TS12.2

EDI
Geometrical characteristics of geological structures in 2- and 3-dimensions

Geological structures such as faults, fractures, folds, and associated fabrics are complex 3-D geological objects and, therefore, their thorough understanding intrinsically requires a 3-, in addition to 2-D analysis. In this session, we invite contributions that address the geometrical complexities of geological structures by taking into account their inherent 3-D nature, and we aim at promoting discussion on any similarities or disparities between the geometries of different structures, and on the processes that may develop them. As the integration of different data types can provide insights on the characteristics of geological structures at different scales, we invite contributions that build on a broad spectrum of data, such as outcrop, geophysical imaging, earthquake seismicity, and analogue and numerical modelling data. Contributions based on innovative quantitative methods for building high-resolution 3-D geological models such as, for example, micro-computed tomography or photogrammetric techniques, are also welcome. Further, discussions on the predictive nature of geological structures are encouraged for use in a wide range of industries. This can include estimating fluid flow in reservoirs associated with hydrogeology and hydrocarbons to “green” industries such as CO2 storage and the production of geothermal energy, as well as discussing their importance for earthquake hazard assessment or within the geotechnical, mining or civil engineering sectors.

Co-organized by NH4
Convener: Giovanni CamanniECSECS | Co-conveners: Marta AdamuszekECSECS, Efstratios DelogkosECSECS, Emma MichieECSECS, Marcel ThielmannECSECS
vPICO presentations
| Thu, 29 Apr, 13:30–15:00 (CEST)

Session assets

Session materials

vPICO presentations: Thu, 29 Apr

Chairpersons: Marta Adamuszek, Efstratios Delogkos, Emma Michie
13:30–13:35
13:35–13:45
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EGU21-2227
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solicited
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Highlight
Anita Torabi, Behzad Alaei, and Audun Libak

Understanding fault geometry and processes of faulting are important research areas for many applications such as petroleum exploration and production; geothermal energy managements; hydrogeology; waste disposal and CO2 storage underground; earthquake seismology and geological hazard studies. Faults can be described as comprising a core and an enveloping damage zone (e.g. Caine et al. 1996).  The fault core accommodates most of the displacement along multiple slip surfaces and may include fault rocks such as fault gouge, cataclasites, breccia, clay smear, fractures, diagenetic features, and lenses of deformed and undeformed rocks trapped between slip surfaces. Whereas, the deformation is less intense in the damage zone and may include fractures and/or deformation bands depending on the initial porosity of the host rock, minor faults, and folds (Torabi et al., 2020). Fault geometric attributes include fault shape, fault displacement, length, damage zone width and fault core thickness (Caine et al., 1996; Torabi and Berg, 2011). Currently, there are uncertainties in defining and understanding of fault 3D geometry. These uncertainties are to some extent related to the accessibility of the fault geometric attributes and the methodological constraints, utilizing biased data. Details of fault damage zone and fault core structures can be mapped at outcrop, however, their descriptions and statistical handling are usually constrained by their accessibility in the field and their definitions by individual researchers.

Reflection seismic data is used to study faults in the subsurface, although the interpretation of faults could be affected by the seismic resolution and the accuracy of interpretation (Marchal et al., 2003; Lohr et al., 2008; Iacopini et al., 2016; Torabi et al., 2016). Utilizing seismic attributes, we are able to directly images faults from seismic without a need for interpretation. Using this method, we extracted fault geometric attributes directly from fault images in the fault attribute volumes and studied the 3D shape and displacement distribution of faults (Torabi et al., 2019). By integrating spectral decomposition with seismic attribute workflows, we created enhanced fault attribute volumes with a high resolution, allowing us to detect, and map fault damaged zone (fault damage zone plus fault core in outcrop scale) in seismic data (Alaei and Torabi, 2017). Finally, we integrated the data from outcrop and seismic study in the scaling relations between the faults geometric attributes in order to predict the fault geometry in the subsurface.

 

 

How to cite: Torabi, A., Alaei, B., and Libak, A.: Fault geometry and architecture, an integrated study, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2227, https://doi.org/10.5194/egusphere-egu21-2227, 2021.

Strike-slip faults
13:45–13:47
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EGU21-2229
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ECS
Jakub Fedorik, Francesco E. Maesano, and Abdulkader M. Alafifi

Strike-slip structures are rarely validated because commonly used 2D restoration techniques are not applicable. Here we present the results of 3D numerical simulation of the restraining bends in Lebanon using boundary element methods of fault deformation implemented in MOVE™. The Lebanon restraining bend is the largest transpressional feature along the Dead Sea Transform (DST), and consists of two mountain ranges: Mount Lebanon on the west, dominated by the active Yammouneh fault, and the Anti-Lebanon Range to the east, influenced by the Serghaya and other faults. We built a new 3D geometrical model of the fault surfaces based on previous mapping of faults onshore and offshore Lebanon, complemented by interpretation of satellite images and DEM, and analogy with experimental models of restraining bend or transpressional structures. The model was simulated in response to the regional stress produced by the left-lateral displacement of the Arabian plate. The simulation accurately predicted the shape and magnitude of positive and negative topographic changes and faults slip directions throughout Lebanon. Furthermore, this simulation supports the hypothesis that the formation of the Anti-Lebanon Range was influenced by the intersection of the DST with the older Palmyrides belt, resulting in failed restraining bend. In contrast, the structure of Mt. Lebanon is similar to laboratory experiments of a restraining bend without inheritance. In addition, our simulation presents an approach of how strike-slip structural models may be validated in areas where subsurface data are limited.

How to cite: Fedorik, J., E. Maesano, F., and M. Alafifi, A.: Numerical simulation of structural growth in the Lebanese restraining bends, Dead Sea fault system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2229, https://doi.org/10.5194/egusphere-egu21-2229, 2021.

13:47–13:49
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EGU21-7016
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ECS
Hardy Medry Dieu-Veill Nkodia, Timothée Miyouna, Florent Boudzoumou, and Damien Delvaux

Damage zones around strike-slip faults constitutes important site of earthquake initiation, propagation, rupture or barrier. They also constitute important sites that host and conduct fluids. Most investigations of these strike-slip damage zones focus on plan view geometries and little attention is paid to subsurface or profile geometries associated. Depending on the presence of a shortening or extensional component during deformation, strike-slip faults do not often show straight path in cross-section. Understanding the expression of damage zones in cross-section is therefore important in predicting subsurface strike-slip faults features. The Paleozoic red feldspathic sandstones of the Inkisi Group in the foreland of the West-Congo Belt show beautiful examples of strike-slip faults with damage zones in both the Republic of Congo and the Democratic Republic of Congo (Nkodia et al., 2020). These strike-slip faults are organized in two major faults system developed in a pure strike-slip regime. The oldest system is dominated by NNW–SSE trending sinistral strike-slip faults and minor E–W striking dextral strike-slip faults. The youngest system consists of dominant NE–SW trending dextral strike-slip faults and minor NW–SE trending sinistral strike-slip faults. Field investigation show four arrangement of flowers structures along the strike-slip faults: (i) those associated with wall damage zones; (ii) those associated with linking damage zones; (iii) those associated with tip damage zones; and (iv) “hourglass” flower structures. Further investigation of strike-slip faults in the Schisto-calaire Group of the West-Congo Belt show also similar flower structures arrangement in limestones. In the Inkisi Group, these arrangements are dependent on the fault growth and propagation. Both strike-slip faults system in the Inkisi Group show an evolving pattern, from closely spaced short faults segments, to highly spaced long faults segments with few interactions of pattern. 

Nkodia, H.M.D.V., Miyouna, T., Delvaux, D., Boudzoumou, F., 2020. Flower structures in sandstones of the Paleozoic Inkisi Group (Brazzaville, Republic of Congo): evidence for two major strike-slip fault systems and geodynamic implications. South African Journal of Geology 123(4), 531-550. Doi: 10.25131/sajg.123.0038.

How to cite: Nkodia, H. M. D.-V., Miyouna, T., Boudzoumou, F., and Delvaux, D.: Integration of flower structures in strike-slip fault damage zones classification – examples from the West-Congo belt and foreland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7016, https://doi.org/10.5194/egusphere-egu21-7016, 2021.

Extensional faults
13:49–13:51
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EGU21-997
Hongdan Deng and Ken McClay
Basement fault reactivation, and the growth, interaction, and linkage with new fault segments are fundamentally three-dimensional and critical for understanding the evolution of fault network development in sedimentary basins. This paper analyses the evolution of a complex, basement-involved extensional fault network on the Enderby Terrace on the eastern margin of the Dampier sub-basin, NW Shelf of Australia. A high-resolution, depth-converted, 3D seismic reflection data volume is used to show that multiphase, oblique extensional reactivation of basement-involved faults controlled the development of the fault network in the overlying strata. Oblique reactivation of the pre-existing faults initially led to the formation of overlying, en échelon Late Triassic – Middle Jurassic fault segments that, as WNW–directed rifting progressed on the margin, linked by breaching of relay ramp to form two intersecting fault systems (F1 and F2-F4). Further reactivation in the Latest Jurassic – Early Cretaceous (NNW–SSE extension) produced an additional set of en échelon fault arrays in the cover strata. The final fault network consists of main or principal faults and subordinate or splay faults, together with branch lines that link the various components. Our study shows that breaching of relay ramps and/or vertical linkages produces vertical and horizontal branch lines giving complex final fault geometries. We find that repeated activity of the basement-involved faults tends to form continuous and planar fault architectures that favor displacement transfer between the main constituent segments along strike and with depth.

How to cite: Deng, H. and McClay, K.: Three-dimensional geometry and growth of a basement-involved fault network developed during multiphase extension, Enderby Terrace, North West Shelf of Australia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-997, https://doi.org/10.5194/egusphere-egu21-997, 2021.

13:51–13:53
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EGU21-15228
Vincent Roche, Giovanni Camanni, Conrad Childs, Tom Manzocchi, John Walsh, John Conneally, Muhammad Mudasar Saqab, and Efstratios Delogkos

Normal faults are often complex three-dimensional structures comprising multiple sub-parallel segments separated by intact or breached relay zones. In this study we outline geometrical characterisations capturing this 3D complexity and providing a semi-quantitative basis for the comparison of faults and for defining the factors controlling their geometrical evolution. Relay zones are classified according to whether they step in the strike or dip direction and whether the relay zone-bounding fault segments are unconnected in 3D or bifurcate from a single surface. Complex fault surface geometry is then described in terms of the relative numbers of different types of relay zones to allow comparison of fault geometry between different faults and different geological settings. A large database of 87 fault arrays compiled primarily from mapping 3D seismic reflection surveys and classified according to this scheme, reveals the diversity of 3D fault geometry. Analysis demonstrates that mapped fault geometries depend on geological controls, primarily the heterogeneity of the faulted sequence and the presence of a pre-existing structure. For example, relay zones with an upward bifurcating geometry are prevalent in faults that reactivate deeper structures, whereas the formation of laterally bifurcating relays is promoted by heterogeneous mechanical stratigraphy. In addition, mapped segmentation depends on resolution limits and biases in fault mapping from seismic data. In particular, the results suggest that the proportion of bifurcating relay zones increases as data resolution increases. Overall, where a significant number of relay zones are mapped on a single fault, a wide variety of relay zone geometries occurs, demonstrating that individual faults can comprise segments that are both bifurcating and unconnected in three dimensions. Models for the geometrical evolution of fault arrays must therefore account for the full range of relay zone geometries that appears to be a characteristic of all faults.

How to cite: Roche, V., Camanni, G., Childs, C., Manzocchi, T., Walsh, J., Conneally, J., Saqab, M. M., and Delogkos, E.: Geometrical characterisation of fault arrays in three dimensions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15228, https://doi.org/10.5194/egusphere-egu21-15228, 2021.

13:53–13:55
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EGU21-150
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ECS
Alexander Peace, Christian Schiffer, Scott Jess, and Jordan Phethean

The inversion of rift-related faults on passive margins through kinematic reactivation is documented globally. Such structures form an integral part in petroleum systems, provide essential constraints on the kinematic and structural evolution of rifts and passive margins, and can be used as global markers for far-field stresses. Despite the importance of inverted normal faults, the controls on their kinematic evolution, as well as existence and interactions within fault populations are often poorly constrained. Here, we present new structural interpretation and kinematic modelling of an inverted relay ramp structure located offshore Nova Scotia, Canada. This structure is imaged on the Penobscot 3D seismic reflection survey down to ~3.5 s TWTT, and is constrained by two exploration wells. We map two major normal faults that display evidence for inversion in their lower portions (reverse faulting and low-amplitude folding), below ~2.5 s TWTT, though retain a normal offset in upper sections. The wider fault population is dominated by ~ENE-WSW striking normal faults that dip both north and south, while both of the two major faults dip approximately south and are associated with antithetic and synthetic faults. This kinematic dichotomy along the major faults is important as inversion such as this may go unrecognised if seismic data does not image the full depth of a structure. To accommodate such depth-dependent inversion, if both horizons co-existed during inversion, a reduction in volume of the sedimentary package is required between the normal and reverse segments of the fault. In this study, we explore possible kinematic mechanisms to explain inversion structure and the mechanisms accommodating the volumetric changes/ or mass movements required using fault restoration and strain modelling. Our results favour a poly-phase deformation history that can be reconciled with other inversion structures on related passive-margin segments, suggesting these could be widespread processes.

How to cite: Peace, A., Schiffer, C., Jess, S., and Phethean, J.: Depth-dependent inversion of normal faults: Structural analysis of the Penobscot 3D seismic volume, offshore Nova Scotia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-150, https://doi.org/10.5194/egusphere-egu21-150, 2021.

Folds and ductile fabrics
13:55–13:57
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EGU21-13661
Andreas Eckert, Xiaolong Liu, Avery Welker, Peter Connolly, John Hogan, and Sarah Tindall

The characterization of folds is often limited to two-dimensional cross-sectional views where folds are approximated as cylindrical. This enables simplification of fold shape analysis (using principles such as dip isogons, stereographs, tangent diagrams, and Bezier curve analysis), allows for a simplified analysis of the distribution of stress and strain, and enables and the analysis and visualization of folding associated fractures. However, in a heterogenous medium folds have to terminate somewhere, resulting in more complex three-dimensional geometries. In this study, a 3D finite element modeling approach using a Maxwell visco-elastic rheology is utilized to simulate 3D periclinal folds resulting from single layer buckle folding. With respect to fold shape analysis, we use the forward modeled pericline geometries to demonstrate that geometrical attitude data collected for various cross sections and plotted using traditional 2D methods such as stereographs and tangent diagrams may lead to the misinterpretation of the fold shape as conical. In contrast 3D geometric data such as Gaussian curvature can describe and quantify the 3D fold geometry in its entirety. With respect to folding associated fracture analysis, the 3D modeling results show that shear fractures of various orientations in the fold limb, which cannot be intuitively explained by the strain/stress regimes during 2D buckling and require unrealistic boundary conditions, are feasible to occur during a single deformation event during the development of a pericline. In summary, accounting for the true 3D geometry of buckle fold structures will lead to a better classification of folds, a better understanding of the processes and parameters affecting their development, and enable post-folding failure analysis.

How to cite: Eckert, A., Liu, X., Welker, A., Connolly, P., Hogan, J., and Tindall, S.: Implications of pericline geometries on 3D fold shape analysis, stress distribution and fracture analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13661, https://doi.org/10.5194/egusphere-egu21-13661, 2021.

13:57–13:59
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EGU21-807
Andreas Scharf, Ivan Callegari, Frank Mattern, Katharina Scharf, and Eugenio Carminati

The Jabal Akhdar Dome (JAD) of the Oman Mountains contains superbly exposed sedimentary Neoproterozoic formations in its core. Carbonates of the Hajir Formation are resistant against erosion in the prevailing semi-arid conditions unlike the subjacent and overlying siliciclastic formations. Structural fieldwork and satellite image analyses reveals that the central-western JAD (Hat Plateau) was affected by three folding events. Each event produced its own fascinating fold style with associated structures. The widely exposed Hajir carbonates displays these folds spectacularly. The geomorphology of these carbonates reflects the folds with differently oriented rides and troughs as anti- and synclines, respectively. Thus, the JAD acted as a natural laboratory where the 3D fold styles can be directly linked to the geomorphology and vice versa.

A previously unrecognized folding event (F1) produced overturned NNE-verging tight folds. The fold amplitude ranges between tens and hundreds of meters, and the overall non-plunging fold axes trend ESE. The F1 folds are associated with a gently to moderately SSW-ward dipping penetrative axial plane cleavage. Open to tight upright kilometric F2 folds refolded the F1 structures. The F2 folds are overall non-plunging and NE/NNE-trending, and contain a penetrative sub-vertical axial plane schistosity, parallelly oriented to the F2 axes. The youngest folding event (F3) produces one open and broad anticline. The F3 fold axis trends WNW through the Hat Plateau and the anticline contains a WNW-striking sub-vertical spaced axial plane schistosity.

The deformation style of the F2 folds and related structures changes abruptly along a NNE-oriented zone at the western end of the Hat Plateau. West of this, the F2 structures are ENE-oriented while east of it the orientation is NE to NNE. Furthermore, the amplitude of the F2 folds decreases from ~3 km in the west to <1 km in the east. We relate this sudden change of the F2 style to the western flank of a pre-existing subsurface basement horst. We suggest that this NNE-striking horst is the northern continuation of the Makarem-Mabrouk High/Horst below the JAD. The eastern horst shoulder would be at the eastern margin of the JAD and parallel to the Semail Gap. A buttressing effect along the western horst’s shoulder during NW/SE to WNW/ESE-directed F2 shortening would explain the dramatic change in the F2 style.

In summary and in 3D terms, the F1 folds were originally oriented parallel to the present F1 anticline, i.e. before the F2 deformation, while the F2 folds strike almost perpendicularly to this direction. The F1 and F2 folding episodes associated with the abrupt change in F2 style are depicted in a steric block diagram, which visualizes the complex findings, allowing for a 3D understanding of the structures.

How to cite: Scharf, A., Callegari, I., Mattern, F., Scharf, K., and Carminati, E.: A textbook example of triply-folded Ediacaran carbonates – insights into geodynamics and geomorphology (Hat Plateau, Jabal Akhdar Dome, Oman Mountains), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-807, https://doi.org/10.5194/egusphere-egu21-807, 2021.

13:59–14:01
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EGU21-2292
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ECS
Chiara Montemagni, Stefano Zanchetta, Salvatore Iaccarino, Chiara Montomoli, Rodolfo Carosi, and Nicoletta Fusi

Kinematic analysis of flow is becoming a well-established methodology, increasingly applied for its capability to contribute to the solution of complex topics in structural geology and tectonics, such as shear zones deforming by general shear.

Vorticity evaluations based on stable porphyroclasts method have been used for many years to deduce large-scale tectonics of shear zones with different kinematics (Fossen & Cavalcante, 2017). However, limitations occur because a complex three dimensional problem, the motion of rigid clasts in a flowing matrix, is reduced to its two-dimensional analysis on the XZ plane of the finite strain ellipsoid (Iacopini et al., 2011; Mancktelow, 2013). Therefore vorticity estimates are limited by the extrapolation to three dimensions of two-dimensional data.

We propose a totally new 3D approach based on the use of X-ray micro-computed tomography (X-ray micro-CT) that reflects the real 3D geometry and orientation of the porphyroclasts population. X-ray micro-CT allows to face the loss of dimensionality information imaging the rock sample in three dimensions and produces stacks of 2D grey-scale value images, called “slices”, that combined in 3D allow observing the internal structure of the scanned sample.

We tested this approach chiefly on mylonitic orthogneiss from an intensively studied crustal scale shear zone: the Main Central Thrust zone (MCTz) of the Himalaya orogenic belt. Mylonites samples from other regional-scale shear zones in the Alps have been also used for comparison.

The first and foremost consideration is that the use of micro-CT certainly increases the number of investigated clasts because hand samples are scanned: all clasts are evaluated. Micro-CT minimizes the problems due to the isolation factor, as it becomes possible to only select the clasts that do not interact with each other. Moreover, observation in three dimensions allows a more realistic evaluation of the aspect ratios and radii of clasts, avoiding erroneous measurements that generate systematic errors in the vorticity evaluation.

We would like to stress that using the microCT we are able to evaluate all the clasts in the sample, avoiding those which do not meet the prerequisites of the method, otherwise not possible using classical 2D thin section based analysis.

 

Fossen H. & Cavalcante G.C.G., 2017. Earth-Sci. Rev., 171, 434–455.

Iacopini D. et alii, 2011. GSL Spec. Publ., 360, 301–318.

Mancktelow N.S., 2013. J. Struct. Geol., 46, 235-254.

Montemagni C. et alii, 2020. Terra Nova, 32, 215-224.

How to cite: Montemagni, C., Zanchetta, S., Iaccarino, S., Montomoli, C., Carosi, R., and Fusi, N.: Comparing 3D vs 2D approach in vorticity estimates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2292, https://doi.org/10.5194/egusphere-egu21-2292, 2021.

Other geological structures
14:01–14:03
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EGU21-4158
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ECS
Franziska Mayrhofer, Bernhard Grasemann, Martin Schöpfer, and Marta Adamuszek

Flanking structures are deflections of an existing planar fabric (e.g., foliation) alongside a cross-cutting element (e.g., a vein) that can develop in a wide range of rock types, ranging from eclogites to unconsolidated sediments, and also glacier ice, which deforms in temperate glaciers dominantly by dislocation creep and can be considered as a monomineralic metamorphic rock analogue. The finite geometry of flanking structures depends on several factors, such as initial orientation of the cross-cutting element (CE) relative to the shear zone boundary and the kinematic vorticity of the shear zone flow. However, nearly all published examples of flanking structures are interpreted to have formed either under simple shear or transpressional general shear, although in theory flanking structures should also form under transtensional general shear. Here we describe the geometry and development of transtensional flanking structures in glacial ice of the Pasterze, Austria’s largest alpine valley glacier. Mapping was carried out with the aid of high-resolution drone photography and the structures’ attitudes were determined using traditional field techniques. The studied flanking structures develop in an area situated on the orographic right side of the glacier tongue and downstream of a transverse crevasse field. The CEs are closed crevasses containing granular ice and rotate clockwise (when viewed from above), consistent with the large-scale flow field of the glacier. The penetrative foliation, which is regionally parallel to the glacier’s flow direction, is locally deflected alongside the CEs, forming a- (antithetic) and s-type (synthetic) flanking structures. The variability of the cross-cutting elements’ orientation systematically decreases downstream as they rotate into a stable position. We compare the mapped flanking structures with model results of a semi-analytical modified Eshelby solutions for a frictionless CE embedded in an isotropic linear viscous matrix. The model results demonstrate that a variety of a- and s-type flanking structures form under transtensional shear flow for a broad range of kinematic vorticity numbers and initial orientations of the CE but also show that shear bands do not form a stable structure. On the other hand, s-type flanking folds may be diagnostic for transtension because they form stable structures (but still accumulate displacement) when the CE has been rotated parallel to the fabric attractor, which is oblique to the shear zone boundary under transtension. Because of the abundance of shear bands and the lack of s-type flanking structures in natural rocks we speculate that transtensional ductile shear zones rarely occur in nature.

 

How to cite: Mayrhofer, F., Grasemann, B., Schöpfer, M., and Adamuszek, M.: Transtensional Flanking Structures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4158, https://doi.org/10.5194/egusphere-egu21-4158, 2021.

14:03–14:05
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EGU21-8993
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ECS
Marta Adamuszek, Dan M. Tamas, Jessica Barabasch, and Janos L. Urai

To predict long-term evolution of underground storage caverns and nuclear waste repositories, information about the mechanical behaviour of halite-dominated evaporites at time scales far longer than possible in the laboratory is critical for safe design and operation. In this project, we aim to interpret the long-term properties of rock salt based on the analysis of natural tectonic structures such as folds that developed over geological time scale. Fold geometry is a sensitive parameter to the rheological properties of the layers and thus it is valuable in the process of deciphering their mechanical behaviour.

We analyse the excellent exposures of layered, folded rock salt in Ocnele Mari salt mine in the Southern Carpathians of Romania. The formation is composed of over 90% of halite, where distinct layering demonstrates variation in the amount of impurities. The layers are millimetres to metres thick and show fold shapes on various scales forming spectacular multiwavelength structures. Our detailed analysis of these structures included field measurements, microanalysis, and 3D model reconstruction models using photogrammetry techniques. Our data clearly indicate that the sequence must be mechanically stratified.

In selected pillars, we digitized folded packages and estimated the relative layer thicknesses based on the assumption of plane strain deformation and no-volume change in the deformed rock mass. The layer thicknesses are then employed to constrain initial geometries for the numerical analysis. With an assumption of the constant fold arclength, we estimate the minimum amount of bulk shortening to be ca. 70-80%. Using FOLDER [1], a numerical tool for analysing the deformation in layered rock, we used different rheological properties of the layers to model the evolving the fold structures after 80% of shortening. For a range of values of viscosity ratio (Newtonian and Power-law) between the layers, our results are very similar to the fold shape pattern observed in the field. Systematic analysis of various models allowed us to constrain the mechanical properties of the formation.

The field observation and numerical data clearly show that the evaporite sequence within the Ocnele Mari salt is mechanically heterogeneous and anisotropic. The long-term viscosity ratio of the layers depends on the amount of impurities and their type. Even a small amount of impurities within the layer can significantly change the viscosity of rock salt. We estimated that viscosity ratio between the selected layers can reach up to 20-30. This points to a significant mechanical anisotropy, even in relatively pure halite deposits. The presence of layers of anhydrite, clay, K-Mg salts etc. will further increase this anisotropy. 

[1] Adamuszek, M., Dabrowski, M., Schmid, D.W., 2016. Folder: a numerical tool to simulate the development of structures in layered media. J. Struct. Geol. 84, 85–101.

How to cite: Adamuszek, M., Tamas, D. M., Barabasch, J., and Urai, J. L.: Role of impurities within the salt layers on the long-term rheological variations within the evaporite sequence. A case study from the Ocnele Mari salt mine, Romania, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8993, https://doi.org/10.5194/egusphere-egu21-8993, 2021.

14:05–14:07
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EGU21-8784
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ECS
Jacopo Natale, Giovanni Camanni, Renato Diamanti, Luigi Ferranti, Roberto Isaia, Marco Sacchi, Volkhard Spiess, Lena Steinmann, Francesco d'Assisi Tramparulo, and Stefano Vitale

The Campi Flegrei volcano is a 12 km wide nested caldera in southern Italy. In the last 15 kyr, over 70 eruptions occurred, clustered in time and space and interspersed by centuries- to millennia-long quiescence periods. The vent sites of the major explosive volcanic eruptions are associated with caldera ring faults, intra-caldera fault zones, and regionally-controlled fault systems. This study focuses on caldera-scale deformation structures hosted in both volcanic and marine successions of the last 15 kyr, exposed inland and detected offshore on seismic reflection profiles. In particular, we describe structural variations that faults display in both their dip and strike directions, and how these relate with fault dip angle, mechanical stratigraphy, and time. While at continental outcrops, except for a few exceptions, only 2D observations are available, in the offshore sector of the caldera we are able to study 3D fault characteristics using a dataset of dense seismic reflection profiles. In this sector, we have the chance to characterize and compare both the faults that bound the caldera and those developed at its center. Furthermore, by using a template for the marine stratigraphy, we obtained information on the timing of the faults. Preliminary results suggest that faults activate in a time frame broadly corresponding to the intense volcanic activity epochs suggesting a strong link between the fault activity and volcanic unrests.

How to cite: Natale, J., Camanni, G., Diamanti, R., Ferranti, L., Isaia, R., Sacchi, M., Spiess, V., Steinmann, L., Tramparulo, F. D., and Vitale, S.: Structural and temporal characterization of volcano-tectonic faults in the Campi Flegrei caldera, southern Italy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8784, https://doi.org/10.5194/egusphere-egu21-8784, 2021.

14:07–14:09
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EGU21-12039
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ECS
Zahra Tajmir Riahi, Khalil Sarkarinejad, Ali Faghih, Bahman Soleimany, and Gholam Reza Payrovian

Abstract

The detailed characterization of faults and fractures can give valuable information about the fluid flow through petroleum reservoir and directly affect the hydrocarbon exploration and production programs. In this study, large- and small-scale fractures in the Asmari horizon of the Rag-e-Sefid oilfield were characterized using seismic attribute and well data analyses. Different spatial filters including finite median hybrid (SO-FMH), dip-steered median, dip-steered diffusion, and fault enhancement filters were used on 3D seismic data to reduce noise, enhance the seismic data quality, and create a 3D seismic steering cube. In the next step, seismic attributes such as coherency, similarity, variance, spectral decomposition, dip, and curvature were applied to identify structural features. In order to check the validity of these structural features, results from seismic attributes calibrated by the interpreted fractures from image logs in the Rag-e-Safid oilfield. Then, the ant-tracking algorithm applied on the selected seismic attributes to highlight faults and fractures. These attributes combined using neural network method to create multi-seismic attributes, view different fault- or fold-sensitive seismic attributes in a single image, and facilitate the large-scale fractures extraction process. Finally, automatic fault and fracture extraction technique used to reduce human intervention, improve accuracy and efficiency for the large-scale fracture interpretation and extraction from edge volumes in the Asmari horizon of the Rag-e-Sefid oilfield. In addition to, small- scale fractures were characterized by the obtained information from the image logs interpretation for sixteen wells. All the detected fractures from seismic and well data have been divided into eight fracture sets based on their orientation and using the statistical analysis. The obtained results show that fractures characteristics and their origin are different in the northwestern and southeastern parts of the Rag-e-Sefid oilfield. The NW Rag-e-Sefid and Nourooz Hendijan Izeh Faults reactivation during Zagros orogeny led to create the dextral shear zone and P, R, R′, T, Y- fracture sets in the northwestern part of the Rag-e-Safid oilfield. Also, activity of the SE-Rag-e-Sefid thrust fault during Zagros orogeny caused to form fault-related fractures sets in the southeastern part of the Rag-e-Sefid field. In addition to, axial, cross axial, oblique fracture sets in the Asmari horizon of the Rag-e-Sefid oilfield were created by folding phase during Zagros orogeny. The obtained results were used to fracture modeling in the Asmari horizon of the Rag-e-Sefid oilfield.

How to cite: Tajmir Riahi, Z., Sarkarinejad, K., Faghih, A., Soleimany, B., and Payrovian, G. R.: Fracture detection using multi seismic attributes ant-tracking in the Rag-e-Sefid oilfield, SW Iran, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12039, https://doi.org/10.5194/egusphere-egu21-12039, 2021.

14:09–14:11
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EGU21-12586
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ECS
Saskia Köhler and Daniel Koehn

The importance of paleostress analysis is dramatically increasing due to its application in diverse fields, such as sustainable exploration of resources, reservoir potential or storage sites. A good understanding of the subsurface geology, the geological stress-history and associated fracture and fault networks is essentially for these applications. Understanding of the complete paleostress history is not only of interest for applied research, but also for an understanding of the dynamics of geological processes in general. In recent years a diverse toolbox of stress inversion methods has been developed including stress inversion from tectonic stylolites (and slikolites). The pressure solution structures not only preserve the direction of the largest principle stress – they are an archive for the complete stress tensor and the absolute stress magnitude at the moment of their development. Here we present the first results of a systematic study of this upcoming method. For comparison we preformed roughness analysis of tectonic stylolites from Mesozoic limestone from SE Germany. In late Cretaceous the area was affected by shortening in a NE-SW direction, which is clearly illustrated by fault-slip analysis and the orientation of tectonic stylolites. During this tectonic event the stress regime changed from thrusting to strike-slip, with the sampled stylolites persevering the transition between these two stress events. With our preliminarily results we show that roughness analysis of tectonic stylolites enables us to record short time intervals during phases of contraction, and therefore offers crucial insights into stress history and tectonic processes with pulsating stress fields.

How to cite: Köhler, S. and Koehn, D.: Tectonic stylolites as a valuable stress archive – new insights from Late Cretaceous intra-plate stresses in Europe, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12586, https://doi.org/10.5194/egusphere-egu21-12586, 2021.

3D geological models
14:11–14:13
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EGU21-1238
Robert Faber and Gisela Domej

To evaluate the functionality of FaultTrace – a tool for semi-automatic structural geological mapping of faults and bedding planes within the software WinGeol by TerraMath –, we demonstrate its detailed use in two different case studies: The Richât Structure in Mauritania is characterized by a volcanogenic anticline with associated fault systems and shows relatively planar fault structures within low-relief topography; the Vineh Structure in Iran consists of complexly faulted sequences of sedimentary and igneous layers in high mountainous terrain affected by the fault systems of the Purkan-Vardij Fault and the North Tehran Fault. The studies discuss which structural geological settings let expect a satisfying performance of FaultTrace, and what factors limit the achievement of meaningful results. 

Used data is freely available and consists of digital elevation models (e.g., SRTM or ALOS Data) and satellite imagery (e.g., Sentinel-2 or Landsat ETM+ Imagery). Where available, additional data such as, for instance, borehole logs and geological cross-sections were displayed to support the mapping process. Results from the structural geological assessments of both case studies were finally compared to previously published studies in order to validate the performance of FaultTrace on the one hand, and to discuss differences on the other hand.

We show that FaultTrace aims to provide a virtual environment allowing for fast-track and optimized data generation for 3D geological models. It can be used for a first remote structural geological assessment without the requirement of being at the site. Therefore, it is well suited for inaccessible terrain – for instance, due to transportation, political restrictions, warfare, natural hazards, or lack of funding. Nevertheless, and to take full advantage of the software, users have to be aware of the limitations and strengths, which are discussed in this work based on two very different case studies.

How to cite: Faber, R. and Domej, G.: 3D Computer-Assisted Geological Mapping with FaultTrace: Results of the Richât Structure (Mauritania) and the Vineh Structure (Iran), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1238, https://doi.org/10.5194/egusphere-egu21-1238, 2021.

14:13–14:15
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EGU21-10725
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ECS
Federico Rabuffi, Massimo Musacchio, Francesco Salvini, Malvina Silvestri, and Maria Fabrizia Buongiorno

Remote Sensing is a proven tool to study the Earth's surface and allows to analyze the wide portion of the surfaces by using different platforms/sensors (e.g. optical and active remote sensing, lidar), giving the possibility of multidisciplinary and multiscale approaches. In the proposed study, remote sensing analysis provides the possibility to understand the relationship between tectonic structures, lithology, and geothermal manifestations, and to test these techniques to monitor geothermal areas. This study allowed us to better understand the structural framework of a geothermal area, located in Southern Tuscany, highlighting the role of brittle deformation to produce an enhanced pathway for fluid migrations and upwelling.

The studied area is the “Parco Naturalistico delle Biancane” (PNB) in the Grosseto province and belongs to the Cenozoic Tyrrhenian-Apennine orogenic system. The tectonic framework includes a fault and thrust belt setting derived from the collision between the Corsica-Sardinia Block and Adriatic Plate during late Oligocene-Miocene times. This process determined the pile-up of several tectonic units which are, from the top: (1) Ligurian Units consisting of ophiolitic rocks and pelagic sediments (Jurassic - Oligocen); (2) Cretaceous-Oligocene terrigenous deposits; (3) The Mesozoic Tuscan Nappe. Successively, the belt was affected by a regional, mainly extensional tectonics, then a magmatic intrusion affected this thinned Tyrrhenian belt to form the Tuscan Magmatic Province. In Recent time, the region underwent a general, yet differentiated uplift, and the major geothermal areas locate to the relative higher zone. This provides the Southern Tuscany to be the main Italian geothermal area.

In this study, we analyzed the area from several points of view. The lineament domain analysis was performed in a multiscale approach: from 90 meters to 5 meters of pixel size, including 30 m and 10 m. This multiscale analysis allowed the identification of a number of lineament clusters related to the different tectonic phases which affected the PNB area. The found lineament distribution (in terms of azimuth and length) reflects the geodynamics effects on the surface, their clustering was related to the various crustal stress trajectories both at the regional and local scales.

How to cite: Rabuffi, F., Musacchio, M., Salvini, F., Silvestri, M., and Buongiorno, M. F.: Brittle deformation effects on the geothermal area framework, in Southern Tuscany, by multiscale lineament domain analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10725, https://doi.org/10.5194/egusphere-egu21-10725, 2021.

14:15–14:17
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EGU21-5892
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ECS
Aurélie Louis-Napoleon, Muriel Gerbault, Thomas Bonometti, Olivier Vanderhaeghe, and Roland Martin

This work aims at investigating the thermo-mechanical conditions required for the development of convective instabilities and polydiapirism in the partially molten root of orogenic belts. First, we tested the volume-of-fluid method (VOF) implemented in codes OpenFOAM (open source) and Jadim (in-house IMFT code). Comparison of theoretical and numerical solutions of Rayleigh-Taylor and Rayleigh-Benard instabilities show that Openfoam is most satisfactory in terms of speed and mass conservation (Louis-Napoleon et al., 2020).

Then, we applied the VOF method to investigate specifically the formation of metamorphic domes in Naxos, Greece. These domes are characterized by nested structures of 2 km sub-domes in a 10 km major dome, and contain zircon grains that recorded dissolution-recrystallization cycles of 1 to 2 Myrs attributed to thermal cycles (Vanderhaeghe et al., 2018). We tried to show that these imbricated domes could result from a combination of convective and diapiric episodes, considering the hot orogenic crust as a system of horizontal layers with power-law temperature-dependent viscosities with internal heating. In both 2D and 3D, small domes are systematically destroyed by convection when it appears.

Therefore in a second step we accounted for the specific lower viscosities induced by partial melting as well as compositional small heterogeneities (inclusions). These inclusions are supposed to represent sub-scale clustering of partially molten heterogeneous material with light-soft and heavy-resistant density and viscosity with respect to the "average" crustal domain. Parametric tests allow to define the conditions for the development of convection cells, diapirs and segregation-sedimentation of the inclusions. Two scenarios are then found to potentially explain the formation of the Naxos domes. A first scenario in which melting viscosity is not accounted for, but the inclusions are initially “active”, generates local convection cells around rising clusters of inclusions. Diapirs then emerge above the local convective cells and accumulate at the base of the upper crust. The second scenario takes into account melting viscosity, the inclusions’ properties are active only when temperatures exceed the melt front, and basal heating is progressively shut down. The light inclusions then rise and form domes above larger convection cells, if their rheological properties are frozen. Both these scenarios do not exclude the role of external lateral forces a posteriori to finalise the exhumation process. More generally, we found that the domes characteristics are determined by their mode of formation. We propose a dimensional analysis to distinguish suspension from sedimentation regimes.

How to cite: Louis-Napoleon, A., Gerbault, M., Bonometti, T., Vanderhaeghe, O., and Martin, R.: Modeling gravitational instabilities in the partially molten crust with a Volume-Of-Fluid method, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5892, https://doi.org/10.5194/egusphere-egu21-5892, 2021.

14:17–14:19
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EGU21-15615
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ECS
Rosibeth Toro, Antonio Casas, Esther Izquierdo, Emilio Pueyo, Javier Navas, Juliana Martín, Carlos Peropadre, and Jon Jiménez

El suroeste de los Pirineos muestra algunas de las características geométricas clave de la cordillera: 1) la terminación hacia el oeste del afloramiento principal de la Zona Axial, la columna vertebral de la cadena donde emergen las rocas del basamento 2) el afloramiento de unidades de basamento aisladas más al oeste (los llamados Macizos Vascos) y 3) la variación lateral de las geometrías de la corteza, caracterizada por la subestimación de la corteza ibérica inferior por debajo de la europea, con la corteza superior formando una cuña orogénica. El número, la secuencia, la cronología y las relaciones laterales de los empujes del sótano que forman esta cuña de la corteza superior son complejos y el foco del debate científico.

En este, mostramos el primer modelo 3D basado en la interpretación de 142 secciones de reflexión sísmica de tiempo disponible en la región (campañas PP, DP, JAT, JA, JAW, PJ & DP, que comprenden en total más de 1600 km de imágenes del subsuelo que cubren más de 9.000 km 2). Para realizar la conversión de tiempo a profundidad, se considera un modelo de velocidad sísmica basado en registros sónicos de varios pozos (ecuación tiempo-profundidad promedio obtenida de los pozos Roncal-1, Sangüesa-1, Aoiz-1 y Pamplona sur). Los resultados preliminares de los datos sísmicos, superficiales y de pozos evidencian que la estructura del área de estudio consiste en un sistema de empuje imbricado en el sótano que está dirigido al sur y se conecta al sistema de cubierta de pliegue y empuje que forma las Sierras Externas. El sistema de empuje del sótano está separado dentro del Paleozoico (con un nivel de desprendimiento identificado a una profundidad de ~ 4 km por debajo de la parte superior del sótano) y avanzando hacia las evaporitas del Triásico Superior hacia el sur. El sistema de empuje del sótano involucra dos empujes principales que en parte resultan de la reactivación de fallas extensionales heredadas del Pérmico-Triásico durante la convergencia cenozoica. Producen con todo diferencias de altura del nivel estratigráfico de referencia (Cretácico Superior) de más de 8000 m. Unidades de sótano en el muro colgante del empuje norte (empuje de Gavarnie) progresivamente poco profundas hacia el este mientras que las unidades de sótano en la hoja de empuje sur (empuje de Guarga) poco profundas hacia el oeste. Las geometrías de los muros colgantes consiste en grandes paneles planos escalonados que también pueden complicarse con empujes de menor escala oblicuos a la principal tendencia pirenaica. 

How to cite: Toro, R., Casas, A., Izquierdo, E., Pueyo, E., Navas, J., Martín, J., Peropadre, C., and Jiménez, J.: 3D basement geometry of the southwestern Pyrenees: Insights from seismic interpretation., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15615, https://doi.org/10.5194/egusphere-egu21-15615, 2021.

14:19–14:21
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EGU21-16192
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ECS
Klodian Skrame, Diego Albini, Carlo Moriconi, Christian Comotti, Redi Muci, Oltion Fociro, and Jeton Pekmezi

In this work, it is intended to highlight the indispensable significance of the geophysical surveys on the hydrogeological research and on the seismic risk mitigation.

This paper describes the acquisition methodologies, the instrumentation used, the techniques and methods of inversion / interpretation and the results of a hybrid geophysical survey carried out for the reconstruction of the 3-D geological modeling of the Borgo Montello case study, in the Province of Latina, in Italy.

The aim of the study was to test the use of hybrid geophysical surveys in order to obtain a detailed geological-stratigraphic and hydrogeological modeling of the subsoil, its interpretation in terms of flow model and to identify the relationships between the parameters that define the geological-hydrogeological-stratigraphic model with the local seismic ground motion amplification of the site.

From a geological point of view, the study area in composed by two main geological formations. The most superficial one is characterized by sedimentary deposits linked to the filling of the Pontine depression: composed by alternations of clays, silty clays and silts, with a subordinate component of silty sands. The second lithological type is linked to the deposition of pyroclastic deposits from the Lazio volcano and in particular from the deposits of reddish pozzolane alternating with thickened tuff, the so-called "Tufo lionato".

A research approach that integrated different geophysical methods, as: resistivity, induced polarization electrical tomography and seismic refraction and high resolution reflection methods were carried out to reproduce the thickness and the extension of the over mentioned deposits.

Afterwards, having obtained 5 independent models (seismic reflection section, seismic refraction section, electrical resistivity tomography, electrical tomography and local seismic amplification section) the authors proceeded, through the k-means algorithm methods, for the analysis of the bivariate dataset cluster, in order to identify the relationships between the 5 sets of variables. The proposed methodology was focuses on characterizing the aquifer potential by using simultaneously all the geophysical parameters obtained together with the stratigraphic data, in order to reduce the uncertainties and ambiguity in the interpretation of the geophysical data for a better modeling of the subsoil.

The obtained results were compared with a collection of existing boreholes, well logs, geotechnical and geophysical data. The 3-D geological models match quite well with the information determined from these previous works.

Lastly, based on the three-dimensional modeling of the subsurface structures, a Local Seismic Response study was carried out.

How to cite: Skrame, K., Albini, D., Moriconi, C., Comotti, C., Muci, R., Fociro, O., and Pekmezi, J.: An integrated methodological approach for the three-dimensional modeling of the subsurface structures: the case of Borgo Montello, in Latina, Italy., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16192, https://doi.org/10.5194/egusphere-egu21-16192, 2021.

14:21–15:00