Gauci, Adam

Microseism is the most continuous and ubiquitous seismic signal on the Earth and is caused by the interaction between the atmosphere, the hydrosphere and the Solid Earth. In literature, there are several studies that deal with the relationship between microseism and cyclonic activity considering in particular hurricanes, tropical cyclones and typhoons. However, the relationships between microseism and the small-scale tropical cyclones that occur in the Mediterranean Sea, called Medicanes, have never been analysed. For this reason, we considered the Medicane Apollo, which developed in the Ionian Sea and impacted the eastern part of Sicily during the period 25th October to 5th November 2021 causing heavy rainfall (> 400 mm/48h), strong wind gusts (104 km/h) and violent sea waves (significant wave height > 3.5 m). Furthermore, the heavy rainfall induced by the presence of Apollo, caused damage to infrastructure and agriculture forcing the Sicilian regional government to declare a state of emergency for 32 municipalities (in the provinces of Catania, Messina, Siracusa and Ragusa) that were mostly affected by the Medicane Apollo.In this work, we analysed the microseism signal recorded by 78 seismic stations installed in South Italy, Malta and Greece coastline during the period under investigation. To obtain information about the significant wave heights, we consider the data obtained by hindcast maps and four wavemeters buoys. The spectral and amplitude analysis allowed us to obtain information about the space-time variations of the microseism amplitude and in addition, we were able both to differentiate the seismic stations that perceive Apollo (stations installed close to the Ionian Sea), the seismic stations that do not perceive the medicane (stations installed close to the Tyrrhenian sea) and the microseism bands influenced by the presence of the Medicane Apollo. Moreover, we tracked the position of the Apollo by using two different methods: i) grid search method based on the seismic amplitude decay using the 78 seismic stations first mentioned and ii) array technique by 15 seismic stations installed on Etna which may be considered an array thanks to their spatial distribution and geometry. We obtain a good match between the real positions of the Medicane Apollo derived from satellite images and the positions computed by the two analysis methods. This work shows that it is possible to extract information about the Mediterranean extreme meteo-marine events from microseism, a seismic signal that until not long ago was considered as noise, both for monitoring and research purposes.

In the last decades, the frequency of extreme weather and marine events has drastically increased. During the last week of October 2021 an intense Mediterranean hurricane (Medicane), named Apollo, affected many countries on the Mediterranean coasts. Eight people died as a consequence of the floodings from the cyclone in the countries of Tunisia, Algeria, Malta, and Italy. A preliminary search for possible signatures of the Apollo Medicane by meteorological satellite, radar HF, marine buoy, and seismic data is performed. This was done in a framework of an international collaboration between Italian and Maltese partners for the monitoring of the sea state in scenarios of climate change. The experimental results confirm, at this preliminary stage, the possibility and the usefulness of jointly looking at such phenomena with multiple aims of retrieving a more robust characterization, having a backup alternative in case a primary monitoring network gets failure, and pathing the way to heuristic and data-driven analytical and predictive approaches to Medicanes issues.

Microseism is the continuous background seismic signal caused by the interaction between the atmosphere, the hydrosphere and the solid Earth. Several studies have dealt with the relationship between microseisms and the tropical cyclones, but none focused on the small-scale tropical cyclones that occur in the Mediterranean Sea, called Medicanes. In this work, we analysed the Medicane Apollo which impacted the eastern part of Sicily during the period 25 October-5 November 2021 causing heavy rainfall, strong wind gusts and violent sea waves. We investigated the microseism accompanying this extreme Mediterranean weather event, and its relationship with the sea state retrieved from hindcast maps and wave buoys. The spectral and amplitude analyses showed the space-time variation of the microseism amplitude. In addition, we tracked the position of Apollo during the time using two different methods: (i) a grid search method; (ii) an array analysis. We obtained a good match between the real position of Apollo and the location constraint by both methods. This work shows that it is possible to extract information on Medicanes from microseisms for both research and monitoring purposes.

i-waveNET project is deploying measurement networks of the sea state in the Mediterranean. Several marine monitoring technologies will be integrated. In particular, HF radar, wave-buoys, seismographs, and tide gauges will be integrated with numerical models establishing a new integrated monitoring system. All the information provided will be analyzed with the aim of setting a Decision System Support (DSS). The DSS will support stakeholder activities to mitigate the coastal risks linked to extreme events, by providing useful information such as marine bulletins and GIS thematic maps.