DETERMINATION OF PRESENT-DAY STRESS TENSOR AND NEOTECTONIC INTERVAL IN THE SPANISH CENTRAL SYSTEM AND MADRID BASIN, CENTRAL SPAIN

A brittle deformation tectonic analysis was performed in central Spain (Spanish Central System and Madrid Basin) in order to decipher and un derstand the deformation processes that take place in a typical intrac ontinental zone. 1174 fault slickensides obtained in materials with ag es between Late Cretaceous and Quaternary have been analyzed by means of fault population analysis methods to reconstruct paleostress tensor s. Nine earthquake focal mechanisms have been determined, with magnitu des ranging between 3 and 4.1. With regard to regional structural feat ures and sedimentary record data, the characteristics of present-day a nd neotectonic stress fields have been figured out, which determine th e neotectonic period for this region. Thus, we have established that t he intraplate zone represented by central Spain has been subjected to a stress held from the Middle Miocene until the present-day with a lar gest horizontal shortening direction (S-HMAX) located between N130E an d N160E. Finally, three paleostress maps with the main active structur es are presented for: (a) Middle Miocene to Late Miocene, the period w hen the Spanish Central System was mainly formed, (b) Late Miocene to Quaternary, and (c) the present-day stress held, deduced from earthqua ke focal mechanisms.