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Abstract

Ultra-slow spreading ridges are characterized by huge volcanic complexes which are separated by up to 150 km long amagmatic segments. The mechanisms controlling these types of mid-oceanic ridges (MOR) are not yet fully understood. We aim to constrain the crustal and mantle structure beneath a segment of the Knipovich ridge (Greenland Sea) by using Receiver functions calculated from teleseismic events. Seismic data, recorded on the ocean bottom, are highly contaminated by different noise sources. Results of our noise reduction algorithm based on harmonic-percussive separation (HPS) techniques of selected KNIPAS station data show a significantly reduced noise level on all three seismometer components (below 1 Hz). Improving the SNR on OBS records reveals the superposition of water and sediment reverberations on the crustal structure information, the latter is strongly hindering the structure interpretation. Here, we compare the real data with a set of synthetic Receiver functions for better analysis of the lithospheric structure. The results of the real data stacks reveal two discontinuities beneath the ridge shoulders: (i) at depths of around 8 km, which can be most likely associated with a Moho, (ii) at depths of around 30 km, which can be linked with the lithosphere- asthenosphere boundary. The center of the MOR and the Logachev seamount are characterized by a strong low-velocity zone at depths of up to 20 km. Comparing the depths of the mantle transition zone discontinuities from KNIPAS data and land station data indicates a low velocity layer east of the Knipovich ridge in the uppermost mantle.