TS3.3 | Studying active faults from the near-surface to seismogenic depth: an open challenge
EDI
Studying active faults from the near-surface to seismogenic depth: an open challenge
Co-organized by NH4
Convener: Fabio Luca Bonali | Co-conveners: Rita De Nardis, Federica Ferrarini, Ramon Arrowsmith, Victor Alania
Orals
| Tue, 25 Apr, 14:00–17:15 (CEST)
 
Room D1
Posters on site
| Attendance Wed, 26 Apr, 10:45–12:30 (CEST)
 
Hall X2
Orals |
Tue, 14:00
Wed, 10:45
The session focuses on research aimed at defining the geometry, kinematics, and associated stress- and deformation fields of active faults, as well as building up tectonic and seismotectonic models, in all tectonic regimes, including volcanic areas. Assessing the geometry and kinematics of faults, key to seismic hazard assessment, can be often challenging due to the possible paucity of quantitative data, both at the near-surface and at seismogenic depths.
Tackling this challenging issue is nowadays possible by combining data from different approaches and disciplines, with the aim of obtaining a more detailed characterization/imaging of single active faults, as well as reliable seismotectonic models. In addition, technological advances in data collection and analysis provide a significant contribution. As an example, photogrammetry and LIDAR-derived models enable collecting a great deal of geological data even in inaccessible areas; these data can then be integrated with field (structural), seismological and geophysical data with the purpose of a better understanding of active faults geometry. Also, the improvement in data processing allows to enhance seismic catalogues in areas with low-level seismicity, as well as collect new and more detailed data from geophysical, geodetic, or remote-sensing analysis.
Contributions dealing with the following topics are welcome: i) active faults, including volcanic areas; ii) classical to innovative multiscale and multidisciplinary geological, seismological and geophysical approaches; iii) new or revised seismological, geophysical, field-and remotely-collected datasets; iv) faults imaging, tectonic-setting definition and seismotectonic models; v) numerical and analogue modelling.

Orals: Tue, 25 Apr | Room D1

Chairpersons: Fabio Luca Bonali, Federica Ferrarini, Rita De Nardis
14:00–14:10
14:10–14:30
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EGU23-17153
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solicited
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On-site presentation
Michele Carafa

Recent seismic hazard models are increasingly relying on fault slip rates as the fundamental quantity for translating the activity of a fault source model into earthquake rates. In this conversion, modelers are often tasked with selecting different estimates and alternative methods to assess the fault slip rates and related uncertainties and incorporate them into the seismic hazard analysis. In the central Apennines, several techniques, such as paleoseismic trenching, mapping of offset geomorphic markers, and dating of scarp profiles have been used to determine slip rates of normal faults. Recently geodetic data have also been used to determine the first estimates of the slip rate (loading) rate on active faults.

Combining measurements obtained with different methods remains challenging because non tectonic processes can introduce noise or spurious signals that are elusive to quantify, and these influence slip rate estimates. After careful and planned data collection, we argue that a rigorous meta-analysis is required to quantify erratic fluctuations and method-related variances. In this case, throw rates are overdispersed with respect to nominal uncertainties in throw and age; therefore, they are commonly affected by unmodeled noise processes to be rigorously quantified for seismic hazard assessment.

Geodetic data can provide slip-rate estimates with a model of elastically unloading seismogenic faults within a viscously deforming lithosphere. However, short-term transients can also infect geodetic data in the central Apennines. Such transients can be isolated and subtracted by time series or included as noise in the long-term covariance matrix; otherwise, the resulting spatial distribution of deformation rates locally fits short-term transients. In some cases, strain rate peaks represent the currently unclear signal of tectonic processes like crustal visco-elasto-plastic deformation and aseismic slip or indicate missing faults in the adopted database. In the central Apennines, we have proved that reasonable estimates of long-term fault slip rates can be extracted even at signal-to-noise ratios of order unity using a more sophisticated modeling approach, including the stress orientations. For well-sampled faults, the slip rate estimates fit the corresponding geological estimates, leading us to conclude that they can be considered for seismic hazard models in regions such as the Apennines.

We remark that geodetic and geological data can be used together to highlight (and possibly model) both the likely occurrence of short-term transients in GPS time series and the existence of non-tectonic processes contributing to the progressive surface exposure of active faults. Given the current understanding of temporal and spatial fault throw rate variability in the central Apennines, producing complex input models for seismic hazard assessment is still not feasible. A base model with a uniform throw rate along the trace (tapering to zero at unconnected fault tips) and merging information from offset features of different ages to constrain a single time-independent rate is still the most reasonable.

How to cite: Carafa, M.: Meta-analysis of fault slip rates across the central Apennines for seismic hazard assessment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17153, https://doi.org/10.5194/egusphere-egu23-17153, 2023.

14:30–14:40
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EGU23-3749
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Virtual presentation
Mohsen Ehteshami-Moinabadi and Shahram Nasiri

Abstract

 The megacity of Tehran, the capital of Iran, is located on the southern slope of the central part of the Alborz Mountain range. The earthquake risk assessment studies in the Tehran metropolis have been focused mainly on earthquake data and technical aspects of buildings and structures. In the meantime, the data on the fault that can cause earthquakes and the related triggered fracture system, like the potential of direct surface rupture that can be developed or occur as the result of an earthquake faulting, have not been significantly updated during the last two decades for mountain front foothills. The land use changes and the growth of the metropolis of Tehran during the last two decades, especially in the city's northern half, with the lack of any regulatory action on the fault zone, are escalating the risk of surface rupture. In this regard, the need to update the fault map and establish a fault zone regulatory act is paramount to importance. By reviewing the existing information and combining it with new satellite data, an updated map of the faults in the northern zone of Tehran city has been presented. The vital point in this map is to recognize the continuation of the fault trends that were introduced before, but their end was unknown. Also, a vast network of fractures or subsidiary faults belonging to the North Tehran fault system has been mapped, especially in its hanging wall part, which has not been published before. The result of the overlapping faults with urban structures and building areas shows that in the lack of regulation, the fault zone's ignoring continues in the new constructions of the Tehran metropolis. It is estimated that more than twenty hospitals, many of which are newly built, along with other strategic and sensitive structures, are in danger of surface rupture, and it is indispensable to think of a solution for them.

Additionally, many important buildings are in danger of fault rupture. We recently found that large ancient mega-landslides exist in the northern foothills of Tehran that are under more investigation. In the end, this research emphasizes the special attention to the lateral investigation of thrusts located in the north of Tehran between the North Tehran fault and the Masha fault, especially the Imamzadeh Dawood, Kigah and Pourkan faults.

Keywords: fault surface rupture, fault setback, earthquake, seismic hazard, Tehran, North Tehran Fault

How to cite: Ehteshami-Moinabadi, M. and Nasiri, S.: A critique review and update of the earthquake surface fault rupture hazard in the northern zone of Tehran metropolis, Iran, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3749, https://doi.org/10.5194/egusphere-egu23-3749, 2023.

14:40–14:50
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EGU23-7228
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ECS
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On-site presentation
Ambrosio Vega Ruiz, Pia Victor, Sara Pena-Castellnou, Klaus Reicherter, Ariane Binnie, and Steven Binnie

The Longitudinal Valley in Northernmost Chile was the main depocenter of widespread fluvial-alluvial systems active through the Neogene. These formed extensive lacustrine systems located at the eastern slope of the Coastal Cordillera until exorheic drainages developed between Arica and Pisagua (~18°30’S – 19°30’S) ca. 3 Ma ago. The top surfaces of the continental deposits form a regional scale pediplain (Pacific Paleosurface), where run-off is focused in present-day perennial streams draining to the Pacific Ocean through deeply incised quebradas. Some geomorphic and climatic constraints and suggestions exist regarding how the uplift of the Coastal Cordillera and the western Andes influence the shift in drainage regimes. However, little is known about how tectonic activity across this region affected landscape evolution since the structural architecture is difficult to unravel in this area of high sedimentation but low displacement rates.

We performed an exhaustive regional mapping of structural and geomorphic evidences of fault activity and drainage patterns based on high-resolution DEMs, satellite, and UAV imagery data, as the long-term hyperaridity of this area leads to well-preserved landforms and lack of vegetation cover. Our investigations reveal evidence of a reactivated complex inherited strike-slip system across the Longitudinal Valley, deforming Miocene to Quaternary surfaces. Local growth strata, angular unconformities, and flower structures within the Late Miocene to Early Pliocene lacustrine deposits suggest syn-sedimentary and dextral transpressional faulting near the boundary between the Longitudinal Valley and Coastal Cordillera. Importantly, we observe that large drainage reorganization patterns can be triggered by only little displacement along often blind fault structures, creating sufficient topography that cannot be surpassed by drainage incision in this hyperarid setting.

The interpretation of a reprocessed ENAP seismic section at ~19°20’S, suggests that this fault system consists of inherited Mesozoic inverted structures deforming Oligocene to Late Miocene strata. Furthermore, progressive abandonment and deformed terraces of low-incised rivers crossing compressive structures suggest that these were active during the Quaternary, most probably ongoing until the recent past. New dating of deformed marker horizons will bring further insights regarding key parameters of fault activity for the Late Cenozoic and Quaternary.

How to cite: Vega Ruiz, A., Victor, P., Pena-Castellnou, S., Reicherter, K., Binnie, A., and Binnie, S.: Evidence of Late Cenozoic transpressive reactivation of an inherited strike-slip fault system and its influence in drainage reorganization in the Longitudinal Valley of Northernmost Chile, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7228, https://doi.org/10.5194/egusphere-egu23-7228, 2023.

14:50–15:00
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EGU23-5102
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ECS
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On-site presentation
Suman Panday, Jia-Jyun Dong, Jiun-Yee Yen, Chih-Heng Lu, and Che-Ming Yang

The fragile geology, tectonically and active seismic mountain belt like Taiwan are exposed to numerous geological controls on development of landforms. Especially North-South elongated suture zone between Eurasian and Philippine sea plate formed a Longitudinal valley remarks very active seismic behaviors and bounded by west dipping Central Range Fault (CRF) and east dipping Longitudinal Valley Fault (LVF). Wuhe table land lies on the western side of central part of valley and approximately 200 meters elevated from Xiuguluan River bed. The unconsolidated Mud layers (>50 ka) with few carbonaceous materials of about ten meters’ thicknesses lies in thick conglomerates of tableland could be the lacustrine deposits based on sedimentary environment, which suggest that there was a short-term damming event which is inclined approximate 30 degrees towards northwest. Deformation of mud layer is further studied to analysis the active tectonics and structural controls on tableland. Numerous boreholes, geophysical prospecting, InSAR data, GPS data and past earthquake information are processed on this study as preparation of 3- dimensional geological model and deformation characteristics. Past earthquake behavior shows that CRF acts as blind strike slip movement and very less surface deformation or ruptures but small-scale fissuring on south along Yuli ruptures (Yuli fault trace from 1951 earthquake) from the tableland and the upliftment rate of tableland is slow approximately about   >1mm/year.  While there are debatable issues regarding to CRF mechanism but this research tries to correlate the active deformation behavior and preservation of Wuhe Tableland on the basis of fault characteristics in this region.

How to cite: Panday, S., Dong, J.-J., Yen, J.-Y., Lu, C.-H., and Yang, C.-M.: Active tectonics and Fault behavior analysis based on deformation of mud layer on Wuhe Tableland, Eastern Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5102, https://doi.org/10.5194/egusphere-egu23-5102, 2023.

15:00–15:10
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EGU23-7834
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ECS
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On-site presentation
Nicolas Harrichhausen, Léo Marconato, Laurence Audin, Stephane Baize, Hervé Jomard, Pierre Lacan, Diana Saqui, Alexandra Alvarado, Patricia Mothes, Frédérique Rolandone, Iván Ortiz, and Mónica Arcila

We present initial remote sensing and field data that suggest active distributed right-lateral faulting at the northern edge of the Quito-Latacunga tectonic block in northern Ecuador and southern Colombia. In this region, oblique subduction of the Nazca Plate beneath the South America plate induces northward migration of the Northern Andean Sliver (NAS), with respect to stable South America. Recent geodetic studies now suggest that this sliver is composed of several independent tectonic blocks, and the boundaries of these blocks are locations where we hypothesize crustal strain is accommodated. One of these blocks, the Quito-Latacunga block, is located in the densely populated Interandean valley of northern Ecuador and southern Colombia, and geodetic modelling predicts approximately 3 mm/yr of right-lateral strain at its northern boundary. A shallow July 25, 2022, MW 5.6 earthquake and damaging historical earthquakes along the northern boundary have illustrated the importance of understanding where this strain is being accommodated. We use available digital surface models (DSMs), local DSMs derived from Pleiades and SPOT satellite stereo-imagery, Interferometric Synthetic Aperture Radar (InSAR), Google Earth imagery, and a field survey to show that this boundary is distributed across several parallel northeast striking right-lateral faults. InSAR shows the July 25 event resulted in right-lateral surface displacement of > 20 cm along an east-northeast striking, steeply dipping fault. Offset volcanic soils and glacial moraines indicate recent earthquakes on two faults north of and subparallel with this rupture. Both faults overlap with the proposed area for the August 15, 1868, M 6.4–6.8 El Angel earthquake, suggesting either fault could be associated with this event. As the DSMs reveal a number of parallel strike-slip faults to the north in Colombia, further paleoseismic studies are needed in this region to delineate active faults and help define regional seismic hazard.

How to cite: Harrichhausen, N., Marconato, L., Audin, L., Baize, S., Jomard, H., Lacan, P., Saqui, D., Alvarado, A., Mothes, P., Rolandone, F., Ortiz, I., and Arcila, M.: Distributed right-lateral faults accommodating strain at the northern boundary of the Quito-Latacunga microblock of the Northern Andean Sliver, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7834, https://doi.org/10.5194/egusphere-egu23-7834, 2023.

15:10–15:20
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EGU23-4966
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ECS
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On-site presentation
Maxime Henriquet, Branko Kordić, Marianne Métois, James Hollingsworth, Cécile Lasserre, Olivier Cavalié, Lucilla Benedetti, Stéphane Baize, Marko Špelić, Matija Vukovski, and Ryan Gold

The Mw 6.4 Petrinja earthquake (2020, Croatia) is among the strongest continental earthquakes that occurred in Eastern Europe for decades. In such low-strain contexts, the sparse terrestrial-monitoring (few seismic and geodetic stations) of rare but strong earthquakes often prevents a detailed analysis of their seismic source. Here, we take advantage of > 160 geodetic benchmarks and optical image correlation to obtain a dense near-field coverage of the coseismic surface displacements. The geodetic dataset is obtained by repeated measurements of benchmark networks designed for civilian purposes and constitutes a unique dataset of coseismic displacements in the near-field of the fault. The optical image correlation is based on pre-earthquake (December 2017) WorldView and post-earthquake (February 2021) Pleiades satellite images with a 50 cm resolution. We also complete these displacement fields with unwrapped coseismic interferograms based on Sentinel-1 products, except in the near field affected by decorrelation. These displacement fields are consistent and thus suitable for modeling the slip distribution of the Petrinja earthquake. The elastic inversion of the geodetic benchmarks revealed interesting characteristics of this event: the rupture occurred on a near-vertical strike-slip fault, at a shallow depth (< 10 km), with significant slip reaching the surface. It also suggests that the deformation was partly accommodated by a subparallel strand 2.5 km from the main source northward. The aim of this research is to improve the source model of Petrinja 2020earthquake sequence, with a joint inversion of the geodetic benchmarks, optical image correlation, and InSAR data. Nevertheless, the comparison of the geodetic and coseismic offsets measurement on the field, shows that > 70% of the slip is likely distributed at the surface. Moreover, the coseismic strain maps derived from the unique benchmark data set helped us to identify zones where deformation appears distributed. Finally, the new data raises questions about whether such moderate earthquakes are accompanied by subsurface off-fault deformation or residual elastic strain.

How to cite: Henriquet, M., Kordić, B., Métois, M., Hollingsworth, J., Lasserre, C., Cavalié, O., Benedetti, L., Baize, S., Špelić, M., Vukovski, M., and Gold, R.: Coseismic slip of the 2020 Mw 6.4 Petrinja earthquake (Croatia) from dense geodetic benchmarks, optical image correlation and InSAR data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4966, https://doi.org/10.5194/egusphere-egu23-4966, 2023.

15:20–15:30
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EGU23-10577
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ECS
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Virtual presentation
Sandro Truttmann, Marco Herwegh, Tobias Diehl, and Stefan Wiemer

Understanding orogen-internal seismic deformation in regions with diffuse spatial earthquake occurrence is challenging. To gain deeper insights into the processes driving seismic fault reactivation, it is crucial to obtain information on the ubiquitous pre-existing fracture patterns. In orogens with long tectonic histories – such as the Alps – such patterns can be complex, and information on their appearance is mainly limited to observations of faults at the surface, while the detailed patterns at depth remain mostly unknown. Moreover, the link between such surface-based fault observations and active seismicity is often ambiguous. However, it has been shown that both earthquake magnitudes (Gutenberg-Richter law) and various fault properties (e.g., length, displacement) follow power-law distributions.

In this work, we aim to investigate the potential relationship between the scaling properties of faults and earthquakes, which has been little explored. To this end, we use statistical tools based on field data collected with remote sensing techniques at different scales to quantitatively characterize the length distributions of exposed fault networks at different study sites in the southwestern Swiss Alps. Due to the good outcrop conditions at high elevations, the dense seismic monitoring network, and the enhanced earthquake activity, this region provides an ideal natural laboratory for the study of orogen-internal seismicity. By combining fault trace maps from three different scales, we are able to derive power law parameters and decipher similarities in scaling exponents for the different sites studied. Assuming that the fault networks exist in a similar form at depth and form the pre-existing discontinuities along which recent earthquakes develop, we compare the derived scaling laws with the frequency-magnitude distribution of local seismicity over the past 15 years. Here we find similar scaling properties between the seismicity and fracture networks only at depths below 3 km. However, in shallower regions, the large discrepancy between the scaling laws suggests that partial seismic ruptures of individual fault segments are more common than at greater depths. Such a statistical comparison of fault and earthquake scaling laws provides interesting insights into orogen-internal seismic deformation and fault reactivation processes that also have implications for regional seismic hazard.

How to cite: Truttmann, S., Herwegh, M., Diehl, T., and Wiemer, S.: The scaling properties of fault networks and their relationship with the size distribution of orogen-internal seismicity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10577, https://doi.org/10.5194/egusphere-egu23-10577, 2023.

15:30–15:40
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EGU23-10516
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ECS
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Virtual presentation
Dehua Wang, John Elliott, Gang Zheng, Tim Wright, and Andrew Watson

The left-lateral Altyn Tagh Fault (ATF) is one of the longest active strike-slip faults in the world. Investigating the present-day state of the ATF is critical for our broader understanding of the India-Asia collision zone and the current motion of the Tibetan Plateau. Previous geodetic studies of the ATF using InSAR focused on relatively small areas, which is insufficient for a whole-fault understanding, but with the launch of the Sentinel-1 SAR constellation and the development of InSAR techniques, we can measure the crustal deformation and stress fields associated with interseismic motion along the fault more systematically as Sentinel-1 has provided high spatial coverage, better spatial resolution compared to GNSS, and shorter repeat times compared to previous SAR satellites. The large spatial coverage from such research could not only allow a better understanding of along-strike variations of fault slip rate and locking depth, but provide an opportunity to see how fault bends influence the deformation and strain fields, both of which are important for synthetic evaluation of future seismic risk along the fault. In this research, we use interferograms, which are produced by LiCSAR processing system, on 7 ascending tracks and 6 descending tracks to map surface velocities for a total area of ~ 600,000 km2 (~ 1,300 km × 450 km) around the central and eastern segment of ATF. Each track uses nearly 180 epochs between October 2014 and July 2022. To reduce the impact of phase biases and nontectonic seasonal signals, we combine both short temporal (< 4 months) and 1-year to 7-year long summer-to-summer baseline interferograms in the network, which generates an average of nearly 2000 interferograms in each LiCSAR frame (a track includes 1 or 2 frames). We use the Generic Atmospheric Correction Online Service (GACOS) to reduce the tropospheric delay in the unwrapped phase. Time-series analysis was applied using LiCSBAS. We estimate 83 3D GPS velocities using the data measured during 1998-2021 from the Crustal Movement Observation Network of China-I/II and then solve for the best-fit model of surface velocities and strain rates for the central-eastern Altyn Tagh fault zone based on both InSAR and GNSS velocities. Our results suggests that deformation and strain in the study area is concentrated along the ATF and show an along-strike variation from west to east. Using a screw dislocation model, we constrain best fit values for the slip-rate, locking depth, creep rate, and fault dip, for 12 fault-perpendicular velocity profiles along the length of the ATF using a Bayesian inversion and the Markov chain Monte Carlo (MCMC) sampler. Our results provide an important constraint on the present-day motion and structure of the Eastern and Central ATF. Additionally, by comparing with previous geodetic and geological investigation results, our study could bring some new thoughts and directions for future research about the ATF and other active faults.

How to cite: Wang, D., Elliott, J., Zheng, G., Wright, T., and Watson, A.: Large-scale crustal deformation and strain rate distribution along the central-eastern Altyn Tagh fault (NW Tibet) from Sentinel-1 InSAR and GNSS data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10516, https://doi.org/10.5194/egusphere-egu23-10516, 2023.

15:40–15:45
Coffee break
Chairpersons: Rita De Nardis, Victor Alania, Ramon Arrowsmith
16:15–16:25
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EGU23-11644
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On-site presentation
Cristiano Collettini and Elisa Tinti

The earthquake Magnitude-Frequency-Distribution, FMD, is usually modelled with the Gutenberg-Richter relation law, where the b-value controls the relative rate of small and large earthquakes. b-value has been documented to show an inverse dependence on differential stress, it increases with the fault roughness or during fluid-induced earthquakes. For some seismic sequences a near real-time characterization of the b-value has been used to discriminate between foreshocks and aftershocks. Here we examine the influence on b-values of different lithologies hosting earthquakes.

In general, seismicity not only localizes along the major structures where mainshocks nucleate, but it can be also distributed within volumes of the seismogenic layer characterized by different lithologies. For the Mw 6.5 2016–2017 Central Italy seismic sequence, the lithology can be properly defined by seismic reflection profiles. Here the fractured carbonate of the Apennines, located at almost 1-2 km and 4-6 km of depth, are characterized by b-values ranging between 1.3 and 1.4 that can be diagnostic of brittle dominated deformation. At 2-4 km and 6-10 km of depth, the Triassic Evaporites showing a bimodal brittle-ductile deformation and compartmentalized fluid overpressure (documented in deep boreholes) are linked to high b-values, in the range of 1.5-1.65 reaching 1.80 for clustered swarms. Between 10-12 km of depth the phyllosilicate rich basement, with its predominant velocity strengthening behaviour, is hosting small magnitude earthquakes with b-values around 1.4. Our results indicate that away from the large earthquake faults, characterized by a stress dependent elasto-frictional rheology, FMD are strongly controlled by rock lithology and style of deformation.

How to cite: Collettini, C. and Tinti, E.: The influence of lithology on the Magnitude–Frequency-Distribution of earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11644, https://doi.org/10.5194/egusphere-egu23-11644, 2023.

16:25–16:35
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EGU23-15827
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On-site presentation
Maurizio Ercoli, Filippo Carboni, Assel Akimbekova A, Ramon B. Carbonell, and Massimiliano R. Barchi

Reflection seismic is the best active geophysical method to constrain the geometry and kinematics of faults at depth. In some specific areas, seismic profiles derived from industry or from past research programs can be nowadays still used in seismotectonic studies to link the surface faults traces with hypocentral earthquake sources. Deep reflection seismic profiles such as the ones recorded in the framework of  the Italian “CROP” aimed shed light on the deep subsurface structures, despite the high levels of random noise hampering the seismic interpretation. Also the CROP-04 “Agropoli-Barletta”, seismic transect acquired from the Tyrrhenian to the Adriatic Sea across the Southern Apennines fold-and-thrust belt and the foreland system, is strongly affected by random noise. Various geological interpretations based on this data are available in literature, as this seismic profile crosses important active faults such as the Irpinia fault, which produced the destructive 1980 Mw 6.9 earthquake. Aiming to improve the data quality, by reducing the noise, to perform a structural interpretation of its shallower sector, we applied a dedicated workflow encompassing pre-conditioning filters, selected seismic attributes and co-rendered views. Following this workflow we have considerably enhanced the reflection patterns and the overall data interpretability, unveil a dense and complex sets of normal faults, thus imaging tectonic structures which were invisible in the original CROP-04. In addition, the master faults mapped at surface well matches the seismic signature. The reprocessed profile displays also clear low-angle W-dipping thrusts and deep regional features, contributing to better understanding the complex subsurface geology of the Southern Apennines. Our advances interpretation strategy is able to efficiently revive deep legacy data like the CROP, which are unique and nowadays hardly to repeat. New important insights across seismically active areas worldwide can be obtained reproposing this workflow in other contexts, extending to depth the surface evidences of outcropping faults as well as revealing unknown structures to survey with targeted fieldwork mapping.

How to cite: Ercoli, M., Carboni, F., Akimbekova A, A., Carbonell, R. B., and Barchi, M. R.: Pre-conditioned seismic attributes applied to deep vintage seismic reflection line: enhancing fault patterns on the Italian CROP-04 ., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15827, https://doi.org/10.5194/egusphere-egu23-15827, 2023.

16:35–16:45
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EGU23-11810
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ECS
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On-site presentation
Claudia Pandolfi, Rita de Nardis, Andrea Carducci, Aybige Akinci, and Giusy Lavecchia

We present SEISC-3D, an ArcGIS geodatabase for 3D SEIsmic Source Characterization. It integrates multi-scale and multi-depth geological and seismological information in a compressional environment to build a detailed regional-scale, geometric and kinematic, 3D curvilinear fault model suitable for seismic hazard modelers and seismotectonic purposes and geodynamic modeling. This first release focuses on the late Pliocene-to-Quaternary arcuate and eastward convex fold-and-thrust belt still active along the Outer front of the Italian Apennines in eastern Central Italy. The near-surfaces, onshore, and offshore thrust faults represent the hanging-wall structures of a potentially seismogenic regional shear zone, known as Adriatic Basal Thrust, which develops from near-surface to MOHO depths (about 35 km).

Three hierarchic levels of structural maps are provided with decreasing details moving from fold-and-thrusts traces, enveloping thrust, and regional thrust alignments.

Different datasets (points, lines, surfaces) are unified, compiled, and held in a common ArcGIS file system folder and linked on the basis of relational models.

SEISC is composed of:

  • one dataset consisting of fold hinges traces (syncline and anticlines)
  • one dataset consisting of individual fold-related thrust
  • one dataset consisting of enveloping thrusts organized in hierarchic orders
  • one dataset consisting of interconnected curvilinear fault surfaces built along the down-dip projection of the enveloping thrusts, segmented along-strike and along-dip
  • one structural data set containing geometric and kinematic point data (attitude, dip-angle, slip-vector, rake, sense of movement) for the node of each triangulated mesh of each fault surface.

A crucial point when dealing with compressional structures is the difficulty in adopting segmentation criteria suitable for a realistic earthquake-fault association. In our methodological approach, the along-strike segmentation is strongly driven by the en-echelon distribution of the fold-related thrusts and by sharp variation in strikes and bending of the enveloping thrusts. On the other hand, the down-dip segmentation is controlled by the mechanical crustal layering derived from earthquake distributions and the rheological investigation.

How to cite: Pandolfi, C., de Nardis, R., Carducci, A., Akinci, A., and Lavecchia, G.: A conceptual 3D fold-and-thrust database for seismic hazard, seismotectonic and geodynamic purposes - a first release from eastern Central Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11810, https://doi.org/10.5194/egusphere-egu23-11810, 2023.

16:45–16:55
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EGU23-5012
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ECS
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On-site presentation
Thomas Gusmeo, Giacomo Carloni, Gianluca Vignaroli, Luca Martelli, and Giulio Viola

Understanding how the brittle deformation pattern at the surface relates to active seismogenic sources at depth is one key element for accurate Seismic Hazard Assessment procedures based on deterministic inputs. Establishing a relationship between surface faulting and deep sources can, however, be very challenging, especially in areas where seismogenic structures lack obvious and readily interpretable geological evidence at the surface. Here, we present results of detailed structural and geological investigations from a field-based study of active and capable faults along the Northern Apennines front (Pedeapenninic margin) between Reggio Emilia and Bologna, in northern Italy. Those results are then implemented into a Probabilistic Seismic Hazard Assessment model (PSHA) that also relies on an accurate surface acceleration model computed by considering site effects from the local stratigraphic amplification factors.

In the study area, the geological framework is characterized by two lithotectonic units: the Eocene-to-Miocene Epiligurian Units and the Pliocene-to-Present successions cropping out along the frontal Pedeapenninic margin. A compressive tectonic regime is currently dominant, with a regional-scale, NE-verging thrust system shaping the first-order architecture of the Pedeappenninic front. This thrust system is complex and is dissected by transverse normal and transpressive/transtensive faults. The architecture of the studied margin reflects exposed NE-verging thrusts within the Epiligurian Units in the more internal domains, and mostly blind thrusts below the Pliocene-to-Present units in the external domains. The Pliocene-to-Present units are also faulted and folded, indicating that tectonic activity is still in full swing, hence with significant seismogenic potential (as also documented by seismic archives). Top-to-NE and -SW normal faults are common in the area and deform the Pliocene-to-Present successions together with mostly NE-SW striking strike-slip and transpressional/transtensional faults.

Based on these structural/stratigraphical constraints we produced a geological model that represents the deterministic input to improve our current knowledge of seismogenic sources in the study area.

Regarding the seismic response at the surface in terms of the maximum expected acceleration, we computed the mean equivalent value of shear wave velocities in the uppermost 30 m of subsoil (VSeq) by using the available geognostic database of the area. The VSeq value allowed to calculate a specific stratigraphic amplification factor at each measurement point. In the study area, amplification varies, on average, from a 1.2 factor within the more rigid substrate to a 2 factor within the less consolidated, Pleistocene-Holocene in age, intra-valley deposits and in the Apennines foothills. This classification will be used as input to the Ground Motion Prediction Equations (GMPEs), as well as the Earthquake Source Model built through the combination of geological information about the sources (width, depth, slip rate, kinematics...) and historical/instrumental seismicity.

How to cite: Gusmeo, T., Carloni, G., Vignaroli, G., Martelli, L., and Viola, G.: Seismic Hazard Assessment along the Northern Apennines front (Italy): Deterministic inputs from the mapping of active and capable faults, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5012, https://doi.org/10.5194/egusphere-egu23-5012, 2023.

16:55–17:05
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EGU23-5098
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On-site presentation
Onise Enukidze, Victor Alania, Tamar Beridze, Paolo Pace, Alexandre Razmadze, Demur Merkviladze, and Tamar Shikhashvili

Collision and subsequent convergence of Arabia and Eurasian plates during the late Alpine time caused extensive intracontinental deformation in the Caucasus region. Inversion of back-arc basins, exhumation and crustal thickening took place in the far-field zone, forming two orogens, and leading to a convergence between the Lesser Caucasus (LC) and Greater Caucasus (GC). Continuous convergence between the LC and GC caused incremental deformation of the Rioni and Kura foreland basins. Recent GPS, earthquakes, and paleoseismic data indicate that the Kura foreland fold-and-thrust belt (KFFTB) is tectonically fairly active (e.g., Sokhadze et al., 2018; Tibaldi et al., 2020; Tsereteli et al., 2016; Stahl et al., 2022).

In this study, we have integrated the post-stack depth-migrated 2D seismic profiles, borehole, and outcrop data to explore the structural geometry and kinematic features of the western KFFTB. Here we show the structural style of deformation of the convergence zone between the frontal part of the LC retro-wedge and the GC pro-wedge based on seismic reflection profiles. The seismic reflection profiles reveal the presence of a triangle zone and south-and north-vergent fault-related fold and south-vergent thrusts.

In combination with surface geology and borehole data, we have analyzed along-strike variations of the south-vergent passive-back thrust and transition from the fault-propagation fold to wedge structure by using 2D seismic profiles in the western KFFTB.

Based on the 2D seismic profiles and field data interpretations as well as our sequential kinematic modeling results, we have established the geometry and structural evolution of the LC-GC convergence zone in the western KFFTB since the Late Miocene.

Acknowledgement: This research was supported by Shota Rustaveli National Science Foundation of Georgia (SRNSFG) [grant # YS-21-612. Geometry and kinematic evolution of frontal part of the Eastern Achara-Trialeti fold-and-thrust belt]

How to cite: Enukidze, O., Alania, V., Beridze, T., Pace, P., Razmadze, A., Merkviladze, D., and Shikhashvili, T.: Structural model of the two orogens convergence zone: A case study from western Kura foreland fold-and-thrust belt, Georgia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5098, https://doi.org/10.5194/egusphere-egu23-5098, 2023.

17:05–17:15
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EGU23-4282
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ECS
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On-site presentation
Martina Pedicini, Fabio Luca Bonali, Alessandro Tibaldi, Noemi Corti, Federico Pasquaré Mariotto, and Kyriaki Drymoni

The Northern Volcanic Zone is a tectonically and volcanically active area, of approximately 220 x 97 km, that accommodates the plate spreading in Northern Iceland. Given its extension, it is clear the need to enhance remote-sensing methodologies that give the possibility to obtain a reliable depiction of the main structures that characterize the area. 

Here we present the study of the Fremrinamar rift, which has a length of 13 km and a width between 8 to 9 km. To cover its entire extension we used a set of  983 historical aerial photos, freely available through the National Land Survey of Iceland. These images were acquired in 3 different years (1983, 1990, 1991), at the same flight elevation (5486 m a.s.l.), and are characterized by 60% of overlap.  Using Agisoft Metashape (v. 1.7.1) we obtain 3 Digital Elevation Models (DEMs) and 3 orthomosaics with a maximum resolution of 2.14 and 0.52 m/pixel respectively. We tested different quality combinations for both photo alignment and dense cloud processing, identifying a medium one as the best compromise between good-quality results (similar resolution levels as the one obtained with high-quality parameters) and relatively short-processing times (4-79 min. to reconstruct orthomosaics, 2-5 min. for DEMs). 

We then outline the geometry of the rift zone through mapping in a GIS environment at a 1:2500 scale. We identified 2528 extension fractures, 1785 normal fault scarps, and 207 eruptive fissures and distinguished between W- and E-dipping normal faults. The recognised structures show an overall strike of N-S to NNE-SSW, with minor values between NE-SW, and length values ranging from 4 to 7000 m. The highest length values are associated with normal faults, while extension fractures are characterized by shorter segments. Both normal faults and extension fractures show the highest length values in association with N-S strikes. E-dipping normal fault scarps show predominant dip-direction towards E-ESE, with minor ENE; W-dipping normal fault scarps dip mostly towards W-WNW, with minor WSW values. The Fremrinamar rift is characterised by a higher frequency of structures, especially eruptive fissures, in its southern and central portions (where volcanic centres are mainly located), while the northern one is defined by a decreased number of structures which also show a rotation in their strike values toward NNW-SSE. These results were finally integrated with field surveys over key areas, allowing us to evaluate and confirm the integrity and consistency of the data collected on the models.

This methodology gave us the possibility to reconstruct the geometry of an entire rift in high detail, without going to the field and with few costs (since the images are freely accessible the only costs derive from the selected software). Moreover, the presence of different sets of aerial photos, taken during different years, provides the opportunity to evaluate the temporal evolution of some key areas of the rift.

How to cite: Pedicini, M., Bonali, F. L., Tibaldi, A., Corti, N., Pasquaré Mariotto, F., and Drymoni, K.: Application of photogrammetry to reconstruct the architecture of the Fremrinamar rift, Northern Volcanic Zone, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4282, https://doi.org/10.5194/egusphere-egu23-4282, 2023.

Posters on site: Wed, 26 Apr, 10:45–12:30 | Hall X2

Chairpersons: Fabio Luca Bonali, Rita De Nardis, Federica Ferrarini
X2.153
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EGU23-1465
Alessandro Tibaldi, Rita De Nardis, Patrizio Torrese, Sofia Bressan, Martina Pedicini, Donato Talone, Fabio Luca Bonali, Noemi Corti, Elena Russo, and Giusy Lavecchia

We present new morphostructural and geophysical data to discuss the recent activity of the Broni-Sarmato structure, an 18 km-long outcropping section of the north-verging Stradella thrust, located 50 km south of Milan, along the pede-Apennine compressional front in the rear of the Emilia Arc. An accurate seismic hazard assessment of this structure is necessary due to the presence in the area of widespread housing settlements, industries, lifeline infrastructures and large towns. Along the fault scarp we quantified the offset of recent river deposits by GPS, DTM and drone surveys; the scarp height values range from 6 to 23 m. Respect to previous works, we also better defined the geometry in plan view of the scarp; it is not continuous along the area, being characterized by several left- and right-stepping segments. We also performed new geoelectrical surveys across the scarp that suggest the presence of a wide zone of shallow deformation along the Broni-Sarmato fault trace. These deformations could correspond to fractures that act as preferential flow path for deep saline waters and facilitate the flow towards the surface. Horizontal interruption and vertical dislocation of a shallow, high resistivity layer also revealed by geoelectrical surveys, suggest that the Broni-Sarmato fault possibly produced shallow deformation along vertical and inclined zones. These data, supported by seismic activity, although quite sparse,  can be interpreted as evidence of late Pleistocene-Holocene tectonic activity of this section of the Stradella thrust.

How to cite: Tibaldi, A., De Nardis, R., Torrese, P., Bressan, S., Pedicini, M., Talone, D., Bonali, F. L., Corti, N., Russo, E., and Lavecchia, G.: Morphostructural and geophysical surveys of the late Pleistocene-Holocene Broni-Sarmato Fault (Emilia Arc, northern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1465, https://doi.org/10.5194/egusphere-egu23-1465, 2023.

X2.154
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EGU23-3849
Active Kinematics of the Greater Caucasus from Seismological and GPS Data: A Review
(withdrawn)
Federico Pasquaré Mariotto, Alessandro Tibaldi, Fabio Luca Bonali, Noemi Corti, Elena Russo, Gulam Babayev, and Nino Tsereteli
X2.155
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EGU23-16336
Giusy Lavecchia, Rita de Nardis, Donato Talone, Sofia Bressan, Martina Pedicini, Fabio Luca Bonali, Noemi Corti, Elena Russo, Patrizio Torrese, and Alessandro Tibaldi

Investigating active tectonics and the structural style of potentially-seismogenic structures at the outer front of active orogenic belts is particularly challenging when the frontal structures are buried and slowly deforming. This is the case of the blind fold-and-thrust belts surrounding the Padanian foreland of Northern Italy and developing across one of the most populated and industrialized Italian territories. In this paper, we focus on the seismogenic role of the Stradella thrust and its possible involvement in the activity of the buried Emilia arc, through a 3D geometric, kinematic, and seismotectonic reconstruction of the overall system. The integrated multi-scale analysis of structural and seismological data, inclusive of new focal mechanisms, highlights two seismological thrust volumes dipping at low-angle southwest-ward, at upper (<12 km) and lower crustal depths (~20-30 km). However, the shallow seismicity only partially illuminates the down-dip prosecution of the Stradella structure. In contrast, the deeper earthquake volume, at the hanging wall of the along-strike southeastward prosecution of the Stradella fault, well highlights the lower crust portion of the Emilia Arc basal thrust.

We interpret the above multi-scale data as evidence of ongoing tectonic activity of the outer fronts of the Emilia arc under a regional NNE-directed compressional stress field, with some minor evidence of involvement of the Stradella thrust along the pede-Apennine front. In our 3D reconstruction, both thrust systems are expressions of a thick-skinned deformation that controls earthquake release at different structural depths.

How to cite: Lavecchia, G., de Nardis, R., Talone, D., Bressan, S., Pedicini, M., Bonali, F. L., Corti, N., Russo, E., Torrese, P., and Tibaldi, A.: Integrated structural-seismological constraints for a 3D multi-depth fault model of the Stradella and  Emilia Arcs (northern Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16336, https://doi.org/10.5194/egusphere-egu23-16336, 2023.

X2.156
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EGU23-680
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ECS
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Fabio Feriozzi, Luigi Improta, Francesco Emanuele Maesano, Pasquale De Gori, and Roberto Basili

The Irpinia region in the Southern Apennines is one of the areas with the highest seismic hazard in Italy, as also testified by several recent and historical earthquakes ranging between Mw 6.6-6.9 (1694, 1732, 1930, 1980). The shallow crust structural setting of this area is characterized by multiple deformational stages, which caused the tectonic stacking of Meso-Cenozoic sedimentary sequences deposited in different paleogeographic domains. The overall structure of the chain still contends between the thin-skinned and thick-skinned models.
We present a 3D geological model of key stratigraphic and tectonic elements based on the analysis of 2D seismic reflection profiles, integrated with well data and surface geology information. We also computed a 3D velocity model of the upper crust (Vp and Vp/Vs) through a local earthquake tomography (LET) to provide inferences on the structure and rock properties of the deep Apulian tectonic stack, especially where this is poorly imaged by seismic reflection imaging. We propose an integrated interpretation of the deep structure based on the analysis of the CROP-04 deep seismic profile and Vp and Vp/Vs patterns.
Our results highlight the presence of a regional thrust separating a shallow domain, characterized by relatively low-angle thrust surfaces (Allochthonous domain), from a deeper domain characterized by high-angle buried thrusts that affect the Apulian carbonate platform. The Plio-Pleistocene Apulian compressional architecture seems to control the rock physical properties in the upper crust and the seismotectonic of the area related to NE-SW regional extension active since the Middle Pleistocene. We observed that background seismicity concentrates in high-V, high-Vp/Vs regions that follow the Apulian structural trends and strictly correlate with the main crustal ramp anticlines. Furthermore, our structural model provides new geological insight regarding the destructive 1980 Irpinia earthquake (Mw=6.9), which ruptured three main fault segments.
From a methodological point of view, the integration of 3D geological model and LET is suitable for future earthquake relocations based on a data-driven velocity model reconstruction that considers the 3D geological complexities.

How to cite: Feriozzi, F., Improta, L., Maesano, F. E., De Gori, P., and Basili, R.: 3D crustal structure of the Irpinia region (Southern Apennines): constraints from the integration of subsurface data and local earthquake tomography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-680, https://doi.org/10.5194/egusphere-egu23-680, 2023.

X2.157
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EGU23-1228
Chung-Ryul Ryoo

In large fault zone, various contractional and extensional structures accommodate horizontal shortening and extension in response to differential plate movements related to the Earth’s rotation. In this study, it was conducted a structural analysis of the Yangsan Fault, developed in the southeast Korea. The fault is about 200 Km long in land and has a general NNE-trend, cutting not only the Cretaceous rocks but also the Quaternary layers. We studied several main fault zones along Yangsan Fault. Here, we discuss some kinematic evidences and characteristics developed in the main fault zones of the Yangsan Fault, Korea. In the core of the Yangsan Fault Zone, fault-bounded sheets or blocks are horizontally rotated, duplexed and folded. From the kinematics of the sheet-bounding faults and intra-sheet minor folds, we suggest some evolutionary models of the Yangsan Fault Zone in which repeated fault-related rotation, dragging and folding are occurred.

How to cite: Ryoo, C.-R.: On the several shearing evidences developed in the Yangsan Fault, Korea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1228, https://doi.org/10.5194/egusphere-egu23-1228, 2023.

X2.158
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EGU23-2420
Victor Alania, Tamar Beridze, Onise Enukidze, Thomas Gusmeo, Demur Merkviladze, Tamar Shikhashvili, and Niko Tevzadze

The Lesser Caucasus (LC) double-wedge orogen accommodates the crustal shortening due to far-field effects of the collision between the Arabian and Eurasian plates. Subsequent convergence of Arabia and Eurasian plates during the late Alpine time caused extensive intracontinental deformation in the LC. Herein we introduce the active deformation structural style of the Georgian part of the LC orogen based on seismic reflection profile, several oil-well, and surface geology data. Seismic reflection data reveals the presence of a Khrami basement thrust sheet, fault-related folds, triangle zone, and duplexes. The rocks involved in the deformation range from Paleozoic basement rocks to Pliocene-Quaternary basaltic lava flows.

Pliocene-Quaternary lava flows are involved in compressional deformation and are related to an out-of-thrust sequence of the Khrami basement thrust sheet. Based on the interpreted seismic reflection profile, the crustal-scale duplex was recognized under the basement thrust sheet which propagates northward along the Early Jurassic shale layers.

The structural architecture and tectonic evolution will be briefly presented and discussed in the new regional balanced and reconstructed cross-section across the axial zone and retro-wedge of the LC and published fission-track data (Gusmeo et al., 2021, 2022), as well as detailed examples of active tectonics, and seismicity (e.g., Tsereteli et al., 2016).

Reference

Gusmeo, T., et al. (2022). Tectono-thermal evolution of central Transcaucasia: Thermal modelling, seismic interpretation, and low-temperature thermochronology of the eastern Adjara-Trialeti and western Kura sedimentary basins (Georgia). J. As. Earth Sci. 238, 105355.

Gusmeo, T., et al. (2021). Structural inversion of back-arc basins-The Neogene Adjara-Trialeti fold-and-thrust belt (SW Georgia) as a far-field effect of the Arabia-Eurasia collision. Tectonophysics 803, 228702.

Tsereteli, N. et al. (2016). Active tectonics of central-western Caucasus, Georgia. Tectonophysics 691, 328-344.

 

 

 

How to cite: Alania, V., Beridze, T., Enukidze, O., Gusmeo, T., Merkviladze, D., Shikhashvili, T., and Tevzadze, N.: Exploration and recognition of active basement thrust sheet and crustal-scale duplex in the central Lesser Caucasus orogen using seismic reflection profile, Georgia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2420, https://doi.org/10.5194/egusphere-egu23-2420, 2023.

X2.159
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EGU23-5530
Roberta Maffucci, Marco Caciagli, Thomas Braun, Mauro Buttinelli, Francesca Cinti, Stefania Danesi, Paolo Marco De Martini, Maddalena Errico, Daniela Famiani, Valerio Materni, Daniela Pantosti, Stefano Pucci, Simone Salimbeni, and Vincenzo Sapia

The Val d’Agri (VA) oilfield in the Lucanian Apennines (southern Italy), represents the largest onshore in Europe. Since the 1990's, hydrocarbons are produced from a fractured carbonate reservoir with an average extraction rate of 7*104 barrels/day of oil and 3*106 Smc/day of gas. Part of the wastewater has been re-injected since 2006 into a marginal portion of the reservoir by a high-rate well (Costa Molina 2, CM2). Charged by the Italian oil and gas safety authority, the National Institute of Geophysics and Volcanology (INGV) monitors the VA industrial hydrocarbon operations through the research activity of a dedicated working group (CMS, Centro di Monitoraggio del Sottosuolo) and according to the governmental monitoring guidelines. The CMS operates the real-time acquisition and offline analyses of seismic data recorded at 56 seismic stations associated with public and private local seismic networks. The principal aim of the CMS is to investigate the risk associated with industrial activities that can induce or trigger seismic events by producing stress changes within the upper crustal volume. Previous works have highlighted a spatio-temporal relationship between micro-seismicity (ML ≤ 2.2) and wastewater injection, delineating a NE-dipping back-thrust near the CM2. Part of the microseismicity recorded in the southwestern portion of the VA has also been associated with the water level changes of the Pertusillo lake. One of the main challenges is to define an accurate structural setting of the VA to understand the potential of earthquakes in the area and investigate the presence of active faults. The VA consists of a Quaternary extensional tectonic basin and it is one of the areas of highest seismic hazard in Italy (Basilicata, 1857, M7 earthquake). The basin is bounded by two parallel and oppositely dipping normal fault systems: the Monti della Maddalena Fault System (MMFS) on its western side and the Eastern Agri Fault System (EAFS) on the eastern one. The characterization of the ongoing tectonic activity of the MMFS and EAFS, and their hierarchical relationship is still generating debate among the scientific community. We adopt a multidisciplinary approach based on detailed geological-structural, geophysical and seismic analyses, and electrical resistivity tomography, aimed at reconstructing the subsurface geology of the area and recognizing and characterizing the active and capable faults, and the associated potential for local seismic hazard. We present and discuss the results of this work, focusing on the relative location of seismic events that occurred between March and June 2022. The outcomes allow inferring interesting geologic constraints, highlighting the relationships between the distribution of local seismicity and the structural setting of the area in the uppermost crust (depth < 6 km).

How to cite: Maffucci, R., Caciagli, M., Braun, T., Buttinelli, M., Cinti, F., Danesi, S., De Martini, P. M., Errico, M., Famiani, D., Materni, V., Pantosti, D., Pucci, S., Salimbeni, S., and Sapia, V.: A multidisciplinary approach gives new insights into the shallow structural setting of the Val d’Agri oilfield (Basilicata, southern Apennines, Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5530, https://doi.org/10.5194/egusphere-egu23-5530, 2023.

X2.160
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EGU23-5836
Mario Anselmi, Mauro Buttinelli, and Francesco Emanuele Maesano

The central-northern Apennines represent a high seismic hazard area characterized in the last decades by multiple seismic sequences (1997 Umbria-Marche, 2009 L’Aquila, 2016-2017 Amatrice-Visso-Norcia) related to the post-orogenic extension.

After the recent Amatrice-Visso-Norcia seismic sequence, the large availability of subsurface geological data and the dense seismological and geodetic networks allowed for better imaging of the shallow crust structural setting and the relationship with the occurred seismic sequences. 

Recent advances in those areas focused on comprehending the role of inherited structures (namely the large thrust faults related to the building up of the Apennines orogen) in compartmentalizing both horizontally and vertically the seismic sequences. Also, they suggested that major compressive structures may play an active role in seismogenesis through their kinematic inversion into the current extensional regime.

Such behavior was already debated after the 1997 Umbria-Marche seismic sequence, characterized by six main shocks with 5 < Mw < 6. All the large shocks originated on adjacent and parallel NW trending normal faults whose extent varies between 5 and 10 km at a hypocentral depth of 5 –6 km.

Our work presents a review of the data available for the 1997 Umbria-Marche seismic sequence. Using a combined dataset of seismic reflection profiles and deep boreholes, as well as detailed data from geological surveys, we present a new 3D geological and velocity model of the area. We also re-analyzed the passive seismic data recorded by both the temporary and permanent seismic networks. As a result, we computed a new 1-D relocation catalog based on the 3-D geological and geophysical imaging of the shallow portion of the crust in the target area.

The comparison of the geological model and the relocated seismicity shows a substantially vertical and horizontal compartmentation of the shallow crust due to the action of the thrusts. The seismicity distribution is strictly conditioned by the organization of crustal volumes separated by major thrusts and is concentrated within the same structural and stratigraphic levels, both on normal faults and pre-existing thrusts, possibly reactivated during the sequences.

The integrated analysis of seismological and geological subsurface data shed light on the open questions related to the interference between Quaternary normal faults and Tertiary thrusts and on the geometry of the causative faults of the 1997 seismic sequence. In addition, they help to define a more robust seismotectonic behavior and to assess the seismic hazard of those areas.

How to cite: Anselmi, M., Buttinelli, M., and Maesano, F. E.: Reviewing the 1997 Umbria-Marche seismic sequence: a fresh look from the integration of new seismological and subsurface data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5836, https://doi.org/10.5194/egusphere-egu23-5836, 2023.

X2.161
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EGU23-7386
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ECS
Selina Bonini, Giulio Viola, Giulia Tartaglia, Stefano Rodani, Massimo Comedini, and Gianluca Vignaroli

The planning phase of a railway line has to carefully consider the potential impact of several geohazards, including the seismic hazard associated with active faults capable to cause significant offset (dm to m) of the ground surface. Italian authorities are investing large resources in the construction of new railway lines in Italy, which is a territory that stands out as high-risk due to the presence of active faults, including those accommodating extension within the Apennines belt. Numerous seismogenic sources have been recognized therein by the geophysical and geological community over the last few years. Their identification and characterization represent the foundation of the seismic hazard map of Italy, which is regularly used to assess the seismic hazard of any given area of the country. Active and Capable Faults (ACFs) may contribute to increasing the seismic hazard of an area, though, and may interfere with railway lines. Following the Italian guidelines for the seismic microzonation procedures, an ACF is capable of producing, within a time interval of concern the society, macro-earthquakes and deformation/displacement at or near the ground surface and should have done so during the last 40 ka (upper Late Pleistocene – Holocene).

We propose a multidisciplinary workflow for improving and standardizing the use of the existing Italian geohazard databases. As the area covered by a railway line may extend for tens or hundreds of kilometers, it is crucial to define systematic criteria that make it possible for the intersected ACFs to be sorted into classes of varying hazard, each requiring different approaches and study levels. The seismicity associated with the ACF’s, the fault geometric and kinematic compatibility with the current regional tectonic setting and stress field, the involvement of < 40 ka old rocks and sediments, the proximity to the ground surface of the historical hypocenters, the geometrical relationships between the ACF’s and the orientation of the railway line are just a few of the aspects to be considered by such an approach.

We aim to define and constrain all the input parameters necessary to perform site-specific fault displacement and seismic hazard analysis, since the currently available Italian seismic hazard map is still too coarse in its resolution (with PGA values every 10 km). Our new approach will allow us to include the detection of near-field effects (e.g., the increasing of the vertical component due to seismic acceleration, forward-directivity phenomena, co-seismic rotation) if the trailway line runs within a 15 km zone from the main fault plane.

Knowing ACFs behavior will make it possible, during the planning, to choose the best railroad options, in order to reduce the vulnerability of the planned infrastructure.

How to cite: Bonini, S., Viola, G., Tartaglia, G., Rodani, S., Comedini, M., and Vignaroli, G.: A multidisciplinary workflow to assess seismic hazard by active and capable faults when planning railway lines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7386, https://doi.org/10.5194/egusphere-egu23-7386, 2023.

X2.162
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EGU23-8823
Rita De Nardis, Federico Pietrolungo, Claudia Pandolfi, Simone Bello, Donato Talone, and Giusy Lavecchia

A recent paper showed the evidence of two well-distinct low-angle and SW-dipping individual reverse shear zones of the Italian Outer Thrust System in Central Italy (de Nardis et al., 2022). One, referred to as Thrust 1 (T1),  corresponds to the down-dip prosecution of the Adriatic Basal Thrust with its major splay; the other, referred to as Thrust 2 (T2), corresponds to a hidden independent structure, illuminated at a depth between 25 and 60 km, for an along-strike extent of ~150 km. Combining geological information with high-quality hypocentral locations and focal mechanisms, a detailed 3D geometric and kinematic fault model of the compressional system, active at upper crust to upper mantle depths, is built. In addition, evidence of coexisting deformation volumes undergoing a co-axial stress field at different lithospheric depths is reported.

November 9, 2022, seismic sequence principally activated T1  at upper crustal depth with pure compressional kinematics. Two significant events (Mw 5.5 and 5.2) enucleated within 1 minute, at depths of about 5 km and 7.5 km, respectively, and ~8 km away in map view. The sequence also released a cluster of microseismic events at mid-crust depths along the up-dip prolongation of the T2, thus opening the questions on the possible stress interaction during an ongoing seismic sequence.

In this paper, we further constrain and detail the T1 upper-crust geometry and investigate the likelihood of static stress interactions between T1 and T2. Considering that in historical and instrumental times, T1 has been responsible for earthquakes with Mw 6-6.5  at upper- and lower-crust depths, we create possible Coulomb stress transfer scenarios using the Coulomb code 3.4 (Lin and Stein, 2004; Toda et al., 2005).

We build three seismic sources (C1, C2, C3) assuming an Mw 6.2 thrust event enucleated on T1 at variable depths (8 km, 15 km, 22 km). The section-view and map-view distribution of the positive lobes of the modeled Coulomb stress scenarios show that a hypothetical T1 earthquake of the above magnitude may well determine, although marginally, stress increase along the underlying T2 segment.

 

 

 

How to cite: De Nardis, R., Pietrolungo, F., Pandolfi, C., Bello, S., Talone, D., and Lavecchia, G.: Geometry and stress interaction of a complex lithospheric-scale thrust system as unveiled by background seismicity and moderate seismic sequences - the Marche-Adriatic case (eastern Central Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8823, https://doi.org/10.5194/egusphere-egu23-8823, 2023.

X2.163
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EGU23-8834
Geoelectric characterization of Quaternary basin bounded by active fault: TEst Site IRpinia fAult project
(withdrawn)
Daniela Tarallo, Pier Paolo Gennaro Bruno, Giuseppe Cavuoto, Giuseppe Ferrara, Nicola Pelosi, Michele Punzo, and Vincenzo Di Fiore
X2.164
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EGU23-10900
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ECS
Dabeen Heo, Tae-Seob Kang, Jin-Han Ree, Kwang-Hee Kim, Junkee Rhie, and YoungHee Kim

The southeastern part of the Korean Peninsula is known to have high seismic activity and many Quaternary faults. Nonetheless, there have been uncertainties in estimating seismic hazards due to insufficient information on potential seismic sources. We investigated the geometrical characteristics of causative faults related to clustered earthquakes in the southeastern Korean Peninsula by detecting microearthquakes and determining their source parameters. We used the seismic data recorded at the Gyeongju hi-density broadband seismic network, the temporary seismic networks operated to monitor the aftershocks of two moderate earthquakes (the 2016 ML 5.8 Gyeongju and 2017 ML 5.4 Pohang earthquakes), and the national seismic network of South Korea. An earthquake catalog for the southeastern Korean Peninsula was built using automatic earthquake detection methods based on measurements of energy ratio. We identified the five clustered earthquake regions via the microearthquake distribution: the 2016 Gyeongju earthquake region (GJ), the 2017 Pohang earthquake region (PH), the eastern part of the Ulsan Fault (UF), eastern offshore Gyeongju (EG), and the western part along the Miryang Fault (MF). We determined the relative location and focal mechanisms of the earthquakes occurring in those regions using the double-difference location method and the P-wave first motion polarity method, respectively. Finally, the geometry of the earthquake causative faults was inferred using the spatial distribution of the relative locations and the focal mechanisms. It was found that there are at least two NNE-SSW trending fault segments and multiple NE-SW trending fault segments in the GJ and PH, respectively. In the case of MF, UF, and EG, it is difficult to relate directly to the surface faults, but the strikes of the causative faults, which are confirmed by the spatial distribution of earthquakes, are similar to those of the surface faults.

How to cite: Heo, D., Kang, T.-S., Ree, J.-H., Kim, K.-H., Rhie, J., and Kim, Y.: The geometrical characteristics of causative faults related to clustered earthquakes in the southeastern Korean Peninsula, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10900, https://doi.org/10.5194/egusphere-egu23-10900, 2023.

X2.165
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EGU23-13060
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ECS
Sofia Bressan, Fabio Luca Bonali, Noemi Corti, Federico Pasquaré Mariotto, Emanuela De Beni, Massimo Cantarero, Marco Neri, Elena Russo, Kyriaki Drymoni, and Alessandro Tibaldi

Mt Etna, located on the east coast of Sicily, Italy, is a basaltic stratovolcano with a volcanotectonic evolution of 500 ka, characterized by a wide horse-shoe-shaped depression on its eastern flank, called Valle del Bove. The study area is located near the northern escarpment of this depression, where it is possible to recognize the 1971 eruptive fissure system, generated by the lateral propagation of a feeder dike. The purpose of this research is to thoroughly examine the area affected by dike-induced surface deformation, which is marked by a textbook example of a graben structure produced by dike propagation. Due to the presence of meters-thick, recent pyroclastic deposits covering the study area and the difficult logistics, the main outcrops are inaccessible for classical field data collection. To overcome this limitation, we used the following methodology based on the analysis of photogrammetry-derived models.

We first designed a structural map related to the development of the 1971 dike-induced structures, using two sets of historical aerial photos characterized by a 2400 DPI resolution. Particularly, the 20 selected images, equally divided between 1954 and 1983, have been processed using the software Agisoft Metashape to produce two referenced orthomosaics with a resolution of 29 and 19.5 cm/pixel, respectively. By comparing the obtained orthomosaics, we identified and mapped all the normal faults associated with the 1971 dike intrusion. This structural map has been used to organize the subsequent drone surveys, performed by a DJI Phantom 4 Pro equipped with RTK high-precision technology, which allowed us to collect 656 pictures with an overlap and a side lap of 85% and 80% respectively. Afterward, we processed the drone-collected photos by using Structure-from-Motion photogrammetry techniques, so as to obtain a Digital Surface Model (DSM) and a 3D Tiled Model, with a resolution of 11 and 5.48 cm/pixel, respectively. Such models have been used to analyze in detail the graben faults, especially the ones along the Valle del Bove steep wall.

The analysis of photogrammetry-derived models over different time windows enabled us to individuate 14 lineaments within the study area, 2 eruptive fissures with a NE-SW strike, and 13 fault scarps associated with the dip-slip faults of the graben. Finally, thanks to the 3D Tiled Model obtained from drone-captured pictures, we were able to quantify the dip direction and dip angles of the graben faults, their vertical offsets, and the graben width related to the elevation.

How to cite: Bressan, S., Bonali, F. L., Corti, N., Pasquaré Mariotto, F., De Beni, E., Cantarero, M., Neri, M., Russo, E., Drymoni, K., and Tibaldi, A.: Application of photogrammetric approaches to studying the 1971 dike-induced surface structures on Mt Etna, Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13060, https://doi.org/10.5194/egusphere-egu23-13060, 2023.

X2.166
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EGU23-13989
David C. Tanner and Sonja H. Wadas

Neotectonic movements can cause severe geohazards and thus require examination for seismic hazard assessment, and utilisation of the subsurface for e.g. nuclear-waste disposal sites and geothermal exploitation. In northern Germany, very little is known about these processes and the associated structures, despite proven neotectonic activity, because many faults are hidden beneath sediments.

The Osning Lineament (OL) in North Rhine-Westphalia is a recently-active fault zones. Three major earthquakes and seven other macro-seismic earthquakes occurred at the OL during the last 400 years. The strongest earthquakes occurred in 1612, 1767, and 1770, with an estimated intensity of VI to VII on the MSK scale. The OL is a unique fault system compared to other faults in northern Germany. The faults of the OL reach the basement, whereas in the north of the Lower Saxony Basin, most faults are decoupled from the basement by salt. Furthermore, the OL dips to the northeast and therefore the vector of the fault plane points towards the former iceload from Scandinavia, enabling glacial isostatic adjustment to occur on the faults. Additionally, the OL has had a history of multiphase reactivation in the geological past.

To better understand the neotectonic evolution of the OL on a regional scale, we carried out a 2D retrodeformation using already existing large-scale cross sections along the lineament, which are based on surface geological maps and sparse drilling information. Balancing of these cross-sections verifies whether the fault geometry and kinematics derived from surface data are justified or need to be revised. Retrodeformation is also used to suggest the path of the fault(s) at greater (seismogenic) depth. Later on, retrodeformation will also be performed including new, highly-detailed seismic profiles and a joint interpretation will be carried out to improve the understanding of the past evolution of the Osning Lineament.

How to cite: Tanner, D. C. and Wadas, S. H.: Reconstruction of the evolution of the Osning Lineament in northern Germany using 2-D retrodeformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13989, https://doi.org/10.5194/egusphere-egu23-13989, 2023.

X2.167
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EGU23-15747
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ECS
Salvatore Giuffrida, Fabio Brighenti, Francesco Carnemolla, Salvatore Gambino, Giorgio De Guidi, Giovanni Barreca, Flavio Cannavò, Luciano Scarfì, and Carmelo Monaco

Since the Late Pliocene - Early Pleistocene, the Calabrian Arc (southern Italy) is affected by extensional and transcurrent tectonic superimposed on the previous collisional context. Various seismogenic sources have been proposed over time to explain such a complex structural framework, but the topic is still matter of debate. 

In this work we apply a multidisciplinary approach, concerning Geology, Geomorphology, Seismology and Geodesy, to develop a reliable 3D model of the Cittanova and Serre faults. These faults are considered the causative faults for the 1783 seismic sequence (M 6.5-7) as proposed by Jacques et alii (2001). We used CROP data to investigate the crustal architecture of the area and to constrain the geometry at depth of the major structures. through two schematic geological sections orthogonal to these two faults. The shallow geometric patterns of the Cittanova and Serre faults, were verified trough geological, geomorphological and structural field data. Earthquakes hypocentres were analysed and relocated in order to recognize possible cluster alignments useful to constrain the faults geometry at depth. The high-density level of crustal seismicity attests that this domain is seismically active, between 0 km and 23 km and it concentrates along the main faults. To compute the strain and velocity field of the area (time span of the last 20 years) we measured the IGM95  (Instituto Geografico Militare) benchmarks and processed several GNSS permanent stations belonging to the RING Network (http://ring.gm.ingv.it) and TopNETlive Italy Network (https://rtk.topnetlive.com/italy/networks/topnet-live-italy) using GipsyX 1.5 Strain inversion (performed through grid_strain 2D software) allowed us to define a predominant WNW-ESE extensional deformation, in agreement with previous studies). Combining all previous data, we built for the first time a reliable 3D model of the Cittanova and Serre fault planes, that are consistent with:  i) fault magnitude/size empirical relations (Magnitude vs rupture Area, Magnitude vs fault length; ii) geological and geomorphological field observation (fault attitude and kinematic), iii) seismological and geodetic data. Results show that our model is compatible with the seismogenic sources of the 1783 seismic sequence.

How to cite: Giuffrida, S., Brighenti, F., Carnemolla, F., Gambino, S., De Guidi, G., Barreca, G., Cannavò, F., Scarfì, L., and Monaco, C.: A multidisciplinary approach for 3D modelling of the Serre and Cittanova Faults, the responsible of the 1783 seismic sequence in Southern Calabria, Italy., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15747, https://doi.org/10.5194/egusphere-egu23-15747, 2023.

X2.168
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EGU23-3365
Maxime Godano, Laeticia Jacquemond, Frederic Cappa, and Christophe Larroque

The geodynamic complexity of the Southwestern Alps (France, Italy) comes from its strong tectonic inheritage due to the European-African plates convergence. The motion being currently mainly accommodated along the Maghrebides, this region of the Alps only registers small to moderate seismicity linked to low-deformation rates (convergence rates of 0.3-0.9 mm/yr). Hence until now, the geometry of the active faults in the Southwestern Alps remains unclear and imprecise. Yet, a better knowledge of these faults is a prerequisite for the establishment of a regional deformation model and the improvement of the seismic hazard assessment.
Taking advantages of a nine-year seismicity catalog (7659 earthquakes of local magnitudes ranging between -0.73 and 5.03), recorded by the French and Italian permanent national networks presenting no major evolution since 2014, a high-resolution relocation is currently ongoing. The purposes are to (1) understand how the seismic events are linked to the mapped faults, (2) highlight unknown deep seismogenic structures and (3) finally improve the overall picture of the 3D geometry of active faults in the Southwestern Alps.
We present here the preliminary analysis of the relocated catalog. The seismicity is relocated using the double-difference relative method HYPODD with both cross-correlation and catalog times. As a result, the relocation is achieved for 5828 earthquakes. The uncertainties are reduced to less than 120m in horizontal and less than 600m in vertical compared to the initial average uncertainties of less than 2 kilometers for both values, referred by previous papers.
We assess the reliability of our results by comparing, at regional scale, our new relocations with those obtained by similar methods in Ubaye region. We illustrate how the double-difference relocation refines active zones imaging at multiple scales, particularly in the swarms. In Isola region located around 60 kilometers from Nice, a swarm, active since summer 2021, initially detected by the national network as a 3-kilometerlong/1-kilometer-large shape, has been precised into a 1-kilometer-long/100-meterlarge spatial activity. This relocation improvement enabled us to detect progressive activation of fault segments. On larger scale, relation between faults that may play a key role in the present-day general dynamics of the Alpine chain and deep seismogenic structures is clarified. It is the case for the High-Durance valley (France), where the precise geometry at depth of the Crustal penninic Front and High-Durance fault is determined.

How to cite: Godano, M., Jacquemond, L., Cappa, F., and Larroque, C.: New high-resolution relocation of the seismicity in the Southwestern Alps (France, Italy) to improve active faults imaging: Preliminary results, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3365, https://doi.org/10.5194/egusphere-egu23-3365, 2023.

X2.169
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EGU23-6140
Fabio Luca Bonali, Alessandro Tibaldi, Elena Russo, Victor Alania, Aleksandre Chabukiani, Onise Enukidze, and Nino Tsereteli

In the present work we showcase a multidisciplinary study aimed at defining the ongoing deformation processes due to fault propagation and folding at the Tsaishi fold, western Caucasus (Georgia).

Our approach consists in the integration of geomorphological observations, field geological-structural data and seismic reflection sections, allowing us to reconstruct a 3D model of this active fold, from depth to surface.

The Tsaishi fold is an anticline located at the southwestern tip of the Rioni Basin uplifted area, at the foothill of the Greater Caucasus. The folding process that has been recognized started at the beginning of the Middle Miocene, although preliminary data suggest the possibility of an initial local uplift in the Oligocene. Considering field observations, we suggest that the folding process continues nowadays, giving rise to a south-verging anticline, as shown by upwarped late Quaternary river deposits.

Integrating seismic reflection sections and field observations, we show that the fold backlimb is affected by three main back-thrusts, whereas, based on seismic sections, at the foot of the forelimb a main north-dipping thrust is very close to the surface. Where the thrust reaches the surface, we recognized the presence of a 13-km-long fault scarp (or fold scarp), where historical seismological data locate the epicenter of the strongest earthquake of the area, with Ms 6.0, the so-called Tsaishi earthquake of 1614 CE.

How to cite: Bonali, F. L., Tibaldi, A., Russo, E., Alania, V., Chabukiani, A., Enukidze, O., and Tsereteli, N.: Data from depth to surface to define the 3D anatomy of an active fault-propagation fold: a key example from the western Caucasus (Georgia), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6140, https://doi.org/10.5194/egusphere-egu23-6140, 2023.