of sinistral movement. The shear plans R’ and R are a couple of conjugate shear plans
of subordinate stress field. P shear plan is with a smaller acute angle ß
1 to the main shear plan
Y. The angle ß
1 is equal to
j/2. The angle direction indicates the move direction of outside
block. P plan exhibits itself as fault or shear joint, move direction is same as plan Y, called syn-movement
shear plan. P plan exhibits the distribution of dextral shear set in main fault zone of
dextral movement, and exhibits the distribution of sinistral shear set in main fault zone of
sinistral movement. The newly formed land slide located at the SE side of Jubilee Reservoir,
that is R’ shear plan in NW direction.
Fig.3 The subordinate shear planes in shear zone
R- Riedel shear plane R'- Negative riedel
