Imaging the Nechako Basin, British Columbia, using ambient seismic noise

• Published in: Canadian journal of earth sciences Vol. 48; no. 6; pp. 1038 - 1049
• Main Authors: Idowu, O. A, Frederiksen, A. W, Cassidy, J. F
• Format: Journal Article
• Language: English
• Published: Ottawa National Research Council of Canada 01.06.2011; NRC Research Press; Canadian Science Publishing NRC Research Press
• Subjects: applied (geophysical surveys & methods); Basins; Bouguer anomalies; British; British Columbia; Canada; Canadian Cordillera; Canadian National Seismograph Network; data processing; Dispersions; Economic geology; elastic waves; energy sources; Evaluation; geophysical methods; geophysical surveys; Geophysics; gravity anomalies; gravity methods; Green function; Green's functions; guided waves; Igneous rocks; Intermontane Belt; inverse problem; Inversions; Lithosphere; Methods; Nechako Basin; Noise; North America; North American Cordillera; one-dimensional models; Outcrops; petroleum; petroleum exploration; Rayleigh waves; Sedimentary basins; Seismic exploration; Seismic tomography; seismic waves; Seismology; Surface waves; surveys; thickness; tomography; two-dimensional models; velocity structure; Volcanic rocks; Volcanoes; Western Canada; Canada; British Columbia Canada; Nechako River
• ISSN: 0008-4077; 1480-3313
• DOI: 10.1139/e11-007

The Nechako Basin in British Columbia, Canada is suspected to have hydrocarbon potential. However, it has been a difficult basin to explore because of the presence of Tertiary volcanic outcrop. The volcanic outcrop makes the use of conventional seismic exploration methods difficult owing to a strong velocity inversion at its base. An alternative is the passive source method known as ambient noise surface wave tomography. The method, which examines the high-frequency surface wave field that is obtained from noise analysis, is sensitive to large-scale crustal structure and has been successfully applied to measuring the depths of sedimentary basins. Station-to-station Green's functions within the basin were estimated by cross-correlating the vertical components of the seismic noise data recorded by 12 POLARIS (Portable Observatories for Lithosphere Analysis and Research Investigating Seismicity) and CNSN (Canadian National Seismgraph Network) seismic stations between September 2006 and November 2007. The resulting Green's functions were dominated by Rayleigh waves. The dispersion characteristics of the Rayleigh waveforms were measured within the microseismic band. Inversion of the dispersion curves produced 1-D and 2-D thickness models and 2-D group velocity models for the Nechako Basin and its surrounding region. The velocity models indicate two low group velocity structures within the basin that might represent sedimentary packages, and some pockets of high-velocity zones that show the presence of volcanic rocks within and on the basin. The thickness models indicated the presence of about six different velocity layers, in which the average thickness of the basin and the crust are 4.8 and 30-34 km, respectively.