Landslide Susceptibility Maps in Slovenia: How to account for the interplay of slope and dip?

Slovenia is currently completing the country-wide mapping of landslide, rockfall, and debris flow susceptibility at the scale of 1:25,000. As outlined in the EGU contribution (EGU25-8639, https://doi.org/10.5194/egusphere-egu25-8639) the concept relies on fuzzy logic and linear membership functions, attributing weights to relevant factors for the formation of landslides, rock falls, and debris flows. As a static susceptibility (i.e., not probability) concept, the notion of return periods for events of specific characteristics does not apply.

The three susceptibility models rely on pixel-wise calculated algorithms that draw on different sets of factors: 6 factors for the landslide, 4 factors for the rockfall, and 7 factors for the debris flow susceptibility model.

One of the factors processed for the landslide as well as the rockfall susceptibility model is the interplay of the aspect of the slope and the azimuth to the dip direction of the underlying lithology in a distinct pixel. Named shortly “aspect” and “dip direction”, both angles are measured horizontally; thus, the factor is named horizontal synchronism.

In analogy, also the vertical synchronism should be possible to compute between the slope and the dip in the same pixel; however, this computation seems not as straightforward to implement since the question of the reference plane arises.

In this contribution, we outline the currently implemented horizontal synchronism model between aspect and dip direction and point out its strengths and weaknesses. Moreover, we move from a possible 2D approach for the vertical synchronism model between slope and dip to a possible formulation in 3D.