Abstract
Abstract. 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.
Highlights
Exploration of new mineral deposits is an important task because the modern world needs many types of minerals for functioning (Reid, 2011)
Passive seismic interferometry is a cost-efficient methodology with a relatively simple setup of field experiments. This methodology allows for retrieving impulse response of a medium, called an empirical Green function (EGF), from ambient seismic noise recorded at two receivers, assuming that the noise field is diffuse (Lobkis and Weaver, 2001; Campillo and Paul, 2003)
We show results of application of passive seismic interferometry for mapping the uppermost crust in the XSoDEx study area
Summary
Exploration of new mineral deposits is an important task because the modern world needs many types of minerals for functioning (Reid, 2011). Passive seismic interferometry is a cost-efficient methodology with a relatively simple setup of field experiments This methodology allows for retrieving impulse response of a medium, called an empirical Green function (EGF), from ambient seismic noise recorded at two receivers, assuming that the noise field is diffuse (Lobkis and Weaver, 2001; Campillo and Paul, 2003). If this condition is satisfied, it is possible to retrieve both surface and body waves from seismic noise using either cross-correlation, autocorrelation, deconvolution or cross-coherence of seismic records (Wapenaar et al, 2011). We show results of application of passive seismic interferometry for mapping the uppermost crust in the XSoDEx study area
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
