Four Years of Earthquake Early Warning in Southern Iberia: 2016–2019

Marta Carranza,Elisa Buforn,Aldo Zollo,Irene Torrego,Maurizio Mattesini

doi:10.3389/feart.2021.696191

Abstract

The performance of an earthquake early warning system (EEWS) for southern Iberia during the period of 2016–2019 is analyzed. The software PRESTo (PRobabilistic and Evolutionary early warning SysTem; the University of Naples Federico II, Italy) operating at the Universidad Complutense de Madrid has detected 728 events (2 &lt; Mw &lt; 6.3), with 680 earthquakes occurring in southern Iberia. Differences between the EEWS origin time and epicenter and those of the Instituto Geográfico Nacional (IGN) catalog are less than 2 s and 20 km, respectively, for 70% of the detected earthquakes. The main differences correspond to the EEWS magnitude that is underestimated for earthquakes that occurred at the west of the Gibraltar Strait (Mw differences larger than 0.3 for 70%). To solve this problem, several relationships have been tested, and a modification to those that currently use PRESTo is proposed. Other improvements, such as to densify the network or to use 3D Earth models, are proposed to decrease the time needed to issue the alert and avoid the false alerts (19 events over a total of 728 events). The EEWS has estimated the depth for 680 events and compared to those from the IGN (491 events). The performance of PRESTo during the 2020–2021 Granada swarm is analyzed. The hypocentral locations for the three largest earthquakes are close to those from the IGN (differences from 1 to 7 km for the epicenter and 0 s for the time origin), although there are some differences in their magnitude estimations that varies from 0.2 to 0.5. The PRESTo first times are 17, 25, and 41 s after the origin time. This study shows that the actual PRESTo EEWS configured for the southern Iberia may generate effective warnings despite the low seismicity rate in this region. To decrease the warning time, the geometry and density of the seismic network must be improved together with the use of 3D Earth models and on-site system approaches.

Highlights

Many large earthquakes have occurred in southern Iberia, located at the plate boundary between Eurasia and Africa, some of which caused severe damage and generated devastating tsunamis [Lisbon 1755, Imax X; Saint Vincent Cape (SVC), 1969 Mw 7.8; Boumerdes 2003, Mw 6.8; Figure 1]
To mitigate the damage generated by earthquakes in the region, the Universidad Complutense de Madrid (UCM) has led two projects to study the feasibility of an earthquake early warning system (EEWS) in the region, namely, the ALERTES (2011–2013) and the ALERTES-RIM (2014–2016) projects, with the participation of the Real Instituto y Observatorio de la Armada, San Fernando (ROA), and the Institut Geologic de Catalunya (IGC, ICGC) (Buforn et al, 2016; Carranza et al, 2017)
The PRESTo software installed at UCM began its operations on October 9, 2015, and 768 earthquakes were detected until

Summary

Introduction

Many large earthquakes have occurred in southern Iberia, located at the plate boundary between Eurasia and Africa, some of which caused severe damage and generated devastating tsunamis [Lisbon 1755, Imax X; Saint Vincent Cape (SVC), 1969 Mw 7.8; Boumerdes 2003, Mw 6.8; Figure 1]. The 20th century has not been very seismically active, with a deficit of large earthquakes (Buforn et al, 2015). Earthquake Early Warning in Southern Iberia as the one observed in the 2016 Alboran Sea (Mw 6.4, Buforn et al, 2017; Stich et al, 2020). The aim of an EEWS is to provide warnings within a few seconds after the occurrence of an earthquake prior to the arrival of the strong shaking, S-wave, at a target site. From the first few seconds of signal receipt, generally 3 s, the system ideally generates a warning before the arrival of the S wave motion at a target location (Wu and Kanamori, 2005; Zollo et al, 2010)

Results

Discussion

Conclusion