Imaging of reflection seismic energy for mapping shallow fracture zones in crystalline rocks

Abstract

The high-resolution reflection seismic technique is being used increasingly to address geologic exploration and engineering problems. There are, however, a number of problems in applying reflection seismic techniques in a crystalline rock environment. The reflection seismic data collected over a fractured crystalline rock environment are often characterized by low signal-to-noise ratios (SIN) and inconsistent reflection events. Thus it is important to develop data processing strategies and correlation schemes for the imaging of fracture zones in crystalline rocks. Two sets of very low SIN, high-resolution seismic data, previously collected by two different contractors in Pinawa, Canada, and the island of Aspo, Sweden, were reprocessed and analyzed, with special emphasis on the shallow reflection events occurring at depths as shallow as 60--100 m.The processing strategy included enhancing the signals hidden behind large-amplitude noise, including clipped ground roll. The pre-and poststack processing includes shot f-k filtering, residual statics, careful muting after NMO correction, energy balance, and coherency filtering. The final processed seismic sec-

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