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Traveltime Inversion (traveltime + inversion)

Distribution by Scientific Domains
Earth and Environmental Science100%

Selected Abstracts

Shallow velocity structure along the Hirapur,Mandla profile using traveltime inversion of wide-angle seismic data, and its tectonic implications

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2000
Kalachand Sain
In order to investigate the velocity structure, and hence shed light on the related tectonics, across the Narmada,Son lineament, traveltimes of wide-angle seismic data along the 240 km long Hirapur,Mandla profile in central India have been inverted. A blocky, laterally heterogeneous, three-layer velocity model down to a depth of 10 km has been derived. The first layer shows a maximum thickness of the upper Vindhyans (4.5 km s,1,) of about 1.35 km and rests on top of normal crystalline basement, represented by the 5.9 km s,1 velocity layer. The anomalous feature of the study is the absence of normal granitic basement in the great Vindhyan Graben, where lower Vindhyan sediments (5.3 km s,1,) were deposited during the Precambrian on high-velocity (6.3 km s,1,) metamorphic rock. The block beneath the Narmada,Son lineament represents a horst feature in which high-velocity (6.5 km s,1,) lower crustal material has risen to a depth of less than 2 km. South of the lineament, the Deccan Traps were deposited on normal basement during the upper Cretaceous period and attained a maximum thickness of about 800 m. [source]

Sequential integrated inversion of refraction and wide-angle reflection traveltimes and gravity data for two-dimensional velocity structures

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2000
Rosaria Tondi
A new algorithm is presented for the integrated 2-D inversion of seismic traveltime and gravity data. The algorithm adopts the ,maximum likelihood' regularization scheme. We construct a ,probability density function' which includes three kinds of information: information derived from gravity measurements; information derived from the seismic traveltime inversion procedure applied to the model; and information on the physical correlation among the density and the velocity parameters. We assume a linear relation between density and velocity, which can be node-dependent; that is, we can choose different relationships for different parts of the velocity,density grid. In addition, our procedure allows us to consider a covariance matrix related to the error propagation in linking density to velocity. We use seismic data to estimate starting velocity values and the position of boundary nodes. Subsequently, the sequential integrated inversion (SII) optimizes the layer velocities and densities for our models. The procedure is applicable, as an additional step, to any type of seismic tomographic inversion. We illustrate the method by comparing the velocity models recovered from a standard seismic traveltime inversion with those retrieved using our algorithm. The inversion of synthetic data calculated for a 2-D isotropic, laterally inhomogeneous model shows the stability and accuracy of this procedure, demonstrates the improvements to the recovery of true velocity anomalies, and proves that this technique can efficiently overcome some of the limitations of both gravity and seismic traveltime inversions, when they are used independently. An interpretation of field data from the 1994 Vesuvius test experiment is also presented. At depths down to 4.5 km, the model retrieved after a SII shows a more detailed structure than the model obtained from an interpretation of seismic traveltime only, and yields additional information for a further study of the area. [source]

Stacking velocities in the presence of overburden velocity anomalies

GEOPHYSICAL PROSPECTING, Issue 3 2009
Emil Blias
ABSTRACT Lateral velocity changes (velocity anomalies) in the overburden may cause significant oscillations in normal moveout velocities. Explicit analytical moveout formulas are presented and provide a direct explanation of these lateral fluctuations and other phenomena for a subsurface with gentle deep structures and shallow overburden anomalies. The analytical conditions for this have been derived for a depth-velocity model with gentle structures with dips not exceeding 12°. The influence of lateral interval velocity changes and curvilinear overburden velocity boundaries can be estimated and analysed using these formulas. An analytical approach to normal moveout velocity analysis in a laterally inhomogeneous medium provides an understanding of the connection between lateral interval velocity changes and normal moveout velocities. In the presence of uncorrected shallow velocity anomalies, the difference between root-mean-square and stacking velocity can be arbitrarily large to the extent of reversing the normal moveout function around normal incidence traveltimes. The main reason for anomalous stacking velocity behaviour is non-linear lateral variations in the shallow overburden interval velocities or the velocity boundaries. A special technique has been developed to determine and remove shallow velocity anomaly effects. This technique includes automatic continuous velocity picking, an inversion method for the determination of shallow velocity anomalies, improving the depth-velocity model by an optimization approach to traveltime inversion (layered reflection tomography) and shallow velocity anomaly replacement. Model and field data examples are used to illustrate this technique. [source]

Sequential integrated inversion of refraction and wide-angle reflection traveltimes and gravity data for two-dimensional velocity structures

GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2000
Rosaria Tondi
A new algorithm is presented for the integrated 2-D inversion of seismic traveltime and gravity data. The algorithm adopts the ,maximum likelihood' regularization scheme. We construct a ,probability density function' which includes three kinds of information: information derived from gravity measurements; information derived from the seismic traveltime inversion procedure applied to the model; and information on the physical correlation among the density and the velocity parameters. We assume a linear relation between density and velocity, which can be node-dependent; that is, we can choose different relationships for different parts of the velocity,density grid. In addition, our procedure allows us to consider a covariance matrix related to the error propagation in linking density to velocity. We use seismic data to estimate starting velocity values and the position of boundary nodes. Subsequently, the sequential integrated inversion (SII) optimizes the layer velocities and densities for our models. The procedure is applicable, as an additional step, to any type of seismic tomographic inversion. We illustrate the method by comparing the velocity models recovered from a standard seismic traveltime inversion with those retrieved using our algorithm. The inversion of synthetic data calculated for a 2-D isotropic, laterally inhomogeneous model shows the stability and accuracy of this procedure, demonstrates the improvements to the recovery of true velocity anomalies, and proves that this technique can efficiently overcome some of the limitations of both gravity and seismic traveltime inversions, when they are used independently. An interpretation of field data from the 1994 Vesuvius test experiment is also presented. At depths down to 4.5 km, the model retrieved after a SII shows a more detailed structure than the model obtained from an interpretation of seismic traveltime only, and yields additional information for a further study of the area. [source]