Abstract
Abstract. Studying the uppermost structure of the subsurface is a necessary part of solving many practical problems (exploration of minerals, groundwater studies, geoengineering, etc.). The practical application of active seismic methods for these purposes is not always possible for different reasons, such as logistical difficulties, high cost of work, and a high level of seismic and acoustic noise. That is why developing and improving passive seismic methods is one of the important problems in applied geophysics. In our study, we describe a way of improving the quality of empirical Green's functions (EGFs), evaluated from high-frequency ambient seismic noise, by using the advanced technique of cross-correlation function stacking in the time domain (in this paper we use term “high-frequency” for frequencies higher than 1 Hz). The technique is based on the global optimization algorithm, in which the optimized objective function is a signal-to-noise ratio of an EGF, retrieved at each iteration. In comparison to existing techniques, based, for example, on weight stacking of cross-correlation functions, our technique makes it possible to significantly increase the signal-to-noise ratio and, therefore, the quality of the EGFs. The technique has been tested with the field data acquired in an area with a high level of industrial noise (Pyhäsalmi Mine, Finland) and in an area with a low level of anthropogenic noise (Kuusamo Greenstone Belt, Finland). The results show that the proposed technique can be used for the extraction of EGFs from high-frequency seismic noise in practical problems of mapping of the shallow subsurface, both in areas with high and low levels of high-frequency seismic noise.
Highlights
Seismic methods as tools for studying the shallow subsurface structures in exploration geophysics have been developed for many years
We describe a way of improving the quality of empirical Green’s functions (EGFs), evaluated from high-frequency ambient seismic noise, by using the advanced technique of crosscorrelation function stacking in the time domain
The errors that inverse S transforms may introduce to subsequent phase-velocity measurements were analysed in Li et al (2018). Another approach, based on stacking only cross-correlation functions of highly coherent signals, was used in global-scale coda wave interferometry studies (Boué et al, 2014). These algorithms do not use signal-to-noise ratios (SNRs) of cross-correlation functions for improving the final EGF, and it is assumed that signal coherence by itself is a guarantee that all non-suitable cross-correlation functions are either excluded from the final stack or minimized by using weights, and the SNR is automatically improved
Summary
Seismic methods as tools for studying the shallow subsurface structures in exploration geophysics have been developed for many years. The errors that inverse S transforms may introduce to subsequent phase-velocity measurements were analysed in Li et al (2018) Another approach, based on stacking only cross-correlation functions of highly coherent signals, was used in global-scale coda wave interferometry studies (Boué et al, 2014). These algorithms do not use signal-to-noise ratios (SNRs) of cross-correlation functions for improving the final EGF, and it is assumed that signal coherence by itself is a guarantee that all non-suitable cross-correlation functions are either excluded from the final stack or minimized by using weights, and the SNR is automatically improved This may be true for teleseismic coda wave interferometry (Phm et al, 2018), in which source location is a priori known and it is easy to control that only signals within the so-called “stationary phase” area are cross-correlated (Wapenaar et al, 2010). We present details of this algorithm and illustrate its performance using passive seismic ambient noise data acquired in two areas of Fennoscandia: Pyhäsalmi mine (as an example of area with a high level of industrial noise) and the Kuusamo Greenstone Belt area (a quiet area prospective for new mining projects (Weihed et al, 2005; Lehtonen and O’Brien, 2009)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
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 call
