Abstract
Abstract. The Gulf of Cadiz, as part of the Azores-Gibraltar plate boundary, is recognized as a potential source of big earthquakes and tsunamis that may affect the bordering countries, as occurred on 1 November 1755. Preparing for the future, Portugal is establishing a national tsunami warning system in which the threat caused by any large-magnitude earthquake in the area is estimated from a comprehensive database of scenarios. In this paper we summarize the knowledge about the active tectonics in the Gulf of Cadiz and integrate the available seismological information in order to propose the generation model of destructive tsunamis to be applied in tsunami warnings. The fault model derived is then used to estimate the recurrence of large earthquakes using the fault slip rates obtained by Cunha et al. (2012) from thin-sheet neotectonic modelling. Finally we evaluate the consistency of seismicity rates derived from historical and instrumental catalogues with the convergence rates between Eurasia and Nubia given by plate kinematic models.
Highlights
Introduction and geodynamic settingThe Gulf of Cadiz is known to be the source area for the 1 November 1755 destructive earthquake and tsunami that affected Portugal, southwestern Spain and northern Morocco
According to Zitellini et al (2009) the SWIM (SouthWest Iberian Margin) lineaments could represent the transition from a diffuse plate boundary (Sartori et al, 1994; Hayward et al, 1999) to a discrete transform fault zone setting
We will estimate the recurrence of large earthquakes in the area using the fault slip-rates inferred from the thin-sheet neotectonic modelling of Cunha et al (2012), we will explore the derived model to evaluate the consistency of seismicity rates computed from historical and instrumental catalogues with the convergence rates between Eurasia and Nubia given by plate kinematic models
Summary
The Gulf of Cadiz is known to be the source area for the 1 November 1755 destructive earthquake and tsunami that affected Portugal, southwestern Spain and northern Morocco. In an effort to evaluate the likelihood of the different seismotectonic settings proposed for the Gulf of Cadiz, Cunha et al (2012) applied the thin-sheet modelling methodology developed by Bird (1999) to estimate seismic strain rates, stress orientations, fault slip rates and local velocities that could be compared to observations These authors observed that the consistency between model and observations indicates that forcing by slab sinking beneath Gibraltar is not required to reproduce current horizontal deformation in these areas. We will estimate the recurrence of large earthquakes in the area using the fault slip-rates inferred from the thin-sheet neotectonic modelling of Cunha et al (2012), we will explore the derived model to evaluate the consistency of seismicity rates computed from historical and instrumental catalogues with the convergence rates between Eurasia and Nubia given by plate kinematic models. The generation model presented may have other future applications, such as for Probabilistic Seismic Hazard Assessment, for Probabilistic Tsunami Hazard Assessment or for the computation of synthetic strong motion records (like in Carvalho et al, 2008)
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