| Title | Source-Generated Seismic Noise in 2-D Reflection Surveys in the Basin and Range Physiographic Province: Issues, Attenuation and Case Histories |
|---|---|
| Authors | Smith, David A.; Hild, Jim; Pfeiffer, Jim; Drakos, Peter |
| Year | 2011 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Coherent noise; geothermal; ground roll; linear noise attenuation; noise trains; reflection multiples; reflection seismic; refracted energy; signal scattering; source-generated noise; survey design; vertical faults |
| Abstract | Igneous rocks present in geothermal and other hard rock sites are notorious for seismic signal scattering because of internal heterogeneities in those environments. The complex structural settings create intricate subsurface wave fields. Given these factors, continuous reflections across stacked sections at these sites are seldom apparent. Rather, subsurface acoustic interfaces will typically manifest themselves as a series of short, discontinuous reflections within a background of scattered acoustic energy. The resulting data sets are not easy to process and interpret. A common problem in geothermal seismic data is coherent source-generated noise. This noise includes ground roll, which is amenable to attenuation by using appropriate source and receiver arrays, survey geometry, and specific processing algorithms. In addition to ground roll, these seismic data commonly include linear noise trains parallel to first breaks. A third type of coherent noise is reflection multiples. The first section of this paper examines the causes of coherent noise, its attenuation during data acquisition and processing, and provides a review of basic quality control checks on the data acquisition and processing sequence. The second section of the paper contains case histories of successful 2-D seismic reflection surveys. The first is at a site where access was limited and the main objective was detection of vertical faults. Alteration of the underlying rocks is pervasive. The second is a hard rock site where low angle and intrusive features were of interest. Mining activities taking place during the survey added to the noise issues. Success at these sites resulted from application of various noise avoidance and attenuation factors discussed above, plus extensive collaboration between the project geophysicists and the client geologists and geophysicists. |