Geoacoustic profile estimation by inversion of head wave data

Abstract

An approach is described for estimation of geoacoustic model parameters in shallow water based on inversion of head wave data obtained in experiments with vertical line arrays (VLA). Analysis of head waves obtained in seismic refraction surveys with horizontal arrays is a widespread practice in exploration seismology. However, in shallow water, there can be practical advantages in the use of VLAs. Inversion of head wave data obtained with a VLA provides estimates of the layer depths, and compressional wave speeds and attenuations. Three inversion techniques are compared: inversion of travel time versus range data for a single sensor, direct measurement of the critical angle using the VLA, and inversion of travel time versus hydrophone depth data for a specific range. The techniques are applied to data from an experiment on the continental shelf off Vancouver Island. Shallow explosive charges were used as sound sources out to ranges of 5 km. Strong head wave signals were recorded from two distinct layers, and the data were inverted using the travel time versus depth method. The estimated values of 1750 and 1900 m/s for the compressional wave speeds are consistent with results from conventional seismic surveys in the vicinity.