Interval Velocity Research Articles

Limits on resolution enhancement for PS data mapped to PP time

Motivated by the desire for greater resolution in PS data, and an interest in methods designed to produce this, we have explored some fundamental concepts of PS resolution in order to better understand proposed methods. Our study has produced three key results: PS-to-PP mapping using either interval or average velocity ratios yields identical results. Although mapping changes the bandwidth of the PS signal, it does not change its wavelength or resolution. Modest increases in resolution can be realized after mapping if the wavelet is known, but any method designed to increase bandwidth without such knowledge should be treated with caution.

The QT Interval Could be a Marker of Subclinical Atherosclerosis in Patients with Type 2 Diabetes

Several studies have shown that prolongation of QT interval predicts the risks of all-cause and cardiovascular mortality. Moreover, a close association was reported between prolongations of QT interval and pulse wave velocity (PWV) in general population without preexisting cardiovascular disease. The aim of this study was to evaluate the relationship between QT interval and PWV in patients with type 2 diabetes without preexisting cardiovascular disease. In a cross-sectional study of 251 Japanese patients with type 2 diabetes, we examined the correlation of the heart rate-corrected QT interval duration (QTc) with PWV or other various parameters, including age, duration of diabetes, body mass index, systolic blood pressure, hemoglobin A1c, serum cholesterol, creatinine, uric acid, potassium, severity of diabetic nephropathy or retinopathy and current treatment of diabetes. The QTc correlated positively with PWV (r=0.268, p<0.0001). Multiple regression analysis demonstrated that the QTc was independently correlated with PWV (β=0.155, p=0.0119), after adjustment for known risk factors. According to the receiver operator characteristic analyses (ROC), the area under the ROC curve (AUC) of QTc and the Framingham 10-year coronary heart disease risk score (FRS) for arterial stiffness were 0.69 and 0.64, respectively. The AUC of QTc for arterial stiffness was similar to that of FRS for artificial stiffness (p=0.6532). In conclusion, the QT interval could be a marker of subclinical atherosclerosis in patients with type 2 diabetes.

The Missing Dark Energy of the Cosmos from Light Cone Topological Velocity and Scaling of the Planck Scale

The paper presents an exact analysis leading to an accurate theoretical prediction of the amount of the mysteriously missing hypothetical dark energy density in the cosmos. The value found, namely 95.4915028% is in full agreement with earlier analysis, the WMAP and the supernova cosmic measurements. The work follows first the strategy of finding a critical point which separates a semi-classical regime from a fully relativistic domain given by topological unit interval velocity parameter then proceeds to wider aspects of a topological quantum field of fractal unit interval. This idea of a critical velocity parameter was first advanced by Sigalotti and Mejias in 2006 who proposed a critical value equal . A second interesting proposal made in 2012 by Hendi and Sharifzadeh set the critical point at 0.8256645. The present analysis is based upon a light cone velocity quantized coordinate. This leads to the same quantum relativity energy mass relation found in earlier publications by rescaling that of Einstein’s special relativity. Two effective quantum gravity formulae are obtained. The first is for the ordinary measurable energy of the quantum particle while the second is for dark energy density of the quantum wave which we cannot measure directly and we can only infer its existence from the measured accelerated expansion of the universe E(D) = where . The critical velocity parameter in this case arises naturally to be . The results so obtained are validated using a heuristic Lorentzian transformation. Finally the entire methodology is put into the wider perspective of a fundamental scaling theory for the Planck scale proposed by G. Gross.

Study of Interval Velocity Calculating and its Application in Geologic Structure Complex Region Area

The distinctive terrain and physiognomy character, sedimentary environment in the geological structure complex region maybe because the seismic wave velocity to change largely in the vertical direction. In this program, first set continental zone QDN-3D in slope zone of continental shelf of Southeast Hainan Basin, aim to the phenomenon of theoretical Dix formula with the assumption that horizontal structure and constant horizontal seismic wave always leads to the obtain velocity uncertain. .Then apply the constrained Dix inversion based on the exponential asymptotically bounded velocity model and the well seismic unity establish model to solve the velocity calibration technique. The structure distortion affection caused by depth variation, layer velocity varied in the vertical direction can be removed well by the twice velocity obtain technique, and the algorithm is accurately and fast. Not only the trial calculation of synthetic model but also the processing of actual data all produces a geological plausible, stable result, predicts oil and gas reservoir.

Task-parallel implementation of 3D shortest path raytracing for geophysical applications

This paper discusses two variants of the shortest path method and their parallel implementation on a shared-memory system. One variant is designed to perform raytracing in models with stepwise distributions of interval velocity while the other is better suited for continuous velocity models. Both rely on a discretization scheme where primary nodes are located at the corners of cuboid cells and where secondary nodes are found on the edges and sides of the cells. The parallel implementations allow raytracing concurrently for different sources, providing an attractive framework for ray-based tomography. The accuracy and performance of the implementations were measured by comparison with the analytic solution for a layered model and for a vertical gradient model. Mean relative error less than 0.2% was obtained with 5 secondary nodes for the layered model and 9 secondary nodes for the gradient model. Parallel performance depends on the level of discretization refinement, on the number of threads, and on the problem size, with the most determinant variable being the level of discretization refinement (number of secondary nodes). The results indicate that a good trade-off between speed and accuracy is achieved with the number of secondary nodes equal to 5. The programs are written in C++ and rely on the Standard Template Library and OpenMP.

Seismic reflection imaging of the mafic-ultramafic Windimurra Igneous Complex, Yilgarn Craton, Western Australia

A deep seismic reflection survey was carried out over the Meso-Neoarchean Youanmi Terrane, Yilgarn Craton in Western Australia, including 3 seismic lines across the Windimurra Igneous Complex. This gabbroic intrusion is the largest exposed single mafic-ultramafic intrusion in Australia, currently mined for magnetite-hosted vanadium in its upper zone. Acquisition was carried out with 3 Hemi 60 vibrators, 80 or 40 m VP interval, 40 m group interval, and a 300 channel symmetric split spread, resulting in 75 to 150 fold high quality data. Key processing steps included refraction and residual automatic statics, spectral equalisation, detailed stacking velocity analysis, dip moveout (DMO) correction and post stack Kirchhoff migration. The Windimurra Igneous Complex exhibits high seismic velocity (approximately 6.5 km/s), both in interval velocity from stacking velocity and bedrock velocity from refraction statics analysis. Seismic attenuation is low, resulting in high frequency and good resolution to the base of the complex, seen at a maximum two way time of around 2.5 seconds. Gross structure on the seismic sections is also consistent with the gravity and magnetic data. An inward dipping conical structure is evident and consistent with surface geological observations. The base of the complex is marked by distinctive high amplitude multi-layered reflectors, which may represent significant thicknesses of ultramafic zone material unexposed at the surface. This zone has been a long sought after target for Cr-PGE exploration. The complex internal structure of the intrusion, possibly including discordant igneous layering features, has been well imaged up to the base of regolith.

From two-way time to depth and pressure for interpretation of seismic geometries and velocities offshore

SUMMARY The effect of water and rock loading on seismic velocities and consequently on interpreted geometries is often underestimated in offshore studies. Direct comparative analysis of interval velocity patterns between areas of significantly different water depth and thickness of rock overburden requires various pressure related changes in velocity to be accounted for. Presentation of velocity models as a function of pressure rather than two-way time, or depth, emerges as a possible solution. An accurate velocity model is essential for meaningful timeto-depth conversion of interpreted seismic horizons. Ideally, it should be based on integration of seismic velocities from well log measurements, refraction seismic surveys and from stacking of multi-channel marine reflection data. In some cases velocities derived from stacking of high quality long streamer marine reflection seismic data correlate reasonably with well log measurements and velocities derived from refraction seismic studies, and provide clues to reasonable depth conversion and lithology interpretation.

A case study: travel time inversion for P-wave velocity using OBS data of South China Sea

It is very important for converting the seismic data from the time domain to the depth domain. Here we discuss the approaches of inverse modeling of travel times for determination of the P-wave velocity (Vp). The migration section of the single channel seismic data is used to define the model horizons and help to control their geometry. Wide angle hydrophone data of OBS are used to determine P-wave travel times. The picked travel times from various shots are inverted for P-wave interval velocities using RayInvr, which calculated theoretical travel times via ray tracing. Damped least squares optimization is performed to fine tune the fits between observed and calculated travel times. In the end, the Vp curve is achieved and the results are compared with that derived from the conventional hyperbolic curve velocity analysis method, the shape of the two curves are similar, and the velocity increases in the layer where gas hydrates are present.

Gas hydrate and associated free gas in the Dongsha Area of northern South China Sea

A large ongoing cold seep, named Jiulong Methane Reef, was discovered in the Dongsha Area of northern South China Sea (SCS) in 2004. To understand links among seafloor methane seepage, subsurface gas hydrate, origin of gas source and structural styles controlling the formation and accumulation of gas hydrate, high resolution multi-channel seismic data were interpreted in this region. Bottom Simulating Reflectors (BSRs), known as the base of gas hydrate stability zone, were identified and mapped. Additionally, seismic attributes, interval velocity model, and acoustic P wave impedance were obtained to better delineate the spatial distribution of gas hydrate. Hydrate-bearing sediments are characterized by weak reflection (i.e. blanking zone) above BSRs, high velocities and relatively small acoustic impedance differences, while enhanced reflection, low frequency, and low velocities beneath BSRs suggest the presence of underlying free gas beneath solid hydrate. A number of faults, mud diapirs and a possible submarine landslide were observed in seismic profiles. Both faults and mud diapirs are useful conduits, allowing methane gas to migrate upward and linking free gas zones beneath BSRs, hydrate zones and seafloor methane seepage. A submarine landslide with a length scale of ∼10 km is observed in a seismic profile. The landslide may trigger dissociation of gas hydrate, accounting for the occurrence of Jiulong Methane Seepage. Seismic observations and estimated heat flow coupled with geochemical analyses suggest that gas source of methane in this region probably originates from mixture of biogenic and thermogenic methane. This study would not only help to understand gas hydrate system in the Dongsha Area, but also provide insights to geological hazards associated with the dissociation of gas hydrate.

From two way time to depth and pressure for interpretation of seismic velocities offshore: Methodology and examples from the Wallaby Plateau on the West Australian margin

The effect of water loading can account for sub-seafloor seismic P-wave velocity increases exceeding 1km/s from shallow to deep water, but it is commonly ignored in offshore studies. Direct comparative analysis of interval velocity patterns between areas of significantly different water depths requires various water pressure related changes in velocity to be accounted for. This apparently simple task is not easy to implement in practical terms. One approach is to try to predict velocity increase at any given depth due to the pressure effect of water layer above, and then to reduce the observed interval velocity at that depth by subtraction of the predicted velocity increase. Interval velocities at different locations thus reduced can be compared and conclusions about rock lithology can subsequently be made. The application of water depth adjustments to seismic velocities, and the methods used to apply them, remain controversial. The presentation of velocity models as a function of pressure rather than two-way time, or depth, emerges as a possible solution.Analysis of appropriately adjusted seismic interval velocities from Geoscience Australia's 2008/09 seismic survey GA 310 in conjunction with seismic reflection interpretation provides new insights into the geology of the Wallaby Plateau, offshore of Western Australia. Seismically distinctive divergent dipping reflector sequences (DDRS), identified in the area, are similar in seismic character to seaward dipping reflector sequences (SDRS) of inferred volcanic composition.The water depth adjustment of seismic velocities analysed in our study reduces the distinction between SDRS, DDRS and sedimentary strata such that discrimination between volcanic and sedimentary strata in DDRS or SDRS is equivocal. A major uncertainty of this interpretation is caused by a lack of global reference velocity models of SDRS and DDRS.

Interval velocity analysis using multiparameter common image gathers

We developed a nonconventional approach to interval velocity analysis. The motivation for this approach is based on the argument that when the subsurface structure is complex, velocity error cannot be related to a single parameter. The suggested analysis uses multiparameter common image gathers (MPCIGs), generated by standard prestack depth migration. The parameterization of these multiparameter gathers is directly related to the structural characteristics of the subsurface image points. The undesirable summation, which is usually involved in the generation of conventional common image gathers, is avoided. During the velocity analysis procedure, depth slices taken out of the calculated MPCIGs are examined. Each depth slice contains all seismic data that were migrated into a single image point associated with the specific depth slice. When the MPCIGs are generated with the correct velocity function, each depth slice holds all structural information associated with the corresponding image point. Through detailed analysis of 2D synthetic and real data examples, the influence of migration velocity errors on the accuracy of the migrated multiparameter gathers is demonstrated. A Kirchhoff-based algorithm is used for the migration along with a layer-stripping method, relying on velocity scans, for the analysis. A velocity correctness criterion was also verified, along with some suggestions on the practical usage of the method.

Pure Acceleration Is the Primary Determinant of Speed to First-Base in Major-League Baseball Game Situations

The purposes of this research were to (a) quantify interval sprint times between Home-Plate and the Foul-Line and the Foul-Line and First-Base, (b) determine if differences exist in interval velocities and acceleration between left- and right-handed batters or between-position groupings, and (c) to quantify determinants of time to First-Base in Major-League Baseball players during actual games. A total of 1,896 sprint times to the Foul-Line (13.7 m) and First-Base (27.4 m) were recorded in 302 baseball players by a single coach, positioned in the dugout with a hand-held stopwatch. Interval velocities and accelerations were computed between Home-Plate and the Foul-Line and the Foul-Line and First-Base; average velocity and acceleration were also determined over the entire 27.4 m. Velocity and acceleration for left-handed batters were greater than for right-handed batters from Home-Plate to the Foul-Line and from Home-Plate to First-Base; however, there were no differences in velocity or acceleration from the Foul-Line to First-Base. Interval velocity was significantly greater for outfielders and infielders compared with that for catchers from Home-Plate to the Foul-Line and from the Home-Plate to First-Base. Outfielders were faster than catchers from the Foul-Line to First-Base; no other between-group differences were evident. Accelerations from Home-Plate to the Foul-Line and from Home-Plate to First-Base were greater for outfielders compared with infielders and catchers. Infielders accelerated at greater rates than did catchers between these intervals. There were no between-position differences in acceleration from the Foul-Line to First-Base. These data indicate that time to First-Base is most affected by acceleration from Home-Plate to the Foul-Line. Coaches should implement strategies that encourage players to sprint maximally over the first 13.7 m to maximize chances of successfully reaching First-Base.

Crustal features of the northeastern South China Sea: insights from seismic and magnetic interpretations

We interpret seven two-dimensional deep-penetration and long-offset multi-channel seismic profiles in the northernmost South China Sea area, which were collected by R/V Marcus G. Langseth during the TAIwan GEodynamics Research (TAIGER) project in 2009. To constrain the crustal characteristics, magnetic inversion and forward magnetic modeling were also performed. The seismic results clearly show tilted faulting blocks in the upper crust and most of the fault plane connects downward to a quasi-horizontal detachment as its bottom in the south of the Luzon-Ryukyu transform plate boundary. North of the plate boundary, a small-scale failed rifted basin (minimum 5 km in crustal thickness) with negative magnetization probably indicates an extended continental origin. Significant lower crustal material (LCM) was imaged under a crustal fracture area which indicated a continent and ocean transition origin. The thickest LCM (up to 6.5 km) is located at magnetic isochron C15 that is probably caused by the magma supply composite of a Miocene syn-rift volcanic event and Pliocene Dongsha volcanic activity for submarine volcanoes and sills in the surrounding area. The LCM also caused Miocene crustal blocks to be uplifted reversely as 17 km crustal thickness especially in the area of magnetic isochron C15 and C16. In addition, the wide fault blocks and LCM co-existed on the magnetic striped area (i.e. C15–C17) in the south of the Luzon-Ryukyu transform plate boundary. Magnetic forward modeling suggests that the whole thick crustal thickness (>12 km thick) needs to be magnetized in striped way as oceanic crust. However, the result also shows that the misfit between observed and synthetic magnetic anomaly is about 40 nT, north of isochron C16. The interval velocity derived from pre-stack time migration suggests that the crust is composed of basaltic intrusive upper crust and lower crustal material. The crustal nature should refer to a transition between continent and ocean. Thus, the magnetic reversals may be produced in two possible ways: basaltic magma injected along the crustal weak zone across magnetic reversal epoch and because some undiscovered ancient piece of oceanic crust existed. The crustal structure discrimination still needs to be confirmed by future studies.

Shallow oceanic crust: Full waveform tomographic images of the seismic layer 2A/2B boundary

We present results of full‐waveform tomographic inversions of four profiles acquired over young intermediate‐ and fast spreading rate oceanic crust. The mean velocity‐depth functions from our study include a 0.25–0.30 km‐thick low‐velocity, low‐gradient region beneath the seafloor overlying a 0.24–0.28‐km‐thick high‐gradient region; together these regions compose seismic layer 2A. Mean layer 2A interval velocities are 3.0–3.2 km/s. The mean depth to the layer 2A/2B boundary is 0.49–0.54 km, and mean velocities within the upper 0.25 km of layer 2B are 4.7–4.9 km/s. Previous velocity analyses of the study areas using 1‐D ray tracing underestimate the thickness of the high‐gradient region at the base of layer 2A. We observe differences in the waveform inversion velocity models that correspond to imaging of the layer 2A event; regions with a layer 2A event have higher velocity gradients at the base of layer 2A. Intermittent high velocities, which we interpret as massive flows, are observed in the waveform inversion velocity models at 0.05–0.10 km below the seafloor (bsf) over 10–25% of the intermediate‐spreading profiles and 20–45% of the fast spreading profiles. The high‐gradient region located 0.25–0.54 km bsf at the base of layer 2A may be associated with an increased prevalence of massive flows, the first appearance of dikes (lava‐dike transition zone), or with increased crack sealing by hydrothermal products. The upper portion of layer 2B, which begins at 0.49–0.54 km bsf, may correspond to sheeted dikes or the top of the transition zone of lavas and dikes.

Velocity versus offset (VVO): a new tool for direct detection of gas in low-impedance sand reservoirs

A new direct hydrocarbon indicator is proposed using velocity information, called velocity variation with offset (VVO) or velocity variation with angle. Velocity is extracted from seismic data to predict hydrocarbon distribution in the reservoir. The theory is derived based on an equation for the dependence of velocity with direction in rocks with weak polar anisotropy. Fluid content in the reservoir affects the anisotropic properties of the rock and thereby alters the variation in interval velocity with offset. We have tested VVO over a low-impedance gas sand reservoir that gives rise to a class 3 AVO anomaly. The seismic data from a known gas field were processed with amplitude preservation and offset-based velocity analysis, and AVO and VVO attributes were generated. The VVO attributes are consistently in agreement with AVO responses around the gas discovery well and other bright amplitudes away from the well location. Thomsen’s anisotropy parameters ε and δ can also be derived from VVO analysis. They have anomalously large positive values at the locations with bright amplitudes.

Characterization of Intrabasin Faulting and Deformation for Earthquake Hazards in Southern Utah Valley, Utah, from High-Resolution Seismic Imaging

We conducted active and passive seismic imaging investigations along a 5.6‐km‐long, east–west transect ending at the mapped trace of the Wasatch fault in southern Utah Valley. Using two‐dimensional (2D) P ‐wave seismic reflection data, we imaged basin deformation and faulting to a depth of 1.4 km and developed a detailed interval velocity model for prestack depth migration and 2D ground‐motion simulations. Passive‐source microtremor data acquired at two sites along the seismic reflection transect resolve S ‐wave velocities of approximately 200 m/s at the surface to about 900 m/s at 160 m depth and confirm a substantial thickening of low‐velocity material westward into the valley. From the P ‐wave reflection profile, we interpret shallow (100–600 m) bedrock deformation extending from the surface trace of the Wasatch fault to roughly 1.5 km west into the valley. The bedrock deformation is caused by multiple interpreted fault splays displacing fault blocks downward to the west of the range front. Further west in the valley, the P ‐wave data reveal subhorizontal horizons from approximately 90 to 900 m depth that vary in thickness and whose dip increases with depth eastward toward the Wasatch fault. Another inferred fault about 4 km west of the mapped Wasatch fault displaces horizons within the valley to as shallow as 100 m depth. The overall deformational pattern imaged in our data is consistent with the Wasatch fault migrating eastward through time and with the abandonment of earlier synextensional faults, as part of the evolution of an inferred 20‐km‐wide half‐graben structure within Utah Valley. Finite‐difference 2D modeling suggests the imaged subsurface basin geometry can cause fourfold variation in peak ground velocity over distances of 300 m.

Hyperbolic estimation of sparse models from erratic data

We have developed a hyperbolic penalty function for image estimation. The center of a hyperbola is parabolic like that of an [Formula: see text] norm fitting. Its asymptotes are similar to [Formula: see text] norm fitting. A transition threshold must be chosen for regression equations of data fitting and another threshold for model regularization. We combined two methods: Newton’s and a variant of conjugate gradient method to solve this problem in a manner we call the hyperbolic conjugate direction (HYCD) method. We tested examples of (1) velocity transform with strong noise (2) migration of aliased data, and (3) blocky interval velocity estimation. For the linear experiments we performed in this study, nonlinearity is introduced by the hyperbolic objective function, but the convexity of the sum of the hyperbolas assures the convergence of gradient methods. Because of the sufficiently reliable performance obtained on the three mainstream geophysical applications, we expect the HYCD solver method to become our default method.

A Comparison between Porosity Derived from Seismic Reflection Data and That Computed from Well Log Data, Al Amal Field, Gulf of Suez, Egypt

The present study is a trial to predict of porosity from seismic data in the Al-Amal field, Gulf of Suez, Egypt. This is carried out through the inversion of seismic traces, which allows estimation of reservoir porosity from the analysis of transit times derived from pseudo-velocity logs. A four-step computational procedure is illustrated starting with the inversion of seismic traces and calculation of interval velocities; accurate stratigraphic interpretation; determination of the petrophysical parameters for the porosity evaluation; and analysis of the reliability of the results and final corrections.

Suppressing nonphysical reflections in Green’s function estimates using source-receiver interferometry

Seismic interferometry retrieves the Green’s function propagating between two receiver locations using their recordings from an enclosing boundary of sources. Theory requires that sources completely surround the two receivers, but constraints in exploration seismology restrict sources to locations near the surface of the earth. Seismic interferometry by crosscorrelation then introduces usually undesirable nonphysical reflections (spurious multiples) in the Green’s function estimates. We found that the dominant nonphysical reflections can be converted into physical reflections via convolution using source-receiver interferometry. The resultant Green’s functions display fewer nonphysical reflections and show significantly better agreement with the true Green’s functions than those obtained using crosscorrelational interferometry. Nonphysical reflections can be further suppressed by iterating the convolution step. By comparing the velocity spectra of the Green’s functions retrieved by crosscorrelational and source-receiver interferometry, we can retrospectively identify the dominant nonphysical reflections introduced by crosscorrelational interferometry. We found that the nonphysical reflections are particularly important for constructing the primary reflections and internal multiples in source-receiver interferometry. This is because the primary reflections and internal multiples cannot be created via the convolution of physical reflections. Instead, the primary reflections and internal multiples are retrieved by the appropriate convolution between a nonphysical and physical reflection. We compared crosscorrelational interferometry and source-receiver interferometry using synthetic towed streamer data for a 1D acoustic and 2.5D elastic model, respectively. We also found that the nonphysical reflections obtained using crosscorrelational interferometry allow for the direct estimation of interval velocities and layer thicknesses without the need to use Dix inversion in the 1D example.

Optimizing 3-D seismic survey design parameters using genetic algorithm—a case study in southwest of Iran

The crucial advantages of a 3-D seismic survey are the proper migration of the reflection points and the more accurate study on the structural and stratigraphic targets, reservoir characterization, and joint study. In this article we will focus on Pardis Project in southwest of Iran where no 3-D seismic survey has ever been carried out. The local geological information, previous 2-D seismic, VSP data, and interval velocity information obtained from check shots were taken into consideration to determine the requirements of the survey. The objective is to adequately sample the primary and secondary targets at the depth of 1,200 and 5,000 m, respectively. On the base of the logic dominating a genetic algorithm, the best operational layout was offered to satisfy the geophysical requirements looking forward to satisfy financial constraints. Using Genetic Algorithm Toolbox in MATLAB, we could formulate a mathematical constrained optimization problem. Applying this technique we derived nominal designs which are needed to be evaluated to make sure how well they could image the targets.