EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Two decades of seismicity in the West Iberian Margin: current hypothesis and new ideas

Gabriela Fernandez Viejo1, Carlos Lopez-Fernandez1, and Patricia Cadenas2
Gabriela Fernandez Viejo et al.
  • 1Dept. of Geology, University of Oviedo, Spain (
  • 2Earth Sciences Dept., Memorial University of Newfoundland, St. Johns, Canada

The analysis of two decades (2003-2022) of seismicity recorded by the Spanish and Portuguese seismic networks along the West Iberian passive margin results in a picture of the clustered and moderate seismicity observed in this intraplate submarine area.

The study precise the trend of specific alignments, providing an accurate depiction of event distribution along two stripes 700 km long through the ocean floor in WNW-ESE direction. These alignments are parallel to the Africa-Eurasia plate boundary, but distinctly separated from its related seismicity ≈300 and ≈700 km respectively, enough distance to be considered as intraplate.

When trying to relate this seismicity to structural, and/or geophysical features, it doesn’t arise a conclusive picture. The earthquakes occur indiscriminately across thinned continental, hyperextended, and exhumed mantle rift domains. They fade out in the proximity of undisputed oceanic crust, but some events extend beyond. The hypocentral depths signal a considerable amount of events nucleating in the upper mantle. The focal mechanisms are predominantly strike-slip and a superposition of the event map with geophysical data shows a puzzling lack of affinity with any of them.

Considering these observations, different hypothesis are discussed to explain this relatively anomalous distribution of seismicity. Some of them previously advanced in the literature do not portray convincing arguments. Others are too unspecific. None of them are completely flawless, suggesting that maybe there is several factors at play. Despite being one of the most probed passive margins in the world, the present geodynamical state of the West Iberian Margin manifested in its modern seismicity, seems to remain unknown.

Interpreting these data within a global tectonic plate framework, together with the potential addition of sea bottom seismometers may give the key to understand this activity along one of the most archetypical margins of the Atlantic Ocean.

How to cite: Fernandez Viejo, G., Lopez-Fernandez, C., and Cadenas, P.: Two decades of seismicity in the West Iberian Margin: current hypothesis and new ideas, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11824,, 2023.