Seismic Attenuation Research Articles

Constraints on the Cryohydrological Warming of Firn and Ice in Greenland From Rayleigh Wave Ellipticity Data

AbstractRayleigh wave ellipticity measurements from seismic ambient noise recorded on the Greenland Ice Sheet (GrIS) show complex and anomalous behavior at wave periods sensitive to ice (T < 3–4 s). To understand these complex observations, we compare them with synthetic ellipticity measurements obtained from synthetic ambient noise computed for various seismic velocity and attenuation models, including surface wave overtone effects. We find that in dry snow conditions within the interior of the GrIS, to first order the anomalous ellipticity observations can be explained by ice models associated with the accumulation and densification of snow into firn. We also show that the distribution of ellipticity measurements is strongly sensitive to seismic attenuation and the thermal structure of the ice. Our results suggest that Rayleigh wave ellipticity is well suited for monitoring changes in firn properties and thermal composition of the Greenland and Antarctic ice sheets in a changing climate.

Multi-station volcano tectonic earthquake monitoring based on transfer learning

Introduction: Developing reliable seismic catalogs for volcanoes is essential for investigating underlying volcanic structures. However, owing to the complexity and heterogeneity of volcanic environments, seismic signals are strongly affected by seismic attenuation, which modifies the seismic waveforms and their spectral content observed at different seismic stations. As a consequence, the ability to properly discriminate incoming information is compromised. To address this issue, multi-station operational frameworks that allow unequivocal real-time management of large volumes of volcano seismic data are needed.Methods: In this study, we developed a multi-station volcano tectonic earthquake monitoring approach based on transfer learning techniques. We applied two machine learning systems—a recurrent neural network based on long short-term memory cells (RNN–LSTM) and a temporal convolutional network (TCN)—both trained with a master dataset and catalogue belonging to Deception Island volcano (Antarctica), as blind-recognizers to a new volcanic environment (Mount Bezymianny, Kamchatka; 6 months of data collected from June to December 2017, including periods of quiescence and eruption).Results and discussion: When the systems were re-trained under a multi correlation-based approach (i.e., only seismic traces detected at the same time at different seismic stations were selected), the performances of the systems improved substantially. We found that the RNN-based system offered the most reliable recognition by excluding low confidence detections for seismic traces (i.e., those that were only partially similar to those of the baseline). In contrast, the TCN-based network was capable of detecting a greater number of events; however, many of those events were only partially similar to the master events of the baseline. Together, these two approaches offer complementary tools for volcano monitoring. Moreover, we found that our approach had a number of advantages over the classical short time average over long time-average (STA/LTA) algorithm. In particular, the systems automatically detect VTs in a seismic trace without searching for optimal parameter settings, which makes it a portable, scalable, and economical tool with relatively low computational cost. Moreover, besides obtaining a preliminary seismic catalog, it offers information on the confidence of the detected events. Finally, our approach provides a useful tentative label for subsequent analysis carried out by a human operator. Ultimately, this study contributes a new framework for rapid and easy volcano monitoring based on temporal changes in monitored seismic signals.

Variations of intrinsic and scattering seismic attenuation with depth in western Tibet

In this study, the depth-dependent seismic wave attenuation beneath western Tibet have been investigated using 628 local earthquakes recorded at Y2 network operated by US-China collaboration group from July 2007 to May 2011. Initially, we have calculated the attenuation of shear wave (Qs−1) using coda normalization method and coda waves (Qc−1) using single isotropic scattering model. Thereafter, we have estimated the quantitative values of scattering (Qsc−1) and intrinsic (Qi−1) attenuation using Wennerberg approach. The observations are made at five different central frequencies (1.5, 3, 6, 12, and 18 Hz) and five lapse time windows (30, 40, 50, 60, and 70 s). The results show frequency and lapse time dependence of Qc−1, Qsc−1 and Qi−1 values for western Tibet. Qc−1 and Qi−1 shows similar trend suggesting that the key mechanism is intrinsic dissipation for the decay of coda wave in the medium. Qi−1 is found to be as a dominant mechanism over Qsc−1 at all the investigated depth beneath western Tibet. Interestingly, the values of Qc−1 and Qi−1 decrease and get closer to Qsc−1 with increasing lapse time window/depth. It signifies the impact of ongoing underthrusting Indian lithosphere at deeper depth. A stronger intrinsic attenuation at shallow depth reflects the effect of the mid crustal low-velocity zone (LVZ) below Tethyan Himalaya and the southern Lhasa terrane. The obtained results in this study are also in good agreement with other reported results from seismically active regions in the world.

3D Sensitivity Kernels With Full Attenuation Computed by a Combination of the Strong Stability Preserving Runge‐Kutta Method and the Scattering‐Integral Method

AbstractTo date developments of seismic attenuation models of the Earth have lagged those of velocity models. This is partly due to difficulties in isolating waveform perturbations caused by attenuation and velocity heterogeneities and partly due to different theories (e.g., ray theory, finite frequency theory) used in most previous and current studies to approximate sensitivity kernels and invert for the attenuation structure. We present in this paper a new method for computing the 3D waveform Fréchet kernels that account for full physical‐dispersion and dissipation attenuation. For solving the 3D isotropic anelastic wave equation described by the generalized Maxwell body model, we extend our previously proposed full waveform modeling method in Cartesian coordinates to that in spherical coordinates, which can provide stable numerical solutions even in the presence of strong attenuation. Then, we apply the scattering‐integral method for calculating 3D travel time and amplitude sensitivity kernels with respect to velocity and attenuation structures. We demonstrate the accuracy of our forward method and the effectiveness of the implementation of absorbing and free surface boundary conditions through numerical tests. Moreover, by choosing the Northwestern United States region as a realistic example, we verify the accuracy of the computed 3D sensitivity kernels through comparing the waveform measurements with predictions from the kernels. Finally, we discuss the importance of calculating full anelastic sensitivity kernels including both effects of physical dispersion and dissipation, where we specially explore the effect of scattering due to random velocity and attenuation heterogeneities on waveform measurements.

Effect of water on seismic attenuation of the upper mantle: The origin of the sharp lithosphere–asthenosphere boundary

Oceanic lithosphere moves over a mechanically weak layer (asthenosphere) characterized by low seismic velocity and high attenuation. Near mid-ocean ridges, partial melting can produce such conditions because of the high-temperature geotherm. However, seismic observations have also shown a large and sharp velocity reduction under oceanic plates at the lithosphere-asthenosphere boundary (LAB) far from mid-ocean ridges. Here, we report the effect of water on the seismic properties of olivine aggregates in water-undersaturated conditions at 3 GPa and 1,223 to 1,373 K via in-situ X-ray observation using cyclic loading. Our results show that water substantially enhances the energy dispersion and reduces the elastic moduli over a wide range of seismic frequencies (0.5 to 1,000 s). An attenuation peak that appears at higher frequencies (1 to 5 s) becomes more pronounced as the water content increases. If water exists only in the asthenosphere, this is consistent with the observation that the attenuation in the asthenosphere is almost constant over a wide frequency range. These sharp seismic changes at the oceanic LAB far from mid-ocean ridges could be explained by the difference in water content between the lithosphere and asthenosphere.

Attenuation-compensated reverse time migration based on the stereo-modeling operator

The viscosity in the subsurface is ubiquitous. Prestack reverse time migration (RTM) based on the viscoacoustic wave equation is an accurate imaging method to compensate attenuation. The resolution of an imaging result highly depends on the accuracy of the wave equation solution. We extend the nearly analytic center difference (NACD) method to a viscoacoustic wave equation to compensate seismic attenuation. The NACD method can achieve fourth-order accuracy in the time and space domain. We use the pressure and its gradients to approximate the spatial derivatives based on stereo modeling. Numerical simulations and dispersion analysis demonstrate that our NACD has less numerical dispersion and is more accurate than the Lax-Wendroff correction (LWC) method. Thus, the NACD is less expensive in terms of computational time and storage space. Numerical simulations indicate that the forward modeling of the viscoacoustic wavefield via the NACD is able to obtain more accurate wavefields compared with the conventional LWC method and can accurately simulate the effect of the viscosity on waves in attenuative media. When applied to RTM, the viscous effects of the subsurface can be compensated. Synthetic examples demonstrate that the attenuation-compensated RTM using NACD can obtain an image with higher resolution in attenuative media compared with that using the acoustic RTM. Furthermore, the image determined by the NACD is clearer than that of the LWC method in RTM.

Compensating attenuation effects in full-waveform inversion with dissipation-dispersion decoupling

Seismic attenuation poses challenges to velocity model building from acoustic/elastic full-waveform inversion (FWI). In particular, when constructing the FWI gradient for velocity inversion, recent studies have indicated that the high-attenuation structure could distort the gradient by damping the amplitudes and shifting the kinematic phases, resulting in an imbalanced update and thus unreliable velocity model. These Q effects are particularly significant in the reflection acquisition geometry due to the “double-damping” issue. Here, we develop a Q-compensated FWI algorithm for constructing a Q-free FWI gradient. By using a recently developed viscoacoustic wave propagator, this compensation can be done conveniently by keeping the dispersion term and flipping the dissipation term in the wave equation when we simulate the forward and time-reversed adjoint wavefields. The resultant gradient obtained by interacting these two wavefields has correct kinematics and Q-free amplitudes. This Q-compensated FWI can balance the update between Q- and no- Q-areas, which we determine using synthetic examples. In addition, we illustrate how to take advantage of the dissipation-dispersion decoupling to determine the anomalous Q value in the Q model building workflow via Q-compensated reverse time migration.

Seismic noise attenuation using post-stack processing: a case study of Rabeh East Oil Field, Gulf of Suez Basin, Egypt

Seismic noise attenuation using post-stack processing: a case study of Rabeh East Oil Field, Gulf of Suez Basin, Egypt

Direct hydrocarbon indicator analysis to predict reservoir in Deepwater Krishna-Godavari basin: a case study

The amplitude Variations with Offset (AVO) technique is extensively used in hydrocarbon exploration and production for de-risking of the prospect before drilling. The interpretation of AVO results brings more confidence in the presence or absence of hydrocarbon. The AVO and Direct Hydrocarbon Indicator (DHI) analysis have their own inherent limitations. Therefore, to ensure the presence of true AVO in seismic, other attribute supports are crucial. The present prospect in this study was deposited as a channel-levee complex in the shelf-slope of the Krishna-Godavari basin. There is evidence of false AVO within this complex and thus additional attributes were used in this study to support the AVO analysis. The conventional AVO analysis shows the presence of Class-III AVO for a probable reservoir in seismic. However, it is unable to ensure the presence of hydrocarbon in the stacked reservoir unit. The spectral AVO technique was used to check AVO response at low frequencies for laminated and stacked reservoir units. Additionally, seismic attenuation and dispersion attribute studies were incorporated into the de-risking analysis. The drill result showed two distinct reservoir intervals in this prospect, which validated the predrill interpretation. This integrated approach added significant value in de-risking the prospect using AVO and other seismic attributes in complex geologic setups.

Ultrasonic P-Wave to Acquire Parameters of Boise Sandstone

Boise sandstone has a variety of grain diameter, and the heterogeneity makes it difficult to characterize. In this paper, a model of viscous squirt is used to simulate velocity and attenuation of ultrasonic P-wave in the sandstone saturated with water. Phase velocity yielding from the model is fitted against the velocity measured at frequency of 500 kHz, which determinates the quality factor due to viscous squirt ( Q p s ) as a function of frequency. The resulting Q p s appears to be 14.64 at frequency of 0.8 MHz. With the use of the measured total quality factor ( Q p ) of 6.9 at 0.8 MHz, the dry quality factor ( Q p d ) appears to be 13.0 at 0.8 MHz. The resulting dimension of the rock unit is 0.150 multiplied by 0.140 mm, pretty consistent with the mean grain diameter of 0.150 mm. The relative first and second porosities are ascertained to be 0.976 and 0.024, respectively, and the aperture distance of the second porosity is 0.84 μm. Nonetheless, the model represents analytical continuation of small rock samples. Consequently, seismic attenuation predicted by the model is far smaller than field observation. The discrepancy shows that strong seismic attenuation in the field is associated with a scale much larger than pore scale.

Temporal Variations in QP−1 ${Q}_{P}^{-1}$ and QS−1 ${Q}_{S}^{-1}$ Above a Megathrust Following Episodic Slow‐Slip Events

AbstractRecent observations beneath central Japan have shown that periodic fluid drainage occurs during slow‐slip events (SSEs) based on temporal variations in above the megathrust boundary of the subducting Philippine Sea slab. However, no previous studies have estimated associated . A comparison of and can provide clues to the mechanism of seismic attenuation because of different propagation characteristics of the two waves. We estimate temporal variations in and via spectral analyses of waveform data from November 2009 to August 2021 period. The results indicate that both and exhibit temporal variations at about 1‐year periodicity and there are systematic differences between and that have smaller values, less insignificant variation, and weaker correlations with SSEs. Furthermore, increases concurrent with SSEs. These differences suggest that attenuation is caused by the wave‐induced fluid flow. could be an important parameter for detecting the presence of fluid.

Study on vibration damping performance of a petal-shaped seismic metamaterial

Seismic metamaterial (SM) is a new vibration damping technology, but the bandgap is difficult to concentrate in the low frequency range due to the limitation of the lattice size and there is a lack of experiments for validation. Based on this, we propose a petal-shaped seismic metamaterial by numerical simulation combined with experiments to change the internal scatterer into a petal-shaped consisting of four sectors. This structure can form an ultra-low frequency bandgap to cover the frequency band where the seismic energy is concentrated and provide effective attenuation of seismic waves. Firstly, the energy band structure and vibration modes are calculated by numerical simulation. The effects of geometric and material factors on the bandgap are analyzed with the vibration modes. Then the frequency response curves of lamb waves on SM are calculated. And the scaled-down model is fabricated and vibration tests are conducted. The results show that the new two-dimensional SM has excellent vibration damping performance compared with conventional structures and can generate low-frequency bandgap. It has potential applications in the field of seismic isolation and attenuation of buildings.

Fluid identification by nonlinear frequency‐dependent amplitude variation with offset inversion based on scattering theory

AbstractPre‐stack seismic amplitude variation with offset inversion is a crucial technique in seismic exploration, employed to estimate reservoir elastic parameters and thus reservoir fluid properties. However, traditional amplitude variation with offset inversion methods are based on elastic theory and linear approximation, neglecting the inelasticity of medium and nonlinear theory. To overcome this limitation, a quadratic scattering coefficient equation of the viscoelastic fluid factor is derived, which provides the basis for the equation for amplitude variation with offset inversion. Traditional amplitude variation with offset inversion methods typically neglect seismic dispersion and attenuation, failing to account for the influence of the seismic wave velocity attenuation and frequency variation. Quality factors of P‐ and S‐waves represent the degree of attenuation of seismic waves. To comprehensively address the effects of seismic wave dispersion and attenuation, a novel method called pre‐stack seismic nonlinear frequency‐dependent amplitude variation with offset inversion has been developed. This method builds upon the new quadratic scattering coefficient and is utilized for reservoir fluid prediction. The reliability and stability of the method are verified through synthetic and filed data examples. Further analysis reveals that the method is more reasonable and accurate compared to the traditional linear amplitude variation with offset inversion method. The results demonstrate that the proposed pre‐stack seismic nonlinear frequency‐dependent amplitude variation with offset inversion method can effectively identify reservoir fluids, providing a novel solution for reservoir fluid identification.

The Thermal Regime of NW Canada and Alaska, and Tectonic and Seismicity Consequences

AbstractNW Canada and Alaska are the continuation of the North American Cordillera through Mexico, western USA and western Canada. I show that they have similar thermal regimes and thermal control of tectonics and seismicity. I first summarize the multiple constraints to crust and upper mantle temperatures and then discuss some consequences. There are bimodal crust and upper mantle temperatures characteristic of most subduction zones: cool forearc, uniformly hot backarc (Yukon Composite Terrane to Southern Brooks Range, and Mackenzie Mountains), and stable cratonic backstops (Arctic Alaska Terrane and Canadian Shield). The main constraints are as follows: (a) Heat flow measurements, (b) Temperature‐dependent upper mantle velocities and seismic attenuation, (c) Temperature‐dependent topographic elevations; thermal isostasy, (d) Depth and temperature of the seismic lithosphere‐asthenosphere boundary (LAB), (e) Origin temperature and depth of craton kimberlite xenoliths, (f) Geochemically inferred source temperature and depth of recent volcanic rocks. (g) Depth to the magnetic Curie temperature, (h) Depth extent of seismicity. The backarc lithosphere is thin, LAB at 50–85 km and ∼1,350°C ± 25°C. Moho temperatures at 35 km are 850°C ± 100°C compared to cool cratonic areas of 400°C–500°C. The consequences include the following: (a) Thin and weak backarc lithosphere that accommodates pervasive tectonic deformation indicated by wide‐spread seismicity and GPS‐defined motions, in contrast to the stable cratonic regions; (b) Weak backarc lower crust that flattens the Moho and allows detachment and thrusting of the upper crust over the cold strong Arctic Alaska Terrane and Canadian Shield. This article provides a model for how to estimate deep temperatures from multiple constraints.

On the Dynamics of Water Transportation and Magmatism in the Mid‐Mantle

AbstractThe distribution of water within the Earth's mantle has significant implications for the Earth's dynamics and evolution. Recent mineral physics experiments indicate that dense hydrous magnesium silicates can contain large amounts of water stable up to 60 GPa or even beyond along slab geotherms. Here we perform petrological‐thermomechanical numerical simulations of water transportation by deep slab subduction and related magmatism in the mid‐mantle. Key parameters including those defining the slab thermal parameter and the water storage capacity in the oceanic lithosphere and surrounding mantle are explored. The results show two major dehydration events of ultramafic rocks at around 150 and 750 km by dehydration of serpentine at 600°C and superhydrous phase B in the entrained wet upper mantle, respectively. Large amounts of water, ∼1.5 wt% at least locally, are carried down to the mantle transition zone and lower mantle. We estimate an upper limit of slab water flux into the mid‐mantle of 0.1–0.28 × 1012 kg/yr, which is ∼13%–37% of the input water from the serpentinized mantle. Moreover, a substantial fraction of the water released by the slab is absorbed by the entrained mantle and overlying mid‐mantle portions, such that ∼30%–70% of the water injected at the trench could be delivered to the lower mantle. The deepest magmatism is observed at ∼1,500 km in case of phase H breakdown (MgO‐SiO2‐H2O system), coinciding with the depth of strong seismic attenuation. Overall, these simulations suggest that up to 0.2 ocean mass per billion years could be transported down to the mid‐mantle and beyond.

A Comparative Study of Viscoelastic Rheological Models Using Finite-Difference Method and an Evaluation of the Seismic Attenuation in the Búzios Field Data

A Comparative Study of Viscoelastic Rheological Models Using Finite-Difference Method and an Evaluation of the Seismic Attenuation in the Búzios Field Data

Delineation of partial melts and crustal heterogeneities within the crust beneath Kumaon Himalaya, India from Lg wave attenuation

The crustal seismic attenuation or the Q structure is studied by using the Fourier spectra of Lg-wave along the Tanakpur- Dharchula- Dharma transect in the Kumaon Himalaya. The 1 Hz Lg Q (Q0) values are computed between different pairs of two stations and the observed values are later utilized to calculate the lateral variation in the Q0 values by following a back projection algorithm. This computation of Q0 values utilizes five regional distance earthquakes having moment magnitude (Mw) ≥ 4.0, which lie along the great circle path of the transect. Three of the five earthquakes occurred in the Tibetan plateau and the and the others occurred to the southwest on the Indian shield and are well recorded at all the 32 broadband seismographs operated between September 2018 and March 2022. The estimate Qo values range from 63 ± 2 and 203 ± 25, with the lowest value in the Lesser Himalaya and the highest across part of the Indo Gangetic Plain and Siwalik Himalaya. The Q0 model has low values ∼200 along the profile in the Indo Gangetic Plain and the Siwalik Himalaya, and are correlated with 2–5 km thick sedimentary layers below the Himalaya and the adjoining Indo-Gangetic Plain. We observe two distinctly different Q0 values to the northeast in the Lesser Himalaya tectonic unit. The region lying between the South Almora Thrust (SAT) and the Berinag Thrust (BT) shows extremely low Q0 values (∼60) but increases further north towards the Vaikrita Thrust (VT) to ∼200. The possible explanation for observing such huge variation of the Q0 values within a single tectonic unit may be the presence of fluid rich ramp structures, which introduces crustal heterogeneities and traps the aqueous fluids or partial melts lying within the crust. The Lg Q0 values decrease to the North and become ∼166 for station pairs in the Higher Himalaya and Tethys Himalaya tectonic units. The low Q0 values observed in this region may be correlated with low viscous partial melts in the form of Miocene leucogranite plutons, which resulted out of the Indo-Asian collision. The attenuation structure along the profile in the Kumaon Himalaya can be used to estimate ground motions of future earthquakes in the area and can contribute to seismic hazard assessment in the Himalaya and neighbouring regions.

Grain size reduction by plug flow in the wet oceanic upper mantle explains the asthenosphere's low seismic Q zone

The prominent seismic low-velocity zone (LVZ) in the oceanic low-viscosity asthenosphere is approximately coincident with the low seismic Q zone (LQZ; a zone of high seismic attenuation). Small olivine grain sizes could link these seismic and rheological properties because they reduce viscosity, seismic velocity and seismic Q. Because rock deformation reduces grain sizes, the asthenosphere's seismic properties can place constraints on asthenospheric flow. To determine dominant flow patterns, we develop a self-consistent analytical 1-D channel flow model that accounts for upper mantle rheology and its dependence on flow-modified grain-sizes, water content, and melt fraction, for flow driven by both surface plate motions (Couette flow) and/or horizontal pressure gradients (Poiseuille flow). We find that Couette flow dominates if the upper mantle is dry, and plug flow (a Poiseuille flow for power law rheology) dominates if it is weakened by wet conditions. A plug flow configuration spanning the upper 670 km of the mantle best explains the LQZ in the asthenosphere, and can be attributed to significant grain-size reduction due to extensive shearing across the asthenosphere. This flow configuration also explains high seismic Q values below the asthenosphere associated with minimal shear deformation and large grain sizes above the mantle transition zone. We suggest that the asthenospheric LQZ and LVZ seismic anomalies can be largely explained by grain-size variations associated with plug flow in the wet upper mantle.

Seismic random noise attenuation via a two-stage U-net with supervised attention

Random noise, which has a significant impact on subsequent processing and interpretation, easily interferes with seismic data. Current convolutional neural networks (CNN) use a single-stage technique to boost network capacity by exploiting the complicated network structure, but the performance of the network becomes saturated and prone to overfitting at a certain stage. Hence, we propose a two-stage U-Net denoising network with a supervised attention module (UNet-SAM). In this supervised algorithm, the first stage obtains the pre-denoising results, while the second stage achieves more accurate data. The supervised attention module (SAM) block is inserted in the first stage, extracting features with supervised attention to utilise as a priori information and guide the fine denoising in the second stage. The combination of the attention mechanism and two-stage strategy provides prior information that helps to train a network with better denoising performance. Experiments on synthetic and field data illustrate that the proposed UNet-SAM not only has a superior denoising effect but also retains more of the original effective signal.

Elastic scattering dominates high-frequency seismic attenuation in Southern California

We measured high-frequency (1–10 Hz) spectral amplitudes of more than fifty thousand P and S crustal phases from Southern California earthquakes and separately inverted the two datasets for three-dimensional and frequency-dependent models of total attenuation. The independent estimates of the P and S attenuation factors are nearly equal, decay with wavenumber at approximately the same rate, and are strongly correlated in all three spatial dimensions. Attenuation is lower in batholithic regions, higher in deforming regions, and does not correlate with crustal temperatures. We explain the data by combining an absorption-band model of low-frequency anelastic attenuation with a Sato-Fehler scattering model featuring crustal velocity heterogeneities having an outer scale of 8 km, a fractal dimension of 3.85, and a root-mean-square relative amplitude that varies laterally from 5% to 10%. We conclude that elastic scattering from crustal heterogeneities, not anelastic dissipation, dominates high-frequency attenuation in Southern California. Our results disagree with attenuation models derived from coda-wave analysis.