The influence of subsurface geology on the distribution of earthquakes during the 2016‐-2017 Central Italy seismic sequence

Abstract In 2016–2017, a destructive sequence of earthquakes affected a wide portion of Central Italy, activating a complex, 80-km long system of SW-dipping normal faults and causing impressive surface faulting and widespread damage. Former studies providing reconstructions of the fault systems activated during this sequence, are mostly based on high-resolution seismological and geodetic data. In this paper, we integrate surface and subsurface geological data with the ones obtained by an irregular network of seismic reflection profiles, aimed at providing a comprehensive reconstruction of the subsurface lithologies and structures in this area. We have constructed a set of five geological cross-sections, passing through the mainshock epicentral areas (Mw > 5.5) of the seismic sequence. The cross-sections are extrapolated down to a depth of ca. 12 km, along which we have plotted relocated seismicity. Combined geological and seismological data support a new 3D seismotectonic model, illustrating the propagation through time and space of the seismic ruptures during the sequence. Our results show that the litho-mechanical stratigraphy exerted a primary control on the distribution of seismicity, as it is mostly hosted in the more competent lithologies (i.e. the Late Triassic-Paleogene succession, consisting of carbonates and evaporites). In addition, we illustrate the crucial role played by the inherited compressional structures in determining the lateral and vertical variations of the rheological properties of the upper crust and, eventually, the overall geometry and segmentation of the seismogenic extensional system. The workflow proposed here can be applied to other seismogenic zones throughout the world, since reliable seismotectonic models require an accurate reconstruction of the subsurface geological setting, based on a close integration of geological, geophysical and seismological data

Trophic and Microbial Patterns in the Ross Sea Area (Antarctica): Spatial Variability during the Summer Season

In open regions of the Ross Sea, the role of the microbial community in the turnover of organic matter has scarcely been investigated; indeed, very little is known on how microbial distribution and functional diversity respond to environmental conditions and hydrographic structures. During the austral summer of 2017, two pelagic areas of the Ross Sea [the Drygalski Ice Tongue and the nearby Terra Nova Bay polynya (A area), and the continental Shelf Break area near Cape Adare (C area)] were studied at selected depths [surface, Deep Chlorophyll Maximum (DCM), Circumpolar Deep Water (CDW), deep waters]. Trophic properties [nutrient concentrations, particulate (POC), dissolved organic carbon (DOC) and its optically significant fraction (CDOM) were measured, together with the main hydrological variables. Microbial community abundance [total prokaryotes, living, dead, and actively respiring fraction, high- and low nucleic acid cells (HNA and LNA), picoand nano-eukaryotes, culturable heterotrophic bacteria], composition, and metabolism (as whole community and as isolated bacteria) were also assessed. Through a multidisciplinary dataset, this study highlighted the variable response of microbial abundance, diversity, and metabolism of the microbial community to the changing local environmental conditions of the Ross Sea. Different forces, such as organic matter inputs (mostly of detrital nature) released from the Drygalski glacier in the A area, and a coastal-to-offshore gradient in the C area, coexisted within this extreme ecosystem. This resulted in a significant spatial segregation of the edaphic parameters, and of the microbial community distribution and metabolic activity patterns

The 2015 version of the Italian Parametric Earthquake Catalogue (CPTI15)

The Italian Parametric Earthquake Catalogue (CPTI) represents the most extensive and reliable source of parameters for earthquakes in Italy and surrounding areas. Since its first introduction in 1999, CPTI benefits from the results of the 30-years-long Italian tradition in historical earthquake research that, still today, keeps on providing a wealth of studies and macroseismic data. Such data have been collected, homogenized and made available through several releases of the related macroseismic database (DBMI). In 2016, the fourth release of CPTI and DBMI, has been finalized. They provide the most advanced and updated sets of macroseismic and instrumental data and parameters, and cover the time-span 1000-2014 with earthquakes with maximum intensity I ≥ 5 or magnitude Mw ≥ 4.0. The catalogue lists 4574 events, 70% of which accompa- nied by intensity data points (about 125’000 as a whole). Macroseismic data derive from 185 studies, 54 of them are new with respect to the previous version CPTI11. Parameters related to historical earthquakes are completely re-assessed, and magnitudes from macroseismic data are derived with new intensity-to-Mw relationships. Such relationships are based on the same dataset that contributes updated instrumental magnitudes to the catalogue. Either Mw from moment tensor solutions or proxies calculated with new published conversion relationship are considered. If available, both macroseismic and instrumental parameters are provided, together with a set of “preferred ones”, which consist of a selection between the macroseismic and the instrumental epicentres, and the weighted average of the macroseismic and instrumental magnitudes.PublishedTrieste, Italy3T. Storia Sismica4T. Sismologia, geofisica e geologia per l'ingegneria sismica4IT. Banche dat

The 2016–2017 earthquake sequence in Central Italy: macroseismic survey and damage scenario through the EMS-98 intensity assessment

In this paper we describe the macroseismic effects produced by the long and destructive seismic sequence that hit Central Italy from 24 August 2016 to January 2017. Starting from the procedure adopted in the complex field survey, we discuss the characteristics of the building stock and its classification in terms of EMS-98 as well as the issues associated with the intensity assessment due to the evolution of damage caused by multiple shocks. As a result, macroseismic intensity for about 300 localities has been determined; however, most of the intensities assessed for the earthquakes following the first strong shock on 24 August 2016, represent the cumulative effect of damage during the sequence. The earthquake parameters computed from the macroseismic datasets are compared with the instrumental determinations in order to highlight critical issues related to the assessment of macroseismic parameters of strong earthquakes during a seismic sequence. The results also provide indications on how location and magnitude computation can be strongly biased when dealing with historical seismic sequences.Presidenza del Consiglio dei Ministri - Dipartimento della Protezione Civile (DPC)Published2407–24314T. Sismicità dell'Italia1SR TERREMOTI - Sorveglianza Sismica e Allerta Tsunami2SR TERREMOTI - Gestione delle emergenze sismiche e da maremoto5SR TERREMOTI - Convenzioni derivanti dall'Accordo Quadro decennale INGV-DPCJCR Journa

Microbial Biofilms Colonizing Plastic Substrates in the Ross Sea (Antarctica)

Very few studies have investigated marine microbial colonization in polar regions, but climate-changing scenarios stress the importance of these investigations to protect life in such extremely vulnerable ecosystems. In two different coastal sites of the Ross Sea (Road and Tethys Bays, Antarctica) exposed to different stressors, the microbial biofilm colonizing the surface of plastic (polyvinyl chloride, PVC, and polyethylene, PE) panels left submerged in two experiments at different timescales (“short-term”: 3 months, and “long-term”: 9 and 12 months) was studied. The abundance and metabolic enzymatic activities [leucine aminopeptidase (LAP), beta-glucosidase (GLU) and alkaline phosphatase (AP)] of the prokaryotes and the microalgal abundance and species composition were analyzed, in parallel with the main environmental parameters. The prokaryotic community showed higher abundance and metabolic activities on PVC than on PE as opposed to microalgae. A peak in the microfouling prokaryotic abundance and metabolic functions was frequently recorded after 3 months of immersion, corresponding to the late austral summer period. LAP and AP were the most active enzymes, suggesting that microbial metabolic profiles were modulated by labile organic substrates. Our results suggest that the composition and function of microbial biofilm could be considered as sentinels of natural or anthropic-related disturbances

Microbial Biofilms Colonizing Plastic Substrates in the Ross Sea (Antarctica)

Very few studies have investigated marine microbial colonization in polar regions, but climate-changing scenarios stress the importance of these investigations to protect life in such extremely vulnerable ecosystems. In two different coastal sites of the Ross Sea (Road and Tethys Bays, Antarctica) exposed to different stressors, the microbial biofilm colonizing the surface of plastic (polyvinyl chloride, PVC, and polyethylene, PE) panels left submerged in two experiments at different timescales (“short-term”: 3 months, and “long-term”: 9 and 12 months) was studied. The abundance and metabolic enzymatic activities [leucine aminopeptidase (LAP), beta-glucosidase (GLU) and alkaline phosphatase (AP)] of the prokaryotes and the microalgal abundance and species composition were analyzed, in parallel with the main environmental parameters. The prokaryotic community showed higher abundance and metabolic activities on PVC than on PE as opposed to microalgae. A peak in the microfouling prokaryotic abundance and metabolic functions was frequently recorded after 3 months of immersion, corresponding to the late austral summer period. LAP and AP were the most active enzymes, suggesting that microbial metabolic profiles were modulated by labile organic substrates. Our results suggest that the composition and function of microbial biofilm could be considered as sentinels of natural or anthropic-related disturbances

Nutrient regeneration mediated by extracellular enzymes in water column and interstitial water through a microcosm experiment

In coastal lakes the role of microorganisms in driving nutrients regeneration at different water depths and in sediments is not yet fully understood. The dynamics of microbial (algal and bacterial) abundance and bacterial activities involved in organic matter transformation were measured, together with nutrient concentrations, through a microcosm experiment set up using the oligotrophic Faro lake as a study model over a total period of 15 days and with a four-day frequency. Water column at different depths (surface, middle and bottom) and interstitial water obtained by sediment centrifugation were used in appropriate ratios (mixed 1:1 with surface waters) to fill 21-Litre plastic aquaria in order to simulate processes occurring in natural conditions. At early experimental period, the sharp decrease of dissolved organic nutrients and the abundant production of leucine aminopeptidase (LAP) and alkaline phosphatase (AP) in correspondence with high phytoplankton abundance in bottom and interstitial water reflected the relevance of organic nutrients for inorganic nutrients regeneration and phytoplankton growth. Size fractionation of LAP and AP as well as the positive relationship between microbial compartments suggested that bacteria and phytoplankton worked in close reciprocal synergy, and coupling of nitrogen and phosphorus regeneration, especially in bottom and interstitial waters, was observed. At later experimental period, the change in bacterial community, especially the increase of filamentous shaped cells, together with a simultaneous increase of protozoan abundance indicated that nutrient replenishment made the microbial loop structure more competitive. In oligotrophic conditions, such as those in Faro lake, organic nutrient enrichment of bottom and interstitial waters was associated with changes in the bacterial community, with consequent stimulation of extracellular enzymes to support phytoplankton growth. Nutrient availability from microbial regeneration resulted in an increased complexity of the microbial loop structure, with bacteria and phytoplankton adopting specific strategies to respond to the changing environment. (C) 2019 Elsevier B.V. All rights reserved

Microbial Parameters as Predictors of Heterotrophic Prokaryotic Production in the Ross Sea Epipelagic Waters (Antarctica) during the Austral Summer

A regression-based approach was used to test the suitability of a range of parameters, including total prokaryotic cell abundance and biomass, as lipopolysaccharide (LPS) content, and exoenzymatic activities (leucine aminopeptidase, LAP, beta-glucosidase, ß-G, and alkaline phosphatase, AP) as predictors of heterotrophic prokaryotic production (HPP) in the Ross Sea epipelagic waters. A close association between HPP and protein hydrolysis mediated by enzymatic activity (LAP), and to a lower significance level with the other variables, was recorded. Three multiple regression equations were developed from two microbial datasets collected during middle austral summer periods. All showed a good predictive ability for HPP, and this was further validated through a comparison between the predicted and the observed HPP values. The obtained regression equations proved to represent a promising example of empirical models for further predictive studies in the Ross Sea where—through the incorporation of additional microbiological and environmental parameters—the developed models could find a practical application to cover the entire austral summer period

Microbial metabolic rates in the Ross Sea: the ABIOCLEAR Project

The Ross Sea is one of the most productive areas of the Southern Ocean and includes several functionally different marine ecosystems. With the aim of identifying signs and patterns of microbial response to current climate change, seawater microbial populations were sampled at different depths, from surface to the bottom, at two Ross Sea mooring areas southeast of Victoria Land in Antarctica. This oceanographic experiment, the XX Italian Antarctic Expedition, 2004-05, was carried out in the framework of the ABIOCLEAR project as part of LTER-Italy. Here, microbial biogeochemical rates of respiration, carbon dioxide production, total community heterotrophic energy production, prokaryotic heterotrophic activity, production (by 3H-leucine uptake) and prokaryotic biomass (by image analysis) were determined throughout the water column. As ancillary parameters, chlorophyll a, adenosine-triphosphate concentrations, temperature and salinity were measured and reported. Microbial metabolism was highly variable amongst stations and depths. In epi- and mesopelagic zones, respiratory rates varied between 52.4–437.0 and 6.3–271.5 nanol O2 l-1 h-1; prokaryotic heterotrophic production varied between 0.46–29.5 and 0.3–6.11 nanog C l-1 h-1; and prokaryotic biomass varied between 0.8–24.5 and 1.1–9.0 µg C l-1, respectively. The average heterotrophic energy production ranged between 570 and 103 mJ l-1 h-1 in upper and deeper layers, respectively. In the epipelagic layer, the Prokaryotic Carbon Demand and Prokaryotic Growth Efficiency averaged 9 times higher and 2 times lower, respectively, than in the mesopelagic one. The distribution of plankton metabolism and organic matter degradation was mainly related to the different hydrological and trophic conditions. In comparison with previous research, the Ross Sea results, here, evidenced a relatively impoverished oligotrophic microbial community, throughout the water column

Microbial Abundance and Enzyme Activity Patterns: Response to Changing Environmental Characteristics along a Transect in Kongsfjorden (Svalbard Islands)

Svalbard archipelago is experiencing the effects of climate changes (i.e., glaciers’ thickness reduction and glacier front retreat), but how ice melting affects water biogeochemistry is still unknown. Microbial communities often act as environmental sentinels, modulating their distribution and activity in response to environmental variability. To assess microbial response to climate warming, within the ARctic: present Climatic change and pAst extreme events (ARCA) project, a survey was carried out along a transect in Konsfjorden from off-shore stations towards the Kronebreen glacier. Total bacterial abundance and the fraction of actively respiring cells (labelled by cyanotetrazolium chloride, CTC), cultivable heterotrophic bacterial abundance, and extracellular enzymatic activities (leucine aminopeptidase (LAP), beta-glucosidase (GLU), and alkaline phosphatase (AP)) were measured. In addition, water temperature, salinity, dissolved oxygen, turbidity, total suspended matter (TSM), particulate and chromophoric dissolved organic matter (CDOM), chlorophyll-a (Chl-a), and inorganic compounds were determined, in order to evaluate whether variations in microbial abundance and metabolism were related with changes in environmental variables. Colder waters at surface (3.5–5 m) depths and increased turbidity, TSM, and inorganic compounds found at some hydrological stations close to the glacier were signals of ice melting. CDOM absorption slope values (275–295 nm) varied from 0.0077 to 0.0109 nm−1, and total bacterial cell count and cultivable heterotrophic bacterial abundance were in the order of 106 cells/mL and 103 colony forming units/mL, respectively. Enzymatic rates <1.78, 1.25, and 0.25 nmol/L/h were recorded for AP, LAP, and GLU, respectively. Inorganic compounds, TSM, and turbidity correlated inversely with temperature; AP was significantly related with CDOM absorption spectra and heterotrophic bacteria (r = 0.59, 0.71, p < 0.05); and LAP with Chl-a, Particulate Organic Carbon (POC) and Particulate Organic Nitrogen (PON) (0.97, 0.780, 0.734, p < 0.01), suggesting that fresh material from ice melting stimulated the metabolism of the cultivable fraction