Martelli, Leonardo

David Glacier and Drygalski Ice Tongue are massive glaciers in Victoria Land, Antarctica. The ice from the East Antarctic Ice Sheet is drained through the former, and then discharged into the western Ross Sea through the latter. David Drygalski is the largest outlet glacier in Northern Victoria Land, floating kilometers out to sea. The floating and grounded part of the David Glacier are the main focus of this article. During the XXI Italian Antarctic Expedition (2005–2006), within the framework of the National Antarctic Research Programme (PNRA), two GNSS stations were installed at different points: the first close to the grounding line of David Glacier, and the second approximately 40 km downstream of the first one. Simultaneous data logging was performed by both GNSS stations for 24 days. In the latest data processing, the kinematic PPP technique was adopted to evaluate the dominant diurnal components and the very small semi-diurnal variations in ice motion induced by the ocean tide and the mean ice flow rates of both GNSS stations. Comparison of the GNSS time series with predicted ocean tide calculated from harmonic coefficients of the nearest tide gauge stations, installed at Cape Roberts and Mario Zucchelli Station, highlight different local response of the glacier to ocean tide, with a minor amplitude of vertical motion at a point partially anchored at the bedrock close to the grounding line. During low tide, the velocity of the ice flow reaches its daily maximum, in accordance with the direction of seawater outflow from the fjord into the ocean, while the greatest daily tidal excursion generates an increase in the horizontal ice flow velocity. With the aim to extend the analysis in spatial terms, five COSMO-SkyMED Stripmap scenes were processed. The comparison of the co-registered offset tracking rates, obtained from SAR images, with the GNSS estimation shows good agreement.

Da venerdì 4 novembre a domenica 6 novembre 2022, si è tenuta una esercitazione nazionale denominata “Exe Sisma dello Stretto 2022” in un'area del territorio della Regione Calabria e della Regione Sicilia caratterizzata da una elevatissima pericolosità sismica. L’esercitazione è stata indetta e coordinata dal Dipartimento della Protezione Civile e aveva l’obiettivo di verificare la risposta operativa a un evento sismico significativo del Servizio Nazionale della Protezione Civile, di cui anche l’Istituto Nazionale di Geofisica e Vulcanologia fa parte. Durante le tre giornate, l’INGV ha avuto modo di testare tutte le procedure che l’Istituto ha codificato a partire da quelle del “Protocollo di Ente per le emergenze sismiche e da maremoto”. Dopo che INGV ha dato l’avvio all’intera esercitazione simulando il terremoto di magnitudo MW 6.2 (ML 6.0) alle ore 09:00 UTC in provincia di Reggio Calabria (5 km a SW dal comune di Laganadi), e ha, quindi, inviato il messaggio per il potenziale maremoto con un livello di allerta arancione; inoltre, il Presidente INGV ha prontamente convocato l’Unità di Crisi e attivato tutti Gruppi Operativi. Questi ultimi, nell’ambito dello scenario esercitativo, hanno verificato che i flussi di comunicazione interna e tutte le attività necessarie in emergenza sismica, presenti nei relativi protocolli operativi, risultassero rispettati. L’obiettivo primario dell’esercitazione è stato quindi quello di validare le attività previste e di aggiornare il personale afferente ai Gruppi Operativi stessi. Tra di essi, SISMIKO, che rappresenta il GO dedicato al coordinamento delle reti sismiche mobili INGV in emergenza, nelle settimane precedenti l’esercitazione ha predisposto tutte le attività che intendeva testare, descrivendole brevemente nel Documento d’impianto INGV e con maggior dettaglio in quello del Gruppo Operativo. A pochi giorni dalla chiusura dell’esercitazione, un terremoto di magnitudo ML 5.7 (MW 5.5) registrato alle ore 06:07 UTC del 09 novembre 2022 ha spostato l’attenzione dalla simulazione alla realtà.

In this work we present and discuss new geodetic velocity and strain-rate fields for the Euro-Mediterranean region obtained from the analysis of continuous GNSS stations. We describe the procedures and methods adopted to analyze raw GPS observations from >4000 stations operating in the Euro-Mediterranean, Eurasian and African regions. The goal of this massive analysis is the monitoring of Earth’s crust deformation in response to tectonic processes, including plate- and micro-plate kinematics, geodynamics, active tectonics, earthquake-cycle, but also the study of a wide range of geophysical processes, natural and anthropogenic subsidence, sea-level changes, and hydrology. We describe the computational infrastructure, the methods and procedures adopted to obtain a threedimensional GPS velocity field, which is used to obtain spatial velocity gradients and horizontal strain-rates. We then focus on the Euro-Mediterranean region, where we discuss the horizontal and vertical velocities, and spatial velocity gradients, obtained from stations that have time-series lengths longer than 6 and 7 years, which are found to be the minimum spans to provide stable and reliable velocity estimates in the horizontal and vertical components, respectively. We compute the horizontal strain-rate field and discuss deformation patterns and kinematics along the major seismogenic belts of the Nubia-Eurasia plate boundary zone in the Mediterranean region. The distribution and density of continuous GNSS stations in our geodetic solution allow us to estimate the strain-rate field at a spatial scale of ~27 km over a large part of southern Europe, with the exclusion of the Dinaric mountains and Balkans.

Massive analysis of GNSS data (Global Navigation Satellite System) requires the development of specific tools to automate the different steps of processing: from data download to ground displacements estimates. In this technical report we describe the tools and algorithms we have developed to handle the metadata associated with GNSS observations from continuous networks operating in the EuroMediterranean and African area, which are routinely processed by the three main INGV data analysis centers. Obtaining accurate metadata, which records information on how a GNSS station is equipped (receiver, antenna, monument, etc..), is mandatory in order to obtain accurate GNSS stations daily position and their evolution through time. Here we will describe the processing chain, the software developed using opensource programming language, describing the major issues found in treating incomplete, inconsistent or wrong information, and the methods adopted to minimize or resolve these problems. The software developed is going to be implemented in the centralized GNSS data and metadata archive that we are realizing at INGV, and that will serve both institutional activities and research projects. The goal of this tool is to minimize errors and reduce/avoid the human intervention in handling a large set of information, facilitating the automatic analysis of data from thousands of GNSS stations on a daily basis. The software acronym is pyGLogDB, which stands for: “python GNSS Logfile elaboration with the support of DataBase”.

The Global Navigation Satellite System (GNSS) represents a primary data source in Solid Earth Sciences. In order to investigate the Earth’s crustal deformation, time series of the estimated daily positions of the stations are routinely analyzed at the Istituto Nazionale di Geofisica e Vulcanologia (INGV) to investigate the deformation of the Earth’s surface caused by tectonic and non-tectonic processes. The GNSS observations of the stations are processed using the three main scientific software: GAMIT/GLOBK, BERNESE, and GIPSY OASIS II. The accuracy and the strength of geodetic solutions often depend on the geometry and spatial density of the network, and the availability and quality of GNSS data. In many circumstances, GNSS networks are deployed for topographic purposes by private or public institutions, and a significant number of GNSS stations in large regions acquire continuous observations. It may happen that such networks do not collect and distribute data according to IGS standards, so it could be difficult to analyze this data using automated data-processing tools. For that reason, this data is often ignored or partially used by the scientific community, despite their potential usefulness in geodynamic studies. We have attempted troubleshooting this problem by establishing a centralized storage facility in order to collect all available GNSS data and standardize both formats and metadata information. Here we describe the processes and functions that manage this unified repository, called MGA (Mediterranean GNSS Archive), which regularly collects GNSS RINEX files from alarge number of CORS (Continuously Operating Reference Station) located across a wide region of mainly the European and African plates. RINEX observation data and metadata information are provided to the analysts through an FTP server and dedicated web-services. The complete data set is stored in a PostgreSQL database in order to easily retrieve pieces of information and efficiently manage the archive content. The system implements many high-level services that include scripts to download files from remote archives and to detect new available data, web applications such as API (Application Program Interface) to interact with the system, and background services that interact with the database. During the development of this product, particular attention was paid to what has already been achieved by EPOS TCS WP10, whose objective was: "[...] to develop an open source platform with programmatic and web interfaces to store and disseminate raw data and metadata from GNSS stations operating in Europe''. Many ideas and tools presented here were inspired by that project.

The atmospheric humidity in the Polar Regions is an important factor for the global budget of water vapour, which is a significant indicator of Earth’s climate state and evolution. The Global Navigation Satellite System (GNSS) can make a valuable contribution in the calculation of the amount of Precipitable Water Vapour (PW). The PW values retrieved from Global Positioning System (GPS), hereafter PWGPS, refer to 20-year observations acquired by more than 40 GNSS geodetic stations located in the polar regions. For GNSS stations co-located with radio-sounding stations (RS), which operate Vaisala radiosondes, we estimated the PW from RS observations (PWRS). The PW values from the ERA-Interim global atmospheric reanalysis were used for validation and comparison of the results for all the selected GPS and RS stations. The correlation coefficients between times series are very high: 0.96 for RS and GPS, 0.98 for RS and ERA in the Arctic; 0.89 for RS and GPS, 0.97 for RS and ERA in Antarctica. The Root-Mean-Square of the Error (RMSE) is 0.9 mm on average for both RS vs. GPS and RS vs. ERA in the Arctic, and 0.6 mm for RS vs. GPS and 0.4 mm for RS vs. ERA in Antarctica. After validation, long-term trends, both for Arctic and Antarctic regions, were estimated using Hector scientific software. Positive PWGPS trends dominate at Arctic sites near the borders of the Atlantic Ocean. Sites located at higher latitudes show no significant values (at 1σ level). Negative PWGPS trends were observed in the Arctic region of Greenland and North America. A similar behaviour was found in the Arctic for PWRS trends. The stations in the West Antarctic sector show a general positive PWGPS trend, while the sites on the coastal area of East Antarctica exhibit some significant negative PWGPS trends, but in most cases, no significant PWRS trends were found. The present work confirms that GPS is able to provide reliable estimates of water vapour content in Arctic and Antarctic regions too, where data are sparse and not easy to collect. These preliminary results can give a valid contribution to climate change studies.

In Antarctica, the severe climatic conditions and the thick ice sheet that covers the largest and most internal part of the continent make it particularly difficult to systematically carry out geophysical and geodetic observations on a continental scale. It prevents the comprehensive understanding of both the onshore and offshore geology as well as the relationship between the inner part of East Antarctica (EA) and the coastal sector of Victoria Land (VL). With the aim to reduce this gap, in this paper multiple geophysical dataset collected since the 1980s in Antarctica by Programma Nazionale di Ricerche in Antartide (PNRA) were integrated with geodetic observations. In particular, the analyzed data includes: (i) Geodetic time series from Trans Antarctic Mountains DEFormation (TAMDEF), and Victoria Land Network for DEFormation control (VLNDEF) GNSS stations installed in Victoria Land; (ii) the integration of on-shore (ground points data and airborne) gravity measurements in Victoria Land and marine gravity surveys performed in the Ross Sea and the narrow strip of Southern Ocean facing the coasts of northern Victoria Land. Gravity data modelling has improved the knowledge of the Moho depth of VL and surrounding the offshore areas. By the integration of geodetic and gravitational (or gravity) potential results it was possible to better constrain/identify four geodynamic blocks characterized by homogeneous geophysical signature: the Southern Ocean to the N, the Ross Sea to the E, the Wilkes Basin to the W, and VL in between. The last block is characterized by a small but significant clockwise rotation relative to East Antarctica. The presence of a N-S to NNW-SSE 1-km step in the Moho in correspondence of the Rennick Geodynamic Belt confirms the existence of this crustal scale discontinuity, possibly representing the tectonic boundary between East Antarctica and the northern part of VL block, as previously proposed by some geological studies.