Slopes instabilities are complex phenomena and constitute a major hazard for human activities. Slope instabilities affect most of the countries overlooking the Mediterranean Sea and often involve challenging geotechnical conditions and complex geo-material characteristics. In this paper we present a combined field-laboratory multidisciplinary test and monitoring program to characterize slope instability phenomena in the town of Gimigliano (Southern Italy). These phenomena involve complex geo-morphological aspects and the interaction of several landslides with different dimensions and characteristics. The study area is located on the east coast of the Calabria region, in Southern Italy, within the narrow Calabrian Arc subduction zone, where sections of the oceanic plate (one of the oldest in the world) have been thrusted and preserved on land. The area is characterized by the so-called Liguride and Calabride complexes and the presence of Mesozoic ophiolitic rocks. During the period 2008-2010, this area was affected by persistent rainfall events which reactivated various landslides causing damage to buildings and infrastructure systems. To characterize this complex slope instability phenomenon a comprehensive site and laboratory test and monitoring program has been performed. We gathered information on: (1) tectonic, geological, and geomorphological background, (2) hydrogeological conditions, (3) evolution over time and space of the activity by monitoring techniques such as multi-epoch Synthetic Aperture Radar (SAR), inclinometer, and structural monitoring, (4) geotechnical characteristics from boring logs and standard laboratory tests, (5) spatial distribution and variation of geologic units via electrical resistivity tomography, (6) geotechnical field monitoring, and (7) advanced laboratory ultrasonic testing on samples retrieved in the unstable area for the determination of P- and S-wave velocities. This comprehensive multidisciplinary characterization allowed us to understand the complexity of this phenomenon, gaining insights into issues pertaining to slope instabilities in similar geologic and tectonic environments in the Calabria region and in the whole Mediterranean area.

Probabilistic seismic hazard analysis (PSHA) are performed for routine applications using source models and ground motion prediction equations (GMPEs) recommended by a government agency (e.g., US Geological Survey) or an expert panel (e.g., SHARE project). For important projects, site-specific PSHA involves critical analysis of GMPEs and sources for the application region. We adopt the latter approach for a dam site in Calabria (southern Italy), a high seismic hazard region. Following SHARE convention, we consider faults sources, background zones, and area sources. We identify several problems with assigned maximum magnitudes in the SHARE model for fault and in-slab subduction sources. We add two sources not present in some prior inventories – the crustal Lakes fault and the Calabrian arc subduction interface. Following procedures developed for the Global Earthquake Model, we select GMPEs that are much better constrained in the hazard-controlling range of magnitudes and distances than those typically used in prior Italian applications. Short-period spectral accelerations at the 2475 year return period exceed those from prior SHARE studies by about 10-15%. Despite the site being located in a region with finite faults capable of generating large events, the 2475-year hazard is dominated by source zones that allow for earthquakes directly beneath the site.

The performance of a large number of critical infrastructure systems needs to be periodically re-evaluated. This is especially so when such systems are located in seismic areas and are subjected to ageing effects. Seismic re-evaluations are typically performed using numerical response history analyses based on a geotechnical model of the infrastructure and using hazard-consistent ground motions. We depart from the Viadotto Italia (the tallest multi-span bridge in Italy, located in a high-seismicity region) to draw best practices on how to construct a robust geotechnical model and derive appropriate target response spectra to be used in forward applications. Our proposed framework starts with the analysis of historical and new information and data. We then describe how to perform a multi-epoch consistency analysis that deals with the reliability and level of uncertainty of the data, culminating with the definition of a pragmatic geotechnical model that builds upon all available data, including investigation information produced at different spatial resolutions and quality levels. We also propose a consistent approach to perform site-specific probabilistic seismic hazard analysis to develop appropriate ground motions. This last step builds upon experiences with a data-rich high-seismicity zone in southern Italy, where both shallow crustal faults and deep subduction sources are present.

The large majority of existing earth dams were designed with old standards, which often accounted for the effects of earthquakes in a simplified manner. As a result, seismic re-evaluation of these structures is now becoming increasingly important for dam owners. The seismic performance of earth dams can be evaluated at different levels of resolution, typically ranging from simple sliding block analysis, to the use of advanced numerical models. Seismic inputs for these models are typically chosen using code-based or site-specific probabilistic seismic hazard analysis (PSHA). In this study, we analyze the seismic vulnerability of two major earth dams located in Southern Italy, a seismically active area. The two dam systems have different geotechnical characteristics: one of them is founded on potentially liquefiable materials, whereas the other one is not susceptible to liquefaction. Our analyses are based on finite difference numerical simulations using both simplified and advanced constitutive models. Seismic vulnerability of both dams is analyzed by means of analytical fragility functions for various damage mechanisms and ground motion intensity measures (IMs). Such fragility functions are based on nonlinear deformation analyses within the multiple stripe analysis framework. We analyze efficiency and predictability of various IMs in predicting different damage levels and mechanisms. We show that the cumulative absolute velocity is overall the optimal IM in predicting vulnerability of both earth dams. We also analyze the relative importance of PSHA inputs (i.e. alternative ground motion and earthquake rupture forecast models; GMMs and ERFMs, respectively) and numerical models (simplified vs advanced) in the seismic analysis of earth dams by means of tornado diagrams. We show that the choice of GMMs and ERFMs is always more important than that of the constitutive model. However, for dams prone to liquefaction, the choice of the constitutive model has a higher importance than for non-liquefiable earth dams.

Frequency-dependent horizontal-to-vertical spectral ratios (HVSR) can provide information on site resonant frequencies, which are potentially useful for predicting site amplification. We adapt a relational database developed to archive and disseminate VS data to include HVSR and investigate the consistency of HVSR derived from different measurements of ambient noise (temporary instruments, permanent instruments) and earthquake recordings. The database as a whole consists of 2,797 sites in California. HVSR consistency is analyzed using subsets of sites with multiple data sources; noise and seismic data are consistent for 60% of sites, whereas different noise measurements have about 75% consistency.