Exploring the effects of seismicity on landslides and catchment sediment yield: An Italian case study

Recent studies showed that contemporary average catchment sediment yields (SY, [t km- 2 y- 1]) at regional and continental scales are often strongly correlated to spatial patterns of seismic activity. Nonetheless, we currently have little insights into the mechanisms that explain these correlations. We investigated how spatial patterns of SY in Italy are linked to patterns of seismic activity. For a dataset of 103 Italian catchments with average SY measured over a period of years to decades, we extracted tectonic and none-tectonic variables that potentially explain observed differences in SY. These include proxies for vertical uplift rates and cumulative seismic moments (CSM) associated with historic earthquakes of different ranges of magnitude. Results showed that also across Italy, SY is significantly correlated to seismicity. However, SY showed much stronger correlations with proxies of seismicity relating to small but frequent earthquakes (2 <= Mw b 4) than with proxies relating to tectonic uplift or large, potentially landslide-triggering earthquakes (Mw >= 4). Analyses of a dataset of about 500,000 landslides across Italy showed very comparable trends: spatial patterns of landslides within similar lithological units gener- ally show a significant positive correlation with CSM of weak but frequent seismicity and generally not with CSM of large earthquakes. These results suggest that, on a decadal time scale and at a regional/continental spatial scale, frequent but relatively weak seismicity may exert a more important geomorphic impact than large earthquake events or tectonic uplift.