procedures are considered to indicate an area which
has high potential of landslide. Also, in Most
cases, the landslide shows a topograpgical unique
shape. For example, the landslide shows horse-shoe-
shaped land form as a whole, or the landslide is
composed of cliff of steep slope called main scarp
and gentle slope called slide block. This
composition creates the unique topographic pattern.
It is better at present to leave the recognition of
pattern to the judgment of experts. In this study,
therefore, we select the areas which have a high
possibility of landslide distribution excluding the
areas where landslide actually occurred. The
selection results are used as supporting
information for the renewal of landslide
distribution information.
3. Results
3.1 Extraction of factor information
Table 1 shows the area ratio of category among
each factor information at the landslide area and
within the study area. The findings we obtained
here are as follows:
3.1.1 Lithological character: We compared the area
ratio of "colluvial and debris" and "sand stone and
mud stone": within the total study area ‘and
landslide area. The ratio of "colluvial and debris"
is 5.37 (total) against 11.0% (landslide area),
while that of "sand stone and mud stone" is 56.27
(total) against 64.3% (landslide area). Namely, it
means that the landslide area contains more
quantity of these two categories of 1lithologic
character than other categories. Therefore, these
two categories of lithologic character have higher
potential of landslide distributions.
On the contrary, the ratio of area occupied by
"gravel, sand and silt," "mud stone" and "sand
Stone" is lower at the landslide areas comparing
with those ratios in the total study area. In other
words, it means that these categories have lower
potential of landslide distribution.
3.1.3 Ponds: There are !! ponds in the total study
area, of which 30. ponds are located at “the
landslide area (including the ponds only a part of
which is located at landslide area).
3.1.4 Paddy field: There are 644 paddy fields in
the total study area of which 458 paddy fields are
3.1.1 Topographical information: As for the located at the landslide area (including the fields
gradient and aspect calculated from DTM, the only a part of which is at the landslide area).
gradient is classified into 10 grades at the As a result, we decide to use four factors of
interval of 5', and the aspect into 8 directions. (1) gradient, (2) lithologic character, (3)
distribution of ponds and (4) distribution of paddy
field for the analysis.
The ratio of areas with the gradient 5° or more but
less than 25° occupy 71% of the total study area,
while the ratio of it is 807 at the landslide
areas. No significant difference is observed as for
the aspect.
Table.1 The area ratio of factor information
(1) Topographical factor (%)
G ra d i e mn at A s p e € tI
C. a 1 0e 1: O I y Study area | Landslide Category | Study area | Landslide
less than 5 9.1 5.4 N 13.1 13.0
5 or more less than 10 11. 0 13.3 NE 14.0 14.4
10° or more less than 15 20.0 24.5 E 13 2 15.5
15. ‚or more less than 20° 23,2 26.2 SE 8.7 10.1
20 or more less than 25° 17.4 17.0 S 8.6 1.8
25 or more less than 30' 10.3 8.4 SW 10.3 9.0
30 or more less than 35' 5.7 9.4 y 12.6 12.2
35° or more less than 40° 2.2 1.3 NW 14.5 14.2
40 or more less than 45' 0.6 0. 3
45' or more 0.5 0.3
(2) Geological factor (%) (3) Land information factor
L i.t ho l]o gite ch art ac tier P o n d
Category Study area | Landslide Study area | Landslide
Conglomerate 1.7 0. 5 56857 ni 33074
Colluvial and Debris 5.3 11.0 (100.0%) (55. 394)
Gravel,sand and silt 6.3 2.2
Mud stone 10.9 6.6 Paddy fi e. d
Mud stone and sand stone 56.2 64.3
Sandstone 0.1 0.0 Study area | Landslide
Sand stone and mud stone 0.5 0.2 20452672 nt 9925485 ni
Sand stone 18.2 14.3 (100.0%) (48.5%)
Silt, sand and gravel 0.1 0
Tuff 0.7 0.7
Volcanic rock 0.1 0.0
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