Inversion of traveltime data under a statistical model for seismic velocities and layer interfaces

Abstract

We invert large-aperture seismic reflection and refraction data from a geologically complex area on the northeast Atlantic margin to jointly estimate seismic velocities and depths of major interfaces. Our approach combines this geophysical data information with prior information on seismic compressional velocities and the structural interpretation of seismic sections. We constrain expected seismic velocities in the prior model using information from well logs from a nearby area. The layered structure and prior positions of the interfaces follow information from the seismic section obtained by processing the short offsets. Instead of using a conventional regularization technique to smooth the interface-velocity model, we describe the spatial correlation of interfaces and velocities with a geostatistical model, using a multivariate Gaussian probability density function. We impose a covariance function on the velocity field in each layer and on each interface in the model to control the smoothness of the solution. The inversion is performed by minimizing an objective function with two terms, one term measuring traveltime residuals and the other measuring the fit to the statistical model. We calculate the posterior uncertainties and evaluate the relative influence of data and the prior model on estimated interface depths and seismic velocities. The method results in the estimation of velocity and interface geometry beneath a basaltic sill system down to 7 km depth. This method aims to enhance the interpretation process by combining multidisciplinary information in a quantitative model-based approach.

Crust and Lithospheric Structure - Active Source Studies of Crust and Lithospheric Structure

“…Coincident near-vertical reflection data can be used in several ways (Zelt, 1999). From stacked data, the reflector geometries and interval velocities can be used as prior information in the regularization to constrain a layered velocity model (e.g., Bosch et al, 2005). Alternatively, arrivals in prestack reflection data can be picked and inverted jointly with the wide-angle data.…”

Velocity images from stacking depth-slowness seismic wavefields

“…The velocity model was generated during a separate investigation of the same data set by Bosch et al (2005), who selected several arrival phases at both long and short offsets for picking prior to inversion using the JIVE3D traveltime inversion algorithm of Hobro et al (2003). The velocity model was defined by reflections from the top of the sills and diving rays above and below the sills.…”

“… Tomographic inversion velocity model overlain with the depth migrated section obtained from conventional processing, after Bosch et al (2005). Note the multiples that cross the section from 4–5 km downwards.…”

“… (a) A typical τ– p transformed CMP supergather from the Rockall Trough profile. Three reflection ellipses are indicated with the basement reflection expected at an intercept (τ) time of approximately 7 s (Bosch et al 2005). The effect of the hyperbolic Radon filter attenuating the energy at high to intermediate slownesses is evident in the lower right hand half of the wavefield.…”

Adaptive reconstruction method of impedance model with absolute and relative constraints

“…The technique is very effective and belongs to the constrained inversion in a real sense. For instance, Medeiros and Silva (1996), Smith and Ferguson (2000) and Bosch et al (2005) think that the inversion needs to combine absolute constraints of logging data and relative constraints of geological information and utilize various study information. In various constraint information, it is easy to introduce the absolute constraints of both logging data and the prior impedance which improve the low frequency component of the impedance model.…”