Microseismicity and tectonics in the Granada Basin (Spain)

Abstract

A microseismic experiment carried out in 1994 in the Granada Basin (Spain) permitted the precise recording of more than 80 local earthquakes. The dense distribution of the local network, with 40 to 50 instrumental records for each event, enabled us to have well-controlled hypocenters, and also 10 reliable focal mechanisms. The above observations are interpreted together with topographic data, neotectonics, and sub-surface information. Microtectonic observations in Sierra Elvira, Padul and Zafarraya gave a set of fault planes and striae, which were interpreted in terms of the recent regional stress tensor. The actual stress tensor obtained from the microseismic campaign data gives a regime in radial extension, with σ1 vertical and σ3 oriented NS to NNE. Microtectonic information is coherent with these orientations, but closer to 3-axial extension. A set of 64 mechanisms obtained from the permanent Andalusian network favors a NS orientation for σ3. This results are interpreted in terms of the general model implying the lateral ejection of the Betic ranges towards the Atlantic.