Tracking paths of ocean source ambient seismic noise into and through the Earth

Posted by pkm at Mar 15, 2015 01:35 PM |
Anya M. Reading (1), Martin Gal (1), Peter E. Morse (1), Keith D. Koper (2), Mark A. Hemer (3), Nicholas Rawlinson (4), Michelle Salmon (5), Marthijn de Kool (6) & Brian L. N. Kennett (5) - (1) University of Tasmania; (2) University of Utah; (3) CSIRO, Australia; (4) University of Aberdeen; (5) Australian National University; (6) Geoscience Australia

Array measurements of seismic noise (microseisms) are emerging as independent observables that inform our knowledge of ocean storms.  Using an improved implementation of IAS Capon analysis, we can infer the location and amplitude of multiple sources of seismic noise over multiple decades.  For the Southern Ocean, we can use seismic records to assist in identifying shifting patterns of ocean storms.  Thus we can investigate topics such as the disparity between wave height trends identified using calibrated satellite records, which appear to be in increasing over multiple decades, and wave heights measured directly using a wave-rider buoy, which does not show a significant change over the same time frame.  The passage of wave energy from the water column to the solid Earth, and through the 3D Earth to the seismic array must be tracked effectively.

In this contribution, we focus on understanding the passage of seismic noise through the 3D Earth.  In particular, we investigate path deviations from 1D Earth models for body waves sources from a variety of locations in the Southern Ocean recorded at Australian seismic arrays.  We also investigate path deviations of surface waves travelling across the Australian continent, using the AusREM Earth model.  Employing a wavefront tracking technique, fast marching, that can support heterogeneous structure and the consideration of multiple arrivals, we find that storms in some locations are subject to a much larger deviation from the expected path of energy through a 1D Earth.  We also find that, given the extended source characteristics of ocean storms, focusing and defocusing effects have a significant impact on the pattern of seismic noise observed at a given array.  The interplay between these multiple factors results in 'sweet spots': locations in the ocean where storms are very well observed for a particular array.

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