Propagation Velocity Of Seismic Waves Research Articles

KURVA T-X

This seismic method practicum meeting is expected that practitioners are able to meet the objectives of knowing the process of forming the T-X curve in refraction seismic. The practicum was held on Monday, December 5, 2022 at the Faculty of Science and Technology, Jambi University. Based on the T-X curve attached to T-X 1, the reverse direct will be inverted from the forward. This value will be searched for an equation to get the result of rock velocity based on forward and reverse waves. Velocity is the level of rock hardness that will determine the speed of a wave in a rock layer. For interpretation, it can be seen from the table of seismic wave propagation velocity in the rock above. Where for V1 of 333.3333 m/s is included in layered weathered rock. For V2 where the speed value is 1000 m/s is unsaturated sand and gravel. For V3 where the velocity value is 1666,67 m/s, it is sand and shale. The interpretation of these rocks actually requires information about the formation where the data was collected.

Identification of Shallow Fault with Seismic Refraction Modelling in Gondang Area, Bojonegoro

There are various considerations in determining whether a field is said to have geothermal potential or not. One of them is the appearance of shallow faults in the area. This shallow fault can function as a permeable layer that is used as a fluid flow path in the geothermal system. Due to the emergence of manifestations around Mount Pandan in the Gondang area, Bojonegoro, seismic refraction measurements are also needed that can support and validate the geothermal potential in the area with the hope of shallow faults that are visible through the interpretation of seismic wave propagation velocity. This measurement produces an anomaly that is thought to be a shallow fault on the track that passes through the main fault, namely on tracks 1, 2, and 5, not far from the manifestation of the Banyukuning hot spring. This is also reinforced by direct observation of the surface conditions as a result of the appearance of shallow faults.

Research on Seismic Exploration Velocity Modeling Based on Deep Learning

As the core parameter of seismic exploration, seismic wave propagation velocity runs through the seismic exploration process. The construction of reasonable and accurate velocity models is an important basis for exploration technologies such as high-precision seismic offset imaging, data processing and interpretation. The current velocity modeling strategy is limited by the target geological body, which has a long calculation period, high calculation cost, and is seriously affected by human subjective factors, and its adaptability to complex geological formations is poor. Based on this, this paper studies the accurate speed modeling method of universities. Firstly, the principle of earthquake detection is analyzed, and then the speed modeling based on improved fully convolutional neural network is studied. A velocity modeling fully convolutional neural network (VNB-FCN) is constructed to directly extract geological features from seismic data and establish a high-precision velocity model. Compared with the traditional velocity modeling method, the VMB-FCN model effectively avoids the problem of excessive dependence of neural networks on standard seismic datasets, and improves the accuracy and efficiency of seismic exploration velocity modeling.

Comprehensive use of the Gutenberg–Richter law and geotomography for improving seismic hazard evaluation in hard coal mines

Mining-induced seismicity occurs in numerous underground mines worldwide where extraction is conducted at great depths or in areas characterised by complex tectonic structure. It is accompanied by rock bursts, which result in the loss of working functionality and the possibility of accidents among personnel. The issue of a constant and reliable seismic hazard evaluation is of key significance for both the safety of miners and the stability of production. Research on its improvement is directed at developing new interpretive solutions and methods. The nature of the presented solution is the complex interpretation of seismological data that characterise rock mass seismicity and of underground measurement results in the form of a map presenting the longitudinal wave propagation velocity distribution in the rock surrounding the mined coal seam. The solution was tested in hard coal mines located in the Upper Silesian Coal Basin. The mines are equipped with a modern seismological system enabling the constant monitoring of seismicity together with hazard level evaluation as well as with seismic apparatus for conducting periodic measurements of the seismic wave propagation velocity before the mining face. Comprehensive seismic hazard evaluation criteria were determined based on the obtained results, involving the anomaly of the Gutenberg–Richter law “b” value and the maximum longitudinal seismic wave propagation velocity in the roof rock. The obtained experience and the result validation of this new comprehensive hazard evaluation method confirm its practical usefulness and indicate the directions of improvement for the solution in question.

NIOM Analysis of Earthquake Observation Records in a Rockfill Dam

ABSTRACTWe applied the normalized input–output minimization method (a method developed for the analysis of propagation times in vertical array records) to long-term earthquake observation records from Aratozawa Dam (in Kurihara, Miyagi prefecture, Japan), spanning the period from July 1992 to December 2019 to determine the propagation velocity of seismic waves in the embankment, and investigated changes in soil properties. As a result, we showed that (1) the velocities of S and P waves in the upper section were 449 and 993 m/s, respectively, prior to the strong earthquake motions derived from earthquake records from January 1997 through October 2001, whereas 608 and 1538, respectively, in the lower section, (2) in the Iwate–Miyagi Nairiku earthquake, the S-wave velocity in the upper section decreased to 158 m/s in the principal shock, and (3) in subsequent minor earthquakes the propagation velocity increased more or less in proportion with the logarithm of the number of elapsed days, requiring three years or longer to return to the initial value, (4) although similar changes were observed in the Great East Japan earthquake of 2011, the reduction in propagation velocity that remained after the principal shock was smaller than in the case of the Iwate–Miyagi Nairiku earthquake, and it was judged that there were no large effects on the dam body such as those that occurred in the Iwate–Miyagi Nairiku earthquake, and furthermore (5) in the principal shock of the Iwate–Miyagi Nairiku earthquake, the shear modulus in the upper part of the dam body decreased from 400 to 50 MPa (with a maximum shear strain of 10−3), resulting in more pronounced changes than in the lower section, whereas the damping ratio increased by at least 10% in the lower section during the principal shock of the Iwate–Miyagi Nairiku earthquake, resulting in much greater changes than in the upper section.

Seismic microzoning of the Tashkent territory based on calculation methods

This article considers the seismic microzoning of the territory of Tashkent based on calculation methods. The basis of the seismic zoning adopted values of the peak ground accelerations (PGAs) at the free surface. Calculations of the peak free surface accelerations were performed using the STRATA program developed by the Pacific Seismotechnical Research Center (USA). For the calculations, the following input parameters were given: the level of seismic influence on the rock base, the geoseismic parameters of the model soil column (a sequence of layers with a given capacity), the density, the propagation velocity of seismic waves, and the nature of the absorption of elastic energy in the layers for 36 seismic-geological models considering the soil strata response to the seismic impact of the set on a rocky half-space. For each model, the peak acceleration and maximum displacement on the free surface and their changes with depth, as well as the response spectra of the ground layer, were obtained. Seismic microzoning schemes for the city given the probability of an earthquake with return periods of 500 years and 2500 years were presented.

Petrophysical characteristics of the Meso-Cenozoic sediments of the Southeastern subsidence of the Greater Caucasus in connection with their oil and gas potential

In order to assess the prospects for oil and gas potential, the reservoir properties of Mezozoy-Kaynazoic sediments, formed in various geological conditions of the structures of Yalama, Khudat and Siazan monocline, have been studied. The results of the analysis are summarized in tables reflecting the physical and reservoir properties of various types of rocks. On the basis of petrophysical analysis for reservoirs of various lithological types, regularities have been established in changes in density, carbonate content, porosity and permeability of rocks, as well as in the propagation velocity of ultrasonic waves. It was found that changes in reservoir properties of rocks over the area are mainly associated with lithogenesis conditions, with heterogeneity of the lithological composition of sedimentary complexes, with the depth of occurrence of rocks, as well as with the peculiarity of the development of local uplifts. When predicting oil and gas content in deep-seated strata of the territory under consideration, along with exploration and geophysical methods, it is also recommended to use the results of changes in the filtration-volume characteristics of rocks, as well as the nature of the change in the propagation velocity of seismic waves with depth. Keywords: lithological facies; density; porosity; permeability; carbonate content; seismic P-wave velocity.

Determination of the structure of the earth's crust by changing the velocity of seismic waves from the earthquake data

Objective. A study of the structure of the earth's crust by determining the velocities of seismic waves from previously broken sections of the earth's crust.Methods. Two mathematical methods are proposed for determining the seismic wave velocities. The first is based on the weighted average method, and the second is based on the matrix method for solving systems of linear algebraic equations. The initial parameters used in the calculations are data from earthquakes that occurred – the coordinates of earthquake centers of origin and seismic sensors, as well as the travel times of seismic waves from the earthquake center of origin to the seismic sensors.Results. The problem of determining the propagation velocity of seismic waves in different parts of the earth's crust is solved by two different methods. The distribution densities of errors in determining the seismic wave velocities are obtained for the weighted average method, in six different situations, for the distribution of seismic wave velocities on the ground, and the matrix method, in the case of distribution of seismic wave velocities on the ground in staggered order.Conclusion. The proposed methods allow refining the coordinates of the centers of the occurred earthquakes while using the iteration method can significantly improve the accuracy of determining the coordinates of the earthquake center of origin and the speeds of seismic waves in various areas. The presence of seismic wave velocities in various parts of the earth's crust during calculations allows determining the coordinates of the earthquake source using new methods based on the use of second-order hyperboloid figures, which were not previously used by seismologists.

Identifikasi Ketebalan Lapisan Lapuk pada Area Rawan Longsor Menggunakan Metode Seismik Refraksi (Studi Kasus: Desa Kalirejo Kabupaten Kulonprogo)

Kalirejo Village, Pengasih District, Kulonprogo Regency, is an area that is prone to landslides. The purpose of this study is to identify the weathering layer thickness, which is one of the triggering factors for landslides. This study was conducted using the seismic refraction method by applying two lines. Line 1 uses 24 geophones, has a distance of 1 meter between geophones, while Line 2 uses 24 geophones, has a distance of 2 meters between geophones. The results showed that the velocity of seismic wave propagation in the weathering layer for Line 1 was 400 m/s, and in the slip surface was 2,300 m/s. The weathering layer thickness on Line 1 is 7.6 - 9.8 meters and the slope is steep so that this location is predicted to have a potential landslide. While the velocity of seismic wave propagation in the weathering layer for Line 2 was 300 m/s, and in the slip surface was 2,200 m/s. The weathering layer thickness on Line 2 is at less than 2 meters, so this location is predicted not to have a landslide potential even though the slope is steep

Estimating changes in seismic wave velocity from a pneumatic source in an operational mine

Rock mass characteristics such as applied stress, pore pressure, and fracture density are coupled to the seismic wave propagation velocity. Therefore, measuring small relative changes of seismic wave velocities in operational mines has the potential for tracking changes in these important rock mass properties. To this end, we have conducted an experiment with the aim of measuring seismic body wave velocities in situ at Williams mine, Hemlo, Canada, using a pneumatic source and multiple receivers. We determine that the signal-to-noise ratio is improved by deconvolving the source signal from the signal recorded at the remotely grouted geophones. We evaluate the estimated relative changes in traveltimes and assume that these are due to changes in the body wave velocity caused by mining-related activities. We are able to successfully detect the source response at remote receivers in an operational mine at a distance of more than 430 m.

Site classification of Italian accelerometric stations from cluster analysis of residuals of peak ground motion data regressions

One basic element for seismic hazard assessment is the empirical definition of ground motion prediction equations (GMPE) to estimate shaking expected for earthquakes of given magnitude and distance. GMPEs are calibrated from data of accelerometric stations, distinguishing among site categories of different lithological type (e.g. hard rocks, more or less stiff soils) expected to cause different levels of ground motion amplification. Such a site classification is commonly based on geological observations and/or geophysical parameters like the mean propagation velocity of seismic waves through subsoil surficial layers. However, doubts have been raised about the effectiveness of results obtained from these conventional methods. Here we propose a methodology of accelerometric site classification relying on peak ground motion observations, exploiting the large amount of such observations available in the Italian National accelerometric database. The method is based on a cluster analysis of differences between observations and predictions provided by GMPEs whose functional form does not comprise site class among the explanatory variables. The new method was applied to the ITalian ACcelerometric Archive (ITACA), extracting a “training” dataset (used to calibrate some GMPEs through regressions) and a “validation” dataset (to select the optimal GMPE form). A cluster analysis was then applied to regression residuals, grouping stations into three categories with increasing value of residual average. Checking the reclassification effectiveness through the examination of differences between independent “validation” observations and predictions of GMPEs adopting the new classification, these proved to be more consistent with site response properties than predictions provided by GMPEs using current classification.

Regularities of crustal faulting and tectonophysical indicators of fault metastability

The problem of forecasting seismic hazards is discussed. The stress state data characterizing various aspects of brittle failure are reviewed in detail. It is shown that the most convenient tool for analyzing such data is the Mohr stress diagram and the Coulomb criterion. Noted is the role of a fluid in not only reducing the normal stresses responsible for brittle failure, but also predetermining the major processes in fault zones. In each fault body, a node can be distinguished as a fault part wherein the main structural and material transformations take place. The node contains narrow elongated zones of modification of mylonites, from protomylonites to ultramylonites and blastomylonites, that are related to the localization of continuous and discontinuous shear deformation. Due to the metamorphic processes, fault zones are less strong than the surrounding consolidated blocks of the crust. A theoretical analysis of the mechanism of displacements along the discontinuities of different scale ranks shows differences in their manifestation. Tectonic and seismic displacements along the rupture occupy the entire area at once, while displacements along the fault zone occur in stages along its extent and follow the ‘rolling-carpet’ principle that is also typical of intra-crystal dislocations. The stress state in the vicinity of ruptures and faults has different characteristic features. Based on the seismological and tectonophysical data on earthquake focal parameters and discontinuities, it is possible to identify two or three ranks of stresses, which differ in the laws predetermining their mutual relationships. Actually, this conclusion contradicts the hypothesis of self-similarity of discontinuities in their continuous range, from a dislocation to a fault zone, which length amounts to tens of kilometers. Besides, it imposes a restriction on the use of statistical analysis of seismic data. The seismic data show that in the source of a large earthquake, displacement develops as a running band (‘rolling-carpet’ principle). In the source of a weak earthquake, it occupies the entire earthquake focal area at once. The differences in the types of shearing in the sources of weak and strong earthquakes are related to the relationships between three dynamic parameters of the medium: velocity of seismic wave propagation, rate of rupture propagation, and displacement rate of the sides of the fracture. Using tectonophysical methods, the stress state was reconstructed for the seismically active regions of the planet and the sources of the mega-earthquakes of the 21st century. Based on the reconstructions, the mean strength and stress values were calculated, and the specific features of the stress fields were revealed. It is established that the strongest regional earthquakes ‘avoided’ the areas with increased effective isotropic pressure. The sizes of the sources of the strongest earthquakes were controlled by the size of the region with decreased effective pressure. The sites, wherefrom the earthquake were initiated, were often located in the zones of the highest stress gradients. These regularities support the term “metastability of the state of fault zone” (introduced to seismology from the physics of the states of matter) and justify it by a specific distribution pattern of stress values prior to the mega-earthquake. Based on the tectonophysical definition of the metastable state of faults, the important role is outlined for a stress gradient zone that represents a location wherein a trigger earthquake occurs. The ‘maturity’ of the zone with increased stress gradient values is, in essence, a characteristic of the time interval of metastability of the fault zone.

Effects of variations in fluid properties and fracture geometry on dispersion, anisotropy, and reflection in media with planar fractures

ABSTRACTOur objective was to discover the effect of variations in fluid properties and fracture geometry on the velocity of seismic wave propagation in fluid‐saturated media with parallel planar fractures. We used numerical models calculated by analytical solutions to examine the behaviour of P‐wave phase velocity dispersion in the normal direction to layering, in non‐porous and porous media with planar fractures. We also examined the anisotropy of low frequency phase and group velocities of fast and slow P‐waves and angular‐dependent reflection coefficients in media with planar fractures, under conditions of saturation by fluids with varying bulk moduli, densities, and fracture apertures. We defined several parametre , , and characterising dispersion, characterising anisotropy, characterising the difference between fast and slow modes, and R0 and characterising reflection. Our results show that the behaviour of dispersion shows wider stopbands in the case of gas saturation. Concavity indicator of dispersion for gas saturation was greater than that for liquid saturation and is usually greater than one. Anisotropy is more sensitive to bulk modulus contrast than to density contrast between the solid and the fluid, and is more sensitive to density contrast than to bulk modulus contrast. The case of gas saturation usually had a greater negative R0 and a greater value of compared with those of brine and heavy and light oil saturations. Our results are helpful in distinguishing fluid types saturating geophysical fractures and estimating the aperture and spacing of planar fractures. In seismic exploration, bulk modulus and fluid density can provide useful information in distinguishing among brine, oil, and gas; fracture geometry is important to estimate the permeability of reservoirs.

Seismic Refraction Method to Study Subsoil Structure

Seismic waves are used in many fields. It can be applied on determine subsoil structure, and materials. In this work use seismograph for the measurement seismic wave propagation velocity in the real geological (subsoil layers) medium. These investigations are applied in petroleum research institute Egypt. Predication results of subsoil layers thickness and seismic wave’s velocity analysis are obtained. The seismograph recorded receiving sample data from geophones and by “SeisImager” software is extract the final seismogram. The seismograph is dependent on Snell law for wave’s propagation. The obtain result of P and S waves of this work are the same as P and S waves references. P waves are shake ground in the direction they are propagating (longitudinal waves), and S waves are shake perpendicularly or transverse to the direction of propagation.

Random vibration analysis of train–bridge under track irregularities and traveling seismic waves using train–slab track–bridge interaction model

The frequent use of bridges in high-speed railway lines greatly increases the probability that trains are running on bridges when earthquakes occur. This paper investigates the random vibrations of a high-speed train traversing a slab track on a continuous girder bridge subjected to track irregularities and traveling seismic waves by the pseudo-excitation method (PEM). To derive the equations of motion of the train–slab track–bridge interaction system, the multibody dynamics and finite element method models are used for the train and the track and bridge, respectively. By assuming track irregularities to be fully coherent random excitations with time lags between different wheels and seismic accelerations to be uniformly modulated, non-stationary random excitations with time lags between different foundations, the random load vectors of the equations of motion are transformed into a series of deterministic pseudo-excitations based on PEM and the wheel–rail contact relationship. A computer code is developed to obtain the time-dependent random responses of the entire system. As a case study, the random vibration characteristics of an ICE-3 high-speed train traversing a seven-span continuous girder bridge simultaneously excited by track irregularities and traveling seismic waves are analyzed. The influence of train speed and seismic wave propagation velocity on the random vibration characteristics of the bridge and train are discussed.

Prestack time imaging algorithm with simultaneous velocity estimation in hard rock environments

Reflection seismic imaging faces several difficulties in hard rock environments. One of them is the estimation of the propagation velocity of seismic waves. Therefore, imaging algorithms that do not require prior construction of a velocity model seem promising for such environments. In this paper we illustrate an application of prestack time migration, which does not require an input velocity model, to hard rock conditions, and we demonstrate its effectiveness on synthetic data. This approach is based on an estimation of local event slopes (horizontal slownesses) in common-shot and common-receiver gathers and a subsequent calculation of the migration attributes (migration velocity, vertical traveltime and horizontal coordinates of the migrated reflection point). These attributes allow us to derive all the information needed to construct a time-migrated image. We also use the obtained migration velocities as an input velocity model for Kirchhoff prestack time migration (PSTM) and compare the results of the proposed approach with a conventional Kirchhoff migration using as an input the picked NMO velocity model. This application to a hard rock synthetic model illustrates the potential of the presented migration algorithm for imaging in hard rock seismic exploration. We believe that this approach can be used in hard rock seismic processing workflows as an automatic tool to obtain an input velocity model for the Kirchhoff PSTM.

A note on autoregressive spectral estimates for frequency-wavenumber analysis of strong-motion array data

Frequency-wavenumber (f-k) spectra of seismic strong-motion array data are useful in estimating back-azimuth and apparent propagation velocity of seismic waves arriving at the array. Such estimates are required to model wave passage effects while studying spatial variability of strong ground motion. Although periodogram-based spectral estimates are commonly used, practical applications based on them encounter limitations, such as, lack of objective criteria for selecting a proper smoothing window and its associated bandwidth, and relatively large variance of the estimated spectral quantities. We present an alternative spectral estimate based on parametric time series modelling approach. The well-known autoregressive (AR) time series model is used in a system-based approach to estimate the spectral matrix of auto- and cross-spectral densities. Such spectral estimates are found to be smoother than the windowed periodogram estimates, and can directly be used in f-k spectral analysis. We present an example application of the proposed technique using strong-motion data recorded by the SMART-1 array in Taiwan during the January 29 1981 \(M_{L}\) 6.3 earthquake. Our results, in terms of back azimuth and apparent propagation velocity, are found to be in excellent agreement with those reported in the literature.

Velocity-less time migration in application to hard rock environments

Reflection seismic method has a number of constraints to obtain suitable images in hard rock environment. For many seismic migration algorithms it is necessary to know the values of propagation velocity of seismic waves. In sedimentary basins, where layers are usually continuous reflectors, that information could be obtained directly from acquired data. However in hard rock environments there are a lack of such horizontal boundaries. This presents a difficulty for an estimation of the velocity model, so obtaining a satisfactory image in hard rock environments is not a trivial problem. Imaging algorithms that do not require prior construction of a velocity model might be promising for such media. Here we describe an application of a velocity-less time migration to hard rock conditions and demonstrate its effectiveness on synthetic data. This approach is based on an estimation of horizontal slownesses in commonshot and common-receiver gathers and a following calculation of the migration attributes. The algorithm was tested on simple convolution synthetic models and applied to 2D synthetic dataset, which simulate a common geological section in hard rock media.

The bound weighted average method (BWAM) for predicting S-wave velocity

The shear-wave velocity is a very important parameter in oil and gas seismic exploration, and vital in prestack elastic-parameters inversion and seismic attribute analysis. However, shearing-velocity logging is seldom carried out because it is expensive. This paper presents a simple method for predicting S-wave velocity which covers the basic factors that influence seismic wave propagation velocity in rocks. The elastic modulus of a rock is expressed here as a weighted arithmetic average between Voigt and Reuss bounds, where the weighting factor, w, is a measurement of the geometric details of the pore space and mineral grains. The S-wave velocity can be estimated from w, which is derived from the P-wave modulus. The method is applied to process well-logging data for a carbonate reservoir in Sichuan Basin, and shows the predicted S-wave velocities agree well with the measured S-wave velocities.

The influence of sea water velocity variation on seismic traveltimes, ray paths, and amplitude

The main factors affecting seismic exploration is the propagation velocity of seismic waves in the medium. In the past, during marine seismic data processing, the propagation velocity of sea water was generally taken as a constant 1500 m/s. However, for deep water exploration, the sound velocity varies with the season, time, location, water depth, ocean currents, and etc.. It also results in a layered velocity distribution, so there is a difference of seismic traveltime, ray paths, and amplitude, which affect the migration imaging results if sea water propagation velocity is still taken as constant for the propagation wavefield. In this paper, we will start from an empirical equation of seismic wave velocity in seawater with changes of temperature, salinity, and depth, consider the variation of their values, build a seawater velocity model, and quantitatively analyze the impact of seawater velocity variation on seismic traveltime, ray paths, and amplitude in the seawater velocity model.