Source directionality of ambient seismic noise inferred from three-component beamforming

The increased use of ambient seismic noise for seismic imaging requires better understanding of the ambient seismic noise wavefield and its source locations and mechanisms. Although the source regions and mechanisms of Rayleigh waves have been studied extensively, characterization of Love wave source processes are sparse or absent. We present here the first systematic comparison of ambient seismic noise source directions within the primary (~10-20 s period) and secondary (~5-10 s period) microseism bands for both Rayleigh and Love waves in the Southern Hemisphere using vertical- and horizontal-component ambient seismic noise recordings from a dense temporary network of 68 broadband seismometers in New Zealand. Our analysis indicates that Rayleigh and Love waves within the primary microseism band appear to be mostly generated in different areas, whereas in the secondary microseism band they arrive from similar backazimuths. Furthermore, the source areas of surface waves within the secondary microseism band correlate well with modeled deep-water and near-coastal source regions. Key Points Rayleigh and Love wave source regions of the secondary microseism are co-located Rayleigh and Love wave source regions of the primary microseism differ strongly Observed and modeled source directions for the secondary microseism agree well ©2012. American Geophysical Union. All Rights Reserved.