Intrinsic Attenuation Research Articles

Seismic spectrograms of an anelastic layer with different source-receivers configurations

Thin and relatively thin anelastic layers (compared to the signal wavelength) generally represent hydrocarbon reservoirs, where the rock is a sandstone or a source rock saturated with brine, oil and gas. The study of the seismic response of these layers is important to detect the hydrocarbons on the basis of the reflection and transmission coefficients and the wave velocity and attenuation properties. Different seismic experiments (source-receiver configurations) can provide useful information to characterise its properties. In this work, we consider varying thicknesses and Q values of the layer and analyse the reflection and transmission coefficients. Moreover, we obtain spectrograms of surface seismic profiles and vertical and horizontal well profiles (VSP and HSP, respectively) to analyse their frequency content with offset due to variations of the attenuation properties of the layer. In addition, we compare the effects due to NMO stretching and intrinsic attenuation related to the low-frequency shadows (LFS) observed in real data after stacking, since LFS can have several causes. Ambiguity is present in this case, indicating that non-stretch NMO is required, otherwise an offset mute of the data may remove useful information regarding the intrinsic (physical) loss.

A COHERENT STUDY OF EMISSION LINES FROM BROADBAND PHOTOMETRY: SPECIFIC STAR FORMATION RATES AND [O iii]/Hβ RATIO AT 3 < z < 6

ABSTRACT We measure the Hα and [O iii] emission line properties as well as specific star formation rates (sSFRs) of spectroscopically confirmed 3 < z < 6 galaxies in COSMOS from their observed colors versus redshift evolution. Our model describes consistently the ensemble of galaxies including intrinsic properties (age, metallicity, star formation history), dust attenuation, and optical emission lines. We forward-model the measured Hα equivalent widths (EW) to obtain the sSFR out to z ∼ 6 without stellar mass fitting. We find a strongly increasing rest-frame Hα EW that is flattening off above z ∼ 2.5 with average EWs of 300–600 Å at z ∼ 6. The sSFR is increasing proportionally to ( 1 + z ) 2.4 at z < 2.2 and to ( 1 + z ) 1.5 at higher redshifts, indicative of a fast build-up of mass in high-z galaxies within e-folding times of 100–200 Myr at z ∼ 6. The redshift evolution at z > 3 cannot be fully explained in a picture of growth driven by cold accretion. We find a progressively increasing [O iii]λ5007/Hβ ratio out to z ∼ 6, consistent with the ratios in local galaxies selected by increasing Hα EW (i.e., sSFR). This demonstrates the potential of using “local high-z analogs” to investigate the spectroscopic properties and relations of galaxies in the re-ionization epoch.

Apparent Attenuation and Dispersion Arising in Seismic Body-Wave Velocity Retrieval

The fact that seismologists often make measurements, using natural seismic solicitations, of properties of the Earth on rather large scales (laterally and in terms of depth) has led to interrogations as to whether attenuation of body waves is dispersive and even significant. The present study, whose aim is to clarify these complicated issues, via a controlled thought measurement, concerns the retrieval of a single, real body wave velocity of a simple geophysical configuration (involving two homogeneous, isotropic, non-dissipative media, one occupying the layer, the other the substratum), from its simulated response to pulsed plane wave probe radiation. This inverse problem is solved, at all frequencies within the bandwidth of the pulse. Due to discordance between the models associated with the assumed and trial responses, the imaginary part of the retrieved velocity turns out to be non-nil even when both the layer and substratum are non-lossy, and, in fact, to be all the greater, the larger is the discordance. The reason for this cannot be due to intrinsic attenuation, scattering, or geometrical spreading since these phenomena are absent in the chosen thought experiment, but rather to uncertainty in the measurement model.

Estimation of seismic attenuation in carbonate rocks using three different methods: Application on VSP data from Abu Dhabi oilfield

In this study a relationship between the seismic wavelength and the scale of heterogeneity in the propagating medium has been examined. The relationship estimates the size of heterogeneity that significantly affects the wave propagation at a specific frequency, and enables a decrease in the calculation time of wave scattering estimation. The relationship was applied in analyzing synthetic and Vertical Seismic Profiling (VSP) data obtained from an onshore oilfield in the Emirate of Abu Dhabi, United Arab Emirates. Prior to estimation of the attenuation, a robust processing workflow was applied to both synthetic and recorded data to increase the Signal-to-Noise Ratio (SNR). Two conventional methods of spectral ratio and centroid frequency shift methods were applied to estimate the attenuation from the extracted seismic waveforms in addition to a new method based on seismic interferometry. The attenuation profiles derived from the three approaches demonstrated similar variation, however the interferometry method resulted in greater depth resolution, differences in attenuation magnitude. Furthermore, the attenuation profiles revealed significant contribution of scattering on seismic wave attenuation. The results obtained from the seismic interferometry method revealed estimated scattering attenuation ranges from 0 to 0.1 and estimated intrinsic attenuation can reach 0.2. The subsurface of the studied zones is known to be highly porous and permeable, which suggest that the mechanism of the intrinsic attenuation is probably the interactions between pore fluids and solids.

Separation of intrinsic and scattering attenuation in the crust of central and eastern Alborz region, Iran

In this study, more than 380 local earthquakes (2<ML<4.5) have been used to estimate the direct-shear waves (Qd), coda (Qc), intrinsic (Qi) and scattering quality factor (QSc) in the crust of central and eastern Alborz region. The events were recorded by one temporary and two permanent networks. The quality factors of shear and coda waves have been individually estimated at different frequency bands by using coda normalization (CNM) method and single backscattering (SBS) method, respectively. Average frequency-dependent relationships have been estimated for Qd and Qc as 111±4f0.85±0.04 and 112±8f1.02±0.06, respectively. The intrinsic quality factor, Qi, has been separated from the scattering quality factor QSc by using individually estimated Qc and Qd values. The average frequency-dependent relationships of Qi and QSc have been calculated in the form of 108f1.00 and 784f0.56, respectively. The results of this study suggest that S-wave’s attenuation (Qd−1) is dominated by the intrinsic attenuation. The attenuation of coda waves has been observed similar to the intrinsic attenuation, which indicates, the coda decay is mostly caused by the intrinsic attenuation. It has been observed that the scattering mean free path is frequency independent at frequencies greater than 6Hz. The results of this study are similar to the tectonically active regions.

Multiscale seismic heterogeneity in the continental lithosphere

AbstractWe examine the nature of seismic heterogeneity in the continental lithosphere, with particular reference to Australia. With the inclusion of deterministic large‐scale structure and realistic medium‐scale features, there is not a need for strong fine‐scale variations. The resulting multiscale heterogeneity model gives a good representation of the character of observed seismograms and their geographic variation, and is also in good agreement with recent direct results on P wave reflectivity in the lithosphere. Fine‐scale heterogeneity is pervasive, but strongest in the crust. There is a weak quasi‐laminar component above the lithosphere‐asthenosphere transition with horizontal correlation length of 10 km and vertical correlation length of 0.5 km. Within the transition, the aspect ratio of heterogeneity changes and can be well represented with a horizontal correlation length of 5 km and vertical correlation length of 1 km. For the Australian cratons, this transition zone needs low intrinsic attenuation (high Q) to sustain the long high‐frequency coda of both P and S waves. The interaction of the different aspects of the heterogeneity is complex and produces a diversity of behavior depending on the relative thickness of the different lithospheric zones. The multiscale model reconciles many of the divergent concepts of the character of heterogeneity based on interpretations of particular aspects of the seismic wavefield. The varying nature of the heterogeneity also ties well with the variations in tectonic character across the Australian continent.

Seismic attenuation attributes with applications on conventional and unconventional reservoirs

Seismic attenuation, generally related to the presence of hydrocarbon accumulation, fluid-saturated fractures, and rugosity, is extremely useful for reservoir characterization. The classic constant attenuation estimation model, focusing on intrinsic attenuation, detects the seismic energy loss because of the presence of hydrocarbons, but it works poorly when spectral anomalies exist, due to rugosity, fractures, thin layers, and so on. Instead of trying to adjust the constant attenuation model to such phenomena, we have evaluated a suite of seismic spectral attenuation attributes to quantify the apparent attenuation responses. We have applied these attributes to a conventional and an unconventional reservoir, and we found that those seismic attenuation attributes were effective and robust for seismic interpretation. Specifically, the spectral bandwidth attribute correlated with the production of a gas sand in the Anadarko Basin, whereas the spectral slope of high frequencies attribute correlated with the production in the Barnett Shale of the Fort Worth Basin.

Scattering of SH-wave for a non-welded contact fluid saturated natural fracture

Closed-form time-domain formulas have been obtained for reflected and transmitted coefficients of SH-wave across a saturated fracture. SH-wave incident upon a fluid filling saturated fracture at arbitrary angle containing the scattering attenuation and wave-induced fluid flow attenuation mechanism. The fracture linear slip theory is introduced under the saturated condition and the dynamic shear compliance is expressed by the viscous fluid mechanics. A finite jump displacement and velocity across a fracture is expressed as a function of wave frequency and geometrical parameters of fracture. The frequency-dependent wave reflection and transmission in wave equations are given by the discontinuity boundary conditions. Coupling relationship between scattering and intrinsic attenuation can be explained partially based on our model.

Ultrasonic velocity and attenuation anisotropy of shales, Whitby, United Kingdom

We have conducted ultrasonic experiments, between 0.3 and 1 MHz, to measure velocity and attenuation ([Formula: see text]) anisotropy of P- and S-waves in dry Whitby Mudstone samples as a function of stress. We found the degree of anisotropy to be as large as 70% for velocity and attenuation. The sensitivity of P-wave anisotropy change with applied stress is more conspicuous than for S-waves. The closure of large aspect-ratio pores (and/or micro cracks) seems to be a dominant mechanism controlling the change of anisotropy. Generally, the highest attenuation is perceived for samples that have their bed layering perpendicular ([Formula: see text]) to the wave path. The observed attenuation in the samples is partly due to the scattering on the different layers, and it is partly due to the intrinsic attenuation. Changes in attenuation due to crack closure during the loading stage of the experiment are an indication of the intrinsic attenuation. The remaining attenuation can then be attributed to the layer scattering. Finally, the changes in attenuation anisotropy with applied stress are more dynamic with respect to changes in velocity anisotropy, supporting the validity of a higher sensitivity of attenuation to rock property changes.

Spectral Decomposition of Soil Electrical and Dielectric Losses and Prediction of In Situ GPR Performance

The performance of high-frequency ground-penetrating radar (GPR) for high-resolution imaging of the near surface can essentially be controlled by the soil electromagnetic (EM) properties. One of these properties influencing sensing depth and image resolution of GPR is the intrinsic attenuation. We investigated the frequency-dependent electrical and dielectric properties of a broad range of soil samples. In order to derive the effective complex dielectric permittivity between 1 MHz and 10 GHz, we applied the coaxial transmission line (CTL) technique. A generalized dielectric response model, consisting of one Debye and one Cole-Cole type relaxation and a constant low-frequency conductivity term was used to analyze the dielectric relaxation behavior. Splitting the spectra into individual loss processes shows that dielectric relaxation mechanisms play a crucial role in most natural soils. Especially for high-frequency applications, attenuation cannot be described by a dielectric constant and dc-conductivity alone. Therefore, a simple conductivity-attenuation relation without dielectric losses can highly overestimate the GPR performance. As an alternative to the CTL technique in the lab, we suggest to use time-domain reflectometry (TDR) for the in Situ assessment of high-frequency electrical properties and deduced prediction of GPR performance.

Stress-associated scattering attenuation and intrinsic attenuation from ultrasonic measurements

SUMMARY Acoustic attenuation has been proved to be an indicator of stress changes in solid structures. Acoustic coda, as a superposition of incoherent scattered waves, reflects small-scale random heterogeneities in solids. Acoustic coda attenuation, as a combination of intrinsic attenuation and scattering attenuation, contains information on stress changes as a result of changes in the physical state of small-scale heterogeneous structures. Based on the ultrasonic measurements of a rock sample with intra-grain pores and fractures under different pore-pressure induced effective stresses, we compute the stress-associated coda attenuation quality factors QPC and QSC as a function of frequencies. Based on the digital heterogeneous cores of the sample, the experimental results are validated and corrected with numerical results by the finite-difference simulation of Biot’s poroelastic equations and the Monte Carlo simulation of multiple scatterings, respectively. The quality factors characterize its scale dependence of scattering attenuation on stress variations in rocks. We compare them with the intrinsic attenuation quality factors QP and QS calculated by the spectral ratio method and BISQ model, respectively, from ultrasonic measurements. Comparisons demonstrate that the scattering attenuation is much stronger, particularly when ultrasonic wavelengths are comparable to the scale of pores and grains. The intrinsic and coda attenuations versus increasing effective stresses present quite different nonlinear features, where QPC and QSC show a greater sensitivity to pore pressure than QP and QS.

Traveltime dispersion in an isotropic elastic mantle: strong lower-mantle signal in differential-frequency residuals

We study wavefield effects of direct P- and S -waves in elastic and isotropic 3-D seismic structures derived from the temperature field of a high-resolution mantle circulation model. More specifically, we quantify the dispersion of traveltime residuals caused by diffraction in structures with dynamically constrained length scales and magnitudes of the lateral variations in seismic velocities and density. 3-D global wave propagation is simulated using a spectral element method. Intrinsic attenuation (i.e. dissipation of seismic energy) is deliberately neglected, so that any variation of traveltimes with frequency can be attributed to structural effects. Traveltime residuals are measured at 15, 22.5, 34 and 51 s dominant periods by cross- correlation of 3-D and 1-D synthetic waveforms. Additional simulations are performed for a model in which 3-D structure is removed in the upper 800 km to isolate the dispersion signal of the lower mantle. We find that the structural length scales inherent to a vigorously convecting mantle give rise to significant diffraction-induced body-wave traveltime dispersion. For both P- and S-waves, the difference between long-period and short-period residuals for a given source–receiver pair can reach up to several seconds for the period bands considered here. In general, these ‘differential-frequency’ residuals tend to increase in magnitude with increasing short-period delay. Furthermore, the long-period signal typically is smaller in magnitude than the short-period one; that is, wave-front healing is efficient independent of the sign of the residuals. Unlike the single-frequency residuals, the differential-frequency residuals are sur- prisingly similar between the ‘lower-mantle’ and the ‘whole-mantle’ model for corresponding source–receiver pairs. The similarity is more pronounced in case of S -waves and varies between different combinations of period bands. The traveltime delay acquired in the upper mantle seems to cancel in these differential signals depending on the associated wavelengths and the length scales of structure at shallow depth. Differential-frequency residuals may thus prove useful to precondition tomographic inversions for the lower-mantle structure such as to reduce the influence of the upper mantle for certain length scales. Overall, standard deviations of the diffraction-induced traveltime dispersion between the longest (51 s) and the shortest (15 s) period considered here are 0.6 and 1.0 s for P - and S -waves, respectively. For comparison, the corresponding standard deviations of the 15 s residuals are 1.0 s and 2.8 s. In the lower-mantle model, standard deviations are 0.3 and 0.6 s, respectively, which gives an average lower-mantle contribution to the total dispersion of 50 per cent for P -waves and 60 per cent for S -waves.

SPECTRAL ANALYSIS OF FERMI -LAT BLAZARS ABOVE 50 GEV

We present an analysis of the intrinsic (unattenuated by the extragalactic background light, EBL) power-law spectral indices of 128 extragalactic sources detected up to z~2 with the Fermi-Large Area Telescope (LAT) at very high energies (VHEs, E>50 GeV). The median of the intrinsic index distribution is 2.20 (versus 2.54 for the observed distribution). We also analyze the observed spectral breaks (i.e., the difference between the VHE and high energy, HE, 100 MeV<E<300 GeV, spectral indices). The LAT has now provided a large sample of sources detected both at VHE and HE with comparable exposure that allows us to test models of extragalactic gamma-ray photon propagation. We find that our data are compatible with simulations that include intrinsic blazar curvature and EBL attenuation. There is also no evidence of evolution with redshift of the physics that drives the photon emission in high-frequency synchrotron peak (HSP) blazars. This makes HSP blazars excellent probes of the EBL.

Numerical identification of a viscoelastic substitute model for heterogeneous poroelastic media by a reduced order homogenization approach

The paper deals with the computational homogenization of pressure diffusion processes in a poroelastic medium. The underlying physical phenomena are of interest for the interpretation of seismic data with applications in hydrocarbon production and geothermal energy. Pressure diffusion is assumed to take place on a length scale much smaller than the observer scale. Thus, the macroscopic observer is not able to measure the properties of the poroelastic medium directly but notices an intrinsic viscous attenuation. Under these circumstances, the macro-scale can be interpreted as a single-phase solid with (apparent) viscoelastic properties. In this paper, we establish a numerical upscaling procedure based on a volume averaging concept. This enables us to identify the material properties of the viscoelastic substitute model in a numerically efficient manner. For this purpose, the poroelastic medium on the small scale is modelled in terms of the momentum balance of the biphasic mixture and a coupled diffusion equation. We approximate the poroelastic pressure field on the small scale by a linear combination of pressure modes forming a reduced orthogonal basis and being identified by a Proper Orthogonal Decomposition (POD) technique. From the superposition principle, the evaluation of the poroelastic continuity equation results in a proper identification of the evolution equations defining the apparent viscoelastic model. In comparison to the nested FE2 solution schemes, the reduced order approach only requires a small amount of off-line precomputations and, therefore, causes very low numerical costs. The proposed method is validated for the simple setup of a layered porous rock with alternating water-and gas-saturated zones.

Teleseismic P wave spectra from USArray and implications for upper mantle attenuation and scattering

AbstractTeleseismic P wave amplitude spectra from deep earthquakes recorded by USArray are inverted for maps of upper mantle Δt* for multiple frequency bands within 0.08–2 Hz. All frequency bands show high Δt* regions in the southwestern U.S., southern Rocky Mountains, and Appalachian margin. Low Δt* is more common across the cratonic interior. Inversions with narrower frequency bands yield similar patterns, but greater Δt* magnitudes. Even the two standard deviation Δt* magnitude for the widest band is ∼2–7 times greater than predicted by global QS tomography or an anelastic olivine thermal model, suggesting that much of the Δt* signal is nonthermal in origin. Nonthermal contributions are further indicated by only a moderate correlation between Δt* and P travel times. Some geographic variations, such as high Δt* in parts of the cratonic interior with high mantle velocities and low heat flow, demonstrate that the influence of temperature is regionally overwhelmed. Transverse spectra are used to investigate the importance of scattering because they would receive no P energy in the absence of 3‐D heterogeneity or anisotropy. Transverse to vertical (T/Z) spectral ratios for stations with high Δt* are higher and exhibit steeper increases with frequency compared to T/Z spectra for low Δt* stations. The large magnitude of Δt* estimates and the T/Z spectra are consistent with major contributions to Δt* from scattering. A weak positive correlation between intrinsic attenuation and apparent attenuation due to scattering may contribute to Δt* magnitude and the moderate correlation of Δt* with travel times.

Carbon capture and storage reservoir properties from poroelastic inversion: A numerical evaluation

We investigate the prospect of estimating carbon capture and storage (CCS) reservoir properties from P-wave intrinsic attenuation and velocity dispersion. Numerical analogues for two CCS reservoirs are examined: the Utsira saline formation at Sleipner (Norway) and the coal-bed methane basin at Atzbach-Schwanestadt (Austria). P-wave intrinsic dispersion curves in the field-seismic frequency band, obtained from theoretical studies based on simulation of oscillatory compressibility and shear tests upon representative rock samples, are considered as observed data. We carry out forward modelling using poroelasticity theories, making use of previously established empirical relations, pertinent to CCS reservoirs, to link pressure, temperature and CO2 saturation to other properties. To derive the reservoir properties, poroelastic inversions are performed through a global multiparameter optimization using simulated annealing. We find that the combination of attenuation and velocity dispersion in the error function helps significantly in eliminating the local minima and obtaining a stable result in inversion. This is because of the presence of convexity in the solution space when an integrated error function is minimized, which is governed by the underlying physics. The results show that, even in the presence of fairly large model discrepancies, the inversion provides reliable values for the reservoir properties, with the error being less than 10% for most of them. The estimated values of velocity and attenuation and their sensitivity to effective stress and CO2 saturation generally agree with the earlier experimental observation. Although developed and tested for numerical analogues of CCS reservoirs, the approach presented here can be adapted in order to predict key properties in a fluid-bearing porous reservoir, in general.

Estimation of attenuation characteristics of Aswan reservoir region, Egypt

The attenuation characteristics of Aswan reservoir region in Egypt was estimated using microearthquakes records. Frequency-dependent attenuation characteristic of S wave was estimated using coda normalization method. The evaluated quality factor (Q s ) shows strong frequency dependence with its value increasing with increasing frequency. For Aswan region, the average frequency-dependent relation is given by Q s = (34.2 ± 2.9)f(1.023 ± 0.107). The low values of Q s lie within those observed for seismically active regions of the world, although the study area is seismically moderately active and known to be a region where reservoir-induced seismicity occurs. The low value of Q s would mean that the medium is highly heterogeneous. Separation of intrinsic and scattering Q was carried out using estimated Q s values and values of coda Q (Q c ) estimated earlier by other workers from the same data set. It is observed from this that S and coda wave attenuation is primarily controlled by intrinsic attenuation at 1-Hz frequency. At higher frequencies, intrinsic and scattering attenuations contribute almost equally as seismic albedo at 1-Hz frequency is 0.04, and at higher frequencies, it varies between 0.34 and 0.55. Extinction length varies between 16.4 and 23.6 km. The frequency-dependent relationship for scattering Q (Q sc ) and intrinsic Q (Q i ) are Q sc = (699.3 ± 334.5)f (0.13 ± 0.06) and Q i = (52.9 ± 5.6)f (1.09 ± 0.03).

Coda Attenuation Analysis in the West Bohemia/Vogtland Earthquake Swarm Area

Seismic coda represents a valuable source of information about the attenuation of the high-frequency waves in the studied region. The quality factor Q derived from coda is an integral parameter of the volume surrounding the hypocenter and seismic station and, according to the applied method, represents the total attenuation or the intrinsic and scattering parts. We analyzed records of 13 selected earthquakes in the magnitude range 1.7–2.9 of the 2011 swarm from West Bohemian/Vogtland area (central Europe), which were recorded at epicentral distances from 7 to 50 km. Two methods were applied: coda method for estimation of the Qc and the Multiple Lapse Time Windows Analysis for separation of the scattering and intrinsic loss by estimation of Qi and Qsc. Careful selection of the analyzed events was necessary due to the frequent contamination of coda decays by the running seismic swarm activity. The resulting coda Qc is relatively high with respect to the geodynamic activity and varies between 100 and 2500 within the analyzed frequency range of 1–18 Hz. The intrinsic loss dominates over scattering attenuation with Qi increasing from 100 and 1850 and Qsc from 300 to 3400 in the same frequency range, which is consistent with the geodynamic activity of the region. We find that the intrinsic attenuation in West-Bohemia/Vogtland is higher that in neighboring Germany, which could be attributed to the heterogeneity of the crust in central Europe.

Evolution of the oceanic lithosphere inferred from Po/So waves traveling in the Philippine Sea Plate

AbstractPo/So waves are characterized by their high‐frequency content and long‐duration travel over great distances (up to 3000km) through the oceanic lithosphere. Po/So waves are developed by the multiple forward scattering of P and S waves due to small‐scale stochastic random heterogeneities. To study the nature of these heterogeneities, Po/So waves are analyzed in the Philippine Sea Plate, which consists of three regions with different lithospheric ages. In the Philippine Sea Plate, Po/So waves propagate in the youngest region (15 Ma) and propagate more effectively in older regions. We investigate the mechanism of this propagation efficiency using numerical finite difference method simulations of 2‐D seismic wave propagation. The results of this study demonstrate that the increase in propagation efficiency of Po/So waves depends on the age of the oceanic lithosphere, and this relationship can be qualitatively explained by thickening of the oceanic lithosphere including small‐scale heterogeneities and a reduction in the intrinsic attenuation. These small‐scale heterogeneities may form continuously in oceanic lithosphere from the time of its formation at a spreading ridge, via the solidification of melts distributed in the asthenosphere.

Resonant ultrasound spectroscopy of horizontal transversely isotropic samples

AbstractMost crustal rocks present some amount of directional dependence of seismic speeds, particularly mudstones (also termed “shales”). Hence, accurate imaging of the subsurface requires anisotropic models and integration of rock physics information in order to constrain the inherent nonuniqueness of the inversion from seismic data. Resonant ultrasound spectroscopy provides estimates of the full anisotropic stiffness tensor from resonant frequencies of geological core samples, along with a measure of intrinsic attenuation. We have developed new functionality to existing codes which enable horizontal transversely isotropic samples to be analyzed. We compared and discussed estimations of the elastic properties of mudstone samples with hexagonal symmetry; one sample was drilled parallel and one perpendicular to the layering. While spatial heterogeneity in the mudstone prevented a direct correlation of the elastic parameters of each sample, time‐of‐flight measurements reveal frequency dispersion of the elastic parameters that is consistent between the samples.