SM5.6

EDI
Imaging, modelling and inversion to explore the Earth’s lithosphere and asthenosphere

This session will cover applied and theoretical aspects of
geophysical imaging, modelling and inversion using active- and
passive-source seismic measurements as well as other geophysical
techniques (e.g., gravity, magnetic and 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;
- 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.

Co-organized by GD9/GI2/TS12
Convener: Milena Marjanovic | Co-conveners: Monika Ivandic, Andrzej GórszczykECSECS, Pascal Edme, Laura Gómez de la Peña, Matthew Agius
Presentations
| Wed, 25 May, 08:30–11:50 (CEST)
 
Room D3

Presentations: Wed, 25 May | Room D3

Chairpersons: Andrzej Górszczyk, Matthew Agius
08:30–08:34
Controlled source and earthquake tomography
08:34–08:44
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EGU22-8121
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ECS
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solicited
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On-site presentation
Benedikt Braszus, Saskia Goes, Rob Allen, Andreas Rietbrock, and Jenny Collier and the VoiLA Team

Even though the Caribbean region is constantly struck by the impact of geological hazards, the details of the Caribbean plate's evolution are still not completely understood. This interdisciplinary study combines and jointly interprets seismic tomography data with trench positions derived from plate reconstruction which constrains some of the most important events governing the evolution of the Caribbean plate. 
Our new teleseismic P-wave tomography model of the upper mantle beneath the Caribbean includes manually processed and analysed data from 32 ocean-bottom seismometers installed for 16 months during the VoiLA experiment as well as recordings from 192 permanent and temporary land stations. Reconstruction tests show improved resolution compared to previous models and a sufficient recovery of a synthetic anomaly assimilating the Caribbean slab. 
Based on reconstructed trench positions we attribute slab fragments residing in depths of 700-1200km to 90–115 Myr old westward subduction along the Great Arc of the Caribbean (GAC) prior to Caribbean Large Igneous Province volcanism, rather than to eastward dipping Farallon subduction. 
In the mantle transition zone, the imaged slab coincides with predicted trench positions from 50-70 Ma with a slab window approximately at the location of the subducted Proto-Caribbean spreading ridge.
Along the otherwise continous slab in the shallow upper mantle from Hispanola to Grenada several tears are interpreted as ruptures along fault zones in the Proto-Caribbean crust as well as the subducted extinct Proto-Caribbean spreading ridge. 

How to cite: Braszus, B., Goes, S., Allen, R., Rietbrock, A., and Collier, J. and the VoiLA Team: Subduction history of the Caribbean from upper-mantle seismic imaging and plate reconstruction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8121, https://doi.org/10.5194/egusphere-egu22-8121, 2022.

08:44–08:50
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EGU22-562
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ECS
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On-site presentation
Franck Latallerie, Christophe Zaroli, Sophie Lambotte, and Alessia Maggi

Tomographic models suffer from unevenly distributed noisy data and therefore have complicated resolution and uncertainties that can hinder their interpretation. Using linear Backus & Gilbert inversion, it is possible to obtain tomographic models with resolution and uncertainties in a single step. Using such a method, we aim to produce a three-dimensional tomographic model of the Pacific upper mantle from surface-wave data. To linearise the forward problem, we use finite-frequency theory to describe the sensitivity of surface-wave phase-delays to the three-dimensional shear-wave velocity. We build a data-base of phase-delay measurements for surface-waves that cross the Pacific Ocean. We estimate the data uncertainties caused by measurement errors using a multitaper technique and those caused by poor knowledge of the seismic source and crust by a Monte-Carlo method. Using the Backus & Gilbert approach, the phase-delay dataset, and the data uncertainty estimates, we obtain a model of the shear-wave velocity of the Pacific upper mantle together with its three-dimensional resolution and uncertainties. These allow us to discuss, using robust statistical arguments, the existence and the three-dimensional organisation of structures we expect to see in the Pacific upper mantle, such as plume-like upwellings or small-scale sub-lithospheric convections.

How to cite: Latallerie, F., Zaroli, C., Lambotte, S., and Maggi, A.: Toward a three-dimensional tomographic model of the Pacific upper mantle with full resolution and uncertainties, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-562, https://doi.org/10.5194/egusphere-egu22-562, 2022.

08:50–08:56
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EGU22-3507
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Virtual presentation
Natalia Bushenkova, Olga Bergal-Kuvikas, Evgeny I. Gordeev, Danila Chebrov, Ivan Koulakov, Ilyas Abkadyrov, Andrey Jakovlev, Tatiana Stupina, Angelika Novgorodova, and Svetlana Droznina

The strongest earthquakes and the largest explosive eruptions are confined to plate convergent boundaries. Many geodynamics aspects attract the scientific community's attention since answers to the most important questions cannot be obtained without reliable information about the deep structure. Geophysical studies of the crust and mantle provide essential information for lithospheric blocks interactions, mantle convection and fluid migration. This data is necessary to identify reliable criteria for assessing volcanic and seismic risk.

The studied area is central Kamchatka, where the cities of Petropavlovsk-Kamchatsky, Elizovo, and Vilyuchinks are located. It includes territory from the Gorely and Mutnovsky volcanoes in the south to the Bakening volcano and the Verkhneavachinskaya caldera in the north. It extends from the eastern to the western peninsula coasts. The study area includes the Avachinskaya group of volcanoes, the Vilyuchinsky and Zhupanovsky volcanoes, Karymshina caldera and a number of monogenic cinder cones. This region is assumed to be located at a transition between two principle different subduction regimes in the north and south of Kamchatka. Previous studies are sparse and have poor resolution due to the low density and uneven distribution of seismic stations.

In this study, we used a large dataset recorded by a new dense temporary network deployed in 2019-2020, which was specially designed for performing high-quality seismic tomographic studies of the suprasubduction complex structure (crust and upper mantle) beneath central Kamchatka. This dataset was supplemented by data recorded by (1) the temporary network operated on the Avachinskaya group of volcanoes in 2018-2019 and (2) the permanent stations Kamchatka branch of the Federal Research Center of the GS RAS. The seismic model is based on the data from 2687 local earthquakes that occurred during the operation of the mentioned temporary networks and were recorded by 134 regional stationary and temporary stations. In the tomographic inversion we used 59088 travel times of P-waves and 34697 of S-waves.

The new model makes it possible to trace zones of fluid and melt release from the slab, their migration in the mantle wedge and crust, and allows assessing their role in feeding the magmatic systems. Volcanoes of the Avachinskaya group have a common magma plumbing system at a depth more than 50 km, which could be traced from the slab. The Vilyuchinsky volcano feds through an intermediate large magma chamber located at a depth of 30-55 km, which is also related to the feeding of the Bolshebannaya hydrothermal system situated to the west. This large chamber fed from a conduit originated on the slab at more than 70 km depth. The feeding system of the Gorely and Mutnovsky volcanoes is traced to the slab at depths of more than 100 km.

This work was supported by the Russian Science Foundation (project No. 22-27-00215) and the Ministry of Education and Science of the Russian Federation (megagrant No. 14.W03.31.0033). 

How to cite: Bushenkova, N., Bergal-Kuvikas, O., Gordeev, E. I., Chebrov, D., Koulakov, I., Abkadyrov, I., Jakovlev, A., Stupina, T., Novgorodova, A., and Droznina, S.: Seismotomographic structure of the central zone of Kamchatka suprasubduction complex according to the dense seismological networks data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3507, https://doi.org/10.5194/egusphere-egu22-3507, 2022.

Ambient noise, receiver functions, etc.
08:56–09:02
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EGU22-2459
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ECS
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Presentation form not yet defined
Fabrizio Magrini, Luca De Siena, Simone Pilia, Nicholas Rawlinson, and Boris Kaus

South-East Asia hosts the largest and most complicated subduction system of our planet, associated with extensive volcanism and seismicity. Obtaining high-resolution seismic images of South-East Asia can provide important constraints on the lateral variations of physical parameters such as density, composition, temperature, and viscosity of this dynamic patchwork. In turn, this has relevant implications on our ability to forecast its geodynamic evolution by numerical modeling. In this study, we join all the publicly-available seismic data distributed across the Malay Peninsula, Sumatra, Java, Sulawesi, South Borneo, and North Australia (amounting of 468 broad-band seismic receivers) with the continuous seismograms from 70 receivers recently installed in North Borneo, resulting in an unprecedented seismic coverage of the region.
We first use such data to extract Rayleigh and Love phase velocities based on both seismic ambient noise and teleseismic earthquakes. Overall, we retrieve 14,036 Rayleigh- and 12,005 Love-wave dispersion curves, covering surface-wave periods between 3 and 150 s and sensitive to both the shallow crust and the upper mantle. We then invert the dispersion curves for phase-velocity maps at different periods, using a linearized-inversion algorithm based on the ray theory with a roughness damping constraint. In doing so, we adopt an adaptive parameterization, allowing for a finer resolution of the resulting maps in the areas characterized by a relatively high density of measurements. At relatively short periods (<20 s), the phase-velocity maps are characterized by strong lateral heterogeneities. We find, for example, relatively low velocities in correspondence of the Central- and South-Sumatra Basin, ascribed to thick sedimentary layers, and higher velocities in the (adjacent) Barisan Mountains. Low velocities also characterize a large region approximately centered onto the Merapi volcano (Central Java), the Mentawai islands (in correspondence of the Mentawai Fault System), the Sahul Shelf (including the East Timor island), and the marine region between east Borneo and Sulawesi. Relatively high velocities are found below the Banda Sea. The amplitude of such lateral variations quickly decreases at larger periods and, among the most pronounced features, we observe relatively low velocities in the north-east of Borneo (as opposed to its south-western part), and high velocities in the Celebes Sea (north of the North-Sulawesi Trench).
At the time of writing, we are planning to translate the phase-velocity maps thus retrieved into shear-wave velocity (Vs) as a function of depth. Specifically, we plan to extract one Rayleigh- and one Love-wave phase-velocity profile for each grid cell constituting our phase-velocity maps, and (non-linearly) jointly invert them for Vs using the neighbourhood algorithm. The resulting 3-D tomographic model will thus be interpreted in light of the existing literature on the study area, involving (but not limited to) geodynamic and geologic models, geophysical, geochemical, and geodetic observations.

How to cite: Magrini, F., De Siena, L., Pilia, S., Rawlinson, N., and Kaus, B.: Surface-wave tomography of the South-East Asia by joint inversion of Rayleigh and Love phase velocities from seismic ambient noise and teleseismic earthquakes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2459, https://doi.org/10.5194/egusphere-egu22-2459, 2022.

09:02–09:08
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EGU22-7668
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ECS
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On-site presentation
Joseph Fone, Simone Pilia, Nicholas Rawlinson, and Song Hou

Given that subduction is an important driver of plate tectonics on Earth, it is notable that the effects of subduction termination are often complex and poorly understood. Northern Borneo is a prime example of a post-subduction environment, where two subduction zones have terminated within the last 20 Ma. The region however has seen very few seismic studies likely due to the low levels of seismicity in the region compared to the rest of Southeast Asia and due to the challenging deployment environment. The goal of the northern Borneo Orogeny Seismic Survey (nBOSS) network, which operated between 2018 and 2020 and consisted of 47 broadband instruments, was to provide constraints and answer first order questions about the structure of the lithosphere and asthenosphere in this post-subduction setting. Waveform data from this network were supplemented with data recorded by 33 permanent instruments operated by the Malaysian meteorological authority, METMalaysia. In this study we produce the first model of the crustal shear wave velocity structure under northern Borneo using surface wave ambient noise tomography to try and better understand the effects of subduction termination on the crust and to better understand the present day structure of the crust in this region which has not been imaged in this way before. We use a trans-dimensional tomography to produce variable resolution 2D Rayleigh wave phase velocity maps in the period range 2-30 seconds sampled every 2 seconds. Then to produce the final 3D shear wave velocity model a series of 1D inversions were used in combination with a neural network that is trained to find a generalised solution to the 1D inverse problem for this data set. This helps to prevent artefacts forming in the final model as a result of there being no lateral correlations in the 1D inversions by providing the more region specific trained neural network to perform the bulk of the 1D inversions. The result is a model that shows a detailed 3D shear wave velocity structure of the crust that matches expected velocity anomalies from known geological features. This includes the large sedimentary basins in the region, which are revealed as large slow velocity anomalies. Our new model agrees with results from other methods used to study this region, including receiver functions and surface wave tomography.

How to cite: Fone, J., Pilia, S., Rawlinson, N., and Hou, S.: Ambient noise tomography of post-subduction setting in northern Borneo enhanced with machine learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7668, https://doi.org/10.5194/egusphere-egu22-7668, 2022.

09:08–09:14
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EGU22-6235
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ECS
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Presentation form not yet defined
Kamila Karkowska, Monika Wilde-Piórko, Przemysław Dykowski, Marcin Sękowski, and Marcin Polkowski

Gravimetric data show excellent capabilities in long-period seismology. Tidal gravimeters can detect surface waves of periods even up to 500-600 s, while a typical broad-band seismic sensor, due to its mechanical limitation, can detect them only up to the periods of 200-300 s. Consequently, gravimetric data can complement seismic recordings for longer periods, depending on what seismometer the station is equipped with and what seismometer’s cut-off period is. A superconducting gravimeter can act as a single-dimension (only vertical component) of a very broad-band seismometer. 

We selected over a dozen stations worldwide with co-located typical broad-band seismic sensors and superconducting gravimeters. A time series from broad-band seismometers have been downloaded from Incorporated Research Institutions for Seismology (IRIS) database. The raw gravimetric data (1-Hz or 1-min) are available in the International Geodynamics and Earth Tide Service (IGETS) database. Some of the data were made available courtesy of the station’s operators. 

This study presents a joint analysis of the gravimetric and seismometric data to determine group-velocity dispersion curves of Rayleigh surface waves. We created a database of recordings of earthquakes for all stations and instruments. Following, we calculated the individual group-velocity dispersion curves of fundamental-mode Rayleigh waves. Simultaneous seismic and gravity recordings at the same location allow exploring a broader response for incoming seismic waves. In this way, one joint group-velocity dispersion curve of Rayleigh surface waves for a broader range of periods has been estimated for all stations. All curves were then inverted by linear inversion and Monte Carlo methods to calculate a distribution of shear-wave seismic velocity with depth in the Earth’s mantle.    

This work was done within the research project No. 2017/27/B/ST10/01600 financed from the Polish National Science Centre funds.

How to cite: Karkowska, K., Wilde-Piórko, M., Dykowski, P., Sękowski, M., and Polkowski, M.: Exploring the Earth's mantle structure based on joint gravimetric and seismometric group-velocity dispersion curves of Rayleigh waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6235, https://doi.org/10.5194/egusphere-egu22-6235, 2022.

09:14–09:20
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EGU22-4870
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On-site presentation
Matthew Agius, Fabrizio Magrini, Giovanni Diaferia, Emanuel Kastle, Fabio Cammarano, Claudio Faccenna, Francesca Funiciello, and Mark van der Meijde

The evolution of the Sicily Channel Rift Zone (SCRZ), located south of the Central Mediterranean, is thought to accommodate the regional tectonic stresses of the Calabrian subduction system. It is unclear whether the rifting of the SCRZ is passive from far-field extensional stresses or active from mantle upwelling beneath. To map the structure and dynamics of the region, we measure Rayleigh- and Love-wave phase velocities from ambient seismic noise and invert for an isotropic 3-D shear-velocity and radial anisotropic model. Variations of crustal S-velocities coincide with topographic and tectonic features: slow under high elevation, fast beneath deep sea. The Tyrrhenian Sea has a <10 km thin crust, followed by the SCRZ (∼20 km). The thickest crust is beneath the Apennine-Maghrebian mountains (∼50 km). Areas experiencing extension and intraplate volcanism have positive crustal radial anisotropy (VSH>VSV); areas experiencing compression and subduction-related volcanism have negative anisotropy (VSH<VSV). The crustal anisotropy across the Channel shows the extent of the SW-NE extension. Beneath the Tyrrhenian Sea, we find very low sub-Moho S-velocities. In contrast, the SCRZ has a thin mantle lithosphere underlain by a low-velocity zone. The lithosphere-asthenosphere boundary rises from 40-60 km depth beneath Sicily and Tunisia to ∼33 km beneath the SCRZ. Upper mantle, negative radial anisotropy beneath the SCRZ suggests vertical mantle flow. We hypothesize a more active mantle upwelling beneath the rift than previously thought from an interplay between poloidal and toroidal fluxes related to the Calabrian slab, which in turn produces uplift at the surface and induces volcanism.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 843696.

How to cite: Agius, M., Magrini, F., Diaferia, G., Kastle, E., Cammarano, F., Faccenna, C., Funiciello, F., and van der Meijde, M.: Shear-velocity structure and dynamics beneath the Central Mediterranean inferred from seismic surface waves , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4870, https://doi.org/10.5194/egusphere-egu22-4870, 2022.

09:20–09:26
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EGU22-4037
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Virtual presentation
Volker Michel, Naomi Schneider, Karin Sigloch, and Eoghan Totten

The three-dimensional structure of the Earth's interior shapes its geomagnetic and gravity fields, and can thus be constrained by observing these fields. 3-D Earth structure also causes seismological observables to deviate from those predicted for approximated, spherically symmetrical reference models. Travel time tomography is the inverse problem that uses these observed differences to constrain the 3-D structure of the interior.
On the planetary scale, i.e. in a spherical geometry, this linearized inverse problem has been parameterized with a variety of basis systems, either global (e.g. spherical harmonics) or local (e.g. finite elements). The Geomathematics Group Siegen has developed alternative approximation methods for certain applications from the geosciences: the Inverse Problem Matching Pursuits (IPMPs). These methods combine different basis systems by calculating an approximation in a so-called best basis, which is chosen iteratively from a so-called dictionary, an intentionally overcomplete set of diverse trial functions. In each iteration, the choice of the next best basis element reduces the Tikhonov functional. A particular numerical expertise has been gained for applications on spheres or balls. Hence, the methods were successfully applied to, for instance, the downward continuation of the gravitational potential as well as the MEG-/EEG-problem from medical imaging.
Our aim is to remodel the IPMPs for travel time tomography. This includes developing the data-dependent operator, deciding for specific trial functions and applying the operator to them. We also have to define termination criteria and develop the regularization in theory and practice. We introduce the IPMPs and show results from our remodelling.

How to cite: Michel, V., Schneider, N., Sigloch, K., and Totten, E.: Ray theoretical investigations using matching pursuits, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4037, https://doi.org/10.5194/egusphere-egu22-4037, 2022.

09:26–09:32
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EGU22-3755
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ECS
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On-site presentation
Theresa Rein, Zahra Zali, Frank Krüger, and Vera Schlindwein

Ultra-slow spreading ridges are characterized by huge volcanic complexes which are separated by up to 150 km long amagmatic segments. The mechanisms controlling the ultra-slow spreading ridges are not yet fully understood. With the aim to better understand the spreading mechanisms and the flow of the magma beneath the volcanic complexes an ocean-bottom array has been installed along a segment of the ultra-slow spreading Knipovich Ridge in the Greenland sea. The array consists of 23 LOBSTER-type ocean bottom seismometers (OBS) from the DEPAS pool and 5 LOBSTERs from the Institute of Geophysics of the Polish Academy of Sciences. We aim to constrain the crustal and mantle structure beneath the segment of the Knipovich Ridge by using receiver functions calculated from teleseismic events.

Seismic data, recorded on the ocean bottom, are highly contaminated by different noise sources, which are dominating at frequencies below 1 Hz. During the experiment the DEPAS-LOBSTERs were equipped with a MCS recorder and a Güralp CMG-40T seismometer (changed now to 6D6 recorder and Trillium Compact seismometer). This characteristic design introduces electronic noise at selected stations at frequencies below 0.2 Hz. Recently head-buoy-strumming has been identified as additional noise source at frequencies above 0.5 Hz during tidal currents. Hence, most teleseismic signals are masked by the high noise level, especially on the horizontal components. However, a good signal to noise ratio on both, the vertical and horizontal components is crucial for seismological analysis, especially the receiver function method. Applying the HPS noise reduction algorithm on OBS data, as shown by Zali et al (submitted in 2021), allows to separate percussive or transient signals, such as the teleseismic earthquake from more harmonic and monochromatic signals, such as most of the noise generated at the ocean bottom.

The results of the HPS noise reduction algorithm processing of selected KNIPAS station data show a significantly reduced noise level below 1 Hz on all seismogram components, especially on the horizontals. Here, the signal-to-noise ratio increased by up to 3.2-3.7 (average by 1.4-1.6). The increased signal-to-noise ratio on the noise reduced data allows for more reliable receiver function results and their interpretation. Here, we show the reduced noise level on the OBS data and compare the receiver function results calculated from original data with the results from noise-reduced data.

How to cite: Rein, T., Zali, Z., Krüger, F., and Schlindwein, V.: Receiver Function analysis of noise reduced OBS data recorded at the ultra-slow spreading Knipovich Ridge, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3755, https://doi.org/10.5194/egusphere-egu22-3755, 2022.

09:32–09:38
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EGU22-4477
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ECS
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Presentation form not yet defined
Raffaele Bonadio, Sergei Lebedev, Thomas Meier, Pierre Arroucau, Andrew J. Schaeffer, Andrea Licciardi, Matthew R. Agius, Clare Horan, Louise Collins, Brian M. O'Really, Peter W. Readman, and Ireland Array Working Group

The maximum achievable resolution of a tomographic model varies spatially and depends on the data sampling and errors in the data. The significant and continual measurement-error decreases in seismology and data-redundancy increases have reduced the impact of random errors on tomographic models. Systematic errors, however, are resistant to data redundancy and their effect on the model is difficult to predict; often this results in models dominated by noise if the target resolution is too high. Here, we develop a method for finding the optimal resolving length at every point, implementing it for surface-wave tomography. As in the Backus-Gilbert method, every solution at a point results from an entire-system inversion, and the model error is reduced by increasing the model-parameter averaging. The key advantage of our method consists in its direct, empirical evaluation of the posterior model error at a point.

We first measure interstation phase velocities at simultaneously recording station pairs and compute phase-velocity maps at densely, logarithmically spaced periods. Numerous versions of the maps with varying smoothness are then computed, ranging from very rough to very smooth. Phase-velocity curves extracted from the maps at every point can be inverted for shear-velocity (VS) profiles. As we show, errors in these phase-velocity curves increase nearly monotonically with the map roughness. We evaluate the error by isolating the roughness of the phase-velocity curve that cannot be explained by any Earth structure and determine the optimal resolving length at a point such that the error of the local phase-velocity curve is below a threshold.

A 3-D VS model is then computed by the inversion of the composite phase-velocity maps with an optimal resolution at every point. Importantly, the optimal resolving length does not scale with the density of the data coverage: some of the best-sampled locations display relatively low lateral resolution, due to systematic errors in the data.

We apply this method to image the lithosphere and underlying mantle beneath Ireland and Britain. Our very large data produces a total of 11238 inter-station dispersion curves, spanning a very broad total period range (4–500 s), yielding unprecedented data coverage of the area and providing state-of-the-art regional resolution from the crust to the deep asthenosphere. Our tomography reveals pronounced, previously unknown variations in the lithospheric thickness beneath Ireland and Britain, with implications for their Caledonian assembly and for the mechanisms of the British Tertiary Igneous Province magmatism.

How to cite: Bonadio, R., Lebedev, S., Meier, T., Arroucau, P., Schaeffer, A. J., Licciardi, A., Agius, M. R., Horan, C., Collins, L., O'Really, B. M., Readman, P. W., and Working Group, I. A.: Optimal resolution tomography with error tracking and the structure of the crust and upper mantle beneath Ireland and Britain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4477, https://doi.org/10.5194/egusphere-egu22-4477, 2022.

09:38–09:44
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EGU22-2686
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On-site presentation
Panayiota Sketsiou, David Cornwell, and Luca De Siena

The North Anatolian Fault (NAF) is a right-lateral, strike-slip fault in the northern part of the Anatolian peninsula. It is estimated to have a length of up to 1500 km, extending westwards between the Karliova Triple Junction, where it nucleates, to the Aegean Sea. In the west and close to the Sea of Marmara, the NAF splays into northern (NNAF) and southern (SNAF) strands. The splay of the western part of the NAF separates the area into three primary terranes: the Istanbul Zone (north of the northern strand), the Armutlu-Almacik Block (between the two strands of the fault) and the Sakarya Zone (south of the southern strand).

There have been a series of high-magnitude earthquakes along the NAF since the 1930s, migrating from east to west. In order to investigate the western part of the North Anatolian Fault Zone (NAFZ), which is the most seismically active at the moment, the Dense Array for North Anatolia (DANA) temporary seismic network was deployed for 18 months between 2012 and 2013. A set of local earthquakes, recorded by DANA, were utilised to study the 2D scattering and coda attenuation structure in the western NAFZ, between 1 and 18 Hz. P-wave arrival times were manually picked and the events were re-located using the Non-Linear Location software. Peak-delay travel times were calculated as a measure of forward scattering, and the exponential decay of the coda wave envelopes was used to invert for the absorption structure using multiple scattering sensitivity kernels.

The obtained models are 2D averages of the first 10-15 km of the crust, where the majority of the seismic activity is located and they have been compared to recent geophysical studies in the same area. The scattering structure, between 1 and 6 Hz, highlights the three main tectonic units in the area. The absorption structure is generally more heterogeneous than the scattering structure, with the overall absorption decreasing as the frequency increases. The lithological variations and heterogeneity between and within the three terranes of the area, arising from the complex tectonic history of the region, are believed to be the main reasons for the scattering and absorption observations made. The high absorption zones observed along the two branches of the fault, and especially the southern branch, is a very important finding, as the signature of the southern branch in geophysical studies is often unclear.

How to cite: Sketsiou, P., Cornwell, D., and De Siena, L.: Scattering and Absorption Imaging of the North Anatolian Fault Zone, northern Turkey, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2686, https://doi.org/10.5194/egusphere-egu22-2686, 2022.

09:44–09:50
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EGU22-3257
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ECS
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On-site presentation
Claire Doody, Arthur Rodgers, Christian Boehm, Michael Afanasiev, Lion Krischer, Andrea Chiang, and Nathan Simmons

Full waveform inversion models by adjoint methods represent the most detailed seismic tomography models currently available for waveform simulations. However, the influence of starting models on final inversion results is rarely studied due to computational expense. To study this influence, we present three adjoint waveform tomography models of California and Nevada using three different starting models:  the SPiRaL global model (Simmons et al., 2021), the CSEM_NA model (Krischer et al., 2018), and the WUS256 model (Rodgers et al., 2021). Each model uses the same dataset of 103 events between magnitudes 4.5 and 6.5 that occurred from January 1, 2000 to October 31st, 2020. For each event, 175-475 stations record data, creating dense path coverage over California. The model iterations are computed using Salvus. We begin by  running iterations for each starting model at three period bands: 30-100 seconds, 25-100 seconds, and 20-100 seconds. For each period band, we run iterations until the average misfit for all events is no longer reduced; over all period bands, we run more than 55 iterations and see misfit reductions of up to 40% in some period bands. Each model shows velocity anomalies of up to 20%, but the difference in VS values between the models can be significant. Most of these differences seem to correlate with small-scale differences in the starting models. To test whether these differences between the models could affect the interpretation of their results, we utilize k-means clustering to analyze the similarities in large-scale structure in all three models (e.g. Lekic and Romanowicz, 2011). We separate each model into a crustal layer (0-30km depth) and uppermost mantle layer (30-150km), then run a k-means clustering algorithm on absolute Vs wavespeeds and anisotropy [(Vsh/Vsv)^2] separately. We show that regardless of the differences seen on visual inspection, all three models can resolve tectonic-scale structures equally.

 

This work was supported by LLNL Laboratory Directed Research and Development project 20-ERD-008. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-830615.

How to cite: Doody, C., Rodgers, A., Boehm, C., Afanasiev, M., Krischer, L., Chiang, A., and Simmons, N.: Using K-Means Clustering to Compare Adjoint Waveform Tomography Models of California and Nevada, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3257, https://doi.org/10.5194/egusphere-egu22-3257, 2022.

09:50–09:56
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EGU22-6428
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ECS
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Virtual presentation
Xuebin Zhao, Andrew Curtis, and Xin Zhang
The ultimate goal of a scientific investigation is usually to find answers to specific questions: what is the size of a subsurface body? Does a hypothesised subsurface feature exist? Which competing model is most consistent with observations? The answers to these and many other questions are low-dimensional, yet must often be inferred from high-dimensional models and data. To address the questions, existing information is reviewed, an experiment is designed and performed to acquire new data, and the most likely answer is estimated. Typically the answer is interpreted from geological and geophysical data or models, but is biased because only one particular forward function (model-data relationship) is considered, one inversion method is applied, and because human interpretation is a biased process. Interrogation theory provides a systematic way to answer specific questions using statistically unbiased estimators. It combines forward, design, inverse and decision theory, and focuses them to maximise information on the space of possible answers.

This study estimates the volume of the East Irish Sea sedimentary basins in the UK using 3D shear wave speed models derived from surface wave dispersion inversions. In order to answer volume-related questions, it is first necessary to define a target function that translates any (high-dimensional) model into (1-dimensional) volumes of interest. A key revelation of this study is that while the majority of computation may be spent solving inverse problems probabilistically, much of the skill and human effort involved in answering real-world questions may be spent defining and calculating those target function values in a clear and unbiased manner.

How to cite: Zhao, X., Curtis, A., and Zhang, X.: Interrogating the volume of the East Irish Sea sedimentary basins using probabilistic tomographic results, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6428, https://doi.org/10.5194/egusphere-egu22-6428, 2022.

09:56–10:00
Coffee break
Chairpersons: Matthew Agius, Andrzej Górszczyk
Waveform modeling
10:20–10:26
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EGU22-8319
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ECS
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On-site presentation
Xin Zhang, Muhong Zhou, Angus Lomas, York Zheng, and Andrew Curtis

Seismic full-waveform inversion (FWI) produces high resolution images of the subsurface by exploiting information in full seismic waveforms, and has been applied at global, regional and industrial spatial scales. FWI is 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 model. In addition, the optimization methods cannot produce accurate uncertainty estimates, which are required to better interpret the results.

To estimate uncertainties more accurately, nonlinear Bayesian methods have been deployed to solve the FWI problem. Monte Carlo sampling is one such algorithm but it is computationally expensive, and all Markov chain Monte Carlo-based methods are difficult to parallelise fully. Variational inference provides an efficient, 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 (VFWI) have been applied previously to solve 2D FWI problems, but neither of them have been applied to 3D FWI. In this study we apply the VFWI method to a 3D FWI problem. Specifically we use Stein variational gradient descent (SVGD) method to solve the 3D Bayesian FWI problem and to obtain an optimised set of samples of the full posterior probability distribution. The aim of this study is to explore performance of the method in 3D, to assess the computational requirements and to provide useful information for practitioners. Our results demonstrate that the 3D VFWI is practical, at least for small problems, and can be applied to image the subsurface in reality.

How to cite: Zhang, X., Zhou, M., Lomas, A., Zheng, Y., and Curtis, A.: 3D Variational Full-Waveform Inversion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8319, https://doi.org/10.5194/egusphere-egu22-8319, 2022.

10:26–10:32
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EGU22-6399
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Presentation form not yet defined
Ariane Lanteri, Lars Gebraad, Andrea Zunino, and Andreas Fichtner

We present a probabilistic approach to constrain the density distribution in the Earth based on surface wave dispersion. Despite its outstanding importance in studies of the Earth’s thermo-chemical state and dynamics, 3D density variations remain poorly known, thereby posing one of the major challenges in geophysics.

Since the sensitivity of most seismic data to density is small compared to sensitivity with respect to seismic velocities, regularisation in traditional deterministic inversion tends to bias the recovered density image significantly. To avoid this issue, we propose to solve a regularisation-free Bayesian inference problem using the Hamiltonian Monte Carlo Markov Chain algorithm.

In the interest of simplicity, we consider anisotropic stratified media, where dispersion curves and corresponding sensitivity kernels can be computed semi-analytically. Exploiting derivative information for efficient sampling, Hamiltonian Monte Carlo approximates the posterior probability density of all model parameters, namely the P-wave velocities vPV and vPH , the S-wave velocities vSV and vSH , the anisotropy parameter η, and, of course, density ρ.

The proposed method forms the foundation of an open-source tool box that can be used to assess the unbiased ability of surface wave dispersion data, characterised in terms of frequency and modal content, to constrain density variations and their trade-offs with other Earth model parameters.

How to cite: Lanteri, A., Gebraad, L., Zunino, A., and Fichtner, A.: Hamiltonian Monte Carlo Inversion of Surface Wave Dispersion to Evaluate their Potential to Constrain the Density Distribution in the Earth., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6399, https://doi.org/10.5194/egusphere-egu22-6399, 2022.

10:32–10:38
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EGU22-6709
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Presentation form not yet defined
Benchmarking Automated Rayleigh-Wave Arrival Angle Measurements for USArray Seismograms
(withdrawn)
Gabi Laske, William Frazer, and Adrian Doran
10:38–10:44
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EGU22-6893
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Presentation form not yet defined
yder masson

We present the theory and applications of the Distributional Finite Difference Method (DFD). The DFD method is an efficient tool for modeling the propagation of elastic waves in heterogeneous media in the time domain. It decomposes the modeling domain into multiple elements that can have arbitrary sizes. When using large elements, the DFD algorithm resembles the finite difference method because the wavefield is updated using operations involving band diagonal matrices only. This makes the DFD method computationally efficient. When small elements are employed, the DFD method permits to mesh complicated structures as in the finite element or the spectral element methods. We present numerical examples showing that the proposed algorithm accurately accounts for free surfaces, solid-fluid interfaces and accommodates non-conformal meshes. Seismograms obtained using the proposed method are compared to those computed using analytical solutions and the spectral element method. The DFD method requires fewer points per wavelength (down to 3) than the spectral element method (5 points per wavelength) to achieve comparable accuracy. We present examples demonstrating the advantages of the DFD method for modeling wave propagation in the Earth at the global and regional scales. 

How to cite: masson, Y.: Modeling seismic wave propagation in the earth using the distributional finite difference method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6893, https://doi.org/10.5194/egusphere-egu22-6893, 2022.

10:44–10:50
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EGU22-5885
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ECS
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Virtual presentation
Dibyajyoti Chaudhuri, Ayon Ghosh, Shubham Sharma, and Supriyo Mitra

We present maps to show the lateral variation of Lg coda attenuation at 1-Hz across India, Himalaya and Tibet. We use vertical component waveforms from regional earthquakes (epicentral distance<3500 km and Mw>5) recorded by the IISER-K seismological network, ones operated by the Indian Meteorological Department, and data acquired from the IRIS-DMC. Lg-coda waves are modeled as single back-scattered energy, sampling an ellipsoidal volume. The attenuation of Lg-coda is quantified using the quality factor (Q), which is frequency dependent. We use the stacked spectral ratio (SSR) method to calculate the single-trace Lg-coda Q at 1 Hz (Qo) and its frequency dependence (η). A moving-window stack of scaled-logarithmic ratios of spectral amplitudes, for window length of 25.6 s and different central lapse time, is computed for each frequency. Through a linear regression of log (stacked spectral ratio) and log (frequency), using least-squares fitting, we obtain (1-η) and log(Qo), respectively. Lg-coda is selected in a frequency range of 0.2-5 Hz, with coda window starting at 3.15 km/s. Our total coda window lengths vary between 140 s to 780 s. Our preliminary results show low Q values (~200-400) in the Eastern and Western Himalaya - possibly because of scattering of seismic energy from structural heterogeneities. Most of the Indian Shield and the intraplate regions of Shillong Plateau and Brahmaputra valley are characterized by intermediate to high Q values (~600-800), indicating fairly efficient propagation of seismic energy. Intermediate values of Q (~400-500) occur in the Indo-Burman Ranges which may be due to the cold elastic subducting oceanic lithosphere. Patches of low Q in the Tibetan Plateau (~200) are possibly the result of high temperatures and partial melts present in the crust. Our results show how the nature of the Indian Plate changes as we go from an active continent-continent collision zone in the north to eastward subduction of transitional material at the Indo-Burma ranges. Our plots of Qo and η as a function of epicentral distance, coda length and magnitude show no systematic variations.



How to cite: Chaudhuri, D., Ghosh, A., Sharma, S., and Mitra, S.: Seismic Attenuation of India, Himalaya and Tibet using Lg-coda waves, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5885, https://doi.org/10.5194/egusphere-egu22-5885, 2022.

10:50–10:56
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EGU22-1920
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ECS
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Presentation form not yet defined
Chiara Nardoni, Luca De Siena, Fabio Cammarano, Fabrizio Magrini, and Elisabetta Mattei

When seismic information is used to map Earth structures, a primary challenge is modelling the response of seismic wavefields to strong lateral variations in medium properties. These variations are especially relevant across oceanic basins with mixed continental-oceanic crust and including magmatic systems. These highly-scattering and absorption media produce stochastic signatures that are hard to separate from complex coherent reverberations due to shallow Moho. The discrimination between these two effects is fundamental for improving full-waveform techniques when imaging oceanic basins at regional and global scales. Here, we present a joint tomographic and modelling approach focusing on the ~1 Hz frequency band, where seismic scattering and attenuation mechanisms are predominantly resonant. Firstly, we image late-time coda attenuation as a marker of seismic absorption across the Italian peninsula and the Tyrrhenian Sea. Regional-scale data provide the ideal benchmark to explore the potential of attenuation imaging using radiative-transfer-derived sensitivity kernels in a mixed continental-oceanic crust. Then, we explore the response of seismic wavefield to structural variations combining coda-attenuation imaging with simulations based on radiative transfer and wave-equation modelling. The results provide evidence of intra-crustal reverberations and energy leakage in the mantle, finally being able to map Moho depths with regional earthquakes. This work is an ideal forward model of seismic wavefields recorded across the oceanic crust for future full-waveform inversions and imaging of crustal discontinuities.

How to cite: Nardoni, C., De Siena, L., Cammarano, F., Magrini, F., and Mattei, E.: Imaging oceanic basins with wave equation and radiative transfer models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1920, https://doi.org/10.5194/egusphere-egu22-1920, 2022.

10:56–11:02
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EGU22-7767
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ECS
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Virtual presentation
Li-Yu Kan, Sébastien Chevrot, and Vadim Monteiller

Multi-parameter teleseismic full-waveform inversion (FWI) can provide key insights on the composition and thermal state of the lithosphere. In the isotropic version of such inversions, one classically inverts for a set of independent model parameters,  for example (density, Vp, Vs). In this study, we demonstrate that by introducing model covariance matrices with non-diagonal terms to FWI, i.e. accounting for the existing correlations between density, Vp, and Vs, has a dramatic impact on the quality of the reconstructed models. We perform synthetic tests using with a simple subduction model. The teleseismic and regional wavefields are computed with our FK-SEM hybrid method. We invert vertical and radial component P waveforms from four teleseismic events coming from different epicentral distances and azimuths. We use a hierarchical iterative l-BFGS inversion, starting at long period (T > 10 s) to obtain a long wavelength model, and then progressively decreasing the spatial smoothing and cut-off period to 5 s and then 2.5 s. We also demonstrate that a complete non-diagonal model covariance matrix allows us to make the inversion results consistent, i.e. independent of the model parameterization. The inversions which account for the correlations between model parameters provide better models especially for density and Vs, less numerical artifacts, and are characterized by a faster convergence rate compared to inversions performed by assuming that model parameters are independent.

How to cite: Kan, L.-Y., Chevrot, S., and Monteiller, V.: A consistent full waveform inversion scheme for imaging heterogeneous isotropic elastic media, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7767, https://doi.org/10.5194/egusphere-egu22-7767, 2022.

11:02–11:08
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EGU22-6780
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ECS
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Virtual presentation
Xiaoqing Zhang, Hans Thybo, Irina M. Artemieva, Tao Xu, and Zhiming Bai

The Sino-Korean Craton (SKC), which consists of the North China Craton (NCC) in China and North Korea, is one of the oldest cratons on earth. Since the Paleozoic, the SKC has experienced multiple subductions of the peripheral plates and the northeastern SKC is located in a junction area. Its characteristics are being investigated by geophysical and geochemical methods, which provides insights into the formation and subsequent evolution of the continental lithosphere.

We interpret the crustal structure of the northeastern SKC with the refraction/wide-angle reflection perspective using North Korean Nuclear Explosion sources recorded by 40 permanent and 7 temporary broadband stations, which were operated by the China Earthquake Administration and the Institute of Geology and Geophysics, Chinese Academy of Science, respectively.

Primary reflection phases from a discontinuity at 30km depth have an apparent velocity of about 6.2 km/s. This phase is observed to 1200km ultra-long offset, which shows that the average crustal velocity is extremely low. Another spectacular observation is of extremely strong phases which we interpret as Moho to surface multiples of all main phases in the seismic sections. Clear upper mantle refractions (Pn) are observed with an apparent velocity around 8.05 km/s as first arrivals over the offset range 300-1000 km. All observations show that the crust of northeastern SKC is very thin (about 30km), it has a low average crust velocity (6.2km/s), and the velocity contrast at the Moho discontinuity is extraordinarily strong.

We detect the “Seismic Moho” discontinuity, which is marked by a very strong and sharp increase in velocity. We interpret this “Seismic Moho” as the top of a layer consisting of the lower crust in eclogite facies. This “Seismic Moho” does not coincide with the true Crust-Mantle Boundary, which is defined by a change from felsic/intermediate/mafic crustal rocks to the dominantly ultramafic rocks of the upper mantle in petrological terms.

How to cite: Zhang, X., Thybo, H., Artemieva, I. M., Xu, T., and Bai, Z.: An unusually long eclogitic lower crustal body imaged by the Korean nuclear explosion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6780, https://doi.org/10.5194/egusphere-egu22-6780, 2022.

11:08–11:14
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EGU22-10232
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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-petrological 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 this work we develop a new parameterization of the crust where we first invert following global statistical correlations between Vp, Vs and crustal densities for different lithologies in a two-layered model. In a second step we compute the rock physical properties for different metamorphic facies and water contents using computational petrology to derive a plausible and consistent lithological model. In order to optimize the inversion procedure, we perform a sensitivity  analysis assessing the resolution of the different 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.

How to cite: Clemente-Gómez, C., Fullea, J., and Arnaiz-Rodríguez, M. S.: A new Integrated lithological model of the Iberian crust, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10232, https://doi.org/10.5194/egusphere-egu22-10232, 2022.

11:14–11:20
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EGU22-1567
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ECS
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Presentation form not yet defined
Ilya Fomin, Juan Afonso, and Constanza Manassero

Characterising the physical state of the Earth's interior with high resolution requires the joint inversion of complementary geophysical datasets. LitMod3D_4inv is a method/software that allows regional and continental scale joint inversions within a probabilistic framework for the 3D thermochemical structure of the lithosphere and upper mantle. The software can simultaneously invert gravity anomalies, geoid height, gravity gradients, Love and Rayleigh surface-wave dispersion curves, receiver functions, body-wave travel times, surface heat flow, absolute elevation and magnetotelluric data, or any combination of them. The result is a collection of Earth models (a probabilistic distribution) with exceptional explicative power and robust estimates for uncertainties.

We use equations of state and Gibbs free energy minimisation routines to produce self-consistent sets of the seismic velocities, densities, and other properties from the actual parameters (unknowns) of the inversion – mantle chemical compositions, thermal profiles, and properties of the crustal layers (thickness, reference densities, Vp/Vs). The code relies on highly-optimised solvers for gravity, seismic, and magnetotelluric forward problems and multi-level hybrid parallel architecture to make use of multiple interacting markov chains. The modular structure of the code allows for extending the set of solvers to include new observables or to implement new Markov chain Monte Carlo algorithms.

In this presentation we will discuss recent developments in the LitMod3D_4inv suite and illustrate their performance with real examples in eastern Canada, in southern and central Africa, and north eastern Australia.

How to cite: Fomin, I., Afonso, J., and Manassero, C.: LitMod3D_4inv: Multi-observable and multi-scale geophysical inversions for the physical state of the Earth., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1567, https://doi.org/10.5194/egusphere-egu22-1567, 2022.

11:20–11:26
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EGU22-4784
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ECS
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On-site presentation
Chiara Civiero, Sergei Lebedev, Yihe Xu, Raffaele Bonadio, and Javier Fullea

1D reference Earth models are widely used by the geoscience community and include global, regional and tectonic-type reference models. Seismic 1D profiles are used routinely as reference in imaging studies. Multi-parameter models can also include density, composition, attenuation, lithospheric thickness and other parameters, of interest in a broad range of studies. The recent growth in the number of seismic stations worldwide has yielded a dramatic increase in the global sampling of the Earth with seismic data and presents an opportunity for an improvement in the global and tectonic-type reference models. Concurrent developments in computational petrology have provided methods to constrain self-consistent multi-parameter Earth models with seismic and other data. Here, we use a large global dataset of Love and Rayleigh fundamental mode, phase-velocity measurements, performed with multimode waveform inversion using all available broadband data since the 1990s, and compute phase-velocity maps at densely spaced periods in a broad, 17-310 s period range. We then invert the phase velocity curves averaged globally and across 8 tectonic environments (4 continental: Archean cratons, stable platforms, recently active continents, and active rift zones; and 4 oceanic: old, intermediate and young oceans, and backarc regions) for 1D reference models of the upper mantle. For each tectonic type, a multi-parameter 1D model is computed in a petrological inversion, where the lithospheric thickness and temperature at the bottom of the lithosphere and in the underlying mantle are the inversion parameters, and steady-state conductive lithospheric geotherms are assumed. Lithospheric and asthenospheric compositions are taken from geochemical databases, and seismic velocities, densities and Q are computed from composition, temperature and pressure using computational petrology and thermodynamic databases. The models quantify the age dependence of the lithospheric thickness and temperature in continents and oceans. Radial anisotropy is also determined and shows notable variations with depth and with tectonic environments. For most tectonic types, the smooth, accurate observed phase velocity curves can be fit by the 1D models with a misfit under 0.1-0.2% of the phase velocity value. Additionally, we compute models with minimal complexity of seismic velocity structure, also fitting the data but without a sub-lithospheric low-velocity zone as in the thermal multi-parameter models. These purely seismic models, similar in appearance to ak135, do not correspond to realistic geotherms but provide useful reference for seismic imaging studies in different environments.

How to cite: Civiero, C., Lebedev, S., Xu, Y., Bonadio, R., and Fullea, J.: Seismic and multi-parameter 1D reference models of the upper mantle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4784, https://doi.org/10.5194/egusphere-egu22-4784, 2022.

Interdisciplinary approaches
11:26–11:32
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EGU22-9636
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On-site presentation
Youngseok Song, Joongmoo Byun, Sooyoon Kim, Yonggyu Choi, and Sungmyung Bae

Seismic reflection images derived by ambient-noise seismic interferometry (SI) can show subsurface structures without active sources. To image and interpret the upper mantle structures and tectonic boundaries beneath the southern part of Korean Peninsula, we applied SI method to seismic ambient noise data recorded at 119 seismic stations on the Korean Peninsula in 2014 (from the seismic network of the Korean Meteorological Administration). The factor that makes interpretation difficult is the steeply dipping events in reflection images. Most of these events of apparent steeply dips show as true reflection events from steep geologic boundaries. Therefore, we need to attenuate these events to interpret true reflection events. These events overlap many times. Also, the value of the slope has several values close to half of the Rayleigh waves or P waves. To attenuate these events with these complex features, we used machine learning techniques. We attenuated our steeply dipping events by applying the Extraction of diffractions method. As the steeply dipping events are attenuated, horizontal events were strengthened, and noises were attenuated. We can more clearly identify the reflection events of the Moho discontinuity and the lithosphere/asthenosphere (LAB) boundary near the two-way reflection times of 7-11 s and 17-22 s respectively.

How to cite: Song, Y., Byun, J., Kim, S., Choi, Y., and Bae, S.: Machine learning-based attenuation of steeply dipping events of seismic reflection image beneath the Korean Peninsula, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9636, https://doi.org/10.5194/egusphere-egu22-9636, 2022.

11:32–11:38
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EGU22-376
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ECS
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Virtual presentation
Federico Munch and Alexander Grayver

Knowledge about the electrical conductivity structure of the Earth's interior is a key to understanding its thermo-chemical state and evaluate the impact of space weather events. USMTArray is a high quality data set of magnetotelluric measurements that addresses both of these problems. Covering ~70% of the contiguous United States on a quasi-regular 70 km spaced grid, this unique publicly available data led to the development of several regional 3D electrical conductivity models. However, an inversion of the entire data set demands novel multi-scale imaging approaches that can handle and take advantage of a large range of spatial scales contained in the data. We present a 3D electrical conductivity model of the contiguous United States derived from the inversion of ~1100 USArray magnetotelluric stations. The use of state-of-the-art modeling techniques based on high-order finite-element methods allows us to take into account complex coastline and reconstruct Earth’s conductivity across many scales. The retrieved electrical conductivity variations are in overall agreement with well-known continental structures such as the active tectonic processes within the western United States (e.g., Yellowstone hotspot, Basin and Range extension, and subduction of the Juan de Fuca slab) as well as the presence of deep roots (~250 km) beneath cratons.

How to cite: Munch, F. and Grayver, A.: Three-dimensional electrical conductivity structure of the contiguous US from USArray MT data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-376, https://doi.org/10.5194/egusphere-egu22-376, 2022.

11:38–11:44
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EGU22-7544
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ECS
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On-site presentation
Peter Haas, Jörg Ebbing, and Wolfgang Szwillus

In this contribution, we present a global estimate of crustal thickness with emphasis to cratons. In an inverse scheme, satellite gravity gradient data are inverted for the Moho depth, exploiting laterally variable density contrasts based on seismic tomography. Our results are constrained by an active source seismic data base, as well as a tectonic regionalization map, derived from seismic tomography. For the global analysis, we implement a moving window approach to perform the gravity inversion, followed by interpolating the estimated density contrasts of common tectonic units with a flood-fill algorithm.

The estimated Moho depth and density contrasts are especially interesting for the cratons of the Earth. Our results reveal a surprising variability of patterns with average Moho depth between 32-42 km, reflecting an individual tectonic history of each craton. Statistical patterns of Moho depth and density contrasts are discussed for the individual cratons and linked to their stabilization age. For example, Australia shows the lowest average Moho depth (32.7 km), indicating early stabilization in the Archean and removal of a dense lower protocrust. This observation matches well with receiver function studies. The globally inverted Moho depth is validated by gridded seismic Moho depth information, which shows that for many cratons the inverted Moho depth is within expected uncertainties of the seismic Moho depth. In addition, the formerly connected cratons of South America and Africa are analyzed and discussed in a Gondwana reconstruction. Here, the once-connected West African and Amazonian Cratons have a shallow Moho depth, indicating that only little tectonic activity occurred during the Phanerozoic. The tectonically-linked Congo and Sao Francisco Cratons have intermediate Moho depths, with the Congo Craton having a slightly shallower Moho depth. This could reflect dynamic support of the upper mantle on the African side.

How to cite: Haas, P., Ebbing, J., and Szwillus, W.: Global gravity gradient inversion reveals variability of cratonic crust, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7544, https://doi.org/10.5194/egusphere-egu22-7544, 2022.

11:44–11:50
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EGU22-3850
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ECS
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On-site presentation
Emma Chambers, Raffaele Bonadio, Sergei Lebedev, Javier Fullea, Duygu Kiyan, Christopher Bean, Brian O'Reilly, Patrick Meere, Meysam Rezaeifar, Gaurav Tomar, and Tao Ye and the DIG Team

DIG (De-risking Ireland’s Geothermal Potential) integrates inter-disciplinary and multi-scale datasets in order to investigate Ireland’s low-enthalpy geothermal energy potential. Recent deployments of broadband seismic stations and the output surface-wave measurements yield dense data sampling of the crust and mantle beneath Ireland and neighbouring Great Britain, which can be used to determine the lithospheric and asthenospheric structure at a regional scale. In addition, we integrate magnetotelluric measurements, forming the foundations for a region-scale, multi-parameter modelling of the thermal and compositional structure of the lithosphere.

In this study, we utilise the large seismic dataset and extract Rayleigh and Love-wave phase velocity dispersion curves, measured for pairs of stations across Ireland and Great Britain. The measurements were performed using two methods with complementary period ranges; the teleseismic cross-correlation method and the waveform inversion method, yielding a 4-500 s period range for the dispersion curves. 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 the 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, revealing the temperatures and geothermal gradients within the crust and mantle, which will be used for future geothermal exploration and utilisation.

The 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., Bonadio, R., Lebedev, S., Fullea, J., Kiyan, D., Bean, C., O'Reilly, B., Meere, P., Rezaeifar, M., Tomar, G., and Ye, T. and the DIG Team: Joint Geophysical and Petrological Inversion to Image the Lithosphere and Asthenosphere Beneath Ireland and Britain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3850, https://doi.org/10.5194/egusphere-egu22-3850, 2022.