S-wave Attenuation Research Articles

Temporal variation of S-wave attenuation during the 2009 L'Aquila, Central Italy, seismic sequence

SUMMARY We investigate temporal and spatial variations of the spectral decay parameter kappa (κ) before and after the 6 April 2009, L'Aquila earthquake (Mw 6.1), in Central Italy. We analysed foreshocks 10 days before and aftershocks occurring 10 days and 6 months after this main event. We select earthquakes with magnitudes Mw ≥ 3.2 registered by the seismic network of Central Italy within a radius of 20 km from the epicentre of the L'Aquila main shock and having hypocentre distances of less than 170 km. We separate near-source, along-path and near-site contributions of κ for each group of events and we detected temporal variations of this S-wave attenuation parameter. We find that 10 days before the main shock κ along the path has the lowest values, probably due to high tectonic stress accumulated, in agreement with previous investigations performed with other techniques, then κ increases during the main event and remains constant during the first 10 days of aftershocks. The aftershocks that occurred 6 months after show an increase in the regional attenuation probably due to the tectonic stress released during the main shock and the earlier aftershocks. From the spatial point of view, 10 days before the principal event the foreshocks located to the south show an increase in the near-source attenuation towards the northeast, in the direction of the main shock. These spatial variations of κ may be related to the presence of crustal fluids near the rupture area, as evidenced by other previous studies. The first 10 days of aftershocks that concentrate around the main earthquake have high near-source κ, and those located north of the main rupture have lower values. These observations are consistent with previous investigations that show variations of elastic and anisotropic crustal properties during the L'Aquila earthquake sequence due to dilatancy and fluid diffusion processes within the nucleation zone. We conclude that temporal variations of the spectral decay parameter κ provide important clues for the earthquake cycle in Central Italy.

Influence of ice properties on wave propagation characteristics in partially frozen soils and rocks: A temperature-dependent rock-physics model

A better understanding of the temperature effects on the propagation characteristics of elastic waves in frozen soils and rocks is imperative for accurately quantifying their freezing degrees. Although the existing rock-physics models based on the three-phase Biot (TPB) theory adeptly interpret observed velocity variation with temperature (VVT) curves, they often lack a comprehensive understanding of the mechanisms underlying attenuation variation with temperature (AVT) curves. In this study, we first extend the TPB theory to incorporate the temperature-dependent properties of ice, such as changes in volumetric fraction, morphology, and viscoelasticity, by integrating the relevant thermodynamic laws. Model parameters related to ice properties and interactions, such as rigidity, shear moduli, density, and friction, are redefined. Then, using a numerical rock-physics modeling approach, we examine influential factors and modes of the wave VVT and AVT responses. Our results indicate that the P- and S-wave velocities increase with source frequency, consolidation degree, and frame-supporting ice content, whereas they decrease with temperature and pore-floating ice content. The P- and S-wave attenuation factors increase with the frame-supporting ice content and decrease with the consolidation degree. Rising temperatures tend to amplify the peak magnitude of the P-wave attenuation factors and shift the central frequency of the S-wave attenuation factors. Finally, within a temperature-controlled laboratory environment, we conduct ultrasonic wave transmission testing on brine-saturated sediment and rock specimens. The results demonstrate that as the temperature increases from −15°C to −3°C, the P- and S-wave velocities decrease, whereas the P-wave attenuation factors decrease and the S-wave attenuation factors initially rise before declining. Our viscoelastic TPB theory outperforms the existing ones in interpreting the S-wave AVT observations. This temperature-dependent rock-physics model holds promise for interpreting the sonic logging data in the time-lapse monitoring of permafrost, glaciers, and Antarctica.

Seismic attenuation and stress on the San Andreas Fault at Parkfield: are we critical yet?

The Parkfield transitional segment of the San Andreas Fault (SAF) is characterized by the production of frequent quasi-periodical M6 events that break the very same asperity. The last Parkfield mainshock occurred on 28 September 2004, 38 years after the 1966 earthquake, and after the segment showed a ∼22 years average recurrence time. The main reason for the much longer interevent period between the last two earthquakes is thought to be the reduction of the Coulomb stress from the M6.5 Coalinga earthquake of 2 May 1983, and the M6 Nuñez events of June 11th and 22 July 1983. Plausibly, the transitional segment of the SAF at Parkfield is now in the late part of its seismic cycle and current observations may all be relative to a state of stress close to criticality. However, the behavior of the attenuation parameter in the last few years seems substantially different from the one that characterized the years prior to the 2004 mainshock. A few questions arise: (i) Does a detectable preparation phase for the Parkfield mainshocks exist, and is it the same for all events? (ii) How dynamically/kinematically similar are the quasi-periodic occurrences of the Parkfield mainshocks? (iii) Are some dynamic/kinematic characteristics of the next mainshock predictable from the analysis of current data? (e.g., do we expect the epicenter of the next failure to be co-located to that of 2004?) (iv) Should we expect the duration of the current interseismic period to be close to the 22-year “undisturbed” average value? We respond to the questions listed above by analyzing the non-geometric attenuation of direct S-waves along the transitional segment of the SAF at Parkfield, in the close vicinity of the fault plane, between January 2001 and November 2023. Of particular interest is the preparatory behavior of the attenuation parameter as the 2004 mainshock approached, on both sides of the SAF. We also show that the non-volcanic tremor activity modulates the seismic attenuation in the area, and possibly the seismicity along the Parkfield fault segment, including the occurrence of the mainshocks.

Unveiling attenuation structures in the northern Taiwan volcanic zone.

This cutting-edge study delves into regional magmatism in northern Taiwan through advanced 3-D P- and S-wave frequency-dependent attenuation tomography. Positioned at the dynamic convergence boundary between the Philippine Sea Plate and the Eurasian Plate, Taiwan experiences moderate earthquakes and intriguing volcanic activity, with a focus on the Tatun volcano group. Employing the Formosa seismic array for high-resolution results, our research identifies high-attenuation anomalies (low Q) beneath the northern Taiwan volcanic zone (NTVZ) and offshore submarine volcanoes, indicative of potential hydrothermal activities and magma reservoirs at varying depths. Additionally, we explore low-attenuation anomalies (high Q) in the forearc region of the Ryukyu subduction zone, suggestive of partial saturation linked to serpentinization processes resulting from seawater infiltration or forearc mantle hydration. These findings shed light on the complex geological features and provide essential insights into the crustal properties of northern Taiwan, contributing to a deeper understanding of its magmatic evolution and tectonic processes.

Effects of pressure and fluid properties on S-wave attenuation of tight rocks based on ultrasonic experiments

Effects of pressure and fluid properties on S-wave attenuation of tight rocks based on ultrasonic experiments

Water Effects on Elastic S-Wave Propagation and Attenuation Across Single Clay-Rich Rock Fractures: Insights from Ultrasonic Measurements

Though previous studies have shown that the presence of water strongly influences wave responses of rock fractures, water effects on wave behaviours across clay-rich rock fractures have been ambiguous until now. In the present study, we conducted considerable ultrasonic measurements on single rock fractures filled with kaolinite-dominant gouges at varying water saturation degrees to investigate the water effects on elastic S-wave propagation and attenuation across clay-rich rock fractures. The experimental results reveal that the S-wave velocity across single clay-rich rock fractures slightly increases and decreases with the progressively increasing water saturation degree. An increase in water saturation leads to a concave trend of the spectral amplitudes, while it moderately affects the central frequency of transmitted S-waves. In addition, the seismic quality factor across single clay-rich rock fractures follows an exponential growth trend with the water saturation, suggesting the exponentially negative relation between S-wave attenuation and the water saturation. We attribute the water saturation-dependent S-wave attributes across single clay-rich rock fractures to the combined effects of the local flow and the degradation of grain contacts. Compared to P-wave, S-wave exhibits less sensitivity to varying water saturation of clay-rich rock fracture. Upon increasing water saturation, S-waves display similar velocity and central frequency trends with P-waves. The tendencies of spectral amplitude and seismic quality factor for S-waves are approximately opposite to those for P-waves as the water saturation degree increases. We interpret these discrepancies by the fact that S-wave attributes across single water-saturated clay-rich rock fractures mainly depend on the properties of the skeletal frame, while the characteristics of the particles, pore fluid, and skeleton frame dominate P-wave behaviours. The outcomes of the current work facilitate our understanding of the fluid effects on the interaction of waves with clay-rich rock discontinuities.

Modified non-dominated sorting genetic algorithm-II for the optimal design of soil-concrete periodic plane wave barriers

This paper uses the Bloch-Floquet theory based on the modified non-dominated sorting genetic algorithm-II (NSGA-II) to investigate the optimal design of wave barriers to attenuate plane waves. The primary aim is to find the optimal design of the plane wave barriers with a wide bandgap at a low-frequency range having low construction cost. Consequently, a modification of NSGA-II has been developed and adopted to obtain the optimal arrangement of concrete within different 8 × 8, 10 × 10, and 12 × 12 grid sizes in the wave barrier unit cell by considering three objective functions as (1) maximize bandgap width (BW), (2) minimize average bandgap frequency (ABF), and (3) minimize filling ratio (FR). The Pareto fronts represent a wide range of objective functions in the problem space, making the proposed method effective for designing plane wave barriers. The performance of the optimal barriers is examined with the three-dimensional finite element (FE) simulation of the finite lattice in the frequency domain. The finite lattice results confirm the obtained bandgaps for the optimal unit cells and verify their efficacy in attenuating plane S-waves. Furthermore, the effects of the number of barriers and the barrier length are studied as two effective parameters affecting plane S-wave attenuation.

The implications of S-wave attenuation in geothermal reservoirs

An increasing number of research studies have found that S-waves have significant attenuation and travel time delays as they pass through geothermal reservoirs and magma chambers. For this study, we used a micro-seismic dense array of recording stations to model the underground structure of a geothermal volume and analyzed recorded seismic waves. We analyze waveform data from twenty-five stations and identify whether P- and S-waves have been attenuated. We utilize tomographic solutions of P- and S-wave velocities and derived rock physics parameters, including Bulk, Shear, Lambda, Young's Moduli, and Poisson's ratio, to identify underground geological structures. We speculate the cause of S-wave attenuation and travel time delays. From the rock physics interpretations, the subterranean geothermal reservoir may be further explored to identify fractures, porosity, saturation, and permeability properties. We found that unusually high S-wave attenuation is usually related to a geothermal reservoir zone or magma, and few, if any, earthquakes occur within these zones. We test a rapid, simple, and inexpensive means to provide an early preliminary analysis of geothermal potential.

Effects of thermal damage on natural gas transport capacity of tight sandstone after electrical heating

As an environment-friendly method, downhole electric heating can cause thermal damage to the rock around the well, so as to improve the gas transport capacity of tight sandstone gas reservoir (TGR), but its mechanisms are not well established. In the present study, a comprehensive analysis of the thermal damage characteristics of tight sandstones has been conducted, employing a suite of microscopic investigative techniques such as differential thermal gravimetry, X-ray diffraction, and scanning electron microscopy. The experimental results were related to permeability test results and then combined with constant-pressure heating acoustic rock tests. Subsequently, the heating and cooling processes along with the effects of confining pressure on the damage evolution and gas transport capacity were analysed. According to the difference in thermal damage mechanism, three temperature ranges were identified: 100–300 °C, 300–1000 °C, and 1000–1200 °C. In the first stage, free water escaped, clay minerals expanded, and a small number of weak cementation cracked, resulting in a 26.18% decrease (200 °C) and a 56.95% increase (300 °C) in permeability. In the second stage, the clay minerals were stripped of their bound water; with an increase in temperature, heat-induced cracks were initiated, propagated, and aggregated to form a network. The permeability increased exponentially by 938-fold. Finally, in the third stage, with the initiation of feldspar melting, the mineral surface was smooth; furthermore, permeability increased rapidly by 164.08%, after which the pores were blocked rapidly. Acoustic tests under constant-pressure heating conditions showed that thermal damage continued to evolve during the cooling phase because of the temperature variable stress. External pressures could only partially limit the evolution of thermal damage. The findings of this study illustrate that downhole electric heating (300–1000 °C) can improve natural gas transport capacity by eliminating water phase trap damage and creating a multi-scale crack network in a near-wellbore area. In addition, the nonlinear evolution of permeability in tight sandstones is different from that in other rocks, and the S-wave attenuation coefficient can well characterise this phenomenon. Thus, a mathematical model of nonlinear permeability evolution based on the principle of dual percolation is derived. Therefore, the results of this research provide a reference for the temperature selection and acoustic monitoring of the TGR downhole heating process.

P- and S-wave attenuation in the northern region of the Gulf of California, Mexico

P- and S-wave attenuation in the northern region of the Gulf of California, Mexico

Weak Seismicity and Strongest Earthquakes Against the Background of Variations in S-Wave Attenuation Field

Weak Seismicity and Strongest Earthquakes Against the Background of Variations in S-Wave Attenuation Field

A nonparametric spectrum estimation method for dispersion and attenuation analysis of borehole acoustic measurements

Dispersion and attenuation analysis can be used to determine formation anisotropy induced by fractures, or stresses. In this paper, we propose a nonparametric spectrum estimation method to get phase dispersion characteristics and attenuation coefficient. By designing an appropriate vector filter, phase velocity, attenuation coefficient and amplitude can be inverted from the waveform recorded by the receiver array. Performance analysis of this algorithm is compared with Extended Prony Method (EPM) and Forward and Backward Matrix Pencil (FBMP) method. Based on the analysis results, the proposed method is capable of achieving high resolution and precision as the parametric spectrum estimation methods. At the meantime, it also keeps high stability as the other nonparametric spectrum estimation methods. At last, applications to synthetic waveforms modeled using finite difference method and real data show its efficiency. The real data processing results show that the P-wave attenuation log is more sensitive to oil formation compared to S-wave; and the S-wave attenuation log is more sensitive to shale formation compared to P-wave.

Imaging near-surface S-wave velocity and attenuation models by full-waveform inversion with distributed acoustic sensing-recorded surface waves

Distributed acoustic sensing (DAS) technology is, increasingly, the seismic acquisition mode of choice for its high spatial sampling rate, low cost, and nonintrusive deployability. It is being widely evaluated as an enabler of seismic monitoring for [Formula: see text] sequestration in building subsurface time-lapse images and in characterizing near-surface environments. To advance this evaluation, field seismic surveys with optical fibers have been conducted at the Containment and Monitoring Institute’s Field Research Station (CaMI.FRS) in Newell County, Alberta, Canada. In comparison to the standard geophones, optical fibers deployed in surface trenches at CaMI.FRS have recorded high-quality surface waves, rich in low frequencies and exhibiting limited spatial aliasing. These benefits have motivated us to apply the full-waveform inversion (FWI) approach to image the S-wave velocity ([Formula: see text]) and attenuation (quality factor [Formula: see text]) models at shallow site using the surface waves recorded by optical fibers. Compared to the conventional surface-wave dispersion approach, FWI can intrinsically incorporate fundamental and high-order modes and produce [Formula: see text] model with high spatial resolution that resolves horizontal variations. The low-frequency components below 10 Hz measured in the DAS recordings are helpful to overcome the cycle-skipping problem of FWI. Following the adjoint-state method, [Formula: see text] sensitivity kernel can be calculated efficiently with memory strain variables. The [Formula: see text] model is iteratively estimated with a new misfit function measuring root-mean-square amplitude differences, which helps to reduce the trade-off artifacts. The synthetic data obtained from the inverted models are consistent with the observed data in amplitude and phase. The inversion results provide valuable information to characterize the near-surface environments at CaMI.FRS and are expected to support seismic imaging in deeper [Formula: see text] injection zones.

Mapping Heterogeneities of the Short-Period S-Wave Attenuation Field in the Lithosphere of Southwest Alaska

Mapping Heterogeneities of the Short-Period S-Wave Attenuation Field in the Lithosphere of Southwest Alaska

Ground motion simulation for the 21 May 2021 Ms 6.4 Yangbi, China, earthquake using stochastic finite-fault method

On 21 May 2021, a 6.4-magnitude earthquake occurred in Yangbi County, Yunnan Province, China. To reproduce the ground motion characteristics of this earthquake, the stochastic finite-fault method was adopted. The ground motion records were analyzed to determine the source, path, and site parameters. Based on the optimization algorithm, the stress drop was set to 10 bar. The S-wave attenuation relation ( QS = 122.7 f0.44) was calculated by the spectral decay method. For the site effect, the site amplification was corrected using the horizontal-to-vertical spectral ratio method, and the zero-distance kappa filter had a value of 0.0328 s. To verify the reliability of the input parameters, the simulated 5%-damped pseudo-spectral acceleration, time history, and Chinese instrumental intensity were compared with those observed at six stations and finding acceptable consistency. Furthermore, the fitted model was used to simulate the ground motion of 2279 nodal points in the area, and the seismic intensity contours were obtained. Finally, the earthquake damage assessment was performed in the Yangbi County, and the difference between the designed spectral acceleration and that simulated at a specific period was regarded as the degree of earthquake damage. It was found that the reinforced concrete structures near the epicenter have sufficient safety reserves, and the earthquake damage was not serious. In summary, the stochastic finite-fault method with calibrated parameters could effectively synthesize the ground motion of specific sites, thus providing a basis for the earthquake damage assessment of engineering buildings.

The mechanisms of S-wave attenuation in grainstones

Abstract The dominant mechanism of P-wave attenuation in fluid-saturated rock is well known to be the pore-scale squirt. However, the S-wave does not change the average fluid pressure in a pore and the pore volume stays unchanged. As such, the S-wave has a mechanism of attenuation distinctively different from the P-wave. This paper attempts to resolve the mechanisms of S-wave attenuation in fluid-saturated grainstones. The first mechanism is the viscous boundary layer in a fracture, the second is fluid acceleration plus a real-number permeability and the third mechanism is fluid acceleration plus a complex-number permeability (which arises from the viscous boundary layer). D'Euville limestone and Berea sandstone are used as illustrative examples. Ultrasonic velocity and the quality factor due to pore fluid (Qs) are compared between the three models and measurement. The results indicate that fluid acceleration plus the viscous boundary layer is the mechanism of S-wave attenuation in the water-saturated grainstones. In addition, the third model reveals a novel convex in the curve of Qs in the frequency range of 107–108 Hz.

S-Wave Attenuation Variation and its Impact on Ground Motion Amplitudes During 2016–2017 Central Italy Earthquake Sequence

A very energetic seismic sequence struck the central Apennines, Italy, in 2016–2017, with a series of damaging earthquakes, three of them with moment magnitudes M ≥ 5.9, and five of them with M ≥ 5.0, occurred over a few months between 24 August 2016, and late 2017. Several studies explained the phenomenon of a cascading earthquake sequence with fluid movements that provoked the rupture of different parts of the fault segments at different times and locations (e.g., Miller, Nature, 2004, 427, 724–727; Gabrielli, Frontiers in Earth Science, section Structural Geology and Tectonics, 2022; Malagnini, Frontiers in Earth Science, section Solid Earth Geophysics, 2022). In this study, we investigated the variation of crustal S-wave attenuation in terms of the frequency-dependent quality factor Q(f) before and after the main events (including the Amatrice, Visso, and Norcia sub-sequences, hereafter, AVN, and periods before and after the AVN multi-mainshock sequence). The spectral characteristics of regional attenuation in the central Apennines, as well as of the earthquake sources of the AVN sequence, are derived through regression analysis using a large set of seismograms; Q(f) is modeled, together with the bilinear geometrical spreading, g(r), using a widely used tool, namely, random vibration theory, RVT (Cartwright and Longuet-Higgins, 1956). The primary objective of this effort was to examine how the variability of crustal anelastic attenuation would impact the earthquake-induced ground motions. The latter is quantified in terms of peak ground accelerations (PGAs), peak ground velocities (PGVs), and pseudo spectral accelerations (PSAs) at 0.3 and 2 s . Here, we showed that the main events of the AVN sequence strongly affect crustal S-wave attenuation, including its frequency dependence. However, the effects of 1/Q(f) fluctuations on earthquake-induced ground motions are small and have a negligible impact on the seismic hazard.

Upper- to mid-crustal seismic attenuation structure above the mantle wedge in East Anatolia, Turkey: Imaging crustal scale segmentation and differentiation

Multi-frequency P- and S-wave attenuation tomography models of Lake Van area (East Anatolia) have been obtained by estimating coda-normalized wave spectra of 3027 local earthquakes (2.0 < Mw < 7.1). The 6998 waveforms sampled from surface to a depth of 25 km, and were recorded from 2004 to 2020 at seven broadband, three-component digital seismic stations operated by Kandilli Observatory and Earthquake Research Institute (KOERI). We adopted a two-point ray-bending method to trace rays in a 3-D velocity model. We applied the coda normalization (CN) method to P- and S-wave data sets. We inverted the spectral data with a multiple resolution seismic attenuation (MuRAT) approach to obtain final tomographic models. On average, high (low) attenuation corresponds to low (high) velocity anomalies. The P- and S-wave attenuation contrasts delimit four well-known geological zones. High frequency-short wavelength attenuation contrasts constrain the 5-km-deep zone of interaction between magma and sediments within the Lake Van basin. Low frequency-long wavelength attenuation anomalies mark the central section of Lake Van between depths of 10 km and 20 km. This zone coincides with a rigid stable shear zone overlying a possible weak-ductile lower crust, interpreted as a detachment. Both low (5–15 km depth) and high attenuation (>20 km) anomalies mark the area of maximum seismic energy release during the Van event. Their contrast highlights the maximum seismogenetic depth above weak-warm, unstable materials. High attenuation in the SE-part of the Lake Van area coincides with a large hydrothermal and/or magmatic folding-overthrusting, interpreted as a suture-metamorphic complex between depths of 10–15 km. Other minor high-attenuation zones deeper than 5 km focus on complex shear zones in the area damaged by the Van event. The paired attenuation structure of the Lake Van area appears linked to multiple tectonic processes of crust-magma interaction better constrains subsurface segmentation structures and differential deformation types at upper-middle crustal depths.

A study on the use of fundamental antisymmetric-like guided wave for health monitoring of elastic–viscoelastic bilayer structures

This study investigates the ultrasonic guided wave propagation in an elastic–viscoelastic (steel–rubber) bilayer structure. 2D finite element models are developed in the frequency domain to simulate the wave propagation in the steel–rubber bilayer structure. The guided wave A0 mode is generated in the bilayer with a contact L-wave probe and detected with an out-of-plane laser vibrometer. Several wave features, such as amplitude, phase velocity and phase delay, are measured and compared to determine the characteristic changes of the A0 wave mode in the steel layer alone as well as in the bilayer structure. Studies are also performed for the bilayer structure when excited from the steel and rubber surfaces. The amplitude and phase velocity of the A0 mode are reduced in the bilayer compared to the steel layer alone. The phase velocity of the A0 wave mode in the bilayer does not depend on the viscoelastic properties of the rubber layer, rather depends only on the elastic properties of the rubber layer. The viscoelastic rubber layer in the bilayer structure does not sustain any independent wave mode; instead, it carries the A0 mode of the steel layer alone as a modified A0 wave mode in the bilayer structure. A parametric numerical study of the viscoelasticity of the rubber layer in the bilayer structure shows that the attenuation of the modified A0 mode in the bilayer is more affected by the bulk S-wave attenuation than the bulk L-wave attenuation. The rate of attenuation of the modified A0 mode in the bilayer is faster on the rubber surface than on the steel surface. A study on the A0 wave mode interaction with the interfacial disbond between steel and rubber layers is also carried out.

Characterization of coexistence of gas hydrate and free gas using sonic logging data in the Shenhu Area, South China Sea

Recent studies have confirmed the coexistence of gas hydrate (GH) and free gas (FG) in gas hydrate stability zone (GHSZ). However, the acoustic properties of the coexisting sediment, GH-bearing sediment, and FG-bearing sediment are needed to be specified, for discriminating these three coexisting phases using sonic logs. In this study, the compressional- (P-) and shear (S-) wave attenuations of the sediment with coexisting GH and FG are calculated from the sonic logs in the South China Sea (SCS). The obtained results reveal that the P-wave and S-wave velocities of the sediment with coexisting GH and FG are decreased by 14% and 11%, P-wave attenuation enhanced by 104%, and S-wave attenuation decreased by 44%, respectively, as compared with the sediment only containing GH at well SHSC-4J1. A similar result can be obtained for well GMGS6-SH02. The highest P-wave attenuation appears in the sediment with coexisting GH and FG, ∼0.66 at well SHSC-4J1 and ∼0.60 at well GMGS6-SH02, respectively. Moreover, cross plots of the measured P- and S-wave velocities and attenuations suggest that attenuation is more sensitive to the coexistence of GH and FG than velocity. The saturation of coexisting GH and FG in sediment can be calculated from the sonic velocities using rock physics modeling, a maximum value of ∼26% (av. 13%) at well SHSC-4J1 and a maximum value of ∼23% (av. 7%) at well GMGS6-SH02.