Daniel A. Rosales

Wave-equation angle-domain common-image gathers for converted waves

Wavefield-extrapolation methods can produce angle-domain common-image gathers ADCIGs.To obtainADCIGs for converted-wave seismic data, information about the image dip and the P-to-S velocity ratio must be included in the computation of angle gathers. TheseADCIGs are a function of the half-aperture angle, i.e., the average between the incidence angle and the reflection angle. We have developed a method that exploits the robustness of computing 2D isotropic single-modeADCIGs and incorporates both the converted-wave velocity ratio and the local image dipfield. It also maps the final converted-wave ADCIGs into two ADCIGs, one a function of the P-incidence angle and the other a functionoftheS-reflectionangle.Resultswithbothsyntheticand real data show the practical application for converted-wave ADCIGs. The proposed approach is valid in any situation as long as the migration algorithm is based on wavefield downward continuation and the final prestack image is a function ofthehorizontalsubsurfaceoffset.

P S-wave polarity reversal in angle domain common-image gathers

The change in the reflection polarity at normal incidence is a fundamental feature of converted-wave seismology due to the vector nature of the displacement field. The conventional way of dealing with this feature is to reverse the polarity of data recorded at negative offsets. However, this approach fails in presence of complex geology. To solve this problem we propose operating the polarity flip in the angle domain. We show that this method correctly handle the polarity reversal after prestack migration for arbitrarily complex earth models.

Robust moveout without velocity picking

At every point in a CMP gather, a local estimate of RMS velocity is: V 2 R M S D x t d x dt , where dt=d x is the local stepout. We form a median stack of these local velocity estimates to obtain stable estimates of RMS velocity without the conventional need to form many hyperbolic stacks.

Converted‐waves angle‐domain common‐image gathers

Common-image gathers are very useful for velocity and petrophysical analysis. Wavefield-extrapolation methods produce Angle-Domain Common-Image Gathers (ADCIGs). For the conventional PP case, ADCIGs are a function of the opening angle. The representation of ADCIGs for PS data (PS-ADCIGs) is more elaborate than for conventional ADCIGs. In PS-ADCIGs, the P-to-S velocity ratio is a major variable in transforming the subsurface offset to the opening angle, and in transforming this opening angle to either the P-incidence or the S-reflection angle. Numerical studies show that when the P-to-S velocity ratio and image midpoint information are not incorporated the error in computing PSADCIGs is enough to introduce artifacts later in the velocity model.

High-resolution shallow geophysics and geology in the Hudson-Raritan Estuary Ecosystem Restoration, New Jersey

The Hudson-Raritan Estuary of New York and New Jersey is one of the largest estuaries on the East Coast of the United States. It includes part of the New York City metropolitan area and includes the Port of New York and New Jersey. The estuary is an important economic, environmental, and recreational resource and asset for the region. Fresh water enters the estuary from the Hudson, Hackensack, Passaic, and Raritan rivers. Since the 17th century, the estuary has experienced industrialization and residential growth that have profoundly altered the estuary and surrounding land from its precolonial state.

Baseline Geophysical and Ecological Mapping of the Lower Hackensack River System in New Jersey

Summary The Meadowlands and the lower Hackensack River form a connected system that is an important asset for the greater New York City metropolitan region because of its economic, environmental, and recreational value. e4sciences|Earthworks LLC produced geophysical and ecological baseline mapping of the lower 14 miles of the Hackensack River, New Jersey, for the Hudson-Raritan Estuary Ecosystem Restoration Study. The mapping program used sub-bottom seismic profiling, orthosonographs, multibeam bathymetry, magnetic field mapping, digital photographs, aerial photographs, cores, sediment profile images, morphology, stratigraphy, sedimentation, biological data, and benthos. Going into these studies, it was presumed that the river bottom would be covered uniformly with recent industrial-age black silt. Our observations demonstrate otherwise. The black silt is concentrated in Harmon Cove and locally in point bars in the north. Elsewhere, there is tremendous variability in the river bottom. The Hackensack River system is a dynamic asset and resource that deserves continued monitoring, management, and guardianship.

Converted-wave azimuth moveout

A new partial-prestack migration operator to manipulate multicomponent data, called converted-wave azimuth moveout (PS-AMO), transforms converted-wave prestack data with an arbitrary offset and azimuth to equivalent data with a new offset and azimuth position. This operator is a sequential application of converted-wave dip moveout and its inverse. As expected, PS-AMO reduces to the known expression of AMO for the extreme case when the P velocity is the same as the S velocity. Moreover, PS-AMO preserves the resolution of dipping events and internally applies a correction for the lateral shift between the common-midpoint and the common-reflection/conversion point. An implementation of PS-AMO in the log-stretch frequency-wavenumber domain is computationally efficient. The main applications for the PS-AMO operator are geometry regularization, data-reduction through partial stacking, and interpolation of unevenly sampled data. We test our PS-AMO operator by solving 3D acquisition geometry-regularization problems for multicomponent, ocean-bottom seismic data. The geometry-regularization problem is defined as a regularized least-squares-objective function. To preserve the resolution of dipping events, the regularization term uses the PS-AMO operator. Application of this methodology on a portion of the Alba 3D, multicomponent, ocean-bottom seismic data set shows that we can satisfactorily obtain an interpolated data set that honors the physics of converted waves.

Stolt prestack residual migration for converted waves

PS velocity analysis is an important aspect of converted wave seismic imaging. To obtain one consistent image, it is necessary to correctly derive both the P-wave and the S-wave velocity models. Stolt prestack residual migration is a useful technique for velocity analysis and image update. This paper extends Stolt prestack residual migration to handle two different velocity fields. The new operator that we introduce is promising for PS velocity analysis. We present a theoretical discussion of our new operator and discuss its ability to focus PS images. Finally, we present prestack residual migration results on a synthetic and a real dataset.