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Active Seismicity Around a Cretaceous Magmatic Intrusion in Monchique, SW Iberia

Monchique is a prominent topographic high in SW Iberia (Europe) that reaches a maximum altitude of 902 m, standing out from the surrounding plane of southern Portugal. It is located to the north of the Eurasia-Africa plate boundary, which locally accommodates a low rate oblique convergence (~5 mm/yr). At the surface Monchique shows alkaline magmas that intruded during the Late Cretaceous, following the break-up of Pangea. Monchique is a well-known region of hydrothermal activity, with several natural springs and an active natural water bottling industry and spa services. Monchique also hosts the most active seismic cluster in mainland Portugal when considering the number of earthquakes. However, most earthquakes in Monchique are of low magnitude (<M4) and no active seismic faults are mapped in Monchique.

In this work, we present the results of geophysical modelling of the Monchique magmatic intrusion. In particular, we present the results of magmatic and gravity modelling based on locally collected data. The magnetic data was collected using a drone, which allowed for an improved coverage of the region. The seismicity was relocated using NonLinLoc, which implements a non-linear probabilistic inversion methodology, and an appropriate 3D regional tomographic model. We find that earthquakes align along 4 main lineations that radiate outwards from the intrusion. We also find that the intrusion is limited to the topmost 8 km below the surface and that most earthquakes occur below this depth. We discuss the relationship between the seismicity and the magmatic intrusion, as well as the roles of hydrothermal fluids and the nearby plate boundary in facilitating and driving the seismicity of Monchique.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020), LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020) and project RESTLESS (PTDC/CTA-GEF/6674/2020, http://doi.org/10.54499/PTDC/CTA-GEF/6674/2020).

Session: Tectonics and Seismicity of Stable Continental Interiors - III

Type: Oral

Room: Tubughnenq’ 5

Date: 5/3/2024

Presentation Time: 03:00 PM (local time)

Presenting Author: Susana Custódio

Student Presenter: No

Additional Authors