Ambient Noise Tomography (Passive Seismic) to Image the Cape-Karoo Transition Near Jansenville, Eastern Cape
During August and September 2015, a seismic network consisting of 17 stations was installed in the south-eastern Cape-Karoo region, near the town of Jansenville. Ambient seismic signals were continuously recorded for a three week period. In this chapter,
- PDF / 562,277 Bytes
- 6 Pages / 595.276 x 790.866 pts Page_size
- 100 Downloads / 178 Views
Ambient Noise Tomography (Passive Seismic) to Image the Cape-Karoo Transition Near Jansenville, Eastern Cape Lucien Bezuidenhout, Moctar Doucouré, Viera Wagener, and Maarten J. de Wit
Abstract
During August and September 2015, a seismic network consisting of 17 stations was installed in the south-eastern Cape-Karoo region, near the town of Jansenville. Ambient seismic signals were continuously recorded for a three week period. In this chapter, we reconstruct estimates of the seismic Green’s functions between sensor pairs by cross-correlating the ambient seismic signals recorded in the vertical component of each station. The resulting Green’s functions contain clear direct Rayleigh wave arrivals. The measured group velocity dispersion curves of the Rayleigh waves were averaged in the period range from 2.5 to 5.5 s (approximately 2–5 km depth). The arrival times of the Rayleigh waves are picked at different periods and then inverted to compute 2-D group velocity maps. This resulted in a velocity model up to depths of 5 km. The results reveal two different velocity regions, broadly corresponding to the Cape Fold Belt and the flanking Karoo Basin. The higher group velocity anomalies (3–5 km in thickness) most likely represent the Carboniferous-Permian sequences of the Karoo Basin (Dwyka-Ecca-Beaufort Groups). A lowermost velocity region in the south-eastern study area could correspond to the Jurassic-Cretaceous sequences of the Algoa Basin that directly overlie the Cape Fold Belt. Keywords
Ambient noise
3.1
Group velocity maps
Introduction
Previous reflection seismic experiments conducted across the Cape Fold Belt and Karoo Basin using active sources have shown that the upper crust, comprising the Paleozoic– L. Bezuidenhout (&) M. Doucouré V. Wagener M.J. de Wit AEON, Earth Stewardship Science Research Institute, Nelson Mandela Metropolitan University, PO Box 77000Port Elizabeth, 6031, South Africa e-mail: [email protected] M. Doucouré e-mail: [email protected] V. Wagener e-mail: [email protected] M.J. de Wit e-mail: [email protected]
Tomography
Cape-Karoo contact
Algoa basin
Mesozoic Cape and Karoo Supergroups, decreases in thickness from more than 10 km in the south to 2–3 km farther to the north across a distance of about 100 km (Lindeque et al. 2007; 2011; Stankiewicz et al. 2007; Chap. 2 this book). At the front of the Cape Fold Belt, the Karoo Basin sequences are up to 5 km thick as confirmed by deep boreholes (Chap. 1 this book). The most recent reflection data obtained by Lindeque et al. (2007) also contained continuous seismic recordings up to 60 h after each shot. Ryberg (2011) used this ‘by product’ data to detect refracted and reflected body waves from the cross correlation functions derived from the recordings, indicating that the use of the ambient noise technique in this region is feasible. Since it is more common to investigate the surface wave’s component of the ambient noise wave coda, Ryberg (2011) concluded that the high frequency compo
Data Loading...
