TS3.8 | Deformation and faults: From Multi-Scale Observations to Seismic Hazard Characterization.
EDI
Deformation and faults: From Multi-Scale Observations to Seismic Hazard Characterization.
Co-organized by NH4
Convener: Riccardo Lanari | Co-conveners: Sara Martínez-Loriente, Silvia Crosetto, Jacob Geersen, Ylona van Dinther, Francesco Emanuele Maesano, Fabio Corbi
Orals
| Wed, 26 Apr, 10:45–12:25 (CEST)
 
Room K1
Posters on site
| Attendance Wed, 26 Apr, 16:15–18:00 (CEST)
 
Hall X2
Orals |
Wed, 10:45
Wed, 16:15
Deformation zones and faulting processes develop in several geodynamic environments, involving deep and/or shallow crust. In active tectonics contexts, either if they are in subarea or subaqueous environments, unravelling the faults’ long-term evolution has a crucial impact for seismic and tsunami hazard assessment. In case of subaqueous environments, over the last years, new geological and geophysical instrumentation has made possible the acquisition data with unprecedented detail and resolution, providing for a better definition of offshore fault systems and seismic parameter calculations. Moreover, multiple parameters are expected to control fault evolution, such as the tectonic and geodynamic setting, erosion, the amount of sediments deposited on the hanging wall, fluids circulation, or lithology. While the effects of some of these parameters are well established, many others are still poorly constrained by actual data.
This session aims to better define the properties of faults and deformation zones, and to understand how their characteristics change over time. At the same time, this session also aims to compile studies that focus on the use of geological and geophysical data to identify subaqueous active structures, attempting to quantify the seafloor deformation, evaluating their seismogenic and tsunamigenic hazards. We invite contributions dealing with faulting and deformation processes (normal, reverse and strike-slip) worldwide, in different geodynamic contexts, from the scale of the outcrops to mountain ranges, from offshore to lakes, and from the long-term to single seismic events. Since a multidisciplinary approach is the key to deep understanding, studies providing new perspectives and ideas in subaqueous active tectonics or involving diverse methods such as field-data analysis, paleoseismic trenching, stable isotopes, low temperature thermochronology, syn-kinematic U/Pb dating, cosmogenic exposure dating, petrographic analysis, or analogue/numerical modelling are welcome.

Orals: Wed, 26 Apr | Room K1

Chairpersons: Riccardo Lanari, Silvia Crosetto, Francesco Emanuele Maesano
10:45–10:55
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EGU23-11050
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solicited
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Highlight
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On-site presentation
Sascha Brune, Thilo Wrona, Derek Neuharth, Anne Glerum, John Naliboff, and Esther Heckenbach

Understanding how normal fault networks initiate and evolve is important for quantifying plate boundary deformation, assessing seismic hazard and finding natural resources. In recent years, 3D numerical models have been developed that can simulate the entire process of normal fault formation, from the start of rifting to the creation of new ocean floor. However, state-of-the-art methods treat faults as finite-width shear zones not as discrete entities, so additional work is needed to isolate individual faults and their characteristics in order to better understand fault system dynamics over geological scales.

We present 3D numerical rift models of moderately oblique extension using the ASPECT software. These models reproduce the thermo-mechanical behavior of Earth's lithosphere and simulate fault system dynamics from inception to breakup accounting for visco-plastic rheology, strain softening and surface processes. We use a method that extracts surficial fault systems as 2D networks of nodes and edges to study the evolution of normal faulting. By applying data analysis techniques, we group nodes and edges into components that represent individual faults and track their geometry and movement over time.

We find that the initial fault network forms through rapid fault growth and linkage, followed by competition between neighboring faults that leads to their coalescence into a stable network. At this point, modelled normal faults continue to accumulate displacement but do not grow any longer. As deformation localizes towards the center of the rift, the initial border faults shrink and disintegrate, being replaced by new faults in the center of the rift. During that transition, we document strain partitioning between predominantly dip-slip border faults and oblique-slip or strike-slip intra-basin faults. The longevity of faulting is thereby controlled by crustal rheology and surface process efficiency. Quantitative analysis of fault evolution allows us to deduce fault growth and linkage as well as fault tip retreat and disintegration in unprecedented detail.

How to cite: Brune, S., Wrona, T., Neuharth, D., Glerum, A., Naliboff, J., and Heckenbach, E.: Normal fault network evolution in 3D numerical models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11050, https://doi.org/10.5194/egusphere-egu23-11050, 2023.

10:55–11:05
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EGU23-10059
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On-site presentation
Kevin P. Furlong

The northward migration of the Mendocino Triple Junction (MTJ) drives a fundamental plate boundary transformation from convergence to translation; producing a series of strike-slip faults, that become the San Andreas plate boundary. How and why these faults develop where they do is enigmatic. We find that the 3-D structure of the Pacific plate lithosphere in the vicinity of the MTJ controls the location of San Andreas plate boundary formation. Recently developed, high-resolution seismic-tomographic imagery of northern California indicates that (1) the Pioneer Fragment, and extension of the Pacific plate beneath the western margin of North America occupies the western half of the slab window, immediately south of the MTJ; (2) the eastern edge of the Pioneer Fragment lies beneath the newly forming Maacama Fault system, which develops to become the locus for the primary plate boundary structure after approximately 6-10 Ma (eg. the present-day East Bay faults in the SF Bay region); and (3) the placement of the translating Pioneer Fragment adjacent to the asthenosphere of the slab window, and its coupling to the overlying North American crust generate a shear zone within and below the crust that develops into the  plate boundary faults. This plate boundary configuration has been operable since the initial formation of the transform plate boundary. As a result, the San Andreas plate boundary forms within the western margin of North America, approximately 100 km inboard of the western edge of North America, rather than at its western edge. One additional result of this is that blocks of North America lithosphere are detached and become terranes (such as the Salinian and Nacimiento (Franciscan) blocks) that are captured by and translate with the Pacific plate, producing the complex crustal architecture of coastal California.

How to cite: Furlong, K. P.: The Development of the Northern San Andreas Plate Boundary Fault System - Importance of Lower-crustal Ductile Shear in Producing Primary Plate Boundary Structure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10059, https://doi.org/10.5194/egusphere-egu23-10059, 2023.

11:05–11:15
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EGU23-10111
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On-site presentation
Carolyn Boulton, André Niemeijer, Marcel Mizera, Timothy Little, Inigo Müller, Martin Ziegler, and Maartje Hamers

During the interseismic period of an earthquake cycle, creeping patches and locked asperities on crustal faults control the distribution of accumulated elastic strain and thus their seismic potential. Yet the frictional and frictional-viscous processes that facilitate creep on shallow crustal faults, such as near-trench subduction zone décollements, remain poorly understood. At mid-to-low latitudes, calcareous sediments are important subduction zone input materials. Compared with siliciclastic lithologies, calcareous rocks more readily accommodate strain aseismically via crystal plasticity and diffusive mass transfer processes at low temperatures and pressures in the upper crust. Along the Hikurangi Subduction Margin of New Zealand, accretionary prism uplift has exposed the Hungaroa fault zone, an inactive thrust fault developed within fine-grained, calcareous sedimentary rocks.

In this research, we present observational and theoretical evidence that the Hungaroa fault zone accommodated deformation primarily by distributed aseismic creep within a ~33 m-wide fault core.  Syntectonic calcite vein clumped isotope thermometry and maximum differential stress estimates indicate that deformation took place at 2 to 4 km depth. We model the fault zone rheology assuming diffusion-controlled frictional-viscous flow, with deformation at strain rates ≤10-9 s-1 able to have taken place at low shear stresses (τ <10 MPa) given sufficiently short diffusion distances (d <0.1 mm), even in the absence of pore fluid overpressures. Critically, fault zones with diffusion-controlled frictional-viscous flow rheology can exhibit spatially and temporally variable strain rates if grain-scale and fracture-scale processes change the diffusion distance. Thus, the shallow (up-dip) limit of the seismogenic zone is not a simple function of temperature in fault zones governed by a frictional-viscous flow rheology.

How to cite: Boulton, C., Niemeijer, A., Mizera, M., Little, T., Müller, I., Ziegler, M., and Hamers, M.: Frictional-viscous flow and the aseismic-seismic transition at shallow depths, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10111, https://doi.org/10.5194/egusphere-egu23-10111, 2023.

11:15–11:25
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EGU23-4753
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On-site presentation
Gregory Houseman, Philip England, and Lynn Evans

The spatial variation of strain rate in broad regions of continental collision, extension, or shear can often be well represented by the deformation of a thin viscous shell representing the lithosphere. The simplest explanation of this observation is that the deformation of the lithosphere is to first order a ductile process, even though shallow focus earthquakes imply slip on faults and release of elastic strain. In the thin-viscous-shell concept the strain of the upper brittle layer is assumed to simply follow the ductile strain of the stronger layers beneath, at least in the inter-seismic period. If the faults extend only to depths of 10 or 20 km, the brittle upper layer is not sufficiently thick or strong to do otherwise, and the concept of the brittle upper layer controlled by the ductile substrate is consistent with ductile models of the displacement-rate field constrained by GNSS observations. However, some large-scale faults do not comply with this concept and, rather than following the deformation of the ductile layer beneath, the strain localization on these structures appears to constrain the ductile deformation field of the adjoining regions. There are multiple lines of evidence from seismology and geodesy that great continental strike-slip faults, such as the San Andreas fault of California, the Alpine Fault of New Zealand, or the Altyn Tagh fault of China, extend through the crust and at least the upper part of the mantle lithosphere, even though earthquakes on these structures occur only in the upper 20 km. Taken together, the strain-localization and the lack of deep earthquakes suggest that these fault systems might be represented for the purpose of long-term continental deformation models as narrow ductile shear zones. A simple mechanical representation of localized strain on a ductile shear zone is defined by assuming traction is proportional to slip rate, with the proportionality constant described as a fault resistance coefficient. At the cost of ignoring the complexity of the earthquake cycle in such a model, we obtain a simple mechanical representation which we suggest is valid in the representation of long-term (and inter-seismic) continental deformation. In conceptual terms the fault resistance coefficient would be proportional to the effective viscosity of a ductile shear zone and inversely proportional to its width. However, an effective numerical implementation in a two-dimensional finite-element model is obtained by collapsing the narrow ductile shear zone to a one-dimensional structure characterised locally by the fault resistance coefficient. We illustrate the application of this conceptual model to the deformation field around the Alpine Fault in New Zealand, as constrained by an extensive array of GNSS displacement rates. The region as a whole is represented by a thin viscous shell that obeys a non-Newtonian viscous constitutive law, but we enable slip on model faults where there are steep local gradients in the geodetic displacement rates. The magnitude of the fault resistance coefficient is constrained by the requirement to fit the displacement rates and balance the stress.

How to cite: Houseman, G., England, P., and Evans, L.: Combining faulting and ductile deformation in long-term models of continental deformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4753, https://doi.org/10.5194/egusphere-egu23-4753, 2023.

11:25–11:35
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EGU23-8291
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Highlight
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On-site presentation
Wim Simons, Taco Broerse, Lin Shen, Nicolai Nijholt, Olga Kleptsova, Andrew Hooper, Julie Pietrzak, Yu Morishita, Marc Naeije, Stef Lhermitte, Rob Govers, Christophe Vigny, Pieter Visser, and Riccardo Riva

A devastating tsunami struck Palu Bay in the wake of the 28 September 2018 Mw = 7.5 Palu earthquake (Sulawesi, Indonesia). With a predominantly strike-slip mechanism, the question remains whether this unexpected tsunami was generated by the earthquake itself, or rather by earthquake-induced landslides. In this study we examine the tsunami potential of the co-seismic deformation. To this end, we present a novel geodetic data set of Global Positioning System and multiple Synthetic Aperture Radar-derived displacement fields to estimate a 3D co-seismic surface deformation field. The data reveal a number of fault bends, conforming to our interpretation of the tectonic setting as a transtensional basin. Using a Bayesian framework, we provide robust finite fault solutions of the co-seismic slip distribution, incorporating several scenarios of tectonically feasible fault orientations below the bay. These finite fault scenarios involve large co-seismic uplift (>2 m) below the bay due to thrusting on a restraining fault bend that connects the offshore continuation of two parallel onshore fault segments. With the co-seismic displacement estimates as input we simulate a number of tsunami cases. For most locations for which video-derived tsunami waveforms are available our models provide a qualitative fit to leading wave arrival times and polarity. The modeled tsunamis explain most of the observed runup. We conclude that co-seismic deformation was the main driver behind the tsunami that followed the Palu earthquake. Our unique geodetic data set constrains vertical motions of the sea floor, and sheds new light on the tsunamigenesis of strike-slip faults in transtensional basins.

How to cite: Simons, W., Broerse, T., Shen, L., Nijholt, N., Kleptsova, O., Hooper, A., Pietrzak, J., Morishita, Y., Naeije, M., Lhermitte, S., Govers, R., Vigny, C., Visser, P., and Riva, R.: A Tsunami Generated by a Strike-Slip Event: Constraints From GPS and SAR Data on the 2018 Palu Earthquake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8291, https://doi.org/10.5194/egusphere-egu23-8291, 2023.

11:35–11:45
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EGU23-1250
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On-site presentation
Luca Gasperini and Alina Polonia

High-resolution multibeam and seismic reflection data collected during several oceanographic expeditions allowed us to compile an updated morphotectonic map of the North Anatolian Fault below the Sea of Marmara. We reconstructed kinematics and geometries of active fault segments at 10 ka time-scale, an interval that includes several earthquake cycles, taking the base of the latest marine transgression as a stratigraphic marker. Given the high deformation rates relative to sediment supply, most active tectonic structures have a morphological expression at the seafloor, even in the presence of composite fault geometries and/or overprinting due to mass-wasting or turbidite deposits. In the frame of the right-lateral strike-slip domain characterizing the North Anatolian fault system, three types of deformation are observed: almost pure strike-slip faults, mainly oriented E-W; NE/SW-aligned axes of transpressive structures; NW/SE-oriented trans-tensional depressions. Fault segmentation occurs at different scales, but main segments develop along three major right-lateral oversteps, which delimit main fault branches, from east to west: i) the transtensive Cinarcik segment; ii) the Central (East and West) segments; iii) the westernmost Tekirdag segment. We performed a quantitative morphometric analysis of the shallow deformation patterns observed by seafloor morphology maps and high-resolution seismic reflection profiles along the entire basin, to determine the nature and cumulative lengths of individual fault segments. These data were used as inputs for empirical relationships, to estimate maximum expected Moment Magnitudes, obtaining values in the range of 6.8 to 7.4 for the Central, and 6.8 to 7.1 for the Cinarcik and Tekirdag segments, respectively. We discuss such findings considering analyses of inherited geological structures, historical catalogs, and available paleoseismological studies for the Sea of ​​Marmara region, to formulate reliable seismic hazard scenarios.

 

How to cite: Gasperini, L. and Polonia, A.: Active segments along the North Anatolian Fault system in the Sea of Marmara, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1250, https://doi.org/10.5194/egusphere-egu23-1250, 2023.

11:45–11:55
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EGU23-13787
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On-site presentation
Bryndís Brandsdóttir, Robert Detrick, Neal Driscoll, Jeffrey Karson, and Gunnar Guðmundsson

The Tjörnes Fracture Zone (TFZ) is a complex transform fault zone linking the Northern Volcanic Zone (NVZ) on land Iceland, with the offshore Kolbeinsey Ridge. The TFZ is roughly 150 km long (E-W) by 50-75 km wide (N-S) incorporating three major N-S trending pull-apart basins bounded by a complex array of normal and oblique-slip faults. The Skjálfandi Bay is the southern extension of the central basin. Seismicity within the Skjálfandi Bay is mostly confined to its western margin and the Húsavík-Flatey fault system (HFFS) across the southern part of the bay, extending eastwards into the NVZ and westwards into the westernmost basin. The main strands of the HFFS can be traced offshore across the Skjálfandi Bay in both CHIRP and multibeam data, as two WNW-trending, south-facing fault scarps. Several smaller WNW-trending faults are located sub-parallel of the main HFFS, many of which are delineated by pockmarks on the seafloor. Pockmark lineaments in northeastern Skjálfandi are elongated NE-SW, and WNW-ESE in the western part of the bay. The NE-SW pockmarks appear to be aligned along sediment covered marginal faults of the Skjálfandi basin whereas the northwestern pockmark field seems to be linked to WNW-ESE –trending strike-slip faults with little or no vertical displacement. The inferred pattern of WNW-ESE strike-slip faults and NE-SW basin-bounding faults matches results from adjacent areas of the Tjörnes Peninsula and Flateyjarskagi. Paleoearthquake records can be derived from highresolution seismic reflection profiles of active fault-growth sequences where long-term rate of sedimentation exceeds the rate of vertical fault displacement. Dense profiles across strike-slip faults within Skjálfandi exhibit vertical slip of up to 15 m during several earthquake sequences during the last ~12000 years.

How to cite: Brandsdóttir, B., Detrick, R., Driscoll, N., Karson, J., and Guðmundsson, G.: Postglacial strike-slip faulting within the Skjálfandi Bay, N-Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13787, https://doi.org/10.5194/egusphere-egu23-13787, 2023.

11:55–12:05
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EGU23-14659
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ECS
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On-site presentation
Valentina Argante, Sumiko Tsukamoto, David Colin Tanner, Christoph von Hagke, and Christian Brandes

The Brenner Fault (BF) is an extensional low-angle fault in the eastern Alps that borders the western edge of the Tauern Window. The BF was instrumental in the exhumation of the latter, allowing the formation of the tectonic window by the uplift of the footwall. It consists of a wide shear zone, dipping to the west by an angle of 25-30°, overprinted by a brittle and steeper fault zone with a few metres thickness.  Exhumation and cooling history of its footwall has been investigated by several low temperature thermochronometry approaches, which have defined the Neogenic deformation history, using the zircon and apatite U-Th/He dating methods (Wolff et al. 2021). Because of the lack of thermochronological methods able to date the thermal history of the rocks during Quaternary, the most-recent knowledge of this fault activity has not yet been defined. New studies have shown the possible application of ESR dating on quartz as an ultralow-temperature thermochronometer, characterized by a closure temperature of 30°-90°C, and dating range of 103-107 years that is therefore a useful tool to reconstruct the tectonic deformation of the upper crust during the Quaternary. In this work, we show new structural data and the first results of ESR thermochronometry on quartz applied to rocks of BF collected across both the shear and fault zones. An en-echelon system of normal faults can be distinguished within the continuous N-S striking main fault, suggesting the probable start of brittle deformation or a following deformation phase overprinted the previous one. Moreover, ESR measurements of ten samples collected across the BF show that the ESR ages of quartz get younger toward the Tauern Window, in accordance with fission track and (U-Th)/He ages. The ESR ages indicate the Quaternary exhumation of the BF, i.e. the youngest activity of the BF. Our results promise the successful application of ESR thermochronometry in defining the youngest deformation histories of Neogenic faults in the Alpine chain.

How to cite: Argante, V., Tsukamoto, S., Tanner, D. C., von Hagke, C., and Brandes, C.: New insights into the deformation history of the Brenner Fault by the application of ESR thermochronometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14659, https://doi.org/10.5194/egusphere-egu23-14659, 2023.

12:05–12:15
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EGU23-9009
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ECS
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On-site presentation
Giorgio Arriga, Marta Marchegiano, Valentina Argante, Junjie Zhang, Paola Cipollari, Domenico Cosentino, Michele Soligo, Marion Peral, Hsun-Ming Hu, Chuan-Chou Shen, Mauro Brilli, Philippe Claeys, and Federico Rossetti

The central Apennines are a Cenozoic fold-and-thrust belt that has been affected by post-orogenic extension in its axial region since the end of the early Pliocene (ca. 4 Ma). Post-orogenic extension generated several intermontane basins bounded by high-angle normal faults, striking NW-SE, subparallel to the backbone of the chain. The Monte Pettino and the Monte Marine seismogenic faults (MPF, MMF) are the boundary faults of the western portion of the late Pliocene-Quaternary L’Aquila intermontane basin. Their long-term activity is typified by exhumed fault cores that coexist with active fault strands localised at the fault hanging walls, providing evidence of a polyphase tectonic activity. The fault cores are decorated by diffuse dolomitization, which indicates structurally controlled fluid-flow and metasomatism. To constrain the long-term (space-time) evolution of the MPF-MMF faults, we integrated fieldwork, stable isotope systematics (δ18O, δ13C and Δ47), carbonate thermoluminescence and U-Th dating. Our results highlight two main tectonic phases, with different structural evolution and fluid-rock interaction. The first phase corresponds to the development of a major cataclastic zone, defined by meter-thick, SW-dipping (65-70°), fault cores exposed at the piedmont of the MPF-MMF ridges. The C-O systematics of the cataclasite and of the associated calcite slickenfibers, which are in the range of the carbonate bedrock, indicate a "closed" system behaviour during fault nucleation and development. Preliminary results from Δ47 thermometry of syn-kinematic carbonate structures indicate temperatures of 34 ± 2 °C. Thermoluminescence dating of dolomite clasts in the fault zone indicates age in the range of 3.0 – 3.4 Ma, whilst the cataclastic fault core is younger (< 800 ka). The second phase is mainly recorded in upper Pleistocene sedimentary Breccias (ca. 350 ka) which unconformably cover the bedrock and the exhumed fault cores at the SE termination of the MPF. It consists of anastomosed, high-angle WNW-ESE striking fault strands, spaced meters apart and with cm-m displacements, associated with carbonate veining and travertines. Stable isotopes measured from the fault slickenfibers, carbonate veins and travertines show negative δ13C and δ18O values, suggesting a depositional system dominated by meteoric fluid ("open" system) with an important contribution of organic carbon. Travertines and veins precipitated at colder temperatures (12 ± 4 °C), in the range of the average local air temperatures, thus excluding precipitation from a hydrothermal circuit. Moreover, their U-Th ages range between 182 and 331 ka, compatible with the temporal constraints from stratigraphic data. Structural and isotopic results do not support tectonic reactivation of the cataclastic core of the MPF during the middle-late Pleistocene, confirming the stratigraphic evidence. Our results provide the first absolute age constraint on the post-orogenic extensional faulting in the L’Aquila basin, demonstrating a two-stage fault activity, characterised by a change from localised (from ca. 3 to ca. 0.8 Ma) to delocalised faulting (200-300 ka to present). We infer that this change in the style of extensional faulting was consequence of the evolving rheological structure of the fault zones, primarily regulated by the feedback and interactions involving structurally-controlled fluid flow, rock metasomatism and cataclastic processes in space and time.

How to cite: Arriga, G., Marchegiano, M., Argante, V., Zhang, J., Cipollari, P., Cosentino, D., Soligo, M., Peral, M., Hu, H.-M., Shen, C.-C., Brilli, M., Claeys, P., and Rossetti, F.: The long-term evolution of Monte Marine and Monte Pettino seismogenic faults: tectono-stratigraphic, isotopic, and chronological constraints, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9009, https://doi.org/10.5194/egusphere-egu23-9009, 2023.

12:15–12:25
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EGU23-15260
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ECS
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On-site presentation
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Zoe Mildon, Gerald Roberts, Joanna Faure Walker, Joakim Beck, Ioannis Papanikolaou, Alessandro Michetti, Shinji Toda, Francesco Iezzi, Lucy Campbell, Ken McCaffrey, Richard Shanks, Claudia Sgambato, Jenni Robertson, Marco Meschis, and Eutizio Vittori

Surface faulting earthquakes are known to cluster in time from historical and palaeoseismic studies in multiple active tectonic settings, including central Greece, southern California and central Italy. However, the mechanism(s) responsible for clustering, such as fault interaction, strain-storage, and evolving dynamic topography, are poorly quantified and hence not well understood. We combine surface dating of active normal fault scarps in central Italy with stress modelling and quartz flow laws, to produce a quantified replication of observed earthquake clustering.

We study six active normal faults (including the Mt Vettore fault which ruptured during the 2016 central Italy earthquake sequence) using 36Cl cosmogenic dating. This reveals periods of high and low slip rate, which we interpret to be earthquake clusters/anti-clusters. Interestingly, these changes in slip rate (or clustering) are out-of-phase between neighbouring faults, i.e. when one fault slows down, nearby faults speed up at the same time. To explore the underlying processes driving this out-of-phase clustering behaviour, we link stress transfer caused by slip over clusters/anti-clusters on coupled fault/shear-zone structures with viscous quartz flow laws derived from laboratory experiments.

We show that differential stress fluctuates due to fault/shear-zone interactions, and that the magnitude of these fluctuations are sufficient to induce changes in strain-rate and associated slip-rate on neighbouring faults and shear zones. Our results suggest that fault/shear-zone interactions are a plausible and quantifiable explanation for earthquake clustering, thus opening possibilities for process-led and time-dependent seismic hazard assessments.

How to cite: Mildon, Z., Roberts, G., Faure Walker, J., Beck, J., Papanikolaou, I., Michetti, A., Toda, S., Iezzi, F., Campbell, L., McCaffrey, K., Shanks, R., Sgambato, C., Robertson, J., Meschis, M., and Vittori, E.: Linking surface deformation with lower crustal shear zones: insights into drivers of millennial-scale earthquake clustering and time-dependent seismic hazard, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15260, https://doi.org/10.5194/egusphere-egu23-15260, 2023.

Posters on site: Wed, 26 Apr, 16:15–18:00 | Hall X2

Chairpersons: Riccardo Lanari, Francesco Emanuele Maesano, Jacob Geersen
X2.171
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EGU23-2295
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ECS
Mariusz Fiałkiewicz, Bartłomiej Grochmal, Marcin Olkowicz, Kamil Bulcewicz, and Marcin Dąbrowski

The Strzegom – Sobótka Massif has been subject of brittle tectonics studies for more than a century. Due to an ongoing extensive mining activity, numerous good exposures occur in a relatively small area, especially in the western part of the massif. A pioneering tectonic model of jointing in granite was established by Cloos (1922) for the study area, in which the NW-SE striking joint set is the dominant one (Q) and the perpendicular set (S), striking NE-SW, is longitudinal to mineral fabric. Also, there are two sets of the so-called diagonal joints, which are supposedly younger and strike N-S and W-E.


The effects of field work conducted in 20 quarries in the Strzegom – Sobótka Massiff are presented in the form of a tectonic map. In addition to direct measurements in the field, photogrammetric models were produced using aerial photographs to allow structural analysis within hardly accessible walls. For inaccessible quarries joint orientations were extracted using orthophoto maps. Several examples of fault related structures were identified and documented during field work in the studied granite quarries. Faults with slickensides and kinematic indicators were scarce but paleostress analyses were conducted whenever possible.


We discuss our field measurements of joint and fault orientations in relation to different petrographic types of granites and their lateral extent to address the effects of petrographic differentiation on the evolution of brittle tectonic structures in granites. We compare our new measurements to the results of previous tectonic studies of the Strzegom – Sobótka Massiff and paleostress analyses conducted for several other parts of the Sudetes. We also discuss our new results in terms of the Alpine reactivation of the Sudetes Mountains.

How to cite: Fiałkiewicz, M., Grochmal, B., Olkowicz, M., Bulcewicz, K., and Dąbrowski, M.: Brittle tectonics and paleostress analysis of the Strzegom – Sobótka granite massif, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2295, https://doi.org/10.5194/egusphere-egu23-2295, 2023.

X2.172
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EGU23-4713
Youngbeom Cheon, Young Hong Shin, Samgyu Park, Jin-Hyuck Choi, Dong-Eun Kim, Kyungtae Ko, Chung-Ryeol Ryoo, and Moon Son

Integration of geophysical and geological data is essential to illuminate the configuration and geometry of surface and subsurface structures as well as their long-term evolution history. The NNW–SSE-striking incised valley and parallel mountain range in southeastern margin of the Korean peninsula, extended from Gyeongju to Ulsan cities (~50-km-long on land), have been regarded as the most active geographical feature in Korea, which was named as the Ulsan Fault zone (or system). This study presents a new insight of the structural architecture and its deformation history during the Cenozoic based on a combined data of gravity and electronic survey results with previous field observations. Our major results based on integrated data are as follows. First, the incised fault valley is divided into (1) the northern part of several distributed, buried and exposed fault strands and (2) the southern part of a concentrated deformation zone. Different deformation features between the two parts are controlled by the distribution pattern of the pre-existing Miocene structures (i.e., Yeonil Tectonic Line, YTL). Second, the Ulsan Fault is only constrained as a NNW–SSE-striking Quaternary fault zone within the incised valley-mountain range. The fault zone is composed of several interconnected and disconnected strands forming an imbricate thrust zone located along the western front of the mountain range (or eastern margin of the >2-km-wide incised valley). The constituent fault strands mainly exhibit an east-side-up geometry with moderate to low dip angles and reverse-dominant kinematics in near-surface. These strands are interpreted as reactivated ones of the pre-existing subvertical structures, such as the YTL. In here, we newly designate ‘the Ulsan–Yeonil Fault system’, composed of all NNW–SSE to N–S-striking buried and exposed faults on the incised valley-mountain range, regardless of tectonically controlled sequence of movement stages. Third, movements of the NNW–SSE-striking fault system during the Miocene to Quaternary were arrested by the NNE–SSW-striking Yangsan Fault, which is pre-formed prominent mature structure. Our results highlight the spatiotemporal structural characteristics in SE Korea, emphasizing that the configuration of pre-formed structures have strongly controlled the distribution and characteristics (i.e., geometry and kinematics) of the subsequent deformation during the Cenozoic crustal deformation.

How to cite: Cheon, Y., Shin, Y. H., Park, S., Choi, J.-H., Kim, D.-E., Ko, K., Ryoo, C.-R., and Son, M.: Structure and evolution of the active Ulsan Fault Zone, SE Korea: New insights from geophysical studies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4713, https://doi.org/10.5194/egusphere-egu23-4713, 2023.

X2.173
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EGU23-9272
Barreca Giovanni, Gaillot Arnaud, Klingelhoefer Frauke, Dupont Pauline, Lenhof Edgar, Coussin Vincent, Dominguez Stèphane, and Gutscher Marc-Andrè

The goal of the ERC funded FOCUS project is to study an active fault offshore Catania using fiber optics, sea-floor geodesy, seismological stations (onshore and OBS on the seafloor) and detailed in-situ observations using an ROV and an AUV. Here, we report on the latter. In October 2020 using the ROV Victor6000 and in January 2022 using the AUV IdefX, we performed micro-bathymetric mapping (at an altitude of 50 m above the seafloor) of a 15-km-long segment of the North Alfeo Fault, covering water depths of about 1600 m to 2300 m. A prominent lozenge-shaped transpressive ridge or “pop-up” type structure is one of the primary features of this portion of the fault zone. It forms a flat-topped plateau culminating at about 1700 m water depth. It is cross-cut by a network of N-S striking faults resembling domino blocks or books in a book-shelf.

Sub-bottom profiling (using a chirp system on the AUV IdefX at an altitude of 70 m above the seafloor) crossed the transpressive ridge and imaged the network of narrowly spaced (typically 100 - 200 m spacing) N-S striking faults, which are steeply W dipping normal faults. This suggests the transpressive ridge is currently collapsing. Indeed, the eastern part of the plateau is marked by a small (600 m long from headscarp to toe) submarine landslide. The overall pattern in the northern portion of the mapped area (west of the plateau) is a series of oblique secondary faults, crossing the primary fault at an angle of about 30°. Using a very simple analog model of a thin layer of cohesive granular material above two rigid plates, with a slightly curved fault track, it was possible to produce a primary strike-slip fault directly above the cut between the two plates, and several distinct transpressional ridges (pop-ups) as well as transtensional fissures or gashes. Secondary faults form obliquely to the primary fault and are oriented at about a 30° angle clockwise from the trend of the primary fault. This pattern reproduces the large-scale features observed in the micro-bathymetry from the NW prolongation of the North Alfeo fault. A series of analog experiments using different rheologies in the sediment layer is planned in the future to test the likely detachment (nucleation) depth for the strike-slip fault in the basement.

 

How to cite: Giovanni, B., Arnaud, G., Frauke, K., Pauline, D., Edgar, L., Vincent, C., Stèphane, D., and Marc-Andrè, G.: Ultra-high resolution (micro-bathymetric mapping and sub-bottom profiling) imaging of an active strike-slip fault, the North Alfeo Fault, offshore Catania, Eastern Sicily (Ionian Sea, Central Mediterranean), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9272, https://doi.org/10.5194/egusphere-egu23-9272, 2023.

X2.174
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EGU23-12583
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ECS
Vladimir Shipilin, David Tanner, Jennifer Ziesch, and Hermann Buness

Lithospheric flexure is the primary mechanism for the development of normal faults in foreland basins. While the tectonic regime defines the overall fabric of such flexure-induced faults, mechanical heterogeneity of the sedimentary sequence and pre-existing faults exert a major control on the geometry of the individual faults. Interpretation of 3-D seismic reflection data in the central part of the German Molasse Basin, a northern Alpine foreland basin, reveals a normal fault network that exhibits varying degrees of vertical segmentation. Two major faults oriented parallel to the strike of the Alpine orogen are characterised by geometrically coherent displacement of deeper Mesozoic strata and shallower Cenozoic strata. In contrast, another major fault system, oriented obliquely to the orogenic strike, shows an along-strike variation in geometric coupling between deeper and shallower structural levels. Although a thoroughgoing fault in the northeast, it bifurcates laterally to the southwest, with the deep and shallow segments decoupling across a southeastwardly-thickening, mechanically-weak layer. To establish the geometric evolution of these faults and understand to what extent it was governed by mechanical stratigraphy and structural inheritance, we here analyse throw distribution on the faults and variations in stratal thicknesses across the faults. High-resolution throw mapping indicates a general updip decrease in throw for the orogen-parallel faults, whereas the obliquely-oriented fault, in its coupled portion, has two throw maxima separated by a throw minimum at the mechanically incompetent interval. These results, together with syn-kinematic strata observations, show that the former faults initiated with the onset of the Cenozoic foreland flexure and grew upward by radial propagation, whereas the latter fault formed by an oblique reactivation of precursory Mesozoic faults and developed in the Cenozoic as a segmented structure. We hypothesise that the coupling of its deep and shallow segments to the northeast was established by a dip-linkage mechanism, which was inhibited further to the southeast as the mechanical barrier thickens. The reactivation of the pre-existing structures explains the non-optimal orientation of the younger fault segments at a shallower level, with the former acting as kinematic attractors for the latter faults. This study demonstrates how a detailed fault kinematic analysis can help to decipher the effect of multi-layered mechanical stratigraphy and structural inheritance on the spatial evolution of individual flexure-induced faults.

How to cite: Shipilin, V., Tanner, D., Ziesch, J., and Buness, H.: Influence of mechanical stratigraphy and structural inheritance on the geometrical evolution of normal faults in the German Molasse Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12583, https://doi.org/10.5194/egusphere-egu23-12583, 2023.

X2.175
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EGU23-13053
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ECS
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Miriana Chinello, Michele Fondriest, Telemaco Tesei, Elena Spagnuolo, Andrea Schito, Stephen A. Bowden, Luigi Germinario, Claudio Mazzoli, Chiara Cornelio, and Giulio Di Toro

Mirror-like surfaces (MSs) are ultra-polished fault surfaces that reflect visible light thanks to their low surface roughness (nm-scale). These ultra-polished surfaces are often found in seismogenic fault zones cutting limestones and dolostones (e.g., Siman-Tov et al., 2013; Fondriest et al., 2013; Ohl et al., 2020). Both natural and experimentally-produced fault-related MSs were described in spatial association with ultrafine matrix (grain size <10µm), nanograins (<100nm in size), amorphous carbon, decomposition products of calcite/dolomite (i.e., portlandite, periclase) and larger in size but “truncated” clasts (Verberne et al., 2019). However, the mechanism of formation of MSs is still a matter of debate. Indeed, experimental evidence shows that MSs can develop both under seismic (slip rate ≈1 m/s; Fondriest et al., 2013; Siman-Tov et al., 2013; Pozzi et al., 2018; Ohl et al., 2020), and aseismic (slip rate ≈0.1-10 µm/s; Verberne et al., 2013; Tesei et al., 2017) deformation conditions, involving various physical-chemical processes operating over a broad range of P-T conditions, strain and strain rates.

To understand how MSs form and their role in the seismic cycle, 10 samples were collected and analysed from normal faults cutting bituminous dolostones (Central Apennines, Italy). The MSs samples were from faults with increasing cumulated slip (from < 1 mm to few meters) and different resolved stress.

Ultra-high resolution scanning electron microstructural investigations of the MSs and the associated slip zones, show that the mirrors consist of exposed surfaces of ultra-flat dolostone grains and dolomite nanoparticles cemented by a <1-2 μm thick matrix of smeared bitumen. Cataclastic flow and pressure solution aided by the presence of bitumen are the main deformation mechanisms, probably associated with aseismic creep and fault healing/sealing during the seismic cycle.

Surface microroughness measurements (White Light Profilometry) reveal that (1) the RMS microroughness is < 500 nm over a lateral distance < 1 mm and (2) both the profile and the areal RMS show a weak inverse correlation with increasing displacement. Power Spectral Density (PSD) analysis shows that only in the sample with a displacement less than 1 mm is there a dependence of roughness on slip direction (that is, striae are observed).

Finally, Gas Chromatography-Mass Spectrometry analysis of bitumen from a fault MS which accommodated 86 cm of slip displacement has less quantities of larger molecular weight biomarkers and enrichment in lower molecular weight homologues relative to unfaulted rock. A difference that can be explained by frictional heating during seismic slip causing the destruction of higher molecular weight homologues.

This multidisciplinary study, by investigating the mechanism of formation of MSs, show that these ultra-polished features record the main phases of the seismic cycle, including coseismic slip (changes in the biomarkers structure), aseismic creep (viscous flow of bitumen) and inter-seismic fault sealing/healing (pressure-solution and cold sintering).

How to cite: Chinello, M., Fondriest, M., Tesei, T., Spagnuolo, E., Schito, A., Bowden, S. A., Germinario, L., Mazzoli, C., Cornelio, C., and Di Toro, G.: Mirror-like fault surfaces in bituminous dolostones (Central Apennines, Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13053, https://doi.org/10.5194/egusphere-egu23-13053, 2023.

X2.176
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EGU23-13935
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ECS
Renaldo Gastineau, Pierre Sabatier, Stefano C. Fabbri, Flavio S. Anselmetti, Patricia Roeser, Mustafa Şahin, Serkan Gündüz, A. Catalina Gebhardt, Sven O. Franz, Frank Niessen, and Julia De Sigoyer

The North Anatolian Fault (NAF), located in Turkey, is one of the world's most active faults and accommodates Anatolia's westward motion relative to Eurasia. Over the last century, several earthquakes (M>6.8) have migrated from east to west. It is in the Marmara region, south of Istanbul, that the subsequent rupture is expected. However, this is where the geometry of the fault becomes more complex. It divides into three branches, one of which borders Lake Iznik and the southern Marmara Sea. As there is now very little seismic activity along this portion of the NAF (MNAF), and GPS only detects small displacements (Reilinger et al., 2006), it is thought to be inactive. However, the city of Iznik, the cradle of Christianity, has preserved valuable historical evidence in contrast to its observations. Therefore, to better understand the seismic hazard in this area, it is necessary to catalogue the seismic activity and locate past ruptures.

Two active faults were discovered in Lake Iznik thanks to our geophysical and coring campaigns (Gastineau et al., 2021). The study of short (<4m) sediment cores sampled on both sides of the E-W fault running close to Iznik city reveals that the previous rupture (1065 CE) coincides with a highly destructive historical earthquake recorded in the city's archaeological structures (Benjelloun et al., 2020). In addition to this localised rupture, numerous other event deposits are present in the sediments (laterally and temporally). We demonstrated that the same earthquake in 1065 CE is associated with various deposit types. One type of deposition is only observed for the 1065 CE earthquake, which takes place in the lake, unlike the others, suggesting that this type of deposition may depend on ground motion parameters besides the source-core distance.

A compilation of marine and lacustrine palaeoseismological studies was carried out at the scale of the western part of the NAF. We show that the relationship between sedimentation rate and the presence of earthquake-induced slope destabilisation doesn't work in the marine environment, unlike in the lacustrine environment. We also show that Lake Iznik records earthquakes from the NNAF and the MNAF, whereas the Sea of Marmara records only NNAF earthquakes. These observations open new perspectives and demonstrate the need to consider seismology and site effects in marine and lacustrine paleoseismology.

References:

Benjelloun, Y., De Sigoyer, J., Dessales, H., Baillet, L., Guéguen, P., Şahin, M., 2020. Historical earthquake scenarios for the middle strand of the North Anatolian Fault deduced from archeo-damage inventory and building deformation modeling. Seismol. Res. Lett. https://doi.org/10.1785/0220200278

Gastineau, R., De Sigoyer, J., Sabatier, P., Fabbri, S.C., Anselmetti, F.S., Develle, A.L., Şahin, M., Gündüz, S., Niessen, F., Gebhardt, A.C., 2021. Active Subaquatic Fault Segments in Lake Iznik Along the Middle Strand of the North Anatolian Fault, NW Turkey. Tectonics 40, e2020TC006404. https://doi.org/10.1029/2020tc006404

Reilinger, R., McClusky, S., Vernant, P., Lawrence, S., Ergintav, S., Cakmak, R., Ozener, H., Kadirov, F., Guliev, I., Stepanyan, R., others, 2006. GPS constraints on continental deformation in the Africa-Arabia-Eurasia continental collision zone and implications for the dynamics of plate interactions. J. Geophys. Res. Solid Earth 111. https://doi.org/10.1029/2005JB004051

How to cite: Gastineau, R., Sabatier, P., Fabbri, S. C., Anselmetti, F. S., Roeser, P., Şahin, M., Gündüz, S., Gebhardt, A. C., Franz, S. O., Niessen, F., and De Sigoyer, J.: From Lake Iznik to the Marmara Sea (NW Turkey): new insights in marine and lacustrine paleoseismology., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13935, https://doi.org/10.5194/egusphere-egu23-13935, 2023.

X2.177
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EGU23-6973
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Highlight
Francesco Emanuele Maesano, Mauro Buttinelli, Roberta Maffucci, Giovanni Toscani, Roberto Basili, Lorenzo Bonini, Pierfrancesco Burrato, Jakub Fedorik, Umberto Fracassi, Yuri Panara, Gabriele Tarabusi, Mara Monica Tiberti, Gianluca Valensise, Roberto Vallone, and Paola Vannoli

The undersea portion of the Northern Apennines is characterized by blind thrust faults running parallel to the Adriatic Sea coastline in northeastern peninsular Italy. These thrusts are buried below a thick cover of syntectonic Quaternary deposits. Their elusive geological signature at shallow depths and the low seismicity associated with them gave rise to diverging interpretations and views concerning the current activity of these thrusts and their earthquake potential.

On 9 November 2022, a seismic sequence started with an Mw 5.5 earthquake in the Pesaro Offshore. Hypocentral depth, focal mechanism, and aftershocks location all suggest that the earthquake was generated by one of the outermost thrusts of the Northern Apennines front that was already mapped as a potential seismogenic source in the DISS database (https://diss.ingv.it/diss330/sources.php?ITCS106).

We present a 3D reconstruction of the thrust system that caused the Pesaro Offshore seismic sequence obtained through the reinterpretation of publicly available seismic reflection profiles and well logs. The 3D geometry and size of the thrust activated during the seismic sequence suggest that it can also host larger earthquakes. We also present the application of a well-established workflow for calculating the slip rates of this buried thrust already tested in nearby structures. The outcomes of this study represent a step forward for earthquake and tsunami hazard models, the study of the seismic source, the enhancement of earthquake location by mix and match of seismological and geological independent data, and the expected kinematics of future potential earthquake ruptures.

These results are particularly relevant in offshore areas, where neither surface co-seismic ruptures nor GPS/InSAR deformation data are available in the aftermath of a significant earthquake. In these cases, multichannel seismic reflection profiles represent the only tool to appraise the subsurface structural setting. 

How to cite: Maesano, F. E., Buttinelli, M., Maffucci, R., Toscani, G., Basili, R., Bonini, L., Burrato, P., Fedorik, J., Fracassi, U., Panara, Y., Tarabusi, G., Tiberti, M. M., Valensise, G., Vallone, R., and Vannoli, P.: 3D geological modeling of the blind thrust system activated during the November 2022 Pesaro offshore seismic sequence (Adriatic sea, Italy)., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6973, https://doi.org/10.5194/egusphere-egu23-6973, 2023.

X2.178
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EGU23-11843
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ECS
Simona Bongiovanni, Mariagiada Maiorana, Antonino D'Alessandro, Raffaele Martorana, and Attilio Sulli

The central Mediterranean is a geodynamically very complex area included in the convergence zone between the European plate and the African plate. We investigated the western sector of the Sicily Channel , which shows, according to literature data, different deep and shallow tectonic structures than the eastern sector.  Structural data show the presence of a crustal-scale discontinuity that has generated major seismic events such as the Belice earthquake of 1968. This structure has been identified as a wideband roughly oriented N-S from the San Vito Lo Capo to the Sciacca area (SVCS band, San Vito Lo Capo - Sciacca band) (Di Stefano et al., 2015) and continuing offshore to the Pantelleria area. In this work, through multidisciplinary data analysis, we aim to investigate the correlation between the surface structures highlighted onshore and the offshore continuation. For this purpose, we considered offshore data from the Sicily Channel including: gravimetric data, which show negative anomalies in the Pantelleria graben (Palano et al., 2020) and in the Sciacca offshore and velocity models showing the lateral variation of the Moho with values ranging from 30 to 33 km depth and values ranging from 20 to 23 km depth respectively west and est of the Pantelleria graben (Finetti, 2005). These data were compared with our interpretation of crustal reflection seismic profiles and seismic events (since 2005 with M≥2). The results show an alignment of seismic events with roughly N-S direction from offshore Sciacca to Lampedusa. Moreover, the seismic profiles show a lateral variation of the Moho depth deepening estward. From the joint analysis of these data we obtained a geological model of the investigated sector defining the offshore prosecution of the SVCS band present onshore. The present work may be useful for understanding the geodynamic evolution and for studying the seismic hazard of this area.

 

References

Di Stefano P., Favara R., Luzio D., Renda P., Cacciatore M. S., Calò M., Napoli G., Parisi L., Todaro S., Zarcone G. (2015). A regional-scale discontinuity in western Sicily revealed by a multidisciplinary approach: A new piece for understanding the geodynamic puzzle of the southern Mediterranean, Tectonics, 34, 2067–2085, doi:10.1002/2014TC003759.

Finetti I. R. (Ed.). (2005). CROP project: deep seismic exploration of the central Mediterranean and Italy. Elsevier.

Palano M., Ursino A., Spampinato S., Sparacino F., Polonia A., Gasperini L. (2020). Crustal deformation, active tectonics and seismic potential in the Sicily Channel (Central Mediterranean), along the Nubia–Eurasia plate boundary. Scientific reports, 10(1), 1-14.

How to cite: Bongiovanni, S., Maiorana, M., D'Alessandro, A., Martorana, R., and Sulli, A.: Multidisciplinary approach to the study of a crustal tectonic discontinuity: an example from the Central Mediterranean offshore (Sicily channel), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11843, https://doi.org/10.5194/egusphere-egu23-11843, 2023.

X2.179
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EGU23-14121
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ECS
Billy Andrews, Zoë Mildon, and Christopher Jackson

Seismic reflection datasets can help unpick the long term (i.e., 100 kyr to Ma) slip history of active normal faults (e.g., Nicol et al., 2005). To constrain slip-rate from seismically imaged normal faults you measure the across-fault offset of stratigraphic markers of known age.  Ideally, this is undertaken parallel to the slip-vector, i.e., orthogonal to fault-strike. In many active systems this is not possible with only non-optimally orientated 2D surveys available. Here we assess how obliquity effects continuous and discontinuous fault properties (throw, heave, dip, displacement) extracted from normal faults imaged in a 3D seismic cube. We targeted ‘straight’ faults and extracted cut off data from sequentially oblique sample lines ranging from ±50˚, comparing oblique data to that extracted from optimally orientated lines. Additionally, repeat picks were undertaken on two horizons to investigate the relative importance of measurement obliquity and human error.

Oblique measurements showed different along-fault profiles compared to orientated sample lines. This causes some datasets to be statistically different, with >100 % difference occasionally observed. Continuous deformation is more prone to obliquity errors, with the measurement of an apparent dip causing heave, and therefore displacement and dip, to display large differences at high obliquity. The dip of horizons close to the fault and localised complexity at the sample location (e.g., nearby faults) are also important factors. Differences regularly exceed 20% at high obliquity and we therefore suggest obliquity should not exceed 15˚ and were this is not possible measurements are corrected using fault cut offs and local fault strike.

For repeats picks, the shape of along-fault profiles is similar; however, subtle differences exist. Variability depends on the fault and fault parameter, with greater differences observed for faults with low displacement. Several locations along the fault exceeded the population difference. This was locally associated with a particular dataset; however, trends rarely persisted along the whole fault. Factors influencing this include a) shallow folding close to the fault, b) localised complexity at the sample location, and/or c) poor imaging near the fault plane. Unexpectedly, no correlation between variability and obliquity was found. Overall, we suggest errors due to human factors could be ~10-15% for throw and 20-25% for heave, with higher errors possible.

If we consider the fault data extracted using 2D seismic lines across the Cape Egmont Fault by Nicol et al., 2005, >50% of the measurement points exceed our recommended maximum obliquity. Nicol et al. (2005) report that the maximum throw between the 3.2 and 3.7 Ma horizons as 1364 m, giving a throw rate of 0.0028 mm/yr. However, the 2D survey at this location has a measurement obliquity of 21˚. Considering our findings throw rate could range from 0.0022 to 0.0033 mm/yr due to obliquity and human factors. It is therefore important users are aware that spatio-temporal variations in slip-rate may be caused by geological controls, human errors, and measurement obliquity.

Nicol et al., 2005. Growth of a normal fault by the accumulation of slip over millions of years. J. Struct. Geol. 27 (2), 327-342.

How to cite: Andrews, B., Mildon, Z., and Jackson, C.: The impact of human factors and measurement obliquity when extracting geological slip-rate from seismically imaged normal faults., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14121, https://doi.org/10.5194/egusphere-egu23-14121, 2023.

X2.180
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EGU23-8544
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ECS
Judith Gauriau and James Dolan

The Coefficient of Complexity (CoCo) is a metric that quantifies the relative structural complexity of the fault system surrounding a specific study site on a primary fault extending through the system. Specifically, the CoCo metric has been used successfully to correlate the relative constancy or non-constancy of incremental slip rates on major strike-slip faults with the proximity, number, and slip rates of other neighboring active faults within a given radius of observation. Interestingly, our analysis shows that faults that extend through more structurally complex plate-boundary fault systems are characterized by more temporally variable slip behavior than faults that are embedded within simpler settings. Complex stress interactions within structurally complicated tectonic networks, as well as possible temporal changes in fault strength and kinematic interactions amongst mechanically complementary faults, likely explain these different behaviors. The CoCo metric thus not only provides a potential means for better evaluating the future behavior of large plate-boundary faults in the absence of well-documented incremental slip-rate behavior, but also can be used to differentiate faults that typically slip at a constant rate from the ones which do not. Using these results, we explore the relationship between incremental fault slip rates averaged over both short and large displacements on major strike-slip faults and geodetic estimates of strain accumulation rate on faults with different CoCo values. As might be anticipated, our analysis shows that the relatively constant slip rates on faults embedded within structurally simple strike-slip tectonic networks (i.e., low-CoCo faults) generally match rates of elastic strain accumulation of the faults’ shear zones, as measured by geodetic slip-deficit rates. In marked contrast, geodetic slip-deficit rates for faults embedded within structurally complex fault systems (high-CoCo faults) are less consistent with geological rates, whether averaged over short or large displacement scales, indicating significant variations in strain-accumulation rate on high-CoCo faults. We use these data to suggest possible patterns of geodetic-to-geologic rate ratios that may be indicative of the likely near-future behavior of the fault in question.

How to cite: Gauriau, J. and Dolan, J.: Using the CoCo metric of relative structural complexity of major plate-boundary fault networks to explore potentially time-variable fault loading rates on major strike-slip faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8544, https://doi.org/10.5194/egusphere-egu23-8544, 2023.