DETECTING AND MODELING ACTIVE STRUCTURES IN NORTHERN CALABRIA: NEW INSIGHTS FROM DRAINAGE NETWORK MORPHOMETRIC ANALYSIS.

Abstract

ABSTRACT: Santoro E. et al., Detecting and modeling active structures in northern Calabria: new insights from drainage network morphometric analysis.(IT ISSN 0394-3356, 2011). A detailed morphometric analysis of the drainage network on the eastern side of the Pollino mountain range (Northeastern Calabria) was performed in order to gain new insights on the active tectonic frame, the landscape evolution state and the response time of the hydrographic network to the tectonic deformations. The uniform coastal lithology and climate allow us to isolate the tectonic signal from the fluvial morphometric analysis. Previous work, based on detailed mapping and lateral correlation of ten marine terrace orders (Middle Pleistocene – Holocene) between the Pollino range and the southern border of the San Nicola plain (Basilicata), and on analysis of structural, geodetic, geophysical and seismic data, allowed to hypothesize the active uplift of two fault-propagation folds, along the Pollino and the Valsinni ridges, linked to the high-angle transpressive shear zones that affected the region since the Early Pleistocene.  The quantitative analysis of the longitudinal profiles was performed in order to test and improve the above mentioned deformation model. Linear regressions of the logarithms of channel gradient and drainage area data was used to find convexities (knickpoints) and to determine the concavity index (θ) and the steepness index (ks). Based on the θ and ks values the river paleo-longitudinal profiles were reconstructed in order to correlate each knickpoint with a marine terrace and the following glacial eustatic regression. The river vertical incision rates and the along coast variation of the knickpoints elevation linked to the same glacial eustatic regression are in perfect agreement with the deformation model. The rivers that flow through the uplifting Pollino and Valsinni anticlines are characterized by an increase of the: 1. longitudinal gradient; 2. vertical incision rate; 3. knickpoints elevation. They react to the higher uplift rates increasing their steepness in order to gain sufficient energy to incise the river-bed and to reestablish the previous equilibrium state. The hydrographic network response time (~105 year; that is the time for the knickpoint migration through the entire basin) shows that the tectonic morphometric anomalies are linked to active landscape deformation processes. Finally, the drainage network morphometric analysis has confirmed the deformation model derived from the paleo-shoreline profiles and from structural-geophysical data, suggesting that the analyzed sector of the Southern Apennine is still affected by a transpressional tectonic regime.