Shear Wave Noise on OBS Vz Data - Part I Evidence from Field Data

Vertical geophone data on ocean bottom bottom recordings are often contaminated by varying amounts of noise. This noise has the moveout of converted waves, is coherent on common receiver records and random on common shot records. The noise also depends strongly on the condition of the ocean bottom, with muddy bottoms generating strong noise and sandy bottoms giving almost noise free data.<br>In the past it has been commonly assumed that the noise is essentially cross-talk of the shear component on the vertical component caused by design flaws in the recording unit. <br>In the course of the development of a new ocean bottom node system we have tested a number of different OBS configurations. Analysis of the Vz noise as function of configuration type allows us to separate effects into those which are dependent on configuration type and those that are not.<br>We conclude that the 'Vz noise' is not dependent of the recording station configuration and instead is a true measurement of the vertical movement of the ocean bottom. In part II we demonstrate a possible mechanism by which the vertical bottom movement is generated using finite difference modeling.<br>