PSI - Issue 44

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Alberto Castellani et al. / Procedia Structural Integrity 44 (2023) 19–26 Author name / Structural Integrity Procedia 00 (2022) 000–000

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2. BSSA and other statistics In front of the number of theoretical and numerical approaches that have been proposed, rotational ground motions have not been observed directly until the two last decades due to the lack of appropriate instruments. Later, the direct measurement of point rotations has been attempted through “ad hoc” designed devices, as tilt-meter, ring lasers and broadband rotation meters. However, such devices are not in common use, and suitable applications in earthquake engineering have been rare, and an open-challenging task. Valid progress in the knowledge of the spatial distribution has been achieved through statistical studies, Paolucci et Al (2009). A state-of-the-art of the different facets of rotational seismology, concerning theoretical investigations, instrumentation, analysis of ground motion observations, and engineering applications is provided by Lee et Al., (2009), and by Todorovska et Al (2008).

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PRV / PGA (mrad s/m)

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epicenter distance (km)

Fig. 1. Elaboration of data presented by Liu et Al (2009). Ratio between the peak rotation velocity PRV and the peak horizontal acceleration PGA, in mrad  s/m. Average value 1.43. The same ratio, fig. 2, computed according to DAIs cross spectra of accelerations, (2017), is in good agreement with the average value of these data.

Fig. 2. Same data reported in Fig.1 plus, the red circle, results collected at the central station C00, (identified in fig. 3.). Seismic event identification: origin time 1981 1.29, 04:51:36, magnitude 6.9. Max acceleration, cm/s 2 , V 64.5 EW 158 NS 244. Epicentre distance to the centre of the array of instrument 30 km