NATURE OF THE ACOUSTIC BASEMENT IN TERPENIYE BAY, SEA OF OKHOTSK

Abstract

Data obtained earlier by the reflection method [3, 4] enabled rocks of the sedimentary cover in this bay to be divided into two complexes. The upper complex is revealed by long reflecting boundaries, which are virtually horizontal or have gentle dips and are characteristic of a strongly stratified unit of relatively unconsolidated deposits. Then comes a unit where short reflecting boundaries have mostly steep dips and are distributed in disordered pattern, and where diffracted waves are widespread in the wave field. The top of this basement is most conspicuous wherever it is uplifted. Seismic correlation-refraction data obtained in Terpeniye Bay show that the regionally persistent interface with a boundary velocity of 3.8 to 4.2 km·s-1 here coincides with the top of the seismoacoustic basement, as revealed by seismic reflection data. This common structural trend does not persist in the upper crust in some places. In zones of large synclinal troughs delineated by reflecting interfaces, for example, the same refracting boundary controls one of the interfaces within the upper rock complex, but does not coincide with the acoustic basement boundary, which lies at greater depths.