In this session, we welcome studies that focus on intraplate deformation using and/or testing methods to investigate surface and sub-surface evidence of Quaternary tectonic deformation and seismic sources characterization. These methods include but are not limited to geology, geomorphology, paleoseismology, geochronology, geophysics, observational/statistical seismology, seismic tomography, and remote sensing/geodesy. We encourage studies on indirect evidence of regional seismicity such as liquefaction, deformed stalactites, and patterns of regional landsliding.
Orals: Fri, 8 May, 10:45–12:25 | Room G2
Modern global warming causes enhanced melting of ice bodies and desiccation of lakes worldwide. The surface mass changes that occurred over the past decades were sufficiently large to cause discernible crustal deformation and alterations of seismicity patterns in the respective regions. As these climatically induced mass changes will continue to affect continental interiors in the future, assessing their impact on crustal deformation is crucial for future seismic hazard estimates. Here, we use numerical modelling to explore how such climate-induced unloading of Earth's crust may affect the earthquake cycle of thrust faults in continental interiors. In different 2D experiments, we vary the magnitude and width of the load, the duration of unloading, the length of the interseismic phase, the viscosity of the lower crust and the shortening rate to capture low-strain and tectonically active settings. All experiments show that the fault responds to unloading with increased coseismic slip. When unloading phases are equal to or shorter than the interseismic phase, the largest amount of slip occurs toward the end of the unloading period. Even if the load is removed during a single interseismic phase, enhanced coseismic slip may also occur up to thousands of years after unloading. Generally, the increase in coseismic slip is most pronounced for large and narrow loads, long recurrence intervals, low shortening rates and low viscosities of the lower crust. Our findings imply that climate-induced unloading has the potential to increase earthquake magnitudes, to shorten earthquake recurrence intervals, and to increase the earthquake hazard especially in low-strain regions.
Compared to earlier studies, our results provide first insights into the impact that is to be expected from the ongoing deglaciation of glaciers and ice sheets worldwide on the coseismic slip of faults and hence, on approximate earthquake magnitudes. With respect to modern climate change, our results indicate that climate-induced mass changes on Earth's surface have the potential to increase the seismic hazard in various geological settings.
How to cite: Brauns, A.-C. and Hampel, A.: Impact of climatically induced surface mass changes on the earthquake cycle of intra-plate thrust faults: Insights from numerical modelling , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3061, https://doi.org/10.5194/egusphere-egu26-3061, 2026.
While most earthquakes occur at plate boundaries, significant seismic events also occur within stable continental regions (SCRs), despite their low strain rates. These intraplate earthquakes, including rare but damaging events, raise fundamental questions about how elastic strain cumulates, is stored, and released in slowly deforming crust.
We develop a high-resolution seismicity catalog for southeastern Australia, a tectonically stable intraplate region, spanning 2005-2025. The catalog was constructed using the BPMF workflow which integrates backprojection-based detection, deep learning phase picking, nonlinear probabilistic relocation, and matched filtering. Relative to the Geoscience Australia catalog, our approach increases the number of detected events by approximately a factor of six and achieves a magnitude of completeness of Mc = 2.1, enabling robust statistical analyses over two decades. This enhanced resolution enables the exploration of seismicity statistics, clustering behavior, and temporal variability in a low-seismicity environment.
Using this catalog, we identify a statistically significant seasonal modulation of seismicity, with earthquake rates peaking during winter–spring and reaching a minimum during summer–autumn. The seasonal signal persists after declustering and is observed across a range of magnitude thresholds above completeness, indicating modulation of background seismicity rather than dominance by individual earthquake sequences.
Further analysis of GNSS displacement, GRACE-derived hydrological loading, and seismicity using multichannel singular spectrum decomposition identifies coherent temporal modes shared across all datasets. This correspondence suggests that hydrological loading drives elastic stress perturbations that are temporally linked to variations in earthquake occurrence. Together, these results imply that even modest seasonal and environmental stresses can modulate seismicity in stable continental regions, providing new insights into fault stability in intraplate settings.
How to cite: Mohammadi, F., Jolivet, R., and Beaucé, E.: Seasonal modulation of seismicity in an intraplate setting, the case of southeastern Australia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7627, https://doi.org/10.5194/egusphere-egu26-7627, 2026.
Earthquake cycle is a well-accepted concept when dealing with active faults bounding tectonic plates or large lithospheric blocks. Usually, along those faults the slip-rate is large enough, in the range of few cm/yr to few mm/yr, to produce earthquakes often enough at the geological timescale, thus allowing to discuss earthquake cycle.
Away from active plate boundaries, fault systems are less structured, slip-rate can be only few tenths of mm/yr, and earthquake return-time gets longer. Thus, discussing earthquake cycle becomes more difficult. In fact, even the possibility that successive earthquakes occur along the same fault becomes arguable.
Mongolia, at the northern limit of the India-Eurasia collision zone, far from plate boundaries, presents a unique opportunity to examine the relevance of the concept of earthquake cycle in intra-plate context.
The 1967 M7.1 Mogod earthquake occurred in central Mongolia. No unambiguous evidence of past earthquakes could be identified for certain in the morphology, suggesting that this event occurred as an isolated event on some remanent older geological structure. However, paleoseismological investigation shows that at least a previous event occurred along the same fault about 25 kyr BP.
In the NorthWest of Mongolia, in 1905, two M8 earthquakes occurred 14 days apart along respectively the Tsetserleg and the Bulnai faults. The rupture traces associated with each of those two events are only few kilometers apart. Slip-rate along the Bulnai fault was estimated to be about 3 mm/yr. Here we have determined that the slip-rate along the Tsetserleg fault is one order of magnitude lower, about 0.3 mm/yr. Accordingly, paleoseismological trenches along the Tsetserleg fault have revealed that the average earthquake return-time along that fault is about 6 ky, two to three times longer than along Bulnai. Our recent investigation along the Bulnai fault, using lacustrine paleoseismology, shows that such doublet as in 1905 is not unique in the history of this fault system and that, in fact, the fault system shows a pattern resembling a super cycle, similar to what has been document along more active fault systems. When integrating the Bulnai-Tsetserleg fault system together with other documented faults in western Mongolia, it appears that such earthquake super cycle might in fact affect the entire regional fault system, and not only Bulnai-Tsetserleg. The reason why those two faults, which are almost touching each others, did not rupture during the same earthquake remains unclear to date. Our recent monitoring of the microseismicity in the area where those two large faults intersect shows that the current regime of microseismicity is very different between Bulnai and Tsetserleg. Using this microseismicity, we might be able to better constrain the geometry of the Tsetserleg fault at depth, as well as the general fault structure in the intersection area. It might be the key to understand the 2 weeks time-delay between those two events and, overall, how stress build-up in this complex fault system to produce earthquake super cycles.
How to cite: Klinger, Y., Pinzon Matapi, N., Manceau, L., Benjelloun, Y., Bollinger, L., and Choi, J.-H.: Earthquake cycle far from plate boundaries: Learning from Mongolia earthquakes , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10000, https://doi.org/10.5194/egusphere-egu26-10000, 2026.
The largest strike-slip earthquakes ever recorded (M > 8) occurred in Mongolia in the 20th century, far from any plate boundaries. Rupture length-magnitude data indicate that the magnitude of these intraplate Mongolian events is, on average, ~0.5 magnitude larger than that of typical interplate earthquakes. The physical mechanisms that allow for such extra-large events remain mostly unresolved, largely due to the long return time of such events, hence the limited observational data. To address this, we employed a dual approach—numerical simulations with the PyQuake3D boundary element code (Tang et al., 2025) and theoretical analyses using the Rate and State Friction (Aging) Law on the spring slider—focusing on the role of slow plate rates. Our findings show that lower plate rates result in higher slip and greater stress drop, driven by enhanced fault restrengthening (healing). This healing, quantified by the state parameter, increases linearly with the inverse plate rate, in agreement with both analytical spring-slider models and 3D simulations. Critically, however, the observed GNSS plate rates of 1–3 mm/yr are insufficient to account for the ~0.5-unit magnitude excess relative to typical interplate earthquakes. We rigorously examine two scientific hypotheses: First, plate rates may be at residual levels (<1 mm/yr), perhaps reflecting far-field tectonic stresses or gravitational potential energy contrasts in Central/East Asia. Such extremely low driving rates could enable extended interseismic healing and thus unusually large stress drops and magnitudes. Second, the rupture width and depth of these intraplate earthquakes exceed those of typical interplate events. Our argument for this second scenario is strengthened by simulations of thermal pressurization: at high slip rates, rapid heating of pore fluids increases pore pressure and reduces the effective normal stress, thereby facilitating enhanced fault weakening and deeper rupture penetration. Our integrated numerical and theoretical approaches provide a robust basis for these hypotheses, advancing our understanding of the generation of remarkably large intraplate earthquakes and highlighting the importance of tectonic plate rate controlling earthquake magnitude.
Tang, R., Gan, L., Li, F., & Dal Zilio, L. (2025). PyQuake3D: A Python tool for 3-D earthquake sequence simulations of seismic and aseismic slip. Journal of Geophysical Research: Machine Learning and Computation, 2(4), e2025JH000871.
How to cite: Sopacı, E., Klinger, Y., and Dal Zilio, L.: Unraveling the Mechanisms of Giant Intraplate Strike-Slip Earthquakes in Mongolia: The Roles of Slow Plate Rates, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4863, https://doi.org/10.5194/egusphere-egu26-4863, 2026.
Singapore, a highly urbanized city–state of 6 million on a ~730 km2 island, is commonly believed to be “safe” from local earthquakes, with only distant Sumatran earthquakes thought to affect it. This view likely arises from the scarcity of recorded local events since Singapore’s founding in 1824, yet it overlooks two M ≥ 5 earthquakes within ~120 km to the north and northwest in 1922, and a 1948 event — reported only from the island’s southern–central area — that produced EMS intensity IV–V at multiple closely spaced sites, suggesting M ≈ 4 with a local source. Recent mapping has revealed numerous bedrock faults in Singapore, but their capability remains unstudied.
The Downtown Core of Singapore, in the southern–central part of the island, is built atop the low-lying Kallang Basin and adjacent reclaimed land. Sediments, likely MIS 5e (120 ka) and younger, fill the basin to 40 m depth in the west but thin eastward; immediately to the west, Cretaceous to Pliocene bedrock rises up to 50 m above sea level. The steep, unconformable contact between bedrock and overlying layers has been interpreted as either a sea cliff or an inactive fault. We hypothesize instead that it may be an active fault — part of a transtensional stepover in a longer dextral fault system.
Using five decades of legacy borehole data, we are mapping the subsurface architecture of Kallang Basin and drainages to the west. The thalwegs of at least two east-flowing buried paleochannels abruptly drop more than 10 m eastward near the topographic step, and they both appear to shift several hundred meters southward, though resolution is limited by available borehole data. Could this be explained by channel meanders and knickpoint migration, or does it implicate right-lateral transtensional displacement after the two paleochannels were incised? We are extending the investigation to nearby paleochannels to address this question.
How to cite: Meltzner, A. J., Newman, L. L., Huang, W., Foo, M. X. H., and Perry, M. K.: Does Singapore have active faults? Geomorphic and sedimentological investigations in an urbanized tropical city–state , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16483, https://doi.org/10.5194/egusphere-egu26-16483, 2026.
Identifying reliable indicators of past seismic activity in sedimentary archives is crucial for advancing paleoseismology and understanding earthquake-driven sediment deformation. However, micro-scale mineralogical features have remained underexplored. In this study, we present the results of a 12-month-long experimental program simulating earthquake-induced liquefaction using fine-grained siliciclastic sediments and varying chemical conditions.
A total of 108 samples were incubated under reducing conditions in plexiglass cylinders with either Fe(II) sulfate or FeO(OH) additions. Seismic shaking simulations were conducted at intervals using a controlled vibration table calibrated to reproduce magnitude 3.5 equivalents. Micromorphological and mineralogical analyses (SEM, EDS, and Raman spectroscopy) revealed the consistent formation of core–rim structures (CRS) across all experimental variants, regardless of water chemistry or iron source. These features were absent in control samples not subjected to shaking, as well as in naturally deformed sediments of non-seismic origin (e.g., storm-induced structures).
These results suggest that seismic energy may facilitate fluid redistribution, mineral precipitation, and the formation of distinctive microscale deformation features. To ground experimental findings, we compared them to field samples where CRS and sideritic textures were also documented within known SSDS. In contrast, similar structures were absent in sediment samples with storm events and rapid loading genesis.
This integrated field–experimental approach offers a novel framework for identifying microseismic indicators in the sedimentary record. While more research across diverse environments is needed, CRS may represent a promising addition to the paleoseismological toolbox, particularly for low-magnitude or poorly preserved events.
How to cite: Świątek, S., Lewińska, K., Pisarska-Jamroży, M., and Günter, C.: Simulating seismic liquefaction: A laboratory approach to identifying new paleoseismic markers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6382, https://doi.org/10.5194/egusphere-egu26-6382, 2026.
The South Armorican Southern Shear Zone (SASSZ), located in the northwestern France within the Armorican Massif, represents a major structural feature inherited from the Variscan orogeny. Although this region is now far from active plate boundaries and characterized by very low strain rates (i.e. 10-9 yr-1), it’s characterized by a moderate and diffuse seismicity associated with a few large events (up to M~5), suggesting possible fault reactivations.
This study integrates high-resolution mapping, geophysical investigations, and paleoseismic trenching to decipher the SASSZ structure and its possible quaternary activity. Based on high-resolution DEMs (LiDAR, RGEALTI from IGN), the analysis of morphological scarps along the SASSZ shows a wide range of surface trace complexities (bends, secondary splays, step-overs, gaps) associated with initial ductile and more recent brittle deformation. The width of the deformation zone around the SASSZ can reach up to 4 km, alternating between a localized and a distributed shear zone from the Pointe du Raz to Nantes. These measurements are in agreement with slope measurements performed along the SASSZ: the wider the deformation zone (> 0.3 km), the lower the maximum and mean slopes associated with the scarps.
Three geophysical surveys were conducted at sites of interest, along the SASSZ, in order to connect observed scarps at the surface with variations in crustal physical properties. They reveal distinct resistivity contrasts consistent with surface scarp locations. At the Moulin Quilly site, two paleoseismic trenches were excavated across two sub-parallel scarps. Trench 1 across the main surface scarp is not associated with a clear lithological contrast. However, the foliated granitoids are affected by several families of fractures oriented from N50°E to N120°E. The main structure is located at the base of the scarp and is made of sub-horizontal goethite deposits filling a N120°E trending open fracture of 10 cm wide, in the same direction as the SASSZ. Trench 2 crosses a secondary scarp and is divided in to three main structural units: (1) a slightly weathered granite unit preserving subvertical foliation and affected by cryogenic processes dated between 20 and 30 ka (from Optically Stimulated Luminescence dates on sand deposits); (2) a narrow transition unit, associated with a high-strain zone showing sub-vertical fabrics filled by sands; and (3) a fine-grained, strongly altered ultramylonite unit dipping 15°–25° northeast. All units are covered by an undeformed modern soil. From the subvertical fabrics in the transition unit, oriented samples were collected for microstructural analysis. Thin sections in the altered fabric show well-oriented minerals, alteration veins, and kinematic indicators that document higher deformation and alteration processes than in the granite. Further analyses will be conducted to quantify the strain distribution, in close comparison with the dating results.
Our study highlights a brittle deformation phase of the SASSZ, either linked to a recent tectonic activity, or associated with the Mesozoic regional extension, but the latter raises questions about the preservation of surface morphology through geological times. Future dating results of goethite deposits will help clarify whether the brittle fractures and their subsequent infilling reflect quaternary activity or an older phase of deformation.
How to cite: Vazifehdar, M., Perrin, C., Ritz, J.-F., Bonnin, M., Le Roux-Mallouf, R., Beucler, É., Mazzotti, S., Guérin, G., Malservet, H., Lenta, L., Pochat, S., Fligiel, D., and Conway, S.: First Paleoseismological Trench in Northwestern France: A Multidisciplinary Study along the South Armorican Shear Zone., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1639, https://doi.org/10.5194/egusphere-egu26-1639, 2026.
The active orogenic front of Southern Central Andes, at the latitude of ~32°-33°S, is located in the foothills of the Southern Precordillera. This region lies within a flat-slab subduction setting, which defines an area of very high seismic hazard characterized by Quaternary deformation and intense shallow-crustal seismicity. The active deformation in this area is focused on the easternmost thrusts of the Southern Precordillera, particularly along the Las Peñas-Las Higueras range (32°10’-32°45’S). The Las Peñas Thrust System (LPTS) bounds the range to the east and propagates towards the piedmont through both surface-reaching and blind thrusts. Numerous fault and fold scarps, characterized by a N-S strike and eastward vergence, have been active since Pliocene-Pleistocene times, with the most recent expressions located at the easternmost piedmont.
Toward the southern end of the Las Higueras-Las Peñas range, the thrust front corresponds to a transposed east-verging anticline, which becomes blind in the study area of Baños Colorados Creek. Before its geomorphic signature is fully lost towards the south, the morphotectonic expression of the LPTS in this creek shows discontinuous remnants of deformed quaternary alluvial deposits lying unconformably over neogene units. These deposits define fold-limb scarps ~300 m long and with scarp heights ranging from 20 to 45 m. Such exposures provide a unique opportunity to estimate shortening in neotectonic blind thrusts that exhume the bedrock. They also allow quantification of deformation in the hanging wall, where geological markers are commonly removed by erosion. This setting provides an exceptional opportunity to estimate deformation by considering the contribution of adjacent blocks (off-fault analysis), offering key insights into how quaternary deformation is distributed along the SCLP. Moreover, until now, the activity of this thrust system had been evaluated exclusively through indicators obtained directly at the fault zone and its immediate surroundings (on-fault), so this analysis represents a complementary and significant contribution.
We calculated quaternary shortening applying fault-propagation fold models based on the trishear concept using both the reconstructed topography of alluvial surfaces and stratigraphic layers as deformation markers, surveyed with high-resolution techniques (UAV and DGNSS). Shortening rates of 0.17-0.50 mm/yr were obtained for 13-16 ka surfaces, while minimum shortening of 15.6-36.76 m was estimated for an older surface (>13-16 ka and likely <200 ka).
Although estimating shortening rates on blind thrusts involves significant uncertainties, our results refine the characterization of the seismogenic sources affecting the surroundings of Mendoza city, one of the most populated in Argentina, where hazard assessments remain outdated and do not adequately incorporate blind-fault activity.
How to cite: Alvarellos, V., Costa, C., Sagripanti, L., Jagoe, L., Richard, A., and Folguera, A.: Assessing Quaternary shortening through trishear kinematic models at the Andean Orogenic Front, Southern Precordillera, Argentina, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-913, https://doi.org/10.5194/egusphere-egu26-913, 2026.
The Western Alps have been the focus of detailed seismological investigations based on instrumental records, revealing diffuse seismicity predominantly expressed as earthquake swarms (M < 3.5), mainly concentrated along major inherited shear zones. Geological evidence indicates that these structures are compatible with a main cumulated strike-slip motion, whereas GPS data and instrumental seismicity suggest predominantly vertical deformation. Historical archives further document several moderate earthquakes (M > 5), particularly in the Ubaye–Mercantour region. The Durance–Sérenne–Bersezio fault system is identified as the main active structure in this area and is therefore the focus of a multidisciplinary study aimed at detecting and characterizing co-seismic surface ruptures.
At the Lombarde Pass (Mercantour), a 2 km-long fault scarp displays geomorphological markers indicative of right-lateral strike-slip motion along the Bersezio fault. Several ERT profiles across the fault highlight a very localized low-resistivity zone in the bedrock beneath the morphological scarp. Paleoseismological trenches excavated across the fault scarp reveal a clear, single co-seismic rupture, with a maximum vertical apparent offset of ~1 m at the bedrock–Quaternary deposits interface. Radiocarbon dating (¹⁴C) of bulk sediment samples from three trenches constrains this event to 7–6 ka cal BP, consistent with post–Younger Dryas deglaciation.
These results suggest the occurrence of large-magnitude earthquakes (M > 6) in a region currently dominated by swarm seismicity and provide new constraints on fault kinematics and deformation localization at the boundary between the internal and external Alpine domains.
This study sheds new light on discussions held during the PATA Days 2022 field trip, where this unusual tectonic structure in the Western Alps raised passionate questions about its Holocene activity and seismic potential.
How to cite: Thomasset, C., Vassallo, R., Jomard, H., Larroque, C., Sue, C., Martinod, J., Metral, L., and Legal, A.-C.: Active Faults and Surface Ruptures in the Low-Strain Ubaye–Mercantour Region (Western Alps) , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12300, https://doi.org/10.5194/egusphere-egu26-12300, 2026.
Posters on site: Wed, 6 May, 16:15–18:00 | Hall X2
Southwest Portugal is the most seismically active region in Portugal mainland. Historical and instrumental seismicity, transpressive deformation accommodated by brittle structures (from which NNE-trending reverse left-lateral faults are the prominent ones), and uplifted marine landforms attest for the ongoing Quaternary crustal deformation. Geophysics highlights a positive gravimetric anomaly, consistent with the uplifted area. Simultaneously, geodesy suggests this region to be limited northward by a likely continuous right-lateral NW-trending structure, inferred to be 90 km long. However, this inferred structure is poorly understood, and southward partially overlaps a known active fault (São Marcos Quarteira) for ~50 km. The northward remaining length of 40 km lacks recognition of Quaternary deformation, despite a noticeable 50-100 m height scarp in the landscape along a ~10 km segment. This geomorphic feature has not been interpreted as an active fault, but as an inherent Variscan structure, possibly reactivated during the Miocene and since, evolved as a scarp retreated due to differential erosion promoted by the presence of Paleozoic quartzites, which are more resistant to erosion.
We present a preliminary analysis based on recently available 50 cm high-resolution lidar and revisited Plio-Quaternary data, together indicating evidence of likely subtle geomorphic deformation, which is expressed by small linear features NW-trending, some associated with changes of topography across a ~2km wide area. We propose these features to possibly correspond to subtle evidence of a cryptic fault system, likely to correspond to an inherited fabric, that has been reactivated. The newly discovered features will be investigated through combining geology, geophysics, and geochronology methods. Fault reactivation will be investigated through a detailed analysis of the damage zone and fault gouge, applying trapped-charges dating methods, namely OSL (Optically Stimulated Luminescence) and ESR (Electron Spin Resonance).
This work is supported by FCT, I.P./MCTES through national funds (PIDDAC): LA/P/0068/2020-https://doi.org/10.54499/LA/P/0068/2020, UID/50019/2025, https://doi.org/10.54499/UID/PRR/50019/2025 ,UID/PRR2/50019/2025 and by Marie Skłodowska-Curie Actions, European Union (project SEISMO-REACT, GA101211167).
Keywords: Quaternary activity, seismogenic sources, low strain deformation, cryptic structures, SW Iberia
How to cite: Marques Figueiredo, P., Ressurreição, R., Custódio, S., Neres, M., and Tsukamoto, S.: Subtle evidence of Quaternary fault reactivation in Southwest Iberia, Portugal , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14836, https://doi.org/10.5194/egusphere-egu26-14836, 2026.
The Tarim Basin is a multi-stage and multi-cycle superimposed basin developed on a stable craton basement. The Lunnan area is located in the central and eastern part of the Tabei uplift in the northern Tarim Basin. It has developed some fault systems with different strikes, properties, evolution stages. Based on the tectonic interpretation of 3D seismic data, we investigated the geometry ang kinematics of faults in Lunnan area.The formation and evolution of faults in Lunnan area occurred with the help of the pre-existing faults and were influenced by the regional compression/extensional direction transformation.
In the Neoproterozoic, the Tarim Basin was in an extensional tectonic background as a whole. The Lunnan area developed two rifts in the EW and NE directions, and the boundary normal faults were used as pre-existing structures. In the early Caledonian, the near NS direction Cambrian platform margin belt in the eastern part of Lunnan area is developed as the pre-existing weak belt.In the middle of the Caledonian, with a nearly NS-trending extrusion, the near EW-trending Lunnan fault grew and developed upward on the basis of the upper high-angle pre-existing fault surface of the early rift boundary normal fault, and the high-angle thrust fault was developed. Under the pure shear deformation mechanism, an X-type conjugate strike-slip fault system composed of two groups of NNE-and NNW-trending faults was developed.In the late Caledonian-early Hercynian, with a nearly NS-trending extrusion, the rapid uplift in the central and western parts of Lunnan area leads to a large amount of erosion of Ordovician strata to form a NEE-trending lithologic weak zone. Under the action of oblique compression, the pre-existing weak zone was activated by strike-slip and formed a series of NEE-trending strike-slip faults. At the boundary of the nearly NS-trending Cambrian platform margin zone in the eastern part of the Lunnan area, a nearly NS-trending fault was formed by the activation of the pre-existing weak zone under oblique compression.In the late Hercynian, under the NWW-trending extrusion, the near EW-trending Lunnan fault, NEE-trending and near NS-trending strike-slip faults continued to active.The NE-trending Lungu 7 fault inherits the high-angle fracture surface in the upper part of the NE-trending pre-existing rift normal fault, and develops a high-angle thrust fault. The pre-existing structure is not developed in the deep layer of the near EW-trending Sangtamu fault, and a thrust fault with a gentle dip angle conforming to the Anderson model is formed under the forward extrusion.With the change of regional compressive stress direction and the transformation from carbonate strata to clastic strata, the conjugate X-type strike-slip fault gradually disappeared.In the early Indosinian period, the Tarim Basin still showed a near NS-trending compressive stress background. In the middle and late stages, it was transformed into a NW-trending extensional background. The early stage of the fault still inherited the compressional nature, and the late stage superimposed extension-strike slip activity.In the Yanshanian-Early Himalayan period, the NW-trending extensional tectonic background induces the formation of tenso-shear echelon faults in the shallow layer.
How to cite: Cao, M., Li, W., and Zhuo, W.: The development regularity and genetic mechanism of intracratonic faults under the control of regional tectonic background and pre-existing structures--A case study of Lunnan area in northern Tarim Basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4159, https://doi.org/10.5194/egusphere-egu26-4159, 2026.
The Issyk-Ata fault is a key active structure in northern Kyrgyzstan and represents the principal seismogenic source affecting the densely populated Chui basin, including Bishkek, the capital city of the Kyrgyz Republic. In 2025, a sequence of moderate earthquakes with magnitudes exceeding Mw 4 occurred along the fault, providing clear evidence of ongoing deformation and renewed seismic activity. Owing to its proximity to major population centers, the Issyk-Ata fault has been consistently identified as the dominant contributor to regional seismic hazard. The northern Tien Shan is an actively deforming intracontinental region characterized by distributed crustal shortening associated with far-field convergence. Long-term geodetic measurements indicate north–south shortening rates of up to ~20 mm/yr, resulting in recurrent strong earthquakes along the northern Tien Shan margin. The Issyk-Ata fault extends approximately 120 km in an east–west direction and forms the northern boundary of a young and actively growing anticline separating the Kyrgyz Range foothills from the Chui basin. As the youngest major fault system in the region, it transects the southern part of Bishkek, where extensive urban development has largely obscured its surface geomorphic expression. To better constrain the seismic behavior of the Issyk-Ata fault, we integrate high-resolution remote sensing, detailed geomorphological and structural field investigations, and paleoseismological trenching, with a particular focus on the Dzhal area of the Kyrgyz Range. These combined datasets allow systematic mapping of surface ruptures, measurement of cumulative vertical displacements, and identification of fault segmentation. Chronological constraints derived from optically stimulated luminescence and radiocarbon dating reveal at least two surface-rupturing earthquakes during the Holocene. Empirical scaling relationships suggest that these paleoearthquakes reached moment magnitudes of approximately Mw 6.6–7.1. Geological and geomorphological analyses in the Dzhal area indicate a long-term fault slip rate of ~1.15 mm/yr, reflecting sustained Quaternary deformation. The fault exhibits pronounced along-strike variability in rupture style and displacement, with individual segments recording distinct seismic histories and patterns of activity.
These results demonstrate that the Issyk-Ata fault accommodates deformation through segmented rupture behavior typical of low-strain intraplate settings. The occurrence of large Holocene earthquakes, together with recent moderate seismicity in 2025 and the fault’s direct interaction with the urban area of Bishkek, underscores the need for refined, segment-based seismic hazard models. Improved understanding of seismogenic sources and Quaternary deformation along the Issyk-Ata fault is essential for advancing seismic hazard assessment and risk mitigation strategies in the northern Tien Shan.
How to cite: Ha, S. and Cholponbek, O.: Holocene Paleoearthquake Records of the Issyk-Ata Fault near the Densely Populated Chui Basin: Evidence from the Dzhal Area, Kyrgyz Range, Tien Shan, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4708, https://doi.org/10.5194/egusphere-egu26-4708, 2026.
The Raša Fault is a major right-lateral strike-slip structure in the northwestern Dinarides, representing a key active fault in a low- to moderate-strain region. Despite its prominent geomorphic expression and recognized hazard, its seismic history remains poorly constrained. To address this gap, we conducted a multi-trench paleoseismological investigation, including radiocarbon and luminescence dating, to characterize past surface-rupturing earthquakes and assess recurrence intervals of large-magnitude events previously unknown in the region. Our results reveal repeated strong earthquakes during the Late Pleistocene and Holocene, which based on worldwide empirical data likely exceeded magnitudes 6 or even 6.5. Although some age determinations are still in progress, preliminary results from four trenches indicate that at least five surface-rupturing events occurred in the last ~20,000 years, with several clustered in the past 6,000 years. Recurrence intervals vary widely, from a few hundred years to several millennia, reflecting both temporal clustering as well as locally incomplete stratigraphic records due to dynamic environment. These findings highlight the importance of multiple trench sites and extensive dating to resolve complex paleoseismic histories on faults in low- to moderate-strain regions. Our results also underscore the seismogenic potential of the Raša Fault and emphasize its relevance for regional seismic hazard assessment.
How to cite: Jamšek Rupnik, P., Mencin Gale, E., Rupar, L., Jež, J., Preusser, F., Novak, A., Uršič Arko, A., Anžel, A., Maslač Soldo, J., and Atanackov, J.: New insights on large past earthquakes on the Raša Fault in NW Dinarides (Slovenia) revealed from multi-trench paleoseismic study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5677, https://doi.org/10.5194/egusphere-egu26-5677, 2026.
Fluvial denudation along large valleys moves important sedimentary volumes across continents over time, inducing isostasy-related stresses due to unloading of the crust. This work reports numerical experiments with a visco-plastic lithosphere aimed at understanding the patterns and evolution of stresses and uplift associated with differential erosion in wide, tectonically quiescent valleys over 30 million years (Myr). We simulate valleys 30 to 150 km wide and a few hundred meters deep, and observe horizontal deviatoric stresses with maximum magnitudes larger than 10 MPa, the distribution of which is largely controlled by the degree of mechanical coupling between upper crust and lithospheric mantle, associated with the viscosity of the lower crust. The upper crust in simulations with a weakly-coupled lithosphere is strongly compression-dominated beneath the valley. In contrast, scenarios with higher lithospheric coupling are characterized by similar amounts of compression and extension over crustal depths. Moreover, our simulations suggest that a significant part of these stresses persists for tens of Myr after erosion rates have diminished, gradually focusing around the central valley due to progressive viscous relaxation in the lower crust and lithospheric mantle. The adequacy of an elastic plate model in reproducing modeled surface uplift and subsurface stresses in response to fluvial incision is discussed in terms of lithospheric rigidity for each scenario, revealing important departures between stresses predicted from flexural theory and those resulting from our simulations. We conclude that large rivers are an important factor to consider when studying stress fields in stable continental regions, especially if the valley is being actively excavated, and that these might contribute to moderate seismic activity in intraplate settings.
How to cite: Baiadori da Silva, F. and Sacek, V.: The influence of fluvial incision on the lithospheric stress field: a numerical approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5409, https://doi.org/10.5194/egusphere-egu26-5409, 2026.
Intracontinental reverse faults in Otago and South Canterbury, Aotearoa-New Zealand, have complex surface morphologies. The Dunstan Fault and Fox Peak Fault are expressed at the surface by multiple parallel to sub-parallel fault traces. These traces can be hundreds of meters apart from each other and span a deformation zone up to 2-3km in width. We ask the following questions: Do all traces rupture together in each ground rupturing earthquake, or do they rupture independently? If traces rupture independently, is it random which trace ruptures in a given event, or is there a spatio-temporal pattern? What is the likelihood of a new trace rupturing in the next large earthquake? We use paleoseismic techniques to constrain the timings of past earthquakes on each trace. The results are compared to see if the same earthquake ruptured multiple traces. If we can tease out any spatio-temporal patterns, we may be able to answer the question: In a future ground rupturing earthquake, which trace/traces will rupture? The results have implications for fault zonation and fault displacement hazard analysis of intracontinental reverse faults in Aotearoa-New Zealand and beyond.
How to cite: Travers, A., Stirling, M., Stahl, T., Griffin, J., Clark, D., Ostermeijer, G., O'Neill, L., and Gorman, A.: The Past, Present and Future of Multi-Trace Reverse Faults in New Zealand, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10012, https://doi.org/10.5194/egusphere-egu26-10012, 2026.
As part of the revision of the seismic hazard investigations for the Panamá Canal Expansion Project in the Pacific new set of locks, we completed a detailed archeoseismological investigation on the existing ruins of the ancient Panamá La Vieja, which was affected by an earthquake of intensity ≥VIII in AD 1621 (6.9 Mw). Additionally, geomorphic, paleoseismic research together with the analysis of the historical and instrumental seismicity in central Panama allowed to develop different macroseismic scenarios (ShakeMaps) to check the suitability of the different proposed seismic sources in this zone of the isthmus where convergence rates are low (c. 0.7 – 0.8 mm/yr).
The archaeological site of Panamá La Vieja is the only place in which that event is truly documented by the historical report of the vicar Requejo Salcedo (earthquake witness), but also for the different earthquake archaeological effects (EAEs) preserved in the buildings of the present ruins. There were only eight stone buildings and about seventeen masonry buildings (convents, city jail, hospital, etc.) in the year 1621. The old cathedral was under construction then and the rest of the houses were wooden structures. At present, the convents of San Francisco, Sto. Domingo, La Compañia de Jesús, La Concepción and the old Hospital, display severe earthquake damage, the last three buildings practically collapsed. The measured EAEs are (a) penetrative and conjugate fractures in masonry walls; (b) tilted walls; (c) rotated and displaced masonry blocks; and (d) a large amount of dipping broken corners in stone blocks. The structural measures of the EAEs indicate a N10-20E regular orientation for ground movement, consistent with the offshore current seismic activity in the Pacific south of the city. There the NNW-SSE left-lateral Las Perlas Fault (LPF), responsible for two c. 5.0 Mw instrumental events (years 1971 and 2017), that struck the Panama City (c. 15 -20 km far away) with intensity VI MM. This scenario it is not consistent with other proposed seismic sources, such as the right-lateral Pedro Miguel Fault (PMF), cutting across the new set of locks of the Panamá Canal onshore. ShakeMaps (USGS methodology) elaborated to check the PMF and LPF seismic sources strongly suggests that the PMF 6.9 Mw earthquake solution do not explain the oriented damage recorded in the archaeological site. On the contrary, the offshore LPF solution only will need of a lower 6.0 – 6.5 Mw event to explain the destruction at the archaeological site with PGA values c. 0.4g (VIII MM). In addition, the LPF solution can account for the small tsunami flooding the littoral sector of the old city soon after the event described in the historical chronicle of Requejo Salcedo during the evening of 2 May1621. Recent research denies the Holocene and historical and activity of the PMF and our analyses strongly suggest that offshore faults (i.e. PLF) in the Gulf of Panama can be more suitable and realistic candidates than the PMF as the source of the 1621 earthquake.
Contribution supported by the Spanish Research Project I+D+i PID2021-123510OB-I00 (QTECIBERIA-USAL) funded by the MICINAEI/10.13039/501100011033/
How to cite: Silva Barroso, P. G., Elez, J., Roquero, E., Gómez Barreiro, J., and Ayarza, P.: Archeoseismological study of the AD 1621 “Panamá La Vieja” Earthquake: insight on the seismic source (Panamá, Central America) , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5810, https://doi.org/10.5194/egusphere-egu26-5810, 2026.
The Hälsingland earthquake cluster, on the east coast of central Sweden, represents a puzzling case of intraplate seismicity in a tectonically stable continental region. The cluster measures approximately 100 km in length and extends in a near-linear trend from inland in the southwest into the Baltic Sea in the northeast, oriented approximately 35 degrees to the coastline. Unlike many of the earthquake clusters that occur in Sweden, the cause of the Hälsingland seismicity is not well understood, as it has not been possible to associate the cluster with any distinct geological feature, such as old deformation zones or a younger glacially triggered fault. Between September 2021 and September 2025, a temporary network consisting of thirteen broadband seismic stations was deployed in the Hälsingland region in an effort to establish better understanding of the drivers behind the Hälsingland seismicity. During this period, 873 earthquakes were detected and manually analyzed in the region, with local magnitudes ranging from -1.0 to 2.3. Using travel-time data from local quarry blasting, we derived a new, regional seismic velocity model and relocated all the earthquakes in the new model. The earthquake depths range from near-surface down to 39 km, with approximately 80% occurring at depths between 5 and 20 km. As part of this project, a previously unknown glacially triggered fault (GTF) system, the Mörtsjö fault system, was identified in the Hälsingland region, approximately 25 km north of the Bollnäs fault, the southernmost confirmed GTF in Sweden. Both the Mörtsjö and Bollnäs GTFs are small and located outside the most seismically active part of the Hälsingland region. However, relative earthquake relocations reveal multiple events which may be generated by movement on the faults. Waveform cross-correlation analysis shows moderate correlation between most earthquake pairs in the Hälsingland cluster but also identifies multiple families of closely spaced, highly correlating earthquakes, including a single family consisting of more than 30 events. The spread of the earthquake focal mechanisms does not clearly indicate a dominant fault orientation. While strike-slip motion dominates, multiple examples of both reverse and normal motion also occur, often in close proximity to each other. Inverting the focal mechanisms for the earthquake-generating stress field indicates a strike-slip stress state with a NW-SE direction of maximum horizontal stress. The inversion also suggests mostly E-W striking fault planes, suggesting that the faults rupturing in the Hälsingland earthquakes are not oriented in agreement with the general lineament of the cluster. We find that most of the Hälsingland seismicity does not occur on a well defined fault but rather in an active zone which extends to large depth but is only vaguely associated with changes in large scale geological features such as magnetic properties and Moho thickness.
How to cite: Eggertsson, G., Lund, B., Guðmundsson, Ó., and Roth, M.: The puzzling Hälsingland intraplate earthquake cluster in central Sweden, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17331, https://doi.org/10.5194/egusphere-egu26-17331, 2026.
The Himalayan fold-thrust belt, formed due to the collision between the Indian and Eurasian plates, during ~50 Ma, shows the long-term convergence with crustal shortening, duplex development, out-of-sequence thrusting and deformations of the foreland basins. The outer Arunachal Himalaya, in the southern part of the Eastern Himalayan Syntaxis, is one of the most tectonically active areas in the Himalayan arc. Frequent earthquakes of several magnitudes, accompanied by associated ground failures, liquefactions, and subsidence in the foreland basins, as well as significant changes in river courses, indicate prominent surface manifestations that reveal ongoing deformations. Documentation of uplifted and truncated terraces, unpaired terraces, soft-sediment deformation structures, warped and tilted Quaternary layers, strath terraces and fault scarps collectively suggest active deformation along the frontal fold-thrust belt. This study integrates morphometric analysis, river terrace mapping and characterisation of paleoseismic evidences to assess active tectonics in the area. Key morphometric indices derived from remotely sensed datasets, including mountain-front sinuosity (Smf), drainage basin asymmetry (Af), transverse topographic symmetry factor (T), valley floor width-to-height ratio (Vf), stream length-gradient (SL), hypsometric integral (HI), and elongation ratio (El), consistently shows strong tectonic influence in the area. The narrow, V-shaped valleys and steep channel gradients further support ongoing upliftment in the region. Lineament mapping reveals structural trends parallel to the Himalayan Frontal Thrust (HFT) that align with the regional stress field. It is worth mentioning that the upliftment along the HFT is not uniform, leading to the development of unpaired terraces. Additionally, NW-SE and NE-SW transverse faults have segmented the mountain front, that triggered channel offsets and changes in the river widths, and also contributed to the formation of minor pull-apart basins. These transverse structures, along with the south-verging thrust system, are crucial for distribution of strain across the frontal Arunachal Himalayas. Documentation of active scarps, deformed terraces, and related landscape features are crucial for understanding the relation between surface deformation, fault activity, and seismic risk in this highly active part of the orogenic belt.
Keywords: Active tectonics, HFT, Geomorphic evidences, Frontal Arunachal Himalaya.
How to cite: Bora, G., Mahanta, B. N., and Goswami, T. K.: Characterisation of the active tectonics in the outer Arunachal Himalaya, India: Insights from tectono-geomorphic analysis , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-487, https://doi.org/10.5194/egusphere-egu26-487, 2026.
The Sudetic Marginal Fault (SMF) is a prominent tectonic structure, clearly expressed in the morphology of the NE part of the Bohemian Massif in SW Poland. The outcrop of the SMF core zone was recently exposed within the Góry Sowie Massif in the Pieszyce area (Poland) during earthworks carried out in 2022 and 2024. In this unique exposure, a distinct displacement of the contact between the underlying Sowie Góry gneisses and the overlying Quaternary sediments was recognized. The main fault zone steeply dips at 70°to the ENE. In the southern fault block, no sedimentary cover was observed, whereas Quaternary sediments attain a thickness of up to 4.5 m close to the main fault on the northern side.
Tectonically altered gneisses occur within the main fault zone, while the highly weathered crystalline basement beneath the sedimentary cover in the northern block is cut by numerous secondary tectonic zones filled with grayish fault gouge. Within these zones, we documented vertical veins of (up to 15 cm) filled with overlying deposits, including isolated gravel-sized clasts. Some of the observed veins penetrated bedrock to the depth of at least 1 m. Bedrock and fault-zone materials were systematically analyzed using XRF and XRD methods. Elevated concentrations of mercury and arsenic were observed in the fault zones. Micromorphological analysis of two oriented thin sections collected directly from the fault gouge, together with mineral phase identification based on XRD analyses of fault-gouge samples, reveals pervasive grain-size mixing and syn-deformational clay mineral realignment, indicating repeated brittle deformation under near-surface conditions.
Sedimentological studies, including facies and granulometric analyses, allowed to classify the sediments overlying the northern block as preglacial(?), fluvioglacial, and glacial origin. Petrographic analysis of clasts >10 mm revealed a dominance of locally derived material, with a minor contribution of Scandinavian clasts in the upper part of the profile. Clast imbrication measurements in preglacial sediments indicate transport in the WNW-ESE and NE-SW directions, interpreted as progradation of a locally sourced alluvial fan from the Sowie Góry Block. Measurements of cross-bedding and erosional channel axes within the fluvioglacial sediments indicate transport mainly towards the SSE, consistent with meltwater flow from the Scandinavian Ice Sheet margin and mixing with locally supplied Sudetic material derived from the crystalline basement. OSL dating of selected samples confirmed the Middle Quaternary deposition age of the fluvioglacial sediments in the Pieszyce area and provides direct evidence for Quaternary activity of the Sudetic Marginal Fault.
Keywords: Sudetic Marginal Fault, Sudetes, neotectonics, Quaternary sediments, OSL dating
How to cite: Grochmal, B., Sobczyk, A., Słomski, P., Belzyt, S., Kowalski, A., Badura, J., Fiałkiewicz, M., and Dąbrowski, M.: Quaternary neotectonic activity of the Sudetic Marginal Fault in Pieszyce area, Góry Sowie Massif (NE Bohemian Massif, SW Poland) , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10571, https://doi.org/10.5194/egusphere-egu26-10571, 2026.
Within stable continental interiors such as the Australian, South African or North American cratons, seismicity occurs in the absence of measurable tectonic loading. This seismic activity has surprising characteristics. Relative to plate-boundary seismicity, it is more sensitive to seasonal load variations and it seems to develop aftershock sequences sustained for a much longer duration. Both observations are unexpected evidence that the crust in regions with no active tectonics has still found a way to reach a critical stress state, allowing it to be modulated by small variations of stress and to sustain long, efficient cascades of seismicity. Different mechanisms may be considered to explain how the crust reaches failure in the (supposed) absence of loading, that is either by reducing strength or by increasing stress by other means than tectonics. Among others, we propose (i) a progressive weakening of the crust through a brittle-creep-like mechanism, slowly driving cracks to near-critical conditions, (ii) the slow development of a deviatoric load due to erosive exhumation. Understanding which mechanism may dominate the activity, the activity timescales associated and which observables can be used to constrain them is key to make an assessment of the seismic risk in stable continental interiors.
In this work, we explore patterns of activity in high-resolution catalogs of seismicity in Eastern Australia, the Northeastern USA and Northwestern France, as well as in acoustic emissions catalogs from brittle-creep of natural rocks in laboratory experiments. Using aftershock and triggering patterns in time and space, we attempt to constrain elements of the stress-to-failure distribution in the crust and how it evolves in time. These observations are then compared to the order-of-magnitude predictions from both (i) brittle-creep and (ii) erosive theories on how the crust fails in the absence of tectonic loading.
How to cite: Farge, G., Mohammadi, F., Beaucé, É., and Jolivet, R.: Exploring patterns and mechanisms of seismicity in the absence of tectonic loading, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20166, https://doi.org/10.5194/egusphere-egu26-20166, 2026.
ABSTRACT
Oman occupies a uniquely complex tectonic setting at the northeastern edge of the Arabian Plate, where all major plate boundary types converge. However, present-day intraplate deformation in the region remains poorly quantified. To address this, we processed GPS data from 57 continuous stations, mostly spanning from 2014 to 2023, to construct a high-resolution crustal strain map. We derived interseismic velocities within a stable Oman reference frame and used an elastic dislocation model to estimate fault coupling and slip rates on major structures. Velocity gradients were then interpolated to calculate continuous 2D strain rates. Our results reveal the highest tectonic activity along the northern Hawasina Thrust and the Masirah ophiolite front (Batain complex), where the crust undergoes WNW–ESE to NW–SE directed extension at rates up to 50 nanostrain/yr. In contrast, the central and southwestern parts of Oman experience crustal shortening (~20 nanostrain/yr) in NNW–SSE and NE–SW orientations. Significant shear strain (up to 20 nanostrain/yr) localizes along the northern segment of the Hawasina thrust sheet, which our modeling indicates is a normal fault with a ~11 km locking depth and a slip rate of ~4.5 mm/yr. This geodetically derived strain pattern correlates spatially with major structural traces, confirming that these faults currently accommodate regional tectonic loading. This study provides the first geodetic evidence for present-day strain localization on major faults within the northeastern Arabian Plate. The results establish a measurable basis for reassessing seismic hazard in a region often considered tectonically quiescent and demonstrate the value of dense GPS networks for modeling strain in slowly deforming continental interiors.
How to cite: AL-Habsi, Z., Friedrich, A. M., and Abolghasem, A.: Modeling Present-Day Strain Accumulation and Fault Activity in The Northeastern Arabian Plate, Oman: A GPS Geodetic Analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13834, https://doi.org/10.5194/egusphere-egu26-13834, 2026.
The Palomares fault (PLF) in SE Spain is the first tectonic structure with recognized quaternary activity within the Iberian Peninsula in the early 1970 decade. Together with the well-known Lorca-Alhama de Murcia fault (LAF) delineates the so-called Eastern Betic Shear Zone, a large (>180 km length) crustal scale left-lateral strike-slip fault zone crossing-cut across the Betic Cordillera in a SSW-NNE orientation and subject to present low strain and convergence rates (< 4 mm/yr). Whilst the LAF displays clear evidence of Holocene tectonics and historical to recent seismic activity (i.e., 5.1 Mw 2011 Lorca Earthquake), the PLF present scarce to null instrumental seismic records. However, the PLF shows relevant geomorphic and stratigraphic evidence of past Middle to Late Pleistocene seismic activity and scarce historical seismic records. Only the strong EMS X 1518 AD Vera Earthquake in Almería (6.7 Mw) can be theoretically related to this fault, but present seismic records are nearly null.
The present contribution provides support for the recurrent paleoseismic activity of the PLF during the Middle-late Pleistocene with clear morpho-stratigraphic records between the vicinity of the village of Palomares to the south (Almería) to northern localities, such Purias (Murcia). This means about 60 km of Quaternary tectonics nicely preserved in a fault segment, which has been recently considered no-faulted by theoretical approaches based on geophysical-gravity data. Whatever the case, the present contribution indicates that quaternary faulting occurs along the entire fault length, but the degree of fault activity (in timing and slip) largely decreases from south to north. Fault kinematics also varies from nearly pure left-lateral strike-slip to a dominant reverse component south to north according to the progressive westerly bending of the PLF trace. Is in the northern segment where older deformations are present and erosional processes (i.e. gullying) nicely interplayed with fault activity generating deep furrows along the fault zone later refilled by renewed alluvial sediments and subsequently deformed by repeated paleoseismic activity. In other words, the PLF shows unique examples of the erosive record of past earthquakes, illustrating the potentially rich variety of geomorphic evidence for past seismic activity in low strain regions, even in absence of the typical tecto-sedimentary fault records, common in southern locations of this fault.
Acknowledgements: This contribution is supported by the Spanish Research Project I+D+i PID2021-123510OB-I00 (QTECIBERIA-USAL) funded by the MICIN AEI/10.13039/501100011033/.
How to cite: Silva Barroso, P. G., Elez, J., Bardaí, T., Pérez-López, R., Rodríguez-Pascua, M. Á., Giner, J. L., and Roquero, E.: The geomorphic erosive record of past earthquakes: Examples from the Palomares Fault (Almería-Murcia, SE Spain)., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2839, https://doi.org/10.5194/egusphere-egu26-2839, 2026.
Studies of damaging earthquakes that occurred in Peninsular India over 50 years suggest that they occur along favourably oriented pre-existing weaker planes/faults in the ongoing compressional tectonic regime. Many of these pre-existing structural weaknesses developed until the collision between India and Eurasia reversed the style of movement post-Miocene, from a general normal sense of movement to either reverse or strike-slip. However, identifying neotectonic signatures from the plate interior, especially in tropical climatic regions, is very challenging since erosional agents can nullify the signature of tectonic movement. The present article focused on identifying active faults from the zones of two major NW-SE trending structures, separated by about 1600 km, that are being widely deliberated for the reconstruction of the Gondwana assembly, viz., the Mahanadi Shear Zone and the Achankovil Shear Zone.
The NW-SE trending Neoproterozoic Mahanadi Shear Zone opened up as rift basins around 300 to 100 million years ago for the deposition of Gondwana sediments. Our studies at two locations, ~140 km apart along the strike direction, indicate that the litho-contact between crystalline and sedimentary can be easily made out through geomorphic expressions, drainage patterns, and nature of vegetation. The study identified badland topography and structurally controlled meandering of drainages in the area, which are associated with neotectonic adjustments. The brittle faulting, with a reverse sense of movement, identified in crystalline rocks shows wide damage zones with gouge injecting into fractures and also onto the surface, where the soil cover is negligible. The extrusion of gouge is preserved as a conical heap above the surface level. The study also identified the gouge injection into Quaternary sediments at several locations. The reverse faulting is also reflected in the laterite cap that developed over younger sediments deposited over the Gondwana formation.
The NW-SE trending Achankovil shear zone is a major Pan-African structure located close to the southern end of peninsular India, cutting through the Western Ghats. Earlier studies identified two major faults at the southern end of this shear system, viz., the Thenmala and Thenmala South faults, for which there exists a sharp geomorphic expression in the Western Ghats. However, its expression in the plain area east of the mountain terrain is very weak. The present study identified badland topography, abandoned river paths, and anomalous natural depressions associated with these faults as results of neotectonic adjustments in this area. Perturbation of land into the sea along the strike continuity of both faults in the southern side and the drainage divide between them are the other significant effects of neotectonism associated with these faults. Field investigations identified surface ruptures along the faults, preserved in hard laterite that was observed above crystalline rocks. Studies based on the trapped aeolian deposits within hard laterite suggest at least two faulting events within the last 4400 years.
The present series of studies identified a host of geomorphic and structural evidences that can be used to identify active faults. These clues can be touchstones for future studies in the field of active fault evaluation in such terrains.
How to cite: John, B. and Singh, Y.: Subtle structural testimony of Active faults: examples from Peninsular India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7175, https://doi.org/10.5194/egusphere-egu26-7175, 2026.
Posters virtual: Wed, 6 May, 14:00–18:00 | vPoster spot 1a
EGU26-21385 | ECS | Posters virtual | VPS30
Constraining Late Pleistocene to Holocene seismic fault activity in NE Iberia: The value of integrating complementary techniques in a low-strain regionWed, 06 May, 14:18–14:21 (CEST) vPoster spot 1a
The northeastern margin of the Iberian Peninsula, extending from the Vallès-Penedès Graben to the Valencia Depression, constitutes a passive margin related to the opening of the Valencia Trough during the Neogene. It comprises a series of extensive basins bounded by several mountain ranges, where numerous NNE–SSW-oriented normal faults are present, commonly associated with mountain fronts. Previous studies show that some of these faults, such as the El Camp fault, remain active, although at very low slip rates, as low as 0.02 m/kyr for Late Pleistocene.
Recent analyses of high-resolution Digital Elevation Models (DEMs) have revealed several additional morphological escarpments crosscutting different Quaternary alluvial fan systems across the region. These scarps, found from the Sant Jordi Plain to the La Salzadella Basin, share the same orientation as the Neogene faults, suggesting a common tectonic origin. They are discontinuous, arranged in a right-stepped pattern, and locally display vertical offsets of up to 8 m. Furthermore, several geomorphic features indicate recent tectonic activity, including aligned fissures within the fans and entrenched channels developed on the upthrown block that fade out after crossing the escarpments. Each family of escarpments exceeds 10 km in length, with important implications for the seismic hazard of the region.
Geophysical surveys (ERT, GPR, SRT, HVSR, and MT), validated with borehole data, confirm the presence of faults beneath each analysed escarpment system. At the Vinaixarop escarpment, for instance, ERT profiles revealed a steeply dipping discontinuity plane with a vertical offset of approximately 40 m affecting upper Pliocene sediments.
The faulted alluvial fans are interpreted as Lower to Middle Pleistocene in age and are mainly composed of carbonate gravels. Paleoseismological trenches excavated at four sites (L’Ampolla, Vinaixarop, and two at Sant Rafael del Riu) on different scarps revealed consistent evidence of late Quaternary faulting, such as ruptured strata. Additionally, ground-based hyperspectral cameras (400–1700 nm) were deployed on trench walls as an ancillary tool to map faulted
stratigraphic layers and to detect subtle coseismic deformation. As sedimentation on the fans ceased by the Middle Pleistocene, subsequent activity has been primarily recorded through the deformation of pedogenic features (calcretes), commonly found in the study area. To constrain the timing of this activity, U–Th dating was performed on fault-related carbonates and deformed calcretes. Preliminary results indicate that tectonic activity along these faults persisted at least until the Late Pleistocene. However, a deformed colluvial wedge and the presence of open fissures observed on trench walls suggest Holocene activity.
Additionally, three cosmonuclide depth-profiles were sampled to date displaced geomorphic surfaces, and hence estimating the long-term slip rates of the faults. Ongoing analyses aim to demonstrate Holocene seismic activity and to further characterize paleoearthquakes and their seismic parameters.
In summary, studies of active tectonics in regions of very low strain are inherently challenging, especially when recent sedimentation is scarce and pedogenic processes are intense. Nevertheless, this work highlights that integrating multiple complementary techniques is the most effective approach to address such settings.
How to cite: Ollé-López, M., García-Mayordomo, J., Gallego-Montoya, J., Molins-Vigatà, J., Bellmunt, F., Gabàs, A., Andrés, J., Macau, A., Hasözbek, A., Martí, A., Figueiredo, P., Rodés, Á., García, D., Ortuño, M., and Masana, E.: Constraining Late Pleistocene to Holocene seismic fault activity in NE Iberia: The value of integrating complementary techniques in a low-strain region, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21385, https://doi.org/10.5194/egusphere-egu26-21385, 2026.
