The Rioni foreland fold-and-thrust belt is part of the Greater Caucasus pro-wedge and is one of the most important examples of the collision-driven far-field deformation of the Arabia-Eurasia convergence zone. Here we show the deformation structural style of the Rioni foreland fold-and-thrust belt based on seismic reflection profiles and regional balanced cross-section. The main style of deformation within the Rioni foreland fold-and-thrust belt is represented by a set of fault-propagation folds, duplexes, and triangle zone. The regional balanced cross-section shows that fault-propagation folds above the upper detachment level can develop by piggyback and break-back thrust sequences. Formation of fault-bend fold duplex structures above the lower detachment is related to piggyback thrust sequences. A balanced section restoration of compressional structures across the Rioni foreland fold-and-thrust belt provides a minimum estimate of shortening of −40%, equivalent −42.78 km. The synclines within the Rioni foreland fold-and-thrust belt are filled by the Middle Miocene-Pleistocene shallow marine and continental syn-tectonic sediments, forming a series of typical thrust-top basins. Fault-propagation folds and duplex structures formed the main structure of the thrust-top basin. The evolution of the thrust-top basins was mainly controlled by the kinematics of thrust sequences. Using end-member modes of thrust sequences, the thrust-top basins are divided into: 1) Type I-piggyback basin, 2) Type II-break-back basin, and 3) Type III—formation of thrust-top basin characterized by bi-vergent geometry and related to combined, piggyback and piggyback back thrust sequences.

2D seismic reflection profiles revealed the presence of a triangle zone at the frontal part of the western Kura foreland fold-and-thrust belt of the pro-wedge of the Greater Caucasus. To understand the triangle zone geometry, seismic interpretations should be substantiated by forward kinematic modeling, supported by analog experiments. This study presents a new structural model for the region by integrating field observations, well data, and seismic reflection data. East-West directed along-strike structural variation of the frontal thrust is observed on the interpreted seismic profiles which affected the fold geometry. The Bitsmendi breakthrough fault-propagation fold gradually transits into a wedge structure in the W-E direction and is represented by the triangle zone. The seismic profiles interpretation results completely match with analog models of similar triangle zones. The analysis of the experimental results helps us to further understand the kinematic evolution of natural systems and improve seismic interpretation. The triangle zone developed in the western part of the Bitsmendi breakthrough fault-propagation fold is related to double fault-bend fold structural wedges and is characterized by the presence of passive, and active wedges, and passive-backthrust and passive-forethrust.

Our understanding of foreland basin subsurface structures relies heavily on seismic reflection data. The seismic profile across the eastern Rioni foreland basin in western Georgia is critical for characterizing its deformation structural style. We applied fault-related folding and thrust wedge theories to interpret the seismic profile and construction structural cross-section, which reveals that compressional structures are controlled by multiple detachment levels. Both thin-skinned and thick-skinned structures are identified. The seismic profile and structural cross-section reveal the presence of normal faults, reverse faults, thrust faults, duplexes, triangle zone, and crustal-scale duplexes. The deep-level detachment within the basement is responsible for the development of the crustal-scale duplexes. These structures appear to have formed through the reactivation of pre-existing normal faults during compressive deformation. Based on our interpretation, the imaged duplex system likely represents the western subsurface continuation of the Dzirula Massif.

The Greater Caucasus orogen is a typical active double wedge orogen that accommodates the crustal shortening due to far-field effects of the collision between the Arabian and Eurasian plates. Our study area is a central part of the Greater Caucasus pro-wedge and represented by the Dzirula-Imereti Uplift zone and epicentral area of Racha 1991 (MW=7) and 2009 (MW=6) earthquakes - Southern Slope of Greater Caucasus. Here we present a new structural model based on interpreted seismic profiles and regional balanced cross-sections. Seismic reflection data reveals the presence of a basement structural wedge, fault-related folds, triangle zones, and active- and passive-roof duplexes. The most important observation from our study is that the Dzirula massif is a basement wedge and forms a triangle zone. The Dzirula structure is defined by mid-crustal detachment and a roof thrust, constituting a tectonic wedge with a passive back thrust. The regional balanced cross-sections show that the Racha earthquakes are related to crustal-scale duplexes.Acknowledgments. This work was funded by Shota Rustaveli National Science Foundation (SRNSF) (grant# FR-21-26377).

We have presented a new structural model of the Mtskheta 1275 (Mw=6.5) historical earthquake epicentral area. The Mtskheta historical earthquake is located in the frontal part of the Lesser Caucasus orogen pro-wedge (Alania, V., et al., 2023). The frontal part of the Lesser Caucasus orogen is characterized by moderate seismic activity (e.g., Tsereteli et al., 2016). From the determination of the deep structure of the Mtskheta 1275 (Mw=6.5) historical earthquake epicentral area, we use seismic reflection profiles. Seismic reflection profiles show north-vergent duplexes, and structural wedge at the triangle zone beneath the thrust front monocline and is represented by Cretaceous-Neogene strata. In the southern part of the Kura foreland basin, the Oligocene-Lower Miocene strata have been deformed and uplifted by passive-back thrusting at the triangle zone. Based on the new structural model, it has been suggested that the Mtskheta 1275 (Mw=6.5) historical earthquake was related to structural wedge. The results of our subsurface interpretations have important implications for how this fold-and-thrust belt formed, in addition to the effect of structural style on active tectonics in the retro-wedge of the Lesser Caucasus orogen.Acknowledgments. This work was funded by Shota Rustaveli National Science Foundation (SRNSF) (grant# FR-23-8896).

The Greater Caucasus is a typical active double wedge orogen that accommodates the crustal shortening due to far-field effects of the collision between the Arabian and Eurasian plates. Our study area is the western part of the Greater Caucasus pro-wedge, represented by the central and northern parts of the Rioni Foreland basin and the southern slope of the Greater Caucasus. Here, we present a new structural model based on interpreted seismic profiles, regional structural cross-sections, and earthquake focal mechanisms. From SSW to NNE, serial structural cross-sections reveal: (1) basement-involved thrust faults and thick-skinned fault-bend folds, and (2) thin-skinned structures expressed as duplexes and imbricate fault-propagation folds. The dominant compressional structural styles are controlled by multiple detachment horizons.According to the presented serial structural cross-sections, the Enguri HPP dam is located on top of the triangle zone. Major basement-involved thrusts produce first-order thick-skinned fault-bend folds, which move southward, creating second-order fault-propagation folds and duplexes in the sedimentary cover. Preexisting, basement-involved extensional faults inverted during compressive deformation produced basement-cored uplifts that transferred thick-skinned shortening southward onto the thin-skinned structures detached above the basement.The correlation of earthquake hypocenters and focal mechanisms with faults interpreted from 3D structural models enables the identification of active structures. Five potentially active thrust faults are recognized within the study area. Four of these structures are south-vergent thrusts, whereas one corresponds to an out-of-sequence thrust.Acknowledgments. This work was funded by Shota Rustaveli National Science Foundation (SRNSF) (grant# FR-23-8896).