3-D Karoo basin reconstruction from ambient passive seismic noise Earth Stewardship Science Research Institute 3-D Karoo basin reconstruction from ambient passive seismic noise L. Bezuidenhout, V. Wagener, M. Doucouré Department of Physics and Geoscience Objectives Apply the concept of passive seismic tomography using three-component geophones to construct 3-D image of the Karoo sub-surface. Gain an improved understanding of the subsurface geology of the Karoo basin. Construct a seismic (earthquake) survey of the Karoo prior to hydraulic fracturing. WHY Karoo ? Increased interest in the shale gas extraction within the Karoo basin is gaining momentum. A scientifically thorough base-line of this region needs to be established to moderate any negative effects associated with fracking. Study area: surrounds of Graaff Reinet, Aberdeen and Cradock (location of Soekor boreholes) Karoo: Areas of Interest Geological structure of the Karoo indicating the proposed study area System and Data acquisition Data monitoring Battery Data Cube Geophone GPS Acquisition Processing Interpretation Static correction Velocity analysis (Green’s function) NMO/DMO Stacking Migration Seismic data to subsurface geology Seismic equipment Seismograph Methodology This study Deploy passive seismic network of 20 three-component (N-S, E-W, vertical) geophones for predetermined periods in various areas of interest in the Karoo. Collect and monitor ambient seismic signals up to frequencies of 160 Hz. Convert the data acquired from the geophones to a velocity signal. [The highly non-linear inverse problem created from the retrieval of the velocity variation of the travel times is numerically solved using Green’s cross correlation function to construct the 3-D map.] 3-D mapping of the Karoo will possibly allow for identification of natural resources (i.e. shale layers) and localized faults planes (where fracking should not occur). Increase resolution from previous seismic models of the Karoo. The aim of this project is to establish a continuous monitoring microseismic acquisition network across the Karoo to possibly detect any varying subsurface perturbations / ambient noise and image the subsurface. This will be a first of a kind type of work undertaken in South Africa with a view to create a forensic baseline of the Karoo region. Previous seismic modeling of the Karoo and Cape fold belt 1993 ~8 km North South Escarpment Cape Fold Belt Front 2004 Extent of NVR profile ~100 km Prince Albert 2006 2007/8 km 5 10 Halbich et al. (1993) model Chevallier et al. (2004) model Johnson et al. (2006) model Acknowledgement The authors would like to thank Inkaba yeAfrica, DST, NRF and GFZ. Lindeque et al. (2007/8) model