[en] Earthquakes are one of the geological hazards which have produced more human and material loses in the history of manking. Seismic engineering has the purpose of studying the soil dynamic behavior in order to desing structures and buildings adapted to the effects triggered by earthquakes. Within this purpose, one of the most important tasks has been the sutdy of the amplifying effect of seismic movement due to ground characteristics, which is often a major cause responsible of the damage produced by earthquakes, even when their magnitude is not very high. In this article, the soil amplifying effects is considered according to two official sismorresistant regulations in Spain: the current Norma de Construccion Sismorresistente Espanola (NCSE-02) and the European regulation Eurocode 8 (EC-8). First, soils classification different criteria is analyzed and how this affects the soil factor and, particularly, the design seismic action in the form of response spectra. Subsequently, we compared the result of apllying both regulations to typical geological scenarios where the application of either regulation may cause notable differences. The second part of the paper deals with the comparison of NCSE-02 and EC-8 applied in the frame of a real case: the 11^th May, 2011 Lorca earthquake. We compare the response spectra from both regulations to the actual response spectra derived from the accelerometric record of the earthquake at the Lorca station, and discuss which one fits it better. (Author)