Capuano, Paolo

Ground shaking, whether it is due to natural or induced earthquakes, has always been a matter of concern since it correlates with structural/non-structural damage and can culminate in human anxiety. Industrial activities such as water injection, gas sequestration and waste fluid disposals, promote induced seismicity and consequent ground shaking that can hinder ongoing activities. Therefore, keeping in mind the importance of timely evaluation of a seismic hazard and its mitigation for societal benefits, the present study proposes specifically designed ground-motion prediction equations (GMPEs) from induced earthquakes in the St. Gallen geothermal area, Switzerland. The data analysed in this study consist of 343 earthquakes with magnitude −1.17 ≤ ML, corr ≤ 3.5 and hypocentral distance between 4 and 15 km. The proposed study is one of the first to incorporate ground motions from negative magnitude earthquakes for the development of GMPEs. The GMPEs are inferred with a two-phase approach. In the first phase, a reference model is obtained by considering the effect of source and medium properties on the ground motion. In the second phase the final model is obtained by including a site/station effect. The comparison between the GMPEs obtained in the present study with GMPEs developed for the other induced seismicity environments highlights a mismatch that is ascribed to differences in regional seismic environment and local site conditions of the respective regions. This suggests that, when dealing with induced earthquakes, GMPEs specific for the study should be inferred and used for both monitoring purposes and seismic hazard analyses.

Sub surface operations for energy production such as gas storage, fluid injection or hydraulic fracking modify the physical properties of the crust, in particular seismic velocity and anelastic attenuation. Continuously measuring these properties may be crucial to monitor the status of the reservoir. Here we propose a not usual use of the empirical ground-motion prediction equations (GMPEs) to monitor large-scale medium properties variations in a reservoir during fluid injection experiments. In practice, peak-ground velocities recorded during field operations are used to update the coefficients of a reference GMPE whose variation can be physically interpreted in terms of anelastic attenuation and seismic velocity. We apply the technique to earthquakes recorded at The Geysers geothermal field in Southern California and events occurred in the St. Gallen (Switzerland) geothermal field. Our results suggest that the GMPEs can be effectively used as a proxy for some reservoir properties variation by using induced earthquakes recorded at relatively dense networks.

After some centuries of subsidence, following the AD 1538 Monte Nuovo last eruption, the Campi Flegrei caldera has shown unrest episodes since at least 1950. The first uplift episode dates back to 1950–1952 and amounted to 73 cm, without any report or record of seismic activity. Two strong infla- tion episodes occurred in 1970–1972 and 1982–1984. The first accompanied by moder- ate low seismicity, with only few events felt by the population, whereas the second was accompanied by relatively intense swarms of volcano-tectonic earthquakes, reaching up to magnitude 4. The seismic activity caused alarm in the population and a spontaneous nightly evacuation of part of the town of Pozzuoli (44,000 inhabitants). Since this last episode, subsidence has been recorded for several years, interrupted by some mini-uplift events, lasting several weeks and accompa- nied by seismic swarms of low-magnitude volcano-tectonic events. In recent years, high sensitivity instruments have been installed to detect slow earthquake transients and other mechanical/temperature low-intensity precur- sory signals. Since late 2004 another moderate uplift is occurring at very small rate, amount- ing to about 1–2 cm/year, accompanied by long-period events. This uplift is different from the past mini-uplift events due to its duration. This work summarises all seismic and ground deformation data as well as the models proposed to interpret these phenom- ena, suggesting possible methods for detecting precursors of future eruptive activity in the area.

We present a detailed seismic imaging of the harnessed Nesjavellir geothermal area, SW-Iceland, which is one of several geothermal fields on the flanks of the Hengill volcano. We map the vP , vS , and vPvS ratio using seismic data recorded in 2016–2020 and compare them with both a resistivity model of the same area and the rock temperature as measured in boreholes. The results show that the shallower crust (depth less than 1 km) is characterized by low vP and vS , and high vPvS ratio (around 1.9). Shallow low resistivity values at similar depths in the same area have been interpreted as the smectite clay cap of the system. At depths between 1 and 3 km the observed low vPvS ratio of 1.64–1.70 correlates with high resistivity values. In this area, characterized by temperatures larger than 240°C, the seismicity appears to be sparse and located close to the production wells. This seismicity has been interpreted as induced by the production in combination with naturally occurring earthquakes. At depths greater than 4 km, high vPvS ratio of 1.9 correlates well with low resistivity values. In the valley of Nesjavellir, a deep-seated conductive body, domes up at about 4.500 m b.sl. and coincides spatially with a significant high vPvS ratio anomaly (>1.9). Above these anomalies an elevated temperature is registered according to borehole temperature data. This is proposed here to be caused by hot 600°C–900°C cooling intrusives, close to the brittle ductile transition—probably the heat source(s) of the geothermal field above. These anomalies are at the same location as the last fissure eruption in Hengill almost 2,000 years ago. The NNE-SSW trending, deeper seismic cluster at 3–6 km depth is located at the edge of this high vPvS anomaly. The heat source of the Nesjavellir geothermal field is most likely connected to this most recent volcanism as reflected by the deep-seated low resistivity body and high vPvS ratio, located beneath the deep fault that connects the flow path of the high temperature geothermal fluid, resulting in an actively producing reservoir.

A tomographic analysis of Mt. Pollino area (Italy) has been performed using earthquakes recorded in the area during an intense seismic sequence that occurred between 2010 and 2014. 870 local earthquakes with magnitude ranging from 1.8 to 5.0 were selected considering the number of recording stations, the signal quality, and the hypocenter distribution. P- and S-wave arrival times were manually picked and used to compute 3D velocity models through tomographic seismic inversion. The resulting 3D distributions of VP and VS are characterized by high resolution in the central part of the investigated area and from surface to about 10 km below sea level. The aim of the work is to obtain high- quality tomographic images to correlate with the main lithological units that characterize the study area. The results will be important to enhance the seismic hazard assessment of this complex tectonic region. These images show the ductile Apennine platform (VP = 5.3 km/s) overlaying the brittle Apulian platform (VP=6.0 km/s) at depth of around 5 km. The central sector of the area shows a clear fold and thrust interface. Along this structure,most of the seismicity occurred, including the strongest event of the sequence (M W 5.0). High V P (>6.8 km/s) and high V P /VS (>1.9) patterns, intersecting the southern edge of this western seismogenic volume, have been interpreted as water saturated rocks, in agreement with similar geological context in the Apennines. These fluids could have played a role in nucleation and development of the seismic sequence. A recent study revealed the occurrence of clusters of earthquakes with similar waveforms along the same seismogenic volume. The hypocenters of these cluster events have been compared with the events re-located in this work. Jointly, they depict a 10 km × 4 km fault plane, NW-SE oriented, deepening towards SW with a dip angle of 40–45° . Instead, the volume of seismicity responsible for the M L 4.3 earthquake developed as a mainshock-aftershock sequence, occurring entirely within the average-to-low VP /VS Apennine platform. Our results agree with other independent geophysical analyses carried out in this area, and they could significantly improve the actual knowledge of the main lithologic units of this complex tectonic area.

Studying the spatiotemporal distribution and motion of water vapour (WV), the most variable greenhouse gas in the troposphere, is pivotal, not only for meteorology and climatology, but for geodesy, too. In fact, WV variability degrades, in an unpredictable way, almost all geodetic observation based on the propagation of electromagnetic signal through the atmosphere. We use data collected on a dense GPS network, designed for the purposes of monitoring the active Neapolitan (Italy) volcanoes, to retrieve the tropospheric delay parameters and precipitable water vapour (PWV). This study has two main targets: (a) the analysis of long datasets (11 years) to extract trends of climatological meaning for the region; (b) studying the main features of the time evolution of the PWV during heavy raining events to gain knowledge on the preparatory stages of highly impacting thunderstorms. For the latter target, both differential and precise point positioning (PPP) techniques are used, and the results are compared and critically discussed. An increasing trend, amounting to about 2 mm/decades, has been recognized in the PWV time series, which is in agreement with the results achieved in previous studies for the Mediterranean area. A clear topographic effect is detected for the Vesuvius volcano sector of the network and a linear relationship between PWV and altitude is quantitatively assessed. This signature must be taken into account in any modelling for the atmospheric correction of geodetic and remote-sensing data (e.g., InSAR). Characteristic temporal evolutions were recognized in the PWV in the targeted thunderstorms (which occurred in 2019 and 2020), i.e., a sharp increase a few hours before the main rain event, followed by a rapid decrease when the thunderstorm vanished. Accounting for such a peculiar trend in the PWV could be useful for setting up possible early warning systems for those areas prone to flash flooding, thus potentially providing a tool for disaster risk reduction.

Geo-resources are widely exploited in our society, with huge benefits for both economy and communities. Nevertheless, with benefits come risks and impacts. Understanding how such risks and impacts are intrinsically borne in a given project is of critical importance for both industry and society. In particular, it is crucial to distinguish between the specific impacts related to exploiting a given energy resource and those shared with the exploitation of other energy resources. A variety of different approaches can be used to identify and assess such risks and impacts. In particular, Life Cycle Assessment (LCA) and risk assessments (RAs) are the most commonly adopted. Although both are widely used to support decision making in environmental management, they are rarely used in combination perhaps because they have been developed by largely different groups of specialists. By analyzing the structure and the ratio of the two tools, we have developed an approach for combining and harmonizing LCA and MRA; the resulting protocol envisages building MRA upon LCA both qualitatively and quantitatively. We demonstrate the approach in a case study using a virtual site (based on a real one) for geothermal energy production

We simulate the deformation of Somma-Vesuvius volcano due to some overpressure sources by means of a finite element 3D code. The main goal of these simulations is to investigate the influence of topography and structural heterogeneity on ground deformation. In our model the sources of deformation are embedded in an elastic linear isotropic medium and located at various depths. Geometry (shape and lateral extension) of the sources is mainly constrained by the results coming from recent seismic tomography studies. The structural heterogeneity has been modelled in terms of dynamic elastic parameters (Young’s modulus) retrieved from previous seismic tomography and gravity studies. A highresolution digital terrain model is used for the topography of the volcano subaerial edifice. Evidences from our results suggest that real topography and structural heterogeneities are key factors governing the ground deformation, which often turns being one of the most relevant problems in volcano monitoring. A large deviation from the axially symmetrical model of the displacement field is the main result of our modelling. Such an asymmetry is routinely unaccounted for when Mogi’s simplistic modelling in a homogeneous medium with simplified topography is used. Our study clearly demonstrate that a better knowledge of deformation patterns can significantly help in the location of monitoring sensors as well as in the design of an efficient geodetic network.

In this study, we investigate the oscillations of relative sea level through the analysis of tide gauge records about 10-year long collected in the Gulfs of Pozzuoli and Napoli (Southern Italy). The main goal of this study is to provide a suitable resolution model of the sea tides including low frequency (seiches), tidal bands and non-linear tides. The spectral analyses of the tide gauge records lead us to identify a number of seiche periods some of them already known from the literature and some other unknown. Furthermore, we target a non-conventional purpose of the tidal analysis, namely extracting from the tide gauge records the volcanotectonic signal (vertical ground displacement) in the resurgent Campi Flegrei caldera. We suggest a method to filter out the volcano-tectonic signal (bradyseism) from the tide gauge records by deconvolving it from two records, one collected in the active volcanic area (Pozzuoli) and the other one collected in a tectonically stable station (Napoli), located beyond the caldera rim. Finally, we retrieve the relative mean sea level change in the Gulf of Naples and compare it with the trend found in five tide gauges spread along the Italian coast.

Focal mechanisms of selected earthquakes, recorded in the Mount Pollino region (southern Italy) from 2010 through 2014, are used to infer the pore fluid pressure at hypocenter depths. The 3-D excess pore pressure field provides evidence that the sequence occurs in a fluid-filled volume with values reaching 35 MPa. The mechanisms underlying this swarm-like sequence and the triggering of earthquakes are investigated by computing the cumulative static Coulomb stress change at hypocenter depths and analyzing the pore-pressure diffusion mechanism. The results indicate that static Coulomb stress change was lower than 0.01 MPa, which is the value generally assumed as threshold for the triggering, and seismicity distribution was actually driven by pore-pressure diffusion with relatively low diffusivity value. This latter mechanism could also explain the delayed triggering of the two larger events ML 4.3 and ML 5.0, respectively, that occurred about 150 days apart.