The response of a structure composed of anisotropic strata can be built up from the reflection and transmission properties of individual interfaces using a slightly modified version of the recursion scheme of Kennett. This scheme is conveniently described in terms of scatterer operators and scatterer products. The effects of a free surface and the introduction of a simple point source at any depth can be accommodated in a manner directly analogous to the treatment for isotropic structures. As in the isotropic case the results so obtained are stable to arbitrary wavenumbers.
Abstract : The theory and practice of computing synthetic seismograms in layered media are now quite well understood. In applications, these methods can still be unsatisfactorily slow. It may be necessary to work with models having a large number of microlayers. In seeking to determine the variation of material properties in a sedimentary pile, we may start with some generalized reflection data set, containing reflected and refracted signals produced by an impulsive point source and recorded at a number of sensors in the water layer at various offsets from the source. Any true inversion procedure, regardless of details, must compare the observed data with synthetic data for a sequence of models in order to obtain and characterize models which fit the data within some prescribed limits. We thus seek a forward modeling procedure for arbitrary layered models which is fast enough that many repetitions are possible in a reasonable time. The procedure described in this paper is based on a reorganization of the inside loops of a conventional reflectivity algorithm to permit vectorization. Sedimentary rock.
Herein, we rebut Hearty's (2011) claims about our data and interpretations, which hopefully will help bring some clarity to the issue of Oahu's uplift over the past 500 k.y.
Least‐squares, zero‐lag inverse filters may be used for predictive deconvolution of stationary time series and for obtaining autoregressive or maximum entropy spectral estimates. The greatest problem in finding such an inverse filter is determining the optimum operator length for a given finite length of data. The identical problem of determining the correct order of an autoregressive model for the data has been solved by Akaike, whose final prediction error (FPE) statistic is a minimum for the optimum length model. This minimum FPE criterion may be applied to both single and multiple time series. The FPE procedure has been used successfully on simultaneous three‐component seismometer and hydrophone data for the detection of refracted arrivals from explosions up to 1350 km away and for estimation of spectra of microseismic noise observed at the time of each shot. The data were recorded with an ocean bottom seismometer.
The outer half of the Mariana forearc, the region between the trench axis and the active volcanic arc, contains numerous large seamounts formed entirely by nonvolcanic processes. These seamounts are up to 30 km in diameter and rise as much as 2 km from the seafloor around them. Within about 50 km of the trench axis most of the seamounts are horst blocks of uplifted forearc material. From 50 to about 120 km from the trench axis the seamounts are either sites of updomed forearc material caused by diapiric intrusion, or sites of extrusion of diapirically emplaced serpentinized ultra manes fiom the lower crust/upper mantle of the underlying forearc. The formation of the diapiric material comprising these seamounts is dependent on the evolution of the thermal structure of the shallow (above 30 km) portion of the overriding plate as a convergence zone develops. Changes in the thermal structure influence the distribution of the stability fields of various regional metamorphic facies within the forearc region. As a convergence zone evolves, the greenschist stability field retreats from the region of the trench axis and is replaced by the stability field of the lawsonite-albite-chlorite facies at shallow levels, and by that of the the blueschist facies at depth. The disappearance of the greenschist facies stability field from the forearc suggests that the serpentinite diapirs are either emplaced early in the history of the forearc or that serpentinite remains metastable within the outer forearc for tens of millions of years. The growth of the chlorite and blueschist stability fields may explain the apparent capacity of forearc regions to accommodate large amounts of fluids driven off the downgoing slab by compaction, desiccation, and dehydration reactions. Although conditions appropriate for the formation of either fault block seamounts or diapirically formed seamounts may exist in any forearc, the occurrence of the seamounts is dependent on the local tectonic environment. In the case of the Mariana forearc the horsts and diapirs are related to fracturing of the forearc and to subduction related vertical tectonic movement. In those convergent margins with simpler tectonic conditions, horst seamounts may be absent and discrete diapiric seamounts may be replaced by regional upwarp or development of a low forearc ridge.
