Al
2
Si
2
O
5
OH
4
and illite Al,Fe,MgSi,Al
2
O
5
OH + K, where those mineral elements have a plastic or unstable characteristics. Furthermore, the areas with
yellow and cyan colors, caused by weathered rocks which contains same percentage of iron-oxide and clay-hydroxyl, but the characteristics it self not more
stable than rock contains iron-oxide and more stable than rocks which contains clay-hydroxyl. Caused iron-oxide mineral that compose the rock indicating the
resistant rock than clay-hydroxile mineral. Therby, Land Stability Risk Zone can
be obtained by giving weight Table 4.1. toward those mineral distribution in an image.
Unstable
3
Clay I ntermediate
2
I ron-Clay Stable
1
I ron
Description Weight
Mineral Distribution
Table 4.1. Mineral Distribution Weighting
4.3 Slope Stability Risk Zone
Slope distribution weighting Table 4.2. obtained based on charactersitics of the slope categories for land development Table 3.1. Page: 34 which used for
generate slope map from DEM in ArcGIS. Appendix 4.
50 Unstable
3
30 - 50 I ntermediate
2
15 - 30 5 - 15
Stable
1
0 - 5
Description Weight
Slope
Table 4.2. Slope Distribution Weighting
42
Figure 4.3. Slope Stability Risk Zone Map
4.4. Rock Type Risk Zone
Rock type distribution weighting Table 4.3. obtained based on rock type and physical characteristics Table 3.2. Page: 35 as shown in Figure 4.4.
Unstable
3
Claystone Shale, Alluvial I ntermediate
2
Sandstone, Tuff Lapilli, Bedded Limestone, greywacke
Conglomerate Stable
1
I gneous Rocks, Volcanic Breccia, Crystalline Limestone
Description Weight
Rock Type
Table 4.3. Rock Type Distribution Weighting
43
Figure 4.4. Risk Zone by Rock Type
4.5 Geomorphological Interpretation
Based on statistical calculation of 150 lineaments in Figure 4.5., common direction of lineaments will be obtained which is N 10
o
- 20
o
E Figure 4.6.
Figure 4.5. Structural Geology interpretation by fault pattern of back-hill, valey and main stream of research area
44
Figure 4.6. Rosette-diagram of 150 lineaments of research area, show the Southwest-Northeats direction of fault system of research area N
10
o
- 20
o
E.
The pattern consitute one of the four fault pattern system in West Java and
its controled by strike-slip-left fault which influenced by relatively
Northwest-Southeast force in Tertiary period.
Figure 4.7. Drainage pattern interpretation of research area
45
Furthermore, based on interpretation from Figure 4.7, generally, there are three drainages pattern which shapes the land form, i.e. parallel-rectangular,
trellis-rectangular and radial patterns.
Thereby, parallel-rectangular Pr-Rct pattern in research area explains that
area controlled by structure geology dominantly such normal fault and then forced by strike-slip fault on the next period of tectonic occurrence. Whereas
trellis-rectangular Tr-Rct also controlled the research area by structure geology
dominantly, but the first tectonic occurrence produced folded area.
4.6 Geological Hazard Sensitive Area
