Shear wave structure from joint analysis of seismic and seafloor compliance data

Abstract

Determining shear wave structure is the key to identifying the amount and location of fluid within the crust. Seismic and seafloor compliance methods provide independent estimates of shear wave structure, and a joint analysis of the two data sets should provide better constraints on the properties of the uppermost oceanic crust. We consider an example from 9°33′N on the East Pacific Rise. Seismic data from an on-axis expanding spread profile have been reanalysed to determine a shear wave structure for layer 2B; pS arrivals require a high shear wave velocity within this layer (Poisson ratio in the range 0.22-0.25). Compliance data from the same location are seemingly inconsistent with this result, requiring that layer 2B is a region of low shear wave velocity (Poisson ratio in the range 0.33-0.44). The quantitative differences between the two results can be explained by anelasticity and anisotropy; conversely, a knowledge of this discrepancy can be used to constrain the attenuation structure.