Abstract
Near fault seismic records may contain impulsive motions in velocity-time history. The seismic records can be identified as impulsive and non-impulsive depending on the features that their waveforms have. These motions can be an indicator of directivity or fling step effect, and they may cause dangerous effects on structures; for this reason, there is increasing attention on this subject in the last years. In this study, we collect the major earthquakes in Italy, with a magnitude large or equal to Mw 5.0, and identify the impulsive motions recorded by seismic stations. We correlate impulsive motions with directivity and fling step effects. We find that most earthquakes produced impulsive signals due to the directivity effect, though those at close stations to the 30 October 2016 Amatrice earthquake might be generated by the fling step effect. Starting from the analyzed impulses, we discuss on the potential influence of site effects on impulsive signals and suggest a characterization based on the main displacement directions of the impulsive horizontal displacements. Finally, we discuss on the damage of three churches in Emilia, which were subject to impulsive ground motion, underlying in a qualitative way, how the characteristics of the pulses may have had influences the structural response of the façades.
Highlights
IntroductionUsually near neighboring regions of the ruptured fault
Impulsive ground motions occur, usually near neighboring regions of the ruptured fault
We provide the impulsive signals determined by the algorithms explained in the Method Section, where 15093 waveforms with fault normal, fault parallel, and vertical orientation are analyzed in terms of their impulsiveness
Summary
Usually near neighboring regions of the ruptured fault. When the rupture propagates to the direction of the site-of-interest with a propagation velocity close to the shear wave velocity of the medium, rupture front contains all seismic energy [1]. Another driving force of the production of an impulsive motion is the permanent displacement of the ground, known as the fling step effect [2]. Fling step effect can be visible on displacementtime history It can be seen in strike parallel and strike normal components for strike slip and dip-slip earthquakes, respectively [3]. Forward directivity would create velocity pulses with half-cycle(s) (due to Gaussian-like displacement of the ground), whereas fling step effect create Gaussian-like velocity pulse (due to the permanent shift of the ground), and these effects can be seen in both strike normal and strike parallel components [4]
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