Migliaccio, Federica

The activities for establishing the Italian Reference Gravity Network started in 2022. This is in line with the actions promoted by the International Association of Geodesy that during its 2015 General Assembly approved a resolution on the establishment of the new global gravity network the so-called International Terrestrial Gravity Reference System/Frame that will replace IGSN71. An initial set of 30 stations has been defined over the peninsular part of Italy and the two main islands of Sicily and Sardinia. Particularly, the GGOS core station of Matera (the Agenzia Spaziale Italiana Center for Space Geodesy “Bepi” Colombo) is one of the network points as required in the documents of the GGOS-Bureau of Networks and Observations. Thus, this station will provide one link between the Italian national absolute gravity network and the GGOS observation system of IAG. In order to ensure the measurements traceability, as required by the international standards on gravity measurements, the absolute gravimeters used in the measurements participated in international comparison campaigns. Absolute gravity measurements have been supplemented with direct measurements of the local value of the vertical gravity gradient, in order to reduce the absolute values, measured by different instruments at different heights, to an intermediate and common reference height and to the ground reference level to transport it to an external associated station. The gravity field campaigns have been assisted by topographic survey campaigns, allowing a centimetric georeferencing of the gravity stations to the current ITRF. The collected data will be then validated and reduced following the internationally accepted standards and finally published through a dedicate web page of the project. These data will also be submitted to the absolute gravity database maintained by the Bureau Gravimétrique International/Bundesamt fuer Kartographie und Geodaesie where the absolute gravity data that will contribute to the new global absolute gravity reference system are collected.

Studies regarding historical seismic events occurred during the pre-instrumental era are mostly based on the interpretation of coeval records reporting earthquake effects on humans and buildings as experienced and reported by witnesses. Historical sources typically consist of written documents such as letters, newspapers articles, chronicles and memoirs that survived the passage of time; from these documents and their historical context, seismologists isolate the relevant descriptive information on the effects of a seismic event in a place. This information is required to estimate a macroseismic intensity, in turn, used as input to assess the earthquake parameters such as the epicentre location and magnitude. Historical seismologists feel the need of a system for organizing the huge amount of data retrieved in their research, and able to keep trace of the complex relations among these data. A tool addressing these needs may well be used to perform the opposite action: being able to trace back each step of the research procedure, enabling seismologists checking the reliability of the background data, spotting potential errors or potential misinterpretations, and, possibly, to enrich and consolidate the description of an earthquake. This work, carried out with the collaboration of an experienced historical seismologist, investigates the peculiar needs of this field of research and proposes new tools, which are based on a Geographical Information System (GIS). Finally, a prototype system is presented. This solution enables to store, manage and analyse spatial and thematic data related to historical earthquakes, and integrates the relevant data resulting from seismic studies and from their original source documents. In particular, the conceptual model of the GIS spatial database is described and some examples of maps and queries are discussed for a case study represented by two earthquakes which occurred in Locris (Greece) on the 20th and 27th April 1894.