The Urban Seismic Observatory of Catania (Italy): A Real-Time Seismic Monitoring at Urban Scale

We describe the first dense real-time urban seismic–accelerometric network in Italy,
named OSU-CT, located in the historic center of Catania. The city lies in the region with the greatest
danger, vulnerability, and earthquake exposure in the entire Italian territory. OSU-CT was planned
and realized within the project called EWAS “an Early WArning System for cultural heritage”,
aimed at the rapid assessment of earthquake-induced damage and the testing of an on-site
earthquake early warning system. OSU-CT is mainly based on low-cost instrumentation realized
ad hoc by using cutting-edge technologies and digital MEMS (micro-electro-mechanical systems)
triaxial accelerometers with excellent resolution and low noise. Twenty of the forty scheduled
stations have already been set up on the ground floor of significant historic public buildings. In
order to assess the performance of an earthquake early warning (EEW) on-site system, we also
installed wide-band velocimeters (ETL3D/5s) in three edifices chosen as test sites, which will be
instrumented for a structural health monitoring (SHM). In addition to several laboratory and field
validation tests on the developed instruments, an effective operational test of OSU-CT was the Mw
4.3 earthquake occurring on 23 December 2021, 16 km west, south-west of Catania. Peak ground
accelerations (4.956 gal to 39.360 gal) recorded by the network allowed obtaining a first urban
shakemap and determining a reliable distribution of ground motion in the historical center of the
city, useful for the vulnerability studies of the historical edifices.

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