The figure below shows the results of a self-potential survey over a landslide i

Question

The figure below shows the results of a self-potential survey over a landslide in Southern Italy that last mobilised in 1976. The dashed line demarcates the landslide itself – the upper part being the source zone and the lower the accumulation zone.

a) Describe very briefly how the SP signal varies as a function of topography and why this is likely to be the case.

b) Describe very briefly how the SP signal relates to the demarcation of the historic landslide and how you might explain this relationship.

Explanation / Answer

a. Basically, self-potential is a function of permeable loess layer, in any topographic profile, we too find a similar relationship in which the top soil is loose and it provides much better permeability as compared to that of the subsurface rock type. Clay has a much lower pore space and as a result, it will show a lower value of SP where as the sand layer have much better openings so it will show a positive and higher value of SP.
b. Landslide is the free fall of earth material towards the downside of a slope, all the debris will come to a halt at the foot of the elevated ground. The value of the SP will be increased downslope, this is caused by the groundwater infiltrating at the head of the slope and flowing downslope. This will result in a sudden increase in SP values in the historical landslide sites.

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