Following the Mw 5.5 earthquake that occurred in the southern Tyrrhenian Sea today, 23 October 2026, at 12:19 Italian time, the INGV Tsunami Warning Centre (CAT) sent an Information message to the Italian Civil Protection Department (DPC) at 12:23 regarding the potential tsunami threat.
The initial message was based on the rapid calculation of the earthquake magnitude (estimated at 5.7) and hypocentral coordinates. The operational procedure is designed to issue any potential tsunami warning as quickly as possible, consistent with the data available at the time.
Subsequently, at 12:29, the CAT sent an updated message to the DPC, raising the alert level to Advisory (orange alert). This meant that a small tsunami could potentially occur, with wave heights below 50 cm and an expected run-up of less than 1 metre .
The messages were also sent to Mediterranean countries receiving bulletins from CAT-INGV, which acts as a UNESCO Tsunami Service Provider for the Mediterranean region.
As required by SiAM procedures, the DPC forwarded the message to local authorities and all components of Italy’s national civil protection system.
Under these procedures, CAT personnel on duty 24/7 at the Seismic Surveillance Room in Rome subsequently assess whether a tsunami has occurred or is underway along the coastlines closest to the earthquake epicentre. The initial assessment, based on sea-level data from the Strombolicchio and Ginostra tide gauges operated by ISPRA , ruled out an ongoing tsunami in the southern Tyrrhenian Sea. A third message cancelling the alert was therefore issued at 13:22.
Today's event, 23 October 2026, is the first event in the Mediterranean region to be handled by the CAT since the new procedure for tsunami alert level assessment, based on Probabilistic Tsunami Forecasting (PTF), became operational. PTF is a probabilistic method that estimates the probability of an earthquake generating a tsunami and assesses its potential impacts along the coast, taking into account uncertainties related to tsunami generation and wave propagation.
The internal CAT procedures for calculating earthquake parameters and assessing the potential tsunami impact, as well as the procedures for transmitting messages to the DPC and from the DPC to the relevant authorities and stakeholders, worked very well. This event can therefore be considered a successful test of the system.