Displays

The International Lithosphere Program (ILP) was established in 1980 as the Inter-Union Commission on the Lithosphere (ICL) by the International Council for Science (ICSU), following a request from the International Union of Geodesy and Geophysics (IUGG) and the International Union of Geological Sciences (IUGS). In 2005 ICSU transferred its sponsorship to IUGG and IUGS.

The ILP focusses on the nature, dynamics, origin, and evolution of the lithosphere, with special attention to the continents and their margins. Targeting these goals through international and interdisciplinary collaboration, ILP established several task forces and coordinating committees to pursue specific research objectives. Topics always follow one of the four ILP themes: global change, contemporary dynamics and deep processes, continental lithosphere, and ocean lithosphere. ILP’s funding is limited to five year periods and just understood as seed money.

In the last four decades ILP was involved in the composition and set up of a number of worldwide leading light house projects: The GSHAP (Global Seismic Hazard Map), the ICDP (International Continental Drilling Project), the WSM (World Stress Map Project), the TOPO-Europe project and its follow up initiatives TOPO-Asia, TOPO Iberia – just to name a few. Currently ILP supports new initiatives on digitalization.

With its Flinn-Hart Award (until 2007 Hart Award), honouring outstanding young scientists for contributions in the field of solid Earth sciences, ILP motivated and promoted a generation of early career scientists. The new Evgueni Burov Medal from ILP, established in 2018, pays tribute to an outstanding researcher in solid Earth sciences and recognizes pioneering contributions by mid-career scientists.

How to cite: Cloetingh, S. A. P. L., Green, A. G., Negendank, J. F. W., Oberhänsli, R., Rudloff, A., Scheck-Wenderoth, M., and Thybo, H.: Four Decades of Lithosphere and Solid Earth Research - ILP's Role as Stimulus, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9553, https://doi.org/10.5194/egusphere-egu2020-9553, 2020.

Observations in sedimentary basins affected by deformation show that the fault-induced depositional accommodation, at various spatial and temporal scales, is closely linked to basin kinematics. The tectonically-driven sediment infill displays the history of deepening and shoaling facies that are controlled by the activation of faults and changes in their offset rates. Simply stated, this results in shifting sedimentary facies towards the source area or towards the basin centre in response to increasing or decreasing depositional space. We propose a first-principle conceptual model for tectonic successions, controlled by the balance between the rates of creation of depositional space and sediment supply. These sediment bodies are bounded by succession boundaries and comprise sourceward or basinward shifting facies tracts that are separated at a point of reversal. Due to the relatively steep slopes associated with the evolution of faults, changes in sediment supply rates and mass-wasting are common in these systems and may complicate the normal rhythm of the shifting facies tracts. Once tectonic quiescence is achieved, and if the basin is connected to the open ocean, eurybatic or eustatic base level changes may take over and play a greater role in sedimentary rhythm and cyclicity. We illustrate the efficacy of the new concept with a review of examples from extensional, contractional and strike-slip basins. We show that the basic tectonic succession model is applicable at all temporal and spatial scales and whether the tectonics cause subsidence or uplift, and in all types of tectonic settings that determine the evolution of sedimentary basins.

How to cite: Matenco, L. and Haq, B.: Multi-Scale Depositional Successions in Tectonic Settings, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13354, https://doi.org/10.5194/egusphere-egu2020-13354, 2020.

We present a new model, EUNA-rho (Shulgin and Artemieva, 2019, JGR), for the density structure of the European and the North Atlantics upper mantle based on 3D tesseroid gravity modeling and a new regional model for the lithosphere thickness in Europe, Greenland, the adjacent off-shore regions (Artemieva, 2019ab, ESR), and Anatolia (Artemieva and Shulgin, 2019, Tectonics). On continent, there is no clear difference in lithosphere mantle (LM) density between the cratonic and Phanerozoic Europe, yet a ca. 300 km wide zone of a high-density LM along the Trans-European Suture Zone may image a paleosubduction. Kimberlite provinces of the Baltica and Greenland cratons have a low density mantle, while the correlation between LM density and the depth of sedimentary basins indicates an important role of eclogitization in basin subsidence, with the presence of 10-20% of eclogite in LM beneath the super-deep platform basins and the East Barents shelf. The Barents Sea has a sharp transition in lithosphere thickness from 120-150 km in the west to 175-230 km in the eastern Barents. Highly heterogeneous lithosphere structure of Anatolia is explained by the interplay of subduction systems of different ages. The block with 150 km thick lithosphere in the North Atlantics east of the Aegir paleo-spreading may represent a continental terrane. In the North Atlantics, south of the Charlie Gibbs fracture zone (CGFZ) bathymetry, heat flow and mantle density follows half-space cooling model with significant deviations at volcanic provinces. Strong low-density LM anomalies (<-3%) beneath the Azores and north of the CGFZ correlate with geochemical anomalies and indicate the presence of continental fragments and heterogeneous melting sources. Thermal anomalies in the upper mantle averaged down to the transition zone are 100-150^o C at the Azores and can be detected seismically, while a <50^o C anomaly around Iceland is at the limit of seismic resolution.

References:

• Artemieva I.M., 2019. The lithosphere structure of the European continent from thermal isostasy. Earth-Science Reviews, 188, 454-468.     
• Artemieva I.M., 2019. Lithosphere thermal thickness and geothermal heat flux in Greenland from a new thermal isostasy method. Earth-Science Reviews, 188, 469-481.
• Shulgin A. and Artemieva I.M., 2019. Thermochemical heterogeneity and density of continental and oceanic upper mantle in the European‐North Atlantic region. Journal of Geophysical Research: Solid Earth, 124, 1-33, doi: 10.1029/2018JB017025 (open access)       
• Artemieva I.M. and Shulgin A., 2019. Geodynamics of Anatolia: Lithosphere thermal structure and thickness. Tectonics, 38, 1-23, doi: 10.1029/2019TC005594

How to cite: Artemieva, I. and Shulgin, A.: Lithosphere thermo-chemical heterogeneity in the European-North Atlantic region, Greenland and Anatolia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5000, https://doi.org/10.5194/egusphere-egu2020-5000, 2020.

The causes of the high topography in Scandinavia along the North Atlantic passive continental margins are enigmatic, and two end-member models have been proposed. One opinion is that the high topography has been maintained since the Caledonian orogeny, because isostatic rebound has compensated for most of the erosion over >400 My. The other opinion is that the topography is Cenozoic and that it is related to plate tectonic or deep thermal / geodynamic processes. Onshore uplift is related to simultaneous offshore subsidence, and the rapid topographic changes may be the combined result of a series of complementary processes.

Here, we provide new evidence for the upper mantle structure by calculating a tomographic model for Fennoscandia (Scandinavia and Finland) by teleseismic inversion of finite-frequency P- and S- wave travel-time residuals. We use seismic signals from earthquakes at epicentral distances between 30° and 104° and with magnitudes larger than 5.5, gathered on 200 broad-band seismic stations installed by the ScanArray project in Norway, Sweden and Finland, which operated during 2012-2017, together with data from earlier projects and stationary stations..

We measure relative travel-time residuals of direct body waves in high- and low-frequency bands, and carry out an appropriate frequency-dependent crustal correction. The average residuals vary over the region, and show clear trends depending on location and and back-azimuthal directions. This demonstrates the presence of significant heterogeneity of seismic velocities in the upper mantle across the region. Based on the travel-time residuals, we carry out finite-frequency body-wave tomographic inversion to determine the P and S wave seismic velocity structure of the upper-mantle. By use of “relative kernels” we reduce problems related to station coverage with asynchronous datasets, which allows the use of data from different deployments for the inversion. The resulting seismic model is compared to the existing and past topography in order to contribute to the understanding of mechanisms responsible for the topographic changes in the Fennoscandian region, which we relate to the general tectonic and geological evolution of the North Atlantic region. The models provide basis for deriving high-resolution models of temperature and compositional anomalies that may contribute to the understanding of the observed, enigmatic topography.

How to cite: Bulut, N., Maupin, V., and Thybo, H.: Seismic P- and S-wave velocity Tomography in Scandinavia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22265, https://doi.org/10.5194/egusphere-egu2020-22265, 2020.

Upper mantle structures under cratons have recently been investigated by many researchers using receiver functions and surface waves to clarify the nature of the Lithosphere-Asthenosphere Boundary (LAB) and Mid-Lithosphere Discontinuity (MLD). Majority of seismological studies of joint inversions using receiver functions and surface waves have employed dispersion curves of fundamental-mode only, but higher-mode information is essential for resolving the whole depth range of thick continental lithosphere (over 200 km) and its underlying asthenosphere.

In this study, we reconstructed radially anisotropic S wave models including multiple discontinuities in the upper mantle under seismic stations in Australia, using multi-mode surface waves and receiver functions in the framework of the Bayesian inference. We employed a fully nonlinear method of joint inversions incorporating P-to-S receiver functions and multi-mode Rayleigh and Love waves, based on the trans-dimensional hierarchical Bayesian formulation. The method allows us to estimate a probabilistic Earth model taking account of the complexity and uncertainty of Earth structure, by treating the model parameters and data errors as unknowns. The Parallel Tempering algorithm is incorporated for the effective parameter search based on the reversible-jump Markov Chain Monte Carlo method.

Multi-mode phase speed maps of surface waves developed by Yoshizawa (2014) are used to extract localized multi-mode dispersion curves. The use of higher-mode surface waves enables us to enhance the sensitivity to the depth below the continental asthenosphere, while the receiver functions allows us to better constrain the depths of discontinuities and velocity jumps. Synthetic experiments indicate the importance of higher-mode information for the better recovery of radial anisotropy in the whole depth range of the upper mantle.

The method has been applied to Global Seismographic Network stations in Australia. While the S-wave models in eastern Australia show shallow LAB above 100 km depth, those in central and western Australia exhibit both MLD and LAB. Also, seismic velocity jumps equivalent to the Lehmann Discontinuity (LD) are found in all seismic stations in Australia. The LDs under the Australian continents are found at the depth of around 200 - 300 km, depending on locations. Radial anisotropy in the depth range between LAB and LD tends to show faster SH anomalies, which may indicate the effects of horizontal shear underneath the fast-moving Australian plate.

How to cite: Yoshizawa, K. and Taira, T.: Upper mantle discontinuities beneath Australia from trans-dimensional hierarchical Bayesian inversions using receiver functions and multi-mode surface waves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19418, https://doi.org/10.5194/egusphere-egu2020-19418, 2020.

A variety of anthropogenic activities are now known to have triggered earthquakes. These include mining, filling of artificial water reservoirs, production of petroleum and geothermal energy, high- pressure fluid injections into shallow crust and many more. Among these, artificial water reservoir triggered seismicity (RTS) is most prominent, with the largest triggered earthquake of M 6.3 having occurred at Koyna, India in 1967. Whether, the devastating Mw 7.8 Sichuan, China earthquake of 8 May 2008 that claimed some 80,000 human lives was triggered by filling of the nearby Zipingpu reservoir, continues to be debated.

There are over 100 sites globally where RTS events of M ≥ 4 have occurred. Here we present an over view of RTS, common characteristics of the RTS earthquake sequences that help to discriminate them from normal earthquake sequences and also help selection of safer sites for locating dams to create artificial water reservoirs.

Koyna, near the west coast of India continues to be most prominent site where triggered- earthquakes have been occurring since the impoundment of the reservoir in 1962 and have continued till now with 22 M ≥ 5, ~ 200 M ≥ 4 and several thousands smaller earthquakes. It was argued that Koyna is a very suitable site for near field investigations of triggered earthquakes. Discussions were held in dedicated ICDP workshops and finally a go ahead was given. As a precursor to setting up a near field laboratory at ~ 7 km depth, a 3 km deep Pilot Borehole has been completed in June 2017 and investigations are being carried out for necessary input for setting up the deep borehole laboratory. Salient features of this project are also presented.

How to cite: Gupta, H.: Artificial Water Reservoir Triggered Seismicity (RTS), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4745, https://doi.org/10.5194/egusphere-egu2020-4745, 2020.

Geodynamic evolution of Earth’s mantle and lithosphere is inextricably linked to the evolution of its atmosphere, oceans, landscape and life (e.g., Stern, 2016; Pellissier et al., 2017; Zaffos et al., 2017; Zerkle. 2018). In this context, modern-style plate tectonics that was established gradually through geological time (e.g., Gerya, 2019) is often viewed as a strong promoter of biological evolution (e.g., Pellissier et al., 2017; Zerkle, 2018; Stern, 2016). The influences of this global tectono-magmatic style are at least twofold (e.g., Zerkle, 2018; Stern, 2016). Firstly, life is sustained by a critical set of elements contained within rock, ocean and atmosphere reservoirs and cycled between Earth’s surface and interior via various tectonic, magmatic and surface processes (Zerkle, 2018); plate tectonics is very effective for this recycling. Second, plate tectonics is an unparalleled agent for redistributing continents and oceans, growing mountain ranges, and forming land bridges, and provides continuous but moderate environmental pressures that isolate and stimulate populations to adapt and evolve (Stern, 2016). Importantly, modern-style plate tectonics itself exerts continuous moderate environmental pressures that drive evolution and stimulate populations to adapt and evolve without being capable of extinguishing all life (Stern 2016). The power of plate tectonics for both nutrient recycling and paleogeographic rededistributions  suggests that a planet with oceans, continents, and modern-style plate tectonics maximizes opportunities for speciation and natural selection, whereas a similar planet without plate tectonics provides fewer such opportunities (Stern, 2016).  The evolution of life must intimately reflect Earth’s tectonic evolution.

It is important to also point out that timescales of biological evolution of complex life estimated on the basis of the analysis of phylogenies and/or fossils are rather long and comparable to geodynamic timescales (e.g., Alroy, 2008; Marshall, 2017). This timescale similarity creates an opportunity for investigating lithospheric and mantle processes with life evolution by developing and testing novel hybrid bio-geodynamical numerical models. These are currently emerging. Here, we review state of the art for understanding the complex relationship between lithospheric dynamics and life evolution and present some recent examples of numerical modeling studies investigating Earth’s bio-geodynamic evolution.

 References

Alroy, J. (2008). Dynamics of origination and extinction in the marine fossil record. Proceedings of the National Academy of Sciences. 105, 11536.

Gerya, T. (2019) Geodynamics of the early Earth:  Quest for the missing paradigm. Geology, DOI:10.1130/focus-Oct2019.

Marshall, C. R. (2017). Five palaeobiological laws needed to understand the evolution of the living biota. Nature Ecology & Evolution, 1(6), 0165.

Pellissier, L., Heine, C., Rosauer, D.F., Albouy, C. (2017)  Are global hotspots of endemic richness shaped by plate tectonics? Biological Journal of the Linnean Society 123 (1), 247-261.

Stern, R.J. (2016) Is plate tectonics needed to evolve technological species on exoplanets? Geoscience Frontiers, 7, 573-580.

Zaffos, A., Finnegan, S, Peters, S.E. (2017) Plate tectonic regulation of global marine animal diversity. PNAS, 114, 5653–5658.

Zerkle A. L. (2018) Biogeodynamics: bridging the gap between surface and deep Earth processes. Phil. Trans. R. Soc. A 376, 20170401. (doi:10.1098/rsta.2017.0401)

How to cite: Gerya, T., Stern, R., Pellissier, L., and Stemmler, D.: Bio-geodynamics of the Earth: State of the art and future directions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10657, https://doi.org/10.5194/egusphere-egu2020-10657, 2020.

Sub-Moho reflectors have been identified in seismic refraction and wide-angle reflection recordings in western Iberia since the late ‘80s. These control source seismic wide-angle shot records have energy large enough to illuminate the uppermost mantle showing strong sub-Moho arrivals at distant offsets (>180 km) with amplitudes significantly higher than the Pn and a relatively long coda. The kinematics and wavelet characteristics of these features are probably produced by an increase in P-wave velocity, and forward modeling indicates that these arrivals reflect off an interface in the 60-80 km depth range beneath the Iberian Massif. The waveform and time length of this arrival suggests that it can result from the interaction of the seismic energy with a ~10 km thick heterogeneous layer. To test this hypothesis, we used a 2D second-order finite-difference acoustic and elastic full wave-field scheme with a layer consisting of randomly distributed bodies smaller than ¼ of the wavelength of the seismic waves in thickness and ΔVp=±0.2 km/s at the considered depth range. Resulting synthetic shot gathers reproduce well the observed amplitudes and codas as a result of the constructive interference caused by the tuning effect produced by this gradient heterogeneous zone. The contrast in physical properties and depth level of this feature are consistent with the top of the phase transition from spinel to garnet lherzolite, the so-called Hales discontinuity.

Some of the available gathers show a second and deeper reflection. Detailed analysis of the reflected wave-forms suggests that the reflected wavelet has reversed polarity, a feature suggesting. a velocity decrease with depth. Finite difference acoustic and elastic full wave-field modeling places this discontinuity around 90 km depth beneath the Ossa-Morena Zone (south Iberian Massif). A lateral change is observed beneath the Centro-Iberian Zone (central Iberian Massif) where it is imaged at 103-110 km depth on the southeast and shallows up to 80 km depth on the northeast. The indicated depth would be consistent with the depth location of the LAB, which is relatively well constrained for the target area by other geophysical observations.

Funding resources: EU EIT-RawMaterials Ref: 17024_20170331_92304; MINECO: CGL2016-81964-REDE CGL2014-56548-P: JCYL: SA065P17). 

How to cite: Palomeras, I., Ayarza, P., Díaz, J., Andrés, J., and Carbonell, R.: Seismic Modeling of the Subcrustal Reflectivity Beneath the Iberian Massif (Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18492, https://doi.org/10.5194/egusphere-egu2020-18492, 2020.

The receiver function analysis (RF) is a commonly used and well-established method to investigate subsurface crustal and upper mantle structures, removing the source, ray-path and instrument signatures. RF gives the unique signature of sharp seismic discontinuities and information about P-wave (P) and shear-wave (Ps) velocity below the seismic station. In particular using the direct P-wave as a known reference arrival time, and the relative arrival time of P-to-S (Ps) conversions as well as PpPs, PsPs and PsSs reflections allow constraining the principal crustal structures and allows us to study the effects of dipping interfaces and crustal layering.

The aim of this work is to use the RF non-conventional analysis to study the crustal structures of Tenerife. Previous studies on receiver functions analysis an active oceanic volcanic island, showed that the Moho topography have a high dipping under the volcanic edifice and a depth ranging between 11 and 18 km depth. Furthermore, it has been observed that some phases related with a layer of volcanic rocks having a thickness of about 5.5 km and a P-wave velocity (Vp) of approximately 6 Km/s, lies above an old oceanic crust having a thickness of about 7 km and a Vp of about 6.8 km/s.

For this study we applied both time and frequency domain deconvolution to obtain receiver functions. The determination of the average crustal thickness and has been achieved by using the commonly uses H-k method. To constrain the internal crustal layering, we used a non-linear inversion algorithm based on full waveform modeling of the receiver function. Finally, we realized a modelling of the reflected and converted phases in the crust using seismic ray tracing. Our modelling takes into account the surface topography as well as an arbitrary geometry of the Moho.

In conclusion our results showed the presence of a thick layer (up to 5.5 km) of volcanic rocks in the central part of the island overlying an oceanic crust whose total thickness varied from 18 km in the central part to about 11 km in the peripheral areas. This work represents the first step toward further studies devoted at a finer imaging of the crustal structures of Tenerife using receiver function analysis.

How to cite: Ortega, V. and D'Auria, L.: Receiver function analysis for determining the crustal structure of Tenerife (Canary Islands, Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-309, https://doi.org/10.5194/egusphere-egu2020-309, 2020.

Waveform inversion was introduced in global seismic imaging in the early days of seismic tomography, in the beginning of the 1980s. Thanks to the continual improvements in the data sampling and methodology since then, waveform tomography has been getting more and more effective in extracting structural information from seismic records and producing detailed 3D models of the Earth’s crust and upper mantle. Today, tomography’s original problems relating to the large-scale Earth structure have been solved: the structure at the scale of thousands of kilometres is remarkably consistent across recent global models. Resolution of the imaging is now at hundreds of kilometres, the scale of tectonic units and major tectonic and magmatic processes. This has opened a new chapter for waveform tomography. It now fuels discoveries on the structure of individual cratons, evolution of cratons in general, origins of intraplate volcanism, plume-lithosphere interactions and other processes.   

In continents, high-resolution tomography can now map the deep boundaries of different tectonic blocks with useful accuracy.  A global comparison with geological data shows that, as a rule, Archean crust is underlain by thick (180-250 km), cratonic mantle lithosphere. This mantle lithosphere is likely to be of the Archean age as well, as often evidenced by mantle xenoliths. Where Archean crust is unexposed (covered by sediments), its presence can be inferred from the presence of the cratonic mantle lithosphere, imaged by tomography. A growing number of previously unknown cratons in different continents are now being discovered by waveform tomography. The lateral extent of other cratons, hypothesized previously, can now be established.

The lithosphere of most known cratons has been remarkably stable since its Archean formation, thanks to its compositional buoyancy and mechanical strength. In some instances, however, cratonic lithosphere is known to have been eroded. This is inferred from the existence of the thick lithosphere in the past, as evidenced by diamondiferous kimberlites, and its absence at present, as evidenced by  seismic imaging. Waveform tomography of continents now reveals more and more occurrences of this process and offers new insights into its mechanisms.

References

Celli, N.L., S. Lebedev, A.J. Schaeffer, C. Gaina. African cratonic lithosphere carved by mantle plumes. Nature Communications, 11, 92, doi:10.1038/s41467-019-13871-2, 2020.

Schaeffer, A. J., S. Lebedev. Global heterogeneity of the lithosphere and underlying mantle: A seismological appraisal based on multimode surface-wave dispersion analysis, shear-velocity tomography, and tectonic regionalization. In: "The Earth's Heterogeneous Mantle," A. Khan and F. Deschamps (eds.), pp. 3–46, Springer Geophysics, doi:10.1007/978-3-319-15627-9_1, 2015.

Steinberger, B., E. Bredow, S. Lebedev, A. Schaeffer, T. H. Torsvik. Widespread volcanism in the Greenland-North Atlantic region explained by the Iceland plume. Nature Geoscience, 12, 61–68, doi:10.1038/s41561-018-0251-0, 2019.

How to cite: Lebedev, S., Celli, N. L., and Schaeffer, A. J.: Global and regional waveform tomography with massive datasets: new insights into the structure and evolution of the continents, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5010, https://doi.org/10.5194/egusphere-egu2020-5010, 2020.

The southern Baltic Sea area is located in the transition zone between the East European Craton (EEC; Baltica) and the West European Platform (Avalonia). The most prominent tectonic feature in the area is the NW–SE trending Tornquist Zone (TZ), crossing the southern Baltic Sea area between Scania in Sweden and Pomerania in Poland. A peculiar feature of the TZ and its southern prolongation (Teisseyre-Tornquist Zone, TTZ) is possibly a crustal keel that was recently postulated for northern Poland based on potential field modelling. A crustal keel was also imaged in the Baltic Sea by BABEL profile A, which crossed the TZ northwest of Bornholm, and by two TTZ’92 profiles crossing the TTZ south of Bornholm. However, the DEKORP-PQ profile shows a flat Moho across the TTZ.

In order to reconcile those contrasting interpretations of the crustal structure around the TTZ offshore Poland, a 230-km long refraction/wide-angle reflection profile was acquired across the TTZ in the course of RV/MARIA S. MERIAN expedition MSM52 (BalTec) in March 2016. This profile is nearly parallel to the western Polish coast, in half a distance to Bornholm. The data acquisition was conducted with 15 ocean bottom seismometers (OBS) and 3 land stations. The source array consisted of 8 G-guns with the total volume of 32 litres. In total 2227 shot points were recorded. Hydrophone data are of high quality and despite the relatively small source volume, sharp first arrivals of Pg and Pn are observed at over 120 km offsets. Some seismic record sections show clear PmP phases beginning at offsets of 70 km, continuing till the end of the profile.

Two variants of seismic modelling were performed, which results proved to be similar in terms of P-wave velocities and observed features. Tomographic joint inversion of both first arrivals and Moho reflections was used to extend velocity model depth range. Second was trial-and-error forward modelling technique using all identified seismic phases, paying attention to minimize misfit between calculated and observed P-wave travel times for each individual layer.

In the area of the TTZ, a complex upper crustal structure deepening towards the southwest is observed. One of the most interesting features is an increase in Vp (>6.5 km/s) at a depth of 16-25 km, offset by ~40 km from the TTZ on the EEC side. Similar feature was observed along the TTZ in SE Poland. Due to the lack of information from refraction, the presented ray-tracing model is the result of testing various possible velocity values for the lower crust in different parts of the model. A layer with Vp>7 km/s with a thickness of ~6 km along the entire model seems to be the best solution The Moho boundary was inferred at 33-38 km depth, deepening towards the EEC, with ~3 km uplift (but not keel) corresponding to the location of the elevated middle-crust velocities. Final velocity models were further verified by forward potential field modelling, testing various Vp – density relations.

This study was funded by the Polish National Science Centre grant no UMO-2017/27/B/ST10/02316.

How to cite: Wójcik, D., Janik, T., Malinowski, M., Ponikowska, M., Mazur, S., Skrzynik, T., and Hübscher, C.: New refraction/wide-angle reflection profile across the Teisseyre-Tornquist Zone offshore Poland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7394, https://doi.org/10.5194/egusphere-egu2020-7394, 2020.

The distribution of temperature inside active continental margins plays a fundamental role on regulating first order geodynamic processes as the isostatic balance, rheologic behavior of crust and mantle, magmagenesis, volcanism and seismogenesis. In spite of these major implications, well-constrained 3D thermal models are known for few regions of the world (Europe, Western USA, China) where large geophysical databases have been integrated into compositional and structural models of crust and lithospheric mantle from which a thermal model is derived. Here we present a three-dimensional representation of the distribution of temperature underneath the Andean active margin of South America (10°-45°S) that is based on a geophysically-constrained model for the geometry of the subducted slab, continental lithosphere-asthenosphere boundary (LAB), Moho discontinuity and an intracrustal discontinuity (ICD). This input model was constructed by forward modelling the satellite gravity anomaly under the constraint of most of the seismic information published for this region. We use analytical expressions of 1D conductive continental geotherms with adequate boundary conditions that consider the compositional stratification of crust and mantle included in the input model, and the advective thermal effect of slab subduction. The 1D geotherms are assembled into a 3D volume defining the thermal structure of the study region. We test the influence of several thermal parameters and structural configurations of the Andean lithosphere by comparing the resulting surface heat flow distribution of these different models against a database containing heat flow measurements that we compile from the literature. Our results show that the thermal structure and derived surface heat flow is dominantly controlled by the geometry of the thermal boundary layer at the base of the lithosphere, i.e. the slab upper surface below the forearc and LAB inland. Variations on the modeled configuration of the continental lithosphere (i.e. the way on which the geometry of the continental Moho and ICD are considered into the definition of a space-variable thermal conductivity or the length scale for radiogenic heat production) have an effect on surface heat flow that is lower than the average uncertainty of the measurements and therefore can be considered as second-order. The simplicity of our analytical approach allows us to compute hundreds of different models in order to test the sensitivity of results to changes on thermal parameters (conductivity, heat production, mantle potential temperature, etc), which provides a tool for discussing their possible range of values in the context of a subduction margin. We will also show how variations of these models impact on the Moho temperature and therefore in the expected mechanical behavior of crust and mantle in this geotectonic context

How to cite: Tassara, A., Julve, J., Echeverría, I., and Stotz, I.: Temperature structure of the Andean subduction zone as derived from the 3D geometry of crustal and upper mantle discontinuities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20322, https://doi.org/10.5194/egusphere-egu2020-20322, 2020.

Margins of craton lithosphere are prone to ongoing modification process. Marginal tectonism such as slab subduction, continental collision, and mantle dynamics significantly influence properties of lithosphere in various scales. Thus, constraints on the detailed properties of craton margin are essential to understand the evolution of continental lithosphere. The eastern margin of the Eurasian plate is a natural laboratory that allows us to study the strong effects from multiple episodes of continental collision and subduction of different oceanic plates since their formation. Extensive reworking and destruction of the cratonic lithosphere mainly occurred in eastern China during the Mesozoic to Cenozoic, which leaves distinct geochemical and geophysical signatures. Specifically, the Korean Peninsula (KP) is known to consist of Archean–Proterozoic massifs (e.g., Gyeonggi, Yeongnam Massif) located in the forefront in northeast Asia, where current dynamics in the upper mantle and effects due to nearby subducting slabs are the most significant.

Here we present, for the first time in detail, 3-D velocity structure of KP by teleseismic body wave traveltime tomography. Detailed P-wave and S-wave images of the crust and upper mantle were constructed by approximately 5 years of data from dense arrays of seismometers. We newly found a thick high-velocity body beneath the southwestern KP with a thickness of ~150 km, which is thought as a fragment of lithospheric root beneath the Proterozoic Yeongnam Massif. Also, we found low velocities beneath the Gyeonggi Massif, eastern KP margin, and Gyeongsang continental arc-back-arc system, showing significant velocity contrasts (dlnVp of ~4.0% and dlnVs of ~6.0%) to the high-velocity structure. These features indicate significantly modified regions. In addition, there was a clear correlation of the upper mantle low-velocity anomalies and areas characterized by Cenozoic basaltic eruptions, high heat flow, and high tomography, suggesting that there are close associations between mantle dynamics and recent tectonic reactivation.

The presence of a remnant cratonic root beneath the KP and contrasting lithospheric structures across the different Precambrian massifs suggests highly heterogeneous modification along the Sino-Korean craton margin, which includes the KP and North China Craton. A striking localization of lithosphere modification among the different Precambrian massifs within the KP suggests that the structural heterogeneity of the craton margin is likely sharp in scale and thickness within a confined area. We suggest that intense interaction of upper mantle dynamics and inherent structural heterogeneities of a craton margin played an important role in shaping the current marginal lithosphere structure in northeast Asia.

How to cite: Song, J.-H., Kim, S., and Rhie, J.: Heterogeneous modification and reactivation of craton margin in northeast Asia: insight from teleseismic traveltime tomography of the Korean Peninsula, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12562, https://doi.org/10.5194/egusphere-egu2020-12562, 2020.

The World Stress Map (WSM) compiles orientations of the maximum horizontal stress S_Hmax and provides the only public global database of this kind. To make the S_Hmax orientation data from a wide range of stress indicators comparable, a quality ranking scheme has been developed. However, for the assessment of subsurface stability, not only the orientations but also data of the principal stress magnitudes are essential to calibrate 3D geomechanical-numerical models that deliver a continuous description of the complete 3D stress tensor. Thus, a comprehensive extension of the WSM database with quality-ranked stress magnitude data is needed. In a pilot study, we compiled an open-access stress magnitude database for Germany and adjacent regions, consisting of 568 data records. Indicators of stress magnitudes are diverse and include e.g. hydraulic fracturing and overcoring. To make data from different sources comparable, we developed a quality ranking scheme for stress magnitude data for the first time. In contrast to the established WSM quality ranking for S_Hmax orientation data records, estimates of stress magnitudes cannot be averaged over large rock volumes or depth ranges. Instead, each point-wise information has to be considered separately. Thus, we developed a new approach for the quality ranking scheme of S_hmin magnitude data records which considers both the type of stress magnitude indicator and the degree of information availability. We present the results of our work including the data quality ranking scheme, which will serve as a template for a global stress compilation within the framework of the WSM project. The next countries and regions that we will explore are Australia, Scandinavia and India. We invite you to contribute to this project in your area or country of interest and to join the WSM team as an official collaborator.

How to cite: Morawietz, S., Heidbach, O., Ziegler, M., Reiter, K., Rajabi, M., Zimmermann, G., Müller, B., and Tingay, M.: World Stress Map Beyond Orientations - The First Quality Ranking Scheme for Stress Magnitude Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2884, https://doi.org/10.5194/egusphere-egu2020-2884, 2020.

Classical field studies are vital for mapping and understanding volcano-tectonic processes, particularly for those that produce superficial deformation consequently to magmatic and tectonic activity. Unfortunately, very often, key outcrops are inaccessible due to harsh logistic conditions or their location in remote or dangerous areas. In the framework of the ILP Task Force II, we developed and tested modern and innovative methods aimed at overcoming these limitations in field research and data collection, that we combined with classical field mapping. Such methods have been used to provide a more complete picture of the deformation processes that have been taking place in the Theistareykir Fissure Swarm within the Northern Volcanic Zone of Iceland. This rift is characterized by the presence of huge normal faults, several extension fractures and volcanic centres. The modern methods we used derive from the use of UAVs (drones) combined with Structure from Motion (SfM) photogrammetry techniques. The first innovative method consists of analysing UAV-based SfM-derived high resolution orthomosaics and digital surface models where we collected hundreds of quantitative measurements of the amount of opening and opening direction of Holocene extension fractures and measurements of fault scarp height. The second and more innovative method we used is the Immersive Virtual Reality that can be applied to 3D digital outcrop models (DOMs), reconstructed with UAV-based SfM photogrammetry techniques; several sites within the Theistareykir Fissure Swarm have been reconstructed in the framework of the Italian Argo3D project. The reconstructed 3D DOMs were explored using different modalities: on foot, as is often the case during field activity, moving like a drone, above and around the target, as well as flying like an airplane. Thanks to these modes of exploration we were capable of better understanding the geometry of extension fractures, volcanic centres and normal faults. We also measured, in the virtual environment, the opening direction and the amount of dilation along the extensional fractures, the direction of magma-feeding fractures underlying cones and volcanic vents, as well as the amount of vertical offset along normal faults. The quantification and mapping of these features was accomplished through some tools tailored for virtual field activity in the framework of Italian Argo3D project and the Erasmus+ Key Action 2 2017-1-UK01-KA203-036719. Thanks to the merging of classical and modern approaches we are able of providing a complete picture related to the post-LGM deformation field affecting this part of the Icelandic rift, particularly focusing on the spreading direction and the stretch ratio across the whole Theistareykir Fissure Swarm.

How to cite: Bonali, F. L., Tibaldi, A., Pasquaré Mariotto, F., Russo, E., and Corti, N.: Advances in field data collection in volcano-tectonic sensitive areas: examples and results from the Northern Volcanic Zone of Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4517, https://doi.org/10.5194/egusphere-egu2020-4517, 2020.

The whole North Atlantic region has highly anomalous topography and bathymetry. Observations show evidence for substantial topographic change with rapid onshore uplift close to the Atlantic coast and simultaneous subsidence of basins on the continental shelves, most likely throughout the Mesozoic.

We present a review of geophysical data and interpretation of the whole region with emphasis on data relevant for assessing topographic change. We review the available data on topography, bathymetry, density, seismic velocity, and heat flow and present interpretations of the structure and composition of the crust and lithospheric mantle.

We find that most of the northern North Atlantic Ocean has anomalously shallow bathymetry although it follows the “normal” square-root-of-age dependence, which however is elevated by up-to 2 km. The heat flow variation follows the square-root-of-age dependence, although heat flow is anomalously low on the spreading ridges around and on Iceland. In apparent contrast, exceptionally low seismic velocities are observed along the spreading ridges around and below Iceland. Near-zero free-air gravity anomalies indicate that the oceanic areas are mainly in isostatic equilibrium, whereas anomalously low Bouguer anomalies indicate low density in the uppermost mantle. Anomalously thick oceanic crust is observed along the Greenland-Iceland-Faro Ridge and extending into the Davis Strait. We propose that the anomalous bathymetry is caused by compositional variation in the lithosphere, which indicates that the lithosphere in the ocean may include remnants of continental lithosphere.

The onshore circum-Atlantic areas show rapid uplift close to the coast with rates up-to 3 cm/yr. This is surprisingly associated with strong positive free-air gravity anomalies which predicts isostatic subsidence. However, negative free-air gravity anomalies in onshore Canada and Bothnian Bay explain recent uplift in the shields as isostatic rebound after glaciation. Archaean lithosphere is everywhere thick in both Greenland and Fennoscandia, Proterozoic areas have thinner lithosphere and Palaeozoic-Mesozoic areas have very thin lithosphere. It is enigmatic that the presumed Archaean-Proterozoic Barents Sea region is submerged and includes deep sedimentary basins.

How to cite: Thybo, H. and Artemieva, I.: Anomalous Topography, Bathymetry, Crust and Mantle in the North Atlantic Region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6012, https://doi.org/10.5194/egusphere-egu2020-6012, 2020.

The Barents Sea shelf has been covered by numerous wide-angle seismic profiles aiming to resolve the crustal structure of the shelf. However, the overall structural architecture of the crystalline crust is still not fully understood, due to limited and sparse distribution of deep-sampling seismic profiles. 

The petroleum related seismic exploration in Norwegian waters has been ongoing for decades. The recent increase of the seismic broadband stations onshore (including temporal deployments) provokes the idea to use these stations and the active seismic sources from the regional seismic reflection surveys, including academic and industry seismic projects, to reveal the crustal-scale structure of the western Barents Sea.

We have analyzed seismic records from 8 permanent seismic stations from Norway, Sweden and Finland, and 12 temporally deployed broadband seismic stations from the ScanArray seismic network, which recorded more than 100’000 marine airgun shots from academic and oil industry campaigns in the south-western quarter of the Barents Sea.

The overall quality of the seismic records is exceptionally good. We observe clear phases recorded from offsets reaching 750 km. The identified phases include refracted crustal and mantle arrivals as well as Moho reflections, including both P and S waves. The overall quantity, quality, and the geometry of the seismic data makes it perfect for the application of the 3D joint refraction/reflection travel time seismic tomography to study the crustal structure of the Barents Sea. In this work we would like to present our first results from the 3D seismic tomography.

How to cite: Shulgin, A., Lie, J. E., Nilsen, E. H., Faleide, J. I., and Planke, S.: Crustal structure of the Barents Sea from 3D active seismic tomography., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11649, https://doi.org/10.5194/egusphere-egu2020-11649, 2020.

The Scandinavian mountain chain runs approximately parallel to the western coast of Norway with topography up to 2500 m. Since this region lacks recent compressional tectonic forces, we can study the geodynamic evolution of crustal and upper mantle structures which were once participating in continental collision and are now deeply eroded. Together with the ScanArray network we use data from previous and permanent projects, in total more >220 stations, for a surface wave tomography of entire Scandinavia using both earthquake and ambient noise data.

Initially, we performed a beamforming of Rayleigh surface waves which yielded average phase velocities for the study region and several of its sub-regions. However, a remarkable sin(1Θ) phase velocity variation with azimuth is observed in northern Scandinavia and southern Norway/Sweden but not in the central study area. For periods >35 s a 5% deviation between the maximum and minimum velocities was measured for opposite backazimuths of 120° and 300°, respectively. Such a variation is incompatible with azimuthal anisotropy or weak heterogeneity and might be caused by an eastward dipping lithosphere-asthenosphere boundary (LAB), as is implied by the observations of low shallow velocities below southern Norway in previous studies.

In order to test this hypothesis, we carried out 2D full-waveform modeling of the Rayleigh wave propagation in a model with a steep gradient in the LAB in combination with a pronounced reduction in the shear velocity below the LAB. This setup resulted in faster phase velocities for propagation in the direction of shallowing LAB, and slower ones for propagation in the direction of deepening LAB, consistent with the observation. This effect is probably due to the interference of reflected surface wave energy.

From this observed azimuthal bias, we demonstrate that an isotropic distribution of earthquakes is vital for the tomography results, otherwise significant velocity artefacts occur.

Phase velocity maps were derived with the two plane wave method. We merge those ballistic surface wave observations at longer periods with tomographic maps constructed from inter-station phase velocities measured on ambient noise stacks. Finally, we use a 1D transdimensional Bayesian method to invert the merged phase dispersion curves at each grid point for the V_SV structure. Below the entire mountain belt a crustal root is absent consistent with previous studies. The Lofoten peninsula shows very low crustal and lithospheric V_SV with a shallowing Moho towards the continental margin. The LAB is deepening from west to east with a sharp step both in the South (120 km depth) and the North (150 km depth). A high-velocity spot above the LAB in the North can be related to a gravity anomaly. The central area shows rather smooth varying structures from west to east. Additionally, we find low-velocity areas below 150 km depth beneath the Paleoproterozoic Baltic Shield in northern Finland. The sharp gradients in the LAB imaged in southern and northern Scandinavia are consistent with our sin(1Θ) phase velocity variation with azimuth whereas the smoother velocity structure in the central study area explains the absence of 1Θ phase velocity variations there.

How to cite: Mauerberger, A., Maupin, V., Sadeghisorkhani, H., Gudmundsson, O., and Tilmann, F.: Scandinavian Lithosphere Structure derived from Surface Waves and Ambient Noise, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8366, https://doi.org/10.5194/egusphere-egu2020-8366, 2020.

The southern Baltic Sea area is in the transition zone between the Fennoscandian Shield as part of the East European Craton (EEC) and the West European Platform. This area is characterised by a mosaic of various geological blocks separated by several fault zones formed throughout the Phanerozoic. The most prominent tectonic feature is the NW–SE trending Sorgenfrei-Tornquist Zone, crossing the southern Baltic Sea area between Scania in Sweden and Pomerania in Poland. Recently, this area was covered with the new multi-channel seismic data (MCS), acquired during the “BalTec” cruise of the German R/V Maria S. Merian. In addition to MCS data, hydroacoustic and gravity data were collected along the same profiles.

The new data, acquired during the “BalTec” cruise in 2016, include 3500 km of MCS data and 7000 km of gravity data. This is the first such a regional survey in the southern Baltic Sea, which provides a gapless image of sedimentary layer with a high resolution from seafloor to the base of Permian salt (North German-Polish Basin) or Palaeozoic strata (EEC). In addition, a 230-km long refraction/wide-angle reflection (WARR) profile was acquired across the transition zone to image its deeper structure. This profile is nearly parallel to the western Polish coast in half a distance to Bornholm.

The main topic of our study is the structure of Phanerozoic sedimentary cover in the southern Baltic Sea and its relationship to the geological evolution of the area situated at the junction of two major tectonic units of NW Europe. In the methodological part of our research, we are going to develop the process of integration of potential field modelling into seismic interpretation workflow. Another important point is testing the capability of marine versus satellite gravity data to reflect the geometry of shallow tectonic structures.

The first step in analysis of potential field data was integration of marine gravity with a regional gravity dataset. The result was a coherent gravity grid, which was used for further advanced processing, involving calculation of transformations and derivatives. We also included a regional magnetic grid in the advanced processing. Calculated derivatives and filters of gravity and magnetic data were applied for qualitative interpretation, i.e., compilation of a structural map based on the location and nature of gravity and magnetic anomalies. In addition, a preliminary 2D forward model was produced for the WARR profile to provide an image of the broad crustal structure. The next 2D models will be built upon seismic reflection profiles acquired during the “BalTec” cruise. The results will be eventually used to calibrate the three-dimensional model for the top of crystalline basement derived from gravity inversion.

This study was funded by the Polish National Science Centre grant no UMO-2017/25/B/ST10/01348.

How to cite: Ponikowska, M., Mazur, S., Malinowski, M., Hübscher, C., Heyde, I., Janik, T., and Wójcik, D.: Crustal structure in the transition zone from the Precambrian to Palaeozoic platform in the southern Baltic Sea – inferences from newly acquired potential field and seismic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16237, https://doi.org/10.5194/egusphere-egu2020-16237, 2020.

Crustal and uppermost mantle structure along the Teisseyre-Tornquist Zone (TTZ)  was explored along the ~550 km long, NW-SE-trending TTZ-South profile, using seismic wide-angle reflection/refraction (WARR) method. The profile line was intended to follow the border between the East European Craton (EEC) and the so called Palaeozoic Platform (PP) of north-central Europe, believed to contain a number of crustal blocks that were accreted to the craton during pre-late Carboniferous times, defining the Trans-European Suture Zone (TESZ).

The seismic velocity model of the TTZ-South profile shows lateral variations in crustal structure. Its Ukrainian segment crosses the interior of the Sarmatian segment of the EEC, where the crystalline basement gradually dips from ~2 km depth in the SE to ~12 km at the Ukrainian-Polish border. This part of the model shows a four-layered crustal structure, with an up to 15 km-thick sedimentary cover, an underlying crystalline upper crust, a 10-15 km-thick middle crust and a ~15 km thick lower crust. In Poland, the profile passes along the TESZ/EEC transition zone of complex crustal structure. The crystalline basement, whose top occurs at depths of 10-17 km, separates the sedimentary cover from the ~10 km thick mid-crustal layer (Vp=6.5-6.6 km/s), which, in turn, overlies a block of 10-15 km thickness with upper crustal velocities (Vp~6.2 km/s). The latter is underlain by a ~10-15 km-thick lower crust. Along most of the model one can see conspicuous velocity inversion zones occuring at various depths. At intersections of the TTZ-South profile with some previous deep seismic profiles (e.g. CEL02, CEL05, CEL14, PANCAKE) such inversions document complex wedging relationships between the EEC and PP crustal units. These may have resulted from tectonic compression and thick-skinned thrusting due to either Neoproterozoic EEC collision with accreting terranes or intense Variscan orogenic events. Five high velocity bodies (HVB; V_p = 6.85-7.2 km/s) were detected in the middle and lower crust at 15-37 km depth. The Moho depth varies substantially along the profile. It is at ~42 km depth in the NW and deepens SE-ward to ~50 km at ~685 km. Subsequently, it rises abruptly to ~43 km at the border of the Sarmatian segment of the EEC and sinks again to ~50 km beneath the Lviv Paleozoic trough at ~785 km. From this point until the SE end of the profile, the Moho gently shallows, up to a depth of ~37 km, including a step-like jump of 2 km at ~875 km. Such abrupt Moho steps may be related to crust-scale strike-slip faults. Along the whole profile, sub-Moho velocities are ~8.05-8.1 km/s, and at depths of 57-63 km Vp values reach 8.2-8.25 km/s. Four reflectors/refractors were modelled in the upper mantle at ~57-65 km and ~80 km depths.

How to cite: Janik, T., Starostenko, V., Aleksandrowski, P., Yegorova, T., Czuba, W., Środa, P., Murovskaya, A., Zajats, K., Głuszyński, A., Kolomiyets, K., Lysynchuk, D., Wójcik, D., Omelchenko, V., Legostaieva, O., Mechie, J., Tolkunov, A., Amashukeli, T., Gryn’, D., and Chulkov, S.: The transition of the East European cratonic lithosphere to that of the Palaeozoic collage of the Trans-European Suture Zone as depicted on the TTZ-South deep seismic profile (SE Poland to NW Ukraine), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7687, https://doi.org/10.5194/egusphere-egu2020-7687, 2020.

The area of Sudetes, located at the margin of the Bohemian Massif, represents the NE-most part of the Variscan internides between the Elbe Fault in SW and the Odra Fault in NE. The lithosphere of the region is a mosaic of several distinct units/terranes with complex tectonic history ranging from the upper Proterozoic till the Quaternary. The crustal and uppermost mantle structure of this region was studied by seismic wide-angle experiment SUDETES 2003 and the results of 2-D isotropic modelling were published. Recently, this dataset, comprising off-line recordings from a net of intersecting profiles, was interpreted using anisotropic delay-time inversion. This resulted in models of 2-D distribution of upper crustal and uppermost mantle anisotropy based on azimuthal variability of the Pg and Pn traveltimes, respectively. The upper mantle of Sudetic region was the target of a passive seismic experiment AniMaLS. The project involved 23 broadband seismic stations deployed in the area of Sudetes and Fore-Sudetic block in SW Poland, supplemented with the data from 6 permanent seismic stations, operating in this area in Czech Republic and Poland. The measurements cover a ~200x100 km large area, with ~30 km inter-station spacing. The stations, deployed for a period of 24 months (2017-2019), provided broadband recordings of local, regional and teleseismic events. The aim of the experiment is to study the structure, seismic velocity variations including anisotropy distribution, and to map the upper mantle seismic discontinuities (Moho, lithosphere-asthenosphere boundary, mantle transition zone). Currently, the AniMaLS data are being interpreted using shear wave splitting method and receiver function method. The analysis of SKS and SKKS splitting was based on cross-correlation, eigenvalue minimization and transverse energy minimization methods. Resulting time delays between slow and fast S-wave components are ~1.2 sec on average, with fast velocity axis oriented largely in WNW-ESE direction, consistently with results of delay-time inversion of Pn phase traveltimes. Crustal anisotropy is characterized by similar fast axis orientation, but with lower amplitude of anisotropy. The orientation of fast axes in the crust and mantle correlates well with surface trends of tectonic units and with strike directions of major fault zones. This suggests vertically coherent deformation throughout the lithosphere, most likely during consolidation of the Sudetic region in Variscan times.

How to cite: Środa, P., Rewers, J., Materkowska, W., Ke, K.-Y., and Working Group, A.: Passive and active seismic studies of lithospheric structure and anisotropy beneath Sudetes (NE Variscides), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20099, https://doi.org/10.5194/egusphere-egu2020-20099, 2020.

The crustal structure of the Anatolian plateau in Turkey is investigated using receiver functions obtained from the teleseismic recordings of the Kandilli Observatory array (KOERI; KO) and the available IRIS data (e.g., Eastern Turkey Seismic Experiment (ETSE), Northern Anatolian Fault experiment (YL), Continental Dynamics–Central Anatolian Tectonics (CD-CAT) project). The following steps are included for studying the crustal structures in Anatolia Plate: 1) high-resolution crustal structures inferred from Receiver Function (RF) inversion algorithm using multiple-taper correlation (MTC) estimates, we try to distinguish interfaces including Moho, bottom of partial melting and other interfaces by the Ps phase; 2) we calculate RFs by Time Domain Interactive Deconvolution and transform the time domain RFs into the H-Vp/Vs (H-k) domain to find the best fit Moho and Vp/Vs, we classify the quality of the H-k stacking results and record all the possible H-k couples; 3) we determine the H-k values for the stations with low quality by comparing the RF H-k stacking results with nearby stations with good quality. With the dense stations, we present high-quality Moho variations and crustal structures in the Anatolia Plate.

How to cite: Zhou, Z., Thybo, H., Kusky, T., and Tang, C.-C.: Crustal structures of the Anatolian Plate from receiver function analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7872, https://doi.org/10.5194/egusphere-egu2020-7872, 2020.

Formation and evolution of the continental lithosphere, one of the ILP research themes, still belongs to fundamental questions often debated within different geoscience disciplines. We emphasize the role of mantle lithosphere that forms the biggest volume of continents, but is often overlooked, particularly in geologic interpretations of tectonic processes. Investigation of seismic anisotropy from propagation of teleseismic P and S waves in three dimensions (3D) provides a unique constraint on tectonic fabrics and character of past and present-day deformations. We collect independent findings from seismology, petrology and geochemistry to support our 3D anisotropic model of mantle lithosphere with tilted symmetry axes, derived from data of passive seismic experiments organised in tectonically different domains of Archean, Proterozoic and Phanerozoic provinces of Europe. We delimit the extent of lithosphere domains and their boundaries according to changes in orientation of the large-scale anisotropy, associated with a systematic preferred orientation of olivine, originally formed by mantle convection in the oceanic mantle lithosphere and “frozen” deep in continents.

We explain the oriented dipping fabrics in the continental mantle lithosphere by successive subductions of ancient oceanic plates and their accretions enlarging a primordial continent core, consequent supercontinent break-ups and assemblages of wandering micro-plates to create the patchwork structure of the present-day continents. Supporting arguments for such model arise from petrologic and geochemical studies indicating that continental peridotites formed in oceanic environments and became “continental” after significant thickening or underthrusting. Combining seismological, petrologic and geochemical findings can help to bridge the gap between the different viewpoints and evoke further discussions on growth mechanisms and evolution of the continental lithosphere. Data gathered during new large-scale passive seismic experiments, like AlpArray, AdriaArray, PACASE and related projects, including CoLiBrI - Continental Lithosphere: a Broadscale Investigation, will provide new exciting materials for studies of formation and evolution of the continental lithosphere.

How to cite: Babuška, V., Plomerová, J., Vecsey, L., and Žlebčíková, H.: Growth and evolution of continental lithosphere by cycles of oceanic subductions – Evidence from seismic anisotropy supported by petrologic and geochemical findings, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7822, https://doi.org/10.5194/egusphere-egu2020-7822, 2020.

The causes of delamination of the mantle lithosphere in collision zones is actively debated in the scientific community. The main discussions are focused on the initiation of sinking of the continental lithosphere into the asthenosphere to a depth. Most scientists believe that such kind of immersion is impossible. However, there are several articles showing that this process is nonetheless taking place. For example Kay and Kay, (1993), Faccenda, Minelli, Gerya, (2009), Ueda et. al., (2012) and others propose various mechanisms of delamination, for example: eclogitization of the mafic layer of the lower crust, the effect of convection in the upper mantle, or gradual transition of the oceanic subduction into continental collision. Does the mantle part of the lithosphere sink into the mantle or spread laterally, as described in [for example, Deep Geodynamics, 2001; Bird, 1991; Schmeling and Marquart, 1991]?

To answer these questions, we study deep structures beneath the Caucasus and Kyrgyz Tien Shan collision zones. The studies were carried out on the basis of multiscale seismic tomography methods: regional and global. This approach made it possible to study heterogeneities both in the crust and in the upper mantle. The obtained 3D models of seismic heteroheneities reveal similar features for the both collision regions. Beneath the mountain areas, in the uppermost mantle and lower crust, we observe prominent low-velocity anomalies that possibly indicate thickening of the crust and missing (or strongly thinned) mantle part of the lithosphere. At the edges of the collision zones, we reveal inclined high-velocity anomalies appearing as continuations of the continental plates sinking underneath the collision zones, which can be interpreted as delaminating mantle parts of the continental lithosphere.  Based on joint consideration of the tomography models with the existing models of tectonic evolution, we conclude that the mechanisms of delamination in the considered two regions are different. In Caucasus, the delamination could be gradually transformed from oceanic subduction that ended here approximately ~10-15 Ma. In the case of Tien Shan, the detachment of the mantle lithosphere could be triggered by the plume that existed beneath Central Tien Shan or by the eclogitization of the mafic layer of the lower crust.

The reported study was funded by RFBR, project number 19-35-60002.

How to cite: Medved, I., Koulakov, I., and Buslov, M.: Different causes of the delamination on the example of Caucasus and Kyrgyz Tien Shan collision zones., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6412, https://doi.org/10.5194/egusphere-egu2020-6412, 2020.

The Andean orogeny is a ~7000 km long N-S trending mountain range developed along the South American western margin. The formation of this mountain range is driven by the subduction of the oceanic Nazca plate beneath the continental South American plate, being the only known present-day case of subduction-type orogeny. In this tectonic setting, the intrinsic physical properties of the overriding plate govern the formation of zones of crustal strength and weakness and control the localization and the style of deformation. Furthermore, the dynamics of the subducting oceanic lithosphere is strongly conditioned by the properties of the continental counterpart. The southern segment of the Central Andes (29°S-39°S) is a suitable scenario to investigate the relationship between the two plates for several reasons. It is characterized by a complex deformation pattern with variations in horizontal shortening, crustal thickening and mean topographic elevation. In addition, the subduction angle changes at 33°S-35°S latitude from flat in the North to normal in the South. To gain insight into this geodynamic system, a detailed characterization of the lithosphere is needed. Therefore, we constructed a 3D model of the entire segment of the Southern Central Andes that is consistent with the available geological, seismic and gravity data in order to assess the geometry and density variation within the lithosphere. The derived configuration shows a spatial correlation between density domains and known tectonic features. It is also consistent with other independent observations such as S wave velocity variation and surface deformation. The generated structural model allows us to reach the first conclusions about the relationship between the characteristics of the overriding plate and the crustal deformation and dynamics of the subduction system. It is also useful to constrain thermomechanical experiments and therefore contributes to discussions about the crustal thermal and rheological fields within the region.

How to cite: Rodriguez Piceda, C., Scheck-Wenderoth, M., Gómez Dacal, M. L., Bott, J., Prezzi, C., and Strecker, M.: Lithospheric density structure of the Southern Central Andes and their forelands constrained by 3D gravity modelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3313, https://doi.org/10.5194/egusphere-egu2020-3313, 2020.

Qaidam Basin, located in the northern margin of the Tibet Plateau, is the junction of several tectonic blocks. The blocks’ extrusion resulted in large faults and strong historical earthquakes. Previous studies have shown that the crustal structures of the eastern and the western Qaidam Basin are obviously different. In this study, the seismic reflection and refraction phases from Conrad and Moho discontinuity in Qaidam Basin are distinguished by waveform simulation and travel time fitting of 3 regional earthquakes on 32 stations. The results of travel time fitting and waveform simulation show that the first arrivals in the epicenter range of 90km ~ 260km are the P* phases from the Conrad discontinuity. The depth of Conrad discontinuity under the eastern basin is about 4 km shallower than that in the western basin, which can be attributed to different crust thickening models between the eastern and western basin. In addition, the focal depths of regional earthquakes occurred within recent 5 years in Qaidam region also shows the difference of the Conrad discontinuity. The Conrad discontinuity is considered to be the lower boundary of the low velocity layer in the upper crust. The upper crust thickening in the western basin led to the sinking of the layer, while the multiple thrusts resulted in the rise of the lower crust in the east. The two different effects could interpret the depth change of the Conrad discontinuity in the basin from the west to the east. 

How to cite: Yang, B. and Wang, Y.: Characteristics of Conrad Discontinuity in the Northern Margin of Tibet Plateau Obtained from Regional Seismic Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6299, https://doi.org/10.5194/egusphere-egu2020-6299, 2020.

The seismically active western continental margin of India (WCMI) comprises of the three pericratonic rifts (Kachchh, Cambay, and Narmada) and the Saurashtra uplift that has been formed during the northward trek of the Indian plate. In the present study, forward and inverse modeling of the Bouguer anomaly have been done to calculate the topographical variation of the Moho and Lithosphere-Asthenosphere boundary (LAB). Inversion is implemented over the band-pass (cut-off wavelength 100 and 200 km) and low-pass (cut-off wavelength 200 km) filtered Bouguer anomaly with the assumption of constant density contrast between the Moho and LAB interfaces. Results of the inversion reveal significant variation of the Moho and LAB depths over the WCMI that vary between (1) 33-42 km and 82-124 km in the Kachchh rift, (2) 34-42 km and 68-110 km in the Cambay rift and north Gujarat, (3) 36-44 km and 80-95 in the Narmada rift and south Gujarat and (4) 34-41 km and 85-135 km in the Saurashtra peninsula, respectively. Using the present results of the Moho and LAB depths as constraint, forward modeling has been performed over the band-pass filtered (cut-off wavelength of 100 and 500 km) Bouguer anomaly. The result of forward modeling reveals that the magmatic underplating layer is enveloping the entire crust of the WCMI which indicates that the whole region has been affected by the Reunion hotspot volcanic activity. A thin lithosphere beneath the Cambay and Kachchh rift has been observed which expedited the eruption of volcanic material through the pre-existing rift zones. The Cambay rift is the zone of high geothermal gradient where LAB is upwarped and both the signatures indicate the existence of partial melting condition at a shallow depth that is also confirmed by recent seismological studies. 

How to cite: Chouhan, A. K., Choudhury, P., and Pal, S. K.: Evidence of shallow lithosphere and crust in the western continental margin of India through modeling of gravity data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-316, https://doi.org/10.5194/egusphere-egu2020-316, 2020.

We model the depth and Vs structure of the Hales discontinuity (H-D) beneath Eastern Dharwar Craton (EDC) and Southern Granulite Terrain (SGT) using P-wave receiver function (P-RF) analysis and joint inversion with Rayleigh wave phase velocity dispersion. We calculate P-RFs at higher frequency (fmax 0.46 Hz), compared to previous studies, to show that the P-to-S converted phase from the H-D (Phs) is distinct from the crustal reverberations. The Phs at stations in the EDC arrive at ~10 s beneath GBA, and ~11 s beneath HYB. From joint inversion the H-D is modeled at 97 ± 5 km and 108 ± 5 km depth, with 5% and 3% Vs increase, beneath GBA and HYB, respectively. For KOD, in SGT, the Phs coincides with the mid-crustal PpSs+PsPs reverberation at most ray-parameters, causing destructive intereference. This explains the apparent absence of Phs in previous studies. We isolated P-RFs where Phs is distinct at ~10.5 s and model it at depth of 101 ± 5 km with Vs increase of 3%. We demonstrate through forward calculation that the spinel-garnet mineral transformation cannot explain the H-D Vs increase. From data of mantle xenoliths in the Wajrakarur kimberlite field, Southern India, we calculate Vs of mantle peridotite and eclogite, using published bulk rock compositions through Perple-X. At the H-D depth and temperature derived from Indian shield geotherm, we observed a perfect match to the Vs. We hypothesize that H-D marks the surface of a paleo-subducted eclogitic oceanic slab embeded within the upper mantle peridotite. Observations of mantle faults within the Canadian lithosphere, at similar depth, has been related to relict-subduction zones and therefore independently supports our model.

How to cite: Chaudhury, J., Mitra, S., and Sarkar, T.: Imaging Hales Discontinuity beneath India: Seismological and Petrological Model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3286, https://doi.org/10.5194/egusphere-egu2020-3286, 2020.

We study the crustal structure of Sri Lanka by analyzing data from a temporary seismic network deployed in 2016-2017 to shed light on the amalgamation process from the geophysical perspective. Rayleigh wave phase dispersion from ambient noise cross-correlation and receiver functions were jointly inverted using a transdimensional Bayesian approach.

The Moho depths range between 30 and 40 km, with the thickest crust (38-40 km) beneath the central Highland Complex (HC). The thinnest crust (30-35 km) is found along the west coast, which experienced crustal thinning associated with the formation of the Mannar Basin. Vp/Vs ratios lie within a range of 1.60-1.82 and predominantly favor a felsic composition with intermediate-to-high silica content of the rocks.

A major intra-crustal (18-27 km), slightly westward dipping (~4.3°) interface with high Vs (~4 km/s) underneath is prominent in the central HC, continuing in the eastern Vijayan Complex (VC). The dipping discontinuity and a low velocity zone in the central Highlands can be related to the HC/VC contact zone and is in agreement with a well-established amalgamation hypothesis of a stepwise collision of the arc fragments, including deep crustal thrusting processes and a transpressional regime along the suture between the HC and VC.

How to cite: Dreiling, J., Tilmann, F., Yuan, X., Haberland, C., and Seneviratne, S. W. M.: Crustal structure of Sri Lanka derived from joint inversion of surface wave dispersion and receiver functions using a Bayesian approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11544, https://doi.org/10.5194/egusphere-egu2020-11544, 2020.

Temperature and heat flow are key parameters for understanding the potential for source rock maturation in sedimentary basins. Knowledge of the thermal structure of the lithosphere in both a regional and local context can provide important constraints for modelling basin evolution through time.

In recent years, global coverage of heat flow data constraints have enhanced scientific understanding of the thermal state of the lithosphere. However, sample bias and variability in sampling methods continues to be a major obstacle to heat flow-derived isotherm prediction, particularly in frontier areas where data are often sparse or poorly constrained. Consideration and integration of alternative approaches to predict temperature at depth may allow interpolation of surface heat flow in such data poor areas.   

We have attempted to integrate three independent approaches to modelling temperature with depth. The first approach is based on heat flow observations, in which a 1D steady-state model of the lithosphere is constructed from quality-assessed surface heat flow data, crustal thickness estimates and associated lithospheric thermal properties. The second approach is based on terrestrial (airborne, ground and shipborne) magnetic data, in which the maximum depth of magnetisation within the lithosphere is estimated using a de-fractal method and used as a proxy for Curie temperature depth. The third approach is based on satellite magnetic data and estimates the thickness of the magnetic layer within the lithosphere based on the varying amplitudes of satellite magnetic data, accounting for global variations in crustal magnetisation. Curie temperature depth results from each of these approaches have been integrated into a single global grid, then used to calculate temperature-depth variations through the crust.

We have evaluated our isotherm predictions by comparing them with temperature-depth control points and undertook qualitative and quantitative analyses of discrepancies that exist between different modelling approaches; this has provided insights into the origin of such discrepancies that can be integrated into our models to generate a better controlled global temperature-depth result.  

We present details of our methodology and the results of our integrated studies. We demonstrate areas where the independent results are in good agreement, providing vital information for high-level basin screening. We also highlight areas of disagreement and suggest possible causes for these discrepancies and potential resolutions.

How to cite: Masterton, S., Cheyney, S., Green, C., and Webb, P.: Towards a global lithospheric thermal model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19005, https://doi.org/10.5194/egusphere-egu2020-19005, 2020.

The configuration of the lithosphere below sedimentary basins varies in response to the basin-forming mechanism, the lifetime of the causative stress fields and the lithological heterogeneity inherited from pre-basin tectonic events. Accordingly, the deep thermal configuration is a function of the tectonic setting, the time since the thermal disturbance occurred and the internal heat sources within the lithosphere. We compare deep thermal configurations in different settings based on data-constrained 3D lithosphere-scale thermal models that consider both geological and geophysical observations and physical processes of heat transfer. The results presented come from a varied range of tectonic settings including: (1) the extensional settings of the Upper Rhine Graben and the East African Rift System, where we show that rifts can be hot for different reasons; (2) the North and South Atlantic passive margins, demonstrating that magma-rich passive margins can be comparatively hot or cold depending on the thermo-tectonic age; (3) the Alps, where we find that foreland basins are influenced by the conductive properties and heat-producing units of the adjacent orogen; and (4)the Sea of Marmara, along the westernmost sector of the North Anatolian Fault Zone, that suggest strike-slip basins may be thermally segmented.

How to cite: Scheck-Wenderoth, M., Bott, J., Cacace, M., Anikiev, D., Gomez Dacal, M. L., Spooner, C., and Gholamrezaie, E.: Thermal signature of the lithosphere below sedimentary basins in extensional, compressive and transform settings, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22518, https://doi.org/10.5194/egusphere-egu2020-22518, 2020.