United States

The north-eastern sector of the Calabrian Arc includes the Sila Massif, Sibari plain and part of the Taranto gulf. It is a geologically complex area crossed by a system of active faults since the Middle Pleistocene that makes Calabria one of the regions with the highest seismic hazard in the Mediterranean. These faults are responsible for the morphology of the territory, characterized by high relieves and widespread landslides on a large scale, and they generated strong earthquakes in the past centuries. A first fault system is characterized by normal high-angle faults with a N-S direction which displaces the Sila batolith. Continuing towards the northern part of the area, NW-SE trending normal faults displace the Plio-Quaternary sediments. In the Corigliano-Rossano area, the Rossano Fault is the most important. It is a WNW-ESE neogenic tectonic structure characterized by a left normal-transcurrent kinematics and extending for about 12 Km with an en-èchelon arrangement. It puts the Sila Batolith in contact with Tortonian and Plio-Quaternary sediments and is responsible for the catastrophic earthquake of 1836. In this work we focused on a wide area comprised between 39.2°-39.9° N and 16.2°-17.4° E degrees, making a revision of the recent earthquakes occurred in it. We collected all focal mechanisms available in published papers and analyzing with great detail the seismicity of the last 15 years. During the last century only small to medium size earthquakes occurred in the area, both on land and offshore. The seismic catalog includes hundreds of earthquakes of magnitude M&lt;5 recorded during the last few decades. This seismicity appears widespread through the area of our study, with depth in the range from 5 km to 40 km below sea level. Swarms of small events (M&lt;4) are quite common in this seismogenetic area. The increased number of seismic stations available during the last decade allowed for detailed analysis of the local earthquakes. We performed a location as accurate as possible of recent earthquakes, including those occurred along the coast and offshore, and computed the focal mechanism of as many events as possible. To estimate the source kinematics of small earthquakes we applied the software FOCMEC (Snoke, 2003), based on the polarity of body waves, and the software HybridMT (Kwiatek et al., 2016), based on the area below the first P wave pulse. We obtained reliable results for more than 30 earthquakes occurred during the last 15 years (2.5 &lt;= M &lt;= 4.4). Results show a variety of solutions, with predominance of transtensive and reverse kinematics. The location and kinematics of recent earthquakes are in good agreement with the known faults, showing a significant correlation between the computed focal mechanisms and the direction of the tectonic structures. The source analysis of recent seismicity gives interesting insight about the offshore faults.

SGI 2021

Seismotectonic analysis of the north-east sector of Calabrian Arc

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The north-eastern sector of the Calabrian Arc includes the Sila Massif, Sibari plain and part of the Taranto gulf. It is a geologically complex area crossed by a system of active faults since the Middle Pleistocene that makes Calabria one of the regions with the highest seismic hazard in the Mediterranean. These faults are responsible for the morphology of the territory, characterized by high relieves and widespread landslides on a large scale, and they generated strong earthquakes in the past centuries. A first fault system is characterized by normal high-angle faults with a N-S direction which displaces the Sila batolith. Continuing towards the northern part of the area, NW-SE trending normal faults displace the Plio-Quaternary sediments. In the Corigliano-Rossano area, the Rossano Fault is the most important. It is a WNW-ESE neogenic tectonic structure characterized by a left normal-transcurrent kinematics and extending for about 12 Km with an en-èchelon arrangement. It puts the Sila Batolith in contact with Tortonian and Plio-Quaternary sediments and is responsible for the catastrophic earthquake of 1836. In this work we focused on a wide area comprised between 39.2°-39.9° N and 16.2°-17.4° E degrees, making a revision of the recent earthquakes occurred in it. We collected all focal mechanisms available in published papers and analyzing with great detail the seismicity of the last 15 years. During the last century only small to medium size earthquakes occurred in the area, both on land and offshore. The seismic catalog includes hundreds of earthquakes of magnitude M<5 recorded during the last few decades. This seismicity appears widespread through the area of our study, with depth in the range from 5 km to 40 km below sea level. Swarms of small events (M<4) are quite common in this seismogenetic area. The increased number of seismic stations available during the last decade allowed for detailed analysis of the local earthquakes. We performed a location as accurate as possible of recent earthquakes, including those occurred along the coast and offshore, and computed the focal mechanism of as many events as possible. To estimate the source kinematics of small earthquakes we applied the software FOCMEC (Snoke, 2003), based on the polarity of body waves, and the software HybridMT (Kwiatek et al., 2016), based on the area below the first P wave pulse. We obtained reliable results for more than 30 earthquakes occurred during the last 15 years (2.5 <= M <= 4.4). Results show a variety of solutions, with predominance of transtensive and reverse kinematics. The location and kinematics of recent earthquakes are in good agreement with the known faults, showing a significant correlation between the computed focal mechanisms and the direction of the tectonic structures. The source analysis of recent seismicity gives interesting insight about the offshore faults.

poster

The Friuli Venezia Giulia region (FVG) belongs to the easternmost portion of the Southern Alps, where NE-SW trending, S-SE-verging thrusts of the Southalpine Quaternary front interacts with NW-SE-striking right-lateral strike-slip fault-system that characterizes the Italian-Slovenian border area. Both fault systems are still active as testified by historical and instrumental seismicity (e.g. Rovida et al., 2021). During the last millennium six M≥6 earthquakes struck FVG and surrounding regions causing thousands of casualties and widespread damages (1348, Alpi Giulie; 1511, Friuli-Slovenia; 1928, Carnia; 1873, Alpago; 1936, Cansiglio; 1976, Friuli). Despite the abundance of scientific literature produced after the devastating 1976 Friuli earthquake sequence (see for a review Carulli, 2018), before this project FVG was not equipped with a systematic and homogeneous database of active or potential active faults based on the seismotectonic features. For this reason, the Geological Service of the Friuli Venezia Giulia Region promoted a research project in collaboration with the University of Trieste, the University of Udine and the National Institute of Oceanography and Experimental Geophysics (OGS) of Trieste in order to create a database of the active faults in FVG. Input data derives from published papers, studies and maps in FVG produced during the past 50 years and based on geological, geophysical, morphotectonic, seismological, paleoseismological data. The database is organized in direct or indirect clues on the location of active or presumably active faults, as well as on their recent activity (e.g. historical, Holocene, post-LGM, pre-LGM, Quaternary and Pre-Quaternary). These clues served to fix major tectonic structures, and to create the map of the active or presumably active faults. When data are available, the structures are characterized by a full set of geometric, kinematic and seismological parameters (e.g., slip rate, recurrence interval). Each parameter is rated for accuracy (e.g. quality index). We think that this database represents a useful tool to assess both ground shaking scenarios and surface faulting hazard.

Database of active faults in Friuli Venezia Giulia: a basic tool for seismic hazard assessment

During the last millennium, several strong earthquakes have occurred in the Umbria-Marche Apennines, which makes this area one of the most seismically active of Central Italy. Unfortunately, the lack of reliable instrumental data for strong historical seismic events, and the scarce field evidence of faulting within the Quaternary deposits, make the characterization of active seismogenic structures problematic. Moreover, although these areas have been largely studied, robust and commonly accepted seismic sources are still lacking. In this regard, GIS-aided analysis of both the topography and the river network represents excellent tools to recognise areas with different behaviour in terms of vertical motions, thus allowing to infer location of tectonic structures. A tectonic-geomorphology study of the Umbria-Marche Apennine has been carried out through a comprehensive large-scale analysis of the topography and the river network, combined with instrumental seismicity and structural geology data. The topography has been analysed by combining elevation map ad its derivative (e.g., maximum, mean, minimum and relief map) and swath profile. The latter are10 km large and runs roughly perpendicular to the main geological structures and the river valleys. River network has been analysed because rivers rapidly and consistently react to tectonic deformation, with subtle changes in topography recorded by the channels morphology and the river long profile. Moreover, most of the river long profiles show sharp change in channel slope (e.g., knickpoint). These can be either interpreted as due to either lithological or tectonic control. Moreover long profile of some tributaries where also investigated to find indicators of on-going vertical movements. Topography and river network features have been compared with historical and instrumental seismicity. This comparison suggest that some topography and river network anomalies are placed in areas where the possible epicentre of strong historical earthquakes occur (e.g., the 1741 Fabriano seismic event). In this regard, the identification of active faults and the definition of their dimensional parameters have major implications on the correct assessment of the seismic hazard for large and densely populated village of the Marche Region.

Morphostructural evidence of active tectonics in the Umbria-Marche Apennines, central Italy

The hydrodynamic behavior of karst aquifers is usually complex due to the high degree of heterogeneity and anisotropy of their geologic and hydrogeologic properties. Among karstified rocks, metamorphic carbonate rocks (e.g marble and meta-dolostone) are characterized by very low porosity and permeability, but their hydraulic properties can be altered by geologic processes, and significant aquifers can develop into these rocks eventually. However, the functioning of metamorphic karst aquifers is still poorly known. This contribution presents the hydrological monitoring of three of the main karst springs of the Apuan Alps (Italy). This mountain chain is characterized by extensive metamorphosed carbonate outcrops in which karst aquifers have developed. Pollaccia, Renara and Equi springs were equipped with multi parametric sensors for water level and discharge (L, Q), temperature (T), and electrical conductivity (EC). Their hydrographs and chemographs were compared with precipitation time series collected by the meteorological stations to investigate the response of the karst systems to infiltration and to infer their structure. The mean discharge for Pollaccia, Renara and Equi springs were respectively about 900, 200 and 800 l/s, their EC varied between 130 and 300 µS/cm, whereas T ranged between 7.8 and 10.6 °C. Water discharge, T, and EC response to infiltration was quick and impulsive with lag times of few hours. EC and T trends were complex for all the three springs, but dilution was the prevalent hydrodynamic response to precipitation observed during the monitoring. Piston-flow phenomena were scarce and limited to particular conditions. No delay between discharge increments and EC and T responses occurred. These observations suggest that the springs are fed by dominant conduit systems in which water flows only in few, enlarged conduits, with limited fracture storage. Piston-flow phenomena could be related to the presence of secondary flow networks that are connected with the main flow pathways only in specific conditions and/or to the flushing of limited volumes of water stored in the aquifers. Monitoring results suggest that the functioning of meta-carbonate aquifers in the Apuan Alps is controlled by several factors such as the low degree of fracturing of marbles, the local structural arrangement, and the primary porosity of the karstified rocks. As a consequence, storage is limited and flow velocity is high, preventing sustained water-rock interactions.

Monitoring karst aquifers hydrodynamics in metamorphic carbonates: the example of the Apuan Alps, Italy

The north-western sector of the Friuli Venezia Giulia Region, on the border between Italy and Austria, is characterized by the presence of an extensive mountain massif where outcrop the intensely karstified Devonian limestones. The high average rainfall, together with the high permeability of carbonates, has favored the development of an extensive aquifer, the main source of which is represented by the Fontanon di Timau. Due to its high flow rate, between 250 and 5000 l/s, the spring is exploited both for the supply of drinking water and hydroelectric energy. Given the importance of the source, a research project has started, partially funded by the Geological Service of the Friuli Venezia Giulia Region, aiming at the hydrogeological characterization of the survey area in order to identify the its recharge area and evaluate its vulnerability. The present paper proposes a hydrogeochemical characterization of precipitation, surface waters and springs in the area located between Mt. Coglians and the Alta Valle del But, and between Eiskar glacier, the valley of the Valentina and the Anger valley for the Italian and Austrian sectors, respectively. The study was carried out over a period of about 5 years, during which a hydrogeological survey was carried out in order to identify all the sources present in the area and to design a geochemical monitoring network of the waters. Thanks to special rain gauges, monthly precipitations were collected for the isotopic composition analysis in order to determine the isotopic gradient of the area (Plocken, Mt. Croce Carnico, and Rivo). Surface and spring water samples were collected for the study of stable (O and H), unstable (3H) isotopes, radionuclides (Rn), major and trace elements. The trends related to the temperature and electrical conductivity of the water in correspondence of different sampling points were also defined. At the same time, tracing tests were also performed using uranine and tinopal, which made it possible to verify the hydrogeological connection between the western sector of the karst area and the Fontanon di Timau and to define the hydrodynamics of the underground system. Isotopes and trace element results highlighted that Fontanon di Timau spring is significantly fed by the massif of Mt. Coglians-Creta di Collinetta as well as by the waters that infiltrate the area of Pal Piccolo-Creta di Timau and partially also from the waters that infiltrate beyond the watershed in Austrian territory. All the other springs identified in the area, on the other hand, have much lower flow rates and drain waters from neighboring basins limited to the Italian side only.

Geochemical characterization of the Timau Karst aquifer

The circulation of karst water in evaporate terrains (e.g. salt beds, gypsum or anhydrite) may develop long circuits and important morphologies both on the surface and underground. The features of these karst circuits are strongly conditioned by the high solubility and the low mechanical strength of the rock, resulting in a high propensity to develop collapses and subsidence morphologies on the surface (e.g. sinkholes). Nevertheless, the attention of the scientific world was often more focused on karst systems in carbonate rocks that rise interest for the utility of water as drinking resource. Karst aquifers in carbonate rocks (e.g. limestones and dolomite), indeed, often represent an important source of high-quality water, while in evaporite terrains the high salinity of the water usually prevents the use of the aquifers for drinking purpose. The investigation of karst systems in gypsum and anhydrite terrains, however, covers an important role in the minimisation and prevention of risks connected with the interference with civil infrastructures. In particular, karst phenomenon represents one of the main risk factors for the stability and safety of gypsum quarries, especially if underground. The possible filling with clay or pressurized water of the karst cavities exponentially increases the dangerousness of the phenomenon, due to swelling problems and violent water inrushes. If not carefully evaluated, the interference between karst systems and quarry activity may evolve in risk scenarios for the stability of underground tunnels and for the surrounding environment, inducing collapses of karst caves and underground quarry structures, slop instabilities, subsidence phenomena on the surface and modification of the hydrogeological setting of the area. In this study, the features and the development of karst systems in gypsum are described and monitored in correspondence of a series active quarry sites. The karst morphologies are investigated with non-destructive geophysical techniques. Test sites were chosen in the Monferrato area that hosts some of the main gypsum bodies of Italy. The results of the geophysical investigation are integrated with the known geological features of the sites, in order to obtain a more complete and reliable description and interpretation of the phenomenon.

Karst morphologies and related risks in gypsum of Monferrato area (NW Italy)

The North-Adriatic Sea level rise caused by the climate change in progress and the results of a risk analysis of salt water intrusion (SWI) in coastal aquifers, at regional and local scale, are the output of an EU project named ASTERIS (Adaptation to Saltwater inTrusion in sEa level RIse Scenarios) co-funded by Interreg Italy-Croatia Cross Border Cooperation Programme. In order to reduce the environmental and socio-economic losses due to the progression of foreseen salinization along the coastal aquifer in the municipality of Fano (PU – Marche region, Italy), an adaption plan has been built. The municipal adaptation plan matched the actions to be followed, in terms of sustainable use of groundwater resource, designed to maintain the interface between fresh and salt water toward the sea, re-orienteering the pumping systems, lowering the interface zone and creating barriers to SWI. The envisaged adaptation measures are organized according to the hydrogeological effects in different zones of the coastal aquifer and are related to group of stakeholders, planning key-roles in the use of the groundwater resources. A particular focus has been dedicated to surface water bodies into the city, in direct connection with seawater, that shows higher EC values, which denoted the presence of seawater ingression along the riverbed. With reference to the temporal variations of the salt intrusion process, the “dynamic updating” of the adaptation plan seems to be the best method, supported by field observation. For this reason, have been suggested some test sites (“monitoring transects”) that could be provided by installations of monitoring devices, distributed between the emerged beach and the inland. A wide spectrum of measures has been proposed, according to a specific land-use settings and to a “vulnerability zoning” criteria, among which: preventive measures in low-vulnerability coastal areas, in order to delay salinization; mitigation measures in medium-vulnerability coastal areas, accepting the idea of a certain degree of salinization of the coastal aquifer, trying to obtain a reduced impact on the socio-economic and environmental system, through limitation of total damage; recovery/contrast measures in high-vulnerability coastal areas, trying to minimise the impact affecting the socio-economic and environmental system involved by the groundwater salinization. The “Adaptation plan” for the Municipality of Fano must be based on the existence of a control room, oriented to the coastal aquifer system management, with the aid of a numerical forecasting simulation model of flow and salt transport into the coastal aquifer, able to assess and predict SWI evolution; its purpose is to ensure support for the Strategic Planners in order to implement a combination of prevention, mitigation and remediation measures in urban, agricultural and natural contexts.

An adaptation plan for the salt water intrusion into the coastal aquifer of Fano (PU, IT): management of risk in sea level rise scenarios (EU Interreg Asteris Project)

The analysis of pressures and impacts on the Apulian aquifers, as required by the EU WFD, has evidenced physical and chemical parameters related to groundwater salinization, particularly along the coastal strip. Predisposing factors such as lithology, tectonic evolution, aquifer over-exploitation (Passarella et al., 2017), and the ongoing climate change are various. Therefore, distinguishing natural from anthropogenic sources of salinization becomes a fundamental issue for assessing the aquifer's chemical status. In this framework, isotopic measures of O, H, B, and Sr, suitably support distinguishing different sources of salinity, water-rock interaction processes, and the origin of the water molecules (Pennisi et al., 2006). This study focuses on the coastal sector of the Murgia aquifer located on the Adriatic side of the Apulia region (south Italy). It is made up of several hundred-meter-thick Mesozoic calcareous and calcareous-dolomite rocks affected by fracturing and karst phenomena. The aquifer is confined and characterized by irregular geometry. Groundwater flows to the sea where it rises in numerous coastal springs. Paleo-seawater as an additional source of salinity has been suggested by previous studies.

A multi-isotope (O, H, B, Sr) approach for identifying salinity contamination along the coastal sector of Murgia aquifer (Apulia, Southern Italy)

Environmental Tritium is a powerful tracer of groundwater age and it is a key tracer of groundwater movement. Consequently, monitoring of Tritium concentration in groundwater can be a very useful tool for the determination of recent exchanges with surface water and for the presence and the traceability of anthropogenic contributions. Tritium (3H) is a radioactive isotope of hydrogen with a half-life of 12.3 years, which emits low- energy beta particles. It is a naturally occurring radionuclide through the interaction of high-energy cosmic rays with oxygen and nitrogen atoms in the upper atmosphere. The environmental levels of Tritium increased after nuclear weapon tests between 1945 and 1963, and after that it was mainly released from nuclear facilities, especially the heavy water reactor (HWR).However, Tritium concentrations in precipitation have exponentially declined over the past decades as the anthropogenic bomb tritium peak has all but disappeared. At the present, due to the natural decay of tritium and the prohibition of nuclear activities, the activity of tritium in water decreases year by year, and environmental tritium concentrations are close to natural levels of cosmic production. To detect low concentration of tritium in water, a certain degree of enrichment is essential to obtain adequate tritium count rates, through electrolytic system. The principle of electrolytic concentration of tritium is to use the isotope fractionation effect of hydrogen isotopes in the gas and liquid phases. Water samples contain mainly HHO, HDO and some HTO molecules, so by passing an electric current through a conductive water solution, the bonds of the water molecules are broken. Discharge of hydrogen from the cathode is highly isotope-selective for protium, thus, tritium and deuterium are concentrated, leaving most of the tritium in the residual water after reduction of the water sample. One method of 3H electrolytic enrichment was developed and implement in Italy by the ENEA’s Traceability Laboratory (FSN-SICNUC-TNMT – Brasimone research center). The ENEA electrolytic enrichment procedure, which precedes the counting of tritium by liquid scintillation counting (LSC), is performed by an electrolysis system consisting of 20 steel cells, a cooling system, a temperature control unit and three multiple distillation batches for the tritium samples. At present, given the decline in tritium activity in the atmosphere and hydrosphere, low tritium concentrations in groundwater can no longer be neglected, as they can be important indicators of anthropogenic pollutants. A good contribution to the assessment of the vulnerability of aquifers from anthropogenic impact could be offered by the determination of the low tritium in groundwater via the electrolytic enrichment methodology.

Electrolytic enrichment method for the determination of tritium in aquifers: tritium as an indicator of anthropogenic pollution

Dynamic fault strength t and its evolution with seismic slip and slip rate are among the most relevant parameters in earthquake mechanics. Given the large slip rate (up to 10 m/s), displacement (up to tens of meters), effective stress (tens of MPas), typical of seismic faulting, thermo-mechanical effects are outstanding: dynamic fault strength is affected by phase changes, extreme grain size reduction, and the production of amorphous and unstable materials in the slipping zone. In the first earthquake rupture models it was proposed that fault strength decreases inversely with slip rate (t ∼ 1/V, Burridge & Knopoff, 1967). Given the lack of determination of dynamic fault strength through seismological methods, elucidating constraints may arise from experimental studies. However, the experimental evidence for the strong dependence of fault friction with slip rate has been lacking for decades. After the preliminary studies of friction in rocks at seismic slip rates (Bridgman, 1936; Spray, 1987), it has been only with the installation of dedicated machines (Tullis & Weeks, 1986; Shimamoto & Tsutsumi, 1994) that the extreme deformation conditions achieved during earthquakes have been approached in the laboratory and systematically investigated. In 1997, Tsutsumi and Shimamoto reported the first data of dynamic fault strength in cohesive rocks at seismic slip rates: this study opened a new era in experimental rock deformation. Several fault dynamic weakening mechanisms first proposed theoretically (i.e., frictional melting lubrication and, more recently, fluid thermo-mechanical pressurization and elastohydrodynamic lubrication), were eventually reproduced in the laboratory (Cornelio et al., 2019; Aretusini et al., 2021). These experiments allowed us also to explore new dynamic fault weakening mechanisms and other will be probably discovered in the future. Nevertheless, the t ∼ 1/V relation was systematically observed, independently of the rock composition and presence of fluids (e.g., Di Toro et al., 2011). Nowadays, theoretical thermo-mechanical models, calibrated by experimental measures, enable us to construct constitutive equations for dynamic fault strength which find application into numerical modeling of earthquakes ruptures for both natural and human-induced seismicity (Murphy et al., 2018). Despite these recent advancements, the activation of several proposed dynamic fault weakening mechanisms and their occurrence in natural faults are debated. In this contribution, we will focus on the technical challenges and the main limitations (i.e., poor estimate of the temperature in the slipping zone, lack of in-situ observations during rock sliding, determination of the loading conditions that lead to the transition between concurrent dynamic weakening mechanisms, etc.) of the current experimental approach to unravel earthquake-related deformation mechanisms, and their application to the study of earthquakes in nature.

Friction during earthquakes: 25 years of experimental studies

Earthquakes can produce a wide spectrum of surface deformations associated with the main events or between inter-seismic periods. The larger events (Mw > 5.5) can trigger deformations such as surface ruptures related to the activation of main active faults and/or other deformations induced by seismic shaking (e.g. landslides, creeping, sink-hole). In the last three decades remote sensing acquisitions (e.g. Synthetic Aperture Radar Interferometry, Lidar differencing, optical imagery and GPS) have reached an impressive detail, useful for detecting high accuracy deformations. In particular, Differential SAR Interferometry (DInSAR), is one of the most powerful and reliable techniques to provide a snapshot of the coseismic deformation generated by earthquakes occurred within complex geological and morphological settings. In 2016-2017, a long earthquake sequence struck the Apennines in central Italy, producing impressive surface ruptures due to the activation of the SW-dipping extensional M. Vettore fault system (VF). Most of these ruptures are attributed to the 24 August Mw 6.0 and 30 October Mw 6.5 main-shocks and have been investigated by several groups of field geologists soon after the earthquakes. The complex distribution of the observed ruptures reflects the complexity of the geological setting of the epicentral area, where a succession of both carbonate and siliciclastic rocks crops out. Here we present detailed maps of the complex deformation pattern produced by the VF during the October 2016 earthquake in central Italy, derived from ALOS-2 SAR data via DInSAR technique. On these maps, we traced a set of sections to analyse the coseismic vertical displacement, necessary to identify both surface fault ruptures and off-fault deformations, the latter not directly recognizable in the field. At a local scale, we identified a large number of surface ruptures at an unprecedented level of details, improving those previously observed in the field. At a regional scale, the deformation pattern depicts a roll-over anticline, formed at the hangingwall of a main activated fault, with a listric geometry.  The rapid detection of deformation patterns from DInSAR technique can provide important constraints on the spatial distribution of the activated fault segments and their interaction. Such information can be crucial for emergency management by civil protection and helpful to drive and support the geological field surveys during the ongoing seismic crisis. These results demonstrate how the proposed approach can be applied for any worldwide earthquake, aimed to provide a wider and faster picture of the surface deformation in areas characterized by complex geology and morphology.

Seismotectonic analysis of the north-east sector of Calabrian Arc

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