Adjoint Waveform Tomography of South America

Ciardelli, Caio; Assumpção, Marcelo; Bozdag, E.; Lee, Suzan van der

doi:10.1029/2021jb022575

Cited by 16 publications

(14 citation statements)

References 168 publications

(406 reference statements)

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“…The methodology is distinct from previous waveform inversion studies of the region in several ways. Our eight‐stage multiscale inversion procedure uses a conservative approach with many more iterations than have been used in any comparable regional‐scale earthquake waveform tomography studies (Ciardelli et al., 2022; Fichtner et al., 2009; Gao et al., 2021; Krischer et al., 2018; Simuté et al., 2016; Tao et al., 2017; Tape et al., 2010; Wehner et al., 2022; Zhu et al., 2012, 2015, 2017). The trust‐region L‐BFGS inversions automatically make measured model updates with knowledge of the Hessian (misfit surface curvature) and comparison of predicted and actual misfit reductions.…”

Section: Discussionmentioning

confidence: 99%

“…AWT uses 3D simulations and iteratively modifies sub-surface structure to reduce misfit metrics and better match recorded seismograms (Fichtner, 2010;Fichtner et al, 2006;Tromp, 2020;Tromp et al, 2005). We closely follow several recent studies that have inverted earthquake data for regional and continental scale AWT models of Australia (Fichtner et al, 2009(Fichtner et al, , 2010, Southern California (Tape et al, 2010), Europe (Zhu et al, 2012(Zhu et al, , 2015, North America (Zhu et al, 2017), Europe and North America (Krischer et al, 2018), South America (Ciardelli et al, 2022;Gao et al, 2021), East Asia (Chen et al, 2015;Simuté et al, 2016;Tao et al, 2017), and Southeast Asia (Wehner et al, 2022). In the following, we highlight the main components and some distinguishing features of our approach.…”

Section: Methodsmentioning

confidence: 96%

“…One distinguishing feature of this study is the large number of inversion stages and total iterations compared to other studies (e.g., Ciardelli et al., 2022; Gao et al., 2021; Krischer et al., 2018; Zhu et al., 2017). These studies converged or were stopped after 22–44 total iterations across several period bands, while our methodology used this many or more iterations in a single inversion stage before converging.…”

Section: Methodsmentioning

confidence: 99%

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WUS256: An Adjoint Waveform Tomography Model of the Crust and Upper Mantle of the Western United States for Improved Waveform Simulations

Rodgers

Krischer²,

Afanasiev³

et al. 2022

JGR Solid Earth

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We report a new model (WUS256) of radially anisotropic seismic wavespeeds of the crust and upper mantle of the western United States (WUS) obtained from adjoint waveform tomography for the purpose of improving synthetic waveform fits to observed data. WUS256 is based on inversion of over 94,000 waveforms from 72 earthquakes recorded by nearly 3,400 stations. We started with the SPiRaL global model (Simmons et al., 2021, https://doi.org/10.1093/gji/ggab277) and waveforms in the period band of 50–120 s. We followed a conservative multiscale inversion approach with eight stages and 256 total inversion iterations which enabled monotonic misfit reduction to 20‐s minimum‐period waves. WUS256 relied on time‐frequency (TF) phase misfits and a trust region limited memory Broyden–Fletcher–Goldfarb–Shanno (L‐BFGS) optimization. Hessian‐vector products were used to qualitatively assess model resolution. Results indicate that WUS256 has good coverage of the continental regions to depths of about 150 km and is able to resolve features on lateral scales of about 200 km. We quantify waveform fits by the reduction in TF and normalized amplitude difference misfits between WUS256 and the SPiRaL starting model. WUS256 significantly improves waveform fits with misfit reduction ≥ $\ge $64% for both inversion and validation data sets compared to the SPiRaL starting model and shows even better fits compared to other models. Waveform fits illustrate that WUS256 reproduces body‐waves, fundamental mode surface waves as well as late arriving dispersed and/or scattered short period surface waves. The improvement in waveform fit indicates that WUS256 can be used to reproduce path effects on regional complete waveforms and moment tensor inversions.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 96%

Section: Methodsmentioning

confidence: 99%

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WUS256: An Adjoint Waveform Tomography Model of the Crust and Upper Mantle of the Western United States for Improved Waveform Simulations

Rodgers

Krischer²,

Afanasiev³

et al. 2022

JGR Solid Earth

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“…The velocity models were constructed integrating the structural and seismic velocity knowledge of the crust and combining it with the mantle 3D velocity model known for South America (Ciardelli et al, 2022). Since regional 3D velocity models are not available for our area of interest or do not have enough resolution in depth, we constructed velocity laws, that are the relationship between depth and wave's velocity, from already published relevant data for the sediments and crust.…”

Section: Methodsmentioning

confidence: 99%

“…For the mantle velocity model, we used the SAAM23 3D P-and S-wave model for South America (Ciardelli et al, 2022), which is heterogeneously distributed with a horizontal resolution of 0.5°. It is consistent with the global discontinuities at ∼410 and ∼660 km depth (Kennett and Engdahl, 1991); and most important, with the position of the Nazca slab under the Andean and Sub-Andean region, according to Portner et al (2020).…”

Section: Mantle Velocitiesmentioning

confidence: 99%

P- and S-wave 3D velocity models for the South American platform

Rivadeneyra-Vera¹,

Font²,

Bianchi³

2021

Braz J Geophys

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ABSTRACT. With the installation and growth of the Brazilian Seismographic Network (RSBR) since 2011, it is now possible to detect and locate events with magnitudes lower than 3.5 mb for Brazil, and better study the local and regional seismicity. Nevertheless, most of these events are located using 1D velocity models that lead to larger uncertainties precluding any correlation with the known geological structures. The use of heterogeneous 3D velocity models better predicts the travel times and guarantees the accuracy of hypocenter location; however, there is not yet a calibrated 3D velocity model for the South American Platform (SAP). In this study, integrating multiple local and regional geological and geophysical knowledge and average velocities of the crust and mantle, we have elaborated 3D P- and S-wave velocity models for the SAP, including the Central Andes area (down to 900 km). We tested the model locating the well-known 1998 Andean Aiquile earthquake (Bolivia), 6.6 Mw, obtaining successful results when compared with its ground truth location. We also satisfactorily located two other recent important events of the SAP, using local and regional body wave arrivals recorded by the RSBR. Finally, S-wave arrivals of near stations helped to constrain the event depths to expected values.Keywords: heterogeneous velocity model, Brazilian seismicity; hypocenter location; NonLinLoc. P- and S-wave 3D velocity models for the South American platformRESUMO. Em decorrência da implantação da Rede Sismográfica Brasileira (RSBR) em 2011, tornou-se possível detectar e localizar eventos com magnitudes menores de 3,5 mb no Brasil e aprofundar o estudo da sismicidade local e regional. Porém, a maioria desses eventos são localizados utilizando-se modelos de velocidade 1D, resultando em incertezas que não permitem correlacionar os hipocentros com as estruturas geológicas conhecidas. Em contrapartida, o uso de modelos 3D de velocidade prediz melhor os tempos de percurso das ondas e garante precisão na localização de hipocentros; porém, ainda não haviam sido desenvolvidos modelos 3D calibrados para a plataforma Sul-Americana. No presente estudo, integrando-se informações geológica e geofísica, local e regional, e velocidades médias da crosta e manto foram elaborados modelos 3D de velocidade das ondas P e S para a Plataforma Sul-americana e para os Andes Centrais (até 900 km de profundidade). Para testar a confiabilidade dos modelos, foi localizado o evento andino de Aiquile 1998, 6,6 Mw (Bolívia) usando-se chegadas regionais da onda P, com resultados compatíveis com o melhor epicentro conhecido. Também foram localizados satisfatoriamente dois outros eventos importantes. Finalmente, o uso de leituras da onda S de estações próximas restringe a profundidade hipocentral para valores esperados em cada caso.Palavras-chave: modelo de velocidade heterogêneo; sismicidade brasileira; localização de hipocentros, NonLinLoc.

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Crustal and upper mantle structure beneath South America from Rayleigh wave analysis

Corchete

2024

Geological Journal

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A review of the S‐velocity structure beneath South America, for the crust and upper mantle, is performed using a recent methodology based on Rayleigh wave analysis, and a new 3D S‐velocity model (from 0 to 400 km depth) is achieved for this study area. The precise location and structure of the asthenosphere have been both determined from this new model, which have not been obtained in other previous studies, allowing to know how the different geological units that compose South America are delimited in terms of S‐velocity and lithosphere thickness. For example, the highest S‐velocities and the thickest lithosphere of the cratonic areas, are determined at the east of the Amazonian Craton and the São Francisco Craton. The lithosphere beneath the Guyana Shield is thinner than beneath the Central Brazil Shield, and the lithospheric root of the Amazonian Craton is determined deeper than the São Francisco Craton. The lithosphere at the east of the Central Brazil Shield is the thickest (~200‐km thick). Another interesting feature depicted in terms of S‐velocity and lithosphere thickness is the Transbrasiliano Lineament, which is determined in the crust and the upper mantle, confirming that it is not just a surface feature but a deep feature.

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Adjoint Waveform Tomography of South America

Cited by 16 publications

References 168 publications

WUS256: An Adjoint Waveform Tomography Model of the Crust and Upper Mantle of the Western United States for Improved Waveform Simulations

WUS256: An Adjoint Waveform Tomography Model of the Crust and Upper Mantle of the Western United States for Improved Waveform Simulations

P- and S-wave 3D velocity models for the South American platform

Crustal and upper mantle structure beneath South America from Rayleigh wave analysis

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