Velocities In Rocks Research Articles

Factors controlling sonic velocity in dolostones

Although the impact of rock texture and crystal size on porosity and permeability of dolostones is well documented, the impact of such factors on the sonic velocity of these sedimentary rocks remains poorly understood. In this study, 100 samples from five formations outcropping along the Arabian Plate, were analyzed to investigate the main factors controlling the sonic velocity in dolostones. The study integrates results obtained using different techniques including: thin-section petrography, SEM, XRD, digital image analysis, porosity and permeability measurements, velocity measurements, in addition to rock physics modeling. Results indicate that porosity is a major factor in controlling the sonic velocity in dolostone where the porosity-velocity relationship shows a determination coefficient (R2) of 0.82. The scatter in the porosity-velocity relationship can be mainly attributed to variations in the dolostone texture (fabric preserving, FP, versus non-fabric preserving, NFP) and the associated pore types. FP dolostones (characterized by macro interparticle, moldic and shelter pores inherited from the precursor limestone) show higher velocities than NFP dolostones (dominated by intercrystalline pores) at a given porosity. The experimental porosity-velocity data, and the rock texture and pore types observations are consistent with rock-physics modeling incorporating variable equivalent pore aspect ratio (EPAR) values in the differential effective medium (DEM) theory. FP dolostones display higher EPAR values (>0.15) compared to NFP dolostones; a criterion that can be used to differentiate between the two dolostone textures. When classifying data based on texture (FP versus NFP), we observe strong porosity-impedance relationship (R2 > 0.95) for both the studied samples, and literature datasets (regional and global) following a consistent distinct trend for each texture. This implies a universality of the porosity-impedance trends observed here, which when combined with the presented rock physics analysis, can inform the modeling and quantitative interpretation of sonic logs and seismic data in dolostone strata.

Understanding carbonates from Saudi Arabia: Laboratory measurements of elastic properties. Part I

Laboratory measurements of elastic properties are presented for carbonate samples from the Saudi Arabian Arab formation. Compressional and shear wave velocities (at 1 MHz) and the quasi-static strains of 37 carbonate rock samples were measured as functions of the saturating fluid and the confining pressure. Furthermore, P- and S-wave velocities of the saturated samples were measured at constant differential pressure of 15 MPa. The lithology, mineralogy, porosity, pore type and pore size distribution of each sample were obtained using a combination of thin section and scanning electron microscopy, helium porosimetry and mercury intrusion porosimetry. The samples showed a high sensitivity to the applied differential pressure especially for the high porosity samples. Due to the lack of closing microcracks and compliant pores in low porosity samples, the travel times show slight changes with the confining pressure whereas the high porosity samples showed a remarkable reduction of the travel time with an increase in confining pressure for both P- and S-waves. We found that the sample physically deformed at pressure above 25 MPa. Evidence of inelastic deformation were observed in a few samples even at a differential pressure of 25 MPa. Both P- and S-wave velocities show a visible deviation with respect to the conventional velocity-porosity inverse relationships, with large variabilities in the velocities at a given porosity. The tight samples only measured a 3% average increase in velocity over the pressure range, whereas the porous samples measured a 20% average increase in velocity over the same pressure range. Despite the nature of porosity, the measured velocities showed a general increase with pressure. Also, all measured samples showed an increase in the bulk modulus of the rock after water saturation with 60% and less than 1% increases. There was no trivial correlation between porosity and the magnitude of the bulk modulus increase. Indeed, the shear modulus of the rock should be insensitive to any changes in water saturation, however, we observed some changes. The presence of anhydrite reduced both P- and S-wave velocities and had a significant influence on the velocities of carbonate rocks at any given porosity. A second paper will build on the results and will consist of predicting and validating suitable rock physics models using the measured carbonate data. The data that support findings of this study are openly available in ERA: Education and Research Archive University of Alberta at https://doi.org/10.7939/R3091B

Stress Effects on Wave Velocities of Rocks: Contribution of Crack Closure, Squirt Flow and Acoustoelasticity

AbstractThe elastic properties of rocks depend on the mineral constituents, pore structure, saturating fluids, and stress (loading) conditions. To study these properties, we measured ultrasonic P‐ and S‐wave velocities as a function of the differential (confining minus pore) pressure and propose an unrelaxed double‐porosity acoustoelasticity model, which generalizes the single‐porosity one. The new approach includes the effects of crack closure, based on the David‐Zimmerman model, and the squirt‐flow mechanism, based on the Gurevich model. When cracks are open at low differential pressures, their properties dominate the wave velocity variations, followed by the squirt‐flow mechanism. Then, a transition occurs, where cracks partially close, and the squirt‐flow effect vanishes. At high pressures, cracks close and acoustoelasticity effects prevail. This behavior is observed in sedimentary rocks, whereas in granites, which have a low crack content, the acoustoelastic effect is dominant at all pressures.

Seismic velocity and anisotropy of glaucophane and epidote in experimentally deformed epidote blueschist and implications for seismic properties in warm subduction zones

To understand the causes of seismic low-velocity layers and seismic anisotropy of the subducting oceanic crust in warm subduction zones, the seismic properties of glaucophane, epidote, and albite in epidote blueschist were studied. The epidote blueschists were experimentally deformed in simple shear at high pressure (0.9–1.5 GPa), temperature (400–500°C), and shear strain up to γ=4.5. The seismic velocity and anisotropy of polycrystalline glaucophanes, epidotes, albites, and whole rocks were calculated using the lattice preferred orientation (LPO) of grains and elastic constants of each mineral. The average P- and S-wave velocity (Vpaver and Vsaver) of epidote blueschist (whole rock) were in the range of 7.19–7.63 km/s and 4.22–4.47 km/s, respectively, and the anisotropy of P-wave and the maximum anisotropy of S-wave were in the range of 4.5–11.0% and 3.91–6.40%, respectively. The Vpaver and Vsaver values of experimentally deformed epidote blueschists were reduced to 8–13% and 6–11%, respectively, compared to those of lithospheric mantle rocks surrounding the subducting slab. This result indicates that the low-velocity layers can be attributed to the LPOs of the minerals in the epidote blueschist. The delay time of the S-wave, which was calculated using the subducting oceanic crust composed of epidote blueschist, was generally increased with increasing subducting angle of the slab and volume proportion of glaucophane. The calculation of the seismic anisotropy of the subducting slab showed that the trench-normal and trench-parallel polarization directions of the fast S-wave can be caused by different LPO types of glaucophane and epidote with different subducting angles of the slab in the subduction zone. These results suggest that the volume proportion and LPO types of glaucophane and epidote and the subducting angle of the slab are important factors in controlling the seismic velocity and anisotropy of subducting oceanic crust in warm subduction zones.

Heterogeneity evaluation of pore types based on dipole shear sonic imager logs by means of statistical parameters, the central Persian Gulf

AbstractHeterogeneity analysis in carbonate reservoirs is of great importance for the interpretation of their characteristics. This study focuses on the evaluation of pore‐type heterogeneity by means of the sonic wave velocities in the carbonate–evaporite series of Permian–Triassic sequences in the Persian Gulf. Thin section petrography and laboratory measured the porosity and permeability of 1576 samples, as well as routine wire‐line logs, were employed. To manage heterogeneity, six electrofacies (EF) were determined based on an integrated analysis of compressional, shear and Stoneley waves as well as three routine logs (gamma, neutron and density). The frequency of pore types in each electrofacies was calculated. Then, the heterogeneity of pore‐type distribution in each electrofacies was measured by standard error and coefficient of variation. Sonic velocity has been compared with the geological properties of electrofacies. Results indicated that velocity is affected by factors other than the amount of porosity, facies or lithology. The standard error values in all electrofacies were close to zero. The coefficient of variation values ranges from 1.08 to 4.60. The lowest amount of coefficient of variation was observed in EF6 in the Khuff (K) 4 zone for moldic porosity. This value for intercrystalline porosity distribution in EF1 in the K1 zone was low, too. These results indicate the lowest standard deviation and the highest homogeneity in the distribution of intercrystalline and moldic porosities in K1 and K4. Also, comparing the mean values of sonic logs in each electrofacies with the total mean value in the whole sequence indicated that there is a relationship between sonic velocity logs and the type of porosity. High values of sonic velocity correspond to intercrystalline porosity in K1 and low values of velocity correspond to moldic porosity in K4. Results show that integrated pore‐type studies should be carried out to understand the sonic velocities in carbonate reservoir rocks.

Numerical modeling of frequency-dependent velocity and attenuation in a fractured-porous rock saturated with two immiscible fluids

The dispersion and attenuation of seismic-wave propagation induced by ‘squirt flow’ effects in hydrocarbon-saturated reservoirs are significantly affected by their rock properties and fluid content. In this study, we analyse the frequency-dependent velocity, attenuation, and seismic responses when fractured porous rock is saturated with two immiscible fluids. First, when considering reservoir wettability, we calculate the effective fluid viscosity using a stable parameter, the capillary pressure, and a lattice Boltzmann model (LBM)-based relative permeability equation, which is a function of the saturation and viscosity ratio of the immiscible two-phase fluid. Then, we explore the frequency-dependent effects of fractured porous rocks saturated with two immiscible fluids under different cases of viscosity ratios and capillary pressure parameters by employing the Chapman model from the dynamic equivalent-medium theory. Then, we use a four-layer model to analyse the frequency-dependent seismic responses. The results show that the characteristics of frequency-dependent velocity and attenuation are both affected by the wettability, capillary pressure parameter, saturation, and viscosity ratio. The frequency-dependent features are greatly influenced by the capillary pressure parameter and viscosity ratio. For a larger viscosity ratio and lower capillary parameter, a dispersive effect can occur in the seismic frequency band. This indicates that the velocity dispersion anomalies are sensitive to wettability, capillary pressure parameter and viscosity ratio and should not be neglected. Synthetic seismic records demonstrate that the seismic reflection signatures, such as the waveform, amplitude, and reflective travel time, at the interfaces for saturated reservoirs are significantly affected by wettability and saturation. The numerical modeling helps to improve the wave propagation in rocks saturated by two immiscible fluids.

Third‐Order Padé Thermoelastic Constants of Solid Rocks

AbstractClassical third‐order thermoelastic constants are generally derived from the theory of small‐amplitude acoustic waves in isotropic materials during heat treatments. Investigating higher‐order thermoelastic constants for higher temperatures is challenging owing to the involvement of the number of unknown parameters. These Taylor‐type thermoelastic constants from the classical thermoelasticity theory are formulated based on the Taylor series of the Helmholtz free energy density for preheated crystals. However, these Taylor‐type thermoelastic models are limited even at low temperatures in characterizing the temperature‐dependent velocities of elastic waves in solid rocks as a polycrystal compound of different mineral lithologies. Thus, we propose using the Padé rational function to the total thermal strain energy function. The resulting Padé thermoelastic model gives a reasonable theoretical prediction for acoustic velocities of solid rocks at a higher temperature. We formulate the relationship between the third‐order Padé thermoelastic constants and the corresponding higher‐order Taylor thermoelastic constants with the same accuracy. Two additional Padé coefficients and can be calculated using the second‐, third‐, and fourth‐order Taylor thermoelastic constants associated with the Brugger's constants, which are consistent with those obtained by fitting the experimental data of polycrystalline material. The third‐order Padé thermoelastic model (with four constants) is validated by the fourth‐order Taylor thermoelastic prediction (with six constants) with ultrasonic measurements for polycrystals (olivine samples) and solid rocks (sandstone, granite, and shale). The results demonstrate that the third‐order Padé thermoelastic model can characterize thermally induced velocity changes more accurately than the conventional third‐order Taylor thermoelastic prediction (with four constants), especially for solid rocks at high temperatures. The Padé approximation could be considered a more accurate and universal model in describing thermally induced velocity changes for polycrystals and solid rocks.

Calculation Method of the Blasting Throwing Energy and Its Variation Affected by the Burden

Precise control of casting velocity and effective throwing kinetic energy conversion efficiency in blasting engineering are challenges. To provide a theoretical basis and reference for the implementation plan and fine construction of the cast blasting project, we study the problems of casting velocity and energy consumption ratio of broken rock under the impact load of explosions in this manuscript. The calculation methods of casting velocity and throwing energy of broken rock under two blasting modes of spherical charge and cylindrical charge are established by using the theory of dimensional analysis and rock breaking by blasting. A large number of model tests are carried out by using high-speed photography. The results indicate that the casting velocity of broken rock after explosive initiation has two evident stages: instantaneous acceleration to a certain value and subsequent fluctuation; the velocity presents an ordinary distribution law with the step height, and the fitting correlation of high-speed photography results is more than 91%. With the minimum burden increasing from 0.12 m to 0.2 m, the energy consumption decreases from 1306.88 J to 747.49 J and the proportion of energy consumption decreases from 14.77% to 8.45%.

Prediction Method of Water Absorption of Soft Rock Considering the Influence of Composition, Porosity, and Solute Quantitatively

The study of water absorption of soft rock is of great significance to the prevention engineering disasters. However, the research on the prediction method of water absorption of soft rock considering the influence of composition, porosity, and solute is insufficient. Aiming to solve the above problem, water absorption tests are carried out by synthesizing soft rocks and water solutions. Then, the prediction model of water absorption of soft rock is established through quantitative analysis of water absorption data and compared with the water absorption characteristics of natural rock to verify the reliability of the model. The results show that the changes in water content and water absorption velocity of soft rock with time obey the second-order exponential attenuation function and the linear function (double logarithmic coordinates axis), respectively. The types of cations and anions and the type and content of clay minerals have the greatest influence on the process of rock water absorption. In addition, the water absorption prediction model could better predict the water absorption process of natural rock. The research results solve the problem of insufficient research on the soft rock water absorption prediction method considering the influence of composition, porosity and solute.

Assessment of Seismic Vulnerability using the Ambient Noise Recordings in Cachar Fold Belt, Assam

Abstract Northeast India is a seismically active region, with frequent major earthquakes. The impact of seismicity can be assessed by using the values fundamental resonant frequency (F0) and the site amplification factor (A0) to derive the seismic vulnerability index (Kg). In 2011, a network of 65 stations was installed in the Cachar fold belt,Assam to continuously record data for a continuous period of eleven months. In this study, the horizontal-to-vertical spectral ratio (H/V) method is employed to identify the resonant frequencies and site amplification factors using ambient noise data to assess the seismic hazard potential in the Cachar fold belt. The amplification factors ranged between 1.15 to 6, while the resonance frequencies varied between 0.25 to 5 Hz. The ambient noise interferometry is utilized to estimate surface waves between station pairs and invert the group velocity dispersion curves for the near-surface S-wave velocities. The S-wave velocity for the basement rocks varied between 600 to 1600 m/s. The S-wave velocities are in turn used to derive an empirical relationship between resonant frequency and alluvium thickness valid for the study region. It is found that stations located at regions with subsurface anticlines had a relatively high resonance frequency and low amplification factor, whereas receivers in synclinal locations and with a thick layer of alluvium sedimentary deposits have a substantially higher site amplification factor and lower resonant frequencies. Further, it is observed that regions with a substantial alluvium sediment cover and near the course of the Barak river are more seismically vulnerable and susceptible to natural hazards.

Simulation of seismic velocity changes in brittle rocks subjected to triaxial stresses using 3-D microstructural models

SUMMARY Numerical simulation of non-linear elastic wave propagation in rocks is indispensable for understanding stress/damage dependence of wave velocity changes and the associated micromechanisms. A numerical microstructural model is presented here to investigate seismic velocity changes due to stress and damage. By introducing pre-existing cracks and considering the valid microstructures in the bonded particle model, the proposed method successfully reproduces velocity changes of experiments on dry Lac du Bonnet granite and dry Darley Dale sandstone in both loading and unloading processes. Velocity increasing results from the closure of pre-existing cracks during loading stages, while the reopen of cracks during the unloading process causes velocity decreasing. Particle velocity vectors are used to illustrate wave propagation in a micromechanical way. P wave wave fronts are observed from the source to travel through the model, and wave intersections are clearly shown in the medium when the tensile wave front meets the compressive wave. The microstructure of the model shows a significant effect on rock mechanical behaviour and velocities and lends credibility to the velocity simulation. The valid microstructure produces realistic mechanical behaviour and velocity changes. Also, it replicates the initial hardening in the axial stress versus the axial strain curve, while invalid microstructures (e.g. cement overlap) underestimate the elastic modulus. The simulations also show that the wave velocities scale with the square root of the corresponding component of the coordination number, which can be used to quantify the mechanisms behind the velocity changes. Direct relations were established between velocity changes and opened crack density, which displays a similar tendency compared with predictions of the effective elastic theory. The microstructural model provides the ability to simulate the macro behaviour of rock under loadings in a more realistic manner and to directly examine the microprocesses underlying velocity changes.

EXTRACTION OF ICE FLOW VELOCITY BY COMBINATION OF DINSAR AND OFFSET TRACKING METHODS FOR PINE GLACIER, WEST ANTARCTICA

Abstract. West Antarctica is the main contributor to global sea level rise at present and in the coming decades, since it occupies 80% of mass loss in Antarctica. In this paper, a combination of Differential Interferometric Synthetic Aperture Radar (DInSAR) and offset tracking technology is used to extract the ice flow velocity of the Pine Island Glacier (PIG), a typical glacier in West Antarctica. Due to the large deformation gradients in PIG, DInSAR technology is used to extract ice flow velocity in bare rock and mountains, then offset tracking technology is used to extract ice flow velocity in areas where glaciers collapse frequently. Finally, the above two results are mosaiced into a new image of the interannual ice flow velocity of PIG in 2017. Through qualitative and quantitative evaluation, it is found that the ice flow velocity extracted by the combination has high accuracy in both high and low velocity areas. In summary, we concluded that the combination of DInSAR and Offset tracking can obtain reliable ice velocity products in glaciers that change rapidly. This combination is of scientific significance for monitoring the movement and evolution of glaciers in the West Antarctica.

Effect of temperature on elastic properties of biotite and biotite-rich rocks: estimation from experiment and molecular dynamics simulation

SUMMARY We measured the P-wave velocities (VP) of mafic high-grade metamorphic rocks at 1.0 GPa pressure and a range of temperatures from 25 to 400 °C, along orthogonal directions corresponding to macroscopic fabric elements in the specimen. Our results showed that biotite-rich rocks (over 15 vol per cent biotite) displayed a strong decrease in VP with increasing temperature whereas biotite-free rocks did not. The anisotropy of VP (AVP) in biotite-rich rocks also increased with increasing temperature because of differential VP reduction, indicating a thermal dependence of the elastic properties of biotite. We conducted molecular dynamics simulations to investigate the effect of temperature on the elastic stiffness constants (Cij) of phlogopite, an end member of the biotite solid-solution series. The simulations indicated that Cij of phlogopite have a strong anisotropy and temperature dependence. We then estimated Cij of the bulk rock by using the Voigt–Reuss–Hill average procedure based on the estimated Cij of phlogopite, reference values for Cij of hornblende and plagioclase and measured crystal preferred orientations. From the resulting values of bulk-rock Cij, we calculated the quasi-VP and anisotropy parameter ε, under the assumption of transverse isotropy, and confirmed that temperature had a clear effect on velocity whereas AVP remained stable. This result suggests that the thermal effect on VP of biotite-rich rocks can be explained by the thermal dependence of Cij of phlogopite, which we attribute to a lattice rearrangement in phlogopite. This finding implies that the elastic properties of micas may change and affect the elastic properties of bulk rocks in the absence of mechanical breakage, dehydration reactions or phase changes. The thermal effect on AVP of biotite-rich rocks cannot be explained by a thermal dependency of the elastic constants of phlogopite. We speculate that the local concentration of thermal stress on biotite may account for the thermal dependency of AVP of biotite-rich rocks.

Experimental investigations of static mechanical properties and failure characteristics of damaged diorite after dynamic triaxial compression

To investigate the static mechanical properties and failure characteristics of damaged rocks after impact under realistic in-situ stress, dynamic triaxial compression tests with different strain rates and confining pressures were conducted on diorite by a modified split Hopkinson pressure bar . The damage factor was calculated according to the change of the longitudinal wave velocity of rocks before and after the impact, and the residual strengths of the damaged diorite were obtained by uniaxial compression and Brazilian tensile tests . In addition, three brittleness indexes based on the residual strength were adopted to evaluate the brittleness of damaged specimens, and fractal dimension was introduced to study the fragmentation characteristics. The results show that the dynamic peak stress, strain, elastic modulus , damage factor and plastic deformation of diorite all increase with increasing strain rate, i.e., rate dependence, and the increasing rate decreases with increasing confining pressure. The increment in confining pressure leads to the increase of dynamic peak stress, elastic modulus, static residual strength and brittleness, and the increasing rate increases with increasing strain rate, while other physio-mechanical parameters decrease with confining pressure. The post-peak behavior of dynamic stress-strain curves is divided into two classes according to the strain rate and fracture state of rocks under dynamic loading. Upon the strain rate increases above 87 s −1 , the brittleness of damaged specimens generally decreases to moderately brittle or even low brittle, and the corresponding drillability becomes much easier. The fractal dimension of damaged specimens increases with the increase of confining pressure and decreases linearly with the increase of strain rate .

Measurement of debris flow velocity in flume using normal image by space-time image velocimetry incorporated with machine learning

Various methods have been applied to the velocity measurement in the soil and rocks waterway experiment. Although most velocity measurements use observation sensors, soil and rocks are two-phase flow in which water and soil are mixed, and the velocity measurement method using direct contact with soil and sensors has various problems, including the potential for equipment damage and noise. Therefore, a velocity measurement method that employs high-resolution image analysis using a high-speed camera, which is an indirect velocity measurement method, has been proposed. Although the measurement of the velocity using high-resolution image analysis is associated with a very little risk of equipment damage, several problems have been reported, such as expensive system construction costs, analysis methods to eliminate noise present in images, and the low accuracy of the velocity measurement according to the slope (velocity) evaluation by space–time image (STI), indicating the movement velocity for each frame (moving distance). This study aims to measure the velocity of soil and rocks by applying space–time image velocimetry (STIV), which has not yet been applied to the soil and rocks waterway experiment. To evaluate the STIV performance, an indoor waterway experiment was carried out, and the results were compared with the velocity measured using a general-purpose high-speed camera. Machine learning was applied to the STI slope estimation method to improve the performance of the velocity measurement according to the noise interference included in the image. The use of convolutional neural networks (CNNs) is a useful way of extracting the characteristics of images, and they have learned to detect slopes using STI's 2D Fourier transform images. As a result, the performance of the velocity evaluation was significantly improved. Furthermore, it is possible to easily measure the velocity with high accuracy by freely setting an area to be measured in the captured image, such as the approaching velocity of soil and rocks or the overflow velocity at a debris barrier.

Experimental evaluation of the transient propagation fracture properties of rocks under dynamic mode I loading: An insight from digital image correlation

Accurate measurement of dynamic fracture properties is crucial for the safety and stability of the engineering applications. In this study, the dynamic mode I fracture tests are conducted on the notched semi-circular bend (NSCB) specimens with the split Hopkinson pressure bar (SHPB) loading system. By virtue of digital image correlation (DIC) technique combined with high-speed photography, the velocity fields of specimen are revealed, and thus an improved method is proposed to accurately calculate the transient kinetic energy and transient propagation fracture toughness of NSCB specimens under dynamic mode I loading. Our method has obvious merits in its specimen preparation and calculation accuracy since no specific assumptions are required. In addition, the crack propagation gauge (CPG) system is also applied into the tests to capture the transient crack propagation velocity and verify the testing results obtained by DIC technique. The results show that the transient propagation velocity of rocks continues to decrease with a three-stage evolution during the process of rock fracture, while the transient fracture energy of rock gradually increases. Moreover, the transient propagation fracture toughness is inversely proportional to the transient crack propagation velocity. Furthermore, the initiation fracrture toughness, propagation fracture toughness, propagation velocity and fracture energy all feature significant loading rate dependence.

A new acoustoelastic model for velocity-hydrostatic-pressure in rocks based on general acoustoelastic theory for elastic solids

Acoustoelastic model based on classic acoustoelastic theory of solids fails to describe rock acoustoelasticity, where wave velocities in rocks has complex non-linear relations with the applied hydrostatic pressure. In order to extend acoustoelastic model into better prediction for rock acoustoelasticity, a new acoustoelastic model is presented based on general acoustoelasticity of elastic solids having complicated constitutive law of rocks, which combines third-order elastic constants of compact rocks with the exponential terms for the influence of pore/cracks in rocks. The data for P- and S-wave velocities of diabase and greywacke samples subjected to the pressure up to 400 MPa are taken as examples to validate the presented model. The results show that the presented model could not only predict rock acoustoelasticity but also be linked with frequently-used empirical model and meso-mechanical model. The intrinsic connection among mechanical parameters, acoustical parameters, and meso-mechanical parameters could be established clearly, which will benefit the determination of high-resolution constitutive law and the compliant porosity by the measured ultrasonic-wave velocities of rock samples.Article HighlightsGeneral acoustoelasticity of elastic solids having complicated constitutive law yields a new acoustoelastic model of rock acoustoelasticity.New model predicts better non-linear characteristics of rock acoustoelasticity.New model benefits for high-resolution evaluation of constitutive law and meso-mechanical parameters for rocks.

Lithologic Structure of the Anninghe Fault Zone: Constraints From High-Pressure Wave Velocity Experiments

The P-wave velocities of typical rocks in the Anninghe fault zone under pressures of 50–600 MPa were systematically measured. The P-wave velocities of the felsic, intermediate, and mafic rock types under atmospheric pressure were 5.86, 6.06, and 6.50 km/s, respectively, with pressure coefficients of 2.19 × 10–, 3.80 × 10–4, and 4.03 × 10–4 km/s/MPa, respectively. The results were combined with deep-imaging seismic data to establish crustal rock composition models at different depths in the study area. The composition of the Anninghe crust is very different in the horizontal and vertical directions. The most notable feature in the vertical direction is that the lithologic compositional change is gradual rather than abrupt with increasing depth. In the middle and upper crust, shallower than 25 km, the lithologic difference between the southern and northern sections of the Anninghe fault zone is primarily that the rocks in the southern section (Xichang) are more felsic than those in the northern section (Shimian).

Effects of external dynamic disturbances and structural plane on rock fracturing around deep underground cavern

The occurrence of disasters in deep mining engineering has been confirmed to be closely related to the external dynamic disturbances and geological discontinuities. Thus, a combined finite-element method was employed to simulate the failure process of an underground cavern, which provided insights into the failure mechanism of deep hard rock affected by factors such as the dynamic stress-wave amplitudes, disturbance direction, and dip angles of the structural plane. The crack-propagation process, stress-field distribution, displacement, velocity of failed rock, and failure zone around the circular cavern were analyzed to identify the dynamic response and failure properties of the underground structures. The simulation results indicate that the dynamic disturbance direction had less influence on the dynamic response for the constant in situ stress state, while the failure intensity and damage range around the cavern always exhibited a monotonically increasing trend with an increase in the dynamic load. The crack distribution around the circular cavern exhibited an asymmetric pattern, possibly owing to the stress-wave reflection behavior and attenuation effect along the propagation route. Geological discontinuities significantly affected the stability of nearby caverns subjected to dynamic disturbances, during which the failure intensity exhibited the pattern of an initial increase followed by a decrease with an increase in the dip angle of the structural plane. Additionally, the dynamic disturbance direction led to variations in the crack distribution for specific structural planes and stress states. These results indicate that the failure behavior should be the integrated response of the excavation unloading effect, geological conditions, and external dynamic disturbances.

Combining active seismic data from Apollo 14 and 16 with ground penetrating radar results to examine the shallow lunar subsurface

The Active Seismic Experiments conducted during the Apollo 14 and 16 missions represented the first attempt to perform an off-Earth refraction seismic survey. The collected seismic traces have been analyzed by several authors and a two-layer structure has been suggested. The top layer consists of regolith, however the nature of the underlying material is still debated because the measured velocity is too low for a competent or even intensely fractured rock layer. Here we propose a new approach that combines refraction seismic and Ground Penetrating Radar (GPR) data to better constrain the underlying geological units. Given the relative uniformity of the shallow lunar subsurface and the interpretation of GPR data acquired at Von Kármán crater, we assumed that the second layer at the Apollo 14 and 16 landing sites is a mixture of fine materials and rocks. To assess this hypothesis we first reanalyzed the active seismic traces and computed the compressional wave velocities in the first and second layers, obtaining v0=116±5ms−1 and v1=298±52ms−1 at the Apollo 14 landing site and v0=122±3ms−1 and v1=332±23ms−1 at the Apollo 16 landing site. Second, we used a time-average model and laboratory data on the compressional wave velocity in lunar rocks to estimate the rock volume fraction that reproduces the overall compressional wave velocity in the second layer, with values ranging from 20 to 60% and 25 to 60% for the Apollo 14 and 16 landing sites, respectively. Finally, we used the rocks/fine materials ratio to estimate the overall dielectric constant of the second layer, which varies between 3.9 and 5.5. These results are in very good agreement with recent re-analysis of electromagnetic and seismic data collected at the Apollo 17 site and suggest that an ejecta deposit below the regolith might be common to all three sites.