Italy is investigating the potential tsunami threat

Simulations of underwater earthquakes and landslides in the Ionian Sea found they could generate tsunami waves up to 2.5 meters high in southern Italy.

Written by Laura Fattarusso, Simpson Strong-Tie Fellow (@labtalk_laura)

Citation: Fattarusso, L., 2024, Italy investigates potential tsunami threat, Temblor, http://doi.org/10.32858/temblor.340

Earthquakes and landslides in the Ionian Sea could trigger tsunamis up to 2.5 meters (8 feet) high on the southern coast of Italy, according to tsunami models presented at the American Geophysical Union fall meeting in December 2022 in Chicago and published in a recent report from the Ministry of Ecological Transition. Italian. The study focused on the coastal city of Crotone, in Italy's Calabria region, also known as the “toe” of the shoe-shaped peninsula.

The study area is located offshore southern Italy. The locations of three potential landslides (CMS, CCS, CRS) and five potential earthquakes (F1-F5) are indicated as blue stars, with magnitudes ranging from 6.0 to 6.9 (for F1-5, magnitudes are 6.5, 6.9, 6.0, 6.7). , 6.8, respectively). Credit: Galeotti et al. 2022

why worry?

Italy is no stranger to earthquakes or tsunamis. Records dating back to Roman times reveal devastating tsunamis that inundated coastal communities. One such tsunami occurred in 2002 when the eruption of Stromboli volcano triggered landslides that displaced enough water into the Tyrrhenian Sea to produce two tsunamis, with waves rising as high as 10 meters (33 ft) on the island. Volcanic activity, marine earthquakes and landslides were responsible for causing tsunamis in Italy every few decades in the 20th century.

A view of the coastal city of Crotone (Calabria region, southern Italy) where researchers simulated tsunami scenarios. Credit: AlMare, CC BY-SA 2.5 via Wikimedia Commons

Spurred by increased gas extraction in the Adriatic, Ionian and Mediterranean Seas by Italy and other Mediterranean countries, the Italian Ministry of Ecological Transition funded a study to explore the potential effects of tsunami-generating earthquakes and landslides. The idea is that increased drilling and extraction in a tectonically active region could trigger earthquakes on pre-existing faults, which could generate tsunamis, and trigger underwater landslides that generate tsunamis.

Modeling different scenarios

In the first phase of a three-phase research project, researchers estimated the probability of earthquakes occurring on offshore faults. “Earthquake scenarios are based on local structures that have been studied and identified,” explain Filippo Zaniboni and Alberto Armiliato, geophysicists at the University of Bologna in Italy, who co-authored the tsunami study. The researchers also mapped unstable underwater slopes that could collapse in the event of a landslide. Earthquake and landslide hazards have the potential to move large amounts of water, causing tsunamis. This investigation included the entire Italian coast, providing a broader preliminary assessment of the background tsunami risk associated with natural causes (see Antoncecchi et al., 2020).

Five tsunami wave height scenarios based on undersea earthquakes. The epicenters of the earthquakes in the scenario are marked with a yellow star and have magnitudes of 6.5, 6.9, 6.0, 6.7, and 6.8, respectively. The F2 scenario produces the largest wave along the coast. Scenarios F4 and F5 are different magnitude earthquakes on the same fault structure. Credit: Galeotti et al. 2022

In the second phase of the project, the study focused on a specific site, namely the coastal stretch around Crotone. Zaniboni and his colleagues simulated tsunami scenarios to see how much flooding the coast could experience. They modeled tsunamis caused by a variety of potential underwater earthquake and landslide scenarios.

While earthquakes are a common cause of landslides, many other mechanisms can contribute to the collapse of underwater slopes, Zaniboni says. For unstable subsea slopes, water intrusion, sea level changes, underwater currents, and the presence of gas can all contribute to slope instability, which can lead to landslides.

The researchers looked at three possible landslide scenarios. Two of the scenarios involve larger displaced volumes (about 0.4-0.5 km3, or 14-15 billion cubic feet) and occur offshore, at underwater depths of 750-1,250 m (2,500 to 4,100 ft). The third scenario was a smaller landslide scenario (about 0.2 cubic kilometers or 7 billion cubic feet) located near the shore (at depths of about 400-700 meters, or 1,300 to 1,700 feet).

In their model, the larger wave was produced by the smaller landslide. While the two larger landslides are “slump-like” scenarios where the entire earth mass moves at once as a single unit and then stops, the smaller landslide was expected to behave as a debris flow, a type of landslide that typically maintains higher velocities over over a longer period. The smaller landslide also showed more complex dynamics because it would travel along an underwater valley causing it to speed up and slow down several times.

Earthquake scenarios ranged from magnitude 6.0 to 6.9 and could produce waves up to 2 meters (6.6 feet) high. Landslides, which can be triggered by earthquakes or other processes, can generate larger tsunami waves, up to 2.5 meters (8 feet) high. While none of the simulated tsunamis would be catastrophic, Zaniboni points out that local features such as harbor basins and estuaries could enhance tsunamis and cause larger floods. He points out that a more detailed study of the most affected coastal areas could provide better estimates of how the tsunami would affect Crotone and its port.

Three tsunami wave height scenarios generated from underwater landslide simulations. Landslide areas are marked in purple. The smallest and shallowest landslides, CCS, produce the largest wave along the coast. Credit: Galeotti et al. 2022

Tsunami risk assessment

“It's a powerful set of models; “It works well,” says Elena Soleimani, a tsunami modeler at the Alaska Earthquake Center at the University of Fairbanks, Alaska. But Soleimani says she is not aware of any tsunami caused by extraction. For example, decades of offshore drilling in offshore Alaska have not caused tsunamis.

Offshore gas storage was blamed for hundreds of small earthquakes in Spain in 2013, and the Netherlands has seen several small quakes after decades of drilling for natural gas. In the Midwestern United States, there has been a significant rise in earthquakes induced by wastewater injection associated with hydraulic fracturing or “fracking” of natural gas—a special process of extracting gas from tight reservoirs.

Although Ionian Sea tsunami research is motivated by concerns about offshore drilling, earthquake and landslide scenarios are based on existing faults and underwater cliffs. These natural conditions could cause tsunamis regardless of gas extraction in the area, according to Zaniboni. These tsunami scenarios will now be passed on to regional city planners and engineers who can assess the tsunami threat. The third phase of the project will include looking at ways to protect coastal communities.

References

Antoncecchi, I., Ciccone, F., Dialuce, G., Grandi, S., Terlizzese, F., Di Bucci, D.,…& Prota, A. (2020) – SPOT Project – Earthquakes potentially triggered by water Marine and tsunami. Integrated project end report. DOI: 10.5281/zenodo.3732887 ISBN 9788894366945 (in Italian). Gallotti, G., Armigliato, A., Zaniboni, F., Angeli, C., Zanetti, M, Argnani, A., and Rovere, M. (2022 ) Tsunami scenarios off the coast of Calabria, Ionian Coast, Italy. American Geophysical Union Fall Meeting, December 2022, Chicago, IL, USA.

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