Active Rift Research Articles

Where will the next flank eruption at Etna occur? An updated spatial probabilistic assessment

Abstract. The assessment of the spatial probability of future vent opening is one of the key factors in quantifying volcanic hazard, especially for active volcanoes where eruptions can occur at different locations and altitudes over distributed areas. Mount Etna (Italy), one of the most active volcanoes in the world, exhibits such variability, and its flank eruptions can harm people, properties and services over the volcano's slopes. In this paper, we quantify the spatial probability of future vent opening for Etna's flank eruptions, adopting a kernel analysis and testing different functions (exponential, Cauchy, uniform and Gaussian). Starting from the assumption that the location of past fissures is indicative of where future events will occur, we consider the flank eruptions of the last 4000 years, thus accounting for a much longer and complete record than in previous studies. The large dataset of eruptive fissures enables splitting the data into training and testing subsets. This allows selecting the best kernel model, testing the completeness of the fissure dataset and investigating a possible migration through time in fissure location. The results show that neither under-recording nor possible migration over time significantly affects the informative value of previous flank fissures in forecasting the location of future ones. The resulting map highlights that the most likely opening area follows a northeast-to-south trend, corresponding to the location of the most active rifts. It also shows that the southern flank of the volcano, which is the most urbanized one, sits downhill of the largest cumulated probability area for flank eruption. We also run sensitivity analyses to test the effect of (i) restricting the data to the most recent 400 years and (ii) including the information on the stress induced on the mapped fissures by sources of deformation proposed in the literature for recent eruptions of Etna. The sensitivity analyses confirm the main features of the proposed map and add information on the epistemic uncertainty attached to it.

Author Correction: Earth-like lithospheric thickness and heat flow on Venus consistent with active rifting

Author Correction: Earth-like lithospheric thickness and heat flow on Venus consistent with active rifting

Anatomy of the late Pennsylvanian to early Triassic failed rift system of the Cooper Basin, eastern Australia

The onshore intracratonic Cooper Basin of eastern Australia developed during the Late Pennsylvanian to Middle Triassic periods at paleolatitudes of approximately 50°S within the Gondwanan sector of Pangea. Despite the wealth of data available, including the drilling of over 4,800 boreholes, there is limited knowledge about the Cooper Basin’s origins and evolution. To better understand the basin’s geological history, legacy data sets, including composite 2D seismic sections, well logs, measured sections, and 1D burial history models from the west of the basin, are integrated to reinterpret the basin’s tectonic and sedimentary evolution. Interpretation of the seismic sections and calculated subsidence rates indicates an earlier active rift phase with grabens and half-grabens that transitioned, in the latest Permian, into a regional sag phase. The evolution of tectonic styles heavily influenced the paleogeographic evolution of the basin fill and resulting depositional architecture. The basin sediments are entirely terrestrial in nature and facies reflect a transition from glacial environments in the late Pennsylvanian to warmer and drier conditions in the early Triassic. During much of the Permian the basin was underfilled and the relative low influx of fluvial sediment did not keep pace with creation of accommodation, allowing the development of extensive mire and lake systems. Coal beds are up to 30 m thick. By contrast, the basin appears to have been overfilled during the latest Permian to Triassic with rivers flowing along the central axis of the basin. The synchroneity of commencement of rifting, termination of rifting, and commencement of a sag phase within the failed rift systems of the Cooper Basin, the East Gondwana Interior Rift, and the East Australian Rift strongly suggests a continent-wide period of extension related to significant changes in plate motions during the Late Pennsylvanian to Middle Triassic.

Mud diapirs in a continental extensional basin: 3D seismic interpretation of the Central Recôncavo Basin (northeast Brazil)

Mud diapirs are present in different tectonic environments around the globe and are particularly prevalent in large deltas. The onshore Jurassic-Cretaceous Recôncavo Basin in northeast Brazil represents an atypical example of mud diapir occurrence in a rift basin. The intensity of mud diapirism is different in the three sectors of the basin, with the central sector exhibiting the best development. In the southern sector, diapirism is less significant, and it is practically nonexistent in the northeast sector. The 3D seismic, outcrop, and well data are used to geomorphologically characterize the onshore mud diapirs in the central sector of the Recôncavo Basin and correlate them with the structural and morphological aspects of the basin, in addition to elucidating the possible origins of their movement. After seismic interpretation, four mud diapirs are identified in the study area: Apraius-Miranga Norte, Pedra do Salgado, Biriba, and Carijó. Two internal seismic facies are identified as F1 and F2, with F1 having more disruptive features and F2 being more reflection-free. The eastern diapirs, close to the border fault conglomerates, are dominated by disrupted seismic facies (F1). The diapiric movement is associated with paleoseismicity and the rupture of an ancient delta front, together with the rapid basinward advancement of conglomerates during an active rifting phase. The Biriba diapir is possibly the first to arise, followed by Carijó and Apraius-Miranga Norte, and finally, Pedra do Salgado; this variable timing influences the location and migration of the depocenters in the area.

Geomorphic expressions of active rifting reflect the role of structural inheritance: a new model for the evolution of the Shanxi Rift, northern China

Abstract. Many rifts are influenced by pre-existing structures and heterogeneities during their evolution, a process known as structural inheritance. During rift evolution, these heterogeneities may aid rift nucleation, rift growth, and the segmentation of faults; encourage the linkage of various segments; or even inhibit the formation of faults. Understanding how structural inheritance influences early rift evolution could be vital for evaluating seismic risk in tectonically active areas. The Shanxi Rift in the north of China is an active rift system believed to have formed along the trend of the Proterozoic Trans-North China Orogen; however, the influence of these pre-existing structures on the present-day rift architecture is poorly understood. Here, we use tectonic geomorphological techniques, e.g. the hypsometric integral (HI), channel steepness (ksn), and local relief, to study the evolution of the Shanxi Rift and identify areas of higher tectonic activity. We found that the HI was less sensitive to lithology and more valuable in evaluating the tectonic signal and that activity is concentrated in two rift interaction zones (RIZs) formed between the Xinding, Taiyuan, and Linfen basins. We then evaluated the relationship between the active faults and mapped pre-existing structures, finding that many faults formed parallel to inherited structures, while faults in the RIZs often cross-cut these structures. Based on these observations, we propose a new model for the evolution of the Shanxi Rift, where inherited structures play an important role in the initial segmentation of the rift, which, in turn, controls the development of the RIZ structures.

The Role of Upper Mantle Forces in Post‐Subduction Tectonics: Plumelet and Active Rifting in the East Anatolian Plateau

AbstractThe spatiotemporal interaction of large‐ and regional‐scale upper mantle forces can prevail in collisional settings. To better understand the role of these forces on post‐subduction tectonics, we focus on mantle dynamics in the East Anatolian Plateau, a well‐documented segment of the Arabian‐Eurasian continental collision zone. Specifically, we analyze multiple forces in the upper mantle, which have not been considered in previous studies in this region. To this end, we use a state‐of‐the‐art 3D instantaneous geodynamic model to quantify the dynamics of thermally defined upper mantle structures derived from seismic tomography data. Results reveal a prominent SW‐NE‐oriented mantle flow from the Arabian foreland to the Greater Caucasus–a plumelet–through a lithospheric channel under the East Anatolian Plateau. This plumelet induces localized dynamic topography (∼500 m) around the extensional Lake Van province, favoring NE‐directed compression and westward escape of the Anatolian plate. We suggest that the Lake Van region is an active magma‐rich intraplate rift in the Africa‐Arabia‐Anatolian plume‐rift system. The rift zone was probably initiated by Neotethyan subduction‐related forces and has been reactivated and/or sustained by the plumelet‐induced convective support. Our findings are consistent with numerous observations, including the recent low‐ultralow seismic velocities with a SW‐NE splitting anisotropy pattern, geochemical and petrological studies, and local kinematics showing upper mantle‐induced extensional tectonics in the collisional region.

Multi‐mode gravity tectonics during northern North Sea rifting: the Snorre fault block case

AbstractContinental rifts are characterized by up to 30 km wide rotated fault blocks with stratigraphic dip away from the central rift axis. Although gravity‐induced mass movements are well known features of collapsed fault block crests, I here demonstrate the occurrence of polymodal gravity‐driven mass transport down the back slope of a first‐order rift fault block. I identify (1) early sliding related to syntectonic crestal collapse of second‐order rift faults, (2) large‐scale bed‐parallel sliding of the L‐M Jurassic sedimentary package, and (3) the accumulation of two 7 km long, 1–2 km wide and up to 750 m thick volumes of complexly slumped material in the hanging walls of two ramp‐forming faults. Early sliding is documented by 100 m of repeated Brent Group stratigraphy in a cored well in the study area (well 34/4‐15A). These smaller slides have intact internal stratigraphy but show elevated deformation band densities. The seismic data also show evidence for ca. 2 km of massive translational sliding of the ca. 400 m thick and ca. 300 km2 large Jurassic section above a lowermost Jurassic bedding‐parallel detachment. This translational slide did not deform much internally, except for ductile folding where it slid over underlying active rift faults. Chaotic seismic facies in fault hanging walls are interpreted as contorted Jurassic beds, formed by multiple slumping and sliding events that stacked mobilized sediments into a 750 m thick column. These complex slump volumes occur where fault displacement is highest along two relayed faults. A model is favoured where the large translational slide ruptured with an opening of space against the fault that was progressively filled with slumped material from the footwall. While the large‐scale translational sliding only caused moderate internal subseismic deformation, early sliding and, particularly, the complex slumping caused significant internal deformation. This study shows the importance of carefully searching for and distinguishing between different types of mass movement in rift systems.

Workshop report: Afar Dallol Drilling – ONset of sedimentary processes in an active rift basin (ADD-ON)

Workshop report: Afar Dallol Drilling – ONset of sedimentary processes in an active rift basin (ADD-ON)

The influence of the strength of pre-existing weak zones on rift geometry and strain localization

Continental rifts normally initiate within previously deformed lithosphere and thus their evolution and architecture can be largely controlled by inherited weak zones in the pre-rift crust. Here, we quantify the role of the strength and obliquity of pre-existing crustal-scale weak zones in the evolution of continental rift systems. We use a 3D numerical geodynamic model to assess strain localization, associated fault development, and rift segmentation during the early stages of tectonic extension. We find that both the strength and obliquity of the weak zones significantly influence the patterns of strain localization. A pre-existing very weak zone with low obliquity can promote the development of continuous and long-lived border faults parallel to the rift axis. Conversely, a comparatively strong weak zone with high obliquity leads to a staggered en-echelon rift geometry that lacks rectilinear laterally persistent strain localization. Furthermore, we find that rift obliquity and weak zone strength may modulate rift fault length, throw, and azimuth. These results provide new and compelling insights into the structure and evolution of natural active rifts that develop within orogenic basement terranes.

Evolution of the transtensional Barreirinhas pull-apart system in the Brazilian Equatorial margin and its correlation with the African conjugate counterpart

The Barreirinhas pull-apart system encompasses marginal basins in divergent and transform margin segments in the central sector of the Brazilian Equatorial Margin and its African conjugate counterpart. This ancient pull-apart system evolved through transtensional strike-slip motion within a highly heterogeneous crystalline basement affected by multiple rift phases. The geometry and development of pull-apart structural elements during the final rifting phase before continental breakup and the mechanisms and extent to which they were influenced by preexisting crustal heterogeneities are comprehensively addressed using an extensive database of potential field (magnetic and gravity) and 2D seismic reflection data. We also assess the lithospheric thermomechanical conditions and their influence on transtensional extension throughout Curie Point Depth, Heat Flow, and Moho depth, derived from potential field data and published seismological models. Plate reconstruction of Brazilian and African equatorial margins based on gravity patterns and comparison with sandbox analog models allow a 3D synoptic model to reveal the Barreirinhas pull-apart system evolution during the Equatorial Atlantic opening. During the rift phase I, the location of major grabens was controlled by favorably oriented Neoproterozoic shear zones, while the cooler, stronger, and thicker crust beneath cratonic areas formed the western barrier to strike-slip rift activity during rift phase II. This same geological domain anchored the onset of the pull-apart system in the last rift phase III, whose principal displacement zones developed along the extensive oceanic fracture zones linked by sigmoidal fault systems. Toward the end of the rift phase, a large asymmetric lozangle to a lazy-Z-shaped, pull-apart basin developed above low overlapping ∼90°, releasing stepover in oblique transtensional strike-slip motion.

Density structures of the upper mantle in the East African Rift System: implications for the evolution of intracontinental rifting

The East African Rift System (EARS) provides an ideal natural laboratory for studying the mechanisms of tectonic plate breakup and continental drift, as well as a unique perspective for exploring the maturation process of continental rifting and its drivers. This study combines high-resolution satellite gravity data and seismic tomography model with an integrated geophysical approach to reveal the density structures in the upper mantle of the EARS. The results show that the northeastern to central Congo and Zimbabwe Craton exhibit significant high-density anomalies extending up to 250 km, which is indicative of a thicker and more intact lithosphere. In contrast, the Uganda, Tanzania, eastern and southern Congo, and Kaapvaal Craton show shallow high-density anomalies underlain by low-density anomalies that are clearly derived from the deeper mantle, indicating a thining of the lithosphere with some degree of possible melting at the base. The various rift segments of the EARS exhibit different rift morphologies. The Main Ethiopian Rift and the Kenya Rift of the Eastern Rift Branch show strong low-density anomalies, indicating intense melting, which is much stronger than that observed in the Western Rift Branch. However, the two rifts may have originated from the same mantle uplift in which the low-density anomalies of the Eastern and Western Rift Branches connected in the deep upper mantle. The lower portion of the Malawi Rift exhibits weaker low-denstiy anomalies, which can be observed to the south of the Malawi Rift, extending further south as a continuation of the EARS. Combining the results of previous kinetics simulations and our density perturbation results, it can be inferred that the Eastern Rift Branch is mainly affected by active rifting, while the Western Rift Branch is affected by both active and passive rifting.

Source‐To‐Sink Analysis in the Mesozoic SW Junggar Basin, Central Asia: Evidence From Detrital Garnet and Tourmaline Geochemistry

AbstractSource‐to‐sink systems respond to and therefore potentially record topographic and tectonic changes. North of the Tian Shan Belt, the Sikeshu subbasin of the SW Junggar Basin transitioned from active extension in the Triassic to post‐extensional subsidence in the Jurassic‐Cretaceous. Sediment in the Sikeshu subbasin has been shown to be derived from the Tianshan. However, the details of the source‐to‐sink system remain unclear and discrepancies exist between proxy records. The heavy minerals in the Middle Triassic in the Sikeshu subbasin are dominated by garnets. To investigate the garnet sources and decipher the Mesozoic source‐to‐sink evolution, we conducted petrological and sedimentary analysis and detrital garnet and tourmaline geochemistry. We found that the geochemistry of garnets in the Middle Triassic sandstone is most consistent with that of the skarns in the Yili Block (YB) in Tianshan, while the geochemistry of 55%–84% of garnets in other Mesozoic sandstones is consistent with that of garnets in amphibolites in the YB. The geochemistry of the tourmalines since the Upper Triassic is consistent with that of the meta‐sedimentary rocks in the YB and Central Tianshan Block. The dominance of garnets sourced from skarns in the Middle Triassic probably indicates a near‐source point provenance and the broader range of garnet compositions from the Upper Triassic–Lower Cretaceous suggests multiple sources. We infer that the point source changed to multiple sources, which is consistent with the zircon spectra changing from unimodal to multimodal. This change reflects the expansion of the drainage that accompanies a change from active rifting to a post‐rift stage.

Oil shale enrichment mechanisms in the Lower Cretaceous Jiufotang Formation from the Ludong sag, Songliao Basin, Northeast China

In order to investigate the oil shale enrichment mechanisms and the relationship among gravity flows, volcanism, and oil shale deposition, detailed petrological, sedimentological, and organic geochemical research have been carried out on the Lower Cretaceous Jiufotang Formation in the Ludong sag, Songliao Basin, Northeast China. Seven facies were recognized and were grouped into three facies associations, namely hyperpycnites and intrabasinal turbidites, delta, and lacustrine facies associations. During the deposition of the lower Jiufotang Formation, hyperpycnites were developed during catastrophic flooding events that caused an abrupt increase in the discharge of water and sediment into the deep lacustrine environments, and a delta persisted during normal river discharge intervals and prograded into lacustrine environments. During the deposition of the upper Jiufotang Formation, deep lacustrine facies further expanded, and the extent of hyperpycnites decreased. Four types of oil shales were recognized in the Ludong sag of which those in the lower and upper Jiufotang Formation were defined as medium-to good-quality and good-to best-quality source rocks, respectively, exerting an overall thermal maturity of early oil generation. The lacustrine redox conditions show oxic to dysoxic conditions in the lower Jiufotang Formation, and anoxic to dysoxic conditions in the upper Jiufotang Formation. Oil shales were poorly-developed in the lower Jiufotang Formation and were well-developed in the upper Jiufotang Formation. During the active rift stage of the lower Jiufotang Formation, frequent occurrences of gravity flows and water-carried re-sedimentation of tuffaceous materials were unfavorable for oil shale accumulation. During the waning rift phases of the upper Jiufotang Formation, minor wind-transport of volcanic ash input into the deep lacustrine environments fertilized the lake water and supported algae blooms, leading to reduced oxygen concentrations in the bottom lacustrine waters along with high bioproductivity that were favorable for organic matter preservation and oil shale formation.

Hydrogeomorphology and recharge mechanism of a coastal aquifer in tectonic-controlled watersheds: A multi-proxy approach based on remote sensing and environmental isotopes

Coastal aquifers worldwide can be considered an essential water source required for preservation of the coastal ecosystems. However, these aquifers are vulnerable to seawater intrusions and over-pumping due to their proximity to the sea and human activities, respectively. Therefore, the investigation of recharge mechanism has special importance in the regions of tectonic rift activities where they exhibit complex geological structures and hydrogeological characteristics. In the current research, an integrated approach of remote sensing and environmental isotopes together with field investigation and subsurface datasets (aeromagnetic, gravity and well logs) are employed to identify the nature and factors affecting groundwater recharge of the Miocene coastal aquifer along the Red Sea-Gulf of Suez western margin (continental rift basin). The research findings reveal that: (1) The coastal Miocene aquifer consists of both clastic (sandstone, sand and gravels) and carbonate rocks (limestone and dolomite) with subsurface thickness ranges between 100 and 200 m. (2) Its groundwater shows contrast salinity values (expressed by total dissolved solids, TDS) between 2755 and 10,996 mg/l, due to the variation in recharge rates and the lithologic dissimilarity of the water bearing formations. (3) The environmental isotopes indicate that the Miocene groundwater has a mixed isotopic signature between modern meteoric (rainfall) and fossil waters. (4) The isotopic data of the Miocene aquifer and the enriched Gulf of Suez verifies that no seawater intrusions are affecting this aquifer with existing hydraulic barriers (clogged/sealed faults or impermeable massive blocks). (5) The hydrogeomorphological investigations, aeromagnetic and gravity data reveal an existence of two morphotectonic depressions (water collectors) which have paleo and recent recharge opportunities for the subsurface sedimentary layers (2–4 km thick). From the applied viewpoint, these two depressions have potential prospects for future groundwater exploration, which has significant impact on food security and land reclamation.

Rift obliquity in the Northern Volcanic Zone in Iceland using UAV-based structural data

Rift obliquity is known to be very frequent at divergent plate boundaries and shear components in the opening of fissures have been detected through seismicity in the monitoring of recent rifting events. However, the field structural evidence of obliquity in active rifts for Holocene events is still poorly studied, despite its relevance at both the lithospheric and upper-crust scales.We performed extensive high resolution UAV surveys on Holocene terrains in four areas along the active rift in the Northern Volcanic Zone of Iceland, to map structures and morphotectonic features in detail. We did a kinematic analysis and found an increase of the obliquity from N to S.We further discuss the origins of this obliquity and suggest that the combination of inherited structures reactivation, magmatic intrusions, and topography influence on the propagation of both fractures and magma intrusions can have an impact on the mismatch between rift opening direction and the far-field strain.We conclude that obliquity can be inferred for Holocene rifting events from surface structural data. It is thus fundamental to take into account the existing structural pattern and its (re)activation history in active rift zones to avoid missing out on possible preferential structure reactivation, magma propagation ways, and eruption sites during the monitoring of ongoing rifting events.

New insights into tectonostratigraphy and structural style of the Late Cretaceous sediments of Gongola Basin, Northern Benue Trough, NE Nigeria

Tectonostratigraphy of the Gongola Basin is still least understood. This study aims to present a new insight into tectonic evolution and structure of Gongola Basin based on field geology. The study revealed that sedimentation processes commenced in the depression created by tectonic subsidence as a result of Early Cretaceous tectonic events, which affected the basin and subsequently, reactivated the Santonian/Maastrichtian compression. The sediments were affected by Santonian and Maastrichtian compressions resulting in syn-sedimentary deformation and post-depositional faulting and folding. The imprints of dextral strike-slip faults and reverse faults on pre-Maastrichtian and Maastritchtian sediments formed as a result of reactivation of the pre-Santonian and Santonian faults. Active rifting phase followed by uplift and subaerial exposure as in Gombe inlier, and adjacent areas such as Teli Fault, Kaltungo, Burashika inliers followed by subsidence allowing for initial deposit of continental sediments and later, marine ingression which causes a change from continental to marine environments during Cenomanian. Eustatic adjustment in Late-Cenomanian to Early-Turonian led to first major transgression and short-regressive phase in middle Turonian-early Santonian. Mid-Santonian compression folded the sediments and was followed by subaerial erosion of parts of the folded sediments. Another eustatic adjustment in Late-Santonian-Campanian led to a short-lived transgression. A gradual retreat of the sea in the Maastrichtian resulted in progradation of Gombe Sandstone. Late Maastrichtian compression in end-Cretaceous tectonic event folded and tilted Gombe Sandstone, responsible for the angular unconformity that existed between Gombe Formation and overlying Paleocene sediments of Kerri-Kerri Formation, mostly restricted to NW of the basin.

Quantifying the migration rate of drainage divides from high-resolution topographic data

Abstract. The lateral movement of drainage divides is co-influenced by tectonics, lithology, and climate and therefore archives a wealth of geologic and climatic information. It also has wide-ranging implications for topography, the sedimentary record, and biological evolution and thus has drawn much attention in recent years. Several methods have been proposed to determine drainage divides' migration state (direction and rate), including geochronological approaches (e.g., 10Be) and topography-based approaches (e.g., χ plots or Gilbert metrics). A key object in these methods is the channel head, which separates the hillslope and channel. However, due to the limited resolution of topography data, the required channel-head parameters in the calculation often cannot be determined accurately, and empirical values are used in the calculation, which may induce uncertainties. Here, we propose two methods to calculate the migration rate of drainage divides based on the relatively accurate channel-head parameters derived from high-resolution topographic data. We then apply the methods to an active rift shoulder (Wutai Shan) in the Shanxi Rift and a tectonically stable area (Yingwang Shan) in the Loess Plateau, to illustrate how to calculate drainage-divide migration rates. Our results show that the Wutai Shan drainage divide is migrating northwestward at a rate between 0.21 and 0.27 mm yr−1, whereas the migration rates at the Yingwang Shan are approximately zero. This study indicates that the drainage-divide stability can be determined more accurately using high-resolution topographic data. Furthermore, this study takes the cross-divide differences in the uplift rate of channel heads into account in the measurement of drainage-divide migration rate for the first time.

Blind magmatism abets nonvolcanic continental rifting

Tectonic forces alone cannot drive rifting in old and thick continental lithosphere. Geodynamic models suggest that thermal weakening is critical for lithospheric extension, yet many active rifts lack volcanism, seeming to preclude this process. We focus on one such rift, the Tanganyika-Rukwa segment of the East African Rift System, where we analyze local seismicity for shear wave anisotropy and couple the results with numerical modeling. The strongest splitting measurements are from earthquakes with paths sampling lower crustal regions of high compressional-to-shear wave velocity ratios and have fast polarization directions parallel to the local mantle flow, implying the existence of oriented melt lenses. This lower crustal magmatism and observed high surface heat flow are consistent with substantial lithospheric weakening and explain the enigmatic relief and increasing strain accommodation along the rift axis. We conclude that progressive nonvolcanic rifting is assisted by deep crustal melts yet to breach the surface.

Applying Geostatistics to Understand Seismic Activity Patterns in the Northern Red Sea Boundary Zone

A comprehensive geostatistical analysis was conducted on a dataset comprising 24,321 seismic events in the Red Sea region, spanning from 1997 to 2020. This analysis involved the creation of a new seismic activity database, incorporating data from both Egyptian and Saudi Seismic Networks. This enriched database provided a robust foundation for a detailed examination of the seismic patterns and activities in the region. Utilizing geographic information systems and various spatial analytic methods, it identifies seismic patterns and tectonic influences. The findings reveal significant seismic clustering along the Central Red Sea axis, indicative of active rifting between the Nubian and Arabian plates. The study demonstrates spatial autocorrelation in seismic activities, with high-high clusters marking zones of elevated seismicity. Kernel Density Estimator analyses highlight concentrated seismic activity in the Gulfs of Aqaba and Suez. Higher magnitude events are shown to localize in areas of greater tectonic stress, aligning with known geological features. This research provides critical insights into the seismic dynamics of the Red Sea, showcasing the effectiveness of geostatistical techniques in analyzing seismic data in tectonically active regions.

Pre-existing structural control on the recent Holuhraun eruptions along the Bárðarbunga spreading center, Iceland

The active rift zones in Iceland provide unique insight into the geodynamic processes of divergent plate boundaries. The geodynamics of Iceland are studied intensively, particularly, by geophysical methods sensitive to active and/or visible structures such as earthquake seismic and Synthetic Aperture Radar observations or aerial photographs. However, older and less active structures, that may exert a strong control on the presently active geodynamics, are often buried beneath recent volcanic or sedimentary deposits and are—due to their passive mode—overseen by the typical geophysical investigations. Aeromagnetic surveys provide spatial information about subsurface magnetization contrasts relating to both active and inactive structures. However, the aeromagnetic data in Iceland were collected in the 1970-80s and are relevant only to large-scale regional rift studies. With the availability of reliable drones and light-weight atomic scalar sensors, high-quality drone magnetic surveys can provide an unprecedented spatial resolution of both active and passive structures of rift systems as compared to conventional airborne surveys. Here, we present the results of a drone-towed magnetic scalar field and scalar gradiometry study of the north-northeast trending Bárðarbunga spreading center to the north of the Vatnajökull ice cap, Iceland. Our results provide new information about the structural complexity of rift zones with evidence of densely-spaced, conjugate and oblique faults throughout the area. Evidence is shown of a hitherto unknown and prominent east-northeast trending fault structure that coincides with the northern tip of the main eruption edifice of the 1797 and 2014-15 Holuhraun volcanic events. We suggest that this pre-existing structure controlled the locus of vertical magma migration during the two Holuhraun events.