Ambient noise H/V spectral ratio and its application for estimating thickness of overburden in XSoDEx project

• Main Author: Karjalainen, J. (Jari)
• Format: Dissertation
• Language: English
• Published: University of Oulu 2019
• Online Access: http://jultika.oulu.fi/Record/nbnfioulu-201908062744

Abstract. This study is about Horizontal-to-Vertical Spectral Ratio (HVSR) analysis and its application for estimating thickness of overburden in northern part of Fennoscandian Shield. Data from Experiment of Sodankylä Deep Exploration (XSoDEx) project was used for HVSR analysis. The XSoDEx project was mainly active seismic survey done in collaboration of Geological Survey of Finland (GTK), TU Bergakademie Freiberg (TUBAF) and the University of Oulu. The main purpose of this study was to apply HVSR method to continuous three-component seismic data recorded during the XSoDEx survey and investigate what kind of estimations of overburden thickness could be obtained by this technique. The results of HVSR analysis were also compared to geological data about thickness and composition of superficial deposits acquired by GTK. Oulu University took part in XSoDEx seismic survey with 39 three-component and 59 one-component seismic receivers. Recording of ambient seismic noise was successfully performed in parallel with active seismic survey, which was the primary task. The stations were deployed along the survey lines with 160 m spacing. One exception was made along so-called high-resolution line, where the receivers were deployed with 10 m spacing. HVSR analysis was done with Geopsy open source software and the results of analysis were utilized in interpretation of overburden thickness. The interpretation also required estimation of S-wave velocity, which was obtained by utilizing in situ reference data of bedrock contacts by GTK and by calculating the S-Wave velocity from estimations of P-wave velocity reported in literature. Comparison of the results of HVSR analysis to geological information demonstrated clear H/V spectral peaks being obtained mostly for the stations located at sites with diamicton sediment type, while for stations located at sites with other types of sediments the H/V spectral peaks are less reliable. Flat H/V curves were obtained as an indication of bedrock being near the surface. Estimations for thickness of overburden were done for diamicton, but the results have to be treated with caution due the uncertainties of information about S-wave velocity.