The present study analyses the spatial pattern of quaternary gravitational
slope deformations (GSD) and historical/present-day instabilities
(HPI) inventoried in the Swiss Rhone Valley. The main objective is
to test if these events are clustered (spatial attraction) or randomly
distributed (spatial independency). Moreover, analogies with the
cluster behaviour of earthquakes inventoried in the same area were
examined. The Ripley's K-function was applied to measure and test
for randomness. This indicator allows describing the spatial pattern
of a point process at increasing distance values. To account for
the non-constant intensity of the geological phenomena, a modification
of the K-function for inhomogeneous point processes was adopted.
The specific goal is to explore the spatial attraction (i.e. cluster
behaviour) among landslide events and between gravitational slope
deformations and earthquakes. To discover if the two classes of instabilities
(GSD and HPI) are spatially independently distributed, the cross
K-function was computed. The results show that all the geological
events under study are spatially clustered at a well-defined distance
range. GSD and HPI show a similar pattern distribution with clusters
in the range 0.75?9 km. The cross K-function reveals an attraction
between the two classes of instabilities in the range 0?4 km confirming
that HPI are more prone to occur within large-scale slope deformations.
The K-function computed for GSD and earthquakes indicates that both
present a cluster tendency in the range 0?10 km, suggesting that
earthquakes could represent a potential predisposing factor which
could influence the GSD distribution.