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This study deals with the impact of deep-soil discontinuities on ground-motion amplification in the Po alluvial basin (northern Italy), and consequently, on long-period probabilistic seismic-hazard analysis estimates. The focus is on Castelleone, where a seismic station of the Italian National Seismic Network has been deployed since 2009. To define a detailed shear-wave velocity (VS) profile, extensive active and passive geophysical surveys were carried out. The active measurements included seismic profiles examined through standard refraction techniques and multichannel analysis of surface waves. The passive methods included ambient vibration measurements in both single and array configurations. In particular, three microtremor arrays with increasing apertures were performed to capture the experimental dispersion curve down to 0.2 Hz. The horizontal-to-vertical spectral ratio (HVSR) showed two main peaks, at 0.17 and 0.70 Hz. A joint inversion of the experimental phase-velocity dispersion and HVSR curves was performed to obtain the VS profile. The data show two main discontinuities at ~160 and 1350 m in depth. According to the Italian and European seismic codes, the shallow VS discontinuity can be ascribed to the seismic bedrock (i.e., VS>800 m/s), whereas the deeper one is observed at the transition between Pliocene-Quaternary deposits and Miocene marls. Preliminary site-specific seismic-hazard analysis in terms of displacement response spectra for periods up to 10 s shows that neglecting the effects of the deeper discontinuity implies underestimation in hazard estimates of up to about 49% for mean return period (MRP) of 475 years and about 57% for MRP of 2475 years, with possible consequences regarding the design of very tall buildings and large bridges. [ABSTRACT FROM AUTHOR]

In August 2016, a magnitude 6.0 earthquake struck Central Italy, starting a devastating seismic sequence, aggravated by other two events of magnitude 5.9 and 6.5, respectively. After the first mainshock, four Italian institutions installed a dense temporary network of 50 seismic stations in an area of 260 km 2 . The network was registered in the International Federation of Digital Seismograph Networks with the code 3A and quoted with a Digital Object Identifier ( https://doi.org/10.13127/SD/ku7Xm12Yy9 ). Raw data were converted into the standard binary miniSEED format, and organized in a structured archive. Then, data quality and completeness were checked, and all the relevant information was used for creating the metadata volumes. Finally, the 99 Gb of continuous seismic data and metadata were uploaded into the INGV node of the European Integrated Data Archive repository. Their use was regulated by a Memorandum of Understanding between the institutions. After an embargo period, the data are now available for many different seismological studies.

Since the beginning of the 1980s, when Mandelbrot observed that earthquakes occur on 'fractal' self-similar sets, many studies have investigated the dynamical mechanisms that lead to self-similarities in the earthquake process. Interpreting seismicity as a self-similar process is undoubtedly convenient to bypass the physical complexities related to the actual process. Self-similar processes are indeed invariant under suitable scaling of space and time. In this study, we show that long-range dependence is an inherent feature of the seismic process, and is universal. Examination of series of cumulative seismic moment both in Italy and worldwide through Hurst's rescaled range analysis shows that seismicity is a memory process with a Hurst exponent H ≈ 0.87. We observe that H is substantially space- and time-invariant, except in cases of catalog incompleteness. This has implications for earthquake forecasting. Hence, we have developed a probability model for earthquake occurrence that allows for long-range dependence in the seismic process. Unlike the Poisson model, dependent events are allowed. This model can be easily transferred to other disciplines that deal with self-similar processes.