Seismic scattering and absorption of oceanic lithospheric Swaves in the Eastern North Atlantic

• Published in: Geophysical Journal International
• Main Authors: Hannemann, Katrin, Eulenfeld, Tom, Krüger, Frank, Dahm, Torsten
• Other Authors: Deutsche Forschungsgemeinschaft
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2021
• Subjects: Pacific; North Atlantic
• Online Access: http://dx.doi.org/10.1093/gji/ggab493; https://academic.oup.com/gji/advance-article-pdf/doi/10.1093/gji/ggab493/41512350/ggab493.pdf; https://academic.oup.com/gji/article-pdf/229/2/948/42334945/ggab493.pdf

SUMMARY The scattering and absorption of high-frequency seismic waves in the oceanic lithosphere is to date only poorly constrained by observations. Such estimates would not only improve our understanding of the propagation of seismic waves, but also unravel the small-scale nature of the lithosphere and its variability. Our study benefits from two exceptional situations: (1) we deployed over 10 months a mid-aperture seismological array in the central part of the Eastern North Atlantic in 5 km water depth and (2) we could observe in total 340 high-frequency (up to 30 Hz) Po and So arrivals with tens to hundreds of seconds long seismic coda from local and regional earthquakes in a wide range of backazimuths and epicentral distances up to 850 km with a travel path in the oceanic lithosphere. Moreover, the array was located about 100 km north of the Gloria fault, defining the plate boundary between the Eurasian and African plates at this location which also allows an investigation of the influence of an abrupt change in lithospheric age (20 Ma in this case) on seismic waves. The waves travel with velocities indicating upper-mantle material. We use So waves and their coda of pre-selected earthquakes to estimate frequency-dependent seismic scattering and intrinsic attenuation parameters. The estimated scattering attenuation coefficients are between 10−4 and 4 × 10−5 m−1 and are typical for the lithosphere or the upper mantle. Furthermore, the total quality factors for So waves below 5 Hz are between 20 and 500 and are well below estimates from previous modelling for observations in the Pacific Ocean. This implies that the Atlantic Ocean is more attenuative for So waves compared to the Pacific Ocean, which is inline with the expected behaviour for the lithospheric structures resulting from the slower spreading rates in the Atlantic Ocean. The results for the analysed events indicate that for frequencies above 3 Hz, intrinsic attenuation is equal to or slightly stronger than scattering attenuation and that the So-wave ...