Estimation Of Seismic Attenuation Research Articles

Estimation of Seismic Attenuation from Ambient Noise Coda Waves: Application to the Hellenic Subduction Zone

ABSTRACT The decay of surface-wave coda in ambient noise cross correlations can facilitate the estimation of seismic attenuation. The coda quality factor (Qc) can be measured in longer period bands using ambient noise cross correlations, which is the main advantage of using them over earthquakes. The classic model of Aki and Chouet (1975) has been applied previously to estimate coda Q in the Alps using ambient noise cross correlations. The Alps represents an ideal environment for ambient noise study, because it has very high and near-uniform station density, and the region is away from oceanic noise sources. However, many regions around the world do not have uniform station density and may be seismically more active than the Alps. One such region is the Hellenic subduction zone (HSZ), because it has a high rate of seismicity, sparser station coverage, and is surrounded by seas from outside and within. In this study, we estimate ambient seismic noise Qc in 2.5–5, 5–10, and 10–20 s period bands for the HSZ, which did not exist previously. Then, we mitigate the effects of lapse time and window length, distance, azimuth, as well as the number of stacked days on the Qc. Mapping of Qc measurements in such a geographically heterogeneous setting poses additional challenges, which we solve using a novel approach that adaptively selects paths based on their lengths and azimuthal distribution. The major tectonic zones are identified in the resulting Qc maps in the form of low Qc such as the North Anatolian fault, the Kefalonia transform zone, the Gulf of Corinth, the volcanic centers, and so on. The results also show a good correlation with large topographical features such as the Hellenides and the Thessalian plains, which have also been noticed from Qc analysis in other parts of the world.

Domain adaptation-based sparse time-frequency analysis and its application on seismic attenuation estimation

Time-frequency (TF) transform is a commonly used tool for geologic structure interpretation and attenuation estimation, mainly including the linear and nonlinear methods. The former consists of short-time Fourier transform, continuous wavelet transform, S-transform, etc., which can be efficiently implemented. However, they suffer from the Gabor uncertainty principle, which limits their TF readability. The latter can effectively enhance TF readability; nevertheless, it has several unavoidable drawbacks, such as low computational efficiency and parameter selection. For seismic sparse TF (STF) analysis (STFA), we develop a domain adaptation-based STFA (DASTFA) model. This model mainly contains two steps. First, we suggest an STF network (STFNet) for mapping a 1D seismic signal to a 2D STF spectrum, which is pretrained using synthetic traces and STF labels. Second, based on the pretrained STFNet, we design a DASTFA model for transferring to field data. Note that the synthetic traces are generated using well-log data and horizon at the study area, located in the Ordos Basin, China, which can reduce the gap between synthetic and field data. Afterward, we use synthetic traces with their STF labels for model pretraining in the first step and field data without STF labels for model transferring in the second step. Here, model transferring indicates transferring the pretrained model parameters based on field traces. Finally, to test the validity and effectiveness of DASTFA, we apply it to synthetic and field data. Moreover, we test the availability of seismic attenuation estimation by adopting the suggested model for 3D poststack field data volume, which achieved encouraging results.

Joint Analysis of Seismic and Electrical Observables Beneath the Central Appalachians Requires Partial Melt in the Upper Mantle

AbstractThe Central Appalachian Anomaly (CAA) is a region of the upper mantle beneath eastern North America that exhibits pronounced anomalies in its seismic velocity, seismic attenuation, and electrical conductivity structure. The CAA clearly expresses itself in low velocity, high attenuation, and high conductivity values; however, the present‐day composition and state of the asthenospheric upper mantle in the anomalous region remains imperfectly known. The collection of data from densely spaced, co‐located seismic and magnetotelluric arrays during the Mid‐Atlantic Geophysical Integrative Collaboration (MAGIC) experiment affords the opportunity to probe the structure and properties of the upper mantle in the CAA region in detail using multiple types of geophysical observations. Here, we present new observations of P and S wave travel times from teleseismic earthquakes measured at MAGIC stations, including a determination of how travel times deviate from the predictions of a standard 1‐D reference model. These observations constrain the ratio of the P to S wave travel time perturbations associated with the CAA, which in turn allows us to estimate the ratio of P and S wave velocity anomalies. We combine these observations with previously published estimates of seismic attenuation and electrical conductivity in the upper mantle beneath the MAGIC array, and carry out forward modeling to determine reasonable ranges of temperature, partial melt fraction, water content, and composition for the CAA. Our results suggest that 1%–2% partial melt is required to simultaneously explain the velocity, attenuation, and electrical conductivity observations beneath the MAGIC array.

Seismic attenuation estimation using multivariate variational mode decomposition

A seismic attenuation estimation approach is proposed based on multivariate variational mode decomposition (MVMD). MVMD, as a multivariable or multichannel signal processing tool, can extract several predefined multivariable modulation oscillations from the seismic data. Intrinsic mode functions (IMFs) obtained by MVMD may highlight some seismic attenuation information in certain frequency bands with lateral continuity. For improving the accuracy of absorption gradient estimation, we define an absorption gradient by using the low-frequency and high-frequency segments of the amplitude spectrum extracted from the time-frequency map, which is generated by applying the Teager energy separation algorithm to each IMF. A weighted factor is used for highlighting the different attenuation contributions of each IMF. Model test and field data examples show that the proposed method can give more accurate absorption gradient estimation results and yield better hydrocarbon-prone interpretations than the traditional methods.

Numerical solution of Biot equations in quasistatic state for seismic attenuation estimation in anisotropic media

An algorithm for numerical upscaling elastic properties of fractured-porous media in low-frequency range is presented. To do so, the algorithm to solve Biot equations in quasi-static state is developed. Paper describes the following aspects: stating the problem of the poroelastic media upscaling to obtain frequency-dependent stiffness tensor, corresponding to the visco-elastic media; the finite-difference approximation of the considered boundary-value problem; peculiarities of the numerical solution of the SLAE with numerical experiments and performance analysis. Numerical experiments are performed to observe the influence of fracture connectivity and fracture-filling material properties on frequency-dependent seismic attenuation in fractured porous fluid-saturated media.

Seismic Attenuation Estimation Using an Enhanced Log Spectral Ratio Method

Seismic attenuation estimation is a significant task for characterizing reservoirs and improving the resolution of seismic data. The logarithmic spectral ratio (LSR) is one of the widely used tools for seismic attenuation estimation. However, how to select a suitable frequency bandwidth for the LSR is a difficult task, especially for field data. Moreover, field data are often contained kinds of noises, which makes seismic attenuation estimation difficult and unstable. We proposed an enhanced LSR (ELSR) workflow to estimate seismic attenuation. First, we built a sparse S-transform (SST) to obtain a sparse time-frequency (TF) spectrum of the analyzed seismic trace. Then, based on the SST spectrum, we introduced an ELSR workflow to estimate seismic attenuation. It should be noticed that we provided an adaptive frequency band selection for the LSR. To demonstrate the effectiveness of the proposed workflow, we apply it on both synthetic and field data. Compared with the results from several traditional attenuation estimation methods, the proposed ELSR provides a more stable and more accurate attenuation estimation result and offers the potentials in improving the resolution of post-stacked seismic data.

Seismic Attenuation Estimation via Unscaled Time–Frequency Representation and Divergence

Time-frequency (TF) representations achieve better TF localization properties compared with Fourier transform (FT) and perform well for Q estimation via methods such as spectral ratio (SR), centroid frequency shift (CFS), and peak frequency shift (PFS). However, these attenuation estimation methods all require a given frequency band or certain source wavelet assumptions, also heavily interfered by noise. In addition, the resolution and accuracy of TF spectrum also determine whether the extracted spectrum can accurately characterize the frequency properties of seismic wavelets, thus affecting the accuracy of seismic estimation results. In this study, we propose an unscaled generalized S-transform (UGST), which achieves better TF localization while avoiding the dominant frequency shift of S-transform (ST). Next, we build a Q estimation method based on the weighted Kullback-Leibler (WKL) divergence and then give an estimation workflow combined with the proposed UGST. Note that the proposed workflow does not need to make specific wavelet assumptions or consider the frequency band selection, which is also proved to be not sensitive to noise. Finally, to demonstrate the effectiveness of the proposed workflow, we apply it to synthetic and field data. Compared with the contrastive methods, our proposed workflow can achieve more accurate estimation results and show better noise immunity, which can benefit delineating seismic hydrocarbon reservoirs.

Monitoring of seismic attenuation change associated with vapor-liquid phase transition using time-lapse reflection seismic data in Kakkonda geothermal field, Japan

Seismic wave attenuation can potentially be used for the investigation of the fluid phase and flow properties in a fractured reservoir. However, seismic attenuation estimation is easily affected by various factors, such as tuning effects, source and receiver coupling, and effects from near-surface weathering layers. Time-lapse seismic attenuation estimation can avoid these problems because the above factors are canceled between surveys. We conducted time-lapse attenuation estimation using three reflection seismic surveys with different timings acquired in the Kakkonda geothermal field during a 12-day period spanning a well shut-in period. To investigate geothermal fluid changes associated with increased pore pressure, we propose an approach for estimating attenuation changes between time-lapse seismic surveys. Firstly, three seismic reflection sections were obtained from the corresponding time-lapse seismic data using the modified prestack time migration method, which can handle the uncertainties of migration velocity estimation in a highly fractured and structurally very complex medium, for which accurate velocity estimation is difficult to achieve using conventional methods. Then, time-lapse attenuation was evaluated for two of the three seismic reflection sections using the spectral ratio and the centroid frequency shift methods. Numerical modeling was conducted to verify our proposed procedure. Careful preprocessing was carried out to enhance the repeatability of time-lapse seismic data, especially on the frequency content, which is indirectly related to seismic attenuation. Finally, we demonstrated an increase of attenuation associated with an increase of pore pressure in and around the known super-shallow vapor-dominated reservoir during a short period (7 days) spanning from one day before the shut-in of producing well to a week after that. A possible cause of this short-period attenuation increase could be the vapor-liquid phase transition in the reservoir.

Recent Developments in Local Wave Decomposition Methods for Understanding Seismic Data: Application to Seismic Interpretation

This article provides a general overview of local wave decomposition (LWD) methods including empirical mode decomposition (EMD), ensemble EMD, complete ensemble EMD with adaptive noise, synchrosqueezed transform and variational mode decomposition applied to seismic interpretation, covering the theoretical background and applications. We explain how LWD methods can be reviewed as a special and stronger case of the classical seismic time–frequency methods and place emphasis on the interest of using such LWD methods in seismic instantaneous frequency extraction, seismic attenuation estimation and seismic resolution enhancement.

The competing effects of stress and water saturation on in situ Q for shallow (< 1 m), unconsolidated sand, evaluated with a modified spectral ratio method

ABSTRACTA publicly available seismic dataset from a lab experiment shows the dependence of quality factor simultaneously on water saturation and stress in unconsolidated sand. Large gradients (e.g., > 10 m−1) necessitate a spectral ratio method modified to assume that Q changes with each ray path, thereby eliminating false values (e.g., < 0). Interval values increase the most with depth and stress in dry sand and the least in partially saturated sand ( and ) where attenuation created by local fluid flow reaches a maximum. Expected values can be extrapolated from and are bounded by of the dry and partially saturated media (e.g., ). deviations outside this range may be explained by changes in effective stress, attenuation mechanism, or sediment composition. Field estimation of seismic attenuation in natural settings may be helped by these constraints, although attenuation remains subject to careful consideration of other factors, e.g., grain size, sorting, and shape.

Attenuated traveltime tomography method for estimation of seismic attenuation

Due to the viscous-elastic properties of subsurface media, seismic waves experience a loss of amplitude and distortion of phase during propagation. Compared with frequency domain methods, tomography methods are designed to calculate a set of Q values simultaneously. But we have noticed that most existing tomography inversion methods may result in inaccurate Q estimation because of many adverse factors. In addition, these methods can only calculate effective Q between layers. Improved attenuated traveltime (t⁎) tomography is introduced here as a more accurate and efficient method for estimation of true Q distribution, instead of effective Q values. The method updates an initial Q guess to the true Q distribution through inversion. The accuracy of t⁎ is essential for t⁎ tomography. Minute errors of t⁎ can cause unreasonable Q inversion results. A stabilized method is designed to improve the accuracy of t⁎ by statistically selecting the optimum frequency band for regression. Synthetic and field data examples demonstrate the feasibility and effectiveness of this method. Depending on the more accurate Q distribution, seismic resolution can be improved after Q compensation migration.

Numerical upscaling in 2‐D heterogeneous poroelastic rocks: Anisotropic attenuation and dispersion of seismic waves

AbstractThe presence of stiffness contrasts at scales larger than the typical pore sizes but smaller than the predominant seismic wavelengths can produce seismic attenuation and velocity dispersion in fluid‐saturated porous rocks. This energy dissipation mechanism is caused by wave‐induced fluid pressure diffusion among the different components of the probed geological formations. In many cases, heterogeneities have elongated shapes and preferential orientations, which implies that the overall response of the medium is anisotropic. In this work, we propose a numerical upscaling procedure that permits to quantify seismic attenuation and phase velocity considering fluid pressure diffusion effects as well as generic anisotropy at the sample's scale. The methodology is based on a set of three relaxation tests performed on a 2‐D synthetic rock sample representative of the medium of interest. It provides a complex‐valued frequency‐dependent equivalent stiffness matrix through a least squares procedure. We also derive an approach for computing various poroelastic fields associated with the considered sample in response to the propagation of a seismic wave with arbitrary incidence angle. Using this approach, we provide an energy‐based estimation of seismic attenuation. A comprehensive numerical analysis indicates that the methodology is suitable for handling complex media and different levels of overall anisotropy. Comparisons with the energy‐based estimations demonstrate that the dynamic‐equivalent viscoelastic medium assumption made by the numerical upscaling procedure is reasonable even in the presence of high levels of overall anisotropy. This work also highlights the usefulness of poroelastic fields for the physical interpretation of seismic wave phenomena in strongly heterogeneous and complex media.

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.

Seismic attenuation estimation using a complete ensemble empirical mode decomposition-based method

The frequency attenuation gradient method can provide important information for hydrocarbon detection. In this paper, a method using Complete Ensemble Empirical Mode Decomposition (CEEMD), Hilbert transform and the least-squares curve-fitting is proposed for seismic attenuation estimation as an effective frequency attenuation gradient estimation approach. We first use CEEMD to obtain the different Intrinsic Mode Functions (IMFs), which have a narrow band and can enhance the physical meaning of instantaneous attributes trace by trace. The time-frequency spectrum, which is computed using a Hilbert transform of each IMF, is represented as a spectrum with a single-peak that has narrow side lobes, which is conducive to frequency attenuation gradient estimation. Second, for each time sample, the frequency-amplitude spectrum of each IMF trace is extracted from the time-frequency spectrum to conduct the attenuation gradient computation. Then, the logarithm operation is performed for each IMF trace. Due to the very narrow bands of some IMFs in some seismic traces, a variable frequency window is adopted along the IMF trace according to the local data characteristics. Finally, the attenuation gradient for each IMF in a seismic trace can be computed using least-squares fitting. A different IMF reflects a seismic trace with a different spatiotemporal scale and can highlight different geologic and stratigraphic information. The correlation weighted average operation is used to highlight some useful details in seismic trace and obtains the attenuation gradient for each seismic trace. Field data examples demonstrate our method and its effectiveness. The proposed method can stably estimate the frequency attenuation gradient.

Estimation of seismic attenuation of gas hydrate bearing sediments from multi-channel seismic data: A case study from Krishna–Godavari offshore basin

Seismic attenuation of gas hydrate bearing sediments is estimated from the multi-channel seismic data acquired in Krishna–Godavari (KG) offshore basin in the vicinity of Site NGHP-01-10, where ∼128 m of fracture-filled hydrate is confirmed by drilling/coring, to understand the effect of gas hydrate on the seismic attenuation. The seismic quality factor (Q), which is the inverse of seismic attenuation, is estimated from two methods – first, the spectral ratio method which utilizes the logarithmic ratio of the seafloor and bottom simulating reflector (BSR) spectra; and second, the peak frequency method which depends upon the variations of the peak frequency of the BSR spectrum as a function of traveltime. In the study area, the complex fault system has perturbed the seafloor resulting in noisy seafloor spectrum. As a result, the logarithm of the spectral ratio was also noisy and the Q-values obtained from spectral ratio method were found to be unstable. On the other hand, the peak frequency method is found to be relatively stable as it depends only on the peak frequency of the BSR which can be reliably obtained by conventional processing. This method yields an effective Q value of BSR which represents a weighted average of the interval Q-values of the water column and the gas hydrate bearing sediments. Since the Q-value of water column can be treated as a constant, the variations in effective Q-value can be interpreted in terms of the variations of Q in the gas hydrate bearing sediments for a constant thickness of water column.The estimated effective Q-values, along the inline and crossline seismic profiles, depend on several factors such as gas hydrate, free gas and the complex fault system. The combined interpretation of the quality factor and the interval velocity model helps to understand these effects in different zones of the seismic data. The attenuation of the background marine sediments is estimated from the analysis of crossline seismic profile. The gas hydrate bearing sediments, as inferred from the velocity model, show low attenuation as compared to that of the background sediments. In contrast, active migration of free gas across the fault system leads to increase in seismic attenuation within the gas hydrate stability zone. The complex fault zone may also lead to an increase in seismic attenuation. The blanked seismic zone shows a marginal decrease in seismic attenuation probably related to load-bearing form of gas hydrate. Our attenuation results are compared against the results obtained from waveform inversion, albeit with a higher resolution. The relative variation of Q estimated from the proposed method is close to the average Q-values estimated from full waveform inversion for most of the CDPs. The proposed methodology can be a useful technique to estimate seismic attenuation from multi-channel seismic data.

Estimation of seismic attenuation from zero-offset VSP acquired in hard rock environments

Understanding of seismic attenuation plays an important role in successful application of seismic imaging and subsurface characterisation techniques based on amplitude analysis. Zero-offset vertical seismic profiling (VSP) is one of the principal tools which can be used to study seismic attenuation.Apparent attenuation estimated from seismic data analyses comprises of scattering and intrinsic components. Scattering mechanism can play significant role in hard rock environments in areas associated with fracture zones or other complex structures. As such seismic attenuation can be an important seismic exploration attribute.Meanwhile attenuation analyses from VSP data are almost routinely done in oil and gas industry they are still uncommon in mineral exploration.In this study we analyse zero-offset VSP data acquired in Western Australia on one of DET CRC test sites using both hydrophones and 3C geophones as receivers. We compare several methods for apparent attenuation estimation and evaluate their applicability to VSP data acquired in crystalline rocks. Extensive wire line log coverage for the well allows us to investigate relative contribution of different attenuation mechanisms.

Quantifying uncertainties in attenuation estimation at methane-hydrate-bearing zones using sonic waveform logs

Application of seismic attenuation estimation using sonic waveform data is limited because the estimation methods have not yet been fully developed. Although the median frequency shift method is considered to be effective and robust compared to the conventional spectral ratio method, we demonstrated that the median frequency shift methods strongly depend on reference data under lower signal-to-noise ratios. We modified an existing median frequency shift method not to depend on arbitrarily choosing a reference value and to quantify the uncertainties in attenuation estimation. Furthermore, we implied the optimum selection of receiver pairs used for more stable attenuation analysis. Our numerical experiments supported the advantage of the proposed method. Although our main findings by applying the proposed methods in methane hydrate-bearing sediments are almost consistent with past field sonic logging measurements, we find some differences in the magnitude of attenuation values compared to existing sonic attenuation measurements and discuss various possible factors. We believe that more stable and reliable attenuation results can lead to clarifying various factors affecting attenuation estimation, such as the effect of scattering, near-field effects, and source-coupling effects. Furthermore, we emphasized the importance of scattering effect caused by the heterogeneity of the formation and demonstrated the limitation of characterizing the 1D heterogeneity using the sonic logging data spatially sampled at 0.15 m to adequately estimate the effect of scattering attenuation.

The robustness of seismic attenuation measurements using fixed- and variable-window time-frequency transforms

Frequency-based methods for measuring seismic attenuation are used commonly in exploration geophysics. To measure the spectrum of a nonstationary seismic signal, different methods are available, including transforms with time windows that are either fixed or systematically varying with the frequency being analyzed. We compare four time-frequency transforms and show that the choice of a fixed- or variable-window transform affects the robustness and accuracy of the resulting attenuation measurements. For fixed-window transforms, we use the short-time Fourier transform and Gabor transform. The S-transform and continuous wavelet transform are analyzed as the variable-length transforms. First we conduct a synthetic transmission experiment, and compare the frequency-dependent scattering attenuation to the theoretically predicted values. From this procedure, we find that variable-window transforms reduce the uncertainty and biasof the resulting attenuation estimate, specifically at the upper and lower ends of the signal bandwidth. Our second experiment measures attenuation from a zero-offset reflection synthetic using a linear regression of spectral ratios. Estimates for constant-[Formula: see text] attenuation obtained with the variable-window transforms depend less on the choice of regression bandwidth, resulting in a more precise attenuation estimate. These results are repeated in our analysis of surface seismic data, whereby we also find that the attenuation measurements made by variable-window transforms have a stronger match to their expected trend with offset. We conclude that time-frequency transforms with a systematically varying time window, such as the S-transform and continuous wavelet transform, allow for more robust estimates of seismic attenuation. Peaks and notches in the measured spectrum are reduced because the analyzed primary signal is better isolated from the coda, and because of high-frequency spectral smoothing implicit in the use of short-analysis windows.

Reply to comments on “Separation of Qi and Qs from passive data at Mt. Vesuvius: A reappraisal of the seismic attenuation estimates” by Ugalde, A. and Carcolé, E.

Reply to comments on “Separation of Qi and Qs from passive data at Mt. Vesuvius: A reappraisal of the seismic attenuation estimates” by Ugalde, A. and Carcolé, E.

Comments on “Separation of Qi and Qs from passive data at Mt. Vesuvius: A reappraisal of the seismic attenuation estimates” by E. Del Pezzo et al. (2006)

In this comment we point out two approximations considered by Del Pezzo et al. [Del Pezzo, E., Bianco, F., Zaccarelli, L., 2006. Separation of Qi and Qs from passive data at Mt. Vesuvius: a reappraisal of the seismic attenuation estimates, Phys. Earth Planet. Int. 159,202–212] for estimating intrinsic absorption and scattering attenuation in Vesuvius volcano region. The first one is the theoretical model used for calculating the synthetic S-wave envelopes for the case of multiple scattering. The second one is based on the stacking of coda envelopes. We consider that both assumptions have no general validity for this kind of analysis and thus may have biased their results.