Orals: Tue, 5 May, 16:15–18:00 | Room K2
Subduction zones are defined by plate convergence, yet their upper plates exhibit a wide range of deformation styles globally. While various hypotheses have been proposed to explain this global variability, the controlling factors remain poorly understood. We analyzed ~24,000 km of active global subduction zones to investigate how subduction obliquity influences trench-parallel and horizontal deformation in the terrestrial inner forearc overriding plate. Using global datasets of GNSS velocities and active fault catalogs, we examined inner deformation across 13 forearcs on both short (decadal) timescales, captured by GNSS, and long (millennial to million-year) timescales, inferred from trench-parallel active strike-slip faults. Our results reveal a strong link between subduction zone obliquity and both the sense and magnitude of upper plate rotation observed in GNSS data, as well as the sense and rate of deformation along trench-parallel strike-slip faults. Unlike earlier studies suggesting that obliquity influences deformation only above a certain threshold, we find that even low to moderate obliquity affects forearc behavior. High-obliquity margins, such as New Zealand and the Philippines, show the highest GNSS-derived vorticity and cumulative slip rates on trench-parallel strike-slip faults. In contrast, lower-obliquity regions, like portions of Cascadia and Peru, exhibit reduced vorticity and either diffuse strike-slip faulting or broadly distributed deformation. Across all forearcs, we find strong correlations between obliquity and both GNSS vorticity and trench-parallel fault slip rates in the inner forearc.
Beyond controlling the magnitude and sense of inner forearc deformation, our results suggest that rheologic factors also influence how trench-parallel shear is accommodated within the inner forearc. We observe a continuum of trench-parallel strike-slip deformation styles within the inner forearc, ranging from motion accommodated on a single, through-going sliver fault with high slip rates to more distributed deformation expressed across multiple shorter strike-slip faults with lower slip rates. Emerging results suggest that this variability is linked to the distance between the down-dip extent of megathrust locking and the volcanic arc. Subduction segments with a short trench-to–locked-zone distance preferentially develop coherent sliver faulting, whereas those with a greater distance between the down-dip locking limit and the arc tend to exhibit more distributed strike-slip deformation across the forearc. We interpret this pattern to reflect a rheological control on how trench-parallel shear is accommodated. If shear strain is concentrated near the down-dip edge of locking, as predicted by simple elastic models, deformation localizes above this region. Where this localization occurs within or near the arc, conditions favor development of a single, through-going strike-slip fault. In contrast, when the locus of strain concentration lies farther trenchward within the forearc, deformation is more likely to be partitioned across pre-existing structures, resulting in distributed strike-slip faulting. These results suggest that while subduction obliquity exerts a first-order control on the sense and magnitude of inner forearc deformation, additional geometric and rheologic factors govern the style of trench-parallel inner forearc strain accommodation.
How to cite: Morell, K., Finley, T., and Newman, A.: Subduction zone obliquity and rheology dictate global trench-parallel inner forearc deformation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5993, https://doi.org/10.5194/egusphere-egu26-5993, 2026.
Subduction zone geodynamics have been a primary area of focus since the early days of plate tectonics theory. Initial approaches using analytical solutions sought to understand the fundamental driving forces, moment balances, and energetics governing oceanic plate subduction. Despite the limitations of scarce geophysical imaging, limited geological sampling, and emerging numerical techniques, these studies provided the foundations of modern geodynamics. As numerical techniques improved, power-law rheologies and complex geological processes were integrated into various codes. These provided more realistic simulations to understand a wide variety of regions on Earth, but they are rarely presented in the context of classical physical approaches. Nowadays, a unique opportunity exists to revisit these classical frameworks, aided by improved subducting slab imaging, an excellent geological record, and a deeper understanding of slab dynamics across active and ancient subduction zones.
In this work, a simplified but physically transparent framework is developed to revisit the force/moment balance, energetic conditions, and dissipation analyses governing slab dynamics. For this purpose, three representative slab geometries (steep, normal, and flat) were selected based on their dip below 40 km depth, where slab behavior is dominated by internal negative buoyancy and viscous lifting forces from the mantle. Slab pull was estimated by varying density contrasts and thickness, while viscous forces were derived from semi-analytical Stokes flow solutions to resolve pressure distributions along the slab surface. Gravitational potential energy changes were calculated to test whether internal density variations (e.g., eclogitization) and crustal thickening from oceanic plateaus drive changes in geometry.
Results show that mantle wedge suction can counteract slab weight in a flat subduction setting, while increased density from eclogitization destabilizes flat slabs and promotes steepening, linking moment balance and buoyancy to the global diversity of slab dips. Total energy dissipation is mainly controlled by mantle wedge flow, with low-angle and flat subduction representing the most dissipative configurations. Once moment balance allows, these tend to evolve toward steeper, more energetically stable states. Slab flattening occurs with increased buoyancy, higher convergence velocities, and greater mantle viscosities, producing flattening within 10–30 Myr. Conversely, reduced buoyancy, slower convergence, and lower viscosities favor steepening and slab rollback on comparable or shorter timescales of 5–10 Myr. This integrated and physically transparent analysis is consistent with the development of arc magmas on western margins of the Americas and provides a clear perspective to explain the diverse slab morphologies observed on Earth.
How to cite: Sanhueza, J. and Angiboust, S.: Revisiting force balance on subduction zones: the missing bridge to numerical simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12561, https://doi.org/10.5194/egusphere-egu26-12561, 2026.
The northeastern Caribbean plate boundary provides a natural laboratory to investigate strain partitioning, fault slip rates, and crustal rheology in an actively deforming tectonic setting, where seismic hazard is a major concern. In this study, we combine GNSS and InSAR observations to improve our understanding of how strain is accommodated and how slip rates are distributed across this plate boundary, with a specific focus on the island of Hispaniola. The inclusion of InSAR data substantially mitigates the effects of the sparse and uneven spatial distribution of GNSS stations that limited earlier models.
Using the combined GNSS-InSAR velocity field, we propose a new kinematic model that allows for internal deformation within selected tectonic blocks, incorporating InSAR-derived velocities for the first time in this type of modeling for the region. While our results are broadly consistent with previous studies, they identify and quantify compressional deformation within the Gulf of Gon\^ave, consistent with independent offshore observations.
We identify and quantify the impact of spatially correlated noise in the InSAR measurements, which is especially significant in this tropical, topographically complex region, where atmospheric artifacts can compete with or obscure the tectonic signal. We ultimately estimate surface strain rates and their associated uncertainties and compare these results with the geometry of faults imposed in block models as well as with the spatial distribution of current seismicity.
Our results confirm that the Enriquillo–Plantain Garden Fault Zone in southern Haiti is dominated by localized strike-slip motion. In contrast, deformation along the Septentrional Fault Zone in the Dominican Republic appears more distributed, suggesting that strain is accommodated by multiple fault strands rather than a single localized structure.
How to cite: Emmanuel, C., Raimbault, B., Calais, E., and Jolivet, R.: Interseismic Strain Accumulation and Partitioning in Hispaniola from GNSS and InSAR, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14468, https://doi.org/10.5194/egusphere-egu26-14468, 2026.
Volcanoes, earthquakes and natural resources along the margins of the Caribbean plate have been shaped by a history of subduction. In this presentation I will provide an overview how a dense deployment of Broadband Ocean Bottom Seismometer (BOBS) helped us to investigate several fundamental processes caused by the subduction of lithospheric crust and mantle through the upper mantel down to the mantle transition zone (MTZ). Using teleseismic tomography and plate reconstruction techniques we unraveled the tectonic history of the Caribbean plate showing clear evidence of a slab window and tear along the subducted Proto-Caribbean ridge, which also hosted one of the largest intermediate depth earthquakes in the region. Using local earthquake tomography, we developed a new slab model for the region and combining travel time and attenuation tomography we were able to identify melt ponds under the upper plate. We also found that serpentine most likely residing along major fracture zones is the dominant supplier of subducted water in the central arc of the Caribbean. Finally, by using P-to-S receiver functions to image the slab and the mantle transition zone beneath the Lesser Antilles we find that the slab flows directly though the mantle transition zone exhibiting super-deep (>700 km) discontinuities caused by a large basalt-rich chemical anomaly. All our findings point in the direction that the tectonic history of the subducting lithospheric crust and mantle has a strong influence on the observed geodynamic processes we image with geophysical techniques in subduction zone settings.
How to cite: Rietbrock, A.: Imaging subduction zone processes along the Lesser Antilles using a broadband ocean bottom seismometer network: The VoiLA experiment , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16545, https://doi.org/10.5194/egusphere-egu26-16545, 2026.
Integrating dynamic paleogeographic reconstructions into biodiversity studies reveals that Caribbean patterns of diversity, endemism, and biotic assembly arose through a combination of geodynamic processes rather than solely through long-distance overwater dispersal across a stable archipelago. Present-day biodiversity reflects the cumulative imprint of long-term geodynamic processes that continuously reshaped the region’s landscapes throughout the Cenozoic. Geodynamic reconstructions that integrate plate kinematics, subduction dynamics, and intraplate deformation show that the Caribbean evolved through successive phases of uplift, subsidence, rotation, and fragmentation, producing a highly dynamic configuration, extent, and connectivity of emerged landmasses. Subduction-related uplift and arc migration periodically generated shallow platforms, emergent volcanic arcs, and island chains that temporarily reduced marine barriers between the American continents and Caribbean islands. Conversely, tectonic reorganization and subsidence fragmented these connections, isolating landmasses and reorganizing drainage systems. These alternations between connectivity and isolation are central to understanding the timing and pathways of biotic dispersal and diversification. By explicitly incorporating block rotations, vertical motions, and plate-boundary reconfigurations, geodynamic reconstructions provide physical constraints on when and where terrestrial and freshwater dispersal routes existed. These reconstructions therefore offer a critical temporal and spatial framework for interpreting phylogenetic divergence times, colonization pulses, and patterns of endemism across the Caribbean biodiversity hotspot. In particular, they help reconcile apparent mismatches between biological and geological timescales by identifying short-lived but recurrent windows of connectivity that facilitated biotic exchange. This integrated geodynamic-biogeographic perspective underscores that Caribbean biodiversity is inseparable from the region’s tectonic evolution: deep Earth processes governed the emergence and disappearance of habitats, structured ecological connectivity, and ultimately shaped the assembly of one of the world’s most diverse and endemic island systems.
How to cite: Bufféral, S., Philippon, M., van Hinsbergen, D., Guillaume, D.-N., Jean-Jacques, C., and Leny, M.: Reconstructing Caribbean Landscapes to Understand Biodiversity Patterns, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22363, https://doi.org/10.5194/egusphere-egu26-22363, 2026.
In Ecuador, in the vicinity of the seismic rupture of the 2016 Mw 7.8 Pedernales earthquake, the megathrust fault is also affected by aseismic slip at shallow depths, including slow earthquakes and post-seismic slow slip.
The Ecuadorian margin is an exceptional natural laboratory. Its relatively narrow marine forearc and shallow megathrust make it an ideal location for studying the relationship between ongoing subduction of topographic highs, such as ridge and seamount, and seismic and aseismic slip behaviour on the plate interface.
The HIPER Project (2020–2022), which aims to better characterize the 3D structure of the Ecuadorian forearc domain, is based on an international collaboration funded by the French Oceanographic Fleet, the French ANR, Karlsruhe Institute of Technology (KIT, Germany), American NSF and IG-EPN (Ecuador). We successfully deployed a large number of OBSs (47), land stations (~200) and nodes (~500) to record both R/V L’Atalante shots and seismic activity.
Here, we present preliminary results from a 3D inversion of P-wave refraction and reflection data, which was performed with TOMO3D. Thanks to our newly developed semi-automatic picking tool, DeepFB, we were able to efficiently compile the catalogue of ~230,000 picks.. DeepFB is a U-Net based neural network designed for robust automatic first-break picking in active-source seismic data. It was extensively applied to our dataset and accounts for approximately 50% of the picked first arrivals. The resulting 3D P-wave velocity model provides new insights into the lateral velocity variations of the Ecuadorian margin and the subducting plate along the trench between latitudes 1°25′N and 0°10′S.
How to cite: Delsuc, A., Galvé, A., Laigle, M., Heuel, J., Frietsch, M., and Rietbrock, A.: 3D P-wave velocity structure of the Northern Ecuadorian seismogenic zone, host to the 2016 M7.8 Pedernales earthquake., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7483, https://doi.org/10.5194/egusphere-egu26-7483, 2026.
The South Peru subduction zone is a complex, highly active region, where the flat slab associated with the Nazca Ridge subduction in the North transitions to a much steeper subduction in the South. This transition not only causes the slab to contort, but affects seismicity patterns in the region. Here we use data from 26 seismic stations active from March 2022 to December 2024 as part of the DEEPTrigger project, along with 16 permanent Peruvian stations and 15 permanent Chilean stations, to create a 3-year seismicity catalogue of South Peru. Using PhaseNet for phase picking and PyOcto for phase association, we obtain a total of 166 971 events. These earthquakes are located with NonLinLoc-SSST using a new 3-D P and S-wave velocity model of the region obtained from full-waveform inversion (Kan et al., 2025), then relocated using double difference methods with cross-correlation times to obtain precise locations. We thus obtain the first dense and precisely-located earthquake catalog of the region.
With this new catalog, we are able to demonstrate the influence of the Nazca Ridge on seismicity patterns. We find numerous shallow seismic swarms where the ridge enters subduction, while they are absent from the rest of the margin. In combination with GPS records of nearby stations, they hint at the likely presence of slow slip. We also find that the edge of the Nazca Ridge is particularly active, down to depths below 80 km. This same edge was activated by the Mw 7.2 Acari earthquake which occurred on June 28th 2024 at the plate interface, and was preceded by a Mw 6.0 intraslab foreshock on June 16th 2024. The Acari mainshock triggered a large aftershock expansion towards the northwest where the Nazca Ridge subducts, and a triggered swarm and possible SSE in that region. It also caused an increase of intraplate seismicity directly downdip along the Nazca Ridge edge, demonstrating the ridge’s ability to concentrate stress.
How to cite: Chalumeau, C., Sanchez Reyes, H., Münchmeyer, J., Langlais, M., Villegas Lanza, J. C., Gonzales, A., Norabuena, E., Tavera, H., and Socquet, A.: Influence of ridge subduction on seismicity in South Peru, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9352, https://doi.org/10.5194/egusphere-egu26-9352, 2026.
The Central Andes are a place of considerable interest for the study of the physical processes involved in subduction. Indeed, it hosts significant seismic events relatively frequently, with four earthquakes of magnitude greater than eight in the last three decades: the 1995 Mw8.0 Antofagasta, the 2001 Mw8.4 Arequipa, the 2007 Mw8.0 Pisco, and the 2014 Mw8.1 Iquique earthquakes. In addition, structural heterogeneities, such as the Nazca and Perdida oceanic ridges, appear to segment seismic ruptures along the Peru-Chile trench. Estimating the seismogenic potential of the Central Andes, particularly in Southern Peru, where the amount of geodetic data available has increased considerably in recent years, is therefore a key issue.
Using 200+ GNSS sites, and InSAR mean velocity maps (2015-2021) processed in the framework of the FLATSIM Andes project (FormaTerre, 2020), we measured the deformation of the overriding plate on the horizontal and vertical components. In order to model interseismic and postseismic processes with a realistic structure and rheology, we developed a finite element method model of the subduction, featuring Newtonian viscoelastic Burgers rheology in the asthenosphere and an elastic cold nose. Accounting for the postseismic displacements associated with great subduction earthquakes, we propose a viscoelastic interseismic coupling model with unprecedented resolution in the area. This model shows significant heterogeneity, with high coupling off the coast of South Peru and Chile, and weaker coupling where oceanic structures, notably the Nazca Ridge and the Nazca Fracture Zone, subduct beneath the South American continent.
The spatial resolution provided by InSAR, notably on the vertical component, is of great interest to investigate the partitioning of the deformation in the upper plate, which is a fundamental aspect in the perspective of a unified interseismic coupling model at the scale of Peru and Chile. For this purpose, we quantified the East and vertical displacements across the Cuzco fault system (up to 3 mm/yr and 2 mm/yr on the East and vertical components respectively) and the Cordillera Blanca (up to 1.5 mm/yr and 3 mm/yr on the East and vertical components respectively), which have been proposed by Villegas-Lanza et al., 2016 to delimitate a rigid block motion referred as the Peruvian Sliver. In addition to this partitioning at crustal structures, primary (3-4 mm/yr) and secondary (2 mm/yr) zones of uplift are observed in Peru and Chile, at about 130 and 250 km from the trench, respectively. The secondary zone of uplift is associated with high topography, suggesting partial interseismic plastic deformation of the upper plate. Also, the secondary uplift zone in Peru is primarily observed in the flat-slab region and tapers with the transition to dipping-slab. Both the primary and secondary uplift zones are collocated with trench-parallel stripes of intraslab seismicity, which could be linked to fluid migration processes or fracturing of the slab.
How to cite: Lovery, B., Chlieh, M., Radiguet, M., Doin, M.-P., Villegas-Lanza, J. C., Audin, L., Chalumeau, C., Norabuena, E., Tavera, H., Durand, P., and Socquet, A.: Active tectonics of Central Andes from GNSS and InSAR time series, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5379, https://doi.org/10.5194/egusphere-egu26-5379, 2026.
Along-strike variations in megathrust coupling modulate forearc deformation through both elastic, seismic-cycle processes and permanent tectonic uplift. Yet the degree to which short-term interseismic deformation is translated into long-term geomorphic expression remains poorly constrained. We investigate this relationship along the hyperarid North Chilean forearc using Sentinel-1 InSAR time series and a set of geomorphic uplift proxies, including marine terraces, coastal topography, and alluvial fan slopes. The preservation of landforms allows direct comparison between geodetic and geomorphic signals across spatial and temporal scales.
The relationship between geodetic uplift rates and long-term uplift indicators varies along strike and becomes weak or alternates between positive and negative correlations in the Mejillones Peninsula region. This peninsula constitutes a tectonic hinge separating two seismotectonic segments characterized by distinct deformation patterns. Alternating correlations and anticorrelations between geodetic uplift and uplifted marine traces imply episodic uplift governed by the interplay of interseismic and coseismic vertical motions. Coastal alluvial fan slopes correlate with geodetic uplift only in the segment north of Mejillones towards the north, whereas south of it their independence from uplift suggests a dominant climatic control. The geodetic uplift rates and coastal topography preserve similar large-scale trends while differing in finer-scale, and the local correlation remains mostly positive across the latitude range. Upper-plate faults align with the north–south aligned inflection zone of geodetic uplift, suggesting that their geometry and distribution may be influenced by regional bending and strain gradients across the uplift–subsidence transition. Their low slip-rates may indicate that these faults do not accommodate significant long-term plate motion; instead, they remain largely quiescent interseismically and are preferentially activated during megathrust earthquakes through transient stress transfer. Our results suggest that long-wavelength, long-term deformation dominates forearc topography, whereas short-wavelength, seismic-cycle deformation adds variability that may be preserved differently across geomorphic features.
How to cite: Kosari, E., Metzger, S., Navarro-Sanchez, V., Oncken, O., Schurr, B., Rosenau, M., Victor, P., Sippl, C., and van Dinther, Y.: From Elastic Strain to Permanent Uplift Along the North Chilean Forearc, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19752, https://doi.org/10.5194/egusphere-egu26-19752, 2026.
Understanding the rheological structure of the lithosphere and the frictional behavior of the interface is essential to evaluate the mechanisms controlling surface deformation and seismic behavior along subduction margins. Postseismic deformation following large megathrust earthquakes provides a unique opportunity to constrain these properties, as it is strongly influenced by afterslip and viscoelastic relaxation processes.
In this study, we analyze the postseismic deformation associated with the 2015 Mw 8.3 Illapel earthquake in Central Chile by jointly exploiting GNSS and InSAR time series spanning up to eight years after the event. While GNSS data offer high temporal resolution, InSAR provides continuous spatial coverage, allowing us to characterize postseismic deformation at both local and regional scales. To separate the contributions of different deformation processes, we perform an Independent Component Analysis (ICA) on GNSS time series, and a pixel-by-pixel parametric decomposition on InSAR data.
Our results reveal two main postseismic deformation patterns. The first one is spatially correlated with the coseismic rupture area and displays a logarithmic temporal decay, consistent with afterslip-driven deformation. The second pattern is located north of the main rupture zone and is characterized by a nearly linear temporal evolution. This signal spatially coincides with a region of persistently low interseismic coupling, suggesting a distinct physical origin.
Based on these observations, we perform numerical modeling using the finite-element solver PyLith to investigate the potential sources of deformation. The models incorporate realistic fault geometry and rheological layering, and are driven by the imposed coseismic slip distribution. Our results indicate that the observed deformation patterns are best explained by the presence of a low-viscosity channel at a ~40 km depth, located at the base of the slab interface. This rheological anomaly spatially correlates with the subduction of the Challenger Fracture Zone (~30°S).
We propose that the subduction of this bathymetric anomaly enhances fluid release, which, through serpentinization processes, reduces the effective viscosity of the medium. These findings have important implications for seismic segmentation and earthquake behavior, as this region commonly acts as a boundary for the rupture of large megathrust earthquakes.
How to cite: Molina, D., Lovery, B., Radiguet, M., Pierre, M., and Socquet, A.: Linking Postseismic Deformation and Slab Rheology to Seismic Segmentation in Central Chile, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19696, https://doi.org/10.5194/egusphere-egu26-19696, 2026.
Posters on site: Mon, 4 May, 16:15–18:00 | Hall X2
The increase in space geodetic measurements for examining plate motion in the past three decades has significantly advanced our understanding of complex deformation processes in subduction zones throughout the earthquake cycle. We now recognize a spectrum of seismic and aseismic behaviors, including slow slip events, non-volcanic tremor, low-frequency earthquakes, fault creep, episodic tremor and slip (ETS), postseismic afterslip, and viscoelastic mantle flow transients. Notably, Materna et al. (2019) observed dynamically triggered increases and decreases in plate coupling associated with nearby earthquakes in southern Cascadia. We have reproduced and extended these findings using an improved semi-automated detection method, which reveals additional examples of time-dependent coupling changes in the region.
This study applies our method to the Chilean subduction zone to investigate similar temporal variability in plate coupling changes. In southern Chile, Klein et al. (2016) and Melnick et al. (2017) documented GNSS velocity increases near the boundaries of the unruptured segments following the 2010 Maule earthquake. GNSS rates south of 21°S accelerate up to 10 mm/year in the second year following the 2014 Iquique earthquake, potentially reflecting a coupling increase (Hoffmann et al., 2018). Additionally, Luo et al. (2020) reported a systematic decrease in seaward velocities from 2010–2019 across the southern half of the great 1960 Valdivia rupture zone. Our ongoing work seeks to detect and characterize such abrupt GNSS velocity changes in Chile using our semi-automated approach and to better understand the underlying physical mechanisms. In particular, we aim to constrain the recently identified phenomenon of dynamically triggered coupling changes, with implications for earthquake cycle models and seismic hazard assessment across global subduction zones.
How to cite: Roy, A. and Jackson, N. M.: The Search for Time-Dependent Coupling Changes on the Plate Interface following the Great Earthquakes of Chile, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-866, https://doi.org/10.5194/egusphere-egu26-866, 2026.
The tectonically active northern Colombian Caribbean margin, where the Magdalena Canyons System (MCS) lies adjacent to the structurally confined La Aguja Canyon (LAC), provides an exceptional natural laboratory to investigate sediment mixing and the partitioning of transport pathways between coastal and deep-marine environments. Here, we integrate new detrital zircon U–Pb geochronology from 18 coastal and offshore samples (~1,900 grains) with published river and coastal datasets to assess how provenance signals are transferred from onshore sources through submarine canyon systems into offshore depocenters. Detrital zircon ages span from <1 Ma to ~2700 Ma.
Our dataset includes 10 offshore samples distributed across the MCS, LAC, and distal sectors of the Magdalena Submarine Fan, together with 8 newly analyzed coastal samples. The coastal samples capture sediment supplied by two contrasting source regions: the Magdalena River, which delivers the largest sediment load to the Caribbean and carries a characteristically multimodal Andean-derived zircon signature, and rivers draining the Sierra Nevada de Santa Marta (SNSM), which provide a lower sediment flux but a compositionally distinct crystalline signal directly to the coast. All samples were analyzed using detrital zircon U–Pb geochronology (LA-ICP-MS), complemented by grain-size analysis, cathodoluminescence imaging, and bulk mineralogical characterization by X-ray diffraction. Detrital zircon U–Pb age distributions were evaluated using kernel density estimates, multidimensional scaling, and inverse mixing models.
River and coastal datasets define two robust provenance end members. Sediments associated with the Magdalena River exhibit a multimodal Andean-derived age spectrum characterized by Neogene–Quaternary (<8 Ma), Jurassic–Cretaceous (~75–180 Ma), and Neoproterozoic (~990 Ma) populations. In contrast, sediments sourced from the SNSM display a narrower Paleogene–Jurassic–Proterozoic spectrum, with prominent peaks at ~50 Ma, ~180 Ma, and ~990 Ma. Offshore samples reflect this partitioning across distinct canyon domains: MCS samples retain the multimodal Magdalena signature, whereas LAC samples preserve the restricted SNSM signal. Distal fan samples integrate both age populations, delineating a downslope mixing zone where sediment contributions from both canyon systems may converge. Statistical analyses consistently support this sediment-routing partitioning, indicating dominant Magdalena-derived input to the MCS and distal fan, and a strongly confined SNSM signal within the LAC with limited distal transfer.
These results demonstrate that sediment routing along the northern Colombian Caribbean margin is strongly partitioned between adjacent submarine canyon systems, yet becomes progressively integrated downslope within the Magdalena Submarine Fan. While Magdalena-derived sediments are routed through the MCS and SNSM-derived material remains largely confined within the LAC at proximal and canyon scales, their provenance signals converge and mix within distal fan depocenters. This transition from canyon-scale partitioning to fan-scale mixing, controlled by tectonic confinement, source-area configuration, and canyon morphology, illustrates how sediment-routing systems operate in tectonically complex, actively deforming continental margins worldwide.
Keywords: detrital zircon U-Pb geochronology, source-to-sink systems, submarine canyons, marine sediment provenance, Caribbean margin
How to cite: Villanueva-García, E., Rojas-Agramonte, Y., Rincón-Martínez, D., Álvarez-Silva, Ó., Rösel, D., Mora, A., and Winter, C.: Detrital zircon mixing and sediment-routing partitioning from rivers to coastal and canyon–fan systems along the Colombian Caribbean margin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1674, https://doi.org/10.5194/egusphere-egu26-1674, 2026.
Subducting slabs and mantle plumes are two end-member mechanisms for driving vertical flow inside the Earth. However, their mutual interactions remain underexplored. One example is the potential interaction between the Galápagos plume and the Cocos slab in Central America. This region hosts many abnormal tectonic features, such as dramatic along-trench variations in heat flow and surface topography, which may represent surface responses to the interacting Cocos slab and Galápagos plume at depth. The slab is found to be torn in tomographic studies and may provide a channel for plume material to travel from the Pacific to the Caribbean mantle. We design 3D finite-element subduction models using the code CitcomS to study the plausible geodynamic processes. In our initial experiments, we find that the evolution of the subducting Cocos slab is strongly influenced by far-field forces associated with the ancient Farallon slab. As the Farallon slab below the eastern Caribbean continues to sink, the increasing lateral pressure gradient across the Cocos trench induces repeated episodes of slab tearing and renewed subduction of the Cocos slab. This process ultimately leads to the formation of an imbricate slab geometry, consistent with structures observed in seismic tomography. After incorporating the Galápagos plume into our model, hot plume material ascends through the tear in the Cocos slab and enters the Central American mantle wedge. The resulting present-day distribution of plume material shows a strong spatial correlation with regions of elevated heat flow and high topography in Central America. These results suggest that that slab–plume interaction dynamically enhances surface heat flow and contributes to regional topographic uplift. Our study provides new insights into slab–mantle dynamics in other subduction systems around the Pacific where nearby hotspots are present.
How to cite: Wang, J., Liu, L., Cao, Z., and Dong, H.: Dynamics of slab-plume interaction in Central America, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6298, https://doi.org/10.5194/egusphere-egu26-6298, 2026.
In the Ecuadorian subduction zone, Global Navigation Satellite System (GNSS) measurements indicate significant spatial variations in the interseismic coupling of the interplate contact, along with diverse seismic and aseismic slip behaviors. These variations are likely linked to local differences in the thermo-mechanical properties of the Ecuadorian margin. The thermal and rheological characteristics of the subducting Nazca plate depend on multiple factors, including lithology, sediment thickness, fracturing degree, structural heterogeneities, frictional properties, and fluid circulation. Surface heat flow variations provide indirect insights into some of these deep-seated features. Heat flow profiles derived from "Bottom Simulating Reflectors" (BSRs) reveal a clear north-south thermal segmentation of the Ecuadorian margin. These profiles consistently show a decrease in heat flow on the accretionary prism with increasing distance from the deformation front, stabilizing at approximately ~40 mW.m−2 along the upper slope. However, heat flow values at the deformation front display significant heterogeneity, ranging from ~60 mW.m−2 to ~160 mW.m−2. During the SUPER-MOUV campaign, 18 heat flow measurements were collected to address the following objectives: 1- To evaluate the reliability of heat flow estimations derived from BSRs in Ecuador by conducting direct measurements at the margin front, allowing for a comparison between in-situ data and BSR-derived values. 2- To measure heat flow within the trench, a region where BSRs are absent. 3- To assess heat flow on the Nazca plate before subduction, an area also lacking BSRs, for which no heat flow data exist within 200 km of the deformation front, and for which numerous seamounts, potential sites of fluid circulation, have been identified near the Ecuadorian margin.
How to cite: Rolandone, F., Marcaillou, B., Poort, J., Michaud, F., and Proust, J.-N.: Thermal Segmentation, Interplate Coupling Variability, and Fluid Circulation in the Ecuadorian Subduction Zone , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6387, https://doi.org/10.5194/egusphere-egu26-6387, 2026.
The northern end of the South American convergent margin is influenced by the interplay between the Nazca, South American, and Caribbean plates. The relatively recently (Miocene) accretion of the Panama arc along the western margin of northernmost South America adds further uncertainty to an already complex tectonic region. Of note is the offset in the Wadati Benioff Zone (WBZ) at ~5.5° N, often referred to as the “Caldas Tear”. The shallowest (50-60 km depth) reach of the northern WBZ lies over 400 km from the nearest plate boundary, an observation that requires one or more subducting slabs to be horizontally emplaced (a.k.a. “flat slab”). But which plate (or plates) comprises this northern WBZ? We know that both the Caribbean and Nazca plates are subducting, but the spatial extent of each plate and their resultant interactions remain unclear. To address these (and many other questions) about this complex region, we installed a temporary array of 66 broadband seismometers straddling the Caldas Tear north-to-south and extending across both WBZs east-to-west as part of the NSF-funded Modeling, Uplift, Seismology, and Igneous geochemistry in the Colombian Andes (MUSICA) project. This deployment was installed in phases from July 2022 to July 2023. The full array was in place from July 2023 until June 2025. Preliminary results of our novel dataset indicate the presence of complex crustal and slab structures, as well as indications of the mantle’s response to the multiple downgoing slabs. Here we present information about our deployment (including the use of direct burial seismometers and Carnegie Quick-Deploy Boxes), as well as early insights from preliminary results.
How to cite: Wagner, L., Monsalve, G., Carchedi, C., and Avellaneda-Jiménez, D.: The MUSICA Seismic Deployment: Illuminating subduction complexities at the northern end of the South American Cordillera, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8350, https://doi.org/10.5194/egusphere-egu26-8350, 2026.
Fluid circulation along active margins represents a key geological process that influences geochemical cycles, sedimentary dynamics and the occurrence of seismic activity and associated natural hazards. The SUPER-MOUV oceanographic cruise (January–February 2024) aimed to investigate seafloor manifestations of these fluid circulations and their relationship with seismic activity along the active margin of northern Ecuador. Multibeam data (bathymetry), water column data (seismic profiles and bathymetry), high-resolution seismic profiles, and in-situ observations from the Nautile submersible were combined to complement data from the HIPER cruises (bathymetry, deep seismic imaging) and a dense grid of industrial seismic profiles. This dataset allows us to reveal seabed fluid manifestations in areas where topographic irregularities, such as seamounts, subduct and create preferential pathways for fluid migration within the upper plate. At approximately latitude ~0°15’N latitude, the subduction of the Atacames seamounts oceanic topography carried by the Nazca plate correlates spatially with extensive seabed fields of carbonate mounds (up to 300 meters long and 15 meters high) build on the continental shelf, the majority of which is associated with active fluid emissions in the water column. Samples collected by the Nautile submersible reveal that these concretions incorporate centimetric clasts containing Eocene foraminifers. This finding suggests a vigorous, “mud-volcano-type” fluid circulation event, which was capable of transporting clasts from the earliest sedimentary deposits resting on the oceanic basement of the Ecuadorian forearc basins, to the seabed surface. Seismic profiles interpretation, including seismic attribute analysis, enabled the characterization of fluid accumulations at depths and highlight their circulation pathways associated with faults, fractures, diapirs and litho-stratigraphic discontinuities. Notably, some diapiric structures, located directly beneath seabed fluid emissions, root as deep as 3 seconds two-way travel time (TWT) into a highly fractured acoustic basement, consistent with the presence of Eocene clasts on the seafloor and suggests the existence of a potentially deeper fluid source.
How to cite: Michaud, F., Laigle, M., Ramirez Parrales, M. F., Collot, J.-Y., Caplette, A., Galvé, A., Schenini, L., Lebrun, J. F., Lebourgois, C., Marcaillou, B., Ratzov, G., Boulart, C., Noël, L., Gay, A., and Proust, J. N.: Impact of seamount subduction on margin fluid dynamics: distribution, seafloor emissions, and upwards migration pathways at the northern Ecuador continental shelf (SUPER-MOUV cruise, 2024), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10298, https://doi.org/10.5194/egusphere-egu26-10298, 2026.
Along the Peruvian margin, the subduction of the Nazca Plate beneath the South American Plate shows significant along-strike variability, including changes in slab dip and the subduction of major bathymetric features such as the Nazca Ridge and several fault zones. Seismic behavior along the Peruvian margin is likewise highly variable, ranging from frequent large megathrust earthquakes in southern Peru to comparably low seismicity in the north, where tsunami earthquakes have nevertheless caused significant historical damage.
To investigate the mechanical strength of the Peruvian forearc, we perform an areal critical taper analysis based on gridded surface slope and slab dip data. The results reveal significant spatial variations in detachment strength along the margin. South of the Nazca Ridge (~15°S), the forearc is characterized by a relatively strong detachment. The central segment (15°S–10°S) shows moderate to weak detachment strength, with particularly weak conditions near the trench. In northern Peru (10°S–4°S), the detachment is generally weak across the entire forearc. Overall, detachment strength tends to decrease toward the trench, except in the region affected by the subducting Nazca Ridge, where an increase in strength is observed.
The long-time-scale spatial variability in detachment strength correlates fairly well with interseismic coupling patterns derived from short-time-scale geodetic observations, with locked portions of the subduction interface generally characterized by higher detachment strength. In our study, we address the question of whether and how short-term seismic behavior is controlled by the long-term mechanical properties of the Peruvian forearc.
How to cite: Kusche, F. and Kukowski, N.: Variable detachment strength along the Peruvian margin estimated from Critical Taper Analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11901, https://doi.org/10.5194/egusphere-egu26-11901, 2026.
Published catalog of instrumental seismicity from French observatories in the Lesser Antilles (OVSG in Guadeloupe and OVSM in Martinique) ranging from 2014 to 2022 is very extensive in space and time but the computed magnitudes are based on various local scales (Saurel et al., 2022; 2024), a common issue for hazard assessment studies. The aim of this study is to unify the magnitudes of this catalog, by establishing a regression relationship between the magnitudes commonly calculated by the observatories and the moment magnitude Mw, and studying the variability of stress drop depending on the tectonic context from trench to depth. The catalog contains 18,784 earthquakes recorded by, with small variations, the same regional seismic stations during the whole period, and with magnitudes ranging from -2.0 to 6.2. Completeness analysis for the entire Lesser Antilles arc reveals two main maximum values: one at M = -0.2, related to volcanic earthquakes from active volcanoes; another at M = 2.5, indicating the approximate completeness magnitude threshold for earthquakes of tectonic origin. In this study we focus on 8,569 earthquakes with M > 2.0. Moment magnitudes Mw were estimated using SourceSpec codes (SSp) (Satriano et al., 2016; 2025), which performs spectral inversion of S-wave displacement spectra. The inversion also provides key parameters such as corner frequency, seismic moment, radiated energy, static stress drop, and apparent stress. Mw values calculated with SSp are consistent with Mw calculated by moment tensor inversion with the Isola software or reported by international agencies, and may support the retroactive inclusion of Mw in older catalogues. Finally, magnitudes Mw computed with SSp codes were validated for 4,238 earthquakes. The relationship between magnitudes does not appear to be linear for the entire M range, and variations in slope and intercept values are observed with depth. Several orthogonal distance regressions with exponential models were then computed for each type of magnitude and for different range of magnitudes and depths. Md appears less stable and, where possible, should be avoided in earthquake location analyses. Uncertainties in magnitude estimations coming from the original catalog were incorporated in the regressions to enhance the results. The different final laws will enable the conversion and incorporation of additional data from instrumental data before 2014. Regarding the preliminary observations of variability of median stress drop values, we observe small differences between the seismotectonic domains from trench to depth.
How to cite: Corbeau, J., Gonzalez, O., Satriano, C., Saurel, J.-M., Bouin, M.-P., and Lemarchand, A.: Relationship between magnitudes commonly calculated by the French observatories and the moment magnitude Mw, and variability of stress drop in the Lesser Antilles subduction zone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15337, https://doi.org/10.5194/egusphere-egu26-15337, 2026.
Andean-type orogens are characterized by prolonged subduction, in which the upper plate can record alternation between contractional and extensional phases. Subduction may involve the accretion of anomalies in the subducted slab, resulting in upper plate deformation and mountain building. The collision of the Caribbean Large Igneous Province (CLIP) with the western margin of South America between 75 - 62 Ma marked the evolution of the Northern Andes.
Despite this structure playing a fundamental role as an inherited structure that could control reactivations during the construction of the Northern Andes, the timing of this collisional event has been constrained through field-based structural observations and cross-cutting relationships. There is still no direct dating of the deformation, nor an understanding of the deformation mechanisms and metamorphic conditions of the shear zone during the collision and the subsequent reactivations. To address this, we propose an integrated study combining field observations, petrographic, geochronological, and mineral chemical analysis.
Extending approximately 2,000 km from Colombia to Ecuador, the Cauca–Romeral Fault System (CRFS) is the tectonic suture between the continental basement of South America and allochthonous oceanic terranes associated with the Caribbean Plate. Along this system, a mylonitic belt with well-developed ductile fabrics locally overprinted by brittle structures reflects a complex history of deformation and reactivation, which is used in this work to constrain the timing and conditions of the deformational phases.
Field relationships and petrographic observations suggest multiple deformation phases, including at least two ductile events and brittle reactivations. The ductile deformation is evidenced by shear zones with well-developed mylonitic fabrics affecting both oceanic and continental domains. The mylonites exhibit a first fabric defined by rotated and fractured hornblende and plagioclase porphyroclasts, with grain boundary migration (GBM) textures in quartz. This fabric is overprinted by a second foliation with neoformed chlorite and titanite, and subgrain rotation (SGR) textures in quartz. Both ductile fabrics are cross-cut by multiple fracture sets filled with epidote and calcite, which are fractured and displaced, as well as by extensive feldspar alteration to sericite, associated with brittle conditions.
These observations are consistent with the chemical compositions of chlorite, which indicate deformation under greenschist facies conditions, whereas hornblende porphyroclasts preserve inherited chemical signatures from the protolith or earlier metamorphic stages.
Apatite fission-track ages of 27.1 ± 1.6 and 28.0 ± 1.57 Ma from mylonites in the western fault of the CRFS suggest that the hanging wall of this fault reached temperatures above ~120°C before the Miocene.
The CRFS records a polyphase deformational history marked by ductile shearing and subsequent brittle reactivation. Textural and chemical evidence in quartz, hornblende, and chlorite suggest that the mylonitic deformation occurred under amphibolite facies conditions (~600°C), possibly associated with the collision of the CLIP, and was subsequently overprinted by lower-temperature deformation under greenschist facies (~350-450°C). These phases are overprinted by hydrothermal alteration, veining, and faulting, reflecting brittle deformation, which can be related to the AFT ages that indicate cooling to shallow crustal levels by the Oligocene.
This work is part of project 111193, funded by Minciencias, Colombia.
How to cite: Calderón Díaz, L. C., Zapata, S., Cardona, A., Parra, M., Ortiz, D., Villa, S., and Paverelli, V.: From ductile shearing to brittle reactivation of a tectonic suture: The evolution of the Cauca–Romeral Fault System, Northern Andes , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15914, https://doi.org/10.5194/egusphere-egu26-15914, 2026.
With the upcoming adoption of a new version of the European construction codes, the French agency for risk mitigation (DGPR) has initiated the update of the probabilistic seismic hazard assessment (PSHA) on its territories. For the French Lesser Antilles territories of Martinique, Guadeloupe, Saint-Martin and Saint-Barthélémy islands, this PSHA update is done in the framework of the ATLAS project. Long period and broad coverage seismic catalogs with homogeneous magnitude estimates are needed as input in PSHA calculation. In the French Antilles, IPGP volcanological and seismological observatories in Martinique (OVSM) and Guadeloupe (OVSG) locate all events seen by their seismic networks since 1981. In 2013, in the framework of the CDSA regional project (centre de données sismologique des Antilles), Massin et al has merged all phases bulletin and location from different agencies, including OVSM and OVSG to produce a multi-origin, automatic relocated catalog available in QuakeML format.
Since 2014 and the completion of the WI VSAT regional network, IPGP publishes every year a validated and unique catalog with the data from both IPGP observatories. In 2025, this catalog between 2014 and 2022 was processed by Gonzalez et al to compute moment magnitudes and establish robust regression laws between Mw and the most commonly used local magnitude scales in OVSM and OVSG.
Based on those two previous studies, we were able to retrieve the original manually validated OVSM and OVSG catalogs from the CDSA database in QuakeML format. We then applied the same validation process we are using to produce the unique yearly catalog since 2014. This process includes identifying and merging events that were located by both observatories, selecting the best solution. A thorough manual review is performed to eliminate any false or badly located event and to ensure no significant events were missed. All events without any magnitude are removed from the database.
Prior to 2013, only one magnitude was used in routine at the observatory, consistently since 1981: the duration magnitude. However, for significant events, this magnitude which saturates around M 4 was replaced by local or moment magnitude from international agencies. For events with magnitude higher than 4, we then look in the ISC earthquake database to replace the local magnitude by GCMT Mw magnitude if it exists, or to tag the observatory magnitude as local. Finally, we apply the regression laws established by Gonzalez et al to produce a final catalog with all magnitude either in calculated Mw or in converted Mw.
This validated catalog of more than 30 000 events covers the central portion of the Lesser Antilles between 1981 and 2013. In addition to the PSHA studies performed in the framework of the ATLAS project, this reference catalog can be used for numerous studies, such as long-term seismo-tectonic variations of the subduction and crustal faults.
How to cite: Saurel, J.-M., Corbeau, J., Gonzalez, O., and Satriano, C.: Lesser Antilles instrumental seismic catalog from the French observatories for seismic hazard assessment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18593, https://doi.org/10.5194/egusphere-egu26-18593, 2026.
The Northern boundary of the Caribbean plate, and more specifically the Gonâve microplate, is the locus of intense tectonic activity partly accommodated by two strike-slip fault systems (the Enriquillo-Plantain Garden Fault Zone (EPGFZ) to the south and the Septentrional-Oriente Fault Zone (SOFZ) to the North) and by the opening of the Cayman Trough to the west and the Haitian fold-and-thrust belt in the east. This region has been extensively studied for several years since the earthquake of 12 January 2010; however, the deformation in the Gonâve Gulf to the west of Hispaniola island has not yet been well characterised. Multibeam bathymetric and seismic reflection data from multiple oceanographic campaigns in the study area have enabled us to identify tilted blocks from the eastern Cayman Through continental margin with low-angle normal faults. Seismic horizons allow us to identify the roof of syn-rift units in the Gonâve Gulf with an initiation of the rifting between 49 and 56 My.
New Ar/Ar dating of granodiorites recovered during submersible dives (CAYVIC cruise) on tilted blocks in the distal part of the margin, together with the interpretation of newly processed seismic profiles from the CASIS oceanographic campaign crossing the Ocean Continent transition, provide the timing and geometry of the tectonic structures of the eastern continental margin. Extending from north of Jamaica to at least the eastern part of the Gonâve Gulf, with a length of 450 km, the continental margin appears relatively classical, with a beta factor of 2.7.
NE-SW compression in the Gonâve Gulf, linked to the collision with the North American plate, reactivates the extensive structures and creates new compressive structures. We propose a spatio-temporal evolution of tectonic structures from the formation of the Eastern Cayman trough margin to the west to its reactivation in the Haitian fold-and-thrust belt to the east.
How to cite: Joyeux, T., Leroy, S., Saspiturry, N., Munch, P., Rojas-Agramonte, Y., Philippon, M., d'Acremont, E., and Mercier de Lepinay, B.: Structure and evolution of the Cayman Trough oriental margin : Legacy seismic data and samples, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19381, https://doi.org/10.5194/egusphere-egu26-19381, 2026.
The Puerto Rico Trench (PRT) marks the oblique subduction of the North American Plate under the Greater Antilles Island Arc and the Caribbean Plate. In 2023 we conducted a geophysical survey of the PRT and across the island of Puerto Rico (PR) using the RV Langseth (cruises MGL2315 and MGL2316). PRISTINA (Puerto RIco Subduction Tectonics seismic INvestigAtion) consists of: a) 2D ultra-long-offset (13.65 km) multichannel seismic (MCS) reflection data; b) a N-S island-crossing wide-angle seismic profile sampling the incoming plate, PRT, Puerto Rico, Muertos thrust belt and Caribbean Plate instrumented with nodal land stations and ocean bottom seismometers (OBS); c) a wide-angle OBS profile crossing the PRT north of the British Virgin Islands; d) Four wide-angle fan profiles; e) Underway bathymetry, gravity and magnetics; and f) a temporary deployment of broadband stations in Puerto Rico.
Here we present a 2-D P-wave velocity (Vp) model along a 310-km-long, North-South-trending seismic transect at Longitude 66°30’W that illuminates the crustal and mantle structure of the Muertos Trough south of PR on the Caribbean Plate, the island of PR, and the PRT. The model is derived from traveltime tomography of active-source wide-angle data acquired with 30 ocean bottom seismometers (nominal spacing of 5-10 km), a temporary land deployment of 48 short-period nodal seismometers (nominal spacing of ~1 km), and 4 permanent broadband stations, all of which recorded marine airgun shots.
Our preliminary results show that along the southern section of the transect, an ~11.5-km-thick Caribbean crust underthrusts the frontal ~30 km of the Muertos Thrust Belt where 2-7-km-thick sediments (Vp<4 km/s) have been accreted against a crystalline terrain (Vp~5.5 km/s) forming the southern submarine slope of PR. Beneath Central-Southern PR, velocities of 6.5 kms are not reached until ~22 km depth, and Vp of 7 km/s at 32 km depth, suggesting an island arc crust of normal thickness but abnormally low Vp. Beneath Central-Northern PR high velocities (6.5-7 km/s) are found at 4-10 km depth, similar to global averages of island arc crustal structure. Along the northern section of the transect beneath the PRT, a narrow sedimentary wedge with very low Vp (3 km/s at 5 km depth) overlies a heavily faulted Cretaceous Atlantic lithosphere shallowly subducting (9°) beneath the northern submarine flank of PR, where Vp of 5-7 km/s suggests a crystalline nature.
How to cite: Canales, J. P., Vanacore, E., Flores, C., Han, S., ten Brink, U., and Grevemeyer, I.: Crustal and Mantle Structure Across Puerto Rico —From the Caribbean Plate to the Puerto Rico Trench— From an Onshore-Offshore Wide-Angle Seismic Transect , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14677, https://doi.org/10.5194/egusphere-egu26-14677, 2026.
Active deformation in the Eastern Central Andes backarc involves ongoing east-west shortening, and crustal strain with the potential to trigger a Mw 7.8 earthquake is accumulating, as indicated by geological records and geodetic data. We focus on the sparsely instrumented northwestern Argentina and southwestern Bolivia to quantify and localize ongoing E–W shortening of the Eastern Andes, and to characterize localized deformation related to other active processes in the backarc.
We analyzed ten years of Interferometric Synthetic Aperture Radar (InSAR) data to measure rates of surface deformation and generate time series. We rely on descending ALOS-2 radar imagery (L-band) and wide-swath (~350 km) ScanSAR mode. We used the “alos2stack” workflow in the ISCE-2 software, and substantially downsampled the interferograms to suppress noise, resulting in a ground-range pixel spacing of ~136 m. We then generated deformation time-series with the MintPy software and applied corrections for topography, solid Earth tides, and stratified tropospheric signal delay using ERA5 weather models. We further applied a range split-spectrum method to suppress the ionospheric phase contribution.
The resulting surface deformation rate maps are complemented by pointwise displacement rates from accurate positioning (GNSS), projected into the satellite line-of-sight (LOS). We also compare InSAR-derived rate maps and LOS gradients along multiple cross-orogen transects with geologic fault maps, seismicity, and topography.
The resulting rates describe the kinematics from the Puna Plateau through the Eastern Cordillera to the highly vegetated Subandes, including the frontal Mandeyapecua thrust. They reveal a variety of active processes in the Central Andean backarc: The long-wavelength E–W crustal shortening signal (~1 cm/yr LOS) is overlaid by local processes like inflation at Cerro Overo volcano (~1.5 cm/yr LOS), the dynamics of salars such as the Salar de Arizaro (~0.5 cm/yr LOS), coseismic displacement of ~8 cm associated with the 2020 Mw 5.8 Humahuaca earthquake, and several landslides.
How to cite: Symmes Lopetegui, B., Metzger, S., Bookhagen, B., and Giambiagi, L.: Surface deformation of the Eastern Central Andes, observed by wide-swath radar interferometric time-series., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17997, https://doi.org/10.5194/egusphere-egu26-17997, 2026.
The convergence of the North American plate with Caribbean plate occurs at a rate of 20.0 ± 0.4 mm/yr towards 254 ± 1º. This results in a highly oblique convergence (20-10º), which is accommodated in the Hispaniola Island by means of strain partitioning, represented in its northern margin by the Northern Hispaniola Deformed Belt (NHDB), accommodating the normal shortening, and the Septentrional Fault Zone (SFZ), which accommodates the along-strike convergence component. Here, we show the preliminary results of an integrated multiscale analysis based on new data acquired at the end of 2025, during the GEOMARHIS marine geophysical cruise, onboard the RRS James Cook. These new data include swath bathymetry data and a dense set of 2D seismic reflection profiles comprising medium, high and ultra high-resolution data. The integration and combined interpretation allow for an identification of the along-strike variability of fault geometry and sediment deformation along the northern Haiti margin. New data reveal active N-verging thrusts and fault-propagation folds in the NHDB, sub-vertical faults associated with the SFZ that produce seafloor scarps, and an extensive field of irregular-shaped seafloor depressions. These features suggest a complex interaction between tectonic, gravitational, and oceanographic processes. This continuous multi-scale approach will advance our understanding of active tectonic and sedimentary processes, which will help future studies assess seismic and tsunami risks in the region.
How to cite: Rueda-Fort, M., Granja-Bruña, J.-L., Muñoz-Martín, A., De la Fuente-Oliver, M.-Á., Berriolópez-Llamosas, M., Muñoz-Cemillán, A., and Martínez-Moreno, F.-J. and the GEOMARHIS: New Bathymetric and Seismic Reflection Data along the Northern Haiti Margin: Preliminary Results on the Active Geological Processes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20693, https://doi.org/10.5194/egusphere-egu26-20693, 2026.
Geophysical and geological records attest that the Northern Hispaniola margin poses major earthquake and tsunami hazards for the Greater Antilles. Along this margin it is located the oblique boundary between the Caribbean and the North American plates. This boundary plate is characterized by the coexistence of seismogenic compressive deformed belts and the strike-slip fault zones that represent a strain partitioning model. Between December 3rd of 2025 and January 3rd of 2026, we carried out a multi-scale controlled-seismic source marine survey between Puerto Rico and Cuba (GEOMARHIS experiment). During the marine cruise we acquired multi-channel seismic reflection profiles along- and across-strike of plate boundary using several experimental setups: 1) 2000 km seismic profiles using a 3 km-long streamer of 240 channels (12.5 m-interval) and a 1760 ci airgun array, 900 km of high-resolution seismic profiles using a streamer of 40 channels (6.25 m-interval), and a 420 ci airgun array and a 3.6 kJ sparker sources. In addition, we acquired systematic continuous ultra-high-resolution seismic data, swath bathymetry-backscatter, gravity and magnetics. Here, we show a preliminary interpretation of the tectonic structure based the new data that will provide key information to assess the seismic and tsunami hazard for Puerto Rico, Dominican Republic, Haiti and Cuba.
How to cite: Granja-Bruña, J.-L., Muñoz-Martín, A., Rueda-Fort, M., De la Fuente-Oliver, M. Á., Díez-García, I., Martínez-Carreño, N., Fiz Barrena, J., Berriolópez Llamosas, M., Muñoz-Cemillán, A., Joyeux, T., and Martínez-Moreno, F. J. and the GEOMARHIS TEAM: New multi-scale geophysical data in the northern Hispaniola offshore margin (GEOMARHIS experiment): Preliminary results on oblique tectonics, strain partitioning and associated geological hazards., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20993, https://doi.org/10.5194/egusphere-egu26-20993, 2026.
Large subduction earthquakes and associated tsunamis pose major hazards to coastal regions worldwide. The Cascadia subduction zone, where the Juan de Fuca plate subducts beneath North America, has historically experienced several devastating megathrust earthquakes (MW > 8.5), most recently in 1700 CE. Nowadays, the Cascadia margin is considered to be in a late stage of the interseismic period and therefore one of the regions in the world, that is most prone to a major subduction earthquake in the foreseeable future. However, despite its high seismic potential, deformation processes at the Cascadia deformation front remain incompletely understood. In this study, we focus on the northern Cascadia margin and perform a systematic analysis of structural variations and fault patterns along the margin, using 14 newly acquired high-resolution 2D multichannel seismic data oriented perpendicular to the deformation front offshore Vancouver Island. These data are complemented by legacy seismic profiles that provide improved velocity constraints as well as high-resolution bathymetric data. Our results show that the deformation front is well marked by a series of bathymetric ridges and is segmented into sections of 4–10 km length. The main frontal thrust is traceable throughout the profiles and changes vergence from mostly seaward verging in the north to a landward verging segment, before swapping back to seaward verging in the south. The high-resolution data enables us to image proto-thrust zones in northern Cascadia for the first time and reveals a link between the occurrence and geometry of these proto-thrusts and the frontal thrust vergence. Landward-verging frontal thrusts are associated with wide proto-thrust zones characterized by mixed vergence, whereas seaward-verging frontal thrusts exhibit sparse, predominantly seaward-verging proto-thrusts both landward and seaward of the main frontal thrust. Velocity analyses reveal compaction-related velocity increases seaward of the deformation front exclusively in areas with well-developed proto-thrust zones, indicating that the proto-thrusts have accommodated a significant amount of strain prior to frontal accretion and play an important role in frontal deformation processes. We will compare our findings to other subduction zones and discuss them in the context of hazard potential expected from potential future megathrust earthquakes in the area.
How to cite: Schäfer, W., Riedel, M., Crutchley, G., and Kopp, H.: Varying fault patterns and the role of proto-thrusts in strain accommodation along the northern Cascadia subduction zone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22939, https://doi.org/10.5194/egusphere-egu26-22939, 2026.
Flat slab subduction has been proposed along the southwestern U.S. margin during the Late Cretaceous. The model is partly based on exposures of garnet-bearing Pelona, Orocopia, and Rand schists (PORS), which crop out in isolated mountain ranges extending from the Los Angeles California area eastward >400 km into western Arizona. These chlorite+muscovite+/-biotite+/-garnet schists have distinctive characteristics that include graphitic inclusions in albite porphyroblasts, interlayering with mafic schists of MORB composition and Mn-rich siliceous marbles and cherts, and local blocks of metasomatized mantle peridotite. The flat slab model interprets the PORS association as oceanic sediment underplated to North American crust and subsequently exhumed by Basin and Range extension. Other models of the tectonic development of the western US call this interpretation into question. Ongoing research focuses on using Quartz-in-Garnet elastic geobarometry (QuiG), elemental exchange thermometry (e.g., GArnet-BIotite - GABI), Phase Diagram Sections (PhaDS), and garnet Sm-Nd geochronology to construct new Pressure-Temperature-time (P-T-t) paths for select PORS rocks along a west-east transect to evaluate the tectono-metamorphic history of this assemblage. We report temperature estimates of 603, 627, and 620°C (±25°C GABI) obtained from the San Emigdio, Portal Ridge, and Plomosa mountains, respectively. QuiG pressure estimates of 0.72-0.97 GPa at 627°C were obtained from Portal Ridge. These new results are consistent with PhaDS models that predict <0.9 GPa for equilibrium of quartz + plagioclase + muscovite + biotite + chlorite + magnetite + ilmenite. We interpret the results from Portal Ridge and the San Emigdios, the two westernmost sites in this study, to indicate shallow depths of 28-38 km of overlying crust. These crustal thicknesses are significantly lower than ~70 km estimates for North American crustal thickness during the Late Cretaceous. Future P-T-t paths, including garnet Sm-Nd ages, will provide a critical test for models of accretion to the base of the western Cordilleran continental crust by shallow/flat slab subduction of the Farallon oceanic plate.
How to cite: Stowell, H., Seymour, N., Autrey, S., and Gregory, C.: Evaluating Tectonic Models for the Pelona, Orocopia, and Rand schists in the Southwestern USA, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15378, https://doi.org/10.5194/egusphere-egu26-15378, 2026.
The northeastern Caribbean is a key region for understanding how subduction dynamics, internal plate deformation, and paleogeographic change interact to shape long-term Earth surface systems. Traditionally modeled as part of a rigid Caribbean plate, this region is now recognized as having undergone substantial internal deformation since the Eocene. Integrating paleomagnetic constraints with kinematic and paleogeographic reconstructions reveals a far more dynamic tectonic evolution than previously assumed. Significant vertical-axis rotations and relative translations affected major tectonic domains of the northeastern Caribbean throughout the Cenozoic. These rotations, reaching several tens of degrees, occurred in multiple phases and reflect the cumulative effects of oblique subduction, arc-parallel shearing, and progressive reorganization of plate-boundary structures. Deformation was distributed across rotating blocks rather than localized along discrete plate boundaries, fundamentally modifying regional geometry and challenging rigid-plate models. Incorporating these kinematic constraints into plate reconstructions highlights a highly variable paleogeographic history. Subduction-related uplift, subsidence, and arc migration episodically altered the extent and connectivity of emerged landmasses in the eastern Caribbean. During the Eocene and Oligocene, tectonic uplift and shallow platforms likely formed transient land connections or island chains between northern South America and the northern Caribbean islands. These connections were later disrupted by tectonic fragmentation and subsidence as convergence dynamics evolved. Overall, this integrated framework demonstrates that deep geodynamic processes exert a first-order control on Caribbean landscape evolution and ecological connectivity, emphasizing the need for interdisciplinary approaches linking tectonics, paleogeography, and Earth surface processes.
How to cite: Philippon, M., Montheil, L., van Hinsbergen, D., Cornée, J.-J., Audemard, F., Leroy, S., and Bufferal, S.: Tectonic Reorganization and Transient Connectivity in the Northeastern Caribbean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21390, https://doi.org/10.5194/egusphere-egu26-21390, 2026.
Fluid circulation through the Earth system plays a particularly important role in subduction zones, where it has a significant influence on seismic activity and metamorphic processes. Fluid circulation around the shallow seismogenic zone is considered to promote episodes of seismic/aseismic slips on the megathrust fault plane as well as on active satellite faults, leading in earthquakes, slow slips, clusters, repeaters, non-volcanic tremors activity.
Recent marine surveys conducted along the Ecuadorian margin, as part of the Fluid2Slip ANR project, have collected bathymetric dataset focusing on the Pedernales segment that ruptured during the M7.8 earthquake in 2016 (HiPER 2020 & 2022, SUPER-MOUV 2024). These data, combined with seismic reflection and refraction profiles, as well as seismological data from temporary dense deployments, provide preliminary insights on the structures potentially involved in the hydration hints of the Nazca oceanic plate.
Interpretation of MCS profiles enables the identification of the network of bending faults along the trench outer-wall and the characterization of the geometry of these faults. These faults exhibit vertical offsets of up to 300 m at the seafloor and, in some cases, shift the oceanic Moho, which may facilitate the hydration of the relatively young Nazca Plate in this area (< 15 Myr).
For the first time, a trench-normal dense OBS profile north of the Atacames seamounts characterizes the geometry and structure of the northern flank area of the Carnegie Ridge. We were able to show that the oceanic crust in this area is significantly thicker than expected (>12 km), well beyond the topographic signature of the Carnegie Ridge. By recording converted P-to-S waves along this OBS profile, we were able to quantify the P and S velocities of the oceanic crust at the trench. Local seismicity detected by the OBS refraction grid in the plate bending area close to the trench provides highlights to the in-depth crustal structure.
This work is complemented by the 3D tomographic inversion of HIPER2 cruise and by new hints on fluid pathways through the margin by the SUPER-MOUV cruise, both presented in the same session.
How to cite: Laigle, M., Galve, A., Michaud, F., Skrubej, A., Schenini, L., Ribodetti, A., Delsuc, A., Erb, A., Duclos, C., Segovia, M., Vaca, S., Higaki, A., Font, Y., Régnier, M., Ambrois, D., Chèze, J., and Rietbrock, A.: Hydration clues from the Nazca plate subduction zone in the northern part of the Ecuadorian subduction zone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12929, https://doi.org/10.5194/egusphere-egu26-12929, 2026.
In subduction zones, shallow crustal faults accommodate a fraction of the tectonic deformation and modulate the distribution of marine sediments. The interplay between active faults and sedimentary basins influences seismic hazards and the potential for submarine landslides. Imaging these active structures is crucial for constraining their geometry, physical properties, and contributions to regional geodynamic processes. Distributed acoustic sensing (DAS) offers an opportunity to passively image shallow offshore sediments at high spatial resolution, by converting preexisting submarine telecommunication cables into dense seismic arrays. Using hundreds of kilometers of submarine fibers, DAS enables ambient seismic noise tomography with resolutions of a few hundred meters near the coastline, sufficient to resolve detailed sedimentary velocity structures beneath the cables. Beyond velocity imaging, identifying strong impedance contrasts enables the localization of diffracting structures, such as faults and sedimentary basin edges.
In this study, we present a set of complementary imaging approaches based on both ambient noise and earthquake records, which we use to investigate shallow marine sediments offshore central Chile. Our analysis uses over two years of continuous DAS recordings from three submarine cables located within the study area. Firstly, we apply wavefield separation to the earthquake recordings within a local back-projection framework in order to image fault-related structures at sub-kilometer scales, identifying scattered wavefields that are consistent with fault zones intersecting the cables. Secondly, we use the autocorrelation and cross-correlation of ambient seismic noise to image strong impedance contrasts and reveal sedimentary basin edges along the three cables. Thirdly, we analyze high-resolution power spectral density using earthquakes, ambient noise, and autocorrelation functions to investigate the relationship between high-frequency resonances, shallow sedimentary deposits, local attenuation, and basin-edge effects. These are all key factors in quantifying site response offshore. Finally, we validate our interpretations using numerical wave propagation simulations, which show good agreement with the observed DAS data.
Together, these methods reveal sedimentary accumulations within basins and fault-related structures that are consistent with regional geological constraints. Although variability in coupling and the use of two-dimensional models limit full structural characterization, our results demonstrate the ability of DAS to resolve fine-scale offshore structures and highlight its potential for studying offshore faulting, sediment dynamics, and site effects along the central Chilean margin.
How to cite: Vernet, C., Rivet, D., Trabattoni, A., and Baillet, M.: Shallow crustal imaging with distributed acoustic sensing (DAS) offshore central Chile, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17108, https://doi.org/10.5194/egusphere-egu26-17108, 2026.
The Atacama segment in Northern Chile, a persistent seismic gap since 1922, represents a complex and highly active subduction zone. The region’s seismicity spans a broad magnitude range (M -0.8 to 6.2) and encompasses diverse sources including intraslab, interface, upper-mantle, and outer-rise events. While a dense earthquake catalog exists, systematic information on focal mechanisms has remained sparse, limiting detailed understanding of stress distribution and seismotectonic processes.
Here, we construct a comprehensive focal mechanism catalog for the Atacama seismic gap using P-wave polarity inversions implemented via the SKHASH algorithm based on a grid-search of nodal planes. First-motion polarities were automatically picked using a CNN model trained on 3 millions human-picked examples from diverse tectonic settings to improve cross-regional transferability. Rigorous quality selection was applied, accounting for signal-to-noise ratio, azimuthal coverage and minimum allowed number of polarities, ensuring robust mechanism determination. Under current network configuration and resolution constraints, around ~30% of the catalog (initially counting ~166 000 events) can be resolved.
The resulting catalog provides a detailed statistical overview of mechanisms across different seismic classes and magnitudes. Particular attention is given to markers of slab stress state - along-dip compressions and tensions, its distribution across the double plane seismicity zone, and to mechanisms of upper-plate seismicity, which may reflect fluid transfer and crustal heterogeneities.
How to cite: Kartseva, T., Münchmeyer, J., Gardonio, B., Helmstetter, A., Marsan, D., and Socquet, A.: A dense focal mechanisms catalogue for the Atacama segment in Chile (24◦S - 31◦S) using deep learning polarity picking, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1489, https://doi.org/10.5194/egusphere-egu26-1489, 2026.
