TS12.2

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.