Assessment of relative active tectonics, southwest border of the Sierra Nevada (southern Spain)

Abstract We present a new method for evaluating relative active tectonics based on geomorphic indices useful in evaluating morphology and topography. Indices used include: stream length-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), index of drainage basin shape (Bs), and index of mountain front sinuosity (Smf). Results from the analysis are accumulated and expressed as an index of relative active tectonics (Iat), which we divide into four classes from relatively low to highest tectonic activity. The study area along the southwest border of the Sierra Nevada in southern Spain is an ideal location to test the concept of an index to predict relative tectonic activity on a basis of area rather than a single valley or mountain front. The study area has variable rates of active tectonics resulting from the collision of Africa with Europe that has produced linear east–west anticlinal forms, as well as extension with variable vertical rates of normal faulting to about 0.5 m/ky. We test the hypothesis that areas of known, relatively high rates of active tectonics are associated with indicatives values of Iat.