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SUMMARY:Imaging metallic deposits using ambient seismic noise - Yihe Xu\, 
 Bullard Laboratories
DTSTART:20220202T160000Z
DTEND:20220202T170000Z
UID:TALK169544@talks.cam.ac.uk
CONTACT:Florian Millet
DESCRIPTION:High-frequency seismic surface waves sample the top few tens o
 f meters to the top few kilometres of the subsurface. They can be used to 
 determine 3-D distributions of shear-wave velocities and to map the depths
  of discontinuities (interfaces) within the crust. Passive seismic imaging
 \, using ambient noise as the source of signal\, can thus be an effective 
 tool of exploration for mineral\, geothermal and other resources\, provide
 d that sufficient high-frequency signal is available in the ambient noise 
 wavefield and that accurate\, high-frequency measurements can be performed
  on this signal. Ambient noise imaging using the ocean-generated noise at 
 5–30 s periods is now a standard method\, but less signal is available a
 t frequencies high enough for deposit-scale imaging (0.2–30 Hz)\, and fe
 w studies have reported successful measurements in broad frequency bands. 
 Here\, we develop a workflow for the measurement of high-frequency\, surfa
 ce wave phase velocities in very broad frequency ranges. Our workflow comp
 rises (1) a new noise cross-correlation procedure that accounts for the no
 n-stationary properties of the high-frequency noise sources\, removes band
 pass filtering\, replaces temporal normalization with short time window st
 acking\, and drops the explicit spectral normalization by adopting cross-c
 oherence\; (2) a new phase-velocity measurement method that extends the ba
 ndwidth of reliable measurements by exploiting the (resolved) 2π ambiguit
 y of phase- velocity measurements and (3) interstation-distance-dependent 
 quality control that uses the similarity of subgroups of dispersion curves
  to reject outliers and identify the frequency ranges with accurate measur
 ements. The workflow is highly automated and applicable to large arrays. A
 pplying our method to data from a large-N array that operated for one mont
 h near Marathon\, Ontario\, Canada\, we use rectangular subarrays with 150
 -m station spacing and\, typically\, 1 hr of data and obtain Rayleigh-wave
  phase-velocity measurements in a 0.5–30 Hz frequency range\, spanning o
 ver 5.9 octaves\, twice the typical frequency range of 1.5–3 octaves in 
 previous studies. Phase-velocity maps and the subregion-average 1-D veloci
 ty models they constrain show a high-velocity anomaly consistent with the 
 known\, west-dipping gabbro intrusions beneath the area. The new structura
 l information can improve our understanding of the geometry of the gabbro 
 intrusions\, hosting the Cu-PGE Marathon deposit.
LOCATION:ONLINE - Details to be sent by email
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