Inversion Technique

Reflectivity data can be inverted for changes in P- and S-impedance across an interface and therefore for possible pore fluid transitions. After adequate amplitude recovery through preprocessing, the Blake Outer Ridge data should approximate the reflection coefficient and can thus be used in an elastic parameter inversion using equation . The P- and S-impedance contrasts at each subsurface position are estimated by applying a least-squares elastic parameter inversion method Lumley (1993b). This technique fits seismic gathers at each pseudo-depth and surface position to the theoretical P- and S-impedance curves (see Figure ). The method uses bootstrapping with offset and angles based on the properties of the theoretical impedance contrast curves displayed in Figure . First, $\rm I_{\rm p}$ is estimated for angles $\theta \le 15^{^{\circ}}$. Then a least-squares estimate is found for $\rm I_{\rm s}$ for angles $10^{^{\circ}}\le \theta \le 40^{^{\circ}}$ using the estimate of $\rm I_{\rm p}$ as a constraint. Finally, if the data contain angles above $35^{^{\circ}}$, the density contrast $\rm D$ can be estimated using both $\rm I_{\rm p}$ and $\rm I_{\rm s}$ as constraints.