TS3.3 | Studying active faults from the near-surface to seismogenic depth: an open challenge in seismotectonics
Studying active faults from the near-surface to seismogenic depth: an open challenge in seismotectonics
Co-organized by SM4
Convener: Federica Ferrarini | Co-conveners: Fabio Luca Bonali, Vanja Kastelic, Rita De Nardis, Victor Alania
| Tue, 16 Apr, 08:30–12:30 (CEST)
Room K1
Posters on site
| Attendance Tue, 16 Apr, 16:15–18:00 (CEST) | Display Tue, 16 Apr, 14:00–18:00
Hall X2
Posters virtual
| Attendance Tue, 16 Apr, 14:00–15:45 (CEST) | Display Tue, 16 Apr, 08:30–18:00
vHall X2
Orals |
Tue, 08:30
Tue, 16:15
Tue, 14:00
Even in a recent timeframe, earthquake occurrences like the 6 February 2023, Mw 7.8 and 7.7 Kahramanmaraş (Turkey) and the 8 September 2023, Mw 6.8 (Atlas Mountains, Morocco), put into the spotlight the high seismogenic potential of the Mediterranean regions and, more broadly, delineate a clear reminder for the need to individualise and parametrise the sources of future seismic events.
A key issue for seismic hazard assessment pertains to the identification of active faults as well as the reconstruction, to the best possible extent, of their geometry, kinematics and deformation rates. Such a task can often be challenging, either due to the possible paucity of unambiguous evidence, or quantitative data, both at the near-surface and at seismogenic depths.
Integrating different methodologies, both innovative in their technologies and complementary in their prospecting at different resolution scales, depth- and dimensions (3D to 4D), has become the necessary approach to apply in active fault studies. In this perspective, the multidisciplinary characteristic of seismotectonics integrating structural-geologic, morphologic, seismologic, geophysical, remote-sensing, geodetic data and numerical/analogue modelling methods can help to individualise evidence of active tectonics.
This session is aimed at gathering studies focused on the following topics: i) field-based geological and structural surveys of active faults, including in 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 3D seismotectonic models; v) numerical and analogue modelling. In the above framework, we hope to spark major scientific interest and debate on how to advance our understanding of active faulting as well as producing robust seismotectonic models.

Orals: Tue, 16 Apr | Room K1

Chairpersons: Federica Ferrarini, Fabio Luca Bonali, Vanja Kastelic
On-site presentation
Jyoti Tiwari, Surendra S. Bhakuni, Pradeep Goswami, and Anil Tiwari

Understanding the geodynamics and seismotectonic characteristics of a region requires an integrated approach involving the analysis of structures, active deformations, seismicity, and tectonic stress conditions. Analysing the links between ongoing seismic activities and the development of the landscape provides a deeper understanding of the dynamic interplay between tectonic forces and geological formations. This study focuses on the Kullu-Larji-Rampur (KLR) window in the NW Himalaya, situated just south of the Main Central Thrust (MCT), where seismicity is notably frequent. The primary objective is to comprehensively analyse parameters in this region, located in Himachal Pradesh, India. Extensive fieldwork involved scaling and mapping active deformation and geomorphological features along major transverse routes of the Sutlej and its tributaries in Himachal Pradesh. Structural data collected encompass measurements of foliation/schistosity, lineations, bedding planes, fold hinge lines, limb of folds, axial planes, shear zones/planes, kinematic indicators, and more. Results from structural data, remote sensing data and field investigations indicate active footwall duplexing or faults along bounding surfaces of tectonic horses, including younger thrust splays within the footwall block of the Jutogh Thrust (JT) or within the KLR window. Additionally, the study assesses localized stress behaviour and seismicity parameters (b-value and source mechanisms) in this seismically active region using background seismicity. Notably, significant depth variations and anomalies in stress conditions are observed, interpreted as a brittle-semi-brittle and stress transition zone. The south-eastern section of the KLR window is identified as a high-stress accumulation zone. We have established a correlation between present-day seismicity and the evolving landscape of the region. The study concludes that continuous interseismic and co-seismic deformation, along with the active footwall duplex in the Lesser Himalayan Sequence (LHS), play pivotal roles in shaping the growth of the KLR window and driving active in-sequence thrusting along the younger splays of the Jutogh Thrust.

How to cite: Tiwari, J., Bhakuni, S. S., Goswami, P., and Tiwari, A.: Dynamic Interplay of Tectonic Forces and Seismic Activities: A Comprehensive Analysis of the Kullu-Larji-Rampur Window in the NW Himalaya, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-293, https://doi.org/10.5194/egusphere-egu24-293, 2024.

On-site presentation
Martine Simoes, Christelle Guilbaud, Jérôme Van der Woerd, Guillaume Baby, Laurie Barrier, Haibing Li, and Jiawei Pan

The Tibetan Plateau stands as a prominent topographic feature at the Earth’s surface, characterized by intense seismic activity, in particular along the mountain ranges that form its bounding edges. To the northwest, the Western Kunlun Range has received increasing attention since the 2015 Mw 6.4 Pishan earthquake but its kinematics of deformation remain to be properly documented. Here, we analyse the terrace record of active deformation along the Karakash River, where it crosses the Hotan anticline. We date terraces using in-situ produced cosmogenic isotopes, and show that terrace incision and uplift are spatially correlated with blind duplex ramps beneath the anticline. From there, we quantify the overall slip rate of the duplex to be 1.2-2.8 mm/yr over the last ~250 kyr. Our data are not able to resolve the detailed kinematics on each blind ramp and we cannot exclude that several of them are active at places along the anticline. By comparison to the data available west of our study area, we propose that the blind structures all along the foothills of the Western Kunlun range have an overall slip rate of ~2 mm/yr. However, the way this slip rate is to be partitioned on one or several blind ramps is expected to vary along strike, generating a certain structural and kinematic segmentation of active deformation, and from there possibly explaining the moderate recorded seismicity in this region. Because this slip is transmitted upward and forward onto the Mazar Tagh wide and geometrically simple frontal thrust sheet, we question the possibility of large – but rare – earthquakes rupturing this structure. From there, we propose the idea of a bimodal seismicity in the region, as a mirror of the structural segmentation of active faults.

How to cite: Simoes, M., Guilbaud, C., Van der Woerd, J., Baby, G., Barrier, L., Li, H., and Pan, J.: Kinematics of active deformation and possible segmentation of seismic slip along the foothills of the Western Kunlun (China)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6061, https://doi.org/10.5194/egusphere-egu24-6061, 2024.

On-site presentation
Onise Enukidze, Victor Alania, Nino Kvavadze, Alexandre Razmadze, Anzor Giorgadze, and Demur Merkviladze

The Rioni foreland basin system is located between the Lesser Caucasus (LC) and the Greater Caucasus (GC) orogens. Deformation of the Rioni double flexural foreland basin was controlled by the action of two opposing orogenic fronts, the LC retro-wedge to the south and the GC pro-wedge to the north (Alania et al., 2022). The Rioni foreland fold-and-thrust belt (RFFTB) is part of the Greater Caucasus pro-wedge.  Here we show the deformation structural style of the RFFTB based on seismic reflection profiles and serial structural cross-sections. On the basis of serial structural cross-sections, 3-D structural models. 2-3D structural models show that the Rioni foreland is a thin-skinned fold-and-thrust belt and the main style of deformation within the RFFTB is represented by a set of fault-propagation folds, duplexes, and triangle zones. The presence of two detachment levels in the RFFTB raises important questions about the deformation sequence. The serial structural cross-sections show that fault-propagation folds above the upper detachment level can develop by piggyback and break-back thrust sequences. The formation of fault-bend fold duplex structures above the lower detachment is related to piggyback thrust sequences. 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. The evolution of the thrust-top basins was mainly controlled by the kinematics of thrust sequences. Fault-propagation folds and duplex structures formed the main structure of the thrust-top basin. Recent earthquake data indicate that the RFFTB is still tectonically active and earthquake focal mechanisms within the RFFTB are thrust faults (Tsereteli et al., 2016), and active structures are mainly represented by thrust faults, blind thrusts, and blind wedges. 

Acknowledgments. This work was funded by the Shota Rustaveli National Science Foundation (SRNSF) (grant# FR-21-26377).


Alania, V., et al. (2022). Deformation structural style of the Rioni foreland fold-and-thrust belt, western Greater Caucasus: Insight from the balanced cross-section. Frontiers in Earth Science 10, 10968386.

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

How to cite: Enukidze, O., Alania, V., Kvavadze, N., Razmadze, A., Giorgadze, A., and Merkviladze, D.: 3-D structural model of the Rioni foreland fold-and-thrust belt, Georgia , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7828, https://doi.org/10.5194/egusphere-egu24-7828, 2024.

Virtual presentation
Barreca Giovanni, Pepe Fabrizio, Sulli Attilio, Morreale Gabriele, Gambino Salvatore, Gasparo Morticelli Maurizio, Grassi Sabrina, Monaco Carmelo, and Imposa Sebastiano

Archaeoseismic analysis performed in Western Sicily point to deformed archeological remains at Lilybaeum, a Punic coastal city founded in 397 B.C. at the Island’s westernmost edge. Starting from the direct observation of deformed ruins, an interdisciplinary work-strategy, which has included field-structural analysis, drone-shot high-resolution aerial photogrammetry, and geophysical prospecting, was employed to investigate whether the identified deformations may represent the ground effects of a previously unknown large earthquake in the area. Among the unearthed remains, some mosaics and a stone-paved monumental avenue show evidence of tectonic deformation being fractured, folded, and uplifted. Trend of folding and fracturing is consistent with the NNW-SSE oriented tectonic max stress axis to which western Sicily is currently undergoing. Displacement along a fracture deforming the Decumanus Maximus together with the finding of a domino-type directional collapse, enable us to interpret the observed deformation as the ground signature of a coseismic slip. Seismic rupture occurred along a previously unmapped deformation front that well fits in the seismotectonic context of Western Sicily. Measured offset, geophysical prospecting, and age-constraints all point to the possibility that a highly-energetic earthquake nucleated in the area following a coseismic rupture along a NE-SW trending back-verging reverse fault towards the end of the IV century A.D. Since seismic catalogs do not provide evidence of such a large earthquake, the latter might represent a missed event in the historical seismic record. This finding provides constraints to redefine the seismic hazard of Western Sicily, a region where recurrence-time intervals for large earthquakes are still unknown.

How to cite: Giovanni, B., Fabrizio, P., Attilio, S., Gabriele, M., Salvatore, G., Maurizio, G. M., Sabrina, G., Carmelo, M., and Sebastiano, I.: Deformed archeological remains at Lilybaeum in Western Sicily (southern Italy) as possible ground signatures of coseismically-slipped fault in the area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14973, https://doi.org/10.5194/egusphere-egu24-14973, 2024.

On-site presentation
Tiziano Volatili, Veronica Gironelli, Lucia Luzi, Paolo Galli, Michele Carafa, and Emanuele Tondi

The Inner Abruzzi region ranks among Italy's highest seismic hazard areas, hosting a system of SW-dipping normal faults historically active with moderate-to-large earthquakes (Mw ≥ 5.5). The L’Aquila earthquake in April 2009 (Mw = 6.3) intensified interest in assessing active fault seismogenic potential. Despite extensive studies, the Maiella Massif's historical seismicity, notably the 1706 and 1933 earthquakes (Mw ~6.8 and 5.9, respectively), causing severe damage, remains elusive. The investigation of historical seismic events, such as the 1706 earthquake within the Maiella area, aligns with the pressing need to identify and characterize potential seismogenic sources of future seismic activity. This task is often hindered by the scarcity of unambiguous evidence or quantitative data at both near-surface and seismogenic depths. Many source hypotheses, possibly related to the 1706 earthquake, are present in the literature. These structures, with different geometrical parameters, depths, and kinematics, characterized the tectonic setting of this region.

This study offers a comprehensive overview of these hypotheses in assessing the 1706 earthquake’s source. Their 3D geometrical representation was modelled, considering the available geological and geophysical information. The resultant seismic scenarios were estimated in terms of macroseismic intensity by calculating peak ground motion values (i.e., PGV, PGA) for each point within the 1706 macroseismic field. This procedure incorporates site amplification effects into the synthetic ground motion calculations at each site within the macroseismic field, coupling a Vs,30 map of the Italian territory. Finally, the determination of the best source model involves assessing the misfit (residuals) between the simulated macroseismic intensities and the observed ones. The accuracy of the simulated macroseismic field in reproducing the real field is evaluated by calculating the residual mean and the root-mean-square error (RMSE).

The study outcomes highlight the complexities in determining the exact source of the 1706 earthquake. Despite detailed modelling efforts, discrepancies in intensity distributions and the absence of recent seismic activity on specific faults pose uncertainties in understanding seismicity in the Inner Abruzzi area. While contributing to the ongoing debate, the research underscores the need for further investigations to better constrain the seismic hazard of this region.

How to cite: Volatili, T., Gironelli, V., Luzi, L., Galli, P., Carafa, M., and Tondi, E.: Unrevealing Seismogenic Sources of Historical Earthquakes: New Insights from the Elusive 1706 Maiella Earthquake (Abruzzi Region, Central Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8289, https://doi.org/10.5194/egusphere-egu24-8289, 2024.

On-site presentation
Pierfrancesco Burrato, Andrea Brogi, Paola Vannoli, Martina Zucchi, Umberto Fracassi, Gianluca Valensise, Hsun-Ming Hu, and Chuan-Chou Shen

We explored the behaviour and earthquake potential of an active fault system in the slowly deforming part of southern Tuscany. This region corresponds to the eastern margin of the Siena Basin, a Neogene structural depression that developed during the extensional tectonics that affected the inner northern Apennines. Here, N-, NE- and WNW-trending faults were active during the Zanclean-Latest Quaternary. Clear evidence of the activity of these faults, particularly the most recent WNW-striking ones, is represented by faulted Late Pleistocene-Holocene travertine deposits that preserve also evidence of active seismogenic faulting. Indeed, this area in recent times was mostly interested by low-magnitude seismic sequences that occurred in the uppermost 10 km of the crust, mainly characterized by transcurrent and transtensive faulting mechanisms. However, the historical record includes also damaging earthquakes in the 5.0-6.0 Mw range, such as the 7 August 1414, Mw 5.7, Colline Metallifere, 13 April 1558, Mw 6.0, Valdarno Superiore, and 25 August 1909, Mw 5.3, Crete Senesi events, but, to date, very little is known about the geometry, maximum earthquake potential and slip rate of their causative faults.
In this study, we characterize an active, capable, and seismogenic fault system identified in the saw-cut walls of an active travertine quarry near Serre di Rapolano, a few kilometres south-east of the city of Siena. To document the geometric and kinematic features of the active faults, we carried out a detailed geological and structural field survey of the quarry outcrop, collected samples for U-Th dating and constructed a virtual outcrop model. We found compelling evidence for nearly SW-NE surface-breaking faulting, perpendicular to the main structural fabric of the central and northern Apennines, whose activity extends at least into the Upper Pleistocene. The peculiar geology of the area also suggests that these faults have generated earthquakes associated with surface faulting, namely the occurrence of clastic dykes injected within the fault zones during earthquake-induced liquefaction.
Our results may help to address the current lack of understanding concerning earthquake activity in the slowly deforming region, and improve the current knowledge of the seismotectonic setting of the Siena Basin and the corresponding part of the inner northern Apennines. Our findings hint to a still unexplored tectonic mechanism, which suggests that the earthquakes affecting this part of southern Tuscany may be caused by segments of rather elusive, very long, SW-NE and WNW-ESE lineaments crossing the entire Apennine stack.

How to cite: Burrato, P., Brogi, A., Vannoli, P., Zucchi, M., Fracassi, U., Valensise, G., Hu, H.-M., and Shen, C.-C.: Active faulting and seismogenic potential in low-strain rate southern Tuscany (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19541, https://doi.org/10.5194/egusphere-egu24-19541, 2024.

On-site presentation
Michele M. C. Carafa and Matteo Taroni

The earthquake size distribution is characterized by an exponential function determined by the b-value parameter. Previous studies have demonstrated the dependence of the b-value on both the differential stress and tectonic settings. This study proposes a novel approach to categorize earthquakes based on the kinematics of interseismic geodetic strain rates and horizontal stress directions. When combined with other geological or geophysical information, incorporating stress directions and geodetic data enhances seismotectonic models, reducing arbitrariness in delineating seismic zones.

Using the Italian peninsula as a case study, we observe a significantly larger b-value for extensional faults than thrusts, albeit with smaller differences than previously reported. Additionally, our findings reveal that the spatial fragmentation of uniform tectonic regimes can lead to inaccurate b-value estimates for single faults due to the undersampling of earthquake size distribution.

How to cite: Carafa, M. M. C. and Taroni, M.: Differences in earthquake size distributions for thrusts and normal faults: the case of Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3078, https://doi.org/10.5194/egusphere-egu24-3078, 2024.

On-site presentation
Christian Brandes, David Tanner, Haakon Fossen, Matthias Halisch, and Katharina Müller

The identification of active faults is an important step in the seismic hazard evaluation process. However, this task is often difficult because many faults are unknown, buried below younger sediments. Especially in slowly-deforming intraplate areas with long recurrence intervals between individual seismic events, the detection of hidden blind faults is a major challenge. Furthermore, active faults can undergo long episodes of aseismic creep and thus do not produce typical earthquake-related, soft-sediment deformation structures, which also hinders the detection of these faults. Consequently, there is the demand for a robust universal geological indicator for active blind faults. Based on outcrop studies, we are able to show that disaggregation bands (near-surface deformation bands that develop in unconsolidated sediments due to reorganization of the grain fabric) are such an indicator. Disaggregation bands are developed at several locations in Central Europe and Scandinavia, in near-surface sandy sediments above the tip lines of blind faults. The strike of these bands is parallel to the strike of the underlying faults, which indicates that the disaggregation bands formed as a consequence of fault movement. The disaggregation bands internally show a pore-space reduction and in some cases a clear alignment of elongated grains. The thickness of the disaggregation bands increases with the amount of offset along the bands. Based on these observations, we infer that the bands formed in the process zone of propagating faults due to a shear-related reorganization of the grain fabric that leads to strain-hardening and a growth of the bands into centimetre-thick tabular structures. With analogue shearing experiments we show that disaggregation bands can form at a wide range of deformation speeds, even down to speeds several orders of magnitudes lower than seismogenic fault-slip velocities. Thus, disaggregation bands are key structures that record large parts of the seismic cycle and represent a very suitable indicator for active blind faults, even if the related fault creeps without emitting seismic waves. Disaggregation bands can easily be recognized in outcrops and artificial trenches, and previous studies showed that it is possible to even image them with ground-penetrating radar.

How to cite: Brandes, C., Tanner, D., Fossen, H., Halisch, M., and Müller, K.: Disaggregation bands as indicator for active blind faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1794, https://doi.org/10.5194/egusphere-egu24-1794, 2024.

On-site presentation
Tvrtko Korbar, Ozren Hasan, Dea Brunović, and Snježana Markušić

Kvarner area belongs to the External Dinarides fold-and-thrust belt that is characterized by intensive tectonic deformations of a few kilometers thick sedimentary cover of the central part of the Adriatic microplate. The main deformations occurred predominantly during Eocene to Oligocene thin-skinned tectonics, while late-orogenic thick-skinned deformations and wrenching resulted in the exhumation of the orogenic belt. The latter tectonic mechanism is supposed to be still active, but there is no reported evidence of active faults on the surface of predominantly karstic terrain. Nevertheless, seismological data reveal subsurface activity along various fault plane solutions, and crucial evidence of possible active deformations on the surface is expected within stratified superficial deposits in the area. However, stratified Quaternary sediments are rare onshore and on the Kvarner islands but are widespread on the bottom of the surrounding Adriatic Sea. During the targeted high-resolution sub-bottom geoacoustic seismic survey we focused on the zones that are characterized by earthquakes and on the previously arbitrarily recognized regional seismogenic sources. However, only shallow seismic profiles along and across the Vinodol and the NW part of the Velebit channel revealed clear evidence of fault-related deformations of the youngest Quaternary sediments. The fault zone is up to hundreds of meters wide, limited by parallel sub-vertical fault planes, and characterized by deformations of the strata between the planes either in a positive (uplifted) or a negative (downthrown) manner along the strike, which are typical for strike-slip faults. Besides, the disturbed layering of the uppermost well-stratified unit (Late Pleistocene) resembles fluid/sediment escape structures that could be related to strong shaking during prehistorical earthquakes. The fault zone is also tentatively recognized in the onshore bedrock along the strike of the submerged fault, where it appears as an indistinct fractured zone that is more corroded than surrounding bedrock carbonates. Therefore, sub-bottom profiling has been proven to be a useful tool for identifying active faults and should be used as a key method in future seismotectonic research of submerged seismogenic zones.

How to cite: Korbar, T., Hasan, O., Brunović, D., and Markušić, S.: High-resolution seismic imaging of the sub-bottom Quaternary deposits revealed an active fault in the Vinodol-Velebit channel (Kvarner, Croatia), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14660, https://doi.org/10.5194/egusphere-egu24-14660, 2024.

On-site presentation
Martin Šutjak, Rostislav Melichar, Ivo Baroň, Yi-Chin Chen, Jan Černý, Jia-Jiyun Dong, Václav Dušek, Filip Hartvich, Lenka Kociánová, Tung Nguyen, Matt Rowberry, and Chia-Han Tseng

The Outer Western Carpathians are fractured by several syn-thrust and post-thrust faults. One of them, the Mikulov Fault, has been studied using a combination of surface and subsurface methods. The former comprised the analysis of a LiDAR digital terrain model and aerial photographic interpretation while the latter comprised the analysis of ERT profiles and 2D seismic reflection profiles interpreted with the aid of borehole data. Paleostress analysis has also been used to understand the stress history and progressive development of the fault. By combining these methods it has been possible to define a distinct N-S directed fault zone that intersects or delineates the majority of the Jurassic limestone nappe outliers around the highlands of Pavlov Hills. This almost continuous fault zone runs for several kilometers on the Czech side of the border and extends further south into Austria. The thrusted Jurassic limestone bodies are cut by the fault zone, which tectonically crushed the limestone in its core and the cores of the secondary fault branches. The mapped pattern of the fault zone suggests branching and reattaching with the production of lenticular tectonic slices. Consequently, we interpret the fault as a prominent sinistral shear zone. This is indicated on the surface by block displacement on Svatý kopeček Hill and by the orientation of the accompanying subvertical Riedel shears with identified horizontal lineation. Subsurface kinematic indication derives from the interpretation of a prominent negative flower structure in the deep seismic profiles, just beneath the fault zone. The ERT profiles have revealed that the limestone bodies are tectonically bound by accompanying fault branches. Moreover, paleostress analysis suggest that fault zone activity can be divided into three main stages: (i) NE-SW thrust faults indicate thrusting of the Carpathian accretion wedge over the Bohemian Massif; (ii) NE-SW strike-slip faulting, during which the fault blocks moved along the faults in the direction of propagating wedge; (iii) N-S strike-slip faulting, marking the change in compression direction and transition from thrusting to a strike-slip regime. The main movement along the fault is probably of the late Miocene age and probably continues to the present day.


The research was funded by the Grant Agency of the Czech Republic (GC22-24206J).

How to cite: Šutjak, M., Melichar, R., Baroň, I., Chen, Y.-C., Černý, J., Dong, J.-J., Dušek, V., Hartvich, F., Kociánová, L., Nguyen, T., Rowberry, M., and Tseng, C.-H.: Progressive development of an accretionary wedge margin from oblique thrust to strike-slip fault (Mikulov Fault, Outer Western Carpathians)., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7666, https://doi.org/10.5194/egusphere-egu24-7666, 2024.

Coffee break
Chairpersons: Rita De Nardis, Victor Alania, Fabio Luca Bonali
On-site presentation
Federica Lanza and Tobias Diehl

To better understand seismotectonic processes and the associated seismic hazards within a region, it is imperative to explore the causality between earthquakes, active tectonics, and individual fault structures. Hypocenter locations represent a well-established method to identify active faults, their spatial geometry and temporal evolution. First motion focal mechanisms provide insights into source processes and fault kinematics, aiding in the reconstruction of seismic strain and seismogenic stress regimes. Waveform modelling is key to refine earth structure models and constrain source process parameters.

Here, we present the challenging case of the seismic sequence of Saint-Ursanne of March and April 2000 in Switzerland, where we applied advanced seismological analyses to reduce uncertainties in hypocenter locations and focal mechanisms, commonly encountered in shallow seismicity. The sequence, consisting of five earthquakes of which the largest one reached a local magnitude (ML) of 3.2, occurred in the vicinity of two critical sites, the Mont Terri rock laboratory and Haute-Sorne, which has been approved as a site for the development of a deep geothermal project. Our results, combined with geological data, suggest that the sequence is likely related to a backthrust fault located within the sedimentary cover and shed new light on the hosting lithology and source kinematics of the sequence. These new findings provide new insights into the present-day seismotectonic processes of the Jura fold-and-thrust belt (FTB) of northern Switzerland and suggest that the Jura FTB is still undergoing seismically active contraction at rates likely <0.5 mm/yr. The shallow focal depths provide indications that this low-rate contraction in the NE portion of the Jura FTB is at least partly accommodated within the sedimentary cover and possibly decoupled from the basement. This transpressive regime is confirmed by the ongoing Réclère earthquake sequence, ca. 20 kilometres west of St. Ursanne, which initiated with a reverse event of ML 4.1 on December 24, 2021, and was followed by few aftershocks in January 2022. Seismic activity started again in March 2023 with another ML4.3 reverse event, which activated a left-lateral strike-slip secondary fault just west of the reverse fault. This fault seems to be more active in terms of microseismicity and is responsible for the increased activity over the last years.  

How to cite: Lanza, F. and Diehl, T.: Deciphering seismic sequences with high-precision hypocenter locations, focal mechanisms, and waveform modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14739, https://doi.org/10.5194/egusphere-egu24-14739, 2024.

On-site presentation
Jihong Liu, Sigurjón Jónsson, Xing Li, and Yann Klinger

Large strike-slip earthquakes are usually modeled as slip on localized planar fault planes within a homogeneous or layered elastic half-space. However, geodetic fault-slip inversions often show a shallow slip deficit, where the maximum slip is found at a depth of several kilometers with gradually decreasing slip towards the surface. High-resolution satellite images of earthquake surface ruptures also suggest a reduction in on-fault slip, often termed as off-fault damage or distributed deformation. In this study, we refer to this reduction in near-fault deformation as surface absent deformation (SAD). The presence of coseismic SAD, due to off-fault damange and/or compensated for by shallow interseismic fault creep and afterslip, holds significance for earthquake rupture processes, paleoseismology, and earthquake hazard assessments.

In our study, we quantify the SAD along the main ruptures of the magnitude 7.8 and 7.6 Kahramanmaraş earthquakes, which occurred on 6 February 2023 near the Türkiye-Syria border, by mapping coseismic three-dimensional (3D) surface displacements using differential interferometry and pixel tracking of satellite synthetic aperture radar (SAR) images. The two earthquakes had a combined rupture length of approximately 500 km, exhibiting multi-meter surface fault offsets and diverse fault geometries, necessitating high-resolution deformation mapping near and away from the fault. We obtained the SAD distribution by analyzing fault-perpendicular profiles of fault-parallel displacement from the SAR-derived 3D displacements. For each profile, an arctan function was used to predict the near-fault (e.g., 0-5 km) elastic displacement based on the far-field (e.g., 5-50 km) observations, yielding an estimate of the lack of deformation close to the fault (i.e., the SAD). The results reveal a clear correlation between SAD and geometrical complexities along the two co-seismic ruptures. Using this strategy to determine the SAD, we find that about 35% of the surface fault slip is “missing” and expressed as SAD within a distance of 5-7 km from the coseismic surface ruptures. By comprehensively analyzing the interseismic, coseismic, and postseismic deformation in this area, we find that shallow interseismic fault creep and afterslip cannot explain the coseismic SAD and that it appears to be dominated by off-fault damage. Notably, existing research on off-fault damage has been concentrated within a range of only 1-2 km. Our results therefore underscore the significance of extending investigations of off-fault damage to 5-10 km from fault ruptures, and suggest that relying solely on on-fault offset measurements may lead to an underestimation of fault slip rate estimations by as much as one third.

How to cite: Liu, J., Jónsson, S., Li, X., and Klinger, Y.: Off-fault damage in the 2023 Kahramanmaraş (Türkiye) earthquakes from SAR images, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17289, https://doi.org/10.5194/egusphere-egu24-17289, 2024.

On-site presentation
Daniele Cheloni, Nicola Angelo Famiglietti, Cristiano Tolomei, Riccardo Caputo, and Annamaria Vicari

On September 8, 2023, a magnitude 6.8 earthquake impacted the High Atlas Mountains in western Morocco, approximately 70 km southwest of Marrakesh, resulting in significant devastation and casualties. This study delves into a comprehensive geodetic dataset, utilizing interferometric synthetic aperture radar (InSAR) measurements to analyze the fault segment accountable for the seismic occurrence. Our findings propose two potential fault scenarios: a transpressive NNW-dipping high-angle fault (70°), associated with the Tizi n’Test alignment, or a transpressive SSW-dipping low-angle fault (22°) linked to the North Atlas Fault, where slip (up to 2.2 m) is observed predominantly in deeper sections of the fault. Although seismic catalogs were inconclusive regarding the dip direction of the fault, evidence from mainshock locations, gravity and heat-flow data, along with modeling, and the active shortening direction, collectively indicate the activation of a low-angle, southwesterly dipping oblique thrust of the North Atlas fault during the 2023 Moroccan earthquake. Integrating interferometric analyses with geological, tectonic, and seismological data could be crucial for resolving ambiguities in satellite-based models. This study therefore underscores the complexity of fault identification and the need for a multidisciplinary approach in understanding seismic events.

How to cite: Cheloni, D., Famiglietti, N. A., Tolomei, C., Caputo, R., and Vicari, A.: Insights into the September 8, 2023, MW 6.8 earthquake in Morocco: a deep transpressive fault along the High Atlas Mountain belt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7249, https://doi.org/10.5194/egusphere-egu24-7249, 2024.

On-site presentation
Martin Zeckra, Lahcen El Moudnib, Abderrahime Nouyati, and Sebastián Carrasco

The 2023 Mw 6.9 Al Haouz Earthquake in the Moroccan High Atlas mountains is the most recent example of a destructive event in an intraplate setting under the absence of a causative plate boundary. Their large inter-event times in such seismotectonic regimes hinders the study of single focus regions and apparently underestimates their larger seismic hazard potential, leaving local communities unaware of the scale of their exposure to these risks. One major shortcoming in the immediate scientific analysis of this unprecedented earthquake is the lack of (publicly) available seismic waveform recordings in the source area.

An immediate impact is displayed in the source location uncertainty, including a high variability in focal depth estimations. Associating the earthquake origin to a causative fault remains puzzling, bearing in mind the deeper-than-average focal depth of around 32 km. The complex tectonic history of the Atlas mountain chains is depicted in a plethora of active, reactivated and abandoned faults. In addition, prior studies noticed a lithospheric anomaly underneath the High Atlas mountain range, that lacks a classical mountain root. Thus, this event raise questions on the thermo-elastic parameters at depth in order to support a large seismogenic thickness of the crust.

In the immediate aftermath of the Al Haouz, we initiated a rapid-response task force for setting up a temporal seismic network in the High Atlas. Within two weeks, six autonomous seismological stations have been installed between 20 and 80 km from the estimated epicenter. Due to the large degree of destruction, problematic access and absence of major infrastructure in the epicentral region, we relied on autarkic and robust sensors. As a novelty, the stations consisted of SmartSolo® three component 5 Hz geophone sensors. These industrial-level instruments are light-weight and easy to deploy in any terrain. In a compact casing, the passive sensors host digitizer, data storage, GPS and battery life-time of up to 30 days.

Here, we present the first data of this 2 months temporary network. Based on preliminary analysis, we could obtain more than 1000 events recorded on all stations of the network during the 54 recording days. The largest recorded events had an assigned magnitude of ML 4.5. Considering single stations detections as well, we estimate more than 10,000 earthquake detections overall. This catalog will greatly expand the scientific insight into the mechanisms of this exceptional earthquake in the near-future.

Further, through the use of simple geophone sensors this study presents a proof of concept for rapid response installations of temporary aftershock network. These sensor types strongly outperform the fully elaborated counterparts in installation speed, transportability and external requirements for potential installation sites without large drawbacks in data quality.

How to cite: Zeckra, M., El Moudnib, L., Nouyati, A., and Carrasco, S.: FRAME – a Fast Response Aftershock network for the Moroccan Earthquake (Mw 6.9, 08.09.2023), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20372, https://doi.org/10.5194/egusphere-egu24-20372, 2024.

On-site presentation
Deborah Di Naccio, Cinzia Di Lorenzo, Marco Battistelli, Simona Miccolis, Vanja Kastelic, and Michele MC Carafa

In the past decade, seismic hazard assessment has progressively relied on innovative approaches based on seismotectonic models for robust physical-based short-term and long-term estimations. For this reason, consistency and homogenization are crucial in collecting data for a scientifically sounding seismotectonic model, especially when dealing with large amounts of information at different temporal and spatial scales. Additionally, a solid probabilistic approach is needed to correctly explore the uncertainties of the seismotectonic model components (e.g., offset, age, long-term slip rate). In this contribution, we focus on the active tectonics of the central Apennines because they have been repeatedly investigated in past decades, and a significant amount of complementary data is available. In such a case, we can define an innovative fault database for seismic hazard assessment, exploring in a probabilistic sense the deformation data (age and offset) and rate (long-term slip rate). Our approach provides a substantial methodological upgrade to fault-based input for seismic hazard assessment. The proposed methodology can be easily exported to zones with scarce data availability.

How to cite: Di Naccio, D., Di Lorenzo, C., Battistelli, M., Miccolis, S., Kastelic, V., and Carafa, M. M.: Meta-analyzing geological data for seismic hazard assessment: the case study of central Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6563, https://doi.org/10.5194/egusphere-egu24-6563, 2024.

On-site presentation
Kristina Matraku, Francois Jouanne, and Edmond Dushi

Outer Albanides experienced a seismic sequence starting on 21 September 2019, with an Mw 5.6 earthquake, followed by an Mw 5.1 aftershock 10 minutes later considered as foreshocks, and culminated with the main shock Mw 6.38 on 26 November 2019, preceded by several immediate foreshocks (Mw 2.0-4.4), followed by numerous aftershocks (Mw > 5.0). We model the co-seismic slip distribution using InSAR, permanent and campaign GNSS measurements. Two hypotheses are tested: an earthquake on a thrust plane with direction N160°, and an earthquake on a backthrust. Varying the depth and dip angle for the first hypothesis and only the dip angle for the second, it is concluded that the optimal solution is a blind thrust at a depth of 15 km with an eastward dip of 40°, a maximum slip of 1.4 m and a Mw of 6.38. The GNSS time series obtained after 2020 shows two slow slip events (SSE): the first 200 days after the main shock up to about 26 days, and the second 300 days after the main shock up to about 28 days. We tested three hypotheses: SSE occurred along the basement thrust where the main shock was localised, SSE occurred along the flat formed by the detachment layer of the cover, and SSE occurred along these two faults. It has therefore been concluded that SSE has occurred along the detachment layer or along both the detachment layer and the basement thrust activated during the Mw 6.38 Durres earthquake.

How to cite: Matraku, K., Jouanne, F., and Dushi, E.: The 26 November 2019 Durres earthquake, Albania: coseismic displacements and occurrence of slow slip events in the year following the earthquake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15944, https://doi.org/10.5194/egusphere-egu24-15944, 2024.

On-site presentation
César R. Ranero, Paraskevi Nomikou, Filomena Loreto, Irene Merino, Valentina Ferrante, Danai Lampidou, Elisavet Nikoli, and Serafeim Poulos

The cruise POSEIDON from 10-22 June 2023, mapped the tectonic structure of the region extending from the western Peloponnese across the Ionian Islands. This is one of the most complex and comparatively little evaluated regions, with demonstrated seismic hazard, in the Mediterranean.

The region contains a complex fault system with numerous strands controlling much of the submarine and subaerial relief and with dramatic lateral changes in deformation rates. The fault system has produced large earthquakes, mostly offshore, recorded during the past few decades in the Greek national seismological network. However, the largest recent Mw~6.8-7.0 Kephalonia 1953 event was recorded in few stations available then. This earthquake - possibly the most destructive in recent Greek history - cause the collapse of ~85% of all buildings on Kephalonia Island, ~1k deaths, and ~145k people homeless. However, the 1953 earthquake is poorly understood compared with more recent, albeit less destructive events. The epicentre of the 1953 event is not well constrained, and the location and dimensions of the causative fault are unknown. Likewise, the hypocenter depth of the 1953 event thrust-fault focal mechanism, that occurred E or SE of Kefalonia, is defined from <50 km to <20 km, depending on the analysis. Studies in the islands interpret active shallow thrusting to propose that the 1953 event ruptured the upper 5 km of several shallow faults, but such a rupture cannot explain a Mw~6.8-7.0 even.

The goal of POSEIDON is to define the regional fault system structure and kinematics and to place it in the proper geodynamic context that helps understand hazards and eventually evaluate associated risks. The DEM displays a rugged terrain from the Ionian Islands to the Peloponnese Peninsula, with numerous features that indicate active deformation across the entire region. Major submarine tectonic structures around the islands trend from NE-SW to NNW-SSE, similar to the basins and ranges on the islands. Elongated shallow troughs offshore laterally project to the relief trends on the islands, supporting widespread active faulting.

A further complication in the research area is that the upper-crust fault system, might be located above, or sole into, a mega-thrust plate boundary fault of the Hellenic subduction zone, inferred -in publications- to dip in a NE direction at ~25-40 km depth under the surface. However, the location of a mega-thrust seismogenic zone is yet not well constrained. POSEIDON seismic data image the tectonic features in the crust and integrated with the high-resolution bathymetry allow to define the main faults across the offshore region in unprecedented detail.


We acknowledge the professional and dedicated work of the National Institute of Oceanography and Applied Geophysics (OGS-Trieste) technical party and the technical party of the Marine Technology Unit (UTM) from the Spanish National Research Council (CSIC) to make the experiment a success. We also acknowledge the professional and dedicated work of the master, officers and crew of the R/V Laura Bassi during the POSEIDON experiment.

How to cite: Ranero, C. R., Nomikou, P., Loreto, F., Merino, I., Ferrante, V., Lampidou, D., Nikoli, E., and Poulos, S.: POSEIDON Project: Seismic Hazards in the western Peloponnese - Ionian Islands Domain, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20764, https://doi.org/10.5194/egusphere-egu24-20764, 2024.

On-site presentation
Gulam Babayev, Yashar Aliyev, and Mirzali Aliyev

In this research, we combine seismic and tectonic approaches in an attempt to apply the empirical relationships between fault parameters and earthquake magnitudes aiming to assess the maximum possible magnitude for the prediction of intensity ground motion in the areas close to active faults. The case we study is the Talysh area in southern Azerbaijan with the total area of 3960 km². It stretches to 38054'N northern latitude and 48035'E eastern longitude and spreads to the north through the Alborz mountains of Iran. The earthquakes with a higher depth are concentrated mainly in the central part of the Talysh zone (up to 70 km) and in the southwestern part of the Caspian Sea (up to 55 km), with the local magnitude range of up to M5.5.

The earthquake magnitudes calculated on the basis of the surface fault length were compared with the catalogued magnitudes. As a procedure, (1) a comprehensive catalogue of all available known faults was compiled; (2) earthquake magnitude is then derived from fault length; (3) the resulting fault-length-earthquake-magnitudes were compared by the mathematical difference with catalogued earthquake magnitudes; and (4) as a final, intensity simulation of ground motion on near-fault areas was plotted. The results show the approximate consistence of the calculated fault-length-earthquake-magnitude with the catalogued seismicity. The map shows that the highest intensity areas of VII are observed in the central and western parts of the zone. An intensity VI covers majority of the Talysh zone. The results will contribute to the implementing more solid analyses for advancing seismic hazard analysis. Our research emphasizes the seismotectonic areas in southern Azerbaijan where further comprehensive studies on faults are required.

How to cite: Babayev, G., Aliyev, Y., and Aliyev, M.: Magnitude and intensity simulation of ground motion on near-fault areas: the case of Talysh (southern Azerbaijan), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3646, https://doi.org/10.5194/egusphere-egu24-3646, 2024.

On-site presentation
Wei-Hau Wang, Yi-Shen Lin, Wei-Cheng Huang, and Strong Wen

We employed dense seismic arrays to reveal the seismogenic zones beneath the foreland basin and the foothills in southwestern Taiwan. We used EqTransformer to pick earthquakes and P and S wave arrival time, GaMMA to associate earthquakes, and NonLinLoc to locate the earthquakes. Our results show that the thin-skinned thrust belts were mostly locked above a shallow decollement at a depth of ca. 6 km. Below it, a foreland-dipping seismogenic belt extends from the base of the shallow decollement to a depth of about 15 km, the deep decollement, beneath the coastal plain. We interpret this westward-dipping seismogenic belt as a passive roof duplex by inversion of the pre-existing graben-and-horst structure sliding along a ductile shear zone at a depth of 15 km during the ongoing orogeny.

How to cite: Wang, W.-H., Lin, Y.-S., Huang, W.-C., and Wen, S.: Inversion tectonics and dual decollements in southwestern Taiwan: implication from a dense seismic array, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13778, https://doi.org/10.5194/egusphere-egu24-13778, 2024.


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

Display time: Tue, 16 Apr 14:00–Tue, 16 Apr 18:00
Burçin Didem Tamtaş and Hazel Deniz Toktay

The faults and the fault zones are essential to determine the seismotectonic features and the regime of a region and to produce seismic hazard and risk maps. Many geophysical methods, such as seismic, magnetic and gravity are used to determine the location and direction of faults. This study aims to detect potential fault edges located in the south-southwest of Nisyros Island and west of Tilos Island in the southeastern Aegean Sea and to interpret the seismic activity and faulting characterization. To this end, the potential fault edges were initially detected using the total horizontal derivative method on the gravity dataset collected from the WGM2008 database. The obtained spatial locations were combined with the seismicity and the focal mechanisms of the earthquakes. The detected fault has a northeast-southwest orientation with normal faulting. It was proved that this obtained fault is not included in the active faults of the Eurasia database (AFEAD), European Fault - Source Model 2020 (EFSM20) database and the Mineral Research and Exploration General Directorate (MTA) active fault map. Moreover, this observed fault was detected as longer than the fault shown on the National Observatory of Athens (NOAFAULTs) in terms of length. Consequently, it is highly recommended that this potential fault, which produces earthquakes with a moment magnitude greater than 4.0 (on instrumental period) must be added to such fault databases to increase and spread the knowledge of seismological and seismotectonic research.

How to cite: Tamtaş, B. D. and Toktay, H. D.: Seismotectonic interpretation and edge detection of the potential fault on the SE Aegean Sea using the total horizontal derivative method, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-785, https://doi.org/10.5194/egusphere-egu24-785, 2024.

Tamar Shikhashvili, Mariam Mariam Bekurashvili, Anzor Giorgadze, Aleksander Razmadze, Onise Enukidze, and Victor Alania

Collision and subsequent convergence of Arabia and Eurasian plates during the late Alpine time caused extensive intracontinental deformation in the Caucasus region (e.g., Cavazza et al., 2023). 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 Kura foreland basin (Alania et al., 2023). Our study area is located within the LC-GC convergence zone in the western Kura foreland basin and is represented by the lenticular-shaped compressional basin formed by northward and southward-directed thrusting. 2D seismic reflection profiles revealed the presence of triangle zones at the frontal part of the LC retro-wedge and GC pro-wedge. According to analog, seismic, and sequential kinematic modeling results, the frontal part of the GC is represented by a double wedge-dominated triangle zone and is characterized by the presence of passive, active wedges and passive-forethrust. In the frontal part of the LC orogen, the syn-kinematic (Middle-late Miocene) strata have been deformed and uplifted by passive-back thrusting at the triangle zone. Seismic reflection profiles show north-vergent duplex and structural wedge at the triangle zone beneath the thrust front monocline and is represented by Cretaceous-Paleogene strata. Western part of the triangle zone of the Kavtiskhevi-Akhalkalaki area is introduced by south-vergent imbricated fan (passive-back thrusts). The imbricated fan is characterized by fault-propagation folding. The kinematic evolution of south-vergent fault-propagation folds is related to northward propagating duplex. Recent and historical earthquakes and paleoseismic data indicate that the frontal part of LC and GC is tectonically active (e.g., Stahl et al., 2022; Tsereteli et al., 2016).



Alania, V., et al. (2023). Interpretation and analysis of seismic and analog modeling data of triangle zone: a case study from the frontal part of western Kura foreland fold-and-thrust belt, Georgia. Frontiers in Earth Sciences 11, 1195767.

Cavazza, W., et al. (2023). Two-step exhumation of Caucasian intraplate rifts: a proxy of sequential plate-margin collisional orogenies, Geoscience Frontiers 15, 101737.

Stahl, T. A., et al. (2022). Recent Surface Rupturing Earthquakes along the South Flank of the Greater Caucasus near Tbilisi, Georgia. Bull. Seism. Soc. Am. XX, 1–19.

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

How to cite: Shikhashvili, T., Mariam Bekurashvili, M., Giorgadze, A., Razmadze, A., Enukidze, O., and Alania, V.: Active triangle zones within the two orogens convergence zone, central Caucasus, Georgia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1278, https://doi.org/10.5194/egusphere-egu24-1278, 2024.

Mariam Bekurashvili, Tamar Shikhashvili, and Victor Alania

Our study area, Tbilisi urban area is located in the eastern Achara-Trialeti fold-and-thrust belt. The Achara-Trialeti fold-and-thrust belt, which is one of the good examples of collision-driven far-field deformations, is located within the northernmost part of the Lesser Caucasus orogen and is associated with Arabia-Eurasia convergence. Our interpretation has integrated seismic reflection profiles, several oil wells, and surface geology data to reveal the deformation structural style of the eastern Achara-Trialeti fold-and-thrust belt. Fault-related folding theories were used for seismic interpretation. Seismic reflection data reveal the presence of south-vergent and north-vergent fault-propagation folds, duplexes, and structural wedge. Interpreted seismic reflection profiles, structural cross-section, and recent earthquakes reveal the presence of an active blind thrust fault and structural wedge(s) beneath Tbilisi and the surrounding area. The structural model shows that the 2002 Mw 4.5 Tbilisi earthquake was related to a north-vergent blind thrust and the Kumisi and Teleti earthquakes are related to a north-vergent blind wedge thrust system.

How to cite: Bekurashvili, M., Shikhashvili, T., and Alania, V.: Structural architecture of the active eastern Achara-Trialeti fold-and-thrust belt (Tbilisi urban area), Georgia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1557, https://doi.org/10.5194/egusphere-egu24-1557, 2024.

Silvana Martin, Laura Montresor, Pina Zambotti, Giovanni Monegato, Guido Roghi, Gianluca Piccin, Alessia Modesti, and Francesco Gosio

In the Valsugana area (Southern Italian Alps) a NE-SW trending pre-permian Southalpine phyllitic basement is intruded by an Early to Middle Permian granitoids (Cima d’Asta,190 km2) and includes volcanic calderas of the Athesian Volcanic Group (125 km2) of the same age, and is locally covered by Upper Permian to Miocene sedimentary sequences. A complex system of faults juxtaposes these different geological domains. In particular, the Permian tectonic structures have been repeatedly reactivated during Mesozoic and Tertiary. The phyllitic basement, which suffered Variscan metamorphism and deformation, and the granitoids were dismembered by NNW-SSW and N-S tectono-magmatic faults associated with the opening of permian calderas. The main tectonic system of this area is the ENE-WSW oriented Valsugana fault system of Middle-Late Miocene age (Heberer et al., 2017 ). The master fault separates the metamorphic basement from the sedimentary sequences (e.g., M. Armentera, M. Civerone and M. Lefre). At the footwall of the master fault, other faults deformed in a compressive to transpressive regime the sedimentary sequences. Some of these are extensional faults were reactivated many times from Triassic to Lower Jurassic. The Valsugana fault system ends against the Permian to Mesozoic Calisio fault to the SW, while it continues to the NE towards Brocon and Cereda Passes (Gianolla et al. 2022). The Valsugana fault system is cut across by the Val di Sella fault of Late Miocene-Pliocene age, oriented c.a. E-W which deformed the northern walls of the Asiago Plateau (Barbieri & Grandesso, 2007), transporting slices of metamorphic basement and Permo-Mesozoic sequences to the north, over the Middle Miocene sandstones and marls of Valsugana. The most recent tectonic system consists of a set of NNW-SSE to N-S faults which cut across the ENE-WSW Valsugana and E-W Val di Sella fault systems. The N-S Grigno-Tolvà fault cuts across the Cima d’Asta magmatic complex from Val Vanoi to the north to Asiago Plateau to the south over XX km, and dislocates the Belluno and Val di Sella thrust faults at the footwall of the Valsugana fault system. All these faults are still seismically active.

Barbieri G. & Grandesso P. (2007) - Note Illustrative della Carta Geologica d'Italia alla scala 1:50.000, F. 082, Asiago.

Heberer B., Reverman R.L., Fellin M.G., Neubauer F., Dunkl I., Zattin M., Seward D., Genser J. & Brack P. (2017) - Postcollisional cooling history of the Eastern and Southern Alps and its linkage to Adria indentation. International Journal of Earth Sciences (Geologische Rundschau), 106:1557–1580.

Gianolla G., Caggiati M. & Riva A. (2022) - Note Illustrative della Carta Geologica d'Italia alla scala 1:50.000, F. 046, Longarone.

How to cite: Martin, S., Montresor, L., Zambotti, P., Monegato, G., Roghi, G., Piccin, G., Modesti, A., and Gosio, F.: The Valsugana area (TN, Italy): a structural knot, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1713, https://doi.org/10.5194/egusphere-egu24-1713, 2024.

Vasileios Karakostas and Eleftheria Papadimitriou

The Kefalonia Transform Fault Zone (KTFZ) in central Ionian Islands (Kefalonia and Lefkada Islands), Greece, a dextral strike slip transform zone, exhibits the fastest rates of relative plate motion in the Mediterranean. Strong (Mw>6.0) earthquakes associated with the fault segments comprised in KTFZ are frequent as historical information and instrumental record reveals. Four main shocks of this order magnitude, among other earthquakes of Mw>5.0 occurred since 2003 on almost along strike adjacent fault segments, with high aftershock productivity extended far beyond the fault tips forming aftershocks zones remarkably wider than expected of strike slip faulting. This enhanced aftershock seismicity is associated with the shear deformation zone surrounding the mainshock rupture plane. It has been suggested that it results from the reactivation of secondary faults, its width decreases as a power law with cumulative fault displacement being narrower around mature faults than around immature faults. As the structural maturity may have a strong impact on earthquake behavior, such as magnitude, stress drop, distribution of slip, rupture velocity, ground motion amplitude, and number of ruptured segments, as prior studies have suggested, we aim at investigating the shear deformation zone along KTFZ. We used the relocated aftershock seismicity of the four recent (2003 – 2015) strong (Mw>6.0) main shocks that occurred on almost along strike positioned strike slip faults for defining the fault width in conjunction with the fault length, as we have already done in the case of the 2015 Lefkada main shock, and the activation of secondary faults, most probably triggered by stress changes and stress redistribution due to the main shock coseismic slip. Detailed slip models, when available, are engaged for this scope for investigating possible triggering of the secondary fault segments taking part in each seismic excitation, due to the stress transfer, taking also into account the stress sensitivity on the geometry and faulting properties of the minor faults, along with the accurately relocated aftershock seismicity. After the main fault width definition, we investigated the decrease of aftershock frequency and spatial density as a function of distance from the main fault.

Acknowledgments: Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or European Commission – Euratom. Neither the European Union nor the granting authority can be held responsible for them.

How to cite: Karakostas, V. and Papadimitriou, E.: The shear deformation zone along the KTFZ: implications for faulting properties, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1802, https://doi.org/10.5194/egusphere-egu24-1802, 2024.

Federico Pasquaré Mariotto, Alessandro Tibaldi, Fabio Luca Bonali, Noemi Corti, Martina Pedicini, Babayev Gulam, and Tsereteli Nino

The convergence between the Arabian and the Eurasian plates resulted in the development of the Greater Caucasus (GC) and the Lesser Caucasus fold-and-thrust belts, separated across most of their length by the Transcaucasian depression. The whole sub-horizontal shortening of the Caucasus was quantified at hundreds of kilometers and, according to several studies, reached its maximum rate in the Miocene-Pliocene. At present, convergence between the Eurasian and African-Arabian plates is still active, producing widespread deformation within the mountain belt and in surrounding regions, as testified to by seismological, paleoseismological and GPS data.

Understanding the active tectonics of the Caucasus is of paramount importance for a better assessment of geohazards, especially seismic hazard. Moreover, there is a major concentration of residents in Tbilisi, the capital of Georgia, hosting 1.2 million citizens, and in Baku, the capital of the Azerbaijan Republic, with over 2.3 million citizens; both cities are located in active tectonic basins at the southern foothills of the GC. Hundreds of rural villages are scattered in the mountain regions, and all were built without taking into consideration antiseismic criteria. All the above shows that the Caucasus and Transcaucasus regions are subject to an extreme seismic hazard and risk.

Here, we describe the active kinematics of the Greater Caucasus (territories of Georgia, Azerbaijan and Russia) through an integrated analysis of seismological, structural-geological and GPS data. Alignments of crustal earthquake epicentres indicate that most seismic areas are located along the southern margin of the mountain belt and in its north-eastern sector, in correspondence of major, activeWNW-ESE faults, parallel to the mountain range. Focal Mechanism Solutions (FMS) delineate dominant reverse fault kinematics in most sectors of the mountain belt, although swarms of strike-slip FMS indicate the presence of active transcurrent faulting, especially along the southeastern border of the Greater Caucasus. The mountain belt is characterized by dominant NNE-SSW-oriented P-axes. In the central-southern sector, in correspondence of the local collision between the Lesser and Greater Caucasus, P-axes are mainly NNW-SSE oriented. GPS data show dominant motions to the NNW, with rates increasing in eastward direction. All observations are consistent with a component of eastward escape of the central-eastern part of the Greater Caucasus.

How to cite: Pasquaré Mariotto, F., Tibaldi, A., Bonali, F. L., Corti, N., Pedicini, M., Gulam, B., and Nino, T.: Active Kinematics of the Greater Caucasus from Seismological and GPS Data: A Review, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2168, https://doi.org/10.5194/egusphere-egu24-2168, 2024.

Valeria Fedeli and Anna Maria Marotta

 Discontinuities affect the Earth’s dynamics, yet the Earth is often represented in geodynamical models as a continuous material. The challenge of representing discontinuities in numerical models has been addressed in several ways in literature. The split node method, originally introduced by Jungels (1973) and Jungels and Frazier (1973) for elastic rheology and then modified by Melosh and Raefsky (1981) to simplify its implementation, allows the introduction of discontinuity into a finite element model by imposing an a-priori slip at a designated node, where the displacement depends on the element which the node is referred to. Originally, this method requires that the discontinuity’s geometry and slip are pre-established.

More recently, Marotta et al. (2020) modify this approach by introducing a coupling factor that indicates the percentage difference between the velocities of the element to which the slip node belongs, while the velocity consistently derives from the dynamic evolution of the system. However, this method still requires the pre-establishment of the discontinuity’s geometry.

We here present a new technique that enables the dynamic identification of the discontinuity’s during the thermomechanical evolution of the system, based on physical parameters and without predefining the slip or the geometry.

We have implemented a new algorithm that identifies one or more discontinuities in a finite-element scheme operating through two phases: nucleation and propagation. Nucleation involves selecting a yield physical property and identifying the potential slip nodes, i.e., nodes on which the chosen physical property exceeds a yield value. The nucleus is then identified as the potential slip node where the chosen property most exceeds the yield. Propagation can be performed by choosing between three approaches of propagation: single simple fault, multiple simple fault and single double fault; and three schemes for the identification of neighboring nodes: grid-bounded, pseudo-free and free. The resulting discontinuity is the line connecting the nucleus and the propagation nodes.  Once the discontinuity has been identified, a coupling factor is introduced and the algorithm continues to operate following the Marotta et al., (2020)’s scheme.

The results of several benchmark tests, performed through both simple and complex finite-elements models, confirm the success of the algorithm in recognizing yield conditions and introducing a discontinuity into a finite-element model and demonstrate the correctness of the propagation’s geometry.


Jungels P.H.; 1973: Models of tectonic processes associated with earthquakes. PhD thesis.

Jungels P.H., Frazier G.A. Frazier; 1973: Finite element analysis of the residual displacements for an earthquake rupture: source parameters for the San Fernando earthquake. Journal of Geophysical Research.

Marotta A.M., Restelli F., Bollino A., Regorda A., Sabadini R.; 2020: The static and time-dependent signature of ocean-continent and ocean-ocean subduction: The case studies of Sumatra and Mariana complexes. Geophysical Journal International.

Melosh H.J., Raefsky A.; 1981: A simple and efficient method for introducing faults into finite element computations. Bulletin of the Seismological Society of America.

How to cite: Fedeli, V. and Marotta, A. M.: A dynamic identification of continuous discontinuities in geodynamic numerical models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5338, https://doi.org/10.5194/egusphere-egu24-5338, 2024.

Victor Alania, Onise Enukidze, Nino Kvavadze, Anzor Giorgadze, Demur Merkviladze, Alexander Razmadze, and Tornike Xevcuriani

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).

How to cite: Alania, V., Enukidze, O., Kvavadze, N., Giorgadze, A., Merkviladze, D., Razmadze, A., and Xevcuriani, T.: Active crustal-scale duplexes and structural wedge in the central part of Greater Caucasus orogen pro-wedge, Georgia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6771, https://doi.org/10.5194/egusphere-egu24-6771, 2024.

Xianwei Zeng, Chunquan Yu, and Gongheng Zhang

The 2021 MS 6.4 Yangbi earthquake occurred near the southwestern boundary of the Chuandian block in the SE Tibetan Plateau. Previous studies found that the mainshock occurred to the west of the main boundary fault – the Weixi-Qiaohou-Weishan fault, but the detailed seismogenic structure of the Yangbi earthquake sequence remains unclear. Accurate spatiotemporal characteristics of aftershocks and precise fault-zone structure are crucial for a more thorough understanding of the seismogenic structure and nucleation mechanisms of the Yangbi earthquake. Five days after the mainshock, we deployed a dense array with 200 short-period nodal seismometers spaced approximately 2 to 3 km in the vicinity of the Yangbi earthquake source region. In this study, we use the three-month-long continuous recordings of the dense array to study aftershock source parameters and fault-zone structures. We first obtained an earthquake catalog containing 88934 high-resolution event locations and 625 high-quality focal mechanisms. The entire aftershock sequence has a complete magnitude of -0.2, and a b-value of 0.97, with earthquake depths concentrated between 1 and 7 km below sea level. Combining precise aftershock locations and focal mechanisms, we constructed a detailed three-dimensional fault-zone structure model for the Yangbi earthquake sequence. The results reveal significant geometric variations in both strike and dip directions of the main fault. Along the dip direction, a conspicuous flower-like structure is present in the shallow part, transitioning to a listric structure inclined to the southwest at deeper levels. Along the strike direction, a noticeable bend exists in the central part. Several conjugate or intersecting faults are also present around the main fault. One of these faults, intersecting the main fault at a depth of about 4 km and dipping to the northeast, is likely the seismogenic fault of the largest foreshock. Additionally, below the main fault, there is another listric fault which appears to connect to the known Weixi-Qiaohou-Weishan fault at the surface. Our study provides new insight into the mechanism of the 2021 Yangbi earthquake sequence. The 3D fault-zone geometry can potentially be used for dynamic source modeling to better understand the initiation and rupture process of the mainshock.

How to cite: Zeng, X., Yu, C., and Zhang, G.: Complex fault-zone structure of the 2021 Yangbi Earthquake sequence revealed by dense array observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7731, https://doi.org/10.5194/egusphere-egu24-7731, 2024.

Alessandro Tibaldi, Fabio Bonali, Federico Pasquaré Mariotto, Paolo Oppizzi, Nino Tsereteli, Hans Havenith, Gulam Babayev, and Tomáš Pánek

We present the main features of the frontal structure, known as Kur Fault, of the Plio-Quaternary Kura fold-and-thrust belt in the Greater Caucasus (Azerbaijan). The Kur Fault has been analysed thanks to geological-structural and geomorphological surveys of its whole length, integrated by a relocation of instrumental seismicity, data on historical seismicity, new focal mechanism solutions, and ambient vibration measurements across the fault trace. The in-depth study of the frontal structure can: i) provide insights into the shallow propagation of a regional reverse fault, ii) contribute to a better understanding of the earlier stage of development of a young continent-continent collision, and iii) have implications for seismic hazard assessment because the area is seismically active and hosts the most important infrastructure for energy production in the country. The results show that the fault deforms the surface for a total length of 123 km. The shallow expression is given by four main scarp segments, with a right-stepping arrangement, which have different structural significance; they are represented by an alternation of fault-propagation folds, folds with offset frontal limbs, and shallow faulting. Analyses of the age of deformed deposits and landforms suggest activity from Mid-Late Miocene times to the Holocene. The fault attitude and its reverse kinematics are coherent with the Holocene and present-day state of stress, characterised by a N-S to NNE-SSW horizontal s1, suggesting the capability for seismic reactivation. Earthquake focal mechanism solutions indicate from pure reverse motions to transpressional kinematics in the area. Calculation of potential Mw indicates values in the range 7.5-7.9 if we consider its entire fault length, 6.1-7.2 if we consider the single segments.     

How to cite: Tibaldi, A., Bonali, F., Pasquaré Mariotto, F., Oppizzi, P., Tsereteli, N., Havenith, H., Babayev, G., and Pánek, T.: Structure, morphology and seismicity of the frontal part of a propagating fold-and thrust belt: The Holocene 123-km-long Kur Fault, Greater Caucasus, Azerbaijan , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10101, https://doi.org/10.5194/egusphere-egu24-10101, 2024.

Cinzia Di Lorenzo, Michele Carafa, Deborah Di Naccio, and Vanja Kastelic

The large amount of long-term fault slip rate measurements allows for determining the long-term tectonic moment rate for the central Apennines (Italy). Converting the long-term moment rate in seismicity rates requires a correct estimation of the long-term seismic coupling due to aseismic creep, possibly responsible for some of the observed dislocations. Ignoring this issue could induce a gross overestimation of the regional seismic hazard. Consequently, we must quantify the fraction of tectonic deformation released as earthquakes to correctly use the fault-based approach for forecasting long-term seismicity and assessing the seismic hazard of a region. To this aim, we introduce the seismic coupling in the calculation and treat it as a statistical variable. The probabilistic approach also considers the uncertainties in each parameter of active faults (depth of seismicity cutoff, length, and slip rate). The parameters of a regional Tapered Gutenberg-Richter distribution are determined to reproduce the observed earthquake size distribution. We found that about three-quarters of the long-term tectonic moment rate goes into earthquake activity, suggesting a non-marginal role of aseismic deformation for active faults in the central Apennines.

How to cite: Di Lorenzo, C., Carafa, M., Di Naccio, D., and Kastelic, V.: Fault offset rate and historic earthquake catalogue-based seismic coupling estimate for the central Apennines (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10669, https://doi.org/10.5194/egusphere-egu24-10669, 2024.

Rita de Nardis, Alessandro Vuan, Luca Carbone, Donato Talone, Maria Adelaide Romano, and Giusy Lavecchia

Our study extensively explores the analysis of successive swarms and seismic sequences that followed the 2009 L'Aquila mainshock (Mw 6.3) in the southern-central Apennines of Italy—a region historically recognized for seismic events, some reaching ~M7.

The study area is characterized by active fault alignments well-documented in the geological literature. Bounded eastward by the Fucino-Marsicano-Barrea SW-dipping faults and westward by the southern termination of the Ernici NE NNE-dipping fault systems, it is also crosscut by the Villavallelonga-Pescasseroli–San Donato-Val Comino and the innermost right-stepping en-echelon Balsorano-Posta Fibreno sets, as well as the Sora fault.

Despite its active fault systems, the study area exhibits a low level of seismicity, prompting extensive investigation in previous experiments conducted by temporary seismic networks (Bagh et al., 2007; Romano et al., 2013) and more recent contributions by Frepoli et al. (2017). Notwithstanding, the paucity of seismicity, coupled with the deep geometry of faults and their association with historical earthquakes, remains a topic of ongoing debate in the literature.

Through the application of template matching techniques (Vuan et al., 2018) to enhance the available seismic catalog, we unveil previously undetected low-level seismicity with a completeness magnitude ML ~ 0.0. The space-time evolution of the intense seismicity, along with the characterization of each seismic episode, migration velocity, and Vp/Vs ratios, combined with the 3D distribution of seismicity and geological data, revealed both a clear tectonic influence and the role of fluids in seismic processes. This exploration illuminated previously unknown geometric aspects and provided the first evidence of the WNW-ESE deformation zone in the southernmost segment of the Villavallelonga fault at depths ranging from 11 to 15 km. Our results indicate that deeper seismicity (>16 km) suggests an ascending trend of possible mantle-derived CO2.

These findings significantly contribute: (1) to the understanding of tectonic seismic swarms in extensional domains, (2) to provide insights into fluid involvement in seismic processes, and (3) to the discussion of the seismotectonic setting in high seismic-risk areas. The acknowledgment of the value of microseismicity for regional seismotectonic studies serves as a compelling conclusion, underscoring the broader significance of these findings.


Bagh, S., Chiaraluce, L. et al. 2007. Background seismicity in the Central Apennines of Italy: The Abruzzo region case study. Tectonophysics, 444,80–92.

Frepoli, A, Cimini, G.B et al., 2017. Seismic sequences and swarms in the Latium-Abruzzo-Molise Apennines (central Italy): New observations and analysis from a dense monitoring of the recent activity, Tectonophysics, 312-329.

Vuan, A., Sugan, M., et al., 2018. Improving the Detection of Low‐Magnitude Seismicity Preceding the Mw 6.3 L’Aquila Earthquake: Development of a Scalable Code Based on the Cross Correlation of Template Earthquakes. BSSA 108, 471–480.

Latorre, D., Di Stefano, R., et al., 2023. An updated view of the Italian seismicity from probabilistic location in 3D velocity models: The 1981–2018 Italian catalog of absolute earthquake locations (CLASS): Tectonophysics, 846, 229664.

Romano, M. A., de Nardis, et al., 2013. Temporary seismic monitoring of the Sulmona area (Abruzzo, Italy): A quality study of microearthquake locations. NHESS, 13, 2727–2744.

How to cite: de Nardis, R., Vuan, A., Carbone, L., Talone, D., Romano, M. A., and Lavecchia, G.: Dual Role of Fluids in Activating Extensional Seismicity at Middle and Lower Crust Depth: the Deformation Corridor Throughout the Southern-Central Apennines (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11665, https://doi.org/10.5194/egusphere-egu24-11665, 2024.

Renier Viltres, Cécile Doubre, Marie-Pierre Doin, and Frédéric Masson

The present-day tectonics of the northernmost Africa region is dominated by the oblique convergence
between the Nubia and Eurasia plates initiated 35 Ma ago. GNSS-derived velocities indicate that the
relative plate motion of only ~5 mm/yr is accommodated within a wide region involving inland
and offshore tectonic structures, from Morocco to Tunisia and from the Mediterranean Sea to the Sahara
platform. Due to limited and sparse geodetic measurements, the main zones of strain accommodation as
well as the strain partitioning between thrust and strike-slip faults remain unresolved. However, despite
the low strain budget, significant seismicity and destroying earthquakes have been recorded in the region
with five M>6 events nucleated on both inland and offshore faults during the last decade.

To better identify the active inland faults and constrain their interseismic behavior for a better seismic
hazard assessment in northernmost Africa, we used multi-temporal InSAR analysis to produce the first
regional-scale interseismic velocity map of the region. The primary data consists of up to ~8 years of
SAR imagery from the Sentinel-1 satellite constellation for 6 tracks in both the ascending and descending
orbits. The data processing and the generation of InSAR-based time series describing the spatio-temporal
evolution of surface deformation were performed using the New Small Baselines Subset processing chain
(NSBAS, Doin et al. 2011). We followed a three-blocks processing strategy leading to (1) interferograms
generation, (2) phase unwrapping, and (3) time series estimation. Within the first block, interferometric
networks combining image pairs with short and long temporal baselines were defined to mitigate potential
bias introduced by changes in soil properties (e.g., snow, vegetation growth, dunes). Before unwrapping,
interferograms flattening, multi-looking, and atmospheric phase screen (APS) corrections based on the
ECMWF ERA-5 atmospheric model were implemented. The resulting time series of surface displacement
along the line-of-sight direction (LOS) for the 2014-2022 period were decomposed into the near-vertical
and horizontal (E-W) components and expressed into a Eurasia-fixed reference frame using the GNSS
velocities in Billi et al. (2023).

Our estimated deformation maps reveal multi-scale present-day motions, with large- and small-scale
signals suggesting tectonic origin and ground response to anthropogenic activity or landslides, respectively.
The oblique plate convergence involves the interseismic loading of a series of E-W oriented right-lateral
strike-slip inland faults. Between the longitudes ~3°W and ~9°E, this inland deformation is localized
within a 25-75 km wide zone consistent with a unique linear strike-slip fault without any clear uplift related
to thrusting on already mapped transfer structures. The rates and directions of surface displacements
suggest that the shortening component of the Nubia-Eurasia relative plate motion is almost entirely
accommodated by offshore tectonic structures which has an important impact on the assessment of
seismic and tsunamigenic hazards.



How to cite: Viltres, R., Doubre, C., Doin, M.-P., and Masson, F.: Active deformation within the slow-straining northernmost Africa region constrained by InSAR time-series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12862, https://doi.org/10.5194/egusphere-egu24-12862, 2024.

Chung-Hsiang Mu, Ching-Chou Fu, Hao Kuochen, Kuo-Hang Chen, and Kuo-Wei Chen

Our goal is to comprehend fluid circulation within fault zones and its impact by monitoring hydrochemical and hydrophysical aspects across multiple dimensions. We also monitor nearby micro-seismicity and surface deformation. MAGIC (Multidimensional Active fault of Geo-Inclusive observation Center) is located at the Chihshang creeping fault, situated at the boundary of tectonic plates in eastern Taiwan. This fault exhibits aseismic creep at a rate of 2 cm per year, alongside high seismic activity.

The earthquake sequence of 2022 began with a magnitude 6.4 event on September 17 (local time), followed by a magnitude 6.8 earthquake the next day. The epicenters were within the Central Range fault system, positioned to the west of our monitoring network. This presents a significant opportunity to observe co-seismic changes in pore pressure within the footwall and fault zone.

The findings revealed that after the initial earthquake in the adjacent fault system, the pore pressure within the footwall swiftly decreased by nearly 100 cm within 15 hours. Simultaneously, the pore pressure within the fault zone increased by approximately 25 cm during the same period. Subsequently, the footwall's pore pressure continued to decrease with the second earthquake and then slowly recovered. These alterations in pore pressure suggest that fractures underwent both opening and closure during stress migration.

How to cite: Mu, C.-H., Fu, C.-C., Kuochen, H., Chen, K.-H., and Chen, K.-W.: Monitoring earthquake-induced pore pressure changes in the creeping fault system triggered by the 2022 Chihshang earthquake sequence, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13981, https://doi.org/10.5194/egusphere-egu24-13981, 2024.

Seongjun Lee, Youngbeom Cheon, Jong-won Han, Sangmin Ha, Jeong-Heon Choi, Yeong Bae Seong, Hee-Cheol Kang, and Moon Son

The 2017 Pohang earthquake (ML 5.4) ranked as the second-largest instrumental earthquake in Korea and the most destructive seismic event. Before this event, the absence of documented instrumental seismic activity and no mapped Quaternary faults near the epicenter raised questions about the paleoseismic history of the region. This study aims to gather and trace evidences of the paleoseismic ruptures along the surface projection of seismogenic fault, reported by previous study, and interpret their implications. To achieve it, we conducted comprehensive paleoseismological investigations, including geomorphic analysis, fieldwork, drilling survey, trench excavation and numerical age dating. Through geomorphic analysis and drilling survey, we identified two lineaments: NNE–SSW-striking Fault-1 and NE–SW to NNE–SSW-striking Fault-2. In the excavation site of fault-1, stratigraphic features and numerical ages indicate that the PE event occurred between 11±1 ka and 2.6±0.1 ka, and then the MRE event activated after 0.17±0.01 ka.  On the other hand, the combined results of two outcrops of Fault-2 show that the MRE and PE of Fault-2 could be constrained to have occurred between 148±7 ka and ca. 40 ka and around 200 ka, respectively. Our findings present that even before the 2017 Pohang earthquake, seismic events causing surface ruptures of moderate to large magnitude have occurred at least three times in this area during the late Quaternary.

This work was supported by a grant (2022-MOIS62-001) of National Disaster Risk Analysis and Management Technology in Earthquake funded by Ministry of Interior and Safety (MOIS, South Korea).

How to cite: Lee, S., Cheon, Y., Han, J., Ha, S., Choi, J.-H., Seong, Y. B., Kang, H.-C., and Son, M.: Paleoseismic records around epicenter of the 2017 Pohang earthquake, SE Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14319, https://doi.org/10.5194/egusphere-egu24-14319, 2024.

Mara Monica Tiberti, Francesco Emanuele Maesano, Mauro Buttinelli, Pasquale De Gori, Fernando Ferri, Liliana Minelli, Maria Di Nezza, and Chiara D'Ambrogi

In the Central Apennines (Italy), the project RETRACE-3D provided a reliable 3D model of the crust in the area affected by the 2016-17 Amatrice-Visso-Norcia seismic sequence, highlighting that the coseismic rupture at the surface can involve old inherited normal faults while the seismogenic sources lay at depth, possibly reactivating and inverting previous thrust faults, as in the case of the Mw 6.5 Norcia earthquake (30 october 2016). Here we present a 2D gravity model across the Central Apennines, spanning from the Tyrrhenian coast to the Adriatic Sea, aimed at completing and verifying the crustal geometries resulting from the 3D model itself. The cross-section was built integrating different types of data, such as surface geology, hydrocarbon wells, seismic lines, and results from receiver function analysis. It was then checked against gravity anomalies and the velocity distribution from Local Earthquake Tomography (LET), adding further details, and, finally, against seismicity recorded during the 2016-2017 sequence. The results substantiate the reliability of the geometries proposed in the RETRACE 3D model, as they fit well, except for some local misfits, with the other independent data, such as the Bouguer anomalies and the velocity distribution from LET. Furthermore, the integration of different types of data allowed us to describe in detail the structural setting of the Apennine chain also in the surroundings of the RETRACE study area, where the cross-section length exceeds the 3D model, and to add some new elements at seismogenic depths, that exceed those typical of hydrocarbon exploration. In particular, we were able to investigate the nature of the basement top and its relationship with seismotectonics.

How to cite: Tiberti, M. M., Maesano, F. E., Buttinelli, M., De Gori, P., Ferri, F., Minelli, L., Di Nezza, M., and D'Ambrogi, C.: Multidisciplinary geophysical approach to investigate the deeper portion of the Central Apennines (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15305, https://doi.org/10.5194/egusphere-egu24-15305, 2024.

Nino Kvavadze, Victor Alania, and Onise Enukidze

The Caucasus region, which is one of the good examples of collision-driven far-field deformations, is located in the northernmost part of the Arabia/Eurasia collision zone and is classified with moderate seismic activity. Racha region, a part of Greater Caucasus orogen, in particular is characterized with the highest activity. In recent year several moderate earthquakes were observed in the region, notably 2009 September 7 (Mw = 6.0), 2011 August 18 (Mw = 4.8), and also 2024 January, 2 (Mb = 4.4), with depths varying from 10 to 15 km. The strongest event during the instrumental period recorded in Racha was observed in 1991 April 29, with magnitude Mw=7.0 and Depth = 17.2 km. Which was the largest earthquake recorded in the region, causing casualties. This event caused a number of fore- and aftershocks. Following the Racha 1991 earthquake temporary, dense seismic network was installed around the area to study aftershock activity, around 2000 aftershocks of different magnitudes were recorded by this network in total. This data was analyzed in several papers (for example Triep, et al., 1995, Fuenzalida, et al., 1997), including hypocenters and focal mechanisms. Depths of the aftershocks were observed ranging from 0 to 15 km. The mechanism of Racha 1991 main shock was shown to be reverse faulting on a gently sloping (35°) plane. Also, strong earthquake mechanisms show reverse faulting with strike-slip components. This work was oriented to analyze existing earthquake data and see its correlation to a 2-3D structural model created for the area.

Acknowledgments. This work was funded by Shota Rustaveli National Science Foundation (SRNSF) (grant# FR-21-26377).

How to cite: Kvavadze, N., Alania, V., and Enukidze, O.: Earthquake data analysis in the Racha region, Georgia: Implication for 3D structural model active faults, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16075, https://doi.org/10.5194/egusphere-egu24-16075, 2024.

Giulia Patricelli, Maria Eliana Poli, Emanuela Falcucci, Stefano Gori, Giovanni Paiero, Enzo Rizzo, Andrea Marchesini, and Riccardo Caputo

We present the findings of a multimethodological study made on the Budoia-Aviano Thrust System conducted as part of the NASA4SHA PRIN Project “Fault segmentation and seismotectonics of active thrust systems: the Northern Apennines and Southern Alps laboratories for new Seismic Hazard Assessments in northern Italy”.

The NW dipping, SW-NE striking Budoia-Aviano Thrust System represents the southeast-verging external front of the Plio-Quaternary Eastern Southalpine Chain, occurring at the front of the western Carnic Pre-Alps, between Polcenigo and Montereale (PN).

The recent activity of the Budoia-Aviano thrust is evidenced by numerous geological and morphostructural features, including the exposure of Mio-Pliocene reliefs emerging from the Last Glacial Maximum alluvial plain, the upwarping of the LGM fan of the Artugna stream, and geomorphic anomalies of the surface hydrographic network (Poli et al., 2014).

Moreover, to identify sites to perform excavation aimed at exploring the Holocene movements of the thrust system, we performed multiscale geophysical investigations, such as Deep Electric Resistivity Tomography, Electric Resistivity Tomography and Ground Penetrating Radar across the entire thrust system. They revealed the presence of a series of possible north-verging shear planes, whose trace seemed to correspond to the more pronounced up-ward convex profile of the Artugna alluvial fan.

Based on geophysical results, two NNW-SSE paleoseismological trenches were excavated along selected GPR profiles. The trenches exposed late LGM-to-Holocene alluvial fan deposition of the Artugna stream. Notably, a paleosoil embedded in alluvial sequence yielded a 14C age interval between 16 Ky and 5 ky BCE.

In both trenches, the entire excavated late Quaternary succession was affected by a set of north-verging reverse planes, coinciding with the discontinuities identified in GPR profiles. In each trench, the total vertical displacement measured across all thrust planes is of about 4.5 meters, resulting from at least three displacement events occurred in the last 7,000 years. Moreover, the involvement of the bottom of the ploughed soil supports the hypothesis of the backthrust being activated during the MW 6.3 Alpago-Cansiglio earthquake (Rovida et al., 2022) as suggested by Galadini et al. (2005).

The integration of paleoseismology, photogrammetry, and high-resolution geophysics enabled the construction of a detailed 3D model of the Budoia-Aviano Thrust System, revealing a 20-meter-wide deformation zone on the hanging wall of the main south-verging Budoia-Aviano Thrust. In the perspective of seismic hazard assessment and regional planning, it is worth to consider the proximity of this active and capable fault to industrial complexes, urban centres, and vulnerable structures characterizing the Budoia and Aviano area.


  • Galadini, M.E. Poli, Zanferrari, A. (2005). Seismogenic sources potentially responsible for earthquakes with M≥ 6 in the eastern Southern Alps (Thiene-Udine sector, NE Italy). Geophysical Journal International161(3).
  • M.E. Poli, G. Monegato, A. Zanferrari, E. Falcucci, A. Marchesini, S. Grimaz, P. Malisan, E. Del Pin (2014). Seismotectonic characterization of the western Carnic pre-alpine area between Caneva and Meduno (Ne Italy, Friuli). DPC-INGV-S1 Project.
  • Rovida, M. Locati, R. Camassi, B. Lolli, P. Gasperini, A. Antonucci (2022). Catalogo Parametrico dei Terremoti Italiani (CPTI15), versione 4.0. Istituto Nazionale di Geofisica e Vulcanologia (INGV). https://doi.org/10.13127/CPTI/CPTI15.4

How to cite: Patricelli, G., Poli, M. E., Falcucci, E., Gori, S., Paiero, G., Rizzo, E., Marchesini, A., and Caputo, R.: First evidence of Holocene activity and surface diplacement of the Budoia-Aviano Thrust System in north-eastern Italy, unravelled through the integration of geological, geophysic and paleoseismological analyses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16527, https://doi.org/10.5194/egusphere-egu24-16527, 2024.

Ludmila Shumlianska and Victor Vilarrasa

There is a growing interest among seismologists on the nonlinearity of seismic processes, corresponding to the synergetic approach to the development of the Earth as a nonlinear, open, self-organizing system. In the analysis of very complex multi-component geological-geophysical systems, it is important to assess the degree of their nonlinearity based on a set of control parameters. For the analysis of the seismic process, we propose to use seismic-tectonic stress in the Earth's crust and lithosphere as a control parameter. Also, in the analysis of processes releasing tectonic stresses in the form of earthquakes, the synergetic of choosing the initial state becomes important.

To choose the initial state of the Earth's crust and lithosphere, we consider them as an oscillatory block-hierarchical system, interconnected and developing over time but differing in various layers of the Earth's crust – sedimentary, consolidated crust, lower crust, and mantle beneath the Moho boundary, as each layer has its lithological properties and is in different physical conditions, at least due to the change in pressure. Block sizes are determined based on the thickness of the layer, and vertical planes of the block are determined based on the morphology of the layer, as well as the presence of a fault inside the block. Changes in the seismic-tectonic deformation vector indicate a change in the initial state of seismic-tectonic deformation of each block. Thus, for the analysis of the nonlinear seismic process, we obtain a continuous series of changes in seismic-tectonic stresses in different layers and for each block of the layer. Thanks to the known time of deformation changes, as well as the known size of each block, we have an approximation of the nonlinear oscillatory process in the block-hierarchical system of the Earth's crust and lithosphere, manifested as seismicity. Within the designated time interval, the seismic-tectonic deformation process in each block follows a linear law. We have tested our methodological approaches to the analysis of the nonlinear seismic process in the example of the Crimean-Black Sea region. We have processed earthquakes contained in the new catalog of seismic events for the period 1970-2012, recalculated according to the Seismological Bulletins of the USSR and Ukraine. The method of Aki was used to determine the seismic-tectonic deformation regime by constructing averages foci by the signs of the first arrivals of P-waves taken from the bulletins. Time series of changes in seismic-tectonic deformation regimes in different layers of the Earth's crust and lithosphere show that each layer has its peculiarities of deformation but fits into the general context of tectonic processes in the region. One of the interesting features of the tectonic process in the region turned out to be the unexpected variability of regimes and their duration from 2 to 10 years in different areas of the Crimean-Black Sea region. An important consequence of our study is the definition of clear spatial-temporal frameworks for the analysis of the amounts of seismic energy release in each of the blocks, which will improve the quality of seismic risk assessment for individual regions.

How to cite: Shumlianska, L. and Vilarrasa, V.: Approximation of nonlinear seismic processes based on space-time series of changes in seismotectonic deformation regimes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-641, https://doi.org/10.5194/egusphere-egu24-641, 2024.

Posters virtual: Tue, 16 Apr, 14:00–15:45 | vHall X2

Display time: Tue, 16 Apr 08:30–Tue, 16 Apr 18:00
Chairpersons: Vanja Kastelic, Rita De Nardis, Federica Ferrarini
Nianfa Yang and Zonghu Liao

Characterizing the structures of buried faults is inherently challenging due to a lack of data. However, the seismic survey has demonstrated the potential to reveal geometrical features of faults in the subsurface. In this study, we utilized three-dimensional seismic data and its associated attributes of variance, edge detection, and azimuth for investigating the distribution and structural characteristics of the buried faults in the Bohai Basin, eastern China. The results indicate: (1) there are two 7-km NNE strike-slip carbonate faults (F1, F2, in the Figure) dominated in this region, with fault sub-systems of horst and graben, stepped combinations, and "Y"-shaped; (2) F1 fault is approximately 6.5km with a fault damage zone of about 0.75km in width, and F2 fault is about 7.5km with a fault damage zone of 1.0km in width; (3) The width of fault damage zones increases from south to north, with increasing fault displacement. The maximum fault displacements of F1 and F2 are estimated at 420m and 700m, respectively. We argue that fault displacement leads to the growth of fault damage zones, which potentially controls the evolution of fault architecture. The geometrical information from the subsurface may provide crucial insights for understanding the fault mechanisms and associated earthquakes.

Figure 1. (A) Seismic attribute map of edge detection and time structure showing the two carbonate faults (F1, F2); (B) Measured fault displacement and damage zone width along the fault striking direction of F1 and (C) F2.

How to cite: Yang, N. and Liao, Z.: Geometrical characteristics of buried fault damage zones in the Bohai Basin, eastern China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9839, https://doi.org/10.5194/egusphere-egu24-9839, 2024.