SM5.1 | Imaging, modelling and inversion to explore the Earth’s lithosphere and asthenosphere
EDI
Imaging, modelling and inversion to explore the Earth’s lithosphere and asthenosphere
Convener: Laura Gómez de la PeñaECSECS | Co-conveners: Milena Marjanovic, Andrzej GórszczykECSECS, Pascal Edme, Kevin Growe, Alexandra Moshou
Orals
| Thu, 27 Apr, 14:00–18:00 (CEST)
 
Room D2
Posters on site
| Attendance Thu, 27 Apr, 08:30–10:15 (CEST)
 
Hall X2
Posters virtual
| Attendance Thu, 27 Apr, 08:30–10:15 (CEST)
 
vHall GMPV/G/GD/SM
Orals |
Thu, 14:00
Thu, 08:30
Thu, 08:30
This session will cover applied and theoretical aspects of
geophysical imaging, modeling and inversion using active- and
passive-source seismic measurements as well as other geophysical
techniques (e.g., gravity, magnetic, electromagnetic) to
investigate properties of the Earth’s lithosphere and asthenosphere,
and explore the processes involved. We invite contributions focused on
methodological developments, theoretical aspects, and applications.
Studies across the scales and disciplines are particularly welcome.

Among others, the session may cover the following topics:
- Active- and passive-source imaging using body- and surface-waves;
- Full waveform inversion developments and applications;
- Advancements and case studies in 2D and 3D imaging;
- DAS imaging;
- Interferometry and Marchenko imaging;
- Seismic attenuation and anisotropy;
- Developments and applications of multi-scale and multi-parameter inversion; and,
- Joint inversion of seismic and complementary geophysical data.

Orals: Thu, 27 Apr | Room D2

Chairpersons: Laura Gómez de la Peña, Andrzej Górszczyk, Pascal Edme
14:00–14:05
Waverform modelling
14:05–14:15
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EGU23-3788
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ECS
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On-site presentation
Xin Zhang, Angus Lomas, Muhong Zhou, York Zheng, and Andrew Curtis

Seismic full-waveform inversion (FWI) produces high resolution images of the subsurface by exploiting information in full acoustic, seismic or electromagnetic waveforms, and has been applied at global, regional and industrial spatial scales. FWI inverse problems are traditionally solved by using optimization, in which one seeks a best model by minimizing the misfit between observed waveforms and model-predicted waveforms. Due to the nonlinearity of the physical relationship between model parameters and waveforms, a good starting model is often required to produce a reasonable result. In addition, the optimization methods cannot produce accurate uncertainty estimates, which are required to better interpret final model estimates.

In principle, nonlinear Bayesian methods can be deployed to solve both issues. Monte Carlo sampling is one such class of algorithms which are computationally expensive, and all Markov chain Monte Carlo-based methods are difficult to parallelise fully. Variational inference provides a fully parallelisable alternative methodology. This is a class of methods that optimize an approximation to a probability distribution describing post-inversion parameter uncertainties. Both Monte Carlo and variational full waveform inversion have been applied previously to solve 2D Bayesian FWI problems, but neither of them have been applied in 3D.

In this study we apply three variational methods to a 3D FWI problem and analyse their performance. Specifically we apply automatic differential variational inference (ADVI), Stein variational gradient descent (SVGD) and stochastic SVGD (sSVGD), and compare their results and computational costs. These tests show that ADVI is the least computationally demanding method, but its results are systematically biased as uncertainty is underestimated. The method might therefore be used to provide relatively rapid but approximate insights into the Bayesian solution. SVGD demands the highest computational cost, yet produces equally biased results. Adding a randomized term in the SVGD dynamics produces sSVGD, a Markov chain Monte Carlo method based on variational principles. This provides the most accurate results, at intermediate computational cost. We conclude that 3D variational full-waveform inversion is practically applicable, at least in small problems, and can be used to image the Earth’s interior and to provide reasonable uncertainty estimates on those images.

How to cite: Zhang, X., Lomas, A., Zhou, M., Zheng, Y., and Curtis, A.: 3D Bayesian Variational Full-Waveform Inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3788, https://doi.org/10.5194/egusphere-egu23-3788, 2023.

14:15–14:25
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EGU23-5219
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ECS
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On-site presentation
Kaoutar Khazraj, Christophe Barnes, and Bertrand Maillot

Oil and gas industry is particularly interested in subsalt imaging because salt bodies often serve as seals for hydrocarbon reservoirs especially on the flanks and underneath the salt body. Classical imaging or full-wave inversion have encountered many difficulties in imaging such subsalt regions. The high velocity contrast between the salt body and its surroundings, the shape of the salt body, and the strong attenuation of waves propagating in the salt make accurate imaging difficult.

Imaging from surface seismic data has already been addressed. We propose to apply the full-wave inversion approach to borehole seismic data.  These data are supposed to provide more informative seismic signals (one-way, transmitted waves, scattered field near receivers, …) and should better constrain the salt flanks and bottom imaging. Unfortunately, this inverse problem is severely ill-posed due to the lack of data redundancy.  Introducing geological prior information through the parameterization of the salt geometry using the level set method partly overcomes this problem. This approach implicitly defines the salt/sediments interface through a smooth function. This hybrid  full-wave inverse problem combines the classical field gradient and the level set geometric gradient, allowing us to retrieve respectively the physical parameters and the salt body geometry.

The forward wave equation for a heterogeneous elastic domain is solved using the spectral element method. This method allows us to have a better representation of the salt/sediments interface, thus a more accurate modeling of the scattered wavefield due to interactions at the interface. Regarding the level set inversion, we define the implicit function in a parametric framework. We use compactly supported B-spline basis functions for their ability to represent a wide range of geometries compared to radial basis functions, for instance.

During the level set inversion process, when the salt/sediments interface evolves, updating the physical model parameters near the interface becomes an issue. We propose to perform a continuous deformation of the medium while conserving the mesh topology. The interface nodes are moved consistently with the implicit level set function. Furthermore, this approach  preserves a meshed representation of the interface through the inversion process allowing a more accurate seismic modeling. The mesh deformation is obtained by geostatistical kriging of node locations, constrained by the updated interface position.

In short, we propose a hybrid full-wave inversion method to estimate both material parameter fields and geometric parameters of the salt/sediments interface. The method is validated on several elastic models using synthetic seismic well data in a subsalt imaging context.

How to cite: Khazraj, K., Barnes, C., and Maillot, B.: Hybrid  full-wave inversion based on a B-spline level set mesh deformation method of borehole seismic data for a subsalt imaging context, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5219, https://doi.org/10.5194/egusphere-egu23-5219, 2023.

14:25–14:35
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EGU23-10671
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On-site presentation
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Chuntao Liang, Feihuang Cao, and Zhijin Liu

The Wave Gradiometry Method(WGM) has emerged as a powerful multipurpose tool to  extract strain and rotation tensor, identify phases, and most importantly to image the near surface or deep structure. The WGM measures the spatial gradients of the wavefield within a subarray to extract 4 major attributes: phase velocity, wave directionality, geometrical spreading and radiation pattern. These attributes can be further used to extract strain and rotation tensor (Langston and Liang CT, 2008; Sollberger et al. 2016) and structural information. An azimuth-dependent dispersion curve inversion (ADDCI, Liang et al. 2020) is applied together with the WGM method to extract both 3D shear wave velocity and 3D azimuthal anisotropy. Additionally, the geometrical spreading extracted by the WGM is used to find the attenuation of the materials. In this study, we review the theoretical foundation, technical development, major applications of the WGM and compare the WGM with other major array-based imaging method.

 Similar with the Ambient Noise tomography, the WGM is also boiled down to dispersion curve inversion. Even though it can be applied to arrays with a wide range of scales, here we concentrate on the applications to large scale arrays such as the USARRAY (average spacing of 70km), CHINARRAY (average spacing of 40km). It may also be applied to any other dense regional array, such as the ALPARRAY and others. The imaging depth is only limited by the corner frequency of the seismometer. We will compare our results with that from other techniques to highlight its advantage and disadvantages.

References:

Cao F H, Liang C T. 2022, 3D velocity and anisotropy of the southeastern Tibetan plateau extracted by joint inversion of wave gradiometry, ambient noise, and receiver function, Tectonophysics, https://doi.org/10.1016/j.tecto.2022.229690

Cao, F., Liang, C., Zhou, L., & Zhu, J. (2020). Seismic azimuthal anisotropy for the southeastern Tibetan Plateau extracted by Wave Gradiometry analysis. Journal of Geophysical Research: Solid Earth, 124, e2019JB018395.  https://doi.org/10.1029/2019JB018395

Liang, C., Liu, Z., Hua, Q., Wang, L., Jiang, N., & Wu, J. (2020). The 3D seismic azimuthal anisotropies and velocities in the eastern Tibetan Plateau extracted by an azimuth‐dependent dispersion curve inversion method. Tectonics, 39, e2019TC005747. https://doi.org/10.1029/2019TC005747 

Langston, C. A. (2007). Wave gradiometry in two dimensions. Bulletin of the Seismological Society of America, 97(2), 401–416. https://doi.org/10.1785/0120060138 

Porter R, Liu YY, and Holt WE (2016). Lithospheric Records of Orogeny within the Continental U.S.. Geophysical Research Letters, 43(1), 144–153. https://doi.org/10.1002/2015GL066950

Sollberger D Schmelzbach C, Manukyan E, Greenhalgh SA, Van Renterghem C and Robertsson JOA (2019). Accounting for receiver perturbations in seismic wavefield gradiometry. Geophysical Journal International, 218(3), 1748–1760. https://doi.org/10.1093/gji/ggz258.

How to cite: Liang, C., Cao, F., and Liu, Z.: A Review on the Wave Gradiometry Method and Applications to Image the 3D Shear Wave Velocity, Anisotropy and Attenuation of the Lithosphere and Asthenosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10671, https://doi.org/10.5194/egusphere-egu23-10671, 2023.

Interdisciplinary approach
14:35–14:45
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EGU23-10364
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ECS
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Virtual presentation
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Lu Li, Alan Aitken, Lutz Gross, and Andrea Codd

A knowledge of Antarctica’s lithospheric properties is essential for understanding tectonic history and solid-earth influences on ice sheet dynamics. For example, the spatial variation of mantle temperature impacts both geothermal heat flow and mantle viscosity, which influence the ice sheet basal melt rate and glacial isostatic adjustment. Seismic tomography models can be used to constrain the mantle temperature. However, seismic velocity to temperature conversion is sensitive to variations in mantle composition, which are linked to changes in density that are also resolved in the gravity field.

Here we model Antarctica’s density distribution using a 3D finite element gravity inversion approach based on the esys-escript model in python. We derived a correction to an initial density distribution based on a seismic tomography model (ANT-20). From the resulting density distribution and the initial seismic velocity distribution we estimated mantle temperature and composition and calculated the lithosphere thickness, mantle viscosity, and geothermal heat flow. The result shows that East Antarctica has a dense, thick (>150 km) and cold lithosphere, whereas West Antarctica has a thin (<100 km) hot lithosphere. The new heat flow model suggests a higher heat flow estimation than previous continental scale estimations.

Our result highlights compositional heterogeneity within East Antarctica, with a highly depleted cratonic mantle in central East Antarctica. By considering compositional change, modelled mantle temperature increases up to 150 °C in depleted regions to accommodate lower density with fast seismic velocity. Higher modelled temperatures cause reduced lithospheric thickness up to 80 km compared with the initial model. In comparison to previous results in interior East Antarctica, a 5-10 mW/m2 higher heat flow is suggested by our model. In West Antarctica, large areas show heat flow of up to 110 mW/m2. Our result also suggests low mantle viscosity including Amundsen Sea Embayment, Marie Byrd Land and Antarctic Peninsula.

How to cite: Li, L., Aitken, A., Gross, L., and Codd, A.: Density, temperature and composition of Antarctica’s lithosphere and impact on geothermal heat flux and mantle viscosity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10364, https://doi.org/10.5194/egusphere-egu23-10364, 2023.

14:45–14:55
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EGU23-14389
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ECS
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Virtual presentation
Carlos Clemente-Gómez, Javier Fullea, and Mariano S. Arnaiz-Rodríguez

The Earth’s crust hosts most of the geo-resources of societal interests (e.g. minerals, geothermal energy etc.). Integrative approaches combining geophysical and petrological observations to study the mantle assuming thermodynamic equilibrium are relatively common nowadays. However, in contrast to the mantle, where thermodynamic equilibrium is prevalent, vast portions of the crust are thermodynamically metastable. This is because equilibration processes are essentially temperature activated and the temperature in the crust is usually too low to trigger them. Consequently, the mineralogical assemblage of crustal rocks is mostly decoupled from the in situ pressure and temperature conditions, reflecting instead the conditions present at the moment of rock formation. Here we present a new methodology for integrated geophysical-lithological multi-data modelling of the crust. Our primary constraining data are fundamental mode Rayleigh wave surface wave dispersion curves determined by interstation cross-correlation measurements and teleseisms, as well as surface elevation (isostasy) and heat flow. Additional prior information is provided by P-wave velocities coming from controlled source and body wave tomography data. The inversion is framed within an integrated geophysical-petrological setting where mantle seismic velocities and densities are computed thermodynamically as a function of the in situ temperature and compositional conditions. In the crust we invert for a three-layered crust defined by Vs, density and Vp/Vs ratios (or Poisson coefficients) linked according to statistical correlations from global petrophysical data sets. The new methodology is applied to the Iberian Peninsula and adjacent margins where we jointly invert for both the crustal and lithospheric mantle structure. Our results show that the Iberian upper-middle crust is characterized by a clear dichotomy between the high Vs and felsic lithologies (Vp/Vs<1.76) in the Iberian Massif, and the low Vs and mafic lithologies (Vp/Vs>1.81) in the Betic, Pyrenees and Cantabrian Alpine mountain chains. The pattern changes in the lower crust where we obtain felsic lithologies  in  the Central system, NE Betics and N Mediterranean margin, and mafic lithologies in the Ossa-Morena, South-Portuguese, Galician, and Asturian-Leones terranes in the Variscan Iberian Massif. Overall we find a good correlation with previous geophysical studies (receiver functions, controlled source seismics) and the petrology of the main magmatic episodes since the Neoproterozoic (575 Ma).

How to cite: Clemente-Gómez, C., Fullea, J., and Arnaiz-Rodríguez, M. S.: Integrated geophysical-petrological inversion of surface wave and other data for the lithological structure of the Iberian crust, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14389, https://doi.org/10.5194/egusphere-egu23-14389, 2023.

14:55–15:05
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EGU23-6864
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ECS
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On-site presentation
Emma Chambers, Yihe Xu, Raffaele Bonadio, Javier Fullea, Sergei Lebedev, Duygu Kiyan, Brian O'Reilly, Patrick Meere, Meysam Rezaeifar, Tao Ye, Aisling Scully, and Gaurav Tomar and the DIG Team

High-quality maps of the geothermal gradient and temperature are essential when assessing the geothermal potential of a region. However, determining geothermal potential is a challenge as direct measurements of in situ temperature are sparse and individual geophysical methods are sensitive to a range of parameters, not solely temperature. Here, we develop a novel approach to determine the geothermal gradient using a joint geophysical-petrological inversion which requires thermal property data, seismic and additional geophysical datasets. The seismic data provide new constraints on lithospheric boundaries which influence crustal geotherms. We utilise large seismic datasets and extract Rayleigh- and Love-wave phase velocity dispersion curves, measured for pairs of stations. The measurements were performed using two methods with complementary period ranges; cross-correlation of teleseismic earthquakes and waveform inversion, yielding measurements in a broad period range (4-500 s).

The joint analysis of Rayleigh and Love measurements constrains the isotropic-average shear-wave velocity, relatable to temperature and composition providing essential constraints on the thermal structure of a region's lithosphere. We demonstrate this by inverting the data using an integrated joint geophysical-petrological thermodynamically self-consistent approach (Fullea et al., GJI 2021), where seismic velocities, electrical conductivity, and density are dependent on mineralogy, temperature, composition, water content, and the presence of melt. The multi-parameter models produced by the integrated inversions fit the surface-wave and other data and reveal the temperatures and geothermal gradients within the crust and mantle which will be used for future geothermal exploration and utilisation.

We use Ireland as a case study (part of the De-risking Ireland's Geothermal Potential project - DIG) and find that our new methodology produces results comparable to past temperature and geophysical measures, and enhances resolution. Lithospheric and crustal thickness play a key control on the temperature gradient with areas of thinner lithosphere resulting in elevated geotherms. In some locations we observe geotherms elevated beyond expectations which result from high radiogenic heat production from granitic rocks. This new methodology provides a robust workflow for determining the geothermal potential in areas with limited direct measurements.

The DIG project is funded by the Sustainable Energy Authority of Ireland under the SEAI Research, Development & Demonstration Funding Programme 2019 (grant number 19/RDD/522) and by the Geological Survey of Ireland.

How to cite: Chambers, E., Xu, Y., Bonadio, R., Fullea, J., Lebedev, S., Kiyan, D., O'Reilly, B., Meere, P., Rezaeifar, M., Ye, T., Scully, A., and Tomar, G. and the DIG Team: Developing Joint Geophysical and Petrological Inversion to Determine Temperature and Image the Lithosphere and Asthenosphere: De-risking Ireland's Geothermal Potential (DIG), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6864, https://doi.org/10.5194/egusphere-egu23-6864, 2023.

15:05–15:15
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EGU23-7579
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ECS
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On-site presentation
Raffaele Bonadio, Sergei Lebedev, and David Chew

Spectacular Paleogene uplift and volcanism in Ireland and Britain are thought to be associated with the Iceland Plume but their mechanisms are still unclear, considering, in particular, that the Iceland Hotspot was many hundred kilometres away from the volcanism. We obtain new insights into the mechanisms by combining new evidence from seismic tomography, petrological inversion of seismic data, and the geological data on uplift and volcanism. Optimal resolution tomography is a new approach, developed for surface wave tomography, that allows us to find the optimal resolving length at every point of a tomographic model grid. With this approach we evaluate the posterior model error at a point of the model grid empirically, estimating it by isolating the roughness of the phase-velocity curve that cannot be explained by any Earth structure. We apply this method to the region of Ireland and Britain, using more than 11,000 interstation phase-velocity curves measured at station pairs recording simultaneously, to image the lithosphere and underlying mantle beneath the area. The use of cross-correlation of teleseismic earthquakes and waveform inversion produces measurements in a very broad period range, leads to an unprecedented data coverage of the region, and allows us to unveil exciting new insights into the structure and evolution of the area, from the crust to the deep asthenosphere at a unprecedented level of detail.

The composite, optimal resolution phase-velocity maps are inverted for a 3-D VS model, which reveals pronounced, previously unknown variations in the lithospheric thickness beneath the area. The model shows evidence of a robust, low-velocity anomaly beneath the Irish Sea and its surroundings that persists in the models from ~60 to at least 140 km depth, indicating an anomalously thin lithosphere and demonstrating that the assumption of a nearly constant lithospheric thickness across the area, previously adopted, is not valid. Phase velocity data at key locations are inverted using integrated geophysical-petrological inversion, to estimate the thermal structure of the lithosphere-asthenosphere system consistent with the seismic data, surface elevation, and heat-flow. The circum-Irish Sea area reveals a pronounced lithospheric thinning and matches the region of the Paleogene uplift previously suggested to be caused by a lateral branch of the Iceland mantle plume, which may have flowed into thin lithosphere areas surrounded by continental lithosphere during the evolution of the North Atlantic Ocean over the past 60 M.y. Our results show a striking correlation between lithospheric thickness and exhumation thermochronological measurements (as well as proposed underplating thickness, denudation, and the locations of the intraplate volcanism of the enigmatic North Atlantic Igneous Province) suggesting a significant lithospheric control on the volcanism of the area.

How to cite: Bonadio, R., Lebedev, S., and Chew, D.: Lithospheric control on the Paleogene uplift and volcanism in Ireland and Britain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7579, https://doi.org/10.5194/egusphere-egu23-7579, 2023.

Ambient noise, Receiver functions, etc.
15:15–15:25
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EGU23-30
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ECS
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On-site presentation
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Saman Amiri, Alessia Maggi, Mohammad Tatar, Dimitri Zigone, and Christophe Zaroli

Imaging seismic velocity of the Earth has been implemented widely for years. The majority of these studies are based on linear or non-linear methods that minimize the difference between seismic observations and predictions of these observations from simplified models of the Earth (tomographic models). Another family of methods, based on the work of Backus & Gilbert (1968), constrains Earth models by maximizing their resolution. A numerically tractable version of such linear local averaging methods, called SOLA, was recently been adapted to seismic tomography by Zaroli (2016). When correctly implemented, SOLA tends to reduce artifacts caused by uneven path coverage. It also provides information about model uncertainties and resolutions.

We are the first to have applied the SOLA Backus-Gilbert method to group velocity dispersion tomography of the Northwest Iranian plateau. We used Rayleigh wave dispersion curves obtained from vertical component seismograms of local and regional M ≥ 4.5 earthquakes that occurred from 2010 to 2021. We also used cross-correlations of ambient seismic noise from January 2013 to the end of December 2015. We allowed the resolution to vary with location and adapted the target resolution based on the local path density. We included data uncertainties based on the location uncertainties of the earthquakes and on the energy in the dispersion curves at each period. We selected the trade-off parameter between model resolution and model uncertainties using a standard L-curve.

We present group velocity maps at periods between 10 and 50 seconds as well as maps of model resolution lengths and uncertainties. We also present maps that mask regions where the anomalies are within the uncertainties to highlight the strongly anomalous regions. Our short-period maps reveal the relatively lower velocities in eastern Anatolia and western parts of NW Iran can be explained by partially melt zones in the crust, in accordance with the study of keshin (2003) who proposed extensive melting in the crust because of the interaction of hot asthenosphere with the Eastern Anatolian Accretionary Complex. Also, higher velocity anomalies along the Sanandaj-Srijan metamorphic zone (SSZ), can be related to the sedimentary and metamorphic Paleozoic-Cretaceous rocks. The low velocities observed along the Zagros fault thrust belt are also well correlated with high and shallow seismicity in this zone (Maggi et al 2000) which implies the presence of an upper crust tectonically very active.

Our long-period maps reveal high-velocity anomalies beneath the Alborz and low-velocity zone in SSZ. The low-velocity anomalies are mainly due to a thin lithosphere or the absence of a lithospheric mantle, while high velocities can be related to the presence of a stable continental mantle lid or an oceanic-like lithosphere.

Keywords: SOLA Backus-Gilbert, Group Velocity, Inverse theory, North-West of Iran, Tomography.

How to cite: Amiri, S., Maggi, A., Tatar, M., Zigone, D., and Zaroli, C.: SOLA Backus-Gilbert Rayleigh wave group velocity dispersion tomography of North-West of Iran using local-regional earthquakes and ambient seismic noise. , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-30, https://doi.org/10.5194/egusphere-egu23-30, 2023.

15:25–15:35
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EGU23-1214
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On-site presentation
Derek Schutt, Robert Porritt, Clément Estève, Pascal Audet, Jeremy Gosselin, Andrew Schaeffer, Richard Aster, Jeffrey Freymueller, and Joel Cubley

Global-scale seismic velocity models of the Northern Canadian Cordillera show high velocities to the east of the Cordilleran deformation front and low velocities to the west.    This velocity contrast is consistent with other geophysical observables, such as regional seismological studies, that indicate a weak and thin lithosphere to the west that transitions quickly to a strong and thick craton-like lithosphere at the deformation front.    We present new results using data collected by the Mackenzie Mountains EarthScope Project, which included an ~875 km-long line of 40 broadband seismographs across the Cordillera and into the craton extending from roughly Skagway, Alaska to Great Bear Lake, Northwest Territories.    The 3-year overlap of this deployment with other broadband seismic stations in the region, most notably the EarthScope Transportable Array and the Yukon Northwest Seismic Network, allows for detailed 3-D Rayleigh wave ambient noise imaging of the upper lithosphere.    Results show large velocity variations west of the deformation front.   Notably, we image a 5% Vs low that extends from the upper crust to the asthenospheric mantle.   This plume-like structure, and associated weakening, may be a primary cause for the ongoing uplift of the Mackenzie Mountains at their unusually eastward location.   We also image a low velocity feature in the lower crust extending to the west of the deformation front, which may facilitate eastward crustal translation along a large-scale (~800 km) decollement system driven by the Yakutat indentor consistent with the orogenic float hypothesis of Mazzotti and Hyndman (2002).    We also note strong lithosphere-scale lateral heterogeneity suggesting that 3-D effects are important in focusing deformation in the Mackenzie Mountain area.

How to cite: Schutt, D., Porritt, R., Estève, C., Audet, P., Gosselin, J., Schaeffer, A., Aster, R., Freymueller, J., and Cubley, J.: Large Lithospheric Seismic Velocity Variations Across the Northern Canadian Cordillera Imaged by Ambient Noise Tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1214, https://doi.org/10.5194/egusphere-egu23-1214, 2023.

15:35–15:45
Coffee break
Chairpersons: Milena Marjanovic, Alexandra Moshou, Laura Gómez de la Peña
Controlled source and Earthquake tomography
16:15–16:35
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EGU23-4416
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ECS
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solicited
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On-site presentation
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Michelle Lee, Suzanne Carbotte, and Adrien Arnulf

Axial Seamount is an active submarine volcano formed by the intersection of the Juan de Fuca Ridge and the Cobb-Eickelberg hot spot. The Axial Seamount volcanic system includes the central volcano marked by a caldera and bounding northern and southern rift zones. Prior studies of the last three eruptions at Axial (Jan. 1998, Apr. 2011, Apr. 2015) indicate lava flows and earthquake swarms extending from the summit caldera and into the rift zones. These eruptions are believed to have been sourced from the well-imaged large magma reservoir found beneath the summit caldera of Axial (Arnulf et al., 2014, Carbotte et al., 2020). However, areas beyond the summit caldera have not been explored for potential magma sources that could have contributed to these events.

In this study, we process and analyze multi-channel seismic (MCS) data acquired in 2002 from the Juan de Fuca Ridge to characterize the internal structure of the rift zones. The reflective profiles reveal small crustal magma bodies beneath and in the vicinity of lava flows in rift zones from the three prior eruptions. These magma bodies are less than 5km wide and are located at depths of ~1.5-5.2km beneath the seafloor. We also image wide magma bodies within the overlap regions between the rift zones and the neighboring Juan de Fuca segments. We image a 6.4km wide body under the eastern flank of the northern rift zone overlapping with the Coaxial segment and a 1km wide, ~400-500km thick magma body under the overlapping basin between the southern rift zone and Vance segment. Collectively the new observations from the MCS data reveals that, in addition to the main magma reservoir, there are also multiple small and discontinuous crustal magma bodies underlying the Axial segment. Through interpretations of the seismicity pattern and lava flow compositions, we believe that these magma bodies likely contribute the rift zone magmatism.  

How to cite: Lee, M., Carbotte, S., and Arnulf, A.: Imaging magma beneath the rift zones of Axial Seamount on the Juan de Fuca Ridge, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4416, https://doi.org/10.5194/egusphere-egu23-4416, 2023.

16:35–16:45
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EGU23-4317
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ECS
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On-site presentation
Lianjun Li, Jenny Collier, Tim Henstock, and Saskia Goes

The most common way to estimate the porosity of the mature oceanic crust, and hence its contribution to geochemical exchange, is from the inversion of active source seismic data. Previous studies have suggested that hydrothermal activity effectively ceases in crust older than 10 Ma. This is based on observations that the seismic velocity of the uppermost crust increases rapidly within 10 Ma but changes little beyond that. The velocity increase is widely explained by reduced porosity and permeability due to hydrothermal mineral precipitation and fracture closure due to sediment blanketing. However, a potential problem with conventional wide-angle Ocean Bottom Seismometer (OBS) modelling over mature oceanic crust is the imaging geometry, where the water wave obscures the onset of the crustal refractions for tomographic inversion needed to resolve the velocity of the upper hundred meters of the igneous crust.

 

To investigate the issue of imaging geometry and accurately extract the physical properties of the upper crust, we applied downward continuation on conventional OBS records across 65 Ma Atlantic Ocean crust. The method eliminates the effect of the thick water column by locating shots on a datum close to the seabed. This enables refractions from the uppermost 100-200 m of igneous crust to be viewed as first arrivals, and hence significantly improves the accuracy of the velocity inversion of the upper layers. Using travel time picks from downward continued and original OBS records, we applied tomographic inversion with three starting models taken from the latest compilation of crustal velocity-depth (VZ) models. The three models have a velocity variation of ±10% for the uppermost crust, representing a low, mean, and high bound for crustal VZ relations. By comparing the results, we show that with downward continued data the inverted velocity of the uppermost crust is less dependent on the starting model and converges to the same trend closer to the low bound of previous VZ relations. The average velocity of the uppermost crust inverted with downward continued data is ~0.3 km/s lower than that inverted with original data. These results would translate into a porosity of 14%, compared to 10% for the non-downward continued analysis. We also resolve stronger along-strike variation in the inverted velocity of the uppermost crust (4.2 km/s to 4.8 km/s) using downward continued data compared to original data, which may correspond to porosity as large as 18%, much higher than previously suggested porosity of 8 % for mature oceanic crust. This implies that open cracks may be still present and thick sediments may seal hydrologically but not close fractures that affect the seismic refraction data. Moreover, our results reconcile with the recent work in the South Atlantic performed with full-waveform inversion (FWI) on streamer data. Therefore, downward continuation, also FWI may need to be incorporated into the workflow of conventional wide-angle OBS modelling, especially for mature oceanic crust. This will improve the resolution and accuracy of the physical properties of the uppermost crust and may shed new light on its evolution and role in off-axis hydrothermal circulation and seawater chemistry.

How to cite: Li, L., Collier, J., Henstock, T., and Goes, S.: Evidence for a higher porosity upper crust in the North Atlantic Ocean  , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4317, https://doi.org/10.5194/egusphere-egu23-4317, 2023.

16:45–16:55
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EGU23-11063
|
ECS
|
Virtual presentation
Silpa Sundaran, Bommoju Padma Rao, and Satish Maurya

The Indian Ocean Geoid Low (IOGL) is a significant negative geoid anomaly (-106 m), located south of the Indian subcontinent. Several studies have been carried out to investigate the causes responsible for IOGL, results indicate that its origin could be low velocity/density anomalies in the depth range of mid-to-upper mantle and/or high velocity/density anomalies in the depth range of lower mantle. However, a concrete model to explain the origin of IOGL and especially the effect of the shallow structure on IOGL is still enigmatic. In the present study, we investigate the high-resolution 3D shear velocity structure beneath the Indian Ocean region down to a depth of 300 km using surface wave tomography. For this analysis, collated extensive data from more than 700 broadband seismological stations of various data centres (IRIS: Incorporated Research Institutions for Seismology, FDSN: International Federation of Digital Seismograph Networks, IN: Indian Stations) to obtain a good azimuthal and spatial coverage. This dataset has been pre-processed and utilized to measure the fundamental mode of Rayleigh wave group velocities sampling the IOGL region. Further, visually checked the quality of the dispersion curves and considered only good-quality ones, which resulted in ~19,300 good-quality dispersion curves in a frequency range of 10-120 s and then applied the regionalization to extract the geographical distribution of local group velocities in different periods. Later, inverted the regionalized dispersion data using the trans-dimensional inversion approach. Regionalized shear wave velocity maps are in good agreement with surface tectonics such as low-velocity anomalies along the large-scale ridges and previous tomography studies. The western Indian Ocean shows very fast velocity anomalies at short-period (~20 s) and low-velocity anomalies in long periods (>100 s) which could be attributed to the magmatic underplating originating from the various hotspots and the presence of channelled flows asthenosphere towards eastward to spreading ridges. Further, the results rules-out that the contribution of the lithosphere could be negligible in explaining the IOGL as there are no low-velocity anomalies beneath the IOGL region. In addition, the obtained high-resolution regional surface wave tomography from this study enables the research community to obtain/measure the precise IOGL anomaly and understand the detailed tectonics and crustal/lithospheric deformation beneath the study region.

How to cite: Sundaran, S., Rao, B. P., and Maurya, S.: Crustal and Uppermost Mantle Structure beneath the Indian Ocean Geoid Low using Surface Wave Tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11063, https://doi.org/10.5194/egusphere-egu23-11063, 2023.

16:55–17:05
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EGU23-12936
|
On-site presentation
Kees Wapenaar and Joeri Brackenhoff

In recent years, the Marchenko method has proven to be a viable tool to create virtual seismic sources and receivers in the subsurface from reflection measurements at the surface. Applications range from suppressing internal multiples in seismic imaging to forecasting responses to induced seismic sources. One of the attractive aspects of the Marchenko method is that no detailed subsurface model is needed; a smooth background model suffices. All information needed to treat the internal multiples correctly comes from the reflection measurements at the surface. 

One of the underlying assumptions of the Marchenko method is that the seismic wave field can be decomposed into downgoing and upgoing waves at any position in the subsurface where one wants to create a virtual source or receiver. Although in many situations this implies no significant restrictions, it may hamper the imaging of steeply dipping flanks and it prevents the treatment of refracted and evanescent waves.

It can be shown that the Marchenko focusing function (the nucleus of the Marchenko method) can be expressed in terms of the so-called propagator matrix. The propagator matrix, which was introduced in geophysics in the nineteen-sixties for 1D systems and developed further in the nineteen-seventies for laterally varying 3D media, ‘propagates’ a wave field from one depth level to another. It does not rely on up-down decomposition and it accounts for propagating waves at all angles and for evanescent waves. By exploiting the link between the Marchenko focusing function and the propagator matrix, the applicability of the Marchenko method can be expanded. In the presentation we will review the underlying theory and discuss the potential application of the Marchenko method for refracted waves.

How to cite: Wapenaar, K. and Brackenhoff, J.: Pushing the limits of the Marchenko method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12936, https://doi.org/10.5194/egusphere-egu23-12936, 2023.

17:05–17:15
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EGU23-6435
|
ECS
|
On-site presentation
Naomi Schneider, Volker Michel, Karin Sigloch, and Eoghan Totten

We attempt the reconstruction of the solid earth’s interior three-dimensional structure using seismic wave observations. The interior structure of the mantle deviates moderately from spherically symmetrical reference models and therefore seismological observables also vary moderately from spherically symmetrical predictions. Hence we consider here the linearized inverse problem of seismic traveltime tomography.

Usually, the solution is approximated in a fixed basis system: either global (e.g. polynomials) or local (e.g. finite elements) basis functions. Here we use a dictionary-based approximation approach, called the Learning Regularized Functional Matching Pursuit (LRFMP). A dictionary is an intentionally redundant set of diverse trial functions from which iteratively an approximation in a best basis is built. The next best basis element is chosen such that the Tikhonov functional is minimized.

The methods have been used for a variety of spherical as well as tomographic tasks from the geosciences as well as medical imaging. Here we apply them to seismic traveltime tomography for the first time. We discuss relevant developments and challenges in the process of tailoring the methods to the problem and show first promising results.

How to cite: Schneider, N., Michel, V., Sigloch, K., and Totten, E.: A dictionary-based approximation approach for seismic traveltime tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6435, https://doi.org/10.5194/egusphere-egu23-6435, 2023.

17:15–17:25
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EGU23-15581
|
On-site presentation
Clara Estela Jimenez Tejero, Cesar R. Ranero, and Valenti Sallares

Seismic methods are one of the most powerful existing geophysical tools to extract information on the structure of the Earth’s subsurface. These techniques continue to be widely used to obtain images of the sediments and crust and to map the variations in physical properties. Particularly the P-wave velocity (Vp) distribution is the most commonly modelled property. 

The most widely applied seismic method to retrieve velocity models is seismic tomography, using either travel-time information as in travel-time tomography (TTT) or a more complete set of waveform attributes in full-waveform inversion (FWI). Whereas TTT is a robust, moderately non-linear technique providing coarse models, FWI is strongly non-linear and computationally demanding, but with the potential to provide higher resolution models. TTT and FWI are considered to be complementary, so that they are often combined and applied together. TTT is applied first to get a moderate-resolution model, which is then used as an initial model for FWI. In fact, the key to successfully apply FWI to seismic data, is the usage of a kinematically correct initial model, in which simulated and recorded waveforms are not cycle-skipped at the lowest frequency available. On this basis, it is crucial to extract the travel-time information of the refracted waves as accurate as possible. Particularly for marine multichannel reflection seismic (MCS) acquisition systems, where most refractions are masked by reflections and noise, data processing techniques like Downward Continuation (DC) allows to better retrieve refractions, and this is achieved by virtually redatuming streamer field data to the seafloor. 
 
We aim at showing the different user-friendly open source HPC software designed and built in the Barcelona Center for Subsurface Image (BCSI) to process seismic data from marine experiments, recorded by ocean bottom seismometers (OBS) and/or multichannel seismic (MCS) data recorded by towed streamers. The three tools, DC, TTT, and FWI, which can be used independently and/or combined together for a better performance, have the potential to produce high resolution models of the physical properties of the subsurface. While DC software is designed for 2D seismic data, the TTT tool also read 3D data, and allows the joint inversion of Vp, Vs and anisotropic properties for active and passive data, including earthquake relocation. At present, DC and TTT software tools are freely available and the last version updated at GitHub repositories and the FWI tool for 2D data is under development.

How to cite: Jimenez Tejero, C. E., R. Ranero, C., and Sallares, V.: Seismic tomography software tools at Barcelona Center for Subsurface Imaging, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15581, https://doi.org/10.5194/egusphere-egu23-15581, 2023.

17:25–17:35
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EGU23-6305
|
On-site presentation
Ping Tong, Jing Chen, Masaru Nagaso, and Shijie Hao

We have witnessed a transit of seismic tomography from ray-based traveltime inversion to wave equation-based waveform inversion during the past two decades. As is widely known, full waveform inversion outperforms traveltime tomography in resolving velocity variations with dimensions comparable and smaller than the dominant wavelength. However, this may not be always true in real practice, mainly due to the presence of unknown data noise, the lack of accurate initial models for the iterative inversion process (including material properties and source mechanisms), and the high demand for computational resources. Further efforts are required to develop techniques for using full waveform contents in seismic imaging studies, especially for the use of high-frequency waveform data (>1 Hz on regional scales). We have attempted to use common-source double-difference traveltime data in wave equation-based adjoint tomography studies of subsurface structures beneath Northeast Japan and Alaska. Because of the high level of waveform similarity, reliable common-source double-difference traveltime data at neighboring seismic stations are measured via cross-correlation approach. Insightful results are obtained. However, it is still computationally prohibitive to model high-frequency data by solving 3-D wave equations, limiting the resolution of seismic images. We admit that there is still a long way to go for the possible wide application of high-frequency full waveform inversion.

Traveltime is the most reliable information that can be extracted from raw seismological recordings.  We have developed a new modality of seismic imaging, called adjoint-state traveltime tomography, to unleash the full potential of traveltime in imaging subsurface structures. To avoid potential failure of ray tracing in 3D complex media, isotropic eikonal equation and anisotropic eikonal equations are used to model seismic traveltime field in heterogenous and anisotropic media, and the associated inverse problems are solved by the efficient adjoint state method. No ray tracing is required for the novel adjoint-state traveltime tomography method. Importantly, the sensitivities of traveltime-related objective functions to material parameters can be accurately measured even in complex media. We view adjoint-state traveltime tomography as a new framework for seismic tomography, as it naturally implements various body wave and surface wave tomographic inversions in a very similar way. Good performances of the adjoint-state traveltime tomography method will be reported via various case studies in regions with typically different tectonic settings. It is worth noting that an accompanying software package, TomoATT, is under development.

How to cite: Tong, P., Chen, J., Nagaso, M., and Hao, S.: Adjoint-state traveltime tomography: A new modality of seismic imaging, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6305, https://doi.org/10.5194/egusphere-egu23-6305, 2023.

17:35–18:00

Posters on site: Thu, 27 Apr, 08:30–10:15 | Hall X2

Chairpersons: Laura Gómez de la Peña, Andrzej Górszczyk, Alexandra Moshou
Interdisciplinary approach
X2.117
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EGU23-4819
Fatimah Abdulghafur, Steven Hansen, and Juan Carlos Afonso

Seismic data from several long-running broadband sensors around the globe will be used to investigate the statistical significance and geologic interpretation of negative velocity discontinuities in the upper-most mantle. Several previous studies have identified negative polarity arrivals in S-wave receiver function data which are variously interpreted as lithosphere-asthenosphere and/or mid-lithosphere boundaries.

One-dimensional joint-inversion is applied using the LitMod framework, which is a Bayesian statistical method driven by a Markov Chain Mote Carlo algorithm.

LitMod uses a thermodynamically consistent physical model of the mantle and thus provides important constraints for the interpretation of the receiver function results.

Joint inversions combine Rayleigh wave phase velocity measurements, both P and S-wave receiver functions, absolute elevation, and geoid height.

Particular attention is given to the calculation and inversion of S-wave receiver function data, which represents a new addition to the LitMod framework. 

How to cite: Abdulghafur, F., Hansen, S., and Afonso, J. C.: Imaging the Earth's Upper Mantle: Markov Chain Monte Carlo Joint Inversion of Geophysical Multi-observables, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4819, https://doi.org/10.5194/egusphere-egu23-4819, 2023.

X2.118
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EGU23-2929
Modeling faults using 2D and 3D seismic simulation
(withdrawn)
Alexandra Moshou and Panagiotis Argyrakis
X2.119
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EGU23-10021
|
ECS
|
Highlight
3D Modelling of Seismically Active Parts of Underground Faults via Deep Learning
(withdrawn)
Theofanis Frantzeskakis, Alexandra Moshou, and Antonios Konstantaras
Waveform modelling
X2.120
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EGU23-4387
|
ECS
Andrzej Górszczyk, Romain Brossier, and Ludovic Métivier

Regional-scale active seismic surveys are the methods of choice to probe the lithosphere. One of the key parameters of these surveys is the spatial sampling of the investigated area. Dense sources and receivers sampling coupled with broadband frequency of signals translates to fine-scale probing of the subsurface from a broad range of perspectives. In practice, however,  acquisition design of academic deep crustal seismic surveys typically assumes a compromise between the experiment logistic and the key parameters of the acquisition geometry. This compromise often leads to 2D surveys realised with few tens of receivers deployed along the profiles that can be up to few hundred kilometers long. As a result the high costs of 3D surveys are mitigated at the price of the quality of the resulting data, that cannot be fully exploited by advanced processing techniques - such as waveform-based inversion methods. In particular, the 2D data acquisition and subsequent imaging pose the inconsistency between the 3D wavepath traveled during the survey and the 2D wavepath forced during the 2D processing. This is because geological heterogeneities cause changes of direction of wave propagation, which is indicated by the three-dimensional wave vector spanned at a given point of subsurface. If the 3D-effect is strong due to the complexity of the underlying structure, then the 2D assumption of wavefield propagation during processing cannot honor the field conditions and must lead to errors in the reconstructed velocity model or migrated image. 

Recent years have shown a massive development of waveform inversion and migration methods. In terms of regional-scale seismic imaging, there were few documented onshore and offshore case studies that attempted to process 2D archival academic data with full-waveform inversion (FWI) and extract structural information beyond the resolution-limit of the traveltime tomography. However, the limitations originating from the legacy acquisition make it difficult to fully exploit the potential of FWI. In this study we evaluate the ability of regional-scale velocity model-building technics to handle out-of-plane propagation and investigate how this effect manifests itself in the data. Through the insight of  wave propagation within complex subsurface models we underline the problem and make first attempts to the broader investigation of the optimization of 3D academic regional surveys. We extract various 3D target models from the synthetic model of a subduction zone and we use those models to generate seismic data along 2D OBS lines. Subsequently we use 2D FWI to evaluate how the out-of-plane propagation affects the results of 2D velocity model-building from the data generated along the 2D OBS lines but using 3D modelling and 3D target models. We compare those results with the scenario where the 2D FWI is applied to the data from the same 2D OBS lines but generated using 2D velocity models and 2D modelling. We perform polarization analysis to demonstrate how the 3D effect manifest itself in the OBS gathers. Finally we also run 3D FWI with different OBS acquisition settings to investigate their impact on the final model reconstruction.

How to cite: Górszczyk, A., Brossier, R., and Métivier, L.: The impact of the 3D effect on the regional-scale velocity model building using 2D full-waveform inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4387, https://doi.org/10.5194/egusphere-egu23-4387, 2023.

X2.121
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EGU23-886
|
ECS
Crust Characterization below North-East India
(withdrawn)
Neeharika Shukla, Sagarika Mukhopadhyay, and Devajit Hazarika
X2.122
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EGU23-15393
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ECS
Three-dimensional Seismic Velocity Model for Upper-Most Mantel of Zagros Collision Zone Using Full Wave Form Inversion
(withdrawn)
Neda Masouminia, Dirk-Philip van Herwaarden, Sölvi Thrastarson, Habib Rahimi, Michael Afanasiev, Lion Krischer, Böhm Christian, Heiner Igel, and Andreas Fichtner
X2.123
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EGU23-13540
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ECS
Johannes Aichele, Jonas Müller, Zabreen Nissar, Dirk-Jan van Manen, and Marc Serra-Garcia
Due to causality wave scattering in time is simpler than scattering in space: In
contrast to multiple spatial boundaries, there are no infinite reflections between
temporal boundaries. Salem and Caloz, 2015 [1] showed that wave scatter-
ing can be simplified by constructing a time-space cross-mapping. We identify
the cross-mapped wavefields as the Focusing functions developed in data-driven
geophysical imaging. Experimentally, Bacot et al, 2016 [2] have shown that
time modulation of the medium properties of a capillary-gravity wave results in
time-refraction and time-reflection of the original wave. This experimental re-
sult should hold true for any system obeying Alembert’s equation. This should
in principle allow us to physically compute wavefields for the single-sided inverse
scattering problem through forward scattering experiments. We set up a sim-
ple comb-like discrete system for time-modulated 1D elastic wave propagation.
Elastic beams act as the masses and an electrostatic force as the springs of our
system. The effective coupling stiffness between the beams is modulated in time
through a variation of the electrostatic force. A Galerkin based wave propaga-
tion model shows that an experimental realization of hundreds of beams can be
achieved through micro-machining. Through time-modulations of the system’s
wavespeed a broadband excitation is refracted and reflected everywhere in space.
Time-scattering preserves the wave vector k, which implies that the frequency
ω is not conserved. To elucidate the dispersion relation at time boundaries,
we employ a correction method for spatial dispersion. Herefore, a correction
method for time-dispersion in finite difference simulations developed by Koene
et al 2018 [3] is mapped to the spatial dimension of our meta-material.
[1] Salem, Mohamed A., and Christophe Caloz. “Space-Time Cross-Mapping
and Application to Wave Scattering.” ArXiv:1504.02012 [Physics], April 7, 2015.
http://arxiv.org/abs/1504.02012. [2] Bacot, Vincent, Matthieu Labousse, An-
tonin Eddi, Mathias Fink, and Emmanuel Fort. “Time Reversal and Holography
with Spacetime Transformations.” Nature Physics 12, no. 10 (October 2016):
972–77. https://doi.org/10.1038/nphys3810. [3] Koene, Erik F M, Johan O A
1
 
 
Robertsson, Filippo Broggini, and Fredrik Andersson. “Eliminating Time Dis-
persion from Seismic Wave Modeling.” Geophysical Journal International 213,
no. 1 (April 1, 2018): 169–80. https://doi.org/10/gcz9wb.

How to cite: Aichele, J., Müller, J., Nissar, Z., van Manen, D.-J., and Serra-Garcia, M.: Back and Through the Looking Glass - Space-time scattering of elastic waves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13540, https://doi.org/10.5194/egusphere-egu23-13540, 2023.

X2.124
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EGU23-8657
Børge Arntsen, Umedzon Khakhorov, and Wiktor Weibull

Ocean Bottom Seismometers (OBS), in conjunction with an active source, have for a longtime been used to investigate the crust and upper mantle. Conventionally a number of Seismometers are deployed along a line with relatively large separation (several kilometers) between each instrument. A large air-gun array is then used to create a number of recordings with distance between the receiver and source varying from zero up to several hundred kilometers.

The data is usually analyzed with tomographic methods leading to a P-wave velocity model. Tomographic methods tend to produce velocity models with low resolution and lack of details. To increase resolution the Full Waveform Inversion (FWI) can be used. Velocity models estimated using FWI shows better resolution and are better constrained than tomographic models.

Our work sets out to develop a FWI workflow for a sparsely sampled OBS data. We demonstrate high resolution crustal-scale velocity model building workflow based FWI for a deep water and sparse (6km) sampled 300 km long wide-angle OBS data. We use an initial model traveltime tomography inversion. We apply waveform inversion to constrain crustal and upper mantle layers more confidently and with increased resolution compared to conventional traveltime tomography with layer-based parameterization. FWI allows to reduce significantly data-fit error (i.e. rms error) and explains better larger offsets of an observed data compared to traveltime tomography.

The workflow is developed and applied to data acquired in 2009 in the Japan Trench where the 130-150 Myrs old oceanic plate is subducting under Eurasia. Subduction zones plays an important role in Earth tectonics . Traveltme tomography inversion was used the 2009 Japan Trench dataset to construct velocity models and showed that P-wave velocities close to the trench axis, where the plate bends downward, are systematically lower than the P-wave velocities at larger seaward distances. This is interpreted as water penetration into the plate from the seafloor, causing serpentinization which decreases P-wave velocities. However, tomographic models does not reveal details of the velocity model, only smoothed averages. We hope that a velocity model generated by FWI has sufficiently increased resolution to reveal more details of the water penetration and geological setting along the Japan Trench.

 

How to cite: Arntsen, B., Khakhorov, U., and Weibull, W.: Crustal-scale Vp velocity model building for a sparse regional OBS survey using full-waveform inversion: a case study from Japan Trench, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8657, https://doi.org/10.5194/egusphere-egu23-8657, 2023.

Ambient noise, Receiver functions, etc
X2.125
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EGU23-4213
|
ECS
Joseph Fone and Nicholas Rawlinson

The two step inversion of ambient noise surface wave data is common practice due to its convenience and reliability of imaging structures that are consistent with other observations. It is performed by taking the inter station dispersion curves produced by cross-correlation of ambient noise and performing individual 2D travel time tomographic inversions to produce maps of phase and/or group velocity for Rayleigh and/or love waves and whichever frequencies and modes have been extracted from the ambient noise data. These maps are then sampled in discrete points to produce location based dispersion curves known as pseudo-dispersion curves. These pseudo-dispersion curves are then inverted for 1D velocity structure. The issue with this method is the many separate inversions that are performed are entirely separate from one another with no regularisation applied to the final 3D model only in the individual steps. This can lead to artefacts in the model, particularly in areas of low data coverage, as the pseudo-dispersion curves can have unphysical spikes and velocity changes and so often produce unrealistic 1D models. Post processing can partially remedy this, such as smoothing the final model, but it does not go all the way to solving the problem. Single step inversions are also possible. The forward problem involves taking the 3D model and sampling it in discrete locations and computing dispersion curves which can be converted into 2D maps of phase/group velocity etc. Then using some Eikonal solver the travel time between stations can be calculated. These calculated travel times are then used with the measured travel times extracted from ambient noise to perform an inversion. This obtains a 3D model directly from the observed dispersion curves with regularisation built into whichever inversion scheme being used. This is often much more computationally expensive than the two step as the forward problem is expensive and needs to be computed many times in a typical inversion scheme. In this preliminary study we investigate the potential of using neural networks to assist in the single step inversion process by training networks to perform the forward and inverse problems in single step tomography of interstation dispersion curves. This may result in significant speed ups in these processes or lead to different ways of approaching the one step process. To examine the potential of this we investigate possible efficient sampling algorithms to produce synthetic training data sets as well as network architectures that produce the most accurate mapping of model parameters to the data and vice versa.

How to cite: Fone, J. and Rawlinson, N.: The potential of machine learning to solve the single step inversion problem in ambient noise tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4213, https://doi.org/10.5194/egusphere-egu23-4213, 2023.

X2.126
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EGU23-5910
|
ECS
Billel Melouk, Abdelkrim Yelles-Chaouche, Fethi Semmane, and Juan Jose Galiana-Merino

Abstract

We investigated the Moho depth and the velocity structure of the crust and upper mantle in northern Algeria. We used teleseismic P-wave receiver functions jointly inverted with Rayleigh wave dispersion curves obtained from local earthquakes. The events used are collected from the seismic broadband stations of the Algerian broadband seismic network. These stations are located in different geological settings including the Tell Atlas, High Plateaus, and the Saharan Atlas. The H–κ stacking method of receiver functions was applied to first obtain the crustal thickness and the Vp/Vs ratio. The inversion results show the variation in Moho depth in the different geological structures. The shallowest depths of the Moho (~20–30 km) are estimated along the Algerian continental margin and Tell Atlas. In the High Plateaus region, the Moho depths vary from 30–36 km, whereas the deepest Moho depths are found in the Saharan Atlas (36–44 km). The crust is divided in two layers in the whole study area. The upper crust, ~8 –14 km thick, presents an average shear velocity of ~3.0 km/s. The lower crust of about 12–30 km thick has an average shear-wave velocity that ranges between 3.4–3.8 km/s. The upper crust is thinner than the lower crust particularly in the Saharan Atlas. The upper mantle shear-wave velocity varies from 4.1 to 4.5 km/s maximum and is stable, generally, below ~60 km depth. We clearly observed two low-velocity zones particularly in the eastern part of the Tell Atlas and the High Plateaus. The obtained results are in accordance with the previous results found in the region, particularly those using land gravity and seismic data. As the first estimate of the Moho depth from earthquake data in northern Algeria, using the receiver function method, this study sheds new insights on the crustal structure and the Moho depth in this region of the world.

How to cite: Melouk, B., Yelles-Chaouche, A., Semmane, F., and Galiana-Merino, J. J.: Shear-wave velocity structure and Moho depth variation in northern Algeria from joint inversion of teleseismic P-wave receiver functions and Rayleigh wave dispersion from local earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5910, https://doi.org/10.5194/egusphere-egu23-5910, 2023.

X2.127
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EGU23-17461
|
ECS
|
Lúcio Quadros de Souza, Amr El-Sharkawy, Marcelo Assumpção, and Thomas Meier

The development of new automated techniques to measure earthquake-based interstation phase velocities allows for more detailed imaging of the South American Lithosphere. We calculated Rayleigh-wave phase velocities using the earthquake records from 1022 broadband seismic stations (South America, Antarctica and the Caribbean) operated between 1990 and 2020. A total of 1.069.259 earthquakes were selected with the following criteria: (1) events aligned within 10° of the 2-station great circle path; (2) a linearly increasing minimum magnitude between 4 and 6 Mw as a function of the epicentral distance; (3) maximum magnitude of 8 Mw; and (4) epicentral distances between 2.5° and 30°.
We used surface wave fundamental mode dispersion curves calculated automatically using a new implementation of the 2-station cross-correlation method and a number of strict quality criteria, which include the selection of the phase velocity curves based on a 3D background model, curve smoothness and width of the considered frequency range. Following this process, we obtained 46.763 broad-band dispersion measurements between 4 and 315 s. Finally, the single-event dispersion curves were averaged for each interstation pair with associated error estimates and further quality control comparing results from both directions, evaluating smoothness and the standard deviation of the resulting dispersion curve.
The dispersion curves were simultaneously inverted for isotropic and anisotropic (2ψ and 4ψ) phase-velocity maps parameterized on a triangular grid with a knot spacing of 30 km.
The isotropic phase velocity maps at periods of 15 and 30 s indicate around 8% high-velocity perturbations in the regions of: (1) cratonic blocks of the South American platform (Brazilian Shield, São Francisco and Rio Apá cratons); and (2) the basement of the Pantanal basin (a 500 m thick sedimentary basin) possibly related to a high-velocity lower crust. For those periods, we also observed between -8 to -4% low-velocity perturbations associated with the Andean Mountain range root below the Altiplano Boliviano region (central Andes), the forelands of the Andes. The Paraná, Chaco and Parecis intracratonic basins also have lower velocities with relation to the neighboring cratonic areas.
At periods of 60 and 100 s, we observed around 4% high-velocity perturbation associated with the deep roots of the oldest region of the Amazonian craton (eastern area of the Brazilian Shield) and the São Francisco craton. Azimuthal anisotropy is laterally and vertically variable within the South American lithosphere. At longer periods, fast directions are pointing to asthenospheric flow guided by LAB topography, for example below the Pantanal basin (central-west Brazil).
For the next steps, we plan to jointly invert for a isotropic and anisotropic 3D model using earthquake and ambient noise dispersion curves with Rayleigh and Love waves.

How to cite: Quadros de Souza, L., El-Sharkawy, A., Assumpção, M., and Meier, T.: Ambient Noise and Earthquake Surface Wave Phase Velocity Tomography of the South American Lithosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17461, https://doi.org/10.5194/egusphere-egu23-17461, 2023.

X2.128
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EGU23-15781
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ECS
Alejandra Neri, Said Badrane, Beatriz Gaite, Antonio Villaseñor, Roberto Cabieces, César R. Ranero, and Arantza Ugalde

With more than 40 years of study, there are still uncertainties about the structure, evolution, and geodynamics of the North African and South Iberian Peninsula lithospheric structure and collision zone. Models of the lithosphere of the region coincide in some anomaly zones, such as the subduction slab under the Gibraltar arc. However, they show discrepancies in the distribution and polarity of the velocity anomalies in the onshore and offshore of most of North Africa.

To contribute to the study of the lithospheric structure and to unveil the tectonics in this controversial region, we constructed an ambient noise tomography (ANT) of Love and Rayleigh waves from temporary and permanent broadband stations located in the Iberian Peninsula, North Africa, and Atlantic islands (Madeira, Canarias, Balearic Islands). 

The methodology employed contemplates phase cross-correlation of 14 months of ambient noise records and the subsequent stacking of the cross-correlograms to obtain the Empirical Green's Function (EGF). To measure the dispersion characteristics of surface wave EGFs present in the ambient noise, we implemented the Frequency-Time Analysis (FTAN). And finally, the inversion of the dispersion measures to get the surface wave tomography.

The distribution of the almost 100 broadband stations in North Africa, Portugal, Spain, and the Atlantic islands, results in a broad path coverage in the North African and South Iberian Peninsula lithospheric structure and collision zone, complementing the previous Rayleigh wave velocity models. Furthermore, current studies in this region are Rayleigh-waves based, so the integration of Love waves in this ANT yields new information on the media velocity anisotropy.

How to cite: Neri, A., Badrane, S., Gaite, B., Villaseñor, A., Cabieces, R., Ranero, C. R., and Ugalde, A.: Rayleigh and Love wave tomography from seismic noise of the North African and South Iberian Peninsula lithospheric structure and collision zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15781, https://doi.org/10.5194/egusphere-egu23-15781, 2023.

X2.129
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EGU23-12551
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ECS
Tatjana Weiler, Amr El-Sharkawy, and Thomas Meier

High-resolution Rayleigh phase velocity maps can help to improve our understanding of the 3-D vs anisotropic structure of the lithosphere of central Europe and its relationship to surface tectonics and volcanism.
Using seismic broad-band recordings for the time period from 1990 to 2020, 600,000 inter-station fundamental mode Rayleigh wave phase velocities have been automatically determined by performing strict quality checks. Only smooth and reliable phase velocity curves with path-wise averaging and a standard error of 0.5% were chosen. For periods between 8 s and 350 s azimuthally anisotropic phase velocity maps were calculated for Central Europe. The phase velocity maps at short periods of up to 30 seconds show an NW-SE fast propagation direction along the East European Craton. At periods longer than 60 s, the anisotropic fast propagation direction shows slight variations from NE-SW to ∼N-S. At 150 s map, a NE-SW fast direction is observed. This might indicate a layering of anisotropy. Along the Tornquist-Teisseyre Zone, the fast propagation direction at all periods is NW-SE, except along its northern part as it shows slight variations. This might be due to the sharp change from the Precambrian continental mantle lithosphere to the younger Phanerozoic Europe. At short periods, central Europe anisotropy is following the Variscan front which changes abruptly to SE-NW near the Elbe line, whereas at longer periods the fast direction follows the Rheic suture and Saxothuringian suture.
For the inversion of local azimuthally anisotropic phase velocity curves, we apply a newly elaborated stochastic inversion algorithm, the Particle Swarm Optimization algorithm (PSO). The result for extensive inversion and parameter tests of Rayleigh dispersion curves tests are shown. The lateral, as well as the vertical resolution of the resulting azimuthally anisotropic S-wave velocities and indications for layered anisotropy, are discussed.  

How to cite: Weiler, T., El-Sharkawy, A., and Meier, T.: Rayleigh phase velocity maps for central Europe including the Eifel volcanic province, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12551, https://doi.org/10.5194/egusphere-egu23-12551, 2023.

X2.130
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EGU23-10971
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ECS
Teleseismic Rayleigh-wave phase velocity tomography in the southern Korean Peninsula
(withdrawn)
Joa Kwon, Hyun Jae Yoo, Tae-Seob Kang, Seongryong Kim, Sang-Jun Lee, and Junkee Rhie
Controlled source and Earthquake tomography
X2.131
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EGU23-2387
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Tomasz Janik, Vitaly Starostenko, Wojciech Czuba, Piotr Środa, Anna Murovskaya, Tamara Yegorova, Alexandra Verpakhovska, Katerina Kolomiyets, Dmytro Lysynchuk, Dariusz Wójcik, Victor Omelchenko, Tanya Amashukeli, Olga Legostaeva, Dmytro Gryn, and Serhii Chulkov

Carried out in 2021, the wide-angle reflection and refraction (WARR) SHIELD’21 profile crosses, from SW to NE, the main tectonic structures of Ukraine. It targeted the structure of the Earth’s crust and upper mantle of the southwestern margin of the East European Craton with overlying Neogene Carpathian Foredeep and Vendian-Paleozoic Volyn-Podolian Monocline, Archaean and Paleoproterozoic segments of Ukrainian Shield and Late Paleozoic Dnipro-Donetsk Basin. The ~650 km long SHIELD’21 profile is an extension of previously realized RomUkrSeis profile carried out in 2014 and running from the Apuseni Mountains to the southwestern Ukrainian Shield (Starostenko et al., 2020). The WARR study along the SHIELD’21 profile using TEXAN and DATA-CUBE short-period seismic stations provided high-quality seismic records. The field work was performed during the summer of 2021, included the deployment of autonomous seismic stations and drilling-explosive works. A total of 264 seismic receivers were involved, (160 DATA-CUBE and 104 TEXAN stations). The average spacing between observation points is about 2.65 km. The sampling interval for all stations was 0.01 s. Seismic energy was generated at 10 shot points (SP) with total charge in all wells 5775 kg. The distance between the SPs was about 50 km.

The main recorded seismic waves are the refractions of P- and S- waves in sediments, basement, crust and uppermost mantle, and reflections from crustal boundaries, Moho interface and boundaries in the uppermost mantle. The correlation picking of their arrival times will allow to build a velocity model not only for P-, but also for S-waves and Vp/Vs ratio.

The main objective of the SHIELD’21 project is to get new seismic data that increase our knowledge on the lithosphere structure and geodynamics of the study region.

 

Starostenko, V., Janik, T., Mocanu, V., Stephenson, R., Yegorova, T., Amashukeli, T., Czuba, W., Środa, P., Murovskaya, A., Kolomiyets, K., Lysynchuk, D., Okoń, J., Dragut, A., Omelchenko, V., Legostaieva, O., Gryn, D., Mechie, J., & Tolkunov, A. (2020). RomUkrSeis: Seismic model of the crust and upper mantle across the Eastern Carpathians — From the Apuseni Mountains to the Ukrainian Shield. Tectonophysics, 794, 228620. https://doi.org/10.1016/j.tec to.2020.228620

How to cite: Janik, T., Starostenko, V., Czuba, W., Środa, P., Murovskaya, A., Yegorova, T., Verpakhovska, A., Kolomiyets, K., Lysynchuk, D., Wójcik, D., Omelchenko, V., Amashukeli, T., Legostaeva, O., Gryn, D., and Chulkov, S.: The SHIELD’21 deep seismic experiment, Ukraine, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2387, https://doi.org/10.5194/egusphere-egu23-2387, 2023.

X2.132
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EGU23-10556
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ECS
Jing Chen, Masaru Nagaso, and Ping Tong

Adjoint-state traveltime tomography (ATT) is a new modality of traveltime tomography for determining subsurface velocity heterogeneity and seismic anisotropy. It formulates the tomographic inverse problem as an eikonal equation-constrained optimization problem solved by the ray-free adjoint-state method. Instead of using the ray-based methods, the theoretical traveltime is predicted by solving the anisotropic eikonal equation in spherical coordinates using the robust grid-based fast sweeping method. The influences of the seismic anisotropy and the Earth’s curvature are taken into account. Besides, the Fréchet derivatives of the objective function with respect to velocity and anisotropy are computed based on the adjoint field obtained by solving the adjoint equation without ray tracing. These two improvements ensure the accuracy of the forward modeling and avoid the potential failure of ray tracing techniques. Meanwhile, compared with wave-equation-based tomography methods, the computational cost of solving eikonal and adjoint equations is drastically cheaper. The usage of the reciprocity principle makes the computation cost nearly independent of the number of earthquakes, enabling the inversion involving massive earthquakes but with moderate computational cost. Due to these advantages, we develop the TomoATT package based on the ATT method, accommodating the tomographic problems on local, regional, and global scales. To be used on high performance computing systems, TomoATT implements a multilevel hybrid parallel algorithm, which utilizes MPI for inter-node parallelization and MPI Shared Memory for intra-node parallelization. The performance on single CPU is also improved using the Single Instruction Multiple Data (SIMD) instructions. This traveltime tomography package has been tested and verified in central California near Parkfield.

How to cite: Chen, J., Nagaso, M., and Tong, P.: TomoATT: A Software Package of Adjoint-State Traveltime Tomography for Imaging Subsurface Velocity Heterogeneity and Seismic Anisotropy., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10556, https://doi.org/10.5194/egusphere-egu23-10556, 2023.

X2.133
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EGU23-6504
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ECS
Yiming Bai, Mohamad Ramdhan, Shun Yang, Tianjue Li, Jing Chen, Masaru Nagaso, and Ping Tong

As one of the most populous regions, Central Java in Indonesia is prone to high seismic and volcanic hazards, mostly due to the progressive northward subduction of the Australian plate beneath the Sunda plate. Detailed velocity structure of the crust and uppermost mantle beneath Central Java is critical for an improved understanding of the subduction processes and the associated seismicity and volcanism. Despite several independent isotropic velocity models proposed for the region, crustal-scale anisotropic structure, which reflects past and ongoing deformation, has rarely been investigated. The reasons behind this include that 1) conventional ray tracing may fail in strongly anisotropic crust, especially in a heterogeneous forearc setting; and 2) reliable anisotropy tomography requires sufficient data coverage, while the existing seismic networks in Central Java are restricted.

In this study, we target on the crustal-scale P-wave azimuthally anisotropic structure beneath Central Java. The acquired seismic data were recorded by more than 200 seismic stations from multiple projects with different execution periods (from 6 months to > 2 years). To make full use of the open access data, machine learning phase picking and subsequent event association and location were applied to build a local earthquake catalog. The machine-learning-based workflow detects more than 1500 events, roughly double the amount by previous manual picking. Notably, the preliminary catalog includes a large number of earthquakes that were located in the offshore areas but were recorded by land stations to the north, resulting in huge back azimuthal gaps and potential bias in earthquake relocation. The current study attempts to involve depth phases, such as sPn and sPg, for more accurate earthquake locations and thus more reliable tomographic images. With the expanded and refined seismicity catalog, a ray-free adjoint-state traveltime tomography package called TomoATT will be used for the 3-D velocity heterogeneity and azimuthal anisotropy beneath Central Java.

How to cite: Bai, Y., Ramdhan, M., Yang, S., Li, T., Chen, J., Nagaso, M., and Tong, P.: Adjoint-state traveltime tomography in Central Java enhanced by a machine-learning-assisted catalog, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6504, https://doi.org/10.5194/egusphere-egu23-6504, 2023.

X2.134
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EGU23-7039
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ECS
Abhisek Dutta and Chandrani Singh

We have studied the spatial variation of body wave (P and S wave) attenuation properties in crust of Bhutan region using small magnitude (2-4 ML) earthquakes. We have used continuous waveform data of 385 local earthquakes recorded by the GANSSER network operated by Swiss Seismological Service at ETH Zurich. Initially, the attenuation quality factors (Qp, Qs) have been estimated using Extended Coda Normalization method for five different frequencies (1.5, 3,6,12,18 Hz) at each station, as well as for two zones (eastern and western Bhutan). Q0 (Q value at 1 Hz) values are found to vary between 21-102 and 43-191 for P wave and S wave respectively for the whole region. We observe Qp = (72 ± 6)f(0.94 ± 0.06) and Qs = (104 ± 6)f(1.03 ± 0.05) for the eastern Bhutan whereas for the western part, Qp = (28 ± 1)f(1.41 ± 0.03) and Qs = (90 ± 5)f(1.07 ± 0.05) are found. Overall, frequency dependent coefficient values indicate the strong frequency dependent nature of Bhutan Himalaya. The spatial maps of Q0 for both waves suggest P-wave attenuates faster in the crust of western Bhutan compared to the eastern part. Paro, located in eastern Bhutan, shows comparatively high attenuation for both P and S waves. Further, azimuthal variation of attenuation properties around each station has been evaluated. The observed results are in good agreement with the tectonic settings of the region. The estimated attenuation properties are well comparable with the tectonically active regions in the world.

How to cite: Dutta, A. and Singh, C.: Lateral variation of body wave attenuation in crust of Bhutan Himalaya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7039, https://doi.org/10.5194/egusphere-egu23-7039, 2023.

X2.135
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EGU23-8214
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ECS
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Highlight
Maria Aurora Natale Castillo and Magdala Tesauro

Exploration and exploitation of natural resources, such as geothermal energy, require a proper understanding of the physical properties of the upper crust, where they are mostly allocated. Indeed, the transition from brittle to ductile deformation (BDT), occurring at these depths, marks a progressive change in crustal rheology and a reduction in the rock’s permeability. Therefore, the characterization of underground conditions is crucial for planning explorative studies in geothermal systems. It has been recently demonstrated that the analysis of the propagation of seismic waves provides information on physical rocks’ behavior and an alternative assessment of the BDT depth [1]. In particular, the decay of the amplitude of the seismic waves (i.e. seismic attenuation), which is usually described by a “quality factor” Q, depends on the seismic frequency, temperature, water content, and grain size of the rocks. Depending on the seismic scale, it could be used as an indicator of subsurface heterogeneities.    

In this study, we investigate the seismic velocity and attenuation sensitivity to the crustal heterogeneities in areas affected by young tectonics and hot thermal conditions. To this aim, we implement a Q seismic tomography in the volcanic system of Krafla. The volcanos of age 0.5–1.8 Myr extend over an area of 21 km by 17 km and are characterized by faults and fissures, which allow water to penetrate and circulate at shallow depths [2] easily. In these geothermal fields, the temperatures, in a range of 400-600 °C at a depth < 5 km [3], make the BDT depth close to the surface.

We apply the method that solves Qp perturbations, using a combination of a spectral decay technique to retrieve the attenuation operator (t*) and tomographic inversion [4]. The distribution of seismic wave velocities is obtained from a 3D tomographic inversion, using 1453 earthquakes detected from a local seismic network (2009-2012) [2]. Qp inversion is performed with the simul2014 algorithm [5], while a linearized technique solves a nonlinear problem that uses a damped least-squares inversion for model perturbations.

We obtain a map of Qp variations for the first 4 km, which we jointly interpret with the seismic wave velocities [2]. In this way, we can discriminate between anomalies related to temperatures and compositional heterogeneities. We also test the possibility to detect the BDT depth on the base of the reduction of the Qp, related to hot temperatures/melt conditions. The obtained results will contribute to understanding the dynamics of the tectonic features and help plan explorative studies of high enthalpy geothermal systems, adding constraints to the correlation between viscous rocks’ deformation and their seismic attenuation.

References

[1] Natale Castillo et al., 2022. Gloplacha 219, 103978, ISSN 0921-8181, https://doi.org/10.1016/j.gloplacha.2022.103978.

[2] Schuler et al., 2015. J. Geophys. Res. Solid Earth 120, 7156–7173, doi:10.1002/2015JB012350.

[3] Scott et al., 2015. Nature communications 6, 7837. 10.1038/ncomms8837. https://doi.org/10.1038/ncomms8837.

[4] Lanza et al., 2020. J. Volc. Geoth. Res. 393, 106804, ISSN 0377-0273. https://doi.org/10.1016/j.jvolgeores.2020.106804

[5] Evans et al., 1994. US Geological Survey Open File Report OFR 94- 431, p. 101. https://doi.org/10.3133/ofr94431

How to cite: Natale Castillo, M. A. and Tesauro, M.: Geophysical characterization of the Krafla volcanic area from seismic tomography and attenuation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8214, https://doi.org/10.5194/egusphere-egu23-8214, 2023.

Posters virtual: Thu, 27 Apr, 08:30–10:15 | vHall GMPV/G/GD/SM

vGGGS.10
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EGU23-7031
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ECS
Sukanta Sarkar, Chandrani Singh, Ashwani Kant Tiwari, M Ravi Kumar, Arun Kumar Dubey, Abhisek Dutta, Gaurav Kumar, and Arun Singh

Seismic attenuation structure of the uppermost mantle is investigated using Sn waves in Bhutan Himalaya. Sn phase is the uppermost mantle-refracted
phase, which travels with a velocity of 4.3 - 4.7 km/s. Visual inspection of all the seismograms are conducted to examine the efficient, inefficient and blocked paths in the region. The inefficient, and blocked S n phases are mainly observed from the western side of our study region. Sn attenuation is determined using the two-station Methodology (TSM ). We have generated 460 station pairs from 1539 seismograms with magnitude ≥ 4 within an epicentral distance of 200 - 1650 km recorded at 38 seismic stations. Furthermore, a 2D Sn Q model is produced to understand the upper mantle rheology of the area. The central part shows a low Q (≤100) value while high Q dominates in northern and western parts of Bhutan Himalaya. The overall results correlate well with the tectonic setting beneath the study region. A comparison study is also made with the adjacent Arunachal Himalaya for better understanding.

How to cite: Sarkar, S., Singh, C., Tiwari, A. K., Kumar, M. R., Dubey, A. K., Dutta, A., Kumar, G., and Singh, A.: Sn attenuation characteristics in the Bhutan Himalaya., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7031, https://doi.org/10.5194/egusphere-egu23-7031, 2023.

vGGGS.11
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EGU23-1574
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ECS
Ziqi Zhang and Tolulope Olugboji

The Earth, in large portions, is covered in oceans, sediments, and glaciers. High-resolution body wave imaging in such environments often suffers from severe reverberations, that is, repeating echoes of the incoming scattered wavefield trapped in the reverberant layer, making interpretation of lithospheric layering difficult. In this study, we propose a systematic data-driven approach, using autocorrelation and homomorphic analysis, to solve the twin problem of detection and elimination of reverberations without a priori knowledge of the elastic structure of the reverberant layers. We demonstrate, using synthetic experiments and data examples, that our approach can effectively identify the signature of reverberations even in cases where the recording seismic array is deployed in complex settings, for example, using data from (1) a land station sitting on Songliao basin, (2) an ocean bottom station in the fore-arc setting of the Alaska amphibious community seismic experiment (AACSE), and (3) a station deployed on ice-sediment strata in the glaciers of Antarctica. The elimination of the reverberation is implemented by a frequency domain filter whose parameters are automatically tuned using seismic data alone. On glaciers where the reverberating sediment layer is sandwiched between the lithosphere and an overlying ice layer, homomorphic analysis is preferable in detecting the signature of reverberation. We expect that our technique will see wide application for high-resolution body wave imaging across a wide variety of conditions.

How to cite: Zhang, Z. and Olugboji, T.: Lithospheric Imaging through Reverberant Layers: Sediments, Oceans, and Glaciers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1574, https://doi.org/10.5194/egusphere-egu23-1574, 2023.