A high-resolution three-dimensional (3D) seismic reflection system for small-scale targets in lacustrine settings was developed. Its main characteristics include a three streamer configuration located 7.5m from each other, navigation and shot-triggering software with real-time control on navigation using differential GPS (Global Positioning System). Receiver positions are accurately calculated with the aid of GPS antennas attached to the end of each of three 24-channel streamers. With a receiver spacing of 2.5 m, the bin dimension is 1.25 m in inline and 3.75 m in crossline direction. A 5-m shot spacing resulted in a nominal fold of 6. A double-chamber bubble-cancelling 15/15 in3 air gun (40-650 Hz) operated at 80 bars and 1 m depth gave a signal penetration of 300 m below water bottom and a best vertical resolution of 1.1 m. Processing followed a conventional scheme, but had to be adapted to the high sampling rates, and our unconventional navigation data needed conversion to industry standards. Here we present two 3D surveys of about 1 km~2 in Lake Geneva, Switzerland. The first one images a complex major fault zone in Tertiary sediments, while the second one features Quaternary glacial and glaciolacustrine deposits. The high-quality data enabled us to construct maps of seismic horizons and fault surfaces in three dimensions. The system proves to be well adapted to investigate complex structures by providing non-aliased images of reflectors with dips up to 30°.
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