Constraining the 410-km discontinuity and slab structure in the Kuril subduction zone with triplication waveforms

SUMMARY The detailed structure near the 410-km discontinuity provides key constraints of the dynamic interactions between the upper mantle and the lower mantle through the mantle transition zone (MTZ) via mass and heat exchange. Meanwhile, the temperature of the subducting slab, which can be derived from its fast wave speed perturbation, is critical for understanding the mantle dynamics in subduction zones where the slab enters the MTZ. Multipathing, i.e. triplicated, body waves that bottom near the MTZ carry rich information of the 410-km discontinuity structure and can be used to constrain the discontinuity depth and radial variations of wave speeds across it. In this study, we systematically analysed the trade-off between model parameters in triplication studies using synthetic examples. Specifically, we illustrated the necessity of using array-normalized amplitude. Two 1-D depth profiles of the wave speed below the Tatar Strait of Russia in the Kuril subduction zone are obtained. We have observed triplications due to both the 410-km discontinuity and the slab upper surface. And, seismic structures for these two interfaces are simultaneously inverted. Our derived 410-km discontinuity depths for the northern and southern regions are at 420$\pm $15 and 425$\pm $15 km, respectively, with no observable uplift. The slab upper surface is inverted to be located about 50–70 km below the 410-km discontinuity. This location is between the depths of the 1 and 2 per cent P-wave speed perturbation contours of a regional 3-D full-waveform inversion (FWI) model, but we found twice the wave speed perturbation amplitude. A wave speed increase of 3.9–4.6 per cent within the slab, compared to 2.0–2.4 per cent from the 3-D FWI model, is necessary to fit the waveforms with the shortest period of 2 s, indicating that high-frequency waves are required to accurately resolve the detailed structures near the MTZ.

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Elastic reflection traveltime inversion with decoupled wave equation

Geophysics ◽

10.1190/geo2017-0631.1 ◽

2018 ◽

Vol 83 (5) ◽

pp. R463-R474 ◽

Cited By ~ 6

Author(s):

Guanchao Wang ◽

Shangxu Wang ◽

Jianyong Song ◽

Chunhui Dong ◽

Mingqiang Zhang

Keyword(s):

Wave Equation ◽

Wave Velocity ◽

Waveform Inversion ◽

P Wave ◽

Model Parameters ◽

Local Minima ◽

S Wave ◽

Traveltime Inversion ◽

Velocity Models ◽

Elastic Reflection

Elastic full-waveform inversion (FWI) updates high-resolution model parameters by minimizing the residuals of multicomponent seismic records between the field and model data. FWI suffers from the potential to converge to local minima and more serious nonlinearity than acoustic FWI mainly due to the absence of low frequencies in seismograms and the extended model domain (P- and S-velocities). Reflection waveform inversion can relax the nonlinearity by relying on the tomographic components, which can be used to update the low-wavenumber components of the model. Hence, we have developed an elastic reflection traveltime inversion (ERTI) approach to update the low-wavenumber component of the velocity models for the P- and S-waves. In our ERTI algorithm, we took the P- and S-wave impedance perturbations as elastic reflectivity to generate reflections and a weighted crosscorrelation as the misfit function. Moreover, considering the higher wavenumbers (lower velocity value) of the S-wave velocity compared with the P-wave case, optimizing the low-wavenumber components for the S-wave velocity is even more crucial in preventing the elastic FWI from converging to local minima. We have evaluated an equivalent decoupled velocity-stress wave equation to ERTI to reduce the coupling effects of different wave modes and to improve the inversion result of ERTI, especially for the S-wave velocity. The subsequent application on the Sigsbee2A model demonstrates that our ERTI method with the decoupled wave equation can efficiently update the low-wavenumber parts of the model and improve the precision of the S-wave velocity.

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Land seismic multiparameter full waveform inversion in elastic VTI media by simultaneously interpreting body waves and surface waves with an optimal transport based objective function

Geophysical Journal International ◽

10.1093/gji/ggz414 ◽

2019 ◽

Vol 219 (3) ◽

pp. 1970-1988 ◽

Cited By ~ 3

Author(s):

Weiguang He ◽

Romain Brossier ◽

Ludovic Métivier ◽

René-Édouard Plessix

Keyword(s):

Objective Function ◽

Surface Waves ◽

Least Squares ◽

Optimal Transport ◽

Waveform Inversion ◽

Body Waves ◽

Model Parameters ◽

Full Waveform Inversion ◽

Initial Model ◽

Full Waveform

SUMMARY Land seismic multiparameter full waveform inversion in anisotropic media is challenging because of high medium contrasts and surface waves. With a data-residual least-squares objective function, the surface wave energy usually masks the body waves and the gradient of the objective function exhibits high values in the very shallow depths preventing from recovering the deeper part of the earth model parameters. The optimal transport objective function, coupled with a Gaussian time-windowing strategy, allows to overcome this issue by more focusing on phase shifts and by balancing the contributions of the different events in the adjoint-source and the gradients. We first illustrate the advantages of the optimal transport function with respect to the least-squares one, with two realistic examples. We then discuss a vertical transverse isotropic (VTI) example starting from a quasi 1-D isotropic initial model. Despite some cycle-skipping issues in the initial model, the inversion based on the windowed optimal transport approach converges. Both the near-surface complexities and the variations at depth are recovered.

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Mapping mantle flows underneath the North American and Caribbean Plates

10.5194/egusphere-egu21-6113 ◽

2021 ◽

Author(s):

Hejun Zhu

Keyword(s):

North American ◽

Subduction Zones ◽

Current Model ◽

Waveform Inversion ◽

Body Waves ◽

Plate Motion ◽

Cascadia Subduction Zone ◽

Fast Axis ◽

The North ◽

Short Period

In this talk, I will present a new 3-D azimuthally anisotropic tomographic model, namely US32, for the North American and Caribbean Plates. This model is constrained by using seismic data from USArray and full waveform inversion. The inversion uses data from 180 regional earthquakes recorded by 4,516 seismographic stations, resulting in 586,185 frequency-dependent phase measurements. Three-component short-period body waves and long-period surface waves are combined to simultaneously constrain deep and shallow structures. The current azimuthally anisotropic model US32 is the result of 32 pre-conditioned conjugate-gradient iterations. In the current model, I observe a complex depth-dependent pattern for fast axis directions across the North American and Caribbean Plates.&#160; At shallow depths, these fast axis directions delineate local geological provinces, such as the Snake River Plain, Cascadia subduction zone, Rio Grand Rift, etc. At greater depths, the fast axis directions follow the absolute plate motion trajectories at most places. At depths around 700 km, the fast axis directions are perpendicular to the strikes of the mapped Farallon slab, suggesting the presence of 2-D corner flows induced by this ancient subduction underneath the mantle transition zone. In addition, underneath the Cascadia and Cocos subduction zones at depths from 250 to 500 km, the fast axis directions suggest the presence of toroid-mode mantle flows, following the geometry of fast downwelling materials.

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Efficient time-domain 3D elastic and viscoelastic full-waveform inversion using a spectral-element method on flexible Cartesian-based mesh

Geophysics ◽

10.1190/geo2018-0059.1 ◽

2019 ◽

Vol 84 (1) ◽

pp. R61-R83 ◽

Cited By ~ 16

Author(s):

Phuong-Thu Trinh ◽

Romain Brossier ◽

Ludovic Métivier ◽

Laure Tavard ◽

Jean Virieux

Keyword(s):

Time Domain ◽

Spectral Element Method ◽

Waveform Inversion ◽

Spectral Element ◽

Body Waves ◽

P Wave ◽

Full Waveform Inversion ◽

Full Waveform ◽

Anisotropic Elastic ◽

Element Method

Viscoelastic full-waveform inversion is recognized as a challenging task for current acquisition deployment at the crustal scale. We have developed an efficient formulation based on a time-domain spectral-element method on a flexible Cartesian-based mesh. We consider anisotropic elastic coefficients and isotropic attenuation. Complete gradient expressions including the attenuation contribution spread into those of elastic components are given in a consistent way. The influence of attenuation on the P-wave velocity reconstruction is illustrated through a toy configuration. The numerical implementation of the forward problem includes efficient matrix-vector products for solving second-order elastodynamic equations for 3D geometries: An original high-order integration for topography effects is performed at nearly no extra cost. Combined adjoint and forward field recomputation from the final state and previously saved boundary values allows the estimation of misfit gradients for density, elastic parameters, and attenuation factors with no I/O efforts. Two-level parallelism is implemented over the sources and domain decomposition, which is necessary for a realistic 3D configuration. The misfit gradient preconditioning is performed by a so-called Bessel filter using an efficient differential implementation based on finite-element ingredients on the forward mesh instead of the often-used, costly convolution approach. A 3D synthetic illustration is provided on a subset ([Formula: see text]) of the SEG Advanced Modeling (SEAM) Phase II Foothills model with 4 lines of 20 sources. The structurally based Bessel filter and a simple data hierarchy strategy considering early body waves before all waves including surface waves allow a precise reconstruction of the P- and S-wavespeeds while keeping a smooth density description.

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A synthetic 2-D-elastic full-waveform inversion study for the Ecuadorian margin—resolution capability of a dense onshore/offshore network

Geophysical Journal International ◽

10.1093/gji/ggaa244 ◽

2020 ◽

Vol 222 (2) ◽

pp. 1236-1244

Author(s):

L Gassner ◽

N Thiel ◽

A Rietbrock

Keyword(s):

Subduction Zone ◽

Waveform Inversion ◽

Wave Model ◽

P Wave ◽

Full Waveform Inversion ◽

S Wave ◽

Traveltime Tomography ◽

Full Waveform ◽

Local Earthquake ◽

Source Orientation

SUMMARY Subduction zones are the places on the Earth where the greatest earthquakes occur. It is now widely accepted that seismic asperities at the interface of subducting plates play a major role in whether a region of a subduction zone behaves seismically, creating strong earthquakes or exhibits aseismic slip. In the last decades, huge advances have been made to decipher the underlying processes; however, the physical parameters along the subduction zone interfaces are still not very well known due to a sparsity of high-resolution experiments and significant costs associated with amphibious seismic experiments. Therefore, synthetic tests are needed to investigate the potential of currently possible high density seismic deployments and to aid future experiment design. As standard local earthquake traveltime tomography in a subduction zone setting cannot resolve structures on a kilometre scale at depth, we explore the suitability of full-waveform inversion (FWI) to increase resolution by using amplitude and phase information in the recorded earthquake seismograms. We apply 2-D-elastic FWI to synthetic earthquake data, using vertical and horizontal receivers, and utilize a realistic model of the seismic velocities at the Ecuadorian margin. We add perturbations within the subducting plates of 4×4 km and 2×2 km in P- and S-wave velocities, respectively, such that potential crosstalk between the two models can be identified. Our results show that the location and amplitude of the perturbations can be reconstructed in high quality down to approximately 70 km depth. We find that the inversion of the S-wave velocity prior to the inversion of the P-wave velocity is necessary to guarantee a good reconstruction of both models; however, the spatial resolution of the S-wave model is superior to the P-wave model. We also show that frequencies up to 1 Hz are sufficient to achieve high resolution. Further tests demonstrate how results depend on the accuracy of the estimated source orientation. Resulting models do not suffer in quality as artefacts near the source positions compensate for the inaccuracy of source orientation. If sources are located within the subducted plate instead of beneath, resulting models are comparable and the convergence of the inversion scheme is sped up. The accuracy of the source position within the model compared to the true earthquake location is critical and implies that earthquake relocation during the inversion process is necessary, in a similar way as in local earthquake traveltime tomography.

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Surface and mantle records reveal an ancient slab tear beneath Gondwana

Scientific Reports ◽

10.1038/s41598-019-56335-9 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 5

Author(s):

Guido M. Gianni ◽

César Navarrete ◽

Silvana Spagnotto

Keyword(s):

Lower Mantle ◽

Subduction Zones ◽

Large Scale ◽

P Wave ◽

Late Triassic ◽

Mantle Dynamics ◽

Geological Record ◽

Slab Tear ◽

Oceanic Plates ◽

Slab Tearing

AbstractVertical slab-tearing has been widely reported in modern convergent settings profoundly influencing subduction and mantle dynamics. However, evaluating a similar impact in ancient convergent settings, where oceanic plates have been subducted and the geological record is limited, remains challenging. In this study, we correlate the lower mantle structure, which retained the past subduction configuration, with the upper-plate geological record to show a deep slab rupture interpreted as a large-scale tearing event in the early Mesozoic beneath southwestern Gondwana. For this purpose, we integrated geochronological and geological datasets with P-wave global seismic tomography and plate-kinematic reconstructions. The development of a Late Triassic-Early Jurassic slab-tearing episode supports (i) a slab gap at lower mantle depths, (ii) a contrasting spatiotemporal magmatic evolution, (iii) a lull in arc activity, and (iv) intraplate extension and magmatism in the Neuquén and Colorado basins. This finding not only has implications for identifying past examples of a fundamental process that shapes subduction zones, but also illustrates an additional mechanism to trigger slab-tearing in which plate rupture is caused by opposite rotation of slab segments.

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Lattice preferred orientation and seismic anisotropy of chloritoid in subduction zone

10.5194/egusphere-egu21-3861 ◽

2021 ◽

Author(s):

Jungjin Lee ◽

Mainak Mookherjee ◽

Taehwan Kim ◽

Haemyeong Jung ◽

Reiner Klemd

Keyword(s):

Subduction Zone ◽

Subduction Zones ◽

Seismic Anisotropy ◽

Elastic Anisotropy ◽

P Wave ◽

Stability Field ◽

S Wave ◽

P Waves ◽

Hydrous Minerals ◽

Natural Rock

Subduction zones are often characterized by the presence of strong trench-parallel seismic anisotropy and large delay times. Hydrous minerals, owing to their large elastic anisotropy and strong lattice preferred orientations (LPOs) are often invoked to explain these observations. However, the elasticity and LPO of chloritoid, which is one such hydrous phases relevant in subduction zone settings, is poorly understood. In this study, we measured the LPO of polycrystalline chloritoid in natural rock samples and obtained the LPO-induced seismic anisotropy and evaluated the thermodynamic stability field of chloritoid in subduction zones. The LPO of chloritoid aggregates displayed a strong alignment of the [001] axes subnormal to the rock foliation, with a girdle distribution of the [100] axes and the (010) poles subparallel to the foliation. New elasticity data of single-crystal chloritoid showed a strong elastic anisotropy of chloritoid with 47% for S-waves (VS) and 22% for P-waves (VP), respectively. The combination of the LPO and the elastic anisotropy of the chloritoid aggregates produced a strong S-wave anisotropy of AVS = 18% and a P-wave anisotropy of AVP = 10%. Our results indicate that the strong LPO of chloritoid along the hydrated slab-mantle interface and in subducting slabs can influence trench-parallel seismic anisotropy in subduction zones with &#8220;cold&#8221; geotherms.

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Subduction zone fluids and arc magmas conducted by lithospheric deformed regions beneath the central Andes

Scientific Reports ◽

10.1038/s41598-021-02430-9 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

E. Contreras-Reyes ◽

D. Díaz ◽

J. P. Bello-González ◽

K. Slezak ◽

B. Potin ◽

...

Keyword(s):

Electrical Resistivity ◽

Subduction Zone ◽

Continental Crust ◽

Subduction Zones ◽

Hydrothermal Systems ◽

P Wave ◽

Complex Permeability ◽

Nazca Plate ◽

Lithospheric Deformation ◽

Permeability Structure

AbstractDehydration of the oceanic subducting slab promotes the formation of magmatic arcs, intra-slab intermediate-depth seismicity, and hydration of the overlying mantle wedge. However, the complex permeability structure of the overriding plate controls the magma and fluid migration and their accumulation at shallower depths. In this regard, mapping the inner structure of the overriding crust and mantle is crucial to understand the magmatic and hydrological processes in subduction zones. We integrate 3-D P-wave, $$V_p/V_s$$ V p / V s , and electrical resistivity tomographic models of the northern Chilean subduction zone to map the magmatic and fluids derived from the subducting oceanic Nazca plate. Results show a continental crust relatively thick (50–65 km) characterized by a lower zone of high $$V_p$$ V p values (7.2–7.6 km/s), which is interpreted as the presence of plutonic rocks. The mantle lithospheric wedge is weakly hydrated ($$V_p/V_s$$ V p / V s = 1.75–1.8) while the forearc continental crust is traversed by regions of reduced electrical resistivity values ($$< 10^2$$ < 10 2 $$\Omega m$$ Ω m ) interpreted as zones of relatively high permeability/fracturing and fluid content. These regions spatially correlate with upper plate trans-lithospheric deformation zones. Ascending melts accumulate preferentially in the back-arc, whereas hydrothermal systems form trenchward of the volcanic arc. The results highlight the complex permeability structure of the upper South American plate.

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1-D elastic waveform inversion: A divide‐and‐conquer approach

Geophysics ◽

10.1190/1.1444463 ◽

1998 ◽

Vol 63 (5) ◽

pp. 1670-1684 ◽

Cited By ~ 16

Author(s):

Ganyuan Xia ◽

Mrinal K. Sen ◽

Paul L. Stoffa

Keyword(s):

Seismic Velocity ◽

Waveform Inversion ◽

P Wave ◽

Divide And Conquer ◽

Rock Properties ◽

Inversion Method ◽

Earth Model ◽

Model Parameters ◽

Waveform Data ◽

True Model

Subsurface rock properties are manifested in seismic records as variations in traveltimes, amplitudes, and waveforms. It is commonly acknowledged that traveltimes are sensitive to the long wavelength part of the velocity, whereas amplitudes are sensitive to the short wavelength part of the velocity. The inherent sensitivity of seismic velocity at different wavelengths suggests an approach that decomposes the waveform data into traveltime and amplitude components. Therefore we propose a divide‐and‐conquer approach to the elastic waveform inversion problem. We first estimate the smoothly varying background velocity from the traveltime and the rapidly changing perturbations from the amplitude by amplitude variation with offset (AVO) inversion based on linearized reflection coefficient. Then we combine the perturbation with the background to obtain a starting model to be used in the final waveform inversion that models all converted waves and internal multiples assuming a 1-D earth model. For estimating the background velocity, we use the flatness of events as the objective criterion, and simulated annealing as a search tool. Three different model parameterization schemes (constant velocity blocks, splines, and arctangent models) are compared, with the arctangent having the most flexibility and least artifacts. Having obtained the background velocities, we analyze the AVO effects to estimate the perturbations to the background, for which we use a linearized inversion method. The combination of the perturbation and background should be sufficiently close to the true model so that the inverse problem becomes quasi‐linear. A full elastic waveform inversion is used to fine‐tune the combined model to obtain P-wave and S-wave velocity and density, again using either a nonlinear optimization method or an iterative linearized solution. Application of the inversion algorithm to synthetic data from an 84-layer model was able to predict the full reflectivity data and recover the true model parameters. Application to one seismic line in the Carolina Trough area found a thin gas zone which produces strong Bottom Simulating Reflectors (BSRs).

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Sinkhole detection using 2D full seismic waveform tomography

Geophysics ◽

10.1190/geo2013-0063.1 ◽

2013 ◽

Vol 78 (5) ◽

pp. R175-R183 ◽

Cited By ~ 51

Author(s):

Khiem T. Tran ◽

Michael McVay ◽

Michael Faraone ◽

David Horhota

Keyword(s):

Waveform Inversion ◽

Standard Penetration Test ◽

Body Waves ◽

P Wave ◽

Waveform Analysis ◽

Inversion Method ◽

Data Sets ◽

S Wave ◽

Seismic Waveform ◽

Waveform Tomography

We have developed an application of 2D time-domain waveform tomography for detection of embedded sinkholes and anomalies. The measured seismic surface wavefields were inverted using a full-waveform inversion (FWI) technique, based on a finite-difference solution of 2D elastic wave equations and the Gauss-Newton inversion method. The key advantage of this approach is the ability to generate all possible wave propagation modes of seismic wavefields (body waves and Rayleigh waves) that are then compared with measured data to infer complex subsurface properties.The pressure-wave (P-wave) and shear-wave (S-wave) velocities are inverted independently and simultaneously. The FWI was applied to one synthetic and two real experimental data sets. The inversion results of synthetic data showed the useful capability of the waveform analysis in identifying an embedded void. The inversion results of real data sets showed that the waveform analysis was able to delineate (1) an embedded concrete culvert and (2) a complex profile with an embedded void and highly variable bedrock laterally and vertically. An independent invasive test (standard penetration test) was also conducted to verify the seismic test results.

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