Moho Discontinuity Structure using Data from Land Stations and a Broad Atlantic OBS Network – Potential and Challenges

In northern Macaronesia in the Atlantic the Azores, Canaries and Madeira are three mantle upwelling surface expressions. While Madeira and the Canaries are located on old oceanic crust as intraplate hotspots (~135 Ma and 150-180 Ma), the Azores result from interaction between a hotspot and the Mid-AtlanticRidge and sit on younger crust (<50 Ma). Mantle upwellings can influence the subsurface discontinuity structure, including shallow crustal contributions, in an area that reaches beyond the locations of the islands into the offshore oceanic subsurface. Therefore, an observation of seismic crust and upper mantle properties in the whole region is key to understanding mantle dynamics and its effect on volcanism.

Since seismic stations are mostly found on land, offshore seismic measurements are more challenging and globally sparse. From 2021 to 2022 an OBS network was deployed in the oceanic region of northern Macaronesia by the UPFLOW project. This deployment enables, for the first time in this region, the investigation of discontinuity variations over a broad offshore area and their comparison with land-station observations from the islands.

With P-S receiver functions we obtain high-resolution point measurements of the Moho and further intercrustal and upper mantle discontinuities beneath 43 stations. We use frequencies of 0.4 to 3 Hz, but add higher frequency ranges to investigate the robustness. Furthermore, we compare frequency- and time-domain deconvolution techniques. Moho depths vary between 5 to 12 km, in some places over short length-scales, which could be linked to melt generation and composition changes. The crustal structure is more complex around the Azores region, reflecting the complex dynamics around the mantle upwellings. Oceanic noise levels, shallow subsurface structure, and thick sediments – particularly in the southeastern part of the region – pose additional challenges by causing receiver-function polarity flips and less well-defined converted-phase arrivals, which complicate interpretation.

This contributes to projects AMULETO (2022.06660.CEECIND) and GEMMA (DOI:10.54499/PTDC/CTA-GEO/2083/2021). This work is supported by FCT, I.P./MCTES through national funds (PIDDAC): LA/P/0068/2020 - https://doi.org/10.54499/LA/P/0068/2020 , UID/50019/2025,  https://doi.org/10.54499/UID/PRR/50019/2025, UID/PRR2/50019/2025.