Near-surface structure of the Sodankylä area in Finland, obtained by passive seismic interferometry
<p>Controlled-source seismic exploration surveys are not always possible in nature-protected areas. As an alternative, the application of passive seismic techniques in such areas can be proposed. In our study, we show results of passive seismic interferometry application for mapping the upperm...
| Main Authors: | , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-07-01
|
| Series: | Solid Earth |
| Online Access: | https://se.copernicus.org/articles/12/1563/2021/se-12-1563-2021.pdf |
| Summary: | <p>Controlled-source seismic exploration surveys are not
always possible in nature-protected areas. As an alternative, the application of
passive seismic techniques in such areas can be proposed. In our study, we
show results of passive seismic interferometry application for mapping the
uppermost crust in the area of active mineral exploration in northern
Finland. We utilize continuous seismic data acquired by the Sercel Unite
wireless multichannel recording system along several profiles during XSoDEx
(eXperiment of SOdankylä Deep Exploration) multidisciplinary geophysical
project. The objective of XSoDEx was to obtain a structural image of the
upper crust in the Sodankylä area of northern Finland in order to
achieve a better understanding of the mineral system at depth. The key
experiment of the project was a high-resolution seismic reflection
experiment. In addition, continuous passive seismic data were acquired in
parallel with reflection seismic data acquisition. Due to this, the length
of passive data suitable for noise cross-correlation was limited from
several hours to a couple of days. Analysis of the passive data demonstrated
that dominating sources of ambient noise are non-stationary and have
different origins across the XSoDEx study area. As the long data registration
period and isotropic azimuthal distribution of noise sources are two major
conditions for empirical Green function (EGF) extraction under the diffuse
field approximation assumption, it was not possible to apply the
conventional techniques of passive seismic interferometry. To find the way
to obtain EGFs, we used numerical modelling in order to investigate
properties of seismic noise originating from sources with different
characteristics and propagating inside synthetic heterogeneous Earth models
representing real geological conditions in the XSoDEx study area. The
modelling demonstrated that scattering of ballistic waves on irregular shape
heterogeneities, such as massive sulfides or mafic intrusions, could
produce a diffused wavefield composed mainly of scattered surface waves. In
our study, we show that this scattered wavefield can be used to retrieve
reliable EGFs from short-term and non-stationary
data using special techniques. One of the possible solutions is application
of “signal-to-noise ratio stacking” (SNRS). The EGFs calculated for the
XSoDEx profiles were inverted, in order to obtain S-wave velocity models
down to the depth of 300 m. The obtained velocity models agree well
with geological data and complement the results of reflection seismic data
interpretation.</p> |
|---|---|
| ISSN: | 1869-9510 1869-9529 |