Performance of an impact-based Earthquake Early Warning System in the Alboran Sea

Earthquakes Early Warning Systems (EEWS) are one of the most effective tools to prevent and mitigate the damage that can be caused by earthquakes. Since October 2015, the Department of Earth Physics and Astrophysics of the Complutense University of Madrid has implemented an operational EEWS throughout the Ibero–Maghrebian Region (IMR). This system is based on the PRESTo (Probabilistic and Evolutionary Early Warning SysTem, Satriano et al. [2011]) software. Currently, a new EEWS (QuakeUp, Zollo et al. [2023]) based on the progressive temporal prediction of ground motion (‘’shaking’’) is being implemented in the same department. Not only does it provide an early determination of the hypocenter and magnitude, like the current EEWS, but the new method also combines Peak Ground Velocity (PGV) predictions calculated from observed P-wave amplitudes and region-specific Ground Motion Prediction Equation (GMPE) for the IMR, while using progressively updated estimates of earthquake location and magnitude.  As a result, it provides an ‘early’ P-wave-based shake map that is updated over time, offering a real-time, evolving map of the Potential Damage Zone (PDZ) defined as those zones where the Instrumental Intensity (I_MM), calculated in terms of PGV, exceeds a previously defined threshold. This EEWS method has been validated using data from the 2016 Alboran Sea seismic series (M_w 5.0–6.4), which showed minimal discrepancies in origin time, epicenter location, and magnitude estimates compared to previous studies. A retrospective performance analysis for the M_w 6.4 main shock indicated lead-times of 14 to 62 s at a PGV threshold of 0.20 cm/s, with lead-times increasing with distance. At a higher threshold of 0.60 cm/s, the lead-time was 20 seconds for distances up to 170 km. The accuracy of impact predictions improved over time, with successful alerts rising from 72% to 90% as the final predictions were made. Despite some limitations due to focusing on moderate-magnitude earthquakes (M_w ≤ 6.4), the EEWS method has proven effective for offshore events in areas with sparse instrumentation.