The Aderklaa- and Seyring faults are part of a series of normal faults accommodating active extension west of a releasing bend of the Vienna Basin strike-slip system. The faults are located in the urban area of Vienna and adjacent Lower Austria. The proximity to the Vienna city centre (ca. 13 km), high population density and the focus on the area for future urban development result in high vulnerability and risk. Exploration for deep geothermal energy in the immediate vicinity of the faults adds a further risk factor. The fault system was therefore the subject of focused paleoseismological investigations including spatial fault mapping of industrial 3D seismic, high-resolution near-surface geophysics, stress modelling (Levi et al. 2023, IJES), drilling and trenching.

The active fault system consists of two sets of (N)E- and (S)W-dipping normal faults, respectively, both offsetting Pleistocene terraces and capturing local streams. While cryoturbation prevents the identification of individual paleoearthquakes for the (S)W-dipping Aderklaa Fault (slip rate: 0,03 mm/y; Weissl et al., 2017, Quaternary International), three trenches (GER1 to GER3) revealed a detailed Late Pleistocene paloeoearthquake history for the (N)E-dipping Seyring faults. GER2 and GER3 exposed four event horizons in loess dated to 25 ka, 17-16 ka (two events) and 15 ka cal BP. Sand intrusions in a rupture surface of the youngest event prove liquefaction and seismic deformation. The exposed faults are antithetic secondary faults with respect to the W-dipping main normal fault formed by crestal collapse of a rollover above the main fault. The main fault does not cut up through the exposed section but offsets the base of a 400-200 ka old river terrace for 7 m and causes a 50-70 cm downward flexure of a 25 ka old paleosurface. Slip rates calculated independently from both markers are 0,02 mm/a, the average recurrence interval of paleoearthquakes is ca. 6.000 a. Trench GER1 excavated a second fault of the Seyring system with a normal offset of the base of aforementioned terrace of 8 m. Oppenauer et al. (2022; Pangeo 2022) identified six events that occurred between 32 and 14.8 ka BP corresponding to an average a recurrence rate of approximately 5,300 years. Two events formed colluvial wedges with 20 cm height each allowing to estimate the associated magnitudes with M≈6,4. The average slip rates calculated from the offset terrace and trench data are 0,02 mm/a. Whether the paleoearthquakes identified in GER2 and GER3 are time-correlated with the events recognised in GER1 is subject of current investigation.

We conclude that the Aderklaa and Seyring fault system consists of a minimum of three active faults with slip rates of 0,03-0,02 mm/a. Each fault needs to be taken into account in the assessment of regional earthquake hazard and risk. Available data for hazard modelling include: reliably determined fault kinematics consistent with the regional seismotectonic model of the Vienna Basin fault system; fault  geometries accurately determined from 3D seismic down to ca. 4 km depth; fault slip rates; average earthquake recurrence intervals; and recent stresses derived from a borehole-derived 1D stress model.

How to cite: Decker, K., Weissl, M., and Flores-Orozco, A.: Paleoseismology of the Seyring-Aderklaa Fault System, Vienna, Austria , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12744, https://doi.org/10.5194/egusphere-egu25-12744, 2025.

Paleoseismology is a vital tool for the study of earthquake hazard and active tectonics. Its application in the context of Late Quaternary basaltic volcanoes encounters considerable limitations due to the inherent highly dynamic nature of such systems. Etna volcano, however, provides an ideal setting for such studies. In particular, the densely populated Mt. Etna eastern flank record frequent surface faulting earthquakes and aseismic fault creep, which result in significant offsets of well-dated historical landforms and stratigraphy, including lava flows, interlayered pyroclastic deposits, and anthropic structures. This allows for the analysis of fault slip rates across various time scales.

We present the first paleoseismological results along the Fiandaca Fault, the source of the 26 December 2018, Mw 4.9 Fleri earthquake. We excavated two exploratory trenches along the coseismic surface ruptures at the Collegio Fiandaca site. Analysis of trench walls allow identifying, besides the 2018 event, two historical surface faulting events. The youngest one occurred in the period 1281-1926 CE, and most likely during the 8 August 1894 Fiandaca earthquake. The oldest one, previously unknown, occurred in the Early Middle Ages (757-894 CE). This paleoseismic evidence strongly suggest increased seismic activity along the Fiandaca Fault in the last centuries. In order to verify this hypothesis, we conducted detailed morphotectonic analyses and throw rate measurements along the Fiandaca and other capable normal faults in the Mt. Etna eastern flank. Throw rates mean values show an increase from 1.4 mm/yr during the 15-3.9 ka time interval to 3.4 mm/yr between 3.9 ka and the Greek-Roman period, with a further increase since the late Middle Ages, reaching 10 mm/yr. This trend suggests a very recent growth in flank instability, in agreement with current geodetic data but also with historical eruptive activity.

These findings highlight an increase of the associated geological hazards along the inhabited eastern flank, emphasizing the need for further research and a multi-hazard approach to risk assessment and land planning for Mt. Etna and similar volcanic regions.

How to cite: Tringali, G., Bella, D., Livio, F., Blumetti, A. M., Groppelli, G., Guerrieri, L., Neri, M., Adorno, V., Pettinato, R., Trotta, S., and Michetti, A. M.: New paleoseismological findings along the Fiandaca Fault reveal the dynamics of Etna volcano's eastern flank, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16385, https://doi.org/10.5194/egusphere-egu25-16385, 2025.

In the 1964 Mw 9.2 megathrust earthquake in South Central Alaska, a megathrust splay fault on Montague Island had co-seismic surface rupture and up to 10 meters of . The offshore expression of this fault has been proposed to be the source of a in Seward. Splay faults can transfer seismic slip from a megathrust rupture to the surface and thus influence tsunami-genesis. The unique exposure of an active megathrust splay fault on Montague Island provides us with the opportunity to investigate the geometry and structure of the fault zone and document the mechanical properties and alteration from wall rock to fault core. Outcrop-scale investigations have identified a 150m wide fault zone, intensely fractured host rock and , an 8m wide continuous gouge zone, and large-scale deformation variability across the fault. Microstructural analysis has documented cataclasite formation, foliated fault gouge, directional shear sense, and clay alteration and formation due to faulting processes. These results insight into co-seismic or aseismic slip behaviors, faulting related mechanical or chemical alteration, and slip weakening/strengthening behaviors. This identification of structural variation and deformation mechanics can be used to constrain empirical constitutive equations that dictate faulting and rupture behavior, provide real-world constraints for large-scale numerical models, and inform interpretations of offshore splay faults imaged by seismic reflection data.

How to cite: Fintel, A., Tobin, H., and Haeussler, P. J.: Outcrop to Microscale Field Observations of a Unique On-Land Exposure of an Active Long-Lived Tsunamigenic Splay Fault in South Central Alaska, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13000, https://doi.org/10.5194/egusphere-egu25-13000, 2025.

The Tell Atlas Mountains are characterized by active tectonics related to
oblique convergence along the Africa-Eurasia plate boundary. The region is
affected by a NNW-SSE to NW-SE transpressive regime, with shortening rates of
2.2 ± 0.5 mm/yr determined from tectonics and paleoseismology, confirmed by
GPS-derived rates of 1-3 mm/yr. The deformation manifests mainly as NE-SW to
E-W trending fault-related-folding structures, affected predominantly Mio-Plio-
Quaternary basins within the Tell Atlas. The Chelif is one such basins which has
experienced a major El Asnam Mw 7.1 seismic event in 1980 along Sara El
Maarouf blind fault. 40 km to the west lies a comparable structure, which is the
Boukadir fault related-folding , responsible for the moderate 2006 Tadjena
earthquake Mw 5.0, causing some damage in Abou El Hassan, Bouzghaïa and
Tadjena villages. The focal mechanism of the 2006 Tadjena earthquake, as well as
that of the 1980 El Asnam event, revealed a reverse fault with a lateral component.
The dislocation model indicated that the Tadjena event is related to a rupture along
a 6 km segment of the entire 35 km Boukadir fault. In this study, we aim to assess
seismic potential of the Boukadir FRF using a plural approach combining geology,
tectonic geomorphology, elastic modeling an Interferometric synthetic aperture
radar (InSAR). Field observations have shown that the Quaternary deposits reveal
progressive unconformities and form terraces along main streams, while the
conglomeratic levels of upper Pliocene are strongly tilted, dipping up to 70° to the
SW where the Boukadir fault is assumed to pass. The study of morphometric
parameters showed a disturbed hydrographic network on the Boukadir fold. We
used InSAR methodology to detect small surface displacements caused by the
Boukadir FRF genesis. PS-InSAR processing of Sentinel data from 2016-2022 in
ascending and descending orbits was employed. Analysis of mean displacement
rates in line of sight (LOS) directions showed subsidence south of the Boukadir
fault system and uplift to the north, consistent with our field investigations and
tectonic geomorphic analysis along the Boukadir reverse fault. Our results reflect
tectonic activity and seismic potential of the Boukadir FRF. They can be integrated
to the Tellian FRF models and contribute to updating the Algerian seismic hazard.

How to cite: Bagdi Issaad, S., Miloudi, S. F., and Meghraoui, M.: The Boukadir active fault-related folding: Active tectonic markers andInSAR analysis (Tell Atlas, Northern Algeria)., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-520, https://doi.org/10.5194/egusphere-egu25-520, 2025.

Recent developments in single grain K-feldspar IRSL (Infra-Red Stimulated Luminescence) dating of sediment coupled to high resolution surface morphology provides significant new opportunities to explore active fault, and fault system, behaviour over multiple earthquake cycles. Results from California and New Zealand demonstrate systematic variations in fault slip rate over multiple earthquake cycles. In New Zealand, sub-parallel faults within the Marlborough Fault System demonstrate complementary behaviour; as slip rate on one fault reduces, slip speeds up on another or others. The construction of these records depends on developing detailed chronologies of multiple slip events on each fault, and on reconstructing past fault slip with geomorphic markers. The approaches that our interdisciplinary collaborative team has developed to do this will be presented, along with an assessment of the reliability of the reconstructions, in particular the dense chronologies that are developed. New avenues to add further resolution and robustness to these approaches will be considered, along with innovative ideas to co-develop palaeoclimate and environmental reconstructions, and build an improved understanding of sediment grain transport trajectories.

How to cite: Rhodes, E., Dolan, J., Ivester, A., McGill, S., and Van Dissen, R.: Improved understanding of spatio-temporal variations in fault activity using high resolution geomorphic markers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14194, https://doi.org/10.5194/egusphere-egu25-14194, 2025.

The South Yellow Sea (SYS) has experienced many moderate-strong earthquakes in the last four decades. On 17 November 2021, an Mw5.0 earthquake with a dextral strike-slip mechanism occurred in the Yancheng area of the SYS, resulting in various degrees of ground motions in many coastal cities of eastern China, such as Shanghai and Nanjing. The epicenter of the Yancheng event was characterized by the prevalent emplacement of hydrothermal vent complexes and strike-slip faults. However, the relationship between the strike-slip fault, the associated fluid migration and the Yancheng earthquake is poorly understood. Based on multichannel seismic profiles and well data acquired over the last 10 years, this study conducted a comprehensive investigation of the seismogenic strike-slip fault of the Yancheng event. Subsequently, the role of fluid migration along strike-slip faults in triggering this earthquake was analyzed. The result suggested that the active faults in the SYS were characterized by a conjugate fault system, the NNE trending strike-slip faults and the NW trending strike-slip faults. The NNE-trending fault F1 passing through the epicenter of this event is suggested as the seismogenic fault. The fault F1 and other active faults in the SYS were probably inherited from the pre-existing strike-slip faults formed during the late Jurassic to early Cretaceous. Various hydrothermal vent complexes were identified near the fault F1. Seismic facies analysis suggested that the hydrothermal activities could have continued to the Miocene and Quaternary in the vicinity of the fault F1, almost simultaneous with the reactivation of the fault F1 and other active strike-slip faults. The reactivation of the pre-existing faults and the associated hydrothermal events were suggested to be caused by the subduction of the Pacific Plate. We proposed that the hydrothermal fluid may have migrated along the F1, which further enhanced the faults’ slip, and finally triggered the Yancheng Mw 5.0 earthquake and other historical events in the SYS.

How to cite: Hu, P. and Yang, F.: The role of fluid migration along strike-slip faults in triggering the 2021 Mw 5.0 Yancheng earthquake in the South Yellow Sea, East Asia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3018, https://doi.org/10.5194/egusphere-egu25-3018, 2025.

Faults in the brittle upper crust are thought to primarily grow due to repeated earthquakes. To understand better fault growth during incremental slip events we analyse geometric and displacement data for timescales of individual earthquakes (since 1840 AD) to millions of years on New Zealand active faults. The active faults studied are from connected networks with a range of orientations, lengths (1–200 km), displacement rates (0.1–27 mm/yr) and slip types. Our data indicate that individual earthquakes produce slip on multiple faults with variable sizes, orientations and slip types; in some cases these earthquakes cross tectonic domain boundaries. Earthquakes generally produce partial rupture of reactivated bedrock faults and show little evidence of tip propagation, characteristics most closely resembling the constant-length fault growth model, with growth primarily achieved by increases in cumulative slip. Earthquake slip profiles display a range of shapes with one or more maxima. High gradients along faults and approaching fault tips reflect coseismic slip transfer to nearby faults. These high slip gradients are consistent with stress interactions and kinematic coherence between faults during individual earthquakes (i.e., timescales of seconds to minutes). Coseismic increments of slip increase with rupture length and are described by a power function of ~0.5, while the power function for cumulative displacement and final length is ≥1. An important consequence of these divergent power functions is that larger faults broadly accrue their finite displacements in more earthquakes than smaller faults. The increase in earthquake number with fault size is achieved by a combination of shorter recurrence intervals and longer faulting histories for larger faults. We believe that our New Zealand observations have global application.

How to cite: Nicol, A., Walsh, J., Mouslopoulou, V., and Parker, M.: Fault growth Models: observations from historical earthquakes and active faults in New Zealand , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13171, https://doi.org/10.5194/egusphere-egu25-13171, 2025.

Strike-slip faults often display complex, along-strike geometries with branches and splays, which play an important role in earthquake rupture processes. Based on field examples of active faults and analogue models, we show that this complexity can be caused by lateral changes in lithology. We use geomorphic and ground-penetrating radar analysis of the Awatere Fault in the South Island of New Zealand, to demonstrate that the number of branch faults and width of the fault zone increases as the fault passes from bedrock to unconsolidated alluvial sediments. With analogue models, we test whether this observation can be reproduced. The setup replicates strike-slip faulting using two plates translated at a constant rate of 3 cm/h relative to each other. This establishes a velocity discontinuity at the centre of the model that leads to the formation of a strike-slip fault zone in the overlying analogue material. Each model incorporates a lenticular sand body that represents a less consolidated sedimentary basin above basement, which is represented by corn starch. During multiple model runs, fault branch-points formed at the boundary between the two different materials in the analogue model, thus confirming that the geometric complexity of strike-slip faults is strongly controlled by lateral changes in the properties of the host material. Two processes could play a role here: 1) the frictional properties change abruptly at the lithological boundary, which promotes the nucleation of branch faults and, 2) the angle of internal friction of the material changes across the lithological boundary, thus fostering fault-bend formation at this point. Our analogue modelling results also show that the thicker the sedimentary basin on top of the basement, the wider the zone of deformation. This implies that the lateral passage of active faults from bedrock into unconsolidated material leads to a widening of the deformation zone, which is confirmed by the ground-penetrating radar survey across the Awatere Fault. The results of the study can be applied to situations in which active strike-slip faults run into sedimentary basins, such as the Newport-Inglewood Fault in the Los Angeles Basin. Based on our analogue models, we postulate that the more diffuse, near-surface en-echelon structure in the northwest of the Newport-Inglewood Fault is a function of the higher sediment-basin thickness, compared to the distinct fault trace that is developed above the shallower basin-fill in the southeast. 

How to cite: Brandes, C., Tanner, D., Igel, J., and Nicol, A.: Lithological control on geometric complexity of active continental strike-slip faults – insight from GPR surveys and analogue modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3740, https://doi.org/10.5194/egusphere-egu25-3740, 2025.

The 2024 Noto Peninsula Earthquake (M7.6) on January 1, 2024 occurred beneath the northern coast of Noto peninsula, central Japan. Focal mechanism of the mainshock, geodetic and seismic observations and their analyses indicate that it was a reverse fault-type earthquake which ruptured > 150 km long. In order to identify the structural characteristics and origins of nearshore and offshore active faults in the eastern Sea of Japan, including off the Noto Peninsula and Toyama trough, we performed structural analysis on offshore and onshore-offshore multi-channel seismic profilings (MCS) obtained before the earthquake. The structural and mechanical boundaries between continental and oceanic crust near the rift axis and surrounding marginal normal faults have been the most important rift structures related to the Miocene back-arc opening in terms of seismotectonics in the Sea of Japan, as demonstrated by the Nihonkai Chubu earthquake of 1983 (M7.7). We also estimate that the eastern portion of the fault plane that caused the 2024 mainshock has a fault bend or concave up shape at a depth of about 10 km, in conjunction with coseismic deformation and aftershock distribution. The discrepancy between the thrust geometry and the spatial distribution of the former shorelines of the MIS 5 marine terraces may indicate that the tectonic uplift of the peninsula at the intermediate (~105 yrs) timescales may be caused by both the 2024 thrust fault and nearby positively reactivated rift structures beneath the Toyama trough, which are underlain by a mechanical "core" made of high-Vp lower crust probably due to mafic intrusion. In the presentation,  we also discuss the late Cenozoic tectonic background of this back-arc seismically active region based on onshore and offshore seismic geophysical data. 

How to cite: Ishiyama, T., No, T., and Sato, H.: Active tectonics, tectonic background, and thrust geometries around the source regions of the 2024 Noto Peninsula earthquake (M7.6), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14116, https://doi.org/10.5194/egusphere-egu25-14116, 2025.

Dynamics of lithospheric plates resulting in localisation of tectonic stresses and their release in earthquakes provides important information for seismotectonics. Numerical modelling of the dynamics and earthquake simulations have been changing our view about occurrences of large earthquakes in a system of major regional faults and about the recurrence time of the earthquakes. Models of tectonic stress generation and its transfer, as well fault dynamics models will be overviewed. I shall present the 35-year efforts in modelling of lithospheric block-and-fault dynamics allowing for better understanding how the blocks react to the plate motion, how stresses are localised and released in earthquakes, and how plate driving forces, the geometry of fault zones, and fault physical properties exert influence on the earthquake dynamics, clustering, and magnitudes. Also, this presentation will illustrate how data analysis and quantitative modelling contribute to advancing seismic hazard assessment.

How to cite: Ismail-Zadeh, A.: Lithosphere dynamics and earthquake modelling for seismotectonic analysis and hazard assessments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5231, https://doi.org/10.5194/egusphere-egu25-5231, 2025.

The East Anatolian Fault Zone (EAFZ), a 580-kilometer-long transform plate boundary within the Anatolia-Arabia-Africa triple junction system, has been the site of several destructive earthquakes. This includes the February 2023 Mw7.8 and Mw7.5 Kahramanmaraş earthquake doublets, which occurred as part of a recent seismic sequence. The aftershock sequence indicates that the first earthquake on the Pazarcık fault segment triggered the second earthquake on the Sürgü Fault, located approximately 100 km north of the initial epicenter. Diffuse deformation in the region is evident by part of this latest earthquake sequence, nucleated on the northern splay of the main EAFZ. These two main shocks were subsequently followed by strong aftershocks in the region, including the October 16, 2024 Mw6.0 Malatya Earthquake. Given the region's seismic potential, complex deformational behavior evident from recent earthquake doublets, and distribution of post-seismic deformation following the latest activity, a proper seismic hazard assessment that incorporates seismological and geodetic constraints is of great importance in the region. The present work endeavors to provide a quantitative discussion on the seismic hazard potential in the EAFZ, with a particular focus on the Malatya region. To achieve this aim we utilize a multi-scale data set comprising precise aftershock distribution around Malatya, 3D Coulomb stress change pattern, spatio-temporal b-value distribution, the InSAR-based surface deformation of the recent Malatya earthquake and 3-D variation of seismic P- and S-wave speeds in and around broken fault segments in the region.

How to cite: Kaya-Eken, T., Zoroğlu, Ç. S., Gedik, M., Tekiroğlu, G., and Özener, H.: Seismic Hazard Implications on the East Anatolian Fault following the October 16, 2024 Mw6.0 Malatya Earthquake , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12543, https://doi.org/10.5194/egusphere-egu25-12543, 2025.

This contribution explores the approach and results of crustal stress and strain rate comparisons across various geological contexts. Since the early 1980s, researchers have investigated the broad applicability of these comparisons in regions with high, intermediate and low deformation rates. The primary data sources for these studies include focal mechanisms and velocity fields from GNSS stations, although additional datasets, such as geological structural data, are also utilized. The stress field is obtained through formal stress inversion, while the strain rate is derived from optimal interpolation of GNSS velocities. The results are compared in terms of stress and strain axes to understand the relationship between them. The increasing number of seismic and geodetic stations over the years has significantly enhanced data quality and coverage, further improving the validity and reliability of this approach.

The multidisciplinary nature of this approach underscores its versatility. In seismotectonics, it has proven valuable for detailed kinematic characterizations of plate boundaries (Stephan et al., 2023) and faults (Zoback and Zoback, 1980). In seismic hazard assessment, it aids in identifying areas with relatively high strain rates but low seismic activity, suggesting the discussion of potential seismic gaps (Chang et al., 2003). In geodynamics, the approach enhances our understanding of the deformation forces driving earthquakes (Palano et al., 2013; Pietrolungo et al., 2024). Furthermore, it has significantly contributed to fault mechanics by providing insights into how crustal segments respond to stress loading (Bird et al., 2006). In volcanic contexts, the approach has been particularly effective in elucidating the interplay between tectonic stress and magmatic processes (Keiding et al., 2009). These findings highlight the need to distinguish between short-term deformation from episodic events and long-term tectonic forces to better understand complex geological dynamics (Townend and Zoback, 2006).

Drawing from an extensive body of literature, this review offers insights into the challenges and opportunities of applying digital technology to stress and strain comparisons. It summarizes key findings, evaluates their potential, and critically discusses their limitations, providing a nuanced perspective on the approach’s applications and future directions.

How to cite: Pietrolungo, F., Madarieta-Txurruka, A., Lavecchia, G., Cirillo, D., Andrenacci, C., Bello, S., Sparacino, F., and Palano, M.: Stress and strain comparison: methods, results and applicability, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16888, https://doi.org/10.5194/egusphere-egu25-16888, 2025.

Iberia represents the westernmost tectonic region involved in the Eurasia-Nubia convergence, playing a key role in shaping the plate tectonics of the westernmost Mediterranean. It is affected by alpine deformation in the Pyrenees in the north and the Gibraltar Arc in the south, alongside other internal mountain ranges. Toward the south, the region is further deformed in the Atlas and Tell Cordilleras.

This study aims to analyze and compare the active stress and strain fields with seismicity and active faults to discuss the geodynamic processes, determine the main active structures, and assess how stresses are accommodated, whether seismically or aseismically.

The stress field is derived from an extensive compilation of available crustal earthquake focal mechanism solutions across the region. The data are inverted using the STRESSINVERSE software (Vavryčuk, 2014) on a 0.5° spaced grid, requiring a minimum of eight focal mechanism for cell. The geodetic dataset includes nearly 500 continuous GNSS stations, with time series spanning up to 25 years, along with 25 episodic GNSS stations. Data processing is performed using GAMIT/GLOBK (Herring et al., 2010), following the methodology outlined by Palano et al. (2020). The resulting velocity field is enhanced with other available velocity fields to increase station density. The strain field is estimated on a 0.5° grid according with the methodology illustrated by Shen et al. (2015). Finally, to compare the stress and strain fields, s_Hmax and e_Hmin are estimated.

The results show that the region is affected by NW-SE compression, causing irregular deformation. Shortening of up to 4–5 mm/yr, parallel to the compression, is mainly concentrated in southern Iberia, along the Eurasia-Nubia plate boundary, accompanied by frequent low-to-moderate seismicity. In southwestern Iberia and in the Tell Cordillera, the NW-SE compression can result in moderate-to-high seismicity. Meanwhile, both central-northern Iberia and the Atlas Cordillera undergo limited deformation under the general NW-SE compression. The first is characterized by zones of low seismicity linked to normal and strike-slip faults. The Atlas Cordillera, in contrast, exhibits sporadic but moderate-to-high magnitude seismicity related to thrusting. The stress pattern significantly changes in the westernmost Gibraltar Arc and in the Pyrenees. The Gibraltar Arc characterises by a slightly rotated NNE-SSW striking compressional axis, while the shortening aligns E-W. The former observation and the absence of seismicity in the front of the arc suggest aseismic displacement to the west of the Gibraltar Arc, perpendicular to the Eurasia-Nubia convergence. Finally, the data show that the shortening in the Pyrenees has ceased, and stress suggest a N-S extension, likely related to isostatic readjustment of the mountain range.

• Herring, T. A., et al. (2010). GAMIT Reference Manual, GPS analysis at MIT, Release 10.4, Dept. of Earth Atmos. and Planet. , Mass. Inst. of Technol., Cambridge, MA, 171pp.
• Palano, M., et al. (2020). Geopositioning time series from offshore platforms in the Adriatic Sea. Scientific Data, 7(1), 373.
• Vavryčuk, V. (2014). Iterative joint inversion for stress and fault orientations from focal mechanisms.Geophysical Journal International, 199(1), 69-77.
• Shen, Z. K., et al. (2015). Optimal interpolation of spatially discretized geodetic data. Bulletin of the Seismological Society of America, 105(4), 2117-2127.

How to cite: Madarieta-Txurruka, A., Prieto, J. F., Escayo, J., Pietrolungo, F., Peláez, J. A., Galindo-Zaldívar, J., Henares, J., Sparacino, F., Ercilla, G., Fernández, J., and Palano, M.: Stress and strain fields in the Iberian Peninsula and adjacent Mountain Ranges, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19452, https://doi.org/10.5194/egusphere-egu25-19452, 2025.

Accurately characterizing Earth's geothermal gradient is critical for a variety of geophysical and environmental studies. Earth’s surface temperature can affect the geothermal gradient to significant depths over long time periods and, in turn, affect calculations of, for example, the brittle-ductile transition depth. It is expected that the geotherm has stabilised with respect to the long-term average surface temperatures, not current or relatively current averaged measurements. Therefore, when using the surface temperature, it is important to account for long-term behaviour without losing spatial variability.

Datasets containing predicted global mean surface temperatures (GMST) throughout the Holocene epoch, spanning the last 12,000 years, offer valuable insights into historic temperature conditions but often lack in spatial resolution. Meanwhile, modern surface temperature data, derived from advanced sensors and satellite observations, provides high-resolution snapshots of global temperatures over relatively short time periods. By combining these sources, we can create a dataset that not only retains the current spatial distribution but also integrates historical thermal data into a single dataset. This high-resolution global mean surface temperature dataset (HRGMST) would more closely match the current stabilised geothermal gradient.

This hybrid dataset would help to refine models which use Earth's surface temperature distribution, providing a more accurate representation of the subsurface thermal state. The improved dataset can offer significant insights for geophysical research, including better assessments of subsurface heat flow, energy resources, and tectonic processes.

This work will outline the development of a new HRGMST dataset that integrates predicted Holocene averages with contemporary direct temperature measurements to more accurately represent Earth's long-term average surface temperature. It will outline the methodology behind the dataset creation and discuss challenges in merging paleoclimate data with contemporary measurements. The enhanced dataset promises to improve the understanding of Earth's internal temperature structure and support more precise calculations in geothermal energy exploration and geophysical modelling. We will explore several methods of combining long-term GMST data with high-resolution data, testing the effect of each method using an existing global model and our software package ShellSet, discussing the changes which arise due to the new surface temperature dataset along with seismotectonic implications.

How to cite: May, J. B., Carafa, M. M. C., and Bird, P.: A new high-resolution global surface temperature dataset – combining recent measurements with global mean surface temperatures through the Holocene epoch, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14055, https://doi.org/10.5194/egusphere-egu25-14055, 2025.

We present a novel supervised learning approach for fault detection in subsurface geological slopes. Synthetic faulted slopes were generated using Delaunay triangulation via the Computational Geometry Algorithms Library (CGAL), enabling precise control over model parameters. A total of 24 features, encompassing local geometric attributes and neighborhood analyses, were introduced for classification. A Support Vector Machine (SVM) classifier was employed, achieving high precision and recall in identifying fault-related features.

Application of the method to real borehole data, specifically elevations of buried stratigraphic contacts, demonstrated its effectiveness in detecting fault orientations. However, challenges remain in distinguishing faults with opposite dip directions. The study highlights the necessity of addressing 3D fault zone complexities for more robust fault identification.

Despite these challenges, the proposed supervised approach represents a significant advancement over traditional clustering-based methods, demonstrating its potential for detecting faults across diverse orientations. Future work will focus on incorporating more complex geological scenarios and refining fault detection methodologies to improve accuracy and applicability. This work underscores the promise of machine learning in advancing fault detection in geological studies.

How to cite: Michalak, M., Gerhards, C., and Menzel, P.: SubsurfaceBreaks: A supervised detection of fault-related structures on triangulated models of subsurface slopes , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4840, https://doi.org/10.5194/egusphere-egu25-4840, 2025.

Faults and fractures can be observed across vast spatial (nm to km) and temporal scales (years to Myrs), often evolving into highly complex networks. Once established, they fundamentally alter the rheological behavior and transportative properties of the host rock. This makes them a critical focus for applications such as seismic hazard assessment, geothermal reservoirs, and carbon storage. The architecture and evolution of fault networks can be studied using recent advances in remote sensing and modelling. Numerical models provide insight into both the top-view and depth expression of faults, while analogue models simulate geodynamic processes to shed light on their mechanics. Furthermore, the topography of natural faults can now be captured with unprecedented accuracy using Tandem-X radar satellites for example. However, the sheer data volume and the continued reliance on manual fault mapping remain major obstacles in fault network analysis.

Here we present Fatbox v2.0, the Fault Analysis Toolbox. This python-based, open-source library is able to extract and characterize individual faults as well as entire fault networks from diverse datasets. Fatbox contains a large number of functions to map and analyze faults and fractures automatically from different types of observational data, geodynamic models and analogue models. Fault systems are described as 2D networks (graphs) using the coupling of nodes, defined by their position, and edges that connect the nodes. This allows us to capture the full complexity of natural fault and fracture systems. It is then possible to analyse features such as fault splays, intersections, and relay ramps, from topography, strain, strain rate, or model cross sections. In addition, the toolbox contains a number of functions to track faults through time, which is particularly useful for modelling data. This library is complemented by a wide range of functions that allow the geometry of the fault network to be filtered and analysed with high spatial resolution.

How to cite: Gayrin, P., Wrona, T., Brune, S., Neuharth, D., Molnar, N., La Rosa, A., and Naliboff, J.: Fatbox v2.0 - the Fault Analysis Toolbox: a python library for identification and geometric analysis of fault networks from numerical analogue, and digital elevation models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12256, https://doi.org/10.5194/egusphere-egu25-12256, 2025.

Identifying active tectonics is a challenging goal, particularly in areas affected by low strain rates, complex structural and geological settings, and significant anthropogenic impact. Across the Italian Apennine belt, the Late-Quaternary activity of normal faults leaves a distinctive footprint on the landscape. This activity is often constrained by paleoseismological investigations and field geology evidence, and is supported by historical and instrumental seismicity, as well as being in agreement with stress and geodetic data. Active tectonics evidence sharply breaks up between the central and southern Apennines (Abruzzo-Molise regions’ boundary – AMB), although the sector is geographically and structurally in continuity with the overall extensional belt. In this sector, a lack of clear fault-geomorphic signature can be observed, likely fostered by lithologic high erodibility and landslide susceptibility. In addition, an evident seismic gap (Rovida et al., 2020) contrasts with geodetic data that, conversely, show as the area is currently undergoing rather fast permanent bulk deformation (Carafa et al., 2020).

To investigate this (apparent?) disconnection between active deformation and surface faulting, we combined a multi-scale and multi-source approach. To detect possible transients in the topography and analyse the spatial distribution of geomorphic features we carried out relief analysis and structural interpretation from stereoscopic imagery. To discriminate between tectonic versus gravitational (slope-related) signals, we used time-series InSAR data analysis.

We identified relief anomalies in three key areas and mapped displaced morphological features interpreted as the result of normal faulting. As well, interferometric data analysis highlighted a clustered spatial pattern on the distribution of gravitative movements that have been considered as a proxy of the control played by tectonic structures. Field survey providing structural evidence of normal-fault kinematics across the alleged structures helped in supporting the clues provided by remote data interpretation.

The overall outcomes, albeit preliminary, converge on evidence of diffuse normal faulting filling a structural gap within the AMB, providing additional hints on the seismic hazard of this area and inputs for future investigations.

Carafa M.M.C., Galvani A., Di Naccio D., Kastelic V., Di Lorenzo C., Miccolis S., Sepe V., Pietrantonio G., Gizzi C., Massucci A., Valensise G. & Bird P. (2020) – Partitioning the Ongoing Extension of the Central Apennines (Italy): Fault Slip Rates and Bulk Deformation Rates From Geodetic and Stress Data. J Geophys Res-Sol Ea, 125, e2019JB018956, https://doi.org/10.1029/2019JB018956

Rovida A., Locati M., Camassi R., Lolli B., Gasperini P. (2020) – The Italian earthquake catalogue CPTI15. B. Earthq. Eng., 18(7), 2953-2984. https://doi.org/10.1007/s10518-020-00818-y

How to cite: Battistelli, M., Ferrarini, F., Bucci, F., Santangelo, M., Cardinali, M., Merryman Boncori, J. P., Cirillo, D., Carafa, M. M. C., and Brozzetti, F.: Reconciling active deformation and Quaternary normal faulting in a poorly understood sector of the central-southern Apennines (Italy): a multi-scale, multi-source data approach., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17882, https://doi.org/10.5194/egusphere-egu25-17882, 2025.

The Inner Northern Apennines (Italy) are a region with a dominant N-S to NNW-SSE fault system. However, E-W to NE-SW oriented structures crossing and dissecting the dominant fault trend have long been recognised. These transversal structures are often believed to be inherited, but our knowledge about their nature, activity and role in current tectonic motions is still limited and debated. Especially their activity and seismotectonic relevance is unclear.

A new seismo-tectonic analysis identified and relocated two distinct earthquake clusters in the Viareggio Basin, western Tuscany, which clearly showed activity along NE-SW oriented fault systems in the vicinity of one of the major transverse structures in the Inner Northern Apennines, the Livorno – Empoli lineament. The relocated clusters show mostly oblique slip, with a depth-dependent switch of motion direction in one cluster, as well as a localised change of the stress field. The position of the clusters and their onshore-to-offshore nature suggest the identified fault system to be related to the reactivation of pre-existing structures. These results show that the transversal structures of the Inner Northern Apennines, even when they do not show a morphologic surface expression, are seismogenic.

Moreover, a new tectono-geomorphic analysis was carried out in the presumed source area of the 1846 ~M6 Orciano Pisano earthquake (Val di Fine Basin), the biggest and most destructive recorded earthquake in western Tuscany. Our investigation, combining an in-field structural analysis with a detailed qualitative and quantitative geomorphic approach (e.g. stream network analysis, knickpoint calculation, slope map) based on a 10x10 m DTM, could not confirm the general assumption which attributes this event to one of the N-S striking faults bounding the basin. Instead, large and small scale geomorphic features as well as structural observations (e.g. an E-W trending water divide, diverted rivers, a newly identified fault) suggest that the event might have originated along a, so far unrecognised, transversal structure with an oblique right-lateral motion direction located at the centre of the basin.

The combined results of the seismo-tectonic & tectono-geomorphic analysis show that a more detailed investigation of the, often elusive and therefore easily overlooked, transversal structures in the Inner Northern Apennines is necessary, as they seem to be holding a seismogenic potential and might pose a so far uncared seismic hazard for the region.

How to cite: Kaerger, L., Del Ventisette, C., Vannucchi, P., Molli, G., Pagli, C., and Keir, D.: Seismo-tectonic activity along transversal structures in the Inner Northern Apennines, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13203, https://doi.org/10.5194/egusphere-egu25-13203, 2025.

The central Po Plain (Italy) is a complex geological system where the outermost fronts of two mountain belts, the Northern Apennines and the Southern Alps, coexist sharing the same foreland. Thanks to a dense dataset of seismic reflection profiles and wells (courtesy of Eni as part of the Ph.D project of Daniel Barrera, Univ. of Pavia) it has been possible to reconstruct in detail the buried structure of the Emilian arc, one of the three structural arcs that compose the outermost fronts of the Northern Apennines and the external fronts of the Southern Alps, buried in the central Po Plain. From these data, it is evident that the Emilian arc of the Northern Apennines is composed of three main thrust systems and related anticlines. It was also possible to reconstruct the geometry of the outermost fronts of the Southern Alps and, most importantly, the top of the Mesozoic carbonates, above which the main detachment levels of the Southern Alps have developed and whose geometry deeply influences the development of the Emilian Arc. The reconstruction of six regional Plio-Pleistocene unconformities of known age allows the restoration of some of the reconstructed tectonic structures, thus obtaining a slip value and the amount of slip rates along different tectonic structures and along the strike of the same structure.

Through these analyses, it is possible to argue on the Plio-Pleistocene kinematics of several tectonic structures in the central Po Plain, quantifying the recent tectonic activity of the main thrusts. The slip distribution and the along-strike deformation are rather inhomogeneous and do not follow the classic pattern of deformation propagation from the inner to the outer sectors of the chain but show evidence of inner thrusts reactivation and external thrusts with little or no activity in recent times. The possible causes of this rather complex kinematics have been investigated through a series of analogue models that, by reproducing the presence of structural highs and rheological inhomogeneities of the Po Plain, allow us to investigate if, and how much, some geological features affect the development of tectonic structures in time (kinematics) and space (along-strike variations).

The preliminary results of the research show how the buried structural highs in the Po Plain and the presence of the outer Southern Alps fronts modify both the structure's kinematics and the distribution of the along-strike deformation, creating the present-day complex structural framework.

This demonstrates the need for a 3D modeling approach and detailed quantitative reconstructions of deformation, not limited to the outer sectors of the Emilian arc, but considering the thrust system that constitutes the Northern Apennine as a whole.

How to cite: De Matteo, A., Barrera, D., Seno, S., Di Giulio, A., and Toscani, G.: Evolution and Plio-Pleistocene fault kinematics and basin infilling in the central Po Plain (Italy): an integrated analysis from subsurface data and analogue models analysis, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21753, https://doi.org/10.5194/egusphere-egu25-21753, 2025.

Understanding the long-term tectono-stratigraphic evolution of active extensional faulting is key to deciphering how continental rifting propagates over time and space. The Pliocene-Quaternary L’Aquila Intermontane Basin (AIB) in the central Apennines serves as an ideal natural laboratory for investigating this process. Seismicity in the AIB is linked to NW-SE striking normal faults that have accommodated crustal stretching since the Late Pliocene. This study integrates fieldwork, mineralogical, geochemical (C-O stable and clumped isotopes), and geochronological (⁴⁰Ar/³⁹Ar, U-Th) analyses to explore the structural connection between the Mount Pettino Fault (MPF) and the Paganica Fault, two active, left-stepping basin boundary faults. The research proposes a two-stage tectono-stratigraphic evolution reflecting a shift from localized to distributed deformation and fault linkage. Stage-1 (pre-Middle Pleistocene) marks the nucleation and growth of the MPF, characterized by a ∼5 m thick fault core of isotopically closed cataclasite (T (∆47) ∼33–50°C). Stage-2 involves the development of a distributed fault zone linking the MPF and the Paganica Fault via a transfer zone. This zone facilitated meteoric fluid circulation, carbonate veining, and travertine formation (T (∆47) ∼8°C). U-Th dating of Stage-2 mineralizations constrains tectonic activity in the transfer zone to ∼182–331 ka. These findings provide insights into the tectono-stratigraphic evolution of the AIB and its seismotectonic behaviour, with implications on the regional geodynamic reconstructions.

How to cite: Arriga, G., Marchegiano, M., Peral, M., Hu, H.-M., Cosentino, D., Shen, C.-C., Dalton, H., Brilli, M., Aldega, L., Claeys, P., and Rossetti, F.: Tectono-Stratigraphic Evolution of a propagating extensional fault network: Insights from the L’Aquila Intermontane Basin, Central Apennines , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19926, https://doi.org/10.5194/egusphere-egu25-19926, 2025.

The Mugello Basin is a WNW-ESE-striking, seismically active intermontane basin currently experiencing post-orogenic extension that affects the hinterland of the Northern Apennines belt (Italy). It lies near the main watershed of the Northern Apennines, a feature traditionally seen as separating the internal, extension-dominated (to the southwest) part of the belt from the external, contractional (to the northeast) part. Therefore, complex and controversial relationships exist between the recorded seismic activity and the surface manifestations of potentially seismogenic faults at depth in the Mugello region. The ITaly HAzard from CApable faults (ITHACA) catalogue reports active and capable faults along both margins of the basin. Moreover, coseismic surface ruptures were observed during the 1919 earthquake. However, surface expressions of active faults in the Mugello region are less pronounced compared to those associated with similar graben-bounding faults in other intermontane basins of the Northern Apennines. Moreover, the subsurface structure of the basin remains poorly constrained and is widely debated, with a significant lack of reliable geophysical data. This has led to contrasting views on the size, geometry, and orientation of the potential seismogenic sources, according to different researchers. Thus, the Mugello Basin offers an excellent opportunity to apply geophysical surveys to address the gaps in knowledge regarding its subsurface structure.

In this study, we used a combined methodological approach to propose a subsurface model for the basin's geometry and mechanical properties. We performed seismic microtremor measurements to be interpreted in the frame of the H/V and H&V methods along four profiles orthogonal to the basin’s axis (i.e., NNE-SSW) and one parallel to it (i.e., WNW-ESE). By integrating surface geological data and geomorphic analysis of the fluvial network (chi-map) based on a 10-m DEM, we were able to refine the geophysical model and more accurately evaluate the seismic behavior of the basin. We combined microtremor measurements with publicly available well log data and field geology observations, which helped us interpret the normalized H/V values and estimate the thickness of the basin’s sedimentary fill. Preliminary results suggest that the basin exhibits an asymmetric across-strike geometry, with active extensional faults likely concentrated along its northern margin. This is consistent with the epicentral distribution of seismic sequence that affected the area between 2009 and 2019, as highlighted by recent studies. Accordingly, geomorphic analysis shows the highest chi values in the northeast sector. This marks a disequilibrium of the river network which might be associated with active faulting, whereas in the southeast chi-values indicate steady state among rivers. The interpretation of the normalized H/V values in terms of bedrock geometry provides new insights into the basin's subsurface structure and offers constraints that challenge previously proposed models. These results have significant implications for evaluating seismic site effects at the scale of the Mugello Basin. Furthermore, they contribute to understanding the tectonic evolution of the basin within the larger geodynamic context of the Northern Apennines, particularly with respect to the transition from syn-orogenic compressive to post-orogenic extensional tectonics.

How to cite: Asti, R., Castellaro, S., Bonini, S., Tiboni, B., Gemignani, L., and Vignaroli, G.: Linking subsurface structure and active faulting in the intermontane Mugello Basin and its implication for the post-orogenic tectonic evolution of the Northern Apennines (Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16580, https://doi.org/10.5194/egusphere-egu25-16580, 2025.

Taiwan, located at the convergent boundary between the Philippine Sea and Eurasian plates, is one of the most seismically active regions globally, with convergence rates reaching 80-90 mm/yr. The Longitudinal Valley suture zone in eastern Taiwan, accommodating ~30 mm/yr of NNW-SSE shortening, hosts two major reverse fault systems: the E-dipping Longitudinal Valley Fault (LVF) and the W-dipping Central Range Fault (CRF). These faults exhibit complex interactions, particularly in the northern sector of the Longitudinal Valley, where cross-cutting relationships and evolving tectonic dynamics generate significant seismotectonic complexity.

The 2 April 2024 M_W 7.4 Hualien earthquake, the strongest instrumentally recorded event near Hualien since the 1951 sequence, exemplifies this complexity. Previous seismic events in this region have been associated with ruptures on both E- and W-dipping faults, reflecting the dynamic interplay between these systems. To investigate the faulting processes and source parameters of this sequence, we analyzed an extensive geodetic dataset, integrating Global Navigation Satellite Systems (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) observations. Elastic dislocation modeling was applied to constrain the rupture geometry and evaluate the interaction between fault segments. GNSS and InSAR data from the 2024 event reveal a rupture pattern involving multiple fault segments, consistent with observations of focal mechanisms, aftershock distributions, and long-term moment release patterns. Although simple single-fault models (e.g., an E-dipping Longitudinal Valley Fault or a W-dipping Central Range Fault) can explain the geodetic data, a composite fault model, incorporating multiple segments, better accounts for the observed displacements, seismicity, and the complex structure of the northern Longitudinal Valley. Our findings provide new insights into the seismogenic processes and fault dynamics underlying this significant seismic event. They highlight the evolving tectonic setting of eastern Taiwan and contribute to the understanding of the processes driving seismotectonic complexity in one of the most tectonically active regions of the world.

How to cite: Cheloni, D., Famiglietti, N. A., Caputo, R., and Vicari, A.: Unveiling Tectonic Complexities in the 2024 Hualien (eastern Taiwan) Earthquake Sequence Using GNSS and InSAR Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5573, https://doi.org/10.5194/egusphere-egu25-5573, 2025.

Since 2019, unrest on the Reykjanes Peninsula, SW Iceland, has demonstrated that fracture movements are a significant component of volcano-tectonic deformation and pose major hazards to infrastructure. TerraSAR-X data covering the Reykjanes Peninsula were processed to produce 57 interferograms for fracture mapping for September 2021 to July 2024. The most extensive fracture movements during this period are associated with the 2022 Meradalir eruption, 2023 Litli-Hrútur eruption, and 2023 Nov. 10-11 Grindavík dike intrusion. Extensive activation of N-S trending strike-slip faults and NE-SW trending normal faults is observed during periods of shallow dike propagation and associated seismicity. Simple elastic modeling suggests that most of the observed displacements are a result of shallow slip within the upper tens to hundreds of meters of the crust. Many have existing topographic expressions and have been activated multiple times since 2020, highlighting the role preexisting weaknesses in the upper crust play in accommodating volcano-tectonic deformation. While some fracture movements can be explained by co-diking stress transfer, e.g. normal faulting directly above dikes or bookshelf faulting along the North American-Eurasian plate boundary, subtle (<10 mm) movements within neighboring fissure swarms occur where Coulomb stress transfer modeling indicates co-diking normal stress changes should suppress fracture movements. As such, other processes like shallow strain localization along preexisting weaknesses may be occurring. InSAR data also reveal repeated fracture movements within the Búrfell graben, SE of Reykjavík and within the Krýsuvík Fissure Swarm, which was surveyed with high-precision geodetic leveling in the summer of 2024. Since 2012, portions of the profile have subsided up to 34 ± 0.3 mm, corresponding to a rate of -2.8 mm/yr, substantially greater than that observed in previous decades. Fracture movements within the graben are only seen in interferograms spanning bursts of shallow microseismicity in October 2018, March 2021, and September 2023. Line of sight deformation of up to 5 cm is also observed during earthquake swarms (M_max= 3.1) in January and June 2024 within the adjacent portion of the Krýsuvík Fissure Swarm. In both cases, observed deformation is larger than expected for the seismic moment released, implying that this deformation is both episodic and has a significant aseismic component. These observations offer insight into the mechanisms of fracture movements and may be applied to locations where similar processes occur such as Iceland’s Northern Volcanic Zone or the East African Rift.

How to cite: Wire, N. and Geirsson, H.: InSAR observations and modeling of volcano-tectonic fracture movements on the Reykjanes Peninsula, SW Iceland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18294, https://doi.org/10.5194/egusphere-egu25-18294, 2025.

New Zealand’s largest city Auckland, 400 km into the overriding Australian plate from the Hikurangi subduction margin, sits on top of the active intraplate Auckland Volcanic Field. Low recurrence interval faults are mapped to the south of the city and ~30 km to the east within the active Hauraki Rift which is opening oblique to the plate boundary trend. Faulting within the urban area is obscured by the distributed <200,000 year old volcanics, Quaternary sedimentation and landscape modification. The potential structural control on magma ascent unclear or variable. While Auckland urbanisation provides the riskscape to motivate seismo-volcano-tectonic characterisation, the setting also provides challenges, and some advantages, to investigation. We discuss the ongoing programme of potential field and borehole studies that characterise crustal structure and geodesy, seismology, geomorphology, field studies that are also indicative of regional deformation.

The NNW-SSE trending Hauraki Rift parallels regional basement fabric characterised by the trend of the Mesozoic, ophiolite bearing Dun Mountain-Maitai basement terrane-sourced Junction Magnetic Anomaly. Geodesy has resolved a rifting rate of ~1 mm/year. Dominant NNW-NW and NE fault trends within/beneath Auckland are resolved from Lidar analysis, field mapping and reconstruction of a regional marker horizon, the “Waitemata Group Erosion Surface”, using extensive urban and urban-fringe borehole datasets. Few boreholes penetrate the deeper areas of Mesozoic basement so modelling of gravity data has proved useful to define the topography of the basement surface and interpret significant basement offsets. Although the historic 1891 ~Mw 6.2 Waikato Heads earthquake ~65 km SE of the Auckland CBD demonstrated the seismic potential in the region, rates of microseismicity are low and have been concentrated in South Auckland and the Hauraki Gulf. New seismometer deployments enhance potential resolution of spatial patterns of seismicity, with use of artificial intelligence in catalogue building investigated. These will also provide the potential for increased resolution crustal, crustal thickness, and mantle characterisation. The establishment of new campaign geodetic sites will also increase confidence in potential dislocations across proposed structures. Geomorphic and field studies attempt to characterise the paleoseismology of exposed faults.     

How to cite: Eccles, J., Pickle, R., Luthfian, A., Kenny, J., Chevallier, H., Martin, H., Miller, C., Hreinsdottir, S., van Wijk, K., and Muirhead, J.: Towards deciphering the tectono-magmatic dynamics of the Auckland Volcanic Field and Hauraki Rift, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7530, https://doi.org/10.5194/egusphere-egu25-7530, 2025.

We introduce a new high-resolution gravity dataset acquired along a profile in the Kumaon Himalaya, extending from the Indo-Gangetic plains in the south to the Main Central Thrust (MCT) zone in the north. The Garhwal-Kumaon Himalaya, located in the central Himalayan region, has not experienced any great earthquake in the last 500 years. Therefore, it is essential to study the detailed crustal structure in order to better understand the stress and seismicity patterns in this area. Power spectrum analysis of the calculated complete Bouguer gravity anomaly (CBA) reveals two distinct crustal interfaces corresponding to the Moho and the Main Himalayan Thrust (MHT). To obtain the residual gravity anomaly related to the upper crustal structure, we apply the modeling-based gravity isolation technique, which involves isolating the gravity responses of deeper intra-crustal interfaces based on previous studies. We find that the sharp variations in the residual gravity anomaly align well with the surface geology of the region. Prominent signatures of major thrust boundaries, such as the Main Boundary Thrust (MBT), North Almora Thrust (NAT), and Main Central Thrust (MCT), are clearly identified in the residual gravity anomaly. We performed the wavelet analysis and particle swarm optimization (PSO)-based fault inversion to extract the fault geometries of different fault/lithotectonic boundaries from the residual gravity anomaly. These results are incorporated as a priori information to constrain the upper crustal structure during the forward modeling of the CBA. The detailed density structure gives insight into the geometries of the Moho, the MHT, and the lithotectonic boundaries for the study region. We will compare the crustal density model of the Kumaon Himalaya with the adjacent Garhwal Himalaya and discuss the crustal architecture in the context of the seismotectonics of the region.

How to cite: Kumar Rana, S. and Chamoli, A.: Insight into the Crustal Density Structure of Kumaon Himalaya, India, based on Gravity Modeling and Inversion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15957, https://doi.org/10.5194/egusphere-egu25-15957, 2025.