Seismic Wave Velocity Research Articles

Using Seismic Cross-Hole Method to Evaluate Soil Improvement for Outside Wall in Al-Abbas Holy Shrine in Holy Karbala, Iraq

The aim of this study is to use the seismic cross-hole survey in evaluating the injection work to fill the cavities spread in the soil underneath the old foundation of the outer wall of the Al-Abbas holy shrine. A seismic cross-hole survey was conducted for eight profiles, four of these are applied before grouting and four profiles are done after grouting at Al-Imam Musa Al-Kadhum and Al-Imam Sahib Al-Zaman gates. Using the longitudinal and shear wave velocities for different depths ranging from 1 to 15 m. The results of the survey indicate that the soil injection process was successful and effective in filling the cavities. The results of cross- hole survey after the grouting show the percent of variation is 0.7-77 percent for seismic shear wave velocity more than before grouting to variant depths.

Determination of Bearing Capacity of the Soil Using Cross-Hole Seismic Survey for a Water Treatment Plant, Thi Qar, Southern Iraq

The geophysical method (Cross-Hole Survey) was used to assess the bearing capacity of the soil in the study area to build a water treatment plant. It was noted, that the velocities of the primary and secondary waves decrease at the depths of 4 and 5 meters compared to the depths above and down, so, the lithology or physical properties of this specific soil have changed. It was also observed that seismic wave velocities are low in general due to the medium density and hardness of the soils in the study area. Furthermore, the elasticity modulus values were shown to decrease at depths of 4 and 5 meters. It is further evidence of the soil's weakness at these depths. When the type of layer changed, the elastic modulus changed as well. The geotechnical properties between the wells were evaluated based on the velocities of seismic waves (S-waves and P-waves) for classifying the load capacity values with the stiffness. The bearing capability of the soil was found to be medium-stiff at depths of 2 and 3 meters, but soft at depths of 4 and 5 meters. At depths of 6, 7, 8, 9, and 10 meters, the bearing capacity is stiff to very stiff.

A geothermal heat flow model of Africa based on random forest regression

Geothermal heat flow (GHF) data measured directly from boreholes are sparse. Purely physics-based models for geothermal heat flow prediction require various simplifications and are feasible only for few geophysical observables. Thus, data-driven multi-observable approaches need to be explored for continental-scale models. In this study, we generate a geothermal heat flow model over Africa using random forest regression, originally based on sixteen different geophysical and geological quantities. Due to an intrinsic importance ranking of the observables, the number of observables used for the final GHF model has been reduced to eleven (among them are Moho depth, Curie temperature depth, gravity anomalies, topography, and seismic wave velocities). The training of the random forest is based on direct heat flow measurements collected in the compilation of (Lucazeau et al., Geochem. Geophys. Geosyst. 2019, 20, 4001–4024). The final model reveals structures that are consistent with existing regional geothermal heat flow information. It is interpreted with respect to the tectonic setup of Africa, and the influence of the selection of training data and observables is discussed.

In Situ Regolith Seismic Velocity Measurement at the InSight Landing Site on Mars.

Interior exploration using Seismic Investigations, Geodesy and Heat Transport's (InSight) seismometer package Seismic Experiment for Interior Structure (SEIS) was placed on the surface of Mars at about 1.2m distance from the thermal properties instrument Heat flow and Physical Properties Package (HP3) that includes a self-hammering probe. Recording the hammering noise with SEIS provided a unique opportunity to estimate the seismic wave velocities of the shallow regolith at the landing site. However, the value of studying the seismic signals of the hammering was only realized after critical hardware decisions were already taken. Furthermore, the design and nominal operation of both SEIS and HP3 are nonideal for such high-resolution seismic measurements. Therefore, a series of adaptations had to be implemented to operate the self-hammering probe as a controlled seismic source and SEIS as a high-frequency seismic receiver including the design of a high-precision timing and an innovative high-frequency sampling workflow. By interpreting the first-arriving seismic waves as a P-wave and identifying first-arriving S-waves by polarization analysis, we determined effective P- and S-wave velocities of m/s and m/s, respectively, from around 2,000 hammer stroke recordings. These velocities likely represent bulk estimates for the uppermost several 10s of cm of regolith. An analysis of the P-wave incidence angles provided an independent v P /v S ratio estimate of that compares well with the traveltime based estimate of . The low seismic velocities are consistent with those observed for low-density unconsolidated sands and are in agreement with estimates obtained by other methods.

Seismic Scattering Property Changes Correlate With Ground Deformation at Suwanosejima Volcano, Japan

AbstractContinuous estimation of changes in seismic velocity and seismic scattering property by passive interferometry using seismic ambient noise is a promising tool for monitoring volcanoes. To improve the usefulness of this method, it is necessary not only to detect subsurface structural changes but also to quantitatively compare the estimated changes in seismic wave velocity and seismic wave scattering property with other observations, such as ground deformation. We applied passive interferometry to continuous seismic records from the Suwanosejima volcano, Japan, recorded between April 2017 and December 2021. We detected repeated significant waveform decorrelations in seismic ambient noise cross‐correlation functions (CCFs), indicating changes in seismic scattering property in the shallow areas of the volcano. These decorrelations were observed from 2 weeks to a few days before the increase in the number of explosions, suggesting that seismic scattering properties changed significantly during that period. We found that the timing of the decorrelation in seismic ambient noise CCFs and tilt changes related to magma accumulation and injection beneath Suwanosejima were well synchronized. The high correlation between the amounts of decorrelation and the tilt change during the magma accumulation period possibly suggests that a large volume of accumulated magma caused great changes in the scattering property. These results provide a significant first step toward a quantitative comparison of the amount of changes in the scattering property with the amount of magma accumulation beneath volcanoes.

Determination of seismic wave velocities on the ground using artificial neural networks

Objective. The purpose of the study is to determine the velocities of seismic waves on the ground.Method. To determine the velocities of seismic waves in different parts of the earth's crust, using a sample obtained by mathematical modeling, an artificial neural network was trained. Using at the input of the trained neural network, the real values of the differences in the times of arrival of seismic waves on the ground, we obtain at its output the values of the velocities of seismic waves on the ground.Result. A method for determining the velocities of seismic waves on the ground using artificial neural networks is proposed. Dependences of the root-mean-square error in determining the velocities of seismic waves on the ground on the training epoch, as well as the distribution of errors in determining the coordinates of the earthquake hypocenter using the obtained information about the structure of the earth, are obtained.Conclusion. The proposed method makes it possible to determine the structure of the earth's crust more accurately than previously proposed mathematical methods.

Static elastic modulus of rocks predicted through regression models and Artificial Neural Network

The statistical analysis of the main physical, mechanical and ultrasonic features of various sedimentary rock samples (limestone, calcarenite, marly calcisiltite and sandstone) is presented with the aim of finding reliable models to predict the static elastic modulus from known properties. Based on the relevance of the static elastic modulus Estat in engineering geological applications and on the increasing need of non-destructive procedures for its estimation, this paper attempts to establish prediction models by means of single and multiple regression approaches and Artificial Neural Network (ANN). While in the first two cases rock properties are plotted against each other to study their mutual dependence, even combining more than one independent variable, the Artificial Neural Network approach allows a self-learning model capable of predicting a target value from known input variables to be built. Results show that the static elastic modulus of tested rocks is mainly related to the rock Uniaxial Compressive Strength and it varies with respect to the seismic wave velocities (both compressional Vp and longitudinal Vs) and, consequently, to the dynamic elastic modulus Edyn calculated by ultrasonic tests. In particular, there is a numerical difference between the static and dynamic values of the elastic modulus, as the dynamic ones are generally higher than the corresponding static values. Satisfactory prediction equations were found by multiple regressions involving Vp, Edyn and the rock bulk density, thus providing useful statistical laws for the indirect calculation of Estat. The results arising from the ANN models are used herein to draft Estat prediction graphs from known variables, in the perspective of a practical utility for the quick and non-destructive estimation of the static elastic property of tested sedimentary rocks.

Identifying Anomalies in Seismic Velocity and Scattering Property Changes at Active Volcanoes Based on Seismic Interferometry and the Local Outlier Probability Method

The identification of anomalies in seismic wave interferometry data is important in the prediction of imminent volcanic eruptions. Herein, we propose using the local outlier probability (LoOP) method to evaluate the degree of anomaly in seismic wave velocities and scattering properties, estimated via seismic wave interferometry. LoOP is the likelihood that an observation is anomalous and is always in the range of 0–1 (0–100%). We quantitatively evaluated the degree of anomaly in seismic wave velocities and scattering properties before and after the eruption of Mt. Aso, Japan, in October 2016 and Mt. Shinmoedake, which lies within the Mt. Kirishima cluster of volcanoes, Japan, in 2017 and 2018. We found that LoOP exceeded 70% 2 to 3 days before Mt. Aso erupted on October 8, 2016, and it exceeded 70% 1 to 5 days before Mt. Shinmoedake erupted on October 11, 2017 and March 6, 2018. Adjusting the reference and quiet periods for the estimation of changes in seismic velocity/scattering property and LoOP calculations can allow the tracking of repeated, significant LoOP increases during times of high volcanic activity. The quantitative evaluation of temporal anomalies in seismic datasets will improve the precision of predictions of imminent volcanic eruptions.

High‐Resolution Monitoring of Controlled Water Table Variations From Dense Seismic‐Noise Acquisitions

AbstractWater‐resource management has become a major global issue in a world threatened by climate change. High‐resolution geophysical methods may be of valuable help in monitoring the water masses, both in space and time. Passive seismic interferometry takes advantage of ambient seismic noise to recover the variations in seismic wave velocity induced by changes in groundwater. We present hereafter the time and space monitoring of an hydraulic dome artificially formed to prevent biological and chemical pollutants from entering the exploitation field of Crépieux‐Charmy (Lyon, France). We use a dense seismic network to passively monitor the water table changes induced by infilling of an infiltration basin at the water supply facility for the two million inhabitants of the Lyon Metropolis (France). We assess the hourly seismic velocity variations over 19 days, during which two filling and drainage cycles were performed. The use of a dense three‐component seismic network allows fine characterization of the seismic wavefield, and offers the possibility to include the analysis of 4,851 raypaths in a robust inversion algorithm based on ray theory. The velocity variations are mapped with high resolution. They are directly related to the water table variations and to residual water saturation changes within the unsaturated zone. This seismic experiment highlights the three‐dimensional (3D) implementation and evolution of a hydraulic dome under the infiltration basin. This dynamic information helps in the understanding and modeling of water flows between the water table and a river, which represents a fundamental issue for discussions on the effectiveness of the barrier.

Subsurface Weathering Zone Determination Using Down-Hole Seismic Surveys, Majnoon Oil Field, Southern Iraq

Detecting the weathering zone is one of the required data correction steps to process reflection seismic data collected at the Majnoon oil field, south of Iraq. Two subsurface layers represent the weathering zone in this field. Those two layers were inferred by primary seismic waves utilizing the down-hole seismic method. Five wells in the studied area were drilled and named DH-1, DH-2, DH-3, DH-4 and DH-5. The collected seismic data was analyzed to determine the depths, thicknesses and lithology of the subsurface layers. The primary seismic wave velocities were calculated and applied to eliminate two sub-surface layers. The average primary wave velocities and thicknesses of the first layer were 374, 240, 211, 277, 370 m/s, and 2.8, 2, 2, 2, 4.9 m, respectively. In the second layer, the primary waves velocities were 1125, 1284, 1201, 1395 and 1008 m/s, and the thicknesses were 13.2, 11, 13, 11.5, 21.4 m. The first weathered layer represented on the five wells is clay. The second layer has different geometry on different wells, which is represented by a sandy clay layer on DH-1, and muddy clay on DH-2. Then, it is changed to be a silt layer in DH-3, sandy clay in DH-4 and DH-5.

High-pressure melting experiments of Fe3S and a thermodynamic model of the Fe–S liquids for the Earth’s core

Melting experiments on Fe3S were conducted to 75 GPa and 2800 K in laser-heated and internally resistive-heated diamond anvil cells with in-situ x-ray diffraction and/or post-mortem textural observation. From the constrained melting curve, we assessed the thermal equation of state for Fe3S liquid. Then we constructed a thermodynamic model of melting of the system Fe–Fe3S including the eutectic relation under high pressures based on our new experimental data. The mixing properties of Fe–S liquids under high pressures were evaluated in order to account for existing experimental data on eutectic temperature. The results demonstrate that the mixing of Fe and S liquids are nonideal at any core pressure. The calculated sulphur content in eutectic point decreases with increasing pressure to 120 GPa and is fairly constant of 8 wt% at greater pressures. From the Gibbs free energy, we derived the parameters to calculate the crystallising point of an Fe–S core and its isentrope, and then we calculated the density and the longitudinal seismic wave velocity (Vp) of these liquids along each isentrope. While Fe3S liquid can account for the seismologically constrained density and Vp profiles over the outer core, the density of the precipitating phase is too low for the inner core. On the other hand, a hypothetical Fe–S liquid core with a bulk composition on the Fe-rich side of the eutectic point cannot represent the density and Vp profiles of the Earth’s outer core. Therefore, Earth’s core cannot be approximated by the system Fe–S and it should include another light element.

Assessment of the bender element sensors to measure seismic wave velocity of soils in the physical model

Abstract In recent decades, the bender element (BE) test has been used to estimate the seismic wave velocity in the laboratory due to several advantages; simplicity, versatility, fastness, inexpensiveness, and non-destructive nature. However, even with the advanced usage of BE in the laboratory, there has been little effort to use the BE in the field. In this article, the BE was used on a physical model at a multilayer mixture soils system and using different methods, patterns, and wave path lengths to evaluate the BE technique in the simulated field. The results indicated that the cross-hole pattern was the most suitable pattern to implement the BE test on the simulated field. BE results were highly influenced by the boundary condition when the distance between the sensor and hard boundary is less than 0.3 of the wave path length. BE sensors were able to detect seismic wave velocity at a ratio of the wave path length to sensor length up to 200 times.

Engineering-geological assessment of rocky soils based on the analysis of the collection of Albazinskoye deposit samples

The article deals with the engineering-geological assessment of the rocky soils of the Albazinskoye deposit located in the north of the Khabarovsk Territory, Russia conducted on the example of the analysis of the collection of samples of various petrographic types of certain geological formations. The purpose of the research is to implement a specially developed complex methodological scheme including an optical method (analysis of thin rock sections), measurement of seismic (surface and through sounding of samples to determine longitudinal seismic wave velocity), strength (vertical compression and tension) and physical (density and water absorption) properties. Using the obtained data, a comparative analysis of samples is performed based on the results of seismic, strength and physical properties taking into account petrographic information. Anisotropy in terms of seismic and strength properties is established. Using a cluster analysis program, the correlation coefficients between property indicators are determined. On example of the materials of the collection, it is shown that the differences in the velocity of longitudinal seismic waves and strength are determined by the textural-structural features and composition of rocky soils, which are studied at the micro level.

Quantitative texture analysis of slates: An insight into slate’s elastic properties and their contribution to the understanding of seismic wave reflections in anisotropic materials

Slates are low-grade metamorphic rocks characterized by an alignment of the phyllosilicates, resulting in the development of a marked foliation. A consequence of this is a strong directional dependence of their elastic properties, which are tightly bound to their texture. The Rietveld analysis applied to synchrotron x-ray diffraction images of slates from the Truchas Syncline (NW Iberian Peninsula) will provide us with the orientation distribution function (ODF) of the principal minerals that constitute the rock. This textural analysis shows an exceptional alignment of phyllosilicates (muscovite and chlorite) in contrast with a poor orientation of other minerals such as quartz. In a later treatment of the data, the elastic properties of the slates, as well the variations of the seismic wave velocities, have been calculated from the ODF and the single crystal stiffness tensors. The results of both the elastic properties and the wave velocities can be used for the construction of models that allow to understand the reflections of seismic waves in markedly anisotropic materials, which is a matter of a great interest in the studies of the Earth’s lithosphere with seismic methods.

Determining the coordinates of the earthquake hypocenter with the simultaneous determination of seismic wave velocities

Objective. The purpose of the study is to determine the coordinates of the earthquake hypocenter with the simultaneous determination of the seismic wave velocity.Method. The study is based on the use of figures of the fourth and second order - the Cassini oval and hyperbola, figures of the second order - ellipse and hyperbola and combined methods that allow, at given seismic wave velocities, according to three seismic sensors, to determine the coordinates of the earthquake hypocenter. In this case, the velocities are assumed to be known a priori. According to the readings of the fourth seismic sensor, and for given seismic wave velocities, the distance from the fourth seismic sensor to the hypocenter is determined. Again, according to the coordinates of the fourth seismic sensor and the hypocenter coordinates calculated from the three seismic sensors, the distance between them is calculated. If the seismic wave velocities do not correspond to the true ones, a discrepancy will appear between the two calculated values of the distances from the hypocenter to the fourth seismic sensor. By varying the velocities of seismic waves when calculating the coordinates of the hypocenter, we achieve a minimum discrepancy.Result. The problem of determining the coordinates of the earthquake hypocenter with the simultaneous determination of seismic wave velocities is solved. The error distribution densities in determining the coordinates of the earthquake hypocenter and seismic wave velocities are obtained.Conclusion. The proposed method makes it possible to increase the accuracy of determining the coordinates of the earthquake source, as well as to refine the values of seismic wave velocities.

The interaction between the SEIS seismometer of the InSight Martian mission and a regolith simulant

A detailed investigation has been conducted of the interaction between a Martian regolith simulant and the foot of a seismometer (SEIS) recently deployed on the surface of Mars within the NASA InSight mission. A specific device used to investigate the SEIS/ground interaction was improved to provide accurate measurements of low forces and displacements, with a higher system stiffness and appropriate thermal insulation. A series of tests was carried out with a 60 mm dia. disc and the SEIS foot (disc with a spike at its centre). The maximum disc penetration in the loose sand used as simulant under the SEIS weight (10 N) was between 400 and 600 μm, with a tiny effect of the spike. Load cycles under various forces were performed to investigate the elastic interaction, with good reversibility and a linear change of the Young's modulus with respect to the average vertical stress. The tests provided comparable values, showing that the Young's modulus was around 20 MPa – which is compatible with that of loose terrestrial sands – and agreed well with the seismic wave velocities at the surface (from laboratory experiments and from measuring on the surface of Mars the travel times of waves received by the SEIS seismometer).

Effect of thermal shock on the permeability and seismic wave velocity of the caprock and reservoir during CO2 injection

The injection of relatively cold CO2 into warmer reservoirs causes rapid cooling of the host reservoir and the overlying caprock in the near wellbore region. This rapid cooling may cause thermal fracturing, which may potentially lead to escape of the CO2. We have here investigated the effect of thermal fracturing, due to rapid quenching, on the permeability and P-and S-wave velocities of caprock and reservoir samples from the In Salah CO2 storage site, Krechba field, Algeria. Injection of CO2 may have cooled the caprock and reservoir by up to 65°C. Laboratory experiments were conducted where caprock and reservoir samples were heated to various temperatures (50, 150, 250, 350 and 500°C) and rapidly quenched to room temperature (20°C). Permeability and P- and S-wave velocities were measured pre- and post-thermal treatment at effective pressures up to 60 MPa. Backscattered scanning electron microscopy analysis revealed that most of the fracturing is mainly within siderite (Fe carbonate). X-ray diffraction analysis showed that the minerals chlorite (Fe-clay) and siderite were destroyed in specimens heated to 500°C. Specimens that were rapidly quenched by 230°C experienced less than half an order of magnitude increase in permeability and very small to negligible changes in the P- and S-wave velocities. We conclude that the effect of thermal shock fracturing in the Krechba field due to CO2 injection is negligible because the change in the permeability and velocities are insignificant for the predicted maximum degree of cooling (approximately 65°C) of the formation due to CO2 injection. The conclusion of the lack of thermal quenching effects due to CO2 injection at In Salah may be applicable to all global Carbon Capture and Storage prospects.

Velocity Analysis Using N-Th Root Stack

The estimation of seicmic wave velocity in the subsurface is one of the most important process in seismic data processing. The result is very crucial for the conversion af seismic data fromtime section into depth section. The N-th Root Stack which has not been widely used in the industry in fact a powerful method for estimating seismic wave velocity from seicmic record. The method attenuates the background/random noise effectiviely which facilitates tre fitting of the velocity spectrum can be done anccurately. In addition, the noise is also effectivdy suppressed during the CDP stackins, yielding the clear inrim i doking amplitude Synthetic records have been used to demonstrate the effectiveness of the N-th Root Stack Comparison with the Delay and Sum method also demonstrate the superiority of the N-th Root Stack.

VELOCITY ANALYSIS USING N-TH ROOT STACK

The estimation of seicmic wave velocity in the subsurface is one of the most important process in seismic data processing. The result is very crucial for the conversion af seismic data fromtime section into depth section. The N-th Root Stack which has not been widely used in the industry in fact a powerful method for estimating seismic wave velocity from seicmic record. The method attenuates the background/random noise effectiviely which facilitates tre fitting of the velocity spectrum can be done anccurately. In addition, the noise is also effectivdy suppressed during the CDP stackins, yielding the clear inrim i doking amplitude Synthetic records have been used to demonstrate the effectiveness of the N-th Root Stack Comparison with the Delay and Sum method also demonstrate the superiority of the N-th Root Stack.

Elasticity of Hydrated Al‐Bearing Stishovite and Post‐Stishovite: Implications for Understanding Regional Seismic VS Anomalies Along Subducting Slabs in the Lower Mantle

AbstractSeismic studies have found seismic scatterers with −2 to −12% shear velocity anomalies along some subducting slabs at 700–1900 km depth. The ferroelastic post‐stishovite transition in subducted mid‐ocean ridge basalt (MORB) has been linked to these seismic features, but compressional and shear wave velocities (VP and VS) and full elastic moduli (Cij) of Al,H‐bearing stishovite and post‐stishovite at high pressure remain uncertain. Here we have determined Raman shifts of optic modes and equation of state parameters of two hydrated Al‐bearing stishovite crystals, Al1.3‐SiO2 (1.34 mol% Al and 0.55 mol% H) and Al2.1‐SiO2 (2.10 mol% Al and 0.59 mol% H), up to ∼70 GPa in diamond anvil cells coupled with Raman spectroscopy and X‐ray diffraction. The experimental data are modeled using a pseudoproper Landau theory to derive full Cij and sound velocities across the post‐stishovite transition at high pressure. The Al and H dissolution in stishovite significantly reduces the transition pressure to 21.1 GPa in Al1.3‐SiO2 and to 16.1 GPa in Al2.1‐SiO2, where the transition is manifested by approximately 29% VS reduction. Considering that stishovite with approximately 1.3 mol% Al and 0.6 mol% H could account for 20 vol% in subducted MORB at the top‐lower mantle, the Al,H‐bearing post‐stishovite transition with a Clapeyron slope of 65 K/GPa would occur at about 1060 km depth with −7(4)% VS anomaly. The VS anomalies across the Al,H‐bearing post‐stishovite transition can help explain the seismically‐observed depth‐dependent VS anomalies along some subducting slabs in the top‐ to mid‐lower‐mantle depths including the Tonga subducting slab.