How can asymmetric detachment faults generate symmetric Ocean Continent Transitions?

Asymmetry or symmetry of magma‐poor rifted margins refers commonly to the crustal architecture and the occurrence or absence of large‐scale extensional detachment faults. While distal parts of magma‐poor rifted margins are often considered to be asymmetric, the observation of downlapping sedimentary sequences over exhumed mantle domains at conjugate margins suggests a symmetric evolution during mantle exhumation. On the basis of seismic observations along the Iberia–Newfoundland and Australia–Antarctica margins, we propose that their most distal parts show evidence for the development of multiple, out‐of‐sequence asymmetric detachment faults. We present evidence for cyclic delocalization and re‐localization of deformation, resulting in an apparent symmetry of the exhumed mantle domain. The interaction between out‐of‐sequence detachment systems and the successive rise of the asthenosphere may explain the observed transition from fault‐controlled to magma‐controlled strain accommodation and the transition to more symmetric and localized accretion associated with the formation of a stable spreading center.     

THE EFFECT OF ENVIRONMENTAL AMENITIES ON HOUSE VALUES: THE EXAMPLE OF A VIEW LOT

For good land management, policy makers need information on the value people attach to environmental amentities. It is demonstrated here that the economic evaluation of such an intangible residental environmental amenity as a view is both possible and useful. Estimation of the implicit price of a view is made through a hedonic-price regression model based on data from a sample of single-family residences in the Los Angeles metroplitan area.     

Estimating geoacoustic parameters using matched-field inversion methods

In this paper, we use matched-field inversion methods to estimate the geoacoustic parameters for three synthetic test cases from the Geoacoustic Inversion Techniques Workshop held in May 2001 in Gulfport, MS. The objective of this work is to use a sparse acoustic data set to obtain estimates of the parameters as well as an indication of their uncertainties. The unknown parameters include the geoacoustic properties of the sea bed (i.e., number of layers, layer thickness, density, compressional speed, and attenuation) and the bathymetry for simplified range-dependent acoustic environments. The acoustic data used to solve the problems are restricted to five frequencies for a single vertical line array of receivers located at one range from the source. Matched-field inversion using simplex simulated annealing optimization is initially used to find a maximum-likelihood (ML) estimate. However, the ML estimate provides no information on the uncertainties or covariance associated with the model parameters. To estimate uncertainties, a Bayesian formulation of matched-field inversion is used to generate posterior probability density distributions for the parameters. The mean, covariance, and marginal distributions are determined using a Gibbs importance sampler based on the cascaded Metropolis algorithm. In most cases, excellent results were obtained for relatively sensitive parameters such as wave speed, layer thickness, and water depth. The variance of the estimates increase for relatively insensitive parameters such as density and wave attenuation, especially when noise is added to the data.