Diffraction velocity analysis in a single-channel seismic survey in the Joetsu Basin

Geophysics ◽  
2020 ◽  
Vol 85 (2) ◽  
pp. U47-U53 ◽  
Author(s):  
Luiz Alberto Santos ◽  
Eloise Helena Policarpo Neves ◽  
Antônio Fernando Menezes Freire ◽  
Marco Antônio Cetale Santos ◽  
Ryo Matsumoto ◽  
...  
Keyword(s):  
Single Channel ◽  
Data Availability ◽  
Acoustic Properties ◽  
Seismic Survey ◽  
Velocity Analysis ◽  
Lateral Velocity ◽  
Velocity Change ◽  
Marine Research ◽  
Time Migration ◽  
Processing Flow

Historically, marine research has been using single-channel seismic (SCS) devices for scientific projects. Despite SCS’s abundant data availability and the contribution it has brought for subsurface comprehension, few efforts have been dedicated to improve the SCS processing flow to extract more information carried by seismic signals and for better imaging. Diffractions present the necessary means to estimate sediment acoustic properties useful for imaging, stability studies, and geohazard prevention. The root-mean-square (rms) velocity is estimated from diffractions using a diffraction velocity analysis workflow composed of the following main steps: separation of diffractions from specular events using stationary phase properties and plane-wave destruction filtering, determination of diffractor locations in time, velocity scanning using constant rms velocity time migration, automatic picking of rms velocity at the diffractor location in the scan volume, and quality control to avoid spurious rms velocity. The method circumvents the sparsity and nonuniform distribution of diffractions for smooth lateral velocity change conditions. Application in a SCS line acquired in the Joetsu Basin, Japan Sea, indicates improvement in the focusing of deeper events compared to the previous processing flow, and it adds consistent information about the acoustic properties of the subsurface.

Migration velocity analysis based on focusing diffractions generated using the CRS wavefront attributes: Application to real land data

Geophysics ◽  
2021 ◽  
pp. 1-50
Author(s):  
German Garabito ◽  
José Silas dos Santos Silva ◽  
Williams Lima
Keyword(s):  
Time Domain ◽  
Real Data ◽  
Normal Incidence ◽  
Velocity Model ◽  
Migration Velocity ◽  
Velocity Analysis ◽  
Velocity Models ◽  
Time Migration ◽  
Migration Velocity Analysis ◽  
The Time Domain

In land seismic data processing, the prestack time migration (PSTM) image remains the standard imaging output, but a reliable migrated image of the subsurface depends on the accuracy of the migration velocity model. We have adopted two new algorithms for time-domain migration velocity analysis based on wavefield attributes of the common-reflection-surface (CRS) stack method. These attributes, extracted from multicoverage data, were successfully applied to build the velocity model in the depth domain through tomographic inversion of the normal-incidence-point (NIP) wave. However, there is no practical and reliable method for determining an accurate and geologically consistent time-migration velocity model from these CRS attributes. We introduce an interactive method to determine the migration velocity model in the time domain based on the application of NIP wave attributes and the CRS stacking operator for diffractions, to generate synthetic diffractions on the reflection events of the zero-offset (ZO) CRS stacked section. In the ZO data with diffractions, the poststack time migration (post-STM) is applied with a set of constant velocities, and the migration velocities are then selected through a focusing analysis of the simulated diffractions. We also introduce an algorithm to automatically calculate the migration velocity model from the CRS attributes picked for the main reflection events in the ZO data. We determine the precision of our diffraction focusing velocity analysis and the automatic velocity calculation algorithms using two synthetic models. We also applied them to real 2D land data with low quality and low fold to estimate the time-domain migration velocity model. The velocity models obtained through our methods were validated by applying them in the Kirchhoff PSTM of real data, in which the velocity model from the diffraction focusing analysis provided significant improvements in the quality of the migrated image compared to the legacy image and to the migrated image obtained using the automatically calculated velocity model.

Interpretation of seismic reflection profiling data for the structure of the San Andreas fault zone

1983 ◽  
Vol 73 (6A) ◽  
pp. 1701-1720
Author(s):  
R. Feng ◽  
T. V. McEvilly
Keyword(s):  
Fault Zone ◽  
Seismic Reflection ◽  
San Andreas Fault ◽  
Velocity Model ◽  
Seismic Reflection Profile ◽  
Lateral Velocity ◽  
Zone Structure ◽  
Ray Method ◽  
Velocity Change ◽  
San Andreas

Abstract A seismic reflection profile crossing the San Andreas fault zone in central California was conducted in 1978. Results are complicated by the extreme lateral heterogeneity and low velocities in the fault zone. Other evidence for severe lateral velocity change across the fault zone lies in hypocenter bias and nodal plane distortion for earthquakes on the fault. Conventional interpretation and processing methods for reflection data are hard-pressed in this situation. Using the inverse ray method of May and Covey (1981), with an initial model derived from a variety of data and the impedance contrasts inferred from the preserved amplitude stacked section, an iterative inversion process yields a velocity model which, while clearly nonunique, is consistent with the various lines of evidence on the fault zone structure.

Time-migration velocity analysis by image-wave propagation of common-image gathers

Geophysics ◽  
2008 ◽  
Vol 73 (5) ◽  
pp. VE161-VE171 ◽  
Author(s):  
J. Schleicher ◽  
J. C. Costa ◽  
A. Novais
Keyword(s):  
Wave Propagation ◽  
Seismic Event ◽  
Velocity Model ◽  
Migration Velocity ◽  
Velocity Analysis ◽  
Reference Velocity ◽  
Time Migration ◽  
Migration Velocity Analysis ◽  
Velocity Image ◽  
The Common

Image-wave propagation or velocity continuation describes the variation of the migrated position of a seismic event as a function of migration velocity. Image-wave propagation in the common-image gather (CIG) domain can be combined with residual-moveout analysis for iterative migration velocity analysis (MVA). Velocity continuation of CIGs leads to a detection of those velocities in which events flatten. Although image-wave continuation is based on the assumption of a constant migration velocity, the procedure can be applied in inhomogeneous media. For this purpose, CIGs obtained by migration with an inhomogeneous macrovelocity model are continued starting from a constant reference velocity. The interpretation of continued CIGs, as if they were obtained from residual migrations, leads to a correction formula that translates residual flattening velocities into absolute time-migration velocities. In this way, the migration velocity model can be improved iteratively until a satisfactory result is reached. With a numerical example, we found that MVA with iterative image continuation applied exclusively to selected CIGs can construct a reasonable migration velocity model from scratch, without the need to build an initial model from a previous conventional normal-moveout/dip-moveout velocity analysis.

Turning movements in real life capture subtle longitudinal and preataxic changes in cerebellar ataxia

2021 ◽  
Author(s):  
Annika Thierfelder ◽  
Jens Seemann ◽  
Natalie John ◽  
Martin A. Giese ◽  
Ludger Schoels ◽  
...  
Keyword(s):  
Effect Size ◽  
Healthy Subjects ◽  
Dynamic Balance ◽  
Real Life ◽  
Longitudinal Change ◽  
Cerebellar Disease ◽  
Lateral Velocity ◽  
Velocity Change ◽  
High Effect Size ◽  
High Effect

OBJECTIVES: Clinical and regulatory acceptance of upcoming molecular treatments in degenerative ataxias might greatly benefit from ecologically valid endpoints which capture change in ataxia severity in patients real life. This longitudinal study aimed to unravel quantitative motor biomarkers in degenerative ataxias in real life turning movements which are sensitive for changes both longitudinally and at the preataxic stage. METHODS: Combined cross-sectional (n=30) and longitudinal (n=14, 1 year interval) observational study in degenerative cerebellar disease (including 8 pre-ataxic mutation carriers) compared to 23 healthy controls. Turning movements were assessed by three body-worn inertial sensors in three conditions: (1) instructed laboratory assessment, (2) supervised free walking, and (3) unsupervised real-life movements. RESULTS: Measures which quantified dynamic balance during turning, lateral velocity change (LVC) and outward acceleration, but not general turning measures such as speed, allowed differentiating ataxic against healthy subjects in real life with high effect size (δ=0.68), with LVC also differentiating preataxic against healthy subjects (δ=0.53). LVC was highly correlated with clinical ataxia severity (SARA score, effect size ρ=0.79) and subjective balance confidence (ABC score, ρ=0.66). Moreover, LVC in real life but not general turning measures, gait measures, or the SARA score allowed detecting significant longitudinal change in one-year follow-up with high effect size (rprb=0.66). CONCLUSIONS: Measures of turning allow to capture specific changes of dynamic balance in degenerative ataxia in real life, with high sensitivity to longitudinal differences in ataxia severity and to the preataxic stage. They thus present promising ecologically valid motor biomarkers for capturing change in real life, even in the highly treatment-relevant early stages of degenerative cerebellar disease.

Angle-domain common-image gathers from plane-wave least-squares reverse time migration

Geophysics ◽  
2021 ◽  
pp. 1-60
Author(s):  
Chuang Li ◽  
Zhaoqi Gao ◽  
Jinghuai Gao ◽  
Feipeng Li ◽  
Tao Yang
Keyword(s):  
Inverse Problem ◽  
Plane Wave ◽  
Least Squares ◽  
Migration Velocity ◽  
Velocity Analysis ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Migration ◽  
Migration Velocity Analysis ◽  
Amplitude Versus

Angle-domain common-image gathers (ADCIGs) that can be used for migration velocity analysis and amplitude versus angle analysis are important for seismic exploration. However, because of limited acquisition geometry and seismic frequency band, the ADCIGs extracted by reverse time migration (RTM) suffer from illumination gaps, migration artifacts, and low resolution. We have developed a reflection angle-domain pseudo-extended plane-wave least-squares RTM method for obtaining high-quality ADCIGs. We build the mapping relations between the ADCIGs and the plane-wave sections using an angle-domain pseudo-extended Born modeling operator and an adjoint operator, based on which we formulate the extraction of ADCIGs as an inverse problem. The inverse problem is iteratively solved by a preconditioned stochastic conjugate gradient method, allowing for reduction in computational cost by migrating only a subset instead of the whole dataset and improving image quality thanks to preconditioners. Numerical tests on synthetic and field data verify that the proposed method can compensate for illumination gaps, suppress migration artifacts, and improve resolution of the ADCIGs and the stacked images. Therefore, compared with RTM, the proposed method provides a more reliable input for migration velocity analysis and amplitude versus angle analysis. Moreover, it also provides much better stacked images for seismic interpretation.

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