Elastic and inelastic systems under near-fault seismic shaking: acceleration records versus optimally-fitted wavelets

Four idealised dynamic systems, which are used as analogues in earthquake and geotechnical engineering, are studied: an elastic single-degree-of-freedom (sdof) oscillator; an elastic–perfectly-plastic sdof oscillator; a rigid block resting in simple frictional contact on a horizontal base; and a rigid block resting on a sloping plane. They are subjected to several near-fault-recorded ground motions bearing the effects of ‘forward-rupture directivity’ and fault surface dislocation (‘fling-step’) phenomena—long-period acceleration pulses and large velocity or displacement steps. Two types of idealized wavelets (the Mavroeidis & Papageorgiou and the Ricker wavelets) are optimally-fitted to each record, applying the matching procedure presented by Vassiliou and Makris (Bull Seismol Soc Am 101(2):596–618, 2011 ). Extensive comparisons between the accelerogram response and the corresponding-fitted wavelets response show if and when the destructive pulse-like part of the records is indeed their most deleterious component, and if and when this destructiveness can be captured with the particular fitted wavelets. For the two purely inelastic systems, in particular, the comparison elucidates the role of the contained pulses in the size of sliding displacements. The results reveal that while the response of elastic and elasto-plastic sdof systems to the wavelets is usually reasonably similar with the response to the actual records, this is not usually the case for the two purely inelastic (sliding) systems. The unpredictable consequences of seismic shaking on such systems, even if the shaking intensity and frequency content were precisely known, is best demonstrated with the sensitivity of the size of sliding displacement to the polarity (+ or - ), the sequence and number of cycles, and even the details of the excitation.