A new approach to determine surface-wave attenuation from seismic
ambient noise: numerical validation and application
Abstract
We validate a new method to determine surface-wave attenuation from
seismic ambient noise, both numerically and by application to recordings
from a dense broadband array. We generate synthetic recordings of
numerically simulated ambient seismic noise in several experimental
setups, characterized by different source distributions and different
values of attenuation coefficient. We use them to verify that: (I)
“cross-terms” cancel out, as predicted by the theory; (II) the source
spectrum can be reconstructed from ambient recordings, provided that the
density of sources and the attenuation coefficient are known; (III) true
attenuation can be retrieved from normalized cross correlations of
synthetic signals. We then apply the so validated method to real
continuous recordings from 33 broadband receivers distributed within the
Colorado Plateau and Great Basin. A preliminary analysis of the
signal-to-noise ratio as a function of azimuth reveals a SW-NE
preferential directionality of the noise sources within the secondary
microseism band (6-29 8 s), as previously reported by other authors. By
nonlinear inversion of noise data we find the attenuation coefficient in
the area of interest to range from ∼ 1 × 10 −5 m−1 at 0.3 Hz to ∼ 4.5 ×
10 −7 m−1 at 0.065 Hz, and confirm the statistical robustness of this
estimate by means of a bootstrap analysis. This result is compatible
with previous observations made on the basis of both
earthquake-generated and ambient Rayleigh waves. In this regard, the new
method proves to be promising in accurately quantifying surface wave
attenuation at relatively high frequencies.