[S-SS03] Seismological advances in the ocean

[SSS03-10] The UPFLOW experiment: Peeking from the sea floor to the deep mantle with an ∼1,500 km aperture array of 50 ocean bottom seismometers in the mid-Atlantic

★Invited Papers

*Ana Ferreira¹, Maria Tsekhmistrenko², Miguel Miranda³, UPFLOW team (1.University College London, UK, 2.ERP, UK, 3.Air Centre, Atlantic International Centre, Portugal)

Keywords:Ocean Bottom Seismology, Mantle upwelling, Atlantic ocean, Teleseismic body-wave tomography

Imaging deep upward mantle flow is key for understanding global mantle flow and to link the Earth’s deep interior with the surface. Yet, plume-like mantle upwellings that connect the deepest mantle to the surface are poorly understood. As part of the UPFLOW project funded by the European Research Council (2021-2025) we conducted the largest and longest amphibian passive seismic experiment done so far in the Atlantic. We focused on the Azores-Madeira-Canary Islands region, which is a unique natural laboratory with multiple upwellings that are poorly understood. UPFLOW deployed 50 and recovered 49 ocean bottom seismometers (OBSs) in a ∼1,000×2,000 km2 area starting in July 2021 for ∼13 months, with an average station spacing of ∼200 km. Most of the instruments had three-component broadband (120s) seismic sensors and hydrophones, and three different designs of OBS frames were used. Our analysis shows 94% UPFLOW data completeness. Noise of vertical component long-period data (T>~30s) is notably decreased compared to previous experiments. Horizontal component data enable the estimation of seismometer orientations using body and surface waves from 149 earthquakes. Earth's free oscillations with frequencies as low as ~1.8~mHz are observed following two Mw > 8 earthquakes and are enhanced after applying tilt and compliance corrections. We show illustrative high-quality recordings and spectrograms of teleseismic and local events and non-seismic signals (whales, instrument resonances). We then present initial results from multi-frequency (T~2.7 – 30 s) teleseismic body P-wave tomography combining over 5 million global measurements from the ISC database with over 100,000 measurements from the UPFLOW project and surrounding permanent and temporary land stations, which greatly enhance the data coverage and resolution in the study region. We interpret our results in terms of possible lateral connections between mantle upwelling beneath the Canaries and the Azores archipelago, as well as with the African low velocity province, and discuss their geodynamical implications.