Seismic Waves Research Articles

Amplitude‐Dependent Energy Dissipation Inferred From Spectral Analyses of Intraslab Earthquakes

AbstractWhile the Earth (rocky planet) can be approximated as an elastic body, it also possesses anelasticity, Q−1, which causes energy dissipation (intrinsic attenuation) during deformation. Rock deformation experiments have demonstrated that Q−1 shows a marked amplitude dependency for strain of >∼10−6, but seismic‐waves‐induced strain is generally much smaller than the threshold value. Therefore, all seismological analyses have assumed amplitude‐independent attenuation. However, theoretical models of dislocation‐induced attenuation have predicted amplitude‐dependent attenuation under high temperatures and pressures equivalent to the crustal and uppermost mantle conditions. This study investigates whether attenuation is actually independent of seismic‐wave amplitudes by a systematic analysis of a large number of spectral amplitudes of co‐located earthquake pairs with different observed amplitudes. We assume the ω2 source and circular crack models to correct for the source parameters of earthquakes. The obtained results suggest that amplitude‐dependent attenuation is required to explain the observations, which contradicts a long‐standing recognition that amplitude‐dependent attenuation is negligible for the propagation of seismic waves. Our model calculation further suggests that Q−1 is proportional to the seismic amplitude, A, whereby Q−1 ∝ A0.1–0.2, which introduces attenuation variations along a given raypath, with significantly enhanced attenuation near the hypocenter. Our result highlights the need to revisit and potentially rethink current models of the physical mechanisms influencing intrinsic attenuation.

Study of the dynamic interactions between helix-stiffened cement mixing piles and soft soil under oblique incidence of SV waves in arbitrary space

Helix stiffened cement mixing (HSCM) piles are extensively utilized in soft soil sites due to their excellent seismic and pullout resistance. Initially, the equivalent nodal force formulas for each face under the oblique incidence of SV waves in any spatial direction are derived based on the viscous-spring artificial boundary. The method's applicability in studying pile–soil interactions is verified based on existing pile–soil tests. Subsequently, the HSCM pile–soil model is constructed using finite element software through a Python program. Various analyses of accelerations, relative displacements, soil reactions, and pile–soil dynamic p-y curves are conducted using two different directions of incidence angles (horizontal and vertical) and various types of seismic waves. Subsequently, the backbone line of the dynamic p-y curve is plotted, revealing the pile–soil interaction mechanism under spatial oblique incidence. Finally, Matlock's formula is modified to ensure its applicability to pile–soil interactions under spatially oblique incidence. The results demonstrate that loading the Kobe wave causes the peak acceleration in the x direction, the peak pile–soil relative displacement, and the peak pile-side soil reaction force to increase by 22.64 %, −18.90 % and 18.42 %, respectively, compared to those of the El Centro wave.

The contradiction between lithospheric thermal and seismic structures reveals a nonsteady thermal state – A case study from Northeast China

The nature of the lithosphere, as the outermost layer of the solid Earth, has long been a focus of the Earth sciences. Many methods have been used to study the properties and structure of the lithosphere, including gravity, magnetism, electricity, seismic, and geothermics. Since the 1970 s, a coupled heat-flow heat-production steady-state model has been employed to study the thermal structure of the continental lithosphere and has helped researchers explain many geothermal observations. However, the steady-state model does not work well in some areas. Taking Northeast China as a case study, we systematically calculated the lithospheric thermal structure, compared the result with seismic research, and concluded that the lithospheric thermal state is nonsteady in the southern Songliao Basin, the southern Greater Xing’an Range and the Changbai Volcano. The lithosphere in southern Songliao Basin features a hot top and a cold bottom. The lithosphere in southern Greater Xing’an Range and the Changbai Volcano feature a cold top and a hot bottom. Our numerical simulation has demonstrated that the response of surface heat flow to thermal disturbance at the bottom of the lithosphere often lags by more than 20 Myr, resulting in a significant disparity between the thermal structure calculated based on surface heat flow and the velocity structure of seismic waves. In addition, this study of the thermal structure in Northeast China shows that the temperature of the Moho in Songliao Basin is very high (>600 °C), which may be an important cause of the lack of Cenozoic volcanism in the Songliao Basin.

Fluid identification in fractured media with genetic algorithm

The fluid identification of fracture media is susceptible to factors such as observation data, fluid sensitivity parameters, and inversion algorithms. However, appropriate nonlinear algorithms can be applied to reduce errors generated during the inversion process, thus helping to improve the reliability of fluid identification. In this paper, analysis and comparison are made to various reflection coefficient approximate formulas, of which the applicability and accuracy are demonstrated in fluid-saturated poroelastic media, and the objective function is constructed further from Russell's reflection coefficient formula. In this sense, the genetic algorithm (GA) can achieve the pre-stack inversion of seismic waves. Based on the inversion results such as P-, S-wave velocity, and density, the Russell fluid indicator, Poisson's ratio, and Poisson impedance are combined to identify the water-, gas-, and oil-bearing fracture. Finally, the applicability and reliability of the method are demonstrated through numerical calculations in some regions of Marmousi2 model and the field data. The results show that the seismic data can be preliminarily analyzed by the inversion method, followed by combining the Russell fluid indicator, Poisson's ratio, and Poisson impedance, effectively reducing the multiplicity of the inversion results and improving the reliability of fluid identification in fractured media.

The Redox State of the Asthenospheric Mantle and the Onset of Melting Beneath Mid‐Ocean Ridges

AbstractThe redox state of the convective asthenospheric mantle governs the speciation of volatile elements such as carbon and, therefore, influences the depth at which (redox) melting can occur, with implications for seismic signals. Geophysical observations suggest the potential presence of carbonatite melts at a depth of 200–250 km. However, thermodynamic models indicate that the onset of (redox) melting would occur at 100–150 km for a mantle with 3%–4% of Fe3+/∑Fe. Here, we present a new oxybarometer that is based on the V/Sc exchange coefficient between olivine and the melt, which is insensitive to surficial alteration, volatile degassing, electron exchange reactions and fractional crystallization. By applying this method to primary mid‐ocean ridge basalts (MORBs) from Southwest Indian Ridge and East Pacific Rise, we demonstrate that the average oxygen fugacity (fo2) of MORBs corrected for the depth of formation is 0.78 ± 0.26 (1σ) log units above the fayalite‐magnetite‐quartz (FMQ) buffer, which is slightly more oxidized than previously estimated (near FMQ buffer). Our findings indicate that the convective asthenospheric mantle exhibits higher oxygen fugacity than the continental lithospheric mantle. Along an adiabat, carbonatitic melts can form from a CO2‐bearing source at a depth of 200–250 km, explaining the asthenospheric mantle's electrical conductivity and seismic velocity anomaly.

Velocity Measurements of Powdered Rock at Low Confining Pressures and Comparison to Lunar Shallow Seismic Velocity

AbstractSeismic methods will be useful for future lunar near‐surface characterization, and high‐fidelity elastic models will be required to aid interpretation of seismic observations. To develop an elastic lunar near‐surface model, we performed ultrasonic velocity measurements of lunar regolith simulant at low confining pressure and developed a rock physics model calibrated to these measurements. Grain contact models based on Hertz‐Mindlin theory produce accurate results at high confining pressure (i.e., several hundred meters or more burial depth) but historically fail to predict observed velocities in unconsolidated media at low pressure. Therefore, we heuristically modified existing models to fit our measured data over a range of porosities and confining pressures. To compare with Apollo 14 and 16 active seismic experiments, we used our new heuristic rock physics model to produce lunar subsurface velocity profiles. We performed ray tracing through our velocity profiles to calculate seismic traveltime, which results in good agreement with first arrivals interpreted from the Apollo experiments. Our model suggests a slightly higher velocity‐pressure dependence than inferred from in situ measurements, which may be due to porosity reduction in the lunar regolith from impact‐induced and natural vibrations.

Ambient Seismic Noise Tomography Within the Floridan Aquifer System, Santa Fe River‐Sink Rise, Florida, US

Ambient Seismic Noise Tomography Within the Floridan Aquifer System, Santa Fe River‐Sink Rise, Florida, US

Design procedure of a shear fuse system for steel moment-resisting frames

In steel moment-resisting frames (MRFs), seismic energy is generally dissipated through the formation of flexural plastic hinges at beam ends. In ensuring such a mechanism, current code provisions limit the utilization of beams with small span-to-length ratios in MRFs. This study presents the design procedure of a novel shear fuse system that integrates replaceable shear links with non-prismatic beams to enhance the performance and repairability of MRFs with small beam span-to-length ratios. The proposed design strategically weakens the beam at its midspan by incorporating a replaceable link, prioritizing shear yielding in the link over flexural yielding in the beam outside the link, thus ensuring adequate frame ductility and protecting the critical beam-to-column connections. It can function as an efficient replaceable shear fuse system, as the damaged fuse can be substituted with a new one following a severe earthquake. In fulfilling the study’s purpose, first, several formulas are developed to provide a comprehensive design procedure. Next, example design calculations are presented for an MRF with a small beam span-to-depth ratio. Ultimately, a numerical investigation is provided to examine the proposed system’s performance compared to conventional MRFs. The results indicate that the proposed shear fuse system provides a more consistent cyclic behavior than the conventional prismatic beam design, exhibiting stable strain-hardening behavior up to the 5 % story drift ratio without noticeable strength degradation. It appropriately shifts the plastic hinges away from the beam-to-column connections while increasing the frame’s overall ductility with 1.14 times greater energy dissipation in the final loading cycles.

Three-dimensional density model of the mantle beneath the Ukrainian shield

Purpose. Mantle density models are key tools for understanding the fundamental geological and physical processes occurring within the Earth and are essential to our scientific and applied understanding of the planet. Methodology. The tasks were solved by a complex research method, including analysis and generalization of literary and patent sources, analytical, experimental studies, using computer and mathematical modelling methods. Findings. One-dimensional models simplify the mantle density distribution by assuming that it is uniform only in the vertical direction. This limitation does not allow for horizontal variations in mantle density, which may be important on a regional scale. 3D models are more complex and require more data and computational resources, so their use may be limited. In this study, we present a quasi-three-dimensional model of mantle density beneath the Ukrainian Shield. This 3D model is obtained using a basic set of one-dimensional seismic tomographic velocity models calculated for 21 mantle domains in the depth range from 50 to 2,600 km. The process of converting the P-wave velocity model into a density model includes the following stages: 1) determining seismic boundaries in the mantle based on P-wave velocity curves for each mantle domain; 2) creating a synthetic mantle model beneath the Ukrainian Shield for the P,S-wave velocity curves; 3) solving the Adams-Williamson equation for each domain, considering polynomial corrections to extract heterogeneities during its solution; 4) analysing existing models by comparing the calculated gravitational potential at the central point of the Ukrainian Shield as the standard reference for selecting one of 5 reference models. Here, we focus on the final stages of constructing the mantle density model by: 1) balancing the mass of the upper and lower mantle for each domain when determining density using the Adams-Williamson equation and introducing polynomial corrections; 2) calculating densities for each of the 21 mantle domains and their 3D integration. Originality. The obtained mantle-density model of the Ukrainian Shield aligns well with the division of the mantle into three main layers: lithosphere, upper mantle, and lower mantle. Each of the mantle’s structural layers has its representation pattern in density heterogeneities. Anomalies of decreased density in the lithosphere of the Ukrainian Shield correlate with thermal anomalies, whereas anomalies of increased density correspond to tectonic zones dividing its megablocks. Practical value. Regions of increased density gradient are associated with mantle thrust faults, which in some cases can be boundaries between different petrological formations and serve as channels for magma ascent into the Earth’s crust at certain stages of geological development of the Ukrainian shield and, in turn, be sources of minerals.

Towards the systematic reconnaissance of seismic signals from glaciers and ice sheets – Part 2: Unsupervised learning for source process characterization

Abstract. Given the high number and diversity of events in a typical cryoseismic dataset, in particular those recorded on ice sheet margins, it is desirable to use a semi-automated method of grouping similar events for reconnaissance and ongoing analysis. We present a workflow for employing semi-unsupervised cluster analysis to inform investigations of the processes occurring in glaciers and ice sheets. In this demonstration study, we make use of a seismic event catalogue previously compiled for the Whillans Ice Stream, for the 2010–2011 austral summer (outlined in Part 1, Latto et al., 2024). We address the challenges of seismic event analysis for a complex wave field by clustering similar seismic events into groups using characteristic temporal, spectral, and polarization attributes of seismic time series with the k-means++ algorithm. This provides the basis for a reconnaissance analysis of a seismic wave field that contains local events (from the ice stream) set in an ambient wave field that itself contains a diversity of signals (mostly from the Ross Ice Shelf). As one result, we find that two clusters include stick-slip events that diverge in terms of length and initiation locality (i.e., central sticky spot and/or the grounding line). We also identify a swarm of high-frequency signals on 16–17 January 2011 that are potentially associated with a surface melt event from the Ross Ice Shelf. Used together with the event detection presented in Part 1, the semi-automated workflow could readily be generalized to other locations and, as a possible benchmark procedure, could enable the monitoring of remote glaciers over time and comparisons between locations.

Very-long-period signal reveals lava lake sloshing and its interaction with a deep reservoir in Nyiragongo volcano

The longevity of lava lakes in open-vent volcanoes reflects a hydraulic connection between the lake and the deep part of the magma plumbing system. Constraining the size of the shallow magmatic system and resolving the rheology of magma filling in the system is essential to evaluate potential hazards like lava flow and other activities. As the lava lake is often perturbed by degassing bursts, rockfall, and even convection, seismic waves radiated from the oscillation of fluid and its mechanical coupling with the surrounding solid walls provide invaluable information on probing system geometry and magma rheology. In this report, I show the first observation of very long-period signals in Nyiragongo volcano, to uncover the sloshing of the world's largest known lava lake and its dynamic interaction with a deep reservoir during the relatively quiet period. The signal is manifested as the ground oscillations with two isolated spectral peaks at ∼15 s and ∼16 s sustaining up to half an hour and a spectral peak at a longer period of ∼76 s. The radiated seismic energy can be well recognized by the stations with distances of <50 km to the lava lake. The traveling time, particle-motion polarization, and deformation inversion suggest that the 15 s' and 16 s' modes are related to two orthogonal horizontal forces at a very shallow depth, likely pointing to the sloshing dynamics of the lava lake. The 76 s' mode is considered as the dynamic coupling between the lake bottom to a deep reservoir at a depth of 8–16 km through a conduit driven by the sloshing. The dynamic modeling of the 76 s' mode points to a deep reservoir storativity of ∼8 m3/Pa and a spherical reservoir with a radius of ∼7.5 km. High-frequency seismic waves before the onset of the 15 s' and 16 s' modes suggest that the signals may be excited by rigorous degassing or rockfall. Variations in the period and quality factor of the modes reflect the changes in the lake/reservoir geometry and magma rheology. This finding may improve our ability to understand the magmatic plumbing system, track magma evolution in Nyiragongo, and further probe the formation of lava lakes in active volcanoes.

Geotechnical assessment of seismicity and liquefaction potential at the Banarli landfill in Tekirdag, Turkey

This study, conducted in the Banarli district of Tekirdag Province, Turkey, focuses on soil reaction analysis and liquefaction potential in an area where a landfill and an associated power plant are planned. The research was examined with a one-dimensional ground response analysis to understand seismic behaviour, revealing the varied responses of soil categories to seismic waves. Soft soil layers were found to lengthen the dominant period of oscillation rather than significantly enhancing peak acceleration during seismic events. Earthquake records specific to the region were crucial for accurate assessments. The study comprehensively assessed liquefaction potential using various estimation methods, including the probability of liquefaction (PL ), liquefaction potential index (LPI), and liquefaction risk index (IR ). Moreover, this study examined liquefaction potential based on Standard Penetration Test (SPT) results, identifying susceptibility in the clayey sand layer at a depth of 3 to 12 meters. Recommendations for soil improvement measures are made to mitigate the risk. This research highlights the need for “customized seismic protocols” and emphasizes the importance of “site-specific assessments” in construction projects. By addressing susceptibility to liquefaction and proposing targeted ground improvement strategies, we contribute to safer and more resilient infrastructure development.

Stability analysis of circular tunnels using spatiotemporal accelerations formulated considering heterogeneity of seismic wave propagation velocities

The space–time dependent horizontal and vertical seismic accelerations in a soil medium owing to the inhomogeneity in the shear and primary wave propagation velocities were analytically derived satisfying the boundary conditions on the ground surface and the base. The developed analytical formulations were applied to study the influence of wave velocity heterogeneity on the support pressure required for the circular tunnel stability placed in granular soils using the stress-based limit analysis in conjunction with finite elements. The support pressure was determined as the maximum normal stress exerted by the surrounding earth at its ultimate failure on the tunnel boundary. Further, the effect of frequency of seismic waves on the seismic accelerations, magnitude of tunnel support pressure and the variation of normal stress around the tunnel periphery has been presented in detail. The support pressure was found to be higher considering the heterogeneous wave velocity than the uniform one. A lower dimensionless frequency resulted in higher support pressures for a lower wave velocity ratio and higher power parameter of the power law used to model the wave velocity profile. Otherwise, for higher wave velocity ratio, the effect of power parameter diminishes, and the support pressure is higher for higher dimensionless frequency.

Pseudo-Helmholtz decomposition for an elastic VTI wavefield based on wavefront phase direction

P and S waves are coupled when propagating in anisotropic elastic media. The separation of P and S waves helps to study the characteristics of different types of seismic waves as well as mitigating crosstalk artifacts in elastic reverse time migration and elastic full-waveform inversion. At present, the methods of seismic wave mode separation in anisotropic media are mainly built on divergence- and curl-like operations, pseudo-Helmholtz decomposition, and low-rank approximation. We develop a new pseudo-Helmholtz decomposition operator based on eigenform analysis and the wavefront phase direction to decompose vertically transversely isotropic elastic wavefields. The corresponding P-/S-wave decoupling formulas are also derived in detail. Compared with the divergence- and curl-like methods, the new method does not change the phase of P and S waves. Compared with existing pseudo-Helmholtz decomposition methods based on eigenform analysis, our method achieves more accurate wavefield separation than the zero-order pseudo-Helmholtz decomposition operator. Our method requires solving one vector Poisson equation only, resulting in much less computational cost than the existing first-order pseudo-Helmholtz decomposition methods. In addition, the accuracy of our method is analyzed by providing homogeneous media with different parameter settings. Finally, the numerical examples demonstrate that the new pseudo-Helmholtz decomposition method is effective, efficient, and robust against random noise.

Mathematical and Physical Characteristics of the Phase Spectrum of Earthquake Ground Motions

This study presents a rigorous investigation into the mathematical and physical properties inherent in the Fourier phase spectrum of earthquake ground motions. This exploration includes a detailed examination of the probability distribution of phase angles and differences, elucidated through two novel numerical experiments utilizing the reduction ad absurdum approach. Moreover, the study scrutinizes the physical attributes of earthquake ground motion’s phase spectrum, employing the circular frequency-dependent phase derivative as a key analytical factor. In a novel approach, the research delves into the relationship between circular frequency-dependent phase derivatives and Fourier amplitudes, shedding light on essential connections within earthquake phenomena, particularly addressing non-stationarity. Expanding the scope, the study comprehensively examines the influence of source, propagation path, and site on both the phase spectrum and accelerogram. Employing the control variate technique facilitates this analysis, providing valuable insights into the underlying physical mechanisms governing earthquake wave behavior. The findings highlight the temporal properties of the phase spectrum, attributing its complexity to the temporal heterogeneity in energy release during the fault rupture and dispersion of earthquake waves. This novel approach not only enhances the understanding of earthquake dynamics, but also underscores the significance of considering temporal variations in earthquake events.

Seismic Anisotropy and Deep Crustal Deformation Across Alaska

AbstractBased on a new seismic surface wave data set, we present a model of Alaskan crustal seismic anisotropy that provides new insight into Alaska's geographically diverse deformation history. We use both Rayleigh and Love wave isotropic phase speed and Rayleigh wave azimuthal anisotropy to estimate crustal anisotropy. Unlike traditional seismic tomography, which focuses on apparent seismic anisotropy in which the symmetry axis of anisotropy is assumed to be known, we resolve the spatial variation of inherent anisotropy by inferring the depth‐dependent tilt of the hexagonally symmetric elastic tensor. The amplitude of inherent anisotropy is typically stronger in the lower than the upper crust. We principally interpret the dip angle (plunge of the symmetry axis) or the tilt of the anisotropy foliation plane, which reflects the influence of vertically and/or horizontally oriented structures or deformation. The depth variation of crustal anisotropy appears in four principal motifs that partition Alaska into six distinct geographical regions, which display characteristic dip angle patterns in the upper and lower crust. By considering geological context, we discuss how each region reflects active or historical crustal deformation.

Pseudo‐dynamic testing, repairability, and resilience assessment of a large‐scale steel structure equipped with self‐centering column bases

AbstractRecent destructive seismic events have underlined the need for increasing research efforts devoted to the development of innovative seismic‐resilient structures able to reduce seismic‐induced direct and indirect losses. Regarding steel Moment Resisting Frames (MRFs), the inclusion of Friction Devices (FDs) in Beam‐to‐Column Joints (BCJs) has emerged as an effective solution to dissipate the seismic input energy while ensuring a damage‐free behavior. Additionally, recent studies have demonstrated the benefits of implementing similar damage‐free solutions for Column Bases (CBs). In this context, the authors have recently experimentally investigated a Self‐Centering CB (SC‐CB) aimed at residual drift reduction. Previous experimental tests only focused on the response of isolated SC‐CBs under cyclic loads. Conversely, the present paper advances the research through an experimental campaign on a large‐scale steel structure equipped with the proposed SC‐CBs, providing valuable insights into the global structural response and improved repairability. A set of eight Pseudo‐Dynamic (PsD) tests were conducted considering different records and configurations of the structure. The experimental results highlighted the effectiveness of the SC‐CBs in minimizing the residual interstory drifts and protecting the first‐story columns from damage, thus enhancing the structure's resilience. Moreover, the consecutive PsD tests allowed investigating the effectiveness of the reparation process in restoring the seismic performance of the ‘undamaged’ structure. An advanced numerical model was developed in OpenSees and validated against the global and component‐level experimental results. Incremental Dynamic Analyses were finally performed to investigate the influence of the SC‐CBs on the structure's seismic response while accounting for the record‐to‐record variability.

Earthquake Detection and Alerting system using ANN and IOT

Earthquakes are one of the deadliest natural disasters. The damage caused by earthquakes is very destructive and the number of deaths are at a very large scale. The National Earthquake Information Centre now detects about 20,000 earthquakes around the globe each year, or approximately 55 per day. Many of the Earth’s earthquake zones coincide with areas of high population density. When a large earthquake occurs in such areas, the results can be catastrophic. The basic parameter to determine an earthquake before it was going to occur is the p wave or primary shock wave which is not destructive to infrastructure because it travels parallel to the propagation of seismic wave. A series of destructive waves that follows p waves are s waves or secondary waves which has a speed of about 60% that of p waves. The movement of the s wave is perpendicular to the direction of propagation of the seismic wave and hence it is extremely risky to infrastructures and cause a lot of damage. This research aims to build an earthquake detection and alerting system using a low-cost accelerometer, ESP32 Wi-Fi module, and ANN algorithm. The input earthquake data is taken by the accelerometer and with the help of the ESP32 Wi-Fi module the data is sent to a system that processes the ANN algorithm with Multi layered perceptron trained with stochastic gradient descent learning algorithm and detects whether an earthquake is going to occur or not and alerts users with ESP32 Wi-Fi module. Key Words: Artificial Neural Networks, ESP32, Accelerometer, Earthquake, Multi-layer perceptron, Sigmoid function, Stochastic Gradient Descent.

The effects of precursory velocity changes on earthquake nucleation and stress evolution in dynamic earthquake cycle simulations

Seismic velocity changes in earthquake cycles have been observed over a wide range of timescales and may be a good indicator of the onset of future earthquakes. Understanding the effects of precursory velocity changes right before seismic and slow-slip events could potentially elucidate the onset and timing of fault failure. We use numerical models to simulate fully dynamic earthquake cycles in 2D strike-slip fault systems with antiplane geometry, surrounded by a narrow fault-parallel damage zone. By imposing S-wave velocity changes inside fault damage zones, we investigate the effects of these precursors on multiple stages of the seismic cycle, including nucleation, coseismic, postseismic, and interseismic stages. Our modeling results show a wide spectrum of fault slip behaviors including fast earthquakes, slow-slip events, and variable creep. One primary effect of the imposed velocity precursor is on the earthquake nucleation phase, and earlier onset of precursors causes earthquakes to nucleate sooner with a smaller nucleation size that is not predicted by theoretical equations. Furthermore, such precursors affect the nucleation of dynamic earthquakes and slow-slip events. Our results highlight the importance of short- and long-term monitoring of fault zone structures for better assessment of regional seismic hazard.

Fast Seismic Anomalies Under Continents Explained by the Delaminated Lower Continental Crust—Implications From High Pressure‐Temperature Elasticity of Jadeite

AbstractSeismic tomography has shown that the shear wave velocities (Vs) under continents, especially under cratons, are extremely fast at 100–200 km depth, which is difficult to explain by low temperatures or high Mg#. Alternatively, delaminated eclogitic lower continental crust has been proposed to account for these fast seismic anomalies. However, the thermoelastic properties of jadeite which constitutes up to 60–80 mol% of clinopyroxene in the potentially delaminated lower continental crust are not well constrained. In this study, we measured the single‐crystal elasticity of jadeite by Brillouin spectroscopy under simultaneous high pressure and temperature conditions for the first time. We found that the temperature dependence of Vs of jadeite is extremely small if not negligible. The seismic velocities of the potentially delaminated lower continental crusts were subsequently modeled and found to match the widely observed fast seismic anomalies under cratons between 100 and 200 km depth.