Abstract
Abstract. This study explores the role of seismic activity in explaining spatial and temporal variation in sediment export from the Siret basin in Romania. Based on long-term (>30 years) sediment export measurements for 38 subcatchments, we found that spatial variation in sediment yield (SY) is strongly correlated to the degree of seismic activity and catchment lithology. Combined, these factors explain 80% of the variation in SY. To investigate the role of earthquake-triggered landslides in explaining these correlations, we studied the temporal variability in sediment concentrations before and after the 7.4 Mw earthquake of 1977 for ten subcatchments. Despite the fact that this earthquake triggered many landslides, only one subcatchment showed a clear (3-fold) increase in sediment concentration per unit discharge after the earthquake. This shows that, although prolonged seismic activity strongly controls average SY, individual earthquakes do not necessarily affect sediment export at short timescales.
Highlights
A growing number of studies show that spatial variation in both erosion rates and contemporary catchment sediment yields (SY, t km-2 year-1) are often strongly correlated with seismicity, even in regions with a relatively limited degree of seismic activity and after correcting for autocorrelations with topography and other factors (Dadson et al, 2004; Vanmaercke et al, 2014)
Our correlation analyses showed that average SY was strongly correlated with seismic activity (PGA) and catchment lithology (L; an area-weighted scoring factor calculated according to a method proposed by Syvitski and Milliman, 2007)
This study demonstrated that differences in average annual catchment sediment yield (SY) in the Siret basin (Fig. 1) are mainly explained by the overall degree of seismic activity and the catchment lithology (Fig. 2)
Summary
A growing number of studies show that spatial variation in both erosion rates and contemporary catchment sediment yields (SY, t km-2 year-1) are often strongly correlated with seismicity, even in regions with a relatively limited degree of seismic activity and after correcting for autocorrelations with topography and other factors (Dadson et al, 2004; Vanmaercke et al, 2014). Hovius et al (2011) explored the effects of the 7.6 Mw Chi-Chi earthquake in Taiwan on the sediment export by rivers near the epicentre. They stated that, due to co-seismic landsliding, sediment export in the months after the earthquake peaked to more than five times the background rate and returned progressively to pre-earthquake levels in about six years (Hovius et al, 2011). Huang and Montgomery (2012) noted no such clear increase in other catchments affected by the earthquake They argued that it is very difficult to unambiguously relate these increases in sediment export to earthquake-triggered landslides as the occurrence of typhoons may provide a plausible explanation (Huang and Montgomery, 2012). Studies focusing on regions other than the exceptionally seismically active, steep and typhoon-affected Taiwan are currently lacking
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