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1
Aldridge, David F., e Douglas W. Oldenburg. "Refractor imaging using an automated wavefront reconstruction method". GEOPHYSICS 57, n. 3 (marzo 1992): 378–85. http://dx.doi.org/10.1190/1.1443252.
Testo completoAbstract (sommario):
The classical wavefront method for interpreting seismic refraction arrival times is implemented on a digital computer. Modern finite‐difference propagation algorithms are used to downward continue recorded refraction arrival times through a near‐surface heterogeneous velocity structure. Two such subsurface traveltime fields need to be reconstructed from the arrivals observed on a forward and reverse geophone spread. The locus of a shallow refracting horizon is then defined by a simple imaging condition involving the reciprocal time (the traveltime between source positions at either end of the spread). Refractor velocity is estimated in a subsequent step by calculating the directional derivative of the reconstructed subsurface wavefronts along the imaged interface. The principle limitation of the technique arises from imprecise knowledge of the overburden velocity distribution. This velocity information must be obtained from uphole times, direct and reflected arrivals, shallow refractions, and borehole data. Analysis of synthetic data examples indicates that the technique can accurately image both synclinal and anticlinal structures. Finally, the method is tested, apparently successfully, on a shallow refraction data‐set acquired at an archeological site in western Crete.
2
Alsamarraie, Mundher. "SEISMIC REFRACTION METHOD IN THE DETERMINATION OF SITE CHARACTERISTICS". Iraqi Geological Journal 53, n. 2D (31 ottobre 2020): 53–63. http://dx.doi.org/10.46717/igj.53.2d.4ms-2020-10-26.
Testo completoAbstract (sommario):
Preliminary site properties need geophysical methods to determine it, the same as the large use of the seismic refraction method to detect the layers of soil and the depth reaching the bedrock. This study was conducted to find out the subsurface profile characteristics of a backyard field in UTM, Skudai following the principles of this method. The analysis of seismic data processed using ZondST2D software by determining the first arrival time until we get a block model of 2D shape based on the primary propagation of seismic velocity wave’s in soil layers. It was found that the investigated subsurface profile consists of four layers showing the level of weathering grade ranges from 600–4000 m/s based on the classification of rock mass in Malaysia. It was found that weathering rates decreased at higher depth, with the increase of density for the material and dampness reduction of seismic velocity. It was concluded that the survey of seismic refraction in development can be used only for shallow subsurface profiles and far from noise and disturbance.
3
Salim, Ashadi. "Analisis Data Seismik Refraksi dengan Metode Generalized-Reciprocal". ComTech: Computer, Mathematics and Engineering Applications 3, n. 1 (1 giugno 2012): 162. http://dx.doi.org/10.21512/comtech.v3i1.2397.
Testo completoAbstract (sommario):
The analysis of seismic refraction data by the generalized reciprocal method can be used for delineating undulating refractors. The forward and reverse times of arrival at different geophones with XY distance along a refraction profile, are used for calculating time depth. The seismic wave velocity in refractor may be obtained from velocity analysis function, and the depth of refractor under each geophone is obtained from time-depths function. This method has been applied at one line of seismic refraction measurement that was 440 m long with 45 geophone positions. The measurement obtained 20 m as the optimum XY-value and 2250 m/s as the velocity of seismic wave in refractor, and the undulating refractor topography with the depths varies 10.4 – 22.1 m. The optimum XY-value was obtained from approximate calculation derived from the observation, that was indicated the absent of undetected layer.
4
Herlambang, N., e A. Riyanto. "Determination of bedrock depth in Universitas Indonesia using the seismic refraction method". IOP Conference Series: Earth and Environmental Science 846, n. 1 (1 settembre 2021): 012016. http://dx.doi.org/10.1088/1755-1315/846/1/012016.
Testo completoAbstract (sommario):
Abstract The seismic refraction method is used to determine the exact bedrock depth for placing a foundation pole. The study was conducted in Universitas Indonesia precisely at the Fasilkom Universitas Indonesia complex. The seismic survey configuration consists of 24 geophone channels with a length of 67.5 m, geophone intervals of 2.5 m, and near offset of 10 m. The wave source was generated using a hammer, and the distance between blows was 5 m. The secondary data used was geological data from SPT (Soil Penetration Test) borehole as a reference for comparison of seismic survey results. Seismic refraction data was processed using traditional techniques, namely the Hagedoorn’s Plus-Minus Method and tomographic inversion using Rayfract software. The correlation between the results of the process with the geological data from SPT drill point shows good results. However, the Plus-Minus Haggedorn method results are only able to show one refractor because of the data limitation, in contrast to the inversion method, which was able to show more than one refractor. There are two main refractors at a depth of 6 meters and 12 meters, and the adequate depth obtained only reaches 15 m. The maximum speed obtained is also around 900 m/s. It can be concluded up to a depth of 15 meters, and there is no recommended rock layer for placement of deep foundations for high rise buildings. A seismic survey with a longer seismic line is needed to get an underground picture exceeding 15 meters.
5
Herlambang, N., e A. Riyanto. "Determination of bedrock depth in Universitas Indonesia using the seismic refraction method". IOP Conference Series: Earth and Environmental Science 846, n. 1 (1 settembre 2021): 012016. http://dx.doi.org/10.1088/1755-1315/846/1/012016.
Testo completoAbstract (sommario):
Abstract The seismic refraction method is used to determine the exact bedrock depth for placing a foundation pole. The study was conducted in Universitas Indonesia precisely at the Fasilkom Universitas Indonesia complex. The seismic survey configuration consists of 24 geophone channels with a length of 67.5 m, geophone intervals of 2.5 m, and near offset of 10 m. The wave source was generated using a hammer, and the distance between blows was 5 m. The secondary data used was geological data from SPT (Soil Penetration Test) borehole as a reference for comparison of seismic survey results. Seismic refraction data was processed using traditional techniques, namely the Hagedoorn’s Plus-Minus Method and tomographic inversion using Rayfract software. The correlation between the results of the process with the geological data from SPT drill point shows good results. However, the Plus-Minus Haggedorn method results are only able to show one refractor because of the data limitation, in contrast to the inversion method, which was able to show more than one refractor. There are two main refractors at a depth of 6 meters and 12 meters, and the adequate depth obtained only reaches 15 m. The maximum speed obtained is also around 900 m/s. It can be concluded up to a depth of 15 meters, and there is no recommended rock layer for placement of deep foundations for high rise buildings. A seismic survey with a longer seismic line is needed to get an underground picture exceeding 15 meters.
6
Shen, Yang, e Jie Zhang. "Refraction wavefield migration". GEOPHYSICS 85, n. 6 (22 ottobre 2020): Q27—Q37. http://dx.doi.org/10.1190/geo2020-0141.1.
Testo completoAbstract (sommario):
Refraction methods are often applied to model and image near-surface velocity structures. However, near-surface imaging is very challenging, and no single method can resolve all of the land seismic problems across the world. In addition, deep interfaces are difficult to image from land reflection data due to the associated low signal-to-noise ratio. Following previous research, we have developed a refraction wavefield migration method for imaging shallow and deep interfaces via interferometry. Our method includes two steps: converting refractions into virtual reflection gathers and then applying a prestack depth migration method to produce interface images from the virtual reflection gathers. With a regular recording offset of approximately 3 km, this approach produces an image of a shallow interface within the top 1 km. If the recording offset is very long, the refractions may follow a deep path, and the result may reveal a deep interface. We determine several factors that affect the imaging results using synthetics. We also apply the novel method to one data set with regular recording offsets and another with far offsets; both cases produce sharp images, which are further verified by conventional reflection imaging. This method can be applied as a promising imaging tool when handling practical cases involving data with excessively weak or missing reflections but available refractions.
7
Aka, Mfoniso U., Okechukwu E. Agbasi, Johnson C. Ibuot e Mboutidem D. Dick. "ASSESSING THE SUSCEPTIBILITY OF STRUCTURAL COLLAPSE USING SEISMIC REFRACTION METHOD". Earth Science Malaysia 4, n. 2 (10 settembre 2020): 140–45. http://dx.doi.org/10.26480/esmy.02.2020.140.145.
Testo completoAbstract (sommario):
Seismic refractive survey is a very important geophysical technique used to investigate the characteristics of the subsurface. The rate of building collapse has demanded the acquaintance about the structure of the subsurface especially in area where lands are recovered from water bodies for the aim of building. This paper presents the technique used in determining the thickness of the overburden for quarry prospecting using a geophysical method called as seismic refraction method. Seismic refraction method was used to delineated two distinct layers with the first layer having a weak and incompetent parameter values. The result revealed that the first layer is composed of unconsolidated formation of soft geomaterials and peaty clay that depict the lower values of parameters. This layer is underlain directly by clay, wet sand and sandy clay of soft and weak incompetent consistencies to a depth of 7 m in the subsurface. The second layer was found to have higher parameters than the first layer. The second layer revealed that the geologic formation composed of dry sand and sandy clay of fair to good competent. The geologic formation in the second layer was found to be more competent than the first layer with high allowable capacity and low ultimate failure potential. Geologically, the composition of the first layer is more recent in age of deposition than the second layer, characterized by unconsolidated geologic formation.
8
Mikesell, T. Dylan, Kasper van Wijk, Elmer Ruigrok, Andrew Lamb e Thomas E. Blum. "A modified delay-time method for statics estimation with the virtual refraction". GEOPHYSICS 77, n. 6 (1 novembre 2012): A29—A33. http://dx.doi.org/10.1190/geo2012-0111.1.
Testo completoAbstract (sommario):
Topography and near-surface heterogeneities lead to traveltime perturbations in surface land-seismic experiments. Usually, these perturbations are estimated and removed prior to further processing of the data. A common technique to estimate these perturbations is the delay-time method. We have developed the “modified delay-time method,” wherein we isolate the arrival times of the virtual refraction and estimate receiver-side delay times. The virtual refraction is a spurious arrival found in wavefields estimated by seismic interferometry. The new method removes the source term from the delay-time equation, is more robust in the presence of noise, and extends the lateral aperture compared to the conventional delay-time method. We tested this in an elastic 2D numerical example, where we estimated the receiver delay-times above a horizontal refractor. Taking advantage of reciprocity of the wave equation and rearranging the common shot gathers into common receiver gathers, isolated source delay times could also be obtained.
9
Lankston, Robert W., e Marian M. Lankston. "Obtaining multilayer reciprocal times through phantoming". GEOPHYSICS 51, n. 1 (gennaio 1986): 45–49. http://dx.doi.org/10.1190/1.1442038.
Testo completoAbstract (sommario):
A critical parameter in interpreting seismic refraction data with the generalized reciprocal method (GRM) is the reciprocal time, which must be available for each layer from which refracted rays return to the surface. The reciprocal time can be measured in the field, but this requires special equipment or procedures. Shooting to obtain the reciprocal time from each layer along a long seismic line may be operationally impractical. However, the method of phantoming arrivals overcame the problems. In phantoming, a reciprocal time is actually measured along any length of the seismic refraction line for any refractor and that value can be used as the reciprocal time in GRM processing if the first‐break arrival times are phantomed properly. Realizing that the reciprocal time may be extracted from overlapping normal forward and reverse shots and phantoming the data accordingly will save much field time and expense. An example shows the results of using a reciprocal time measured across one spread for simultaneously processing and interpreting collinear, overlapping spreads.
10
Palmer, Derecke. "The measurement of weak anisotropy with the generalized reciprocal method". GEOPHYSICS 65, n. 5 (settembre 2000): 1583–91. http://dx.doi.org/10.1190/1.1444846.
Testo completoAbstract (sommario):
Anisotropy parameters can be determined from seismic refraction data using the generalized reciprocal method (GRM) for a layer in which the velocity can be described with the Crampin approximation for transverse isotropy. The parameters are the standard anisotropy factor, which is the horizontal velocity divided by the vertical velocity, and a second poorly determined parameter which, for weak anisotropy, is approximated by a linear relationship with the anisotropy factor. Although only one anisotropy parameter is effectively determined, the second parameter is essential to ensure that the anisotropy does not degenerate to the elliptical condition which is indeterminate using the approach described in this paper. The anisotropy factor is taken as the value for which the phase velocity at the critical angle given by the Crampin equation is equal to the average velocity computed with the optimum XY value obtained from a GRM analysis of the refraction data. The anisotropy parameters can be used to improve the estimate of the refractor velocity, which can exhibit marked dip effects when the overlying layer is anisotropic. In a model study, depths computed with the phase velocity at the critical angle are within 3% of the true values, whereas those calculated with the horizontal phase velocity (which assumes isotropy) are greater than the true depths by about 25%. Anisotropy illustrates the pitfalls of model‐based inversion strategies, which seek agreement between the travetime data and the computed response of the model. With anisotropic layers, the traveltime data provide the seismic velocity in the overlying layer in the horizontal direction, whereas the seismic velocity near the critical angle is required for depth computations. If anisotropy is applicable, then the GRM using the methods described in this paper is able to provide a good starting model for other approaches, such as refraction tomography.
11
Tungka, Marie. "Determining subsurface geology with seismic refraction tomography survey". IOP Conference Series: Earth and Environmental Science 1003, n. 1 (1 aprile 2022): 012037. http://dx.doi.org/10.1088/1755-1315/1003/1/012037.
Testo completoAbstract (sommario):
Abstract Seismic refraction tomography survey is one of the geophysical techniques that is the most popular and commonly used to determine subsurface geology in engineering application. It is fast, reliable, cheaper and cover bigger area in shorter time compared with borehole drilling and other geophysical techniques in providing continuous information on subsurface geology along the lengths of the seismic survey lines. However, the success of seismic refraction tomography survey depends on a few factors such as noise background, top soil features, geology of the site, limitation of the equipment, understanding of the theories and experiences in interpreting the seismic refraction tomography survey data. The method of seismic refraction tomography survey measures the first arrival time of the primary waves through the earth material after seismic signals were generated at several shot points with sledge hammer or explosives. In this paper, the applications of seismic refraction tomography survey in investigating the subsurface geology were discussed in two case studies. The first case study discussed the effect of geophone interval in the limit of depth penetration of seismic refraction tomography survey. Increasing the geophone interval would increase the limit of depth penetration, which helped in mapping the very deep bedrock profile. The second case study showed that the seismic refraction tomography survey results were able to indicate the highly irregular bedrock profiles and complexity of the subsurface geology such as shear zones. It was able to show the extent of the shear zones at the project area, which would have been missed by merely doing borehole drilling. Hydrothermally altered granite and quartz veins were encountered in the boreholes located along the shear zones. Both case studies showed good correlations between boreholes and seismic refraction tomography survey results.
12
Su, Yizhe, Deli Wang, Bin Hu, Xiangbo Gong e Junming Zhang. "Supervirtual Refraction Interferometry in the Radon Domain". Remote Sensing 15, n. 2 (8 gennaio 2023): 384. http://dx.doi.org/10.3390/rs15020384.
Testo completoAbstract (sommario):
Accurate picking of seismic first arrivals is very important for first arrival travel time tomography, but the first arrivals appearing at far offsets are often more difficult to pick accurately due to the low signal-to-noise ratio (SNR). The conventional supervirtual refraction interferometry (SVI) method can improve the SNR of first arrivals to a certain extent; however, it is not suitable for seismic data that interfered by strong noise. In order to better process the first arrivals at far offsets with serious noise interference, we propose a modified method, in which SVI implemented in the Radon domain (RDSVI) due to the cross-correlation in the Radon domain have a better effect. According to the kinematic characteristics of first arrival refractions, SVI is performed in the linear Radon domain. Both synthetic data and field data demonstrate the proposed method can enhance the effective signal and attenuate the strong noise simultaneously, so as to significantly improve the SNR of the first arrival data. Meanwhile, the RDSVI method is tested on the first arrival data with missing traces, which proves that this method can overcome the influence of abnormal traces and is suitable for the reconstruction of sparsely sampled seismic data.
13
Mikesell, Dylan, e Kasper van Wijk. "Seismic refraction interferometry with a semblance analysis on the crosscorrelation gather". GEOPHYSICS 76, n. 5 (settembre 2011): SA77—SA82. http://dx.doi.org/10.1190/geo2011-0079.1.
Testo completoAbstract (sommario):
Crosscorrelating wavefields recorded at two receivers to produce data as if one receiver was a source is commonly referred to as seismic interferometry, or the virtual source method. An artifact in seismic interferometry related to critically refracted waves allowed us to estimate the velocity in the refracting layer. In addition, we devised a new semblance analysis on the crosscorrelation of reflection and refraction energy to robustly estimate the depth and velocity of the slow layer, tested with a numerical example and field data from the Boise Hydrogeophysical Research Site.
14
Mitchell, James F., e Richard J. Bolander. "Structural interpretation using refraction velocities from marine seismic surveys". GEOPHYSICS 51, n. 1 (gennaio 1986): 12–19. http://dx.doi.org/10.1190/1.1442026.
Testo completoAbstract (sommario):
Subsurface structure can be mapped using refraction information from marine multichannel seismic data. The method uses velocities and thicknesses of shallow sedimentary rock layers computed from refraction first arrivals recorded along the streamer. A two‐step exploration scheme is described which can be set up on a personal computer and used routinely in any office. It is straightforward and requires only a basic understanding of refraction principles. Two case histories from offshore Peru exploration demonstrate the scheme. The basic scheme is: step (1) shallow sedimentary rock velocities are computed and mapped over an area. Step (2) structure is interpreted from the contoured velocity patterns. Structural highs, for instance, exhibit relatively high velocities, “retained” by buried, compacted, sedimentary rocks that are uplifted to the near‐surface. This method requires that subsurface structure be relatively shallow because the refracted waves probe to depths of one hundred to over one thousand meters, depending upon the seismic energy source, streamer length, and the subsurface velocity distribution. With this one requirement met, we used the refraction method over a wide range of sedimentary rock velocities, water depths, and seismic survey types. The method is particularly valuable because it works well in areas with poor seismic reflection data.
15
Leung, Tak Ming. "Controls of traveltime data and problems of the generalized reciprocal method". GEOPHYSICS 68, n. 5 (settembre 2003): 1626–32. http://dx.doi.org/10.1190/1.1620636.
Testo completoAbstract (sommario):
Traveltime data required for 2D seismic refraction surveys are 2D first arrivals. To obtain a high degree of consistency between traveltime data and the seismic model, it is important to verify that traveltime data are appropriate for interpretation or an inversion process. Controls or checkpoints presented here inspect compatibility among traveltime data. Similar to the ray‐trace check on the consistency of interpretation, these controls provide an objective means of quality assessment of seismic refraction data. The theoretical aspects of the generalized reciprocal method (GRM) are studied because concerns have been raised regarding the accuracy of some interpretations using this method. The problem of the GRM is that the optimum XY value, which is the most important parameter in the method, is assumed to be twice the offset distance. Consequently, based on this unproven assumption, the efficacy of the optimum XY value is somewhat exaggerated.
16
Popescu, Laurențiu-Ștefan, e Adrian Ceptureanu. "Geophysical Analyses on the Geomechanical Characteristics of the Soil for Choices of the Drilling Rig, in the Area of Târgu Ocna, Bacău County, Romania". Mining Revue 28, n. 3 (1 settembre 2022): 48–58. http://dx.doi.org/10.2478/minrv-2022-0020.
Testo completoAbstract (sommario):
Abstract As part of the company Geoscan Service S.R.L., I was contacted to investigate the possibility of using resistivity, refraction seismic data and MASW seismic to identify the stratification up to 15m deep so that the client could choose the type of drilling rig for installing the conductor in order to drill two water injection wells. The main problem in the choice of geophysical methods was the lack of detailed geological data for calibrating the obtained results, as the presence of groundwater, the thicknesses of the deluvial layer and the bedrock. The choice of geophysical methods and the work procedure are carried out according to the international standards in force, ASTM D6429-99 “Standard guide for Selecting Surface Geophysical Methods”, ASTM D5777-00 “Standard guide for Using the Seismic Refraction Method for Subsurface Investigation, “Standard Guide for Using the Direct Current Resistivity Method for Subsurface Site Characterization”, STAS 1242/7-84 “Geophysical research of the land by seismic methods”.
17
Hatherly, P. J., e M. J. Neville. "Experience with the generalized reciprocal method of seismic refraction interpretation for shallow engineering site investigation". GEOPHYSICS 51, n. 2 (febbraio 1986): 255–65. http://dx.doi.org/10.1190/1.1442085.
Testo completoAbstract (sommario):
The shallow seismic refraction method has been used routinely during the initial investigation at many dam sites in New South Wales. By using computer processing techniques and advanced interpretational features of the generalized reciprocal method, it has been possible to derive a picture of the subsurface layering from the refraction results even in geologically complex environments. Close cooperation between the geophysicist and geologist is necessary to ensure proper use of the seismic results. The results may be used to guide subsequent drilling programs and to aid design and construction. This approach to engineering site investigations is demonstrated with results from two recent investigations.
18
Fadhli*, Zul, Sabrian Tri Anda, Muhammad Syukri, Moehammad Ediyan Raza Karmel, Alfi Sunny Tutifla, Purwandy Hasibuan e Rini Safitri. "Ground Surface Quality Assessment Using P-wave Velocity from 2-D Seismic Refraction Method". Aceh International Journal of Science and Technology 11, n. 3 (31 dicembre 2022): 258–65. http://dx.doi.org/10.13170/aijst.11.3.28818.
Testo completoAbstract (sommario):
A good strength level of the ground surface is the main concern in an area with rapid housing infrastructure development, such as Baitussalam district-Aceh Besar, Indonesia. A seismic refraction method was applied with three similar profile lines using PASI 16S – 24P equipment and 10 Hz vertical geophones to identify the sub-surface layer. The result was processed using Winsism software and Surfer 8. The results of seismic refraction were deduced and correlated with conventional geotechnical investigation obtained by a previous study. The results of 3 survey lines show that the area has two main layers. The first layer was interpreted as overburden (soil and clayey sand) with a compressional wave velocity (Vp) value of fewer than 1.8 km/s. The second layer produces a high velocity of more than 2 km/s. This second layer is interpreted as highly to moderately weathered rock. The results of seismic refraction surveys of the present study suggest a reasonably good correlation with the standard penetration test (SPT) and rock quality designation (RQD) obtained in the previous investigation. The strength level of the second layer showed N-SPT of 65 and RQD of at least 50%.
19
Rolph, Tim C., John Shaw, Edward Derbyshire e An Zhisheng. "Determining Paleosol Topography Using Seismic Refraction". Quaternary Research 42, n. 3 (novembre 1994): 350–53. http://dx.doi.org/10.1006/qres.1994.1085.
Testo completoAbstract (sommario):
AbstractThe seismic refraction reversed profiling technique has been used to investigate the topography of the last interglacial soil (paleosol S1) within the central Chinese Loess Plateau near Xifeng. The results suggest an essentially flat-lying soil at a depth which varies by only a few meters over an area of more than 10 km2. In addition, the results indicate a high-velocity layer at 50-60 m depth which is thought to coincide with a layer of carbonate concretions at the base of paleosol S5. The results agree well with the local loess-paleosol stratigraphy for this area and indicate that the seismic refraction method is a rapid technique for investigating paleotopography.
20
de Franco, Roberto, Grazia Caielli, Alberto Villa, Federico Agliardi e Francesco Franchino. "Ground-penetrating radar refraction imaging with stacked refraction convolution section method". GEOPHYSICS 81, n. 5 (settembre 2016): H33—H45. http://dx.doi.org/10.1190/geo2015-0475.1.
Testo completoAbstract (sommario):
We have evaluated a technique initially developed for the seismic refraction imaging, the stacked refraction convolution section (SRCS), which we have properly adapted to process ground-penetrating radar (GPR) refraction data. Through a mute operation, the subsurface refracting signals, recorded by the receiver from two reciprocal sources, are selected. Following that, a velocity analysis by means of the crosscorrelation of the refracted signals and the convolution of resulting traces is performed. The refraction image in intercept times is successively derived from three main steps, namely: (1) the convolution of the subsurface refracted signals, (2) the crosscorrelation of convolved trace with the reciprocal refracted signal, and (3) the stacking of crosscorrelated traces over all source couples. The technique is not only suitable for the processing of GPR data acquired with two or more reciprocal common source profiles but it is also convenient for its low acquisition cost in addition to the simplicity of software implementation and short processing times. We have evaluated the technique on a real GPR data set to characterize a near-surface morphostructure associated with a deep-seated gravitational slope deformation affecting Mt. Watles (Upper Venosta Valley, Italy). Results of the SRCS technique were validated against the direct trenching log data up to approximately 3 m in depth and complemented by the reflection processing outputs of common-source and common-offset data acquired along the line. The SRCS and common-midpoint processing provide the best reconstruction of the subsurface morphology of a shallow basement (approximately [Formula: see text] depth), characterized by a velocity range of [Formula: see text] and made of strongly to moderately weathered paragneiss. The full-wave modeling response of the reconstructed model demonstrates good agreement with the recorded signals.
21
Andika, P. P., A. Tohari, T. Yudistira, E. Soebowo e J. Arifin. "Understanding of flow liquefaction in Lolu Village based on seismic refraction tomography method". IOP Conference Series: Earth and Environmental Science 1173, n. 1 (1 maggio 2023): 012029. http://dx.doi.org/10.1088/1755-1315/1173/1/012029.
Testo completoAbstract (sommario):
Abstract A big earthquake may induce flow liquefaction phenomena in lowland areas made up of sedimentary deposits. To understand the factors controlling such a hazard, it is necessary to have knowledge of the sub-surface geological conditions of the liquified area. This paper presents the results of a series of seismic refraction measurements in Lolu Village where flow liquefaction occurred during the 2018 Palu-Donggala earthquake. The results of seismic refraction tomography indicate the presence of horst-graben structures, probably associated with the localized pull-apart basin. The results of this study suggest that the sub-surface geological structure is also a governing factor for the occurrence of flow liquefaction phenomena in an area with a complex fault system.
22
Liu, Chuanhai, e Joann M. Stock. "Quantitative determination of uncertainties in seismic refraction prospecting". GEOPHYSICS 58, n. 4 (aprile 1993): 553–63. http://dx.doi.org/10.1190/1.1443438.
Testo completoAbstract (sommario):
We present a model of the propagation of refracted seismic waves in planar (horizontal or dipping) layered structures in which we quantify the errors from various sources. The model, called the (mixed) variance component model, separates the errors originating on the surface from those due to inhomogeneities of subsurface layers. The model starts with the assumption of homogeneous (constant‐velocity) layers, but by taking the principal errors into account, variations from this model (including degree of velocity inhomogeneity, vertical velocity gradients, and gradational interfaces) can be identified. A complete solution to the variance component model by Bayesian methods relies on the Gibbs sampler, a recently well‐developed statistical technique. Using the Gibbs sampler and Monte Carlo methods, we can estimate the posterior distributions of any parameter of interest. Thus, in addition to estimating the various errors, we can obtain the velocity‐versus‐depth curve with its confidence intervals at any relevant point along the line. We analyze data from a crustal‐scale refraction line to illustrate both features of this method. The results indicate that the conventional linear regression model for the first arrivals is inappropriate for this data set. As might be expected, geophone spacing strongly affects our ability to resolve the heterogeneities. Differences in the amount of velocity heterogeneity in different layers can be resolved, and may be useful for lithologic characterization. For this crustal‐scale problem, a velocity profile derived from this method is an improvement over simple linear interpretations, but it could be further refined by more comprehensive methods attempting to match later arrivals and wave amplitudes as well as first arrivals. The method could also be applied to smaller‐scale refraction problems, such as determination of refraction statics, or constraints on the degree of probable lateral variations in velocity of shallow layers, for improved processing of reflection data.
23
Onwubuariri, Chukwuebuka Nnamdi, Emmanuel Kenechukwu Anakwuba, Chidiebere Charles Agoha, Emmanuel Egwuonwu, Joseph Ugochukwu, Lawson-Jack Osaki e Tochukwu Innocent Mgbeojedo. "Subsurface Characterization Using Downhole Refraction Survey: A Case Study of the Niger Delta". Engineering and Applied Sciences 9, n. 1 (7 marzo 2024): 1–13. http://dx.doi.org/10.11648/j.eas.20240901.11.
Testo completoAbstract (sommario):
This study addresses the critical role of downhole refraction as a method for assessing subsurface characteristics, particularly in areas facing challenges such as ground roll issues and weak reflection signals during seismic data acquisition. Focused on the Agudama, Kenfa, and Yenegwe settlements in the Niger Delta region, where frequent engineering structure collapses occur, the research aims to understand the depth and velocity of unconsolidated zones through downhole refraction. The study emphasizes the limitations of relying solely on uphole refraction and highlights the necessity of downhole methods for accurate velocity determination. The research employs various techniques, including borehole drilling, velocity measurements, and seismic pulse generation. The study's primary objectives include investigating the causes of engineering structure failures, proposing geophysical solutions, and contributing valuable insights into the geological context of the Niger Delta region. The fieldwork involved a comprehensive approach, combining reconnaissance surveys, downhole refraction studies, and the use of specialized equipment such as a Geometrics Stratavisor NZXP seismograph and explosives for seismic sources. The results of the downhole refraction survey reveal a double-layer velocity model in the research areas, indicating variations in weathered or unconsolidated layer thickness and velocities. The study establishes a relationship between elevation, weathered layer thickness, and velocities in both weathered and consolidated layers, offering valuable information for engineering considerations. The research concludes that the downhole refraction method is crucial for evaluating weathered strata properties and provides cost-effective subsurface information. The study recommends drilling below the weathered zone for seismic energy source placement, excavation depths for stable structures, and future investigations focusing on closely spaced data points and additional soil properties. These recommendations aim to enhance the safety and durability of structures in the study area, contributing to the understanding and mitigation of engineering structure failures in the Niger Delta region.
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Huang, Huaiyong, Carl Spencer e Alan Green. "A method for the inversion of refraction and reflection travel times for laterally varying velocity structures". Bulletin of the Seismological Society of America 76, n. 3 (1 giugno 1986): 837–46. http://dx.doi.org/10.1785/bssa0760030837.
Testo completoAbstract (sommario):
Abstract In an attempt to speed up the lengthy process of modeling seismic refraction/wide-angle reflection data, a two-dimensional ray tracing routine is used as the basis for an automated travel-time inversion scheme. Laterally varying P-wave velocity structures are represented by arbitrary-shaped blocks of constant velocity gradient. Velocities, gradients, and boundary points of the blocks are parameters in the inversion scheme, and the input data are refraction and reflection travel-time arrivals from both directions of a reversed seismic line. Damped least-squares techniques are used to solve the equations of condition, and inversions are allowed to proceed automatically for several iterations. A synthetic example is presented, and the data from two reversed seismic refraction profiles recorded recently in eastern Canada are inverted to demonstrate the utility of the method under less than ideal conditions. The synthetic test demonstrates that several iterations of the procedure are necessary for accurate recovery of input models and provides a resolving power analysis of the problem, while the real data example produces models comparable to those obtained by experienced interpreters using trial and error methods.
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Colombo, Daniele, Federico Miorelli, Ernesto Sandoval e Kevin Erickson. "Fully automated near-surface analysis by surface-consistent refraction method". GEOPHYSICS 81, n. 4 (luglio 2016): U39—U49. http://dx.doi.org/10.1190/geo2016-0018.1.
Testo completoAbstract (sommario):
Industry practices for near-surface analysis indicate difficulties in coping with the increased number of channels in seismic acquisition systems, and new approaches are needed to fully exploit the resolution embedded in modern seismic data sets. To achieve this goal, we have developed a novel surface-consistent refraction analysis method for low-relief geology to automatically derive near-surface corrections for seismic data processing. The method uses concepts from surface-consistent analysis applied to refracted arrivals. The key aspects of the method consist of the use of common midpoint (CMP)-offset-azimuth binning, evaluation of mean traveltime and standard deviation for each bin, rejection of anomalous first-break (FB) picks, derivation of CMP-based traveltime-offset functions, conversion to velocity-depth functions, evaluation of long-wavelength statics, and calculation of surface-consistent residual statics through waveform crosscorrelation. Residual time lags are evaluated in multiple CMP-offset-azimuth bins by crosscorrelating a pilot trace with all the other traces in the gather in which the correlation window is centered at the refracted arrival. The residuals are then used to build a system of linear equations that is simultaneously inverted for surface-consistent shot and receiver time shift corrections plus a possible subsurface residual term. All the steps are completely automated and require a fraction of the time needed for conventional near-surface analysis. The developed methodology was successfully performed on a complex 3D land data set from Central Saudi Arabia where it was benchmarked against a conventional tomographic work flow. The results indicate that the new surface-consistent refraction statics method enhances seismic imaging especially in portions of the survey dominated by noise.
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Kanasewich, E. R., Z. Hajnal, A. G. Green, G. L. Cumming, R. F. Mereu, R. M. Clowes, P. Morel-a-l'Huissier et al. "Seismic studies of the crust under the Williston Basin". Canadian Journal of Earth Sciences 24, n. 11 (1 novembre 1987): 2160–71. http://dx.doi.org/10.1139/e87-205.
Testo completoAbstract (sommario):
The seismic refraction method was used in 1981 to study the crust under the northern half of the Williston Basin, in Saskatchewan. A new method of spatial seismic recording, based on a triangular arrangement of receivers, was used for the first time to obtain three-dimensional structure and velocity information. The broadside seismic refraction and wide-angle reflection data obtained by the technique were of particular value in defining several faulted blocks. These blocks are also characterized by aeromagnetic anomalies trending in a northerly direction. The crustal thickness in the southern part of the western provinces shows large variation ranging from 35 to 50 km. Much of the area is also notable for the presence of one or more low-velocity layers and a high-velocity lower crust. There is good evidence for significant lateral heterogeneity, and detailed deep seismic reflection and refraction studies would likely yield information on dips and strikes of beds and faults around the basin as well as define the properties of the various terranes of the Hudsonian mobile belt.
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Hunter, J. A., e S. E. Pullan. "A vertical array method for shallow seismic refraction surveying of the sea floor". GEOPHYSICS 55, n. 1 (gennaio 1990): 92–96. http://dx.doi.org/10.1190/1.1442775.
Testo completoAbstract (sommario):
In recent years, specific requirements of offshore geotechnical site investigations, as well as detailed defense research studies, have stimulated research interest in methods for measuring seismic velocities of sea‐floor sediments on the continental shelves. Investigations have used wide‐angie subbottom reflection measurements (McKay and McKay, 1982), bottom‐laid refraction cables (Hunter et al., 1979), and towed refraction arrays, both on the surface (Hunter and Hobson, 1974) and at depth (Fortin et al., 1987; Fagot, 1983).
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Cárdenas Soto, Martín, José Antonio Gámez Lindoro, Valeria Peña Gaspar, Juan Pablo Aguirre Díaz e Alejandro García Serrano. "A Pseudo 3D seismic refraction tomography for exploring archaeological structures". Ingeniería Investigación y Tecnología 23, n. 1 (1 gennaio 2022): 1–9. http://dx.doi.org/10.22201/fi.25940732e.2022.23.1.003.
Testo completoAbstract (sommario):
In the seismic refraction method, refracted waves provide the velocity and irregularity of the substratum. In this study, we took advantage of this method to construct 3D images of the refractor subsurface for two rectangular arrays of sources and receivers. The procedure consists of fitting a straight line to the refracted arrival times that pass through each of the cells that discretize the study surface. The slope inverse is the P-wave velocity, and the intercept time allows us to estimate the substratum depth. We applied this method to two archaeological zones where it was necessary to know the structure of the subsoil velocity and the possible presence of anomalies associated with buried constructions. Although the technique does not allow detecting irregularities of surface layers close to the surface, the results show good agreement with the results of the 2D seismic sections. The velocity distribution shows anomalies related to buried structures and lateral discontinuities due to changes in the composition of the materials.
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Pradnya Andika, Putu, Adrin Tohari e Dadan Dani Wardhana. "Study of the sub-surface geological condition of the Sibalaya flow liquefaction using seismic refraction method". E3S Web of Conferences 464 (2023): 02008. http://dx.doi.org/10.1051/e3sconf/202346402008.
Testo completoAbstract (sommario):
Understanding the occurrence of flow liquefaction requires knowledge of the sub-surface condition controlling its occurrence. This paper presents the results of seismic refraction surveys conducted to evaluate the sub-surface geological condition in the Sibalaya flow liquefaction area. From the interpretation of the seismic refraction model, an inclined boundary presents between the near-surface sediment layers. Further examinations of the SRT images demonstrate the existence of localized basinal structures in the rock layer with the highest P-wave velocity. The basinal structure may be associated with a hidden normal fault system of horst-graben structures. Thus, this study indicates that such a complex sub-surface geological structure also contributed to the Sibalaya flow liquefaction occurrence.
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Boschetti, Fabio, Mike C. Dentith e Ron D. List. "Inversion of seismic refraction data using genetic algorithms". GEOPHYSICS 61, n. 6 (novembre 1996): 1715–27. http://dx.doi.org/10.1190/1.1444089.
Testo completoAbstract (sommario):
The use of genetic algorithms in geophysical inverse problems is a relatively recent development and offers many advantages in dealing with the nonlinearity inherent in such applications. However, in their application to specific problems, as with all algorithms, problems of implementation arise. After extensive numerical tests, we implemented a genetic algorithm to efficiently invert several sets of synthetic seismic refraction data. In particular, we aimed at overcoming one of the main problems in the application of genetic algorithms to geophysical problems: i.e., high dimensionality. The addition of a pseudo‐subspace method to the genetic algorithm, whereby the complexity and dimensionality of a problem is progressively increased during the inversion, improves the convergence of the process. The method allows the region of the solution space containing the global minimum to be quickly found. The use of local optimization methods at the last stage of the search further improves the quality of the inversion. The genetic algorithm has been tested on a field data set to determine the structure and base of the weathered layer (regolith) overlaying a basement of granite and greenstones in an Archaean terrain of Western Australia.
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Bery, Andy A. "Merge-Optimization Method of Combined Tomography of Seismic Refraction and Resistivity Data". ISRN Geophysics 2012 (31 dicembre 2012): 1–6. http://dx.doi.org/10.5402/2012/293132.
Testo completoAbstract (sommario):
This paper discussed a novel application called merge-optimization method that combines resistivity and seismic refraction data to provide a detailed knowledge of the studied site. This method is interesting because it is able to show strong accuracy of two geophysical imaging methods based on many of data points collected from the conducted geophysical surveys of disparate data sets based strictly on geophysical models as an aid for model integration for two-dimensional environments. The geophysical methods used are high resolution methods. The resistivity imaging used in this survey is able to resolve the subsurface condition of the studied site with low RMS error (less than 2.0%) and 0.5 metre electrodes interval. For seismic refraction method, high resolution of seismic is used for correlation with resistivity results. Geophones spacing is 1.0 metre and the total number of shot-points is 15, which provides very dense data point. The algorithms of merge-optimization have been applied to two data sets collected at the studied site. The resulting images have been proven to be successful because they satisfy the data and are geometrically similar. The regression coefficient found for conductivity-resistivity correlation is 95.2%.
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Tryggvason, Ari, Cedric Schmelzbach e Christopher Juhlin. "Traveltime tomographic inversion with simultaneous static corrections — Well worth the effort". GEOPHYSICS 74, n. 6 (novembre 2009): WCB25—WCB33. http://dx.doi.org/10.1190/1.3240931.
Testo completoAbstract (sommario):
We have developed a first-arrival traveltime inversion scheme that jointly solves for seismic velocities and source and receiver static-time terms. The static-time terms are included to compensate for varying time delays introduced by the near-surface low-velocity layer that is too thin to be resolved by tomography. Results on a real data set consisting of picked first-arrival times from a seismic-reflection 2D/3D experiment in a crystalline environment show that the tomography static-time terms are very similar in values and distribution to refraction-static corrections computed using standard refraction-statics software. When applied to 3D seismic-reflection data, tomography static-time terms produce similar or more coherent seismic-reflection images compared to the images using corrections from standard refraction-static software. Furthermore, the method provides a much more detailed model of the near-surface bedrock velocity than standard software when the static-time terms are included in the inversion. Low-velocity zones in this model correlate with other geologic and geophysical data, suggesting that our method results in a reliable model. In addition to generally being required in seismic-reflection imaging, static corrections are also necessary in traveltime tomography to obtain high-fidelity velocity images of the subsurface.
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Aoki, Toru, Toshiyuki Kagawa e Toshifumi Matsuoka. "Analysis of refraction seismic survey using the plus-minus method". BUTSURI-TANSA(Geophysical Exploration) 63, n. 4 (2010): 333–44. http://dx.doi.org/10.3124/segj.63.333.
Testo completo
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Mohd. Nayan, Khairul Anuar, Rahman Yaccup, Abd Rahim Samsudin, Umar Hamzah e Abd Ghani Rafek. "The use of seismic refraction method in slope failure investigation". Bulletin of the Geological Society of Malaysia 40 (30 luglio 1997): 203–13. http://dx.doi.org/10.7186/bgsm40199715.
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Nissen, Johan. "The MINILOC method — a new approach to shallow seismic refraction". Journal of Applied Geophysics 29, n. 1 (febbraio 1992): 63. http://dx.doi.org/10.1016/0926-9851(92)90022-d.
Testo completo
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Zainal, Muzakir, Badrul Munir, Marwan Marwan, Muhammad Yanis e Akmal Muhni. "Characterization of Landslide geometry using Seismic Refraction Tomography in the GayoLues, Indonesia". Journal of Physics and Its Applications 3, n. 2 (30 aprile 2021): 148–54. http://dx.doi.org/10.14710/jpa.v3i2.10601.
Testo completoAbstract (sommario):
Landslides are the most common geological phenomenon in Indonesia.The event is damage to public infrastructure, and fatalities was a big impact. Therefore, mapping the geometry of landslides is a part of the mitigation effort possible by geophysical methods. In this research, we applied seismic refraction tomography (SRT) to study the geometry of the sliding zone from the landslide event.TheNational Disaster Management Authority reported that the area was frequently occurring landslide disaster, i.e. 2018, 2019 and 2020 which caused the public infrastructure and obstructed the road access from the central to the west of Aceh. The SRT was measured in two profileslong the road.Data measurements were conducted on the side of the Babahrot - GayoLues road section that had experienced landslides.Measurements were made using the Seismograph PASI 16S24-P and 24 geophones to obtain a 92-meterlong profile with 2 meter spacing between the geophones. P-wave velocity data modeling is done using ZondST2D software.The results of modeling profiles 1 and 2 describe three different subsurface layers.The SRT profile 1 model consists of slate (0.2 - 0.7 km/s), clay (0.8 - 1.3 km/s), and sandy clay (1.4 - 1.9 km/s).While, the model of profile 2 consists of slate (0.5 - 1.0 km/s), clay (1.1 - 1.6 km/ s), and sandy clay (1.7 - 2.5 km/s).The contrasting wave velocity model shows that the SRT method can be used in landslide studies as a reference in determining the mechanism of the landslide system.
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Wahyu, Anna, Ade Filla Intan, Arddhiles Adhitama, Febrian Nur Fadhli, Ferda Elita Putri, Gunarta Sutantio, Henest Paskah et al. "Integrated Analysis of Microtremor Horizontal to Vertical Spectral Ratio, Surface Waves Dispersion Curve, and Seismic Refraction Tomography to Estimate Weathered Layer Thickness and Seismic Vulnerability: Case Study Kalirejo Village, Kokap Sub-District, Kulon Progo Regency". Jurnal Fisika Indonesia 22, n. 3 (27 aprile 2020): 23. http://dx.doi.org/10.22146/jfi.v22i3.55648.
Testo completoAbstract (sommario):
Subduction of Indo-Australia plate to Eurasia plate and locally active fault nearby Kulon Progo play as major source for earthquake events. After effect due to earthquake has different level of damage which depend on the magnitude and site characteristics. The horizontal-to-vertical spectral ratio (HVSR) passive seismic method is being used drastically to help in mapping the level of site vulnerability to earthquake event. HVSR analysis results help us acquire some physical values including weathered layer thickness where Vs 30 reference came from surface waves dispersion curve analysis of the MASW method as it is used as a parameter in calculating thickness value. Seismic refraction tomography is used to create subsurface model thus we may see the extent of underlying layer and its implication to earthquake event.Data measurements distribution are scattered in Kalirejo Village with the total of 63 passive seismic data, 33 MASW data, and 7 lines of seismic refraction acquisition. Some data show inadequate quality to be taken into further processing step, so data sorting activity should be carefully done. As a result, 21 of 63 passive seismic data are considered adequate to represent site physical values. Dominant frequency values ranging from 2 to 20 Hz, amplification factor varies between 1.5-12.5, and seismic vulnerability indices varies between 0.3-20. Surface waves dispersion curve inversion results are Vs 30 values ranging from 350 m/s to 980 m/s and seismic refraction tomography model shows Vp model with velocity values ranging from 0.2 to 3.2 km/s.
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Hamimu, La, Syamsul Razak Haraty, Al Rubaiyn, La Ode Ihksan Juarzan e Indrawati. "Computation and Modelling of Seismic Refraction Tomography for Anisotropic Medium Based on Pseudo Bending Method". Journal of Physics: Conference Series 2734, n. 1 (1 marzo 2024): 012049. http://dx.doi.org/10.1088/1742-6596/2734/1/012049.
Testo completoAbstract (sommario):
Abstract Seismic refraction tomography is one of the imaging techniques in geophysical methods used to remodel the near-surface velocity layer structure of the Earth. In this study, we carried out a new computational approach and modelling of seismic refraction tomography using the pseudo-bending method. The true model of the near-surface is designed to be anisotropic medium which is having a low velocity anomaly distribution. This anomaly is constructed in such a way as to be similar to a model of liquid waste away spreading, which exhibits seismic velocities ranging from 1600 m/s to 1800 m/s. Based on our computations and numerical modelling results, it was found that the ray tracing path using pseudo-bending method displays an asymmetrical trajectory when the positions of the source and geophone are exchanged. Altering the shooting configuration from direct shoot (DS) to reversed shoot (RS) also reveals a significant difference in travel time values. The results of delay time tomography inversion, which represents the difference between travel times in the true model and the initial model using the SIRT method, indicate the presence of a low velocity anomaly that can be interpreted as the distribution of liquid waste.
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Ayub, Syahrial, Muhammad Zuhdi e Joni Rokhmat. "Aplikasi Metode Seismik Refraksi dalam Menentukan Lapisan dan Tingkat Kekerasan Batuan di Bawah Permukaan Desa Medana Lombok Utara". Kappa Journal 4, n. 2 (30 dicembre 2020): 188–96. http://dx.doi.org/10.29408/kpj.v4i2.2607.
Testo completoAbstract (sommario):
The seismic refraction method is one of the geophysical methods which is based on measuring the response of seismic waves in the soil that are fractured along the soil and rock layers. One of the seismic refraction method application is to determine the layers and rocks types below the surface. This study uses a geophone as a catcher for seismic waves that are emitted below the surface. The waves caught on the geophone are converted into seismic data which can be read in a seismograph. Seismic data read by seismographs are already in digital form and stored in the central unit PASI 16S24-P. The results of the data analysis concluded that below the land surface of the village of Medana, there were 3 rock layers with a thickness of the first layer 3-4 meters, the second layer 2-5 meters and the third layer 10-17 meters. The first and second layers are still in the form of soil (less compact), while the third layer is in the form of rock (compact). The level of hardness (density) will be more compact in linear to the depth, the more the depth will be the more compact the rock. The depth in the form of hard rock starts from 16 meters to 23 meters from the ground level of the village of Medana, Central Lombok.
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Kilty, Kevin T., Roger A. Norris, W. Reid McLamore, Kerry P. Hennon e Kenneth Euge. "Seismic refraction at Horse Mesa Dam: An application of the generalized reciprocal method". GEOPHYSICS 51, n. 2 (febbraio 1986): 266–75. http://dx.doi.org/10.1190/1.1442086.
Testo completoAbstract (sommario):
Horse Mesa Dam is located in the Mazatzal Mountains about 60 miles east of Phoenix, Arizona, and is a part of the Salt River Project. Early in 1981, the management of the Salt River Project decided to solve problems with the existing roadway to the dam by building an improved roadway and retaining wall. Geotechnical engineers on the project originally planned to obtain depth‐to‐bedrock information for the design of these structures by drilling a large number of boreholes to bedrock. However, we decided that more complete information could be obtained less expensively by using fewer drill holes tied together with seismic refraction lines. The complicated physical setting of the site made planning for the survey very important. The bedrock surface at the site is quite irregular, dipping as steeply as 30 degrees across the axis of the roadway, and the space between the stream bank on one side of the roadway and the canyon wall on the other side is very narrow. Because of these constraints, we calculated that head waves refracted along the bedrock surface would never be observed on refraction lines shot across the roadway. Therefore, we decided to shoot two long refraction lines along the axis of the existing roadway—one each on the inside and outside shoulders of the road bed—to provide two points on the bedrock surface at any particular cross‐section of the road. Field work at the site was done between June 10 and June 15, 1981. We obtained reversed coverage on 914 m (3 000 ft) of 70 m (230 ft) spreads along the road. Because of the attenuation of the coarse overburden material, 0.45 kg charges of Kinestik were necessary to deliver seismic energy across these spreads, and 0.15 kg charges were necessary at the center shots. To avoid overwhelming background noise at the site, we performed much of the survey in the evening or early morning when the turbines at the dam were idle. Survey results showed not only a highly irregular bedrock surface, but also indicated substantial velocity variations within both the overburden and bedrock. Overburden velocities varied from 366 m/s (1 200 ft/s) to 549 m/s (1 800 ft/s), while bedrock velocities varied from 1 829 m/s (6 000 ft/s) to nearly 7 620 m/s (25 000 ft/s). We interpreted the results with the generalized reciprocal method (GRM), which is widely used in Australia but is not so well‐known in the United States. This method proved to be particularly well‐suited for situations involving large lateral velocity variations and highly irregular refractor surfaces. When compared with the seven borings that were eventually done on the roadway, the refraction interpretation was accurate to within a few feet; or, in terms of the nominal depth to bedrock, the results were accurate to within about 10 percent. This is remarkable agreement considering the irregularity of the bedrock surface. The Horse Mesa Dam study shows the importance of planning a survey with the physical characteristics of the site and the goals of the survey in mind. It also shows the value of a powerful, flexible interpretation method—in this case, the GRM. Most important, it demonstrates that engineering geophysics is capable of providing useful, accurate information at a lower cost than drilling alone.
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Syifa, Resi Wasilatus, Nur Ichsan Sumardani, Nur Amalia Dewi, Teti Febrianti, Jauhari Arifin e Bebeh Wahid Nuryadin. "Identification of Landfill Using Refraction Seismic Method in LIPI Area - Bandung". Risenologi : Jurnal Sains, Teknologi, Sosial, Pendidikan, dan Bahasa 5, n. 1 (26 aprile 2020): 26–37. http://dx.doi.org/10.47028/j.risenologi.2020.51.76.
Testo completoAbstract (sommario):
Research has been carried out using seismic refraction in the LIPI area - Bandung, which aims to determine the land of embankment in the area. Retrieval of field data was carried out using geometric Es-3000 tool along 46 meters with a spacing of 2 meters and a 7 shoot punch consisting of 2 phantom shoots beginning and ending. Data processing is done by the first step, namely by geometric editing so that data can be read by the computer. The inversion process is done by seismimager software which consists of pickwin to extract data and plotera for modeling the subsurface layer. The results of the data interpretation show the P wave velocity from 315 - 435 m / s. layer grouping based on P wave velocity is at the first color layer having a wave velocity of about 315 - 342 m / s, the second color layer has a wave speed of 355-382 m / s, and the third color layer has a speed of 359 - 422 m / s and thick layer more than 435. Based on the lithological classification of subsurface rock layers, this study area tends to have a layer of soil type with a depth of 5 meters, and can be said to be a layer of soil deposits because of the formation of soil structures that tend to be new
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Harmoko, U., G. Yulianto e R. D. Indriana. "The possibility of geothermal permeability detection by using seismic refraction method". Journal of Physics: Conference Series 1217 (maggio 2019): 012041. http://dx.doi.org/10.1088/1742-6596/1217/1/012041.
Testo completo
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Liu, Sixin, Zhuo Jia, Yinuo Zhu, Xueran Zhao e Siyuan Cheng. "Optimized Refraction Travel Time Tomography". Applied Sciences 9, n. 24 (11 dicembre 2019): 5439. http://dx.doi.org/10.3390/app9245439.
Testo completoAbstract (sommario):
In seismic refraction exploration, travel time tomography is the most widely used method in engineering and environmental geophysical exploration. In this paper, we mainly optimize the travel time tomography of refraction. First, with respect to the forward algorithm, we introduce a new travel time calculation method to improve the accuracy and efficiency of forward calculation. Based on the fast marching method (FMM), we introduce an improved forward calculation method called the multi-stencil fast marching method (MSFM). In the process of inversion, we propose a dynamic prior model composite constraint (DPMCC) method based on the T0 difference method from the idea of multi-scale inversion. Meanwhile, we use the prior information to improve the accuracy of inversion. Furthermore, we use the dynamic regularization factor selection method to make the inversion solution more stable and reliable. Finally, we test and analyze the synthetic data and the measured data to verify the effectiveness of the optimized travel time tomography algorithm.
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Mereu, R. F. "The complexity of the crust and Moho under the southeastern Superior and Grenville provinces of the Canadian Shield from seismic refraction - wide-angle reflection data". Canadian Journal of Earth Sciences 37, n. 2-3 (2 aprile 2000): 439–58. http://dx.doi.org/10.1139/e99-122.
Testo completoAbstract (sommario):
The major features of the individual velocity models, Poisson's ratio values, and crustal complexity derived from the interpretation of seismic data sets from four long-range seismic refraction - wide-angle reflection experiments are summarized. The experiments were conducted from 1982-92 in the southeastern portion of the Canadian Shield. In the conventional analysis of seismic refraction - wide-angle reflection data, only the onset times and amplitudes of the major arrival phases are used to derive seismic velocity models of the region under study. These models are over smoothed, have a number of intermediate discontinuities, are unable to explain the Pg coda, and bear very little resemblance to the models derived from the analysis of near-vertical seismic reflection data. In this paper some of the differences between seismic models derived from near-vertical reflection analysis and those from refraction analysis are reconciled from an analysis of the wide-angle reflection fields of the crustal coda waves that follow the first arrivals. This was done using a migration technique that to a first approximation maps the amplitudes of the record sections into a two-dimensional (2-D) complexity section. These new sections show significant lateral variations in crustal and Moho reflectivity and may be used to complement the 2-D velocity anomaly sections and near-vertical reflection sections. The method was based on a numerical study that showed that the coda can be explained with a class of complex heterogeneous models in which sets of small-scale, high-contrast sloping seismic reflectors are "embedded" in a uniform seismic velocity gradient field.
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Bergmann, Peter, Artem Kashubin, Monika Ivandic, Stefan Lüth e Christopher Juhlin. "Time-lapse difference static correction using prestack crosscorrelations: 4D seismic image enhancement case from Ketzin". GEOPHYSICS 79, n. 6 (1 novembre 2014): B243—B252. http://dx.doi.org/10.1190/geo2013-0422.1.
Testo completoAbstract (sommario):
A method for static correction of time-lapse differences in reflection arrival times of time-lapse prestack seismic data is presented. These arrival-time differences are typically caused by changes in the near-surface velocities between the acquisitions and had a detrimental impact on time-lapse seismic imaging. Trace-to-trace time shifts of the data sets from different vintages are determined by crosscorrelations. The time shifts are decomposed in a surface-consistent manner, which yields static corrections that tie the repeat data to the baseline data. Hence, this approach implies that new refraction static corrections for the repeat data sets are unnecessary. The approach is demonstrated on a 4D seismic data set from the Ketzin [Formula: see text] pilot storage site, Germany, and is compared with the result of an initial processing that was based on separate refraction static corrections. It is shown that the time-lapse difference static correction approach reduces 4D noise more effectively than separate refraction static corrections and is significantly less labor intensive.
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Juhojuntti, Niklas, e Jochen Kamm. "Joint inversion of seismic refraction and resistivity data using layered models — Applications to groundwater investigation". GEOPHYSICS 80, n. 1 (1 gennaio 2015): EN43—EN55. http://dx.doi.org/10.1190/geo2013-0476.1.
Testo completoAbstract (sommario):
We developed a method for joint inversion of seismic refraction and resistivity data, using sharp-boundary models with few layers (typically three). We demonstrated the usefulness of the approach via examples from near-surface case studies involving shallow groundwater exploration and geotechnical investigations, although it should also be applicable to other types of layered environments, e.g., sedimentary basins. In our model parameterization, the layer boundaries were common for the resistivity and velocity distributions. Within the layers, only lateral variations in the material parameters (resistivity and velocity) were allowed, and we assumed no correlation between these. The inversion was performed using a nonlinear least-squares algorithm, using lateral smoothing to the layer boundaries and to the materialparameters. Depending on the subsurface conditions, the smoothing can be applied either to the depth of the layer boundaries or to the layer thicknesses. The forward responses and Jacobian for refraction seismics were calculated through ray tracing. The resistivity computations were performed with finite differences and a cell-to-layer transform for the Fréchet derivatives. Our method performed well in synthetic tests, and in the case studies, the layer boundaries were in good agreement with in situ tests and seismic reflection data, although minimum-structure inversion generally has a better data fit due to more freedom to introduce model heterogeneity. We further found that our joint inversion approach can provide more accurate thickness estimates for seismic hidden layers.
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Edigbue, Paul, Abdullatif Al-Shuhail e Sherif M. Hanafy. "Three-dimensional supervirtual seismic refraction interferometry: A case study in western Saudi Arabia". GEOPHYSICS 86, n. 3 (19 marzo 2021): B123—B133. http://dx.doi.org/10.1190/geo2020-0310.1.
Testo completoAbstract (sommario):
The semiautomatic seismic refraction supervirtual interferometry (SVI) algorithm has been developed to improve the conventional SVI method. The conventional SVI method uses convolution techniques and involves the raw trace, which reintroduces noise back into the enhanced trace. However, the semiautomatic method uses a first-arrival reference picked from a raw trace to compute the arrival times of all enhanced virtual traces. The semiautomatic SVI method has been extended recently from 2D to 3D geometry and applied on a synthetic 3D seismic data set using the raw traces of only one inline. We have developed a case study of the semiautomatic 3D SVI method by applying the algorithm on an active seismic refraction data set that consists of 82,944 raw traces from 288 shot gathers that use an accelerated weight drop source. Due to possible differences in the source wavelet among shots, the semiautomatic 3D SVI method is applied on the 288 raw traces from each shot gather separately. The SVI technique generates 41,328 distinct correlograms from one shot, which results in the production of a trace with a much better signal-to-noise ratio.
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Poormirzaee, Rashed, Siamak Sarmady e Yusuf Sharghi. "A New Inversion Method Using a Modified Bat Algorithm for Analysis of Seismic Refraction Data in Dam Site Investigation". Journal of Environmental and Engineering Geophysics 24, n. 2 (giugno 2019): 201–14. http://dx.doi.org/10.2113/jeeg24.2.201.
Testo completoAbstract (sommario):
Similar to any other geophysical method, seismic refraction method faces non-uniqueness in the estimation of model parameters. Recently, different nonlinear seismic processing techniques have been introduced, particularly for seismic inversion. One of the recently developed metaheuristic algorithms is bat optimization algorithm (BA). Standard BA is usually quick at the exploitation of the solution, while its exploration ability is relatively poor. In order to improve exploration ability of BA, in the current study, a hybrid metaheuristic algorithm by inclusion a mutation operator into BA, so-called mutation based bat algorithm (MBA), is introduced to inversion of seismic refraction data. The efficiency and stability of the proposed inversion algorithm were tested on different synthetic cases. Finally, the MBA inversion algorithm was applied to a real dataset acquired from Leylanchay dam site at East-Azerbaijan province, Iran, to determine alluvium depth. Then, the performance of MBA on both synthetic and real datasets was compared with standard BA. Moreover, the dataset was further processed following a tomographic approach and the results were compared to the results of the proposed MBA inversion method. In general, the MBA inversion results were superior to standard BA inversion and results of MBA were in good agreement with available boreholes data and geological sections at the dam site. The analysis of the seismic data showed that the studied site comprises three distinct layers: a saturated alluvial, an unsaturated alluvial, and a dolomite bedrock. The measured seismic velocity across the dam site has a range of 400 to 3,500 m/s, with alluvium thickness ranging from 5 to 19 m. Findings showed that the proposed metaheuristic inversion framework is a simple, fast, and powerful tool for seismic data processing.
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René, R. M., J. L. Fitter, D. J. Murray e J. K. Walters. "Reflection and refraction seismic studies in the Great Salt Lake Desert, Utah". GEOPHYSICS 53, n. 4 (aprile 1988): 431–33. http://dx.doi.org/10.1190/1.1442475.
Testo completoAbstract (sommario):
Seismic refraction and CDP reflection profiles were acquired across mud flats of the Great Salt Lake Desert, Utah, during the summer of 1983. a combination of weight drops, horizontal hammers, buried explosives, and explosives detonated in air (Poulter method) was used. A 6.4 km refraction and single‐fold reflection profile indicates the presence of a shallow depression (Donner Reed basin) eastb of Donner Reed pass in the Silver Island Mountains. A basin floor ramp of Paleozoic rocks dipping approximately 30 degrees east into the Crater Island graben is interpreted beneath a 4.6 km 12-fold CDP reflection profile obtained by the Poulter method. This ramp extends beneath at least 0.8 km of condolidated Neogene sediments and 0.8 km of younger (largely unconsolidated) sediments. Weight‐drop and horizontal‐hammer profiles for the critical refraction along the Silurian Laketown dolomite yield P-wave and S-wave velocity estimates of 5270 ± 100 and [Formula: see text], respectively. The mud flats, with their laterally uniform finegrained sediments and shallow water table, provided excellent coupling of seismic energy. Air shots of 4.1 to 5.4 kg explosives without a source array gave good penetration to a depth of about 1.6 km. Partial migration before stack facilitated estimation of moveout velocities in the case of layers onlapping against a basin floor ramp, even though the maximum dips were only about 30 degrees. Gravity modeling and seismic ray tracing through intervals of constant velocity bounded by polynomial interfaces aided synergetic interpretation of the reflection, refraction, and gravity data.
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Deen, Tara, e Karsten Gohl. "3‐D tomographic seismic inversion of a paleochannel system in central New South Wales, Australia". GEOPHYSICS 67, n. 5 (settembre 2002): 1364–71. http://dx.doi.org/10.1190/1.1512741.
Testo completoAbstract (sommario):
Buried paleochannels are of significant interest for understanding hydrological mechanisms and their potential as alluvial gold deposits. Seismic tomographic methods are a suitable solution for resolving the vertical and horizontal structure of such features. We assess a method for seismic 3‐D tomographic inversion from refraction arrivals with reflection control over a suspected paleochannel adjacent to the Wyalong gold fields in the Lachlan fold belt of central New South Wales, Australia. A standard multichannel engineering seismic recording and cable–receiver system was used on a 3‐D field geometry of multiple linear arrays. More than 3000 P‐wave first‐arrival traveltime values were inverted using a regularized inversion scheme for which simplified 2‐D models served as initial velocity–depth models for the complete 3‐D inversion. Seismic reflection arrivals provided additional depth estimates to the bedrock and compensated for a lack of refraction phases at that depth. Correlating the 3‐D seismic velocity–depth data with existing drillhole and nonseismic geophysical data resulted in a detailed structural and compositional interpretation of the paleochannel and the incised regolith. The model suggests the presence of a system of deposits from meandering channels overlying a metasedimentary bedrock formation. The general paleodrainage deposit is relatively conductive in electromagnetic surveys, indicating a potential saline storage or transport mechanism.