Where do ocean microseisms come from? A study of Love‐to‐Rayleigh wave ratios. Issue 9 (27th September 2016)

• Record Type: Journal Article
• Authors: Juretzek, C.; Hadziioannou, C.
• Is Part Of: Journal of geophysical research. Volume 121:Issue 9(2016:Sep.)
• Page Start: 6741
• Page End: 6756
• Publication Date: 2016-09-27
• Subjects: seismic noise -- ocean microseism -- seismic noise sources; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2016JB013017
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Our knowledge of the origin of Love waves in the ambient seismic noise is extremely limited. This applies in particular to constraints on source locations and source mechanisms for Love waves in the secondary microseism. Here three‐component beamforming is used to distinguish between the differently polarized wave types in the primary and secondary microseismic noise fields, recorded at several arrays across Europe. We compare characteristics of Love and Rayleigh wave noise, such as source directions and frequency content, measure Love to Rayleigh wave ratios for different back azimuths, and look at the seasonal behavior of our measurements by using a full year of data in 2013. The beamforming results confirm previous observations that back azimuths for Rayleigh and Love waves in both microseismic bands mainly coincide. However, we observe differences in relative directional noise strength between both wave types for the primary microseism. At those frequencies, Love waves dominate on average, with kinetic Love‐to‐Rayleigh energy ratios ranging from 0.6 to 2.0. In the secondary microseism, the ratios are lower, between 0.4 and 1.2. The wave type ratio is directionally homogeneous, except for locations far from the coast. In the primary microseism, our results support the existence of different generation mechanisms. The contribution of a shear traction‐type source mechanism is likely. Key Points: Seismic noise source directions and Love‐to‐Rayleigh wave ratios determined by means of beamforming Love‐to‐Rayleigh ratio stronger in primary than in secondary microseism Ratios depend strongly on direction but stay stable over seasons