The analysis of data recorded by seismic stations during the landslide that hit the island of Ischia in 2022 provides new perspectives for the development of early warning systems in case of potentially destructive geological events.
Three years after the mudslide that hit the town of Casamicciola on the island of Ischia on 26 November 2022, a study has shown how the instrumental networks normally used to study earthquakes and volcanoes could also prove fundamental for analyzing the dynamics of potentially destructive events such as landslides and to plan early warning systems.
The work, entitled “Tracking the November 26, 2022, Casamicciola debris flow through seismic signals (Ischia, southern Italy)”, was conducted by a team of researchers from theNational Institute of Geophysics and Volcanology (INGV) and University of Camerino and analyzed the massive mudslide, triggered by exceptionally heavy rains, which hit Casamicciola on November 26, 2022, causing 12 deaths and the evacuation of more than 200 people, as well as widespread damage to buildings and infrastructure.
“Our study represents one of the few documented cases in which the high-frequency shaking and changes in ground inclination produced by a natural event of this type have been recorded and studied.”, explains Stephanie Danesi, first researcher at INGV. "Data recorded by seismic stations permanent INGV have in fact highlighted the detachment and evolution of the flow from the very first moments, allowing us to reconstruct the different phases of the landslide".
“Seismic waveform analysis It has allowed us to locate in time and space the origins of the multiple detachments and to estimate both the mass of the material mobilized both the speed instantaneous flow propagation (between 10 and 15 meters per second at the moment of impact with the buildings), as well as the size of the largest boulders, which reached 3 meters in diameter”, he adds Stefano Carlino, researcher at INGV. “The calculated impact pressures are consistent with the damage observed in the Celario area, where the landslide caused the greatest damage.”.
The research, published in the scientific journal 'Landslides', highlights the potential of multi-parameter networks as a basis for future early warning systemsAccording to the authors, installing a dedicated network of seismometers and tiltmeters on this side of the island of Ischia could provide a window of several tens of seconds between the triggering of the phenomenon and its impact on residential areas, a valuable timeframe for activating warning systems. In particular, given the relatively small size of the landslide front affecting the area, this timeframe would allow for the implementation of evacuation procedures for the most exposed population.
“Our work highlights how seismological methods allow us to dynamically follow the evolution of potentially catastrophic landslides and obtain quantitative information useful for risk mitigation. In a context of climate change, with increasingly frequent extreme weather events, having dedicated monitoring networks could be a significant step towards ensuring greater safety for the communities most exposed to this type of risk.he concludes Nicola Alessandro Pino, Full Professor at the School of Science and Technology of the University of Camerino.
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Figure 1: Overview. a) Topography of the island of Ischia. The blue triangles indicate the seismic stations of the National Seismic Network that recorded the landslide. The black box delimits the perimeter of the area c). b) The mudflow impacting the buildings. The photo, by the Forio CB Protezione Civile association, is taken from the website https://www.chiesaischia.it/comunicato-emergenza-2022/. c) Zoom in on the affected area. The yellow/orange polygon is the area invaded by the mudflow, detected by Copernicus. The most significant damage occurred along the orange branch, particularly in the Celario area. The dashed line and red dots mark the actual path of the landslide, used for modeling, from the origin (A) to the point of closest approach to the IOCA station (B). The stars are the seismic locations of the 3 subsequent landslides (F1, F2, F3), with the related uncertainties.
Figure 2Observed data and results. On the left, observed data. The time axis, common to all measurements, is expressed in UTC time and in seconds after midnight. a) Rainfall measurement, in mm, recorded every 10 minutes at the Monte Epomeo rain gauge (black line) and cumulative (red line). b) - d) Ground velocity observed at the IOCA seismic station, in the horizontal and vertical components. F1, F2, F3 are the signals of 3 successive landslides. e) - g) Ground acceleration (in gray) observed at the IOCA seismic station in the horizontal and vertical components. In red, the same acceleration signal filtered over a long period. On the right, results. Distance of the landslide front from IOCA, over time, obtained from modeling. Variation in the approach velocity of the landslide front (black) over time, and corresponding topographic elevation (orange) measured on the actual path of the landslide.