The role of local geology in controlling ground motion has long been acknowledged. Consequently, increasing attention is paid to the assessment of the geophysical properties of the soils at the seismic stations, which impact the station recordings and a series of related quantities, particularly those referring to seismic hazard estimates. Not the same level of attention is commonly dedicated to the seismic station installation, to the point that it is generally believed that housings and shelters containing seismic instruments are of no interest, because they can only affect frequencies well above the engineering range of interest. Using examples from seismometric and accelerometric stations, we describe the (1) housing, (2) foundation, and (3) pillar effects on the seismic records. We propose a simple working scheme to identify the existence of potential installation‐related issues and to assess the frequency fidelity range of response of a seismic station to ground motion. Our scheme is developed mostly on ambient noise recordings and, thus, surface waves. The hope is that, besides the parameters that start to be routinely introduced in the seismic archives (⁠ $VS30$⁠, soil classes, etc.), the assessment of the maximum reliable frequency, under which no soil–structure interaction is expected, also becomes a mandatory information. In our experience, for some installation sites, the maximum reliable frequency can even be less than a very few hertz.

In the last few years, interest in the offshore Chilean margin has increased rapidly due to the presence of gas hydrates. We have modelled the gas hydrate stability zone off Chilean shores (from 33° S to 46° S) using a steady state approach to evaluate the effects of climate change on gas hydrate stability. Present day conditions were modelled using published literature and compared with available measurements. Then, we simulated the effects of climate change on gas hydrate stability in 50 and 100 years on the basis of Intergovernmental Panel on Climate Change and National Aeronautics and Space Administration forecasts. An increase in temperature might cause the dissociation of gas hydrate that could strongly affect gas hydrate stability. Moreover, we found that the high seismicity of this area could have a strong effect on gas hydrate stability. Clearly, the Chilean margin should be considered as a natural laboratory for understanding the relationship between gas hydrate systems and complex natural phenomena, such as climate change, slope stability and earthquakes.

The CAGE22-6 cruise on-board R/V Helmer Hanssen hosted UiT´s Arctic Marine Geology and Geophysics (GEO-8144 and GEO-3144) field course for PhD and Master students, and was carried out in collaboration with NPD – the Norwegian Petroleum Directorate and the INTPART project HOTMUD based at Centre for Earth Evolution and Dynamics (CEED) the University of Oslo. The cruise was also a part of the UNESCO Training Through Research program (formerly, The Floating University) and in the framework of this project is also coded as TTR22. The main scientific objectives of the cruise were to investigate: geological controls on fluid-flow dynamics on an uplifted, repeatedly glaciated, and eroded Northern Norwegian Barents Sea shelf and, the fate of the released hydrocarbons in the water column, on the sea surface, and in the atmosphere. The cruise may be known as: CAGE22_6

At the early stages of seismology, seismic stations were installed directly on rock to minimize the effects of the fine sediments/weathering on the recorded seismic waves. The bulky size of permanent installation seismometers, their need for external batteries, cables and levelling, led to place seismic stations on artificial ground, such as ad hoc concrete platforms. In addition, to ensure protection from environmental conditions, vandalism and to facilitate maintenance, many seismic stations were placed inside structures. A common installation in Italy, as an example, is at the base of the (5-8 m tall) towers of the electrical national service.The presence of a structure around the instrument perturbs the recorded motion. This phenomenon, generally referred to as soil-structure interaction, can be summarized into three main effects. The first one is the transmission of the structure own motion to the surrounding ground. When seismic waves hit a building, the building enters forced oscillation and this vibration is re-transmitted to the ground. Sensors placed inside the building record, therefore, a composite signal, made of seismic waves and the response of the structure to them. This affects the sensors also when they are isolated from the building foundations by means of cuts around the sensor pillars, because the ground under the pillar and the ground under the structure is the same and is continuous. The second effect lays in the fact that a foundation, typically made of reinforced concrete, acts as a layer with seismic impedance much higher than any natural soil. Seismic waves travelling upwards will be reflected downwards as they hit the foundation. On one side they shake the structure (effect 1), but on the other only a small fraction of them crosses the foundation (effect 2) and can be recorded by the instruments installed on the foundation. The same applies to the concrete pillars where seismic sensors are installed. These installations violate the basic principle of any physical measurements according to which when an interface is needed between the instrument and the object of measurement (the ground) then the interface must have an impedance as close as possible to the object of measurement, in order to minimize the perturbation of the wavefield. Clearly concrete platforms/pillars do not have this property, unless when installed on very stiff rocks. The third main effect (effect 3) concerns the back reflection of the surface waves reaching the foundation. Similarly to effect 2, when surface waves strike an extended rigid layer, such as the foundations of a building, they are mainly reflected back along the Earth's surface. This implies that, in seismic tremor recordings (or seismic events) carried out inside a structure, a fraction of surface waves will be missing.In this work we show these effects in a number of real cases and we show the consequences that this can have in the assessment of seismic site effects, of PGA, and on the computation of attenuation laws.

Although fault-based approaches to seismic hazard assessment have been increasingly adopted worldwide, the official Italian hazard model, on which the national building code is based, still relies on a catalogue-based framework, with well-known limitations in capturing the long-term recurrences of large-magnitude events. In this study, we present a fault-based application to model seismicity rates for the southern Apennines (Italy) that incorporates a multi-fault rupture assumption. This area is of particular interest due to its active seismicity and the presence of large dams, for which robust long-term hazard estimates are essential. We use the SHERIFS code to model seismicity rates at the fault system-level, which allow us to explore epistemic uncertainties of fault and seismicity parameters (rupture scenarios, scaling laws, b-values and background seismicity). Our results highlight the key role of rupture models: scenarios allowing multi-fault ruptures outperform single-fault rupture models in terms of agreement with the regional seismicity and paleoseismic rates. Our findings support the inclusion of multi-fault rupture models in PSHA logic trees for the region and emphasize the need for improved fault behaviour characterization in southern Italy.

Although fault-based approaches to seismic hazard assessment have been increasingly adopted worldwide, the official Italian hazard model, on which the national building code is based, still relies on a catalogue-based framework, with well-known limitations in capturing the long-term recurrences of large-magnitude events. In this study, we present a fault-based application to model seismicity rates for the southern Apennines (Italy) that incorporates a multi-fault rupture assumption. This area is of particular interest due to its active seismicity and the presence of large dams, for which robust long-term hazard estimates are essential. We use the SHERIFS code to model seismicity rates at the fault system-level, which allow us to explore epistemic uncertainties of fault and seismicity parameters (rupture scenarios, scaling laws, b-values and background seismicity). Our results highlight the key role of rupture models: scenarios allowing multi-fault ruptures outperform single-fault rupture models in terms of agreement with the regional seismicity and paleoseismic rates. Our findings support the inclusion of multi-fault rupture models in PSHA logic trees for the region and emphasize the need for improved fault behaviour characterization in southern Italy.