Impulsive Signals Produced by Earthquakes in Italy and Their Potential Relation with Site Effects and Structural Damage

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.

Seismic Precursors in Central Italy using Autocorrelation Measurements

<p><span>The aim of this study is to identify precursors related to fluid pressure changes at depth to large earthquakes that occured in central Italy such as the 2009 Mw6.3 L'Aquila and the 2016 Mw6.2 Amatrice earthquake. To that end, we monitor the temporal evolution of the crust using a new method called Coherence of Correlated Waveforms [CCW] that uses seismic noise autocorrelation measurements. This allow us to look for changes in the medium with a high temporal resolution of 5 days. Our measurements of the CCW show that the L'Aquila Earthquake (2009-M6.3) is preceded by a 150-day oscillation whose amplitude and frequency progressively increases until the rupture. The high Vp/Vs ratios measured on the foreshocks of L’Aquila earthquake correspond to the CCW drop periods, suggesting the sensitivity of the measurement to crusty fluids. </span></p><p><span>Analysing 17 years of data, we found that this signal occurred only before the L'Aquila and the Amatrice earthquakes. This suggests the existence of a unique nucleation process. </span></p><p><span>Finally, for the 2016 Amatrice Earthquake, using an array of 25 seismic stations we are able to map the geographical extension of this precursory signal. This pattern, evolving over time, suggests diffusion phenomena in the upper crust.</span></p><p align="left"> </p>

Sonic and Impact Test for Structural Assessment of Historical Masonry

Diagnostics is a very important tool of knowledge in the field of historical buildings. In particular, non-destructive techniques allow to deepen the study of the mechanical characteristics of the historical walls without compromising the artistic value of the monumental building. A case study of the use of sonic and impact tests was described, performed using the same instrumented hammer, for the characterization of the masonry walls at the Sanctuary of Santa Maria delle Grazie at Varoni, one of the churches damaged in the 2016 Amatrice earthquake. Sonic tests showed the presence of a discontinous masonry texture, as well as confirming the ineffectiveness of the strengthening work made by injections of lime mortar. The impact test allowed us to obtain the elastic modulus of the omogeneous stones of the masonry. The results obtained from the non-destructive techniques were confirmed by the flat jacks test carried out on the building, confirming the great potential of the non-destructive diagnostics suitable for analyzing important structural parameters without affecting the preservation of historical masonry structures.

Characteristics of the Strong Ground Motion from the 24th August 2016 Amatrice Earthquake

<em>The 2016 August 24 Amatrice earthquake occurred at 03:36 local time in Central Apennines Italy with an epicentre at 43.36^°E, 38.76^°N, Istituto Nazionale di Geofisica e Vulcanologia (INGV), few kilometers north of the city of Amatrice. The earthquake ruptured a North-West (NW)–South-East (SE) oriented normal fault dipping toward the South-West (SW) (Scognamiglio et al., 2016). High values of peak ground acceleration (~0.45 g) were observed close to Amatrice (3 stations being few kilometer distances from the fault). The present study presents an overview of the main features of the seismic ground shaking during the Amatrice earthquake. We analyze the ground motion characteristics of the main shock in terms of peak ground acceleration (PGA), peak ground velocity (PGV) and spectral accelerations (SA, 5 per cent of critical damping). In order to understand the characteristics of the ground motions induced by Amatrice earthquake, we also study the source-related effects relative to the fault rupture directivity.</em>