Comparative Study of SPAC and MASW Methods to Obtain the Vs30 for Seismic Site Effect Evaluation in Lorca town, SE Spain

The determination of seismic hazard oriented to seismic risk management in urban areas requires an investigation over the possibility of resonance in the dynamic behaviour of buildings and soils against natural earthquakes. Recently, two earthquakes hit the Lorca town (SE Spain) with the result of severe buildings damages. At the present, several research teams are acting in the Lorca town to determine relationships between seismic-tectonics, geology, building structure typology, etc. to the building damage degree which took place. Among the different studies which are being carried out the Spatial Autocorrelation method (SPAC) and the Multichannel Analysis Surface Waves method (MASW) are having a predominant role. In fact, it has been found that the main damage areas are on material (unconsolidated sedimentary filling) with very low average shear-wave velocity in the first 30 m depth (Vs30), as low as 180 m/s. On the other hand, medium hard rock (conglomerates, marls, gypsum and sandstones) had Vs30 from 660 to 800 m/s where building damages were not significant.