2-SHIP MULTICHANNEL SEISMIC EXPERIMENTS FOR DEEP CRUSTAL STUDIES - EXPANDED SPREAD AND CONSTANT OFFSET PROFILES

Expanding spread profiles (ESP's) are spatially localized, wide-angle reflection/refraction surveys using two ships, a multichannel array, and Ray-dist ranging. The value of the data is primarily the fidelity with which the data are recorded and the multiplicity of coverage provided by the multichannel array. We feel that the ESP technique has several distinct advantages over other methods of deep crustal studies. These are 1) very accurate range and timing information, 2) fixed and well-known receiver separation (100m) for accurate phase velocity determination across the array, 3) because of accurate timing and range information, traces from different shots may be used to improve velocity determination (this is limited only be the persistence of the particular arrivals), 4) true amplitude recording that allows the use of sophisticated signal processing techniques and tightly constrains models of the observed data, 5) no difficulties with receiver coupling, 6) calibration of charge size changes through overlapping receiver positions, 7) a minimum amount of explosives is required because of the redundancy provided by the multichannel receiving array, 8) minimal deployment and recovery time coupled with low equipment loss rate, 9) 'real-time' data moitoring and analysis to insure the quality of the recorded data, and 10) digital recording in a readily exchangeable standard format to facilitate the use of digital computers in reducing the vast amount of data acquired.-Authors