Seismic Attenuation From Ambient Noise Across the North Sea Ekofisk Permanent Array

Abstract

Quality factor (Q) or equivalently attenuation α=1Q describes the amount of energy lost per cycle as a wave travels through a medium. This is important to correct seismic data amplitudes for near‐surface effects, to locate subsurface voids or porosity, to aid seismic interpretation, or for characterizing other rock and fluid properties. Seismic attenuation can be variable even when there are no discernible changes in seismic velocity or density (Yıldırım et al., 2017, https://doi.org/10.1016/j.jappgeo.2016.11.010) and so provides independent information about subsurface heterogeneity. This study uses ambient noise recordings made on the Ekofisk Life of Field Seismic array to estimate Q structure in the near surface. We employ the method of X. Liu et al. (2015, https://doi.org/10.1093/gji/ggv357), which uses linear triplets of receivers to estimate Q—ours is the first known application of the method to estimate the Q structure tomographically. Estimating Q requires an estimate of phase velocity which we obtain using the method of Bloch and Hales (1968, https://pubs.geoscienceworld.org/ssa/bssa/article-abstract/58/3/1021/116607/) followed by traveltime tomography. The Q structure at Ekofisk has features which can be related to local geology, showing that surface ambient noise recordings may provide a new and robust method to image Q. Our results suggest that there is a nonlinear relationship between Q and compression. They also may explain why it has been found that in the period range of 1 to 2 s considered here, ambient noise cross correlations along paths that span the North Sea Basin are unreliable: Such Q values would attenuate almost all ambient seismic energy during such a traverse.

Quantifying the Effects of Nondiffuse Noise on Ballistic and Coda Wave Amplitude From Variances of Seismic Noise Interferometry in Southern California

“…The phase measurements with uncertainties (Text S3) from the ballistic wave are useful to constrain phase velocity and anisotropy (Lin et al, 2008;Zigone et al, 2015). The amplitude uncertainty directly propagates to the aleatory uncertainty in ground motion prediction based on virtual earthquake approach (Denolle et al, 2013;Prieto et al, 2009), and it is also useful for attenuation and site amplification studies (Bowden et al, 2015;Curtis et al, 2018;Lin et al, 2012;Liu et al, 2015). In addition, the bootstrap method can be applied toward estimating the spatial distribution of uncertainty in the noise sources.…”

Effect of lateral heterogeneity on 2-D Rayleigh wave ZH ratio sensitivity kernels based on the adjoint method: Synthetic and inversion examples

“…However, the effectiveness of this method in real practice still requires more study because of the difficulty of extracting stable ZH ratio measurements from a single source–station pair. Similarly, using amplitude information from an ambient noise cross‐correlation is not always reliable (Allmark et al, 2018).…”

1‐D, 2‐D, and 3‐D Monte Carlo Ambient Noise Tomography Using a Dense Passive Seismic Array Installed on the North Sea Seabed

“…We picked phase velocities and group velocities for each station-pair, which can then be used to perform phase or group velocity tomography. Group velocity tomography can be conducted using straight-ray tomography since the data accuracy usually does not merit a more sophisticated approach and since an accurate phase velocity map is not available in order to trace rays to allow group velocity to be calculated along rays (de Ridder & Dellinger, 2011;Mordret, Landès, et al, 2013;Allmark et al, 2018). However, since that the phase velocity measurements are more accurate than group velocities (Yao et al, 2006) and since Eikonal tomography is more efficient and more accurate than straight- Figure 6.…”

“…This method has been used widely to study the regional scale structure of crust and uppermost mantle (N. M. Shapiro et al, 2005;Yao et al, 2006;Lin et al, 2007Lin et al, , 2009Y. Yang et al, 2007;Yao & Van Der Hilst, 2009;Bensen et al, 2009;Behr et al, 2010;Nicolson et al, 2012Nicolson et al, , 2014 and the near surface uppermost crustal structure (de Ridder & Dellinger, 2011;de Ridder & Biondi, 2013;Mordret, Landès, et al, 2013;Mordret, Landès, et al, 2014;de Ridder et al, 2014de Ridder et al, , 2015Allmark et al, 2018).…”