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.

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.

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.

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.

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, M_W 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.

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.

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.

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.

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.

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.

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.

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 (V_Seq) by using the available geognostic database of the area. The V_Seq 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.

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.

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.