Abstract

The largest and longest ocean bottom seismometer (OBS) experiment so far in the Atlantic Ocean occurred as part of the UPFLOW project to better constrain upward mantle flow, which is crucial to understanding global mantle flow. UPFLOW deployed 50 and recovered 49 OBSs in a ~1,000 × 2,000 km² area in the Azores-Madeira-Canary islands region with a station spacing of ~110-160 km between June 2021 and August 2022. Most instruments had three-component broadband seismic sensors and hydrophones, and three different designs of OBS frames were used. Our analysis shows ~91% data completeness. Vertical-component long-period noise (T > ~30 s) is reduced compared to previous experiments. The orientations of horizontal components were estimated from the polarisation of long-period body and surface waves from teleseismic events. Earth’s free oscillations with frequencies as low as ~1.8 mHz are observed following two Mw > 8 earthquakes, and the signal-to-noise ratio of these observations is enhanced after applying tilt and compliance corrections. We show illustrative recordings and spectrograms of teleseismic and local events as well as non-seismic signals (whales, instrument resonances), demonstrating the wide variety and richness of UPFLOW data and their potential to address many outstanding questions in solid Earth sciences, oceanography, and marine biology.

Keywords: ocean bottom seismometers, UPFLOW, Atlantic Ocean, Azores, seismic noise, free oscillations