The Italian Government has decreed a series of progressive restrictions to delay the COVID-19 pandemic diffusion in Italy since March 10, 2020, including limitation in individual mobility and the ...closure of social, cultural, economic and industrial activities. Here we show the lockdown effect in Northern Italy, the COVID-19 most affected area, as revealed by noise variation at seismic stations. The reaction to lockdown was slow and not homogeneous with spots of negligible noise reduction, especially in the first week. A fresh interpretation of seismic noise variations in terms of socio-economic indicators sheds new light on the lockdown efficacy pointing to the causes of such delay: the noise reduction is significant where non strategic activities prevails, while it is small or negligible where dense population and strategic activities are present. These results are crucial for the a posteriori interpretation of the pandemic diffusion and the efficacy of differently targeted political actions.
On March 5, 2022, a 12 kg meteoroid crossed the sky above Central Italy and was observed by three different observational systems: the PRISMA all-sky camera network (10 stations), the Italian ...national seismic network (61 stations), and a 4-element infrasound array. The corresponding datasets, each with its own resolution, provided three independent assessments of the trajectory, size and speed of the meteoroid. The bolide traveled across central Italy with an azimuth of 102 degrees, becoming visible at about 91 km above sea level with a velocity of about 15.4 km/s. Its visible trajectory lasted about 15 s. Reasonably, the residual portion of the ablated bolide terminated its path in the Adriatic Sea and could not be recovered. Seismic and infrasound data well match optical observations detecting the bolide Mach cone at 68 km above sea level with a back azimuth of 25 degrees with respect to the array. By comparing results from the three different systems, discrepancies are within the estimated uncertainties, thus confirming the mutual consistency of the adopted methodologies. Therefore, this study shows that different approaches can be integrated to improve the detection capability for bolide crossing the sky in monitored regions.
Exploiting supercritical geothermal resources represents a frontier for the next generation of geothermal electrical power plant, as the heat capacity of supercritical fluids (SCF),which directly ...impacts on energy production, is much higher than that of fluids at subcritical conditions. Reconnaissance and location of intensively permeable and productive horizons at depth is the present limit for the development of SCF geothermal plants. We use, for the first time, teleseismic converted waves (i.e. receiver function) for discovering those horizons in the crust. Thanks to the capability of receiver function to map buried anisotropic materials, the SCF-bearing horizon is seen as the 4km-depth abrupt termination of a shallow, thick, ultra-high (>30%) anisotropic rock volume, in the center of the Larderello geothermal field. The SCF-bearing horizon develops within the granites of the geothermal field, bounding at depth the vapor-filled heavily-fractured rock matrix that hosts the shallow steam-dominated geothermal reservoirs. The sharp termination at depth of the anisotropic behavior of granites, coinciding with a 2 km-thick stripe of seismicity and diffuse fracturing, points out the sudden change in compressibility of the fluid filling the fractures and is a key-evidence of deep fluids that locally traversed the supercritical conditions. The presence of SCF and fracture permeability in nominally ductile granitic rocks open new scenarios for the understanding of magmatic systems and for geothermal exploitation.
Starting from late May 2012, the Emilia region (Northern Italy) was severely shaken by an intense seismic sequence, originated from a ML 5.9 earthquake on May 20th, at a hypocentral depth of 6.3km, ...with thrust-type focal mechanism. In the following days, the seismic rate remained high, counting 50 ML≥2.0 earthquakes a day, on average. Seismicity spreads along a 30km east–west elongated area, in the Po river alluvial plain, in the nearby of the cities Ferrara and Modena. Nine days after the first shock, another destructive thrust-type earthquake (ML 5.8) hit the area to the west, causing further damage and fatalities. Aftershocks following this second destructive event extended along the same east-westerly trend for further 20km to the west, thus illuminating an area of about 50km in length, on the whole. After the first shock struck, on May 20th, a dense network of temporary seismic stations, in addition to the permanent ones, was deployed in the meizoseismal area, leading to a sensible improvement of the earthquake monitoring capability there. A combined dataset, including three-component seismic waveforms recorded by both permanent and temporary stations, has been analyzed in order to obtain an appropriate 1-D velocity model for earthquake location in the study area. Here we describe the main seismological characteristics of this seismic sequence and, relying on refined earthquakes location, we make inferences on the geometry of the thrust system responsible for the two strongest shocks.
•First complete analysis of the 2012 Emilia mainshocks–aftershocks seismic sequence.•New catalog of the seismic sequence including data from temporary stations•Sensible improvement in terms of the activated fault system geometry definition•The different dip of the activated fault segments is highlighted and discussed.•Basic information are provided for further specific studies and hazard scenarios.
We model the spatial and temporal evolution of seismicity during the 1997 Umbria‐Marche seismic sequence in terms of subsequent failures promoted by fluid flow. The diffusion process of pore‐pressure ...relaxation is represented as a pressure perturbation generated by coseismic stress changes and propagating through a fluid saturated medium. The values of isotropic diffusivity range between 22 and 90 m2/s. The calculated value of anisotropic diffusivity (Daniso = 250 m2/s) is largest along the average strike (N140°) direction of activated faults. Our results suggest that the observed spatio‐temporal migration of seismicity is consistent with fluid flow.
By extending the conventional Beam-Forming frequency-wavenumber power spectral estimate to the case of arbitrarily-shaped wavefronts, we obtained images of rupture propagation during the 2016 August ...24, Mw=6.0 central Italy earthquake. Using a set of strong-motion accelerometers, we evaluate the beam power along the travel time curves associated with synthetic sources spanning a model fault surface. This allows deriving time-dependent images of the distribution of energy radiation throughout the fault plane. Results indicate bi-lateral rupture propagation toward SE and NW, in rough agreement with surface co-seismic displacement and surface damage pattern. To a first order, our results are also consistent with those obtained from full-waveform inversion of strong-motion data.
We measured shear wave splitting (SWS) parameters from a large dataset of local microearthquakes recorded at the Larderello-Travale geothermal field (LTGF; Tuscany, Italy). For that geothermal area, ...seismic anisotropy is distributed in the upper crust following a complex pattern. Although the overall trend reflects the strike of the normal faults dominating the region, measurements at the southern and central part of the LTGF show large (up to 90°) deviations from the dominant polarization direction. This anomalous pattern suggests that besides the extensive dilatancy anisotropy, the fast wave polarization direction is also likely affected by the presence of over-pressurized geothermal fluids, by local rearrangement of the regional stress, and by the presence of non-vertical cracks. We found large differences in normalised delay times between sparse and clustered seismicity. While the average anisotropy percentage is on the order of 1.7%, a significant amount of our measurements exceeds the 4.5%, reaching values as high as 16%. The highest anisotropy percentages are associated with earthquakes located at the center and at the SE margin of the geothermal area, at depths lower than 5 km and in the 5–10 km range, respectively. This latter occurrence may be interpreted in terms of cracks filled with fluids which, given the expected pressure and temperature conditions, are likely in supercritical conditions. Shear-wave splitting thus confirms to be a powerful tool for better constraining location and extent of those deep fractured rock portions possibly hosting supercritical fluids, that represent the next frontier of geothermal exploitation due to their enhanced heat capacity.
•Shear wave splitting study on geothermal area•Seismic anisotropy is distributed following complex pattern.•Fast polarization direction reveals over-pressurized geothermal fluids.•High anisotropy percentage associated to fluids in supercritical conditions.
In the years between 2011 and 2014, at the edge between the Apennines collapsing chain and the subducting Calabrian arc, intense seismic swarms occurred in the Pollino mountain belt. In this key ...region, <2.5 mm/yr of NE-trending extension is accommodated on an intricate network of normal faults, having almost the same direction as the mountain belt. The long-lasting seismic release consisted of different swarm episodes, where the strongest event coinciding with a
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5.0 shock occurred in October 2012. This latter comes after a
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four nucleated in May 2012 and followed by aseismic slip episodes. In this study, we present accurate relocations for ∼6,000 earthquakes and shear-wave splitting analysis for ∼22,600 event-station pairs. The seismicity distribution delineates two main clusters around the major shocks: in the north-western area, where the
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5.0 occurred, the hypocenters are localized in a ball-shaped volume of seismicity without defining any planar distribution, whilst in the eastern area, where the
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4.3 nucleates, the hypocenters define several faults of a complex system of thrusts and back-thrusts. This different behavior is also imaged by the anisotropic parameters results: a strong variability of fast directions is observed in the western sector, while stable orientations are visible in the eastern cluster. This tectonic system possibly formed as a positive flower structure but as of today, it accommodates stress on normal faults. The deep structure imaged by refined locations is overall consistent with the complex fault system recently mapped at the surface and with patterns of crustal anisotropy depicting fractures alignment at depth. The possible reactivation of inherited structures supports the important role of the Pollino fault as a composite wrench fault system along which, in the lower Pleistocene, the southward retreat of the ionian slab was accommodated; in this contest, the inversion of the faults kinematics indicates a probable southward shift of the slab edge. This interpretation may help to comprehend the physical mechanisms behind the seismic swarms of the region and defining the seismic hazard of the Pollino range: nowadays a region of high seismic hazard although no strong earthquakes are present in the historical record.
We report unprecedented observations of long‐period (LP) seismicity in non‐volcanic setting. Our data are from the Central‐Northern sector of the Apennine chain, Italy. For this area, intense CO2 ...circulation of mantle origin has been documented by either groundwater composition and borehole measurements. We perform waveform correlation and stacking to obtain reliable epicenter estimates. Following Chouet's crack model, we find that both the quality factor and dominant frequency of LP oscillations are consistent with the sustained resonance of a wet crack filled by a water‐CO2 mixture.
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