New procedure for deriving multifrequential dynamic equivalent signals (LEMA_DES): a test-study based on Italian accelerometric records

The here proposed LEMA_DES (Levelled-Energy Multifrequential Analysis for Dynamic Equivalent Signals) procedure is a new approach for defining multifrequential dynamic equivalent signals from real accelerograms, to be applied for physic-analogue and numerical geotechnical modelling of induced seismic effects. In this approach, the resulting equivalent signals satisfy criteria of spectral, energetic and kinematic equivalence to the related real prototypes. The approach was tested to analyse the accelerometric records of the November 23rd, 1980 Irpinia (Italy) earthquake. Based on 48 selected records, correlations were studied between the characteristic parameters of both real and equivalent signals. These correlations demonstrate that the proposed approach guarantees: i) the energy equivalence of the derived signals, except for a half order of magnitude, and ii) the equivalence of the peak ground acceleration (PGA) values with relative errors below 105%. The computed relative error on the cumulative energy of the LEMA_DES signals (Delta r V (eq) %), which have spectral amplitudes at frequencies lower than 1 Hz, drops below 30%, while the same error increases above 2500%, in the same frequency range, for sinusoidal signals obtained according to traditional approaches. The PGAs of the LEMA_DES signals show a good fit with the PGA attenuation law proposed for the central-southern Apennines. Correlations between the Arias intensities and PGAs of the equivalent signals with respect to the actual ones demonstrate that their characteristic parameters: i) well represent the spatial variation in terms of energy and ground motion; ii) reproduce an analogue earthquake scenario with respect to the reference seismic event.