A Threshold-Based Earthquake Early-Warning System for Offshore Events in Southern Iberia

Abstract

The south of the Iberian Peninsula is a region situated at the convergence of the Eurasian and African plates. This region experiences large earthquakes with a long separation in time, the best known of which is the great 1755 Lisbon Earthquake (i.e., maximum macroseismic intensity, Imax=X), which occurred SW of San Vicente Cape (SW Iberian Peninsula). The high risk of damaging earthquakes has recently lead Carranza et al. (2013) to investigate the feasibility of an EEWS in this region. The analysis of the geometrical situation between the Iberian seismic networks and the San Vicente Cape area led the authors to conclude that a threshold-based approach, which would not require the real-time location of the earthquake, might be the best option for EEWS in SW Iberia. The current work explores this hypothesis, and proposes a new EEW approach that extends the standard P-wave threshold based single station analysis to the whole network. The proposed method allows the real-time estimation of the potential damage at stations that are triggered by P-waves, as well as at the not-triggered ones, giving the advantage of a greater lead-time for the release of alerts. Results of tests made with synthetic data mimicking the scenario of the great 1755 Lisbon Earthquake, and those obtained by applying the new approach to available recordings, indicate that an EEW estimation of the potential damage associated with an event in the San Vicente Cape area can be obtained for a very large portion of the Iberian Peninsula.