S. BHALAI – Landslide susceptibility of Portland, Jamaica
Table 6. Calculation of the landslide susceptibility of the distance from major faults classes. Susceptibility values are generally between 9 and 12 suggestive of no correlation at this distance range.
CLASS (km ) CLASS (km )
Table 5. Landslide susceptibility of the geotechnical groups
AREA OF SCARP IN
Figure 16. Susceptibility of the geotechnical groups of the rock types in Portland. Colluvium has the highest weight indicating the proportion of source areas developed in this material.
Figure 17. Susceptibility of the classes of distance from major faults. Note that with increase in distance, there is no correlation. The increase in susceptibility at and after 400 m is irrelevant, considering that the parish contains a dense fault pattern and at this distance, the zone of influence of another fault becomes active.
the three highest zones of susceptibility. With the second technique selected districts of known landslide susceptibility (areas having either high or low susceptibilities) were used and these include the Rio Grande Valley, Claverty Cottage, Buff Bay
Shrewsbury. The model favourably predicted the respective level of landslide susceptibility as interpreted from field observations (Table 8). Table 9 shows the distribution of the refined susceptibility zones.
susceptibility between 1000 m are possibly conditions prevailing at
elevations of 200 m to related to the climatic this topographic level. It is
highly likely that humid conditions dominate, encouraging rapid physical and chemical breakdown of the local rock types. The rock types at these ranges may also be responsible. The Shale and
Limestone geotechnical groups are at these elevations and these rock types
have also been found to susceptibility, as observed in in the Rio Grande Valley.
have high landslide the Moore Town area
5. DISCUSSION Both geomorphical and geological predisposing factors all show correlation with landslide events. An exception to this is the distance from geological faults, where no correlation was seen. The geomorphical factors all show positive correlations with landslide occurrence. High levels of landslide
Lower levels of landslide susceptibility occur at the low and high extremes of the elevation in the parish. The extent of flat areas and alluvial plains account for the low susceptibility at elevations less than 100 m. At the higher extreme of elevation, as the rocks are decomposed, the residue is eroded during periods of rainfall, removing the weathering