PSI - Issue 78

Alessandra Marino et al. / Procedia Structural Integrity 78 (2026) 1753–1758

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that is breaking) to the seismic station. The first waves that arrive at a station are the so called “P waves” that travel at 3-4 miles per sec, on average. The large amplitude (more damaging) “S waves” travel at ~ 2 miles per second. Therefore, the closer a station is to the fault, the more rapidly the earthquake can be detected. Accurate detections often depend on multiple ground motion measurements (multiple measurement stations) station; so, increasing the density of stations near the fault can improve detection times. Data from multiple stations must be collected and analyzed by the regional seismic networks, so ground motion information must be transferred from the station to the processing center. Existing networks use several methods to send data back to the server to improve robustness, including radio links, phone lines, public/private internet, and satellite links. Seismic signals received from the stations are used in real time to detect if an earthquake is occurring and to determine the location and magnitude of the event. The most important component of an earthquake early warning system is a dense network of seismic and geodetic stations with robust communications. Additional sources of ground motion observations (GPS sensors) can be integrated in the EW algorithms and may be able to help in reducing the time for detecting and improve early estimates of earthquake magnitude and location. Off-site systems can be integrated by low cost on site sensors like lower-resolution strong motion seismometers. These sensors use micro-electro-mechanical systems (Fig.1) accelerometers. These low-cost sensors can be hosted in industrial sites, providing, “live” information and activating automatic alert and mitigation systems. It is easy to recognize that the greater the early warning time is, the stronger the possibility of preventing damages to plant installations and possibly mitigating the effects of an earthquake. 4. Early Warning Systems Some sensors (fiber optic sensors and MEMS: Micro-Electro-Mechanical-System) integrated in structural health monitoring (SHM) systems are already applied for the identification of the damage and the release of substances. Their application is generally confined to structural health monitoring (SHM: Structural Health Monitoring) but can also be applied in case of earthquakes. This kind of systems are called Early Warning (EW) and imply the use of sensors for the identification and control of the release of substances, but also of sensors for the evaluation of seismic intensity level in real-time. The advantages in using these systems are clear: the permanent monitoring of critical components of a plant allows, on one hand to plan the maintenance operations, and on the other hand to develop decision making systems able to limit the consequences in case of seismic events. These Early Warning (EW) sensors can be implemented in a smart system and linked to PCS (process control system) in order to detect immediately the effects of an earthquake on industrial plant components and eventually to activate automatically safety systems aimed at controlling major accident hazards and at limiting consequences. These sensors are often used in wireless networks. The placement of sensors must derive from an appropriate risk analysis as described above. 4.1. Deformations and displacements detectors The electrical or optical fiber extensometer are instruments for detecting deformations and displacements of the elements and they are able to detect compressions and/or elongations in the structures. They can be of the mono or triaxial type and work in the temperature range -269 ÷ 950 ° C. 4.2. Leakage detectors Mid-Infrared spectrometer is a system for detection leakage in remote and continuous mode, based on a tunable source of the DFG (Difference Frequency Generation). This system works in chemically aggressive environments and in the presence of different substances and operates in the spectral region between 2.9 and 3.445 micron. The laser spectrometer is able to measure methane, nitrogen dioxide, nitrous oxide, water vapor, ammonia, sulfuric acid, methane.