The research team, led by Lizzeth Vázquez-Caamal and Christian M. Appendini of the National Autonomous University of Mexico, together with colleagues from UNAM’s Morelia campus, the University of Iceland, and UNAM’s Institute of Engineering, took a fundamentally probabilistic approach. Rather than modeling a single worst-case earthquake, they generated a vast ensemble of plausible seismic events using stochastic rupture modeling. The work builds on the framework of probabilistic seismic hazard analysis, which integrates earthquake recurrence statistics, magnitude distributions, and variability in how ruptures unfold to estimate exceedance probabilities. This allows the assessment to capture the full spectrum of possible events, including ones larger than anything in the historical record.

At the heart of the methodology is the FakeQuakes module of the open-source MudPy code, which generates realistic synthetic earthquake slip distributions on a three-dimensional model of the subduction interface. The team used the Slab2.0 model to define the geometry of the plate boundary, discretizing it into a finite mesh extending to about 30 kilometers depth, the range where large thrust earthquakes typically occur in this region. Slip heterogeneity was sampled using a Karhunen-Loève expansion, producing physically plausible variability in how each rupture distributes its energy. In total, the researchers created 4,800 synthetic earthquakes spanning magnitudes from Mw 7.0 to Mw 8.5 in increments of 0.1, with 300 scenarios for each of 16 magnitude bins. Each scenario was weighted according to its annual occurrence rate derived from a regional Gutenberg-Richter relationship, with a correction applied to represent the smaller rupture domain evaluated in the study.

Before trusting the probabilistic results, the team validated the entire modeling chain against a known event. They generated 600 synthetic rupture models constrained to the characteristics of the 1995 Colima-Jalisco earthquake, a magnitude 8.0 event that produced strong tsunami currents in Manzanillo Bay. From this ensemble, 28 realizations with magnitudes within a narrow range of the target were retained for controlled comparison. The simulations were run using GeoClaw, a well-validated solver for the nonlinear shallow water equations that employs adaptive mesh refinement to efficiently handle both broad-scale wave propagation and fine-scale coastal inundation. The comparison with the observed tide gauge record from Manzanillo’s harbor showed that the model captured the first wave, a trough followed by a peak consistent with regional subduction movement, along with the trailing oscillations and their decay over time. The simulated arrival times were slightly delayed by about 3 to 10 minutes across all scenarios, likely due to small inaccuracies in the assumed rupture location or velocity model, but the wave period and overall duration were well reproduced.

The numerical setup was designed to resolve the complex coastal geography of Manzanillo in detail. Five levels of nested grids were used, with the coarsest covering a large portion of the Pacific at 5 arc-minute resolution and the finest centered on the bays and lagoons of interest at about 30 meters. This resolution was adequate to model water flow through narrow channels and around small islands or peninsulas. The team merged global bathymetry with high-resolution local surveys and topographic data to create a seamless digital elevation model capturing features like beach berms and channel connections between the ocean and lagoons. A Manning’s roughness coefficient of 0.025 was applied to account for energy losses from seafloor roughness and onshore terrain friction, a standard reference value for tsunami inundation modeling over mixed coastal environments.

The results reveal a spatially shifting hazard pattern that depends on earthquake size. For a 100-year return period, corresponding to a 40 percent exceedance probability in 50 years, the highest tsunami amplitudes among five virtual gauge stations were found at point P3, situated near the city center in Manzanillo Bay. This suggests that for relatively moderate events, the central bay experiences the largest waves. However, as return periods extend beyond 800 years, the hazard shifts to Santiago Bay, represented by point P2, which begins to show higher levels than the city center. Point P5, representing the open coast near Campos, also shows increased hazard by a 1,000-year return period, consistent with the idea that open-coast segments are prone to the impact of the largest tsunamis. This spatial variability underscores the importance of site-specific assessment rather than relying on regional averages.

The inundation maps generated for 50-, 100-, and 500-year return periods consistently identify low-lying areas near the coast as the most vulnerable. Santiago Bay, the downtown and port area around Manzanillo Bay, and the extensive wetlands around Cuyutlán Lagoon emerge as hotspots of inundation. For the 50-year scenario, roughly corresponding to a magnitude 7.3 earthquake, flood extents primarily affect zones immediately adjacent to the shoreline, though the Cuyutlán Lagoon area experiences the farthest inland flooding at about 5.6 kilometers from the coast, largely because the terrain there is very flat and low. Once water overtops the beach or enters the lagoon inlet, it can propagate far across the marshy land with little resistance. For the 100-year event, roughly a magnitude 7.74 scenario, flooding extends about 1.8 kilometers inland in Manzanillo Bay and up to 5.8 kilometers at Cuyutlán in the static maps, with dynamic simulations showing depths exceeding 6 meters within the port.

The 500-year scenario, approaching the upper magnitude considered at roughly Mw 8.3, delineates the outer envelope of tsunami flooding one might reasonably prepare for. The static map shows very extensive flooding at Manzanillo Bay, covering nearly all urban and port areas with inundation reaching up to 2.6 kilometers inland. Around Juluapan Lagoon, flooding may extend 2.5 kilometers inland, affecting surrounding roads and residential areas. At Cuyutlán, inundation reaches up to 6.2 kilometers, suggesting the entire lagoon would become part of the ocean temporarily. The dynamic simulation for a magnitude 8.49 event indicates extreme water depths, with about 6.2 meters in Cenicero Bay and 6.4 meters on the eastern side of Santiago Bay. The port area records about 7.8 meters of overtopping the breakwaters and 6.9 meters of inundation inside the port, which could cause severe disruption to operations and infrastructure.

A key methodological contribution of the study is the explicit comparison between simplified elevation-based mapping and physics-based hydrodynamic simulation. The elevation-based approach uses Green’s law to scale offshore wave amplitudes to nearshore reference depths and then floods all hydraulically connected terrain below a prescribed elevation. The hydrodynamic approach simulates representative events whose offshore peak coastal amplitudes match the target exceedance levels from the probabilistic curves. For the 500-year event, the static method yields an inundated area of approximately 54.16 square kilometers, compared with 10.82 square kilometers from the full hydrodynamic simulation, indicating the simpler estimate is roughly five times larger. This discrepancy highlights the importance of frictional dissipation, represented by the Manning roughness coefficient, in controlling inland flow. The static method floods all connected terrain below a prescribed elevation without accounting for finite wave duration, momentum losses, topographic steering, or energy dissipation during overland flow. The authors suggest the GIS approach is useful as a conservative screening tool but may substantially overpredict inland penetration in low-gradient lagoonal and urban environments.

The findings carry significant implications for coastal planning and preparedness in Manzanillo. The hazard exceedance curves indicate that moderate tsunami amplitudes up to 1 meter have a high probability of occurrence within a 50-year exposure window, while a 500-year return period event could inundate areas up to 5 or 6 kilometers inland through the city’s water bodies. Critical infrastructure, including the port, power facilities, and tourism centers, largely lie within the 100-year tsunami flood zone. The maps and exceedance curves can support preliminary screening of evacuation zones, land-use planning, and critical infrastructure exposure, though the authors caution they should not be interpreted as final operational evacuation products. The study focuses on earthquake-generated tsunamis from local and regional subduction sources and does not include far-field or volcanic-source events, which the authors note should be addressed in future assessments. They also recommend incorporating spatially variable roughness, sensitivity analyses, and more explicit treatment of epistemic uncertainty, along with interactions with other coastal hazards such as sea-level rise and storm surge, to support more integrated coastal hazard planning for Manzanillo.

Subject of Research: A site-specific probabilistic tsunami hazard assessment and flood modeling study for Manzanillo, Colima, Mexico, using stochastic earthquake sources and hydrodynamic simulations.

Article Title: Probabilistic tsunami hazard assessment and flood modeling: a case study of Manzanillo, Colima, Mexico

Article References: Vázquez-Caamal, L., Appendini, C. M., Solano-Hernández, E. A., Ruiz-Angulo, A., & Ordaz, M. (2026). Probabilistic tsunami hazard assessment and flood modeling: a case study of Manzanillo, Colima, Mexico. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02701-8

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02701-8

Keywords: tsunami, PTHA, Manzanillo, Mexico, flood modeling, GeoClaw, stochastic rupture, subduction zone, coastal hazards, inundation mapping, Cuyutlan Lagoon, hazard assessment

Poikilitic hornblende ultramafic rocks, classically called cortlandtites after their first description along the Hudson River in New York, are among the more enigmatic rock types found in orogenic belts. Their defining texture is unmistakable under the microscope: enormous grains of hornblende, a hydrous calcium-magnesium-iron amphibole, that completely enclose smaller, rounded crystals of olivine and pyroxene. The rounded phases represent earlier-formed crystals, while the giant amphibole grew late, wrapping around everything in its path. Such rocks are minor but recurring constituents of granitic and metamorphic terranes, of the deep crustal and upper mantle sections of supra-subduction ophiolites, and even of xenoliths brought up from beneath active volcanic arcs. Because amphibole can hold enormous quantities of water in its crystal structure, these rocks are direct archives of the volatiles that circulate through subduction zones and drive arc magmatism.

The Abukuma occurrence had been described petrographically in earlier decades, but its origin remained unresolved. What makes this locality special is context: the poikilitic hornblende pyroxenite sits in contact with regionally metamorphosed rocks of the Nishidohira unit, and nearby are amphibole-rich gabbros that appear to be genetically related to it. Together they offer a natural laboratory for studying how amphibole-bearing magmas differentiate from the upper mantle down into the lower crust. The research team collected samples well away from the contacts with the surrounding metamorphic rocks and from thin leucocratic veins that cut the body, minimizing any contamination from later fluids, and then subjected the rocks to an exhaustive campaign of X-ray element mapping, electron microprobe analysis, laser ablation trace element measurements, and uranium-lead dating of zircon.

The resulting mineral inventory is strikingly unusual for an ultramafic rock. Olivine makes up roughly five percent of the mode, pyroxenes about fifty percent, and amphibole about forty-five percent, with only trace amounts of biotite, orthopyroxene and ilmenite. Crucially, no plagioclase is present at all, a detail that would prove central to the interpretation. The amphibole grains display vivid color zoning under transmitted light, from dark brown-black cores through brown margins to pale green rims. The dark cores are titanium-rich pargasite containing 1.3 to 2.1 weight percent TiO2, and they are riddled with exsolution lamellae of ilmenite, evidence that the original crystals were even more titanium-rich before decompression forced the iron-titanium oxide out of solution. The green rims and vermicular intergrowths are far poorer in titanium and aluminum, and their chemistry points to crystallization from an evolved, water-rich residual melt or fluid rather than a primitive magma.

The textural relationships tell a sequential story. The rounded olivine grains, with forsterite contents of only 65 to 76 percent, are too iron-rich to represent residual mantle peridotite and instead point to a cumulate origin, crystals settled out of an earlier magma. High-aluminum clinopyroxene and the dark high-titanium pargasite are in chemical equilibrium and crystallized first from the infiltrating melt. Later, as the melt fractionated and released hydrous fluids, low-aluminum vermicular clinopyroxene and low-titanium amphibole replaced the earlier phases, and orthopyroxene formed by reaction of olivine with a silica-rich melt or fluid. The absence of europium and strontium anomalies in the early amphibole and clinopyroxene confirms that no plagioclase had crystallized before the amphibole, consistent with the total lack of plagioclase in the rock.

The analytical centerpiece of the study is the reconstruction of the melt from which the dark amphibole grew. Amphibole incorporates many trace elements in predictable proportions relative to the melt around it, so with experimentally calibrated partition coefficients, the researchers could invert the crystal chemistry to recover the liquid composition. Using empirical thermobarometric equations and the open-source Thermobar package, they estimated a melt containing roughly 59 to 67 weight percent silica, 17 to 18 percent alumina, and 2 to 4 percent magnesium oxide at around 1000 degrees Celsius. The calculated trace element signature shows high light rare earth element to heavy rare earth element ratios, a weak positive strontium anomaly, and pronounced depletions in high-field-strength elements such as niobium, zirconium and titanium. That combination is the fingerprint of an adakite.

Adakites are intermediate to felsic arc rocks, first defined in 1990, characterized by high strontium but low yttrium and heavy rare earth contents, and generally attributed to partial melting of young, hot subducted oceanic basalt under amphibole or eclogite facies conditions. Alternative pathways exist, including melting of thickened lower crust or extensive garnet and amphibole fractionation, but all require unusual pressure and temperature conditions in the sub-arc system. The melt inferred from the Abukuma amphibole matches adakitic compositions from the Japanese arc record almost exactly, and critically, the spatial and temporal context clinches the connection. Adakitic granites and high-magnesium andesites, dated at 128 to 113 million years, are already documented in the nearby Kitakami Mountains to the northeast, where isotopic modeling indicates derivation from partial melting of subducted basaltic crust with a sedimentary contribution.

Zircon crystals recovered from both the poikilitic hornblende pyroxenite and the associated hornblende gabbro yielded concordant uranium-lead ages of 117.5 plus or minus 0.4 and 116.3 plus or minus 0.5 million years respectively, with all grains showing thorium-uranium ratios above 0.1 that confirm a magmatic rather than metamorphic origin. These ages overlap with the Kitakami adakitic pulse and place the formation of the ultramafic body squarely within the Early Cretaceous. The Irishiken granodiorite that intrudes the region nearby, dated in this study at 105.9 plus or minus 0.6 million years, is younger and marks a later thermal event that previous work has linked to the rapid exhumation of the Nishidohira metamorphic rocks. Thermobarometry on the reconstructed dark amphibole composition, corrected for ilmenite exsolution, gives pressures of 0.4 to 0.7 gigapascals and temperatures of 870 to 940 degrees Celsius, conditions consistent with the amphibole stability field in a magnesian andesitic melt and with the partial resorption of olivine that its rounded shapes record.

The relationship between the two rock types at the locality resolves a broader petrological question. Experiments show that when hydrous basaltic melt reacts with peridotite, hornblende-rich ultramafic rocks form where the melt is scarce and reaction dominates, whereas hornblende gabbro crystallizes where melt is abundant. The Abukuma pair fits this model precisely: at low melt-to-rock ratios, adakitic liquid invading pre-existing ultramafic rock converted it to poikilitic hornblende pyroxenite, buffered to high magnesium numbers by the host; at high melt-to-rock ratios, the same liquid pooled and crystallized as hornblende gabbro, with early amphibole, titanite and apatite sequestering calcium and trace elements before plagioclase finally appeared. Similar relationships between dunitic xenoliths and adakite-related microgabbro in the Kitakami Mountains show the process operating on a regional scale.

Taken together, the evidence portrays the southern Abukuma Mountains as a preserved slice of a plumbing system that tapped slab-derived melts during an extraordinary episode of Early Cretaceous subduction. At that time, the eastern margin of the Eurasian Plate was consuming the Izanagi, or Kula, oceanic plate, and the widespread adakitic magmatism across both the Kitakami and Abukuma regions implies that a young, hot segment of that plate was melting as it descended. The poikilitic hornblende pyroxenite, with its giant amphibole crystals acting as chemical sponges for water and incompatible elements, is thus not a geological curiosity but a key witness to how slab melts transform the deep crust and mantle beneath volcanic arcs. For anyone seeking to understand how continents are built from the inside out, this modest Japanese outcrop now offers one of the clearest windows available into that hidden, melt-rock conversation.

Subject of Research: Petrogenesis of poikilitic hornblende pyroxenite formed by adakitic melt–ultramafic rock interaction in the Early Cretaceous Abukuma Mountains, Japan

Article Title: Poikilitic hornblende pyroxenite in the southern end of the Abukuma Mountains, Northeast Japan, as result of adakitic magmatism

Article References: Wakazono, A., Fukuyama, M., Itano, K., Harigane, Y., Tamura, A., & Morishita, T. (2025). Poikilitic hornblende pyroxenite in the southern end of the Abukuma Mountains, Northeast Japan, as result of adakitic magmatism. Frontiers in Geochemistry, 3, Article 1697337. https://doi.org/10.3389/fgeoc.2025.1697337

Image Credits: AI Generated

DOI: 10.3389/fgeoc.2025.1697337

Keywords: poikilitic hornblende pyroxenite, adakite, Abukuma Mountains, amphibole, U-Pb zircon dating, Early Cretaceous, subduction zone, Izanagi plate, ultramafic rocks, melt-rock interaction, Japan, arc magmatism

The Philippines sits at the restless junction of the Pacific, Philippine Sea, Eurasian, and Indo–Australian plates, and its archipelago is stitched together by oppositely dipping subduction zones and the sweeping Philippine Fault Zone. The country’s historical record, collated from eyewitness accounts dating back to 1589, documents 41 tsunamigenic earthquakes, twenty of which can be directly tied to subduction zones. Three of these reached magnitude 8.0 or greater, including the devastating 1976 Moro Gulf earthquake along the Cotabato Trench, a shallow rupture that killed an estimated 3,000 to 8,000 people and remains the deadliest tsunami disaster in Philippine history. Yet while the Manila, East Luzon, and Philippine trenches have all been constrained by dense GPS networks and coupling models, the Negros–Sulu subduction zone has languished in a data vacuum, with only a handful of instrumentally recorded earthquakes and a GPS coverage too sparse to identify which parts of the plate boundary may be locked and accumulating strain.

To confront this uncertainty, the team built their rupture scenarios from the ground up using a structural approach rather than relying on geodesy. Analyzing the orientation variations of the frontal wedge, the deformed sediments at the leading edge of the overriding plate, they divided the megathrust into four main segments along the Negros and Sulu trenches, then added two alternative configurations to bracket uncertainties in how far the northernmost segment extends and whether the two southern segments could rupture together. Seismic tomography profiles, which show the shallow slab dipping at angles between 9 and 30 degrees, prompted the researchers to model three dip scenarios of 10, 20, and 30 degrees for every segment, yielding 18 distinct rupture scenarios in total.

Feeding these fault geometries into empirical rupture-scaling relations derived from global subduction earthquakes, the team estimated that a full rupture of each segment could produce moment magnitudes ranging from 8.0 to 8.9, corresponding to average slips of 1.68 to 6.23 meters. The longest scenario, a combined rupture of the Sulu Trench segments stretching 379 kilometers, carries the largest potential magnitude of 8.9. The researchers deliberately chose the linear area-magnitude scaling relation over a bilinear alternative because it yields slightly larger magnitudes, a conservative choice given how little is known about this margin. The fault models assume a shallow blind rupture with its top buried five kilometers beneath the seafloor and pure reverse slip, with the down-dip extent of the seismogenic zone capped at 50 kilometers based on the depth distribution of 207 reverse-oblique earthquakes recorded between 1977 and 2023.

The tsunami simulations themselves were run in the JAGURS numerical code, a state-of-the-art solver that goes beyond classical tsunami modeling by incorporating nonlinear shallow-water equations, both vertical and horizontal seafloor displacements, and Boussinesq dispersion effects that describe how short-period waves scatter as they travel. The team merged 15-arcsecond GEBCO bathymetry with resampled 5-meter interferometric radar terrain data from the Philippine mapping agency to build the seafloor and land surface, positioned 34 synthetic tide gauges around the Sulu Sea, and placed 6,879 sampling points at 10-kilometer intervals along the coastlines of 16 defined coastal regions to extract maximum wave heights, flow velocities, and minimum arrival times over a four-hour simulation window.

The results reveal a stark pattern governed by wave directivity. Coastal communities directly facing the rupture segments, including Sipalay–Bayawan on Negros, Sindangan–Labason and Siocon–Sibuco on western Mindanao, Basilan–Sulu, and the Moro Gulf, face the highest exposure, with modeled wave heights of 5 to 8 meters and flow velocities of 5 to 7 meters per second. More alarming still is the timing: because these coasts lie so close to the trench, the first wave arrives in under two minutes, leaving no time for official warnings and demanding immediate self-evacuation. The Negros Trench scenarios generate waves up to 6 meters with flow velocities reaching 7 meters per second, while Sulu Trench ruptures produce up to 8 meters of wave height. Waves from the Sulu segments can even thread through straits into the Celebes Sea, reaching the Moro Gulf in roughly ten minutes.

Not every coastline faces equal danger, and the study uncovers some elegant physical controls on where waves grow and where they fade. Coastlines protected by wide shallow shelves fare dramatically better: the analysis shows that areas hit by waves of at least 2 meters typically have a nearshore width, measured between the 50-meter depth contour and the shoreline, of just 2 to 4.5 kilometers, whereas coasts with shelves wider than 20 kilometers experience dissipation that suppresses waves below 2 meters, and every location with a shelf exceeding 30 kilometers saw minimal wave heights. Front-line islands also act as natural breakwaters, diffracting and attenuating waves before they reach rearward coasts. Conversely, concave embayments and narrow channels in the interior Philippines can trap and amplify tsunami energy through constructive resonance, occasionally pushing waves up to 2 meters even deep inside the archipelago where direct exposure would otherwise be low.

The team validated their models against historical accounts, comparing modeled maxima with eyewitness reports of past events in the Sulu and Celebes seas, including the 1897 magnitude 7.5 earthquake that reportedly produced waves up to 6 meters along the Sulu archipelago. In most regions the modeled waves slightly exceed the historical accounts, but the comparison also revealed a sobering finding for the Moro Gulf: the highest modeled wave from the Sulu Trench reaches 6 meters, demonstrating that this disaster-prone coastline is vulnerable not only to the nearby Cotabato subduction zone, source of the catastrophic 1976 tsunami, but also to ruptures on the Sulu side of the sea. Prehistoric washover deposits previously discovered along Zamboanga del Sur may likewise record extreme waves from either system.

The authors are careful to emphasize that their estimates should be treated as floors, not ceilings. Because the models assume uniform average slip across each fault plane rather than the heterogeneous slip patches that characterize real megathrust earthquakes, and because trench-breaching ruptures and splay faulting, which can dramatically amplify seafloor uplift, were not included, the maximum wave heights and flow velocities are likely underestimates. Real earthquakes that concentrate slip near the trench, as the 2011 Tohoku-Oki earthquake famously did, can generate far larger tsunamis than average-slip models predict. The study also cannot resolve local inundation without higher-resolution nearshore bathymetry, which the authors identify as an urgent data gap given the demonstrated sensitivity of wave heights to shelf width.

Despite these caveats, the work delivers immediately actionable outputs for a region where scientific information has long lagged behind the hazard. The maps of minimum arrival times, maximum wave heights, and flow velocities offer regional planners a baseline for siting evacuation routes, designing coastal defenses such as seawalls, green embankments, and offshore breakwaters, and identifying locations where vertical evacuation into sturdy elevated structures may be the only viable option given the extraordinarily short warning times. The highest-exposure coastlines also double as the most promising search areas for paleotsunami deposits, sedimentary fingerprints of prehistoric waves that could extend the region’s earthquake record far beyond four centuries of written history. As the authors conclude, in a margin where every seismic record spans fewer than 300 earthquakes and recurrence intervals stretch across hundreds to thousands of years, scenario-based modeling is not merely useful; it is the essential bridge between a dangerous knowledge gap and the coastal communities who live directly above it.

Subject of Research: Seismic and tsunami hazard modeling of the Negros–Sulu megathrust subduction zone in the Philippines

Article Title: Seismic and tsunami hazard potential of the Negros–Sulu megathrust, Philippines

Article References: Nawanao Jr., L. P., Ramos, N. T., Baba, T., Chikasada, N., & Satake, K. (2026). Seismic and tsunami hazard potential of the Negros–Sulu megathrust, Philippines. Natural Hazards and Earth System Sciences, 26(10), 5035-5055. https://doi.org/10.5194/nhess-26-5035-2026

Image Credits: AI Generated

DOI: 10.5194/nhess-26-5035-2026

Keywords: megathrust, tsunami, Philippines, Sulu Sea, subduction zone, earthquake hazard, JAGURS, wave directivity, rupture scaling, paleotsunami, disaster mitigation, Negros Trench

The study, published in Communications Earth & Environment, was led by Rikuto Fukushima of Stanford University, together with Masayuki Kano of Kyoto University and the Japan Agency for Marine-Earth Science and Technology, Kazuro Hirahara of RIKEN and Kagawa University, and Makiko Ohtani of Kyoto University. Their target was the 2010 Bungo slow slip event, a well-documented episode of silent fault motion that struck the Bungo Channel region between the islands of Shikoku and Kyushu. What the team found was a striking picture of frictional heterogeneity: the slow slip event nucleated in a localized patch off southwest Shikoku, where frictional properties differ sharply from their surroundings, and then propagated westward along the plate boundary.

To understand why this matters, it helps to grasp the long-standing puzzle of fault behavior. Laboratory experiments on rock samples have shown that faults obey friction laws — mathematical rules describing how resistance to sliding depends on slip rate, contact time, and other variables. When modelers feed these laboratory-derived laws into simulations of fault slip, the simulations naturally produce a rich diversity of behavior: some patches rupture rapidly as earthquakes, others creep slowly, and still others remain locked for centuries, accumulating the strain that eventually powers the largest quakes. The agreement between such simulations and real observations has long supported the hypothesis that the observed diversity of slip — from fast earthquakes to slow transient events — arises from spatial variations in frictional properties stamped into the fault by geology.

But there has been a stubborn gap between that elegant hypothesis and hard data. Confirming it quantitatively would require taking real geodetic observations — the millimeter-to-centimeter shifts of GPS stations as an unseen fault slips below — and working backwards to infer the frictional parameters that must have produced them. That inverse problem is brutally difficult. A fault plane is a two-dimensional surface, and frictional properties vary across it point by point, meaning the unknowns number in the thousands or more. Traditional optimization methods buckle under this high-dimensional search space, so most studies have settled for estimating only the distribution of fault slip itself, leaving the underlying friction physics unconstrained. The new work was designed precisely to close that gap.

The team’s solution was to deploy physics-informed neural networks, or PINNs, a technique that has swept through computational physics in recent years. In a conventional neural network application, the network learns patterns purely from data. In a PINN, the network is additionally constrained to obey the governing equations of the physical system — in this case, the equations of quasi-dynamic fault slip based on rate- and state-dependent friction laws. The researchers used the neural network to represent the spatially variable frictional properties on the fault surface. Because a neural network can encode smooth, structured fields with relatively few internal parameters, it tames the high-dimensional optimization problem that had defeated earlier approaches. The network’s outputs are fed into the fault mechanics equations, and the mismatch between the resulting predicted surface displacements and the actual GPS observations drives the training, pulling the estimated friction field toward one that is simultaneously mechanically consistent and consistent with the data.

Applying this framework to the 2010 Bungo slow slip event, the researchers estimated the heterogeneous frictional parameters along the subducting plate interface beneath southwest Japan. The resulting picture showed frictional properties varying systematically along the fault, with a localized region off southwest Shikoku standing out as the nucleation zone where the slow slip event began. From there, the event propagated westward, a pattern that emerged naturally from the estimated friction distribution. Crucially, the calculated fault slip produced by those frictional properties successfully reproduced the spatio-temporal pattern of the observed surface displacements — not just how much the ground moved, but the sequence and geography of that motion through time.

This dual consistency is what sets the result apart. Many previous slip models could fit geodetic data, but they said nothing about whether the inferred slip was physically achievable given plausible fault friction. Conversely, forward simulations of fault cycles could produce realistic slow slip events, but only for assumed friction distributions, not ones verified against observations. The PINN-based inversion delivers a model that is validated on both fronts: it is a mechanically consistent fault slip model, grounded in laboratory-derived friction physics, and it is quantitatively checked against real measurements. In effect, the team has demonstrated that the frictional heterogeneity hypothesis — the idea that patchy friction generates the spectrum of slip behavior — can be tested against data rather than merely assumed.

The study did not stop at reconstructing the past. The researchers also used their estimated friction model to forecast the future evolution of fault slip, and in doing so they uncovered a practical lesson for the emerging field of earthquake forecasting. The accuracy of such forecasts depends heavily on how much observational history is assimilated into the model. By assimilating observations spanning multiple slow slip event cycles, rather than a single event, the forecasts become substantially more reliable. This finding carries a clear message for monitoring networks: continuous, long-term geodetic observation is not just an archive of past behavior but an essential ingredient for anticipating future fault motion.

The implications reach well beyond the Bungo Channel. Slow slip events are now recognized along many of the world’s subduction zones, including Cascadia in the Pacific Northwest, Mexico, Chile, New Zealand, and Alaska. In several of these regions, slow slip episodes have been linked to heightened stress on adjacent locked patches capable of producing large earthquakes — most notably in the lead-up to the 2011 Tohoku-oki earthquake in Japan, where precursory slow slip near the hypocenter has been documented. If physics-informed inversion can map the frictional architecture of these faults from routine GPS data, it could eventually help scientists identify which slow slip events are routine and which signal dangerous stress transfer toward locked, earthquake-ready patches.

The methodological advance may prove just as consequential as the specific findings. High-dimensional inverse problems pervade geophysics, from imaging Earth’s interior to modeling magma chambers and groundwater flow. By showing that a neural network can serve as a compact, physically constrained representation of a complex field like fault friction — and that training it against both physical laws and observational data yields a solution previously out of reach — the study opens a template that other researchers can adapt. The work was supported by Japan’s MEXT STAR-E and STAR-E NEXT projects, the Earthquake Research Institute at the University of Tokyo, and JSPS KAKENHI grants, reflecting a sustained national investment in earthquake science and machine learning.

For a field that has spent half a century bridging laboratory rock mechanics and field observation, the arrival of a tool that finally connects the two at scale is a genuine milestone. The 2010 Bungo slow slip event slipped silently, registering only as a gentle drift of GPS antennas across Shikoku and Kyushu. Yet within that quiet drift lay the frictional blueprint of the fault itself — and now, with physics-informed deep learning, scientists have learned to read it. The same approach, applied to longer and richer observational records, promises not only a deeper understanding of how faults work but a step toward the long-sought goal of physics-based fault slip forecasting, where the slow whispers of a fault today inform the assessment of its roar tomorrow.

Subject of Research: Physics-informed deep learning estimation of spatially variable fault friction from geodetic observations of slow slip events

Article Title: Physics-informed deep learning links geodetic data and fault friction

Article References: Fukushima, R., Kano, M., Hirahara, K., & Ohtani, M. (2026). Physics-informed deep learning links geodetic data and fault friction. Communications Earth & Environment. https://doi.org/10.1038/s43247-026-04138-y

Image Credits: AI Generated

DOI: 10.1038/s43247-026-04138-y

Keywords: physics-informed neural networks, slow slip events, fault friction, geodesy, subduction zone, Bungo Channel, rate-and-state friction, machine learning, seismology, earthquake forecasting, southwest Japan, fault mechanics

Lawsonite is the star of the story. This hydrous calcium-aluminum silicate contains a remarkable 11.5 percent water by weight and has a strong chemical affinity for elements that matter enormously to Earth’s geochemical cycles, including uranium, thorium, strontium, rare earth elements, and transition metals such as iron, titanium, and chromium. When oceanic crust subducts, lawsonite acts as a conveyor for water and these elements into the mantle, influencing where fluids are released, where melting generates arc volcanoes, and how the subduction interface deforms. Yet despite predictions from experiments, thermodynamic modeling, and geophysical observations that lawsonite should be common in cold subduction zones, rocks that preserve it in pristine form are vanishingly rare. The mineral readily breaks down or is replaced during the return trip to the surface, so most exhumed rocks retain only ghostly traces of it.

Before this study, a global review had identified just nine localities with convincing matrix lawsonite alongside garnet and omphacite: the Sivrihisar massif in Türkiye, Alpine Corsica in France, the Samana Metamorphic Complex in the Dominican Republic, the South Motagua Fault Zone in Guatemala, the Voltri massif in the Western Alps, the Port Macquarie mélange in Australia, rare layers in the Franciscan Complex of California, Pinchi Lake in British Columbia, and the Garnet Ridge xenolith in Arizona. Seven additional sites, including Elekdağ, had reported lawsonite and omphacite only as tiny inclusions trapped inside garnets, with no lawsonite surviving in the matrix. Those inclusion-only occurrences hint at lawsonite eclogite conditions but leave room for doubt, because without coexisting omphacite it is hard to tell whether the lawsonite formed during early blueschist metamorphism or at peak eclogite-grade pressures.

The Elekdağ metabasites occur as blocks and lenses within and along the margins of a large serpentinite body, roughly 35 kilometers long, as part of a Cretaceous subduction complex about 105 million years old. Earlier work had estimated maximum conditions of around 490 degrees Celsius at 1.7 gigapascals, while a tourmaline-bearing eclogite suggested 400 to 430 degrees Celsius at pressures exceeding 1.35 gigapascals. The new sample, designated ELEK23-05b, changes that picture dramatically. Its matrix contains approximately 20 percent garnet, 35 percent omphacite, 20 percent lawsonite, 14 percent phengite, and 9 percent chlorite, along with accessory rutile. Quartz appears only as inclusions in garnet and lawsonite, never in the matrix, a detail that proved crucial for interpreting the pressure-temperature history.

The garnets, about a millimeter across, display intricate concentric zoning that reads like a growth diary. Manganese and calcium decrease from core to edge in the inner regions, then a manganese- and iron-rich annulus gives way to a low-manganese, higher-calcium rim, with a final thin zone of elevated magnesium. Rutile first appears on the inner side of the annulus and continues into the rim, while quartz and titanite inclusions vanish at the same boundary. That switch marks where the rock crossed into eclogite-facies conditions. The omphacite shows patchy zoning with a jadeite component varying between 16 and 28 percent, and the matrix lawsonite is itself zoned, with iron, titanium, and strontium generally increasing from core to rim, and traces of chromium detected in some grains.

To pin down the conditions of formation, the team combined two independent approaches. The first was Zr-in-rutile thermometry, which relies on the temperature-dependent incorporation of zirconium in rutile when rutile, zircon, and quartz coexist. Because quartz in the fresh eclogite occurs only as inclusions, the researchers applied the thermometer to rutile inclusions in a narrow garnet zone where quartz, rutile, and zircon overlap, interpreted as late prograde to near-peak conditions. Zirconium contents of 30 to 50 parts per million yielded temperatures of roughly 490 to 540 degrees Celsius across the evaluated pressure range. The second approach was a bulk-composition-specific phase diagram, or pseudosection, calculated with Perple_X using the Holland and Powell thermodynamic database. The quartz-absent assemblage matching the observed matrix minerals occupies a narrow temperature window of about 470 to 520 degrees Celsius at pressures above 2.1 gigapascals.

Intersecting the eclogite assemblage field with the zirconium isopleths produced a near-peak estimate of approximately 500 degrees Celsius at 2.3 gigapascals, equivalent to burial depths of roughly 75 to 85 kilometers at temperatures corresponding to a geothermal gradient near 5 to 6 degrees Celsius per kilometer. That pressure is substantially higher than previous estimates for the area, yet the conditions closely match those recorded by other fresh lawsonite eclogites worldwide and align with thermal models of the slab surface in modern cold subduction zones such as Tonga and Tohoku. Notably, the team found that recalculating earlier Zr-in-rutile data with a newer pressure-dependent calibration by Kohn raises previously reported temperatures into the same range, suggesting some apparent discrepancies between studies reflect methodological differences rather than geological ones.

The contrast with a second sample from the same locality is instructive. ELEK23-08a2, a retrogressed eclogite now classified as an epidote blueschist, contains large four-to-five-millimeter garnets packed with lawsonite inclusions from core to near-rim, along with rare omphacite, glaucophane, and epidote. Its matrix, however, is dominated by glaucophane, epidite porphyroblasts up to six millimeters long, albite, chlorite, and phengite, with only minor lawsonite. Some lawsonite inclusions in epidote have been partially replaced by lower-iron epidote rims that preserve the original lawsonite outlines as so-called ghosts. Rutile in this rock carries far less zirconium, only 9 to 12 parts per million, yielding temperatures of about 420 to 450 degrees Celsius, and its phengite is less siliceous than that of the fresh eclogite. In short, the retrogressed rock records lower pressures and cooler temperatures than the peak conditions, confirming that such altered samples cannot reliably indicate maximum burial.

The broader implication is a caution about how subduction complexes are read. Most Elekdağ metabasites were retrogressed to epidote-bearing blueschists during exhumation, aided by deformation and fluids that also generated chlorite-rich metasomatic zones along contacts with the serpentinite. The prevalence of epidote in eclogites and blueschists here and elsewhere indicates that exhumation occurred under conditions warmer than prograde or peak metamorphism. The authors emphasize that these relatively warm retrograde conditions should not be extrapolated to characterize the overall thermal state of subduction in the forearc region that subduction complexes typically represent. The fresh lawsonite eclogite, a fortuitously preserved relic, is the true messenger of peak conditions, and it reaffirms that cold subduction, with its capacity to transport water and trace elements deep into the mantle, has operated much as thermal models predict. With only ten confirmed localities globally, and just six with meaningful geological context, each new discovery sharpens our window into the planet’s deepest recycling engine.

Subject of Research: Discovery and pressure-temperature analysis of a rare well-preserved lawsonite eclogite from the Cretaceous subduction complex of the Elekdağ massif, Central Pontides, Türkiye

Article Title: Report of a rare, well-preserved lawsonite eclogite (Elekdağ, Central Pontides, Türkiye)

Article References: Fornash, K. F., Petty, C., Toraman, E., Topuz, G., & Whitney, D. L. (2026). Report of a rare, well-preserved lawsonite eclogite (Elekdağ, Central Pontides, Türkiye). European Journal of Mineralogy, 38(5), 567-574. https://doi.org/10.5194/ejm-38-567-2026

Image Credits: AI Generated

DOI: 10.5194/ejm-38-567-2026

Keywords: lawsonite eclogite, subduction zone, Elekdağ, Central Pontides, Türkiye, metamorphic petrology, garnet, omphacite, Zr-in-rutile thermometry, pseudosection modeling, high-pressure low-temperature metamorphism, blueschist

For decades, seismic hazard assessment in most parts of the world has concentrated on horizontal ground motion, driven by the observation that lateral forces are usually the primary cause of structural collapse. Yet engineers have increasingly recognized that vertical shaking can impose severe axial demands on columns, beams, and connections, particularly in reinforced concrete frames, bridges, and base-isolated structures. Laboratory testing and post-earthquake investigations have repeatedly shown that reinforced concrete columns subjected to combined horizontal and vertical accelerations lose load-carrying capacity faster than those facing lateral motion alone, and that vertical ground motion has been implicated in damage to historical structures and modern buildings alike. Until now, El Salvador’s building codes and hazard maps have lacked a rigorous, nationally calibrated basis for quantifying that vertical threat.

The new work presents time-independent probabilistic seismic hazard maps expressed in terms of vertical peak ground acceleration and spectral ordinates at periods of 0.2 and 1 seconds, computed for 5 percent of critical damping. These values were produced for rock site conditions and flat topography across five return periods: 50, 95, 475, 975, and 2475 years. The return-period framework mirrors the conventions used in modern design standards, allowing engineers to select ground-motion intensities appropriate to the importance and intended lifespan of a structure. A 475-year return period, corresponding to roughly a 10 percent probability of exceedance in 50 years, is the traditional benchmark for ordinary buildings, while the rarer 2475-year event informs the design of critical facilities such as hospitals and emergency centers.

To construct the hazard models, Salazar employed two complementary approaches: the classical area source method and the smoothed seismicity method. The area source approach divides a region into discrete zones assumed to share uniform seismicity characteristics, a technique rooted in Cornell’s foundational 1968 formulation of engineering seismic risk analysis. The smoothed seismicity method, pioneered by Gordon Woo in the 1990s, dispenses with rigid zonation boundaries and instead spreads earthquake occurrence spatially using kernel functions, letting the historical record itself shape the hazard landscape. Using both methods within a logic tree framework allows the analysis to capture epistemic uncertainty, the uncertainty arising from incomplete scientific knowledge about where and how frequently earthquakes occur.

The seismicity evaluation draws on a homogenized earthquake catalog spanning nearly five centuries, from 1528 to 2023, with moment magnitudes ranging from 5.0 to 8.1. Bringing nearly 500 years of historical and instrumental records into a consistent magnitude scale is one of the most labor-intensive aspects of hazard analysis in developing countries, where early accounts may consist only of damage descriptions in colonial archives. From this catalog the study derived classical Gutenberg-Richter frequency-magnitude relationships, which describe the predictable inverse relationship between earthquake size and occurrence rate, as well as average kernel bandwidth distances, a measure of the typical spacing among epicenters of earthquakes of the same size that parameterizes the smoothed seismicity calculations.

A distinctive strength of the study lies in its empirical testing of vertical ground-motion prediction equations against actual accelerometer recordings from El Salvador itself. The candidate equations were evaluated against data from the two destructive earthquakes of 2001: the January 13 event of magnitude 7.7, which ruptured within the Cocos plate subduction zone offshore, and the February 13 event of magnitude 6.5, which struck in the volcanic chain zone where shallow crustal faults cut across the densely populated interior. Both earthquakes caused catastrophic losses, and their contrasting tectonic settings make them ideal calibration points for distinguishing how subduction interface and upper-crustal earthquakes transmit vertical energy to the surface. Salazar also accounted for hanging-wall effects, the amplification of shaking that occurs at sites located above the up-dip edge of a dipping fault rupture, which can substantially elevate ground motions at near-fault locations.

The weighting of competing ground-motion models in the logic tree was informed directly by how well each vertical prediction equation reproduced the observed Salvadoran recordings, rather than being assigned arbitrarily or borrowed wholesale from other regions. This data-driven calibration matters because vertical-to-horizontal spectral ratios vary widely across tectonic regimes, and models developed for Japan, Italy, Taiwan, or the Mediterranean do not necessarily transfer cleanly to Central America’s unique combination of a rapidly subducting oceanic plate and an active volcanic arc. By anchoring the model selection to local data, the study reduces one of the largest sources of uncertainty in vertical hazard estimates.

Among the study’s most practical outputs are proposed relations between horizontal and vertical map accelerations, expressed across all the return periods considered. These vertical-to-horizontal ratios provide an efficient bridge for practicing engineers: instead of requiring new vertical hazard computations for every site, designers can derive vertical design forces directly from the horizontal hazard values already in use, scaled by the locally calibrated ratios. Given that international design provisions, including the American Society of Civil Engineers’ ASCE 7-22 standard, increasingly demand explicit treatment of vertical seismic effects, such locally derived conversion factors are precisely what national code committees need to modernize requirements without embarking on a parallel hazard analysis from scratch.

The implications extend beyond structural engineering practice. El Salvador’s seismic vulnerability was starkly demonstrated in 1986, when the San Salvador earthquake destroyed thousands of buildings, and again in 2001, when the two major quakes within a month devastated communities already struggling with recovery. Recent geodetic work using GNSS and InSAR has continued to map the accumulating tectonic deformation across the country, underscoring that the forces driving the hazard remain fully active. Regional hazard models developed for sovereign parametric insurance also depend on the kind of robust, probabilistic ground-motion characterization this study provides, meaning the new vertical maps could ultimately inform not only building design but financial instruments that transfer catastrophe risk at the national scale.

For a country that sits atop one of the planet’s most active seismic engines, the message of this research is clear: the ground does not only move sideways, and the engineering community must plan for the full three-dimensional character of earthquake shaking. By combining a five-century earthquake catalog, dual seismicity modeling methods, empirically tested vertical ground-motion equations validated against Salvadoran strong-motion records, and practical hazard maps spanning return periods from 50 to 2475 years, the study gives El Salvador a technical foundation that few nations of its size possess. The work was supported by research grants from the Catholic University of El Salvador and made use of Woo’s KERFRACT Fortran code for smoothed seismicity, and it stands as a template for how data-scarce, high-hazard countries can leverage both historical archives and modern instrumental networks to quantify the risks beneath their feet.

Subject of Research: Probabilistic seismic hazard mapping of vertical earthquake ground motion components in El Salvador

Article Title: Seismic hazard maps for El Salvador: the vertical component of motion

Article References: Salazar, W. (2026). Seismic hazard maps for El Salvador: the vertical component of motion. Bulletin of Earthquake Engineering. https://doi.org/10.1007/s10518-026-02665-9

Image Credits: AI Generated

DOI: 10.1007/s10518-026-02665-9

Keywords: seismic hazard, El Salvador, vertical ground motion, probabilistic seismic hazard analysis, ground-motion prediction equations, smoothed seismicity, subduction zone, earthquake catalog, logic tree, return period, vertical-to-horizontal ratio, Bulletin of Earthquake Engineering

The researchers begin from a sober demographic observation. Low-elevation coastal zones cover only about two percent of the planet’s land surface but held ten percent of the world’s population in 2000, and in the Caribbean roughly seventy percent of people live in large coastal cities. Population density on the Anguilla Bank is striking: around 160 inhabitants per square kilometre on Anguilla, about 500 on Saint-Martin/Sint Maarten and some 530 on Saint-Barthélemy. On these flat forearc islands, there is often no high ground within a reasonable walking distance, so even a modest tsunami could trap residents and tourists on narrow coastal strips between the open sea and shallow salt ponds.

Although the Caribbean accounts for only about five percent of global tsunami records — roughly seventy of the 1,540 events catalogued by NOAA — the region’s history is far from quiet. The infamous Lisbon earthquake of 1 November 1755, with an estimated moment magnitude of 8.5 off the Iberian Peninsula, sent destructive waves across the Atlantic that reached the Lesser Antilles about ten hours later. Contemporary documents describe several-metre waves and inundations throughout the arc. On Saint Martin, historical compilations report a run-up of 4.5 metres and a dramatic sea withdrawal: a sloop anchored in roughly 4.6 metres of water was reportedly left lying dry on her broadside. A second, lesser-known transatlantic event followed on 18 November 1755, when the Cape Ann earthquake in Massachusetts apparently produced a sea withdrawal and a six-foot return wave at Saint Martin’s harbour, as recorded in a letter by Professor Winthrop.

The most destructive regional tsunami struck on 18 November 1867, after a magnitude 7.2 earthquake ruptured a 50-kilometre segment of a fault along the northern border of the Virgin Islands basin. Waves reached several metres — up to about ten metres — in the U.S. Virgin Islands within fifteen minutes and were reported from Puerto Rico to Grenada. In the Anguilla Bank, damage was documented in Saint Martin and Saint Barthélemy, where the 2.1-metre-deep Carenage was left dry, vessels were stranded and then swept adrift, and one schooner was carried by currents at a rate of ten knots before being secured hours later. Beyond these three documented events on the bank, geological evidence points to older, pre-colonial tsunamis: boulders transported up to six metres above sea level on Saint Martin, sediment cores from Etang Guichard recording five extreme-wave events over the past 3,500 years with a 300-to-400-year recurrence, and a regionally extensive inundation dated to roughly 1200–1500 years before present identified on Anegada, Saint Thomas and Scrubb Island.

To translate this history into forward-looking hazard estimates, the team built twelve rupture scenarios. Seven (S01 to S07) represent local upper-crustal faults mapped around the Anguilla Bank from high-resolution bathymetry and seismic reflection profiles, selected for their ability to produce magnitude greater than 6 earthquakes and for their near-complete azimuthal coverage of the archipelago. Fault dimensions were converted into moment magnitudes, rupture areas and coseismic slips using the empirical scaling relationships of Wells and Coppersmith, Leonard, and Thingbaijam, with fault dips and slip directions constrained by seismic profiles and seismotectonic data. Three further scenarios reproduce historical events: the 1755 Lisbon source (S08), the 1867 Virgin Islands rupture (S09) and the 1843 Guadeloupe earthquake (S10), the largest known event in the Lesser Antilles at an estimated magnitude 8.5. Two final scenarios (S11 and S12) relocate that 1843 megathrust rupture northward along the subduction interface — one beneath the Anguilla Bank region and one in the Puerto Rico subduction zone — to test how source position controls impact.

The simulations were run with COMCOT, the Cornell Multi-grid Coupled Tsunami model, which solves linear and non-linear shallow-water equations on a system of nested grids. Three grid levels were used: a 2-arcminute grid of the North Atlantic built from GEBCO bathymetry, an intermediate 15-arcsecond grid over the northeastern Caribbean, and a finely resolved 3.75-arcsecond grid — about 115 metres — covering the Anguilla Bank itself, assembled from the HOMONIM and Litto 3D datasets offshore and SRTM topography on land, all referenced to local mean sea level. Seafloor displacement for each scenario was computed with Okada’s elastic dislocation model, and inundation was activated on the two inner grids with Manning’s friction coefficients of 0.013 for the seabed and 0.0025 for land. Local and regional scenarios were propagated for ten hours; the Lisbon teletsunami was tracked for thirty-six.

The results reveal a strongly source-dependent hazard. The pure strike-slip scenario S01 produces little more than 30 centimetres of wave amplitude, consistent with the small tsunamis that followed recent large strike-slip earthquakes elsewhere in the region. In contrast, six of the seven local fault scenarios push coastal amplitudes above 30 centimetres, at least one location above 1 metre, and five of them above 2 metres somewhere along the coast. Scenario S05 emerges as the most impactful, with maximum amplitudes of 2 to 5 metres at some coastal sites, waves exceeding 2 metres on the northern coast of Saint Martin and more than 2 metres at Saint-Barthélemy’s low-lying, northeast-facing Baie de Saint-Jean. The bank’s numerous submarine canyons play a decisive role, focusing wave energy onto the flanks of canyon heads while sheltering the areas directly in front of them — a pattern well documented in other ocean basins.

The historical scenarios tell a subtler story. The 1755 Lisbon simulation produces generally modest impacts, with amplitudes above 30 centimetres in bays near the populous towns of Marigot and Sandy Ground and between 0.5 and just over 1 metre at Nettlé Bay and Great Bay, but the modelled wave fails to enter Simpson Bay Lagoon and falls far short of the reported 4.5-metre run-up. The authors suggest the historical observation may be erroneous, misattributed to another island, or that the current 115-metre grid resolution cannot fully capture coastal shoaling and refraction. The 1867 Virgin Islands scenario produces 0.3-to-1-metre offshore amplitudes, overtops the Sandy Ground spit and floods parts of the east coast, while the 1843 megathrust scenario drives amplitudes above 1.5 metres along most of Saint Martin and about 2 metres inside Simpson Bay Lagoon. When the same rupture is shifted northward (S11), it generates the largest amplitudes of all twelve cases — 2 to 5 metres along nearly every coast of the archipelago.

Currents prove as consequential as wave heights. Previous studies identify 1.5 metres per second as the threshold at which tsunami flows become dangerous to people and navigation, and experiments show an adult can begin sliding backward in only 26 centimetres of water at 1.8 metres per second. The Lisbon scenario stays mostly below this threshold around Saint Martin, with localized hotspots off Pointe du Bluff, Pinel Island and in Great Bay. The 1867 event pushes speeds to or beyond the threshold at those same sites plus Marigot, Baie de Grand Case and Baie de l’Embouchure, while the 1843 scenario exceeds it along nearly the entire coastline. Conversely, zones of low current speed — below 0.5 metres per second — could serve as sheltering anchorages during a tsunami alert. Overlaying the simulations on satellite-derived building footprints shows that Saint Martin’s largest urban centres sit either within modelled flood zones or directly facing high-amplitude, high-current areas.

The authors stress that their twelve scenarios are a preliminary, deliberately limited set: alternative rupture geometries, uncharacterized faults and non-seismic sources such as submarine landslides and volcanic eruptions could produce larger waves. The steep slopes flanking the Anguilla Bank on both its Caribbean and Atlantic sides are candidates for future collapse, and the nearby volcano Saba represents a direct threat, with at least 47 flank-collapse events identified along the Lesser Antilles Arc, 15 of them within the last 12,000 years. Tsunami management plans for Saint Martin and Saint Barthélemy are still under construction, and the study argues that horizontal evacuation along limited coastal roads should be supplemented with vertical shelters. It also calls for an expanded monitoring network: the northern Lesser Antilles currently hosts only a handful of working sea-level gauges, the Saint Martin gauge has delivered no usable signal since February 2020, the planned Gustavia station was never completed, and the nearest deep-ocean DART buoys lie roughly 630 to 750 kilometres away — leaving these idyllic islands, for now, largely blind to the next approaching wave.

Subject of Research: Earthquake-related tsunami hazard assessment for the Anguilla Bank Archipelago in the northern Lesser Antilles using historical data, fault characterization and numerical tsunami simulation.

Article Title: Tsunami hazard in the Anguilla Bank Archipelago, Lesser Antilles: historical data, fault characterization and numerical simulation

Article References: Roger, J. H. M., & Philippon, M. (2026). Tsunami hazard in the Anguilla Bank Archipelago, Lesser Antilles: historical data, fault characterization and numerical simulation. Natural Hazards, 122(19), Article 636. https://doi.org/10.1007/s11069-026-08367-4

Image Credits: AI Generated

DOI: 10.1007/s11069-026-08367-4

Keywords: tsunami hazard, Anguilla Bank, Lesser Antilles, Caribbean, numerical modelling, COMCOT, earthquake, subduction zone, Saint Martin, Saint Barthélemy, crustal faults, natural hazards

The Guerrero gap is a segment of the Mexican subduction margin where the Cocos Plate dives beneath the North American Plate. Unlike many portions of the boundary, this region has experienced a relative absence of large, recently recorded earthquakes, even though it is capable of storing enormous tectonic stress. That combination has made the area a focus of research into earthquake hazards, slow slip, and the processes that determine whether accumulated strain is released suddenly or gradually.

At a subduction zone, the incoming oceanic plate does not descend as a perfectly smooth slab. Its surface may carry ridges, volcanic seamounts, fractures, sediment, and variations in crustal thickness. As these features enter the trench, they can alter the geometry and frictional behavior of the plate interface. Scientists have therefore often expected a direct relationship between the structure arriving at the trench and the distribution of slip along the megathrust, the broad fault where the two plates meet.

Slip describes the relative movement between the plates during an earthquake or a slower tectonic event. In some sections of a subduction boundary, the fault may remain locked for years or centuries before rupturing in a powerful earthquake. Elsewhere, the same interface can creep continuously or release energy through slow-slip events that last weeks or months and produce little or no shaking. Mapping where and how this movement occurs is central to estimating seismic risk, but the physical controls remain difficult to isolate.

The study by T. Acquisto, A. Bécel, V. M. Cruz-Atienza and colleagues examined whether changes in slip behavior at the Guerrero gap could be directly explained by the structure of the plate entering the subduction zone. Its central conclusion, reflected in the paper’s title, is that the relationship is limited. In other words, incoming plate architecture may influence the fault system, but it does not provide a simple one-to-one explanation for why some parts of the interface slip differently from others.

That finding matters because it shifts attention away from single-factor explanations. If a seamount, ridge, fracture zone, or change in crustal properties does not consistently correspond to a particular style or amount of slip, then researchers must consider a wider combination of influences. These may include the composition and thickness of sediments in the trench, the pressure of fluids within the fault, the roughness and orientation of the plate boundary, temperature, mineral transformations, and the history of previous earthquakes and slow-slip episodes.

Fluids are especially important in this setting. Water carried downward by the oceanic plate can be released as minerals change under increasing pressure and temperature. The resulting fluids may raise pore pressure within the fault zone, reducing the effective force pressing the two plates together. In principle, that can make the interface more likely to slide. Yet fluid pathways are highly variable and may be controlled by fractures and permeability rather than by the large-scale shape of the incoming plate alone, helping explain why structural correlations can be weak.

The Guerrero gap is also a natural laboratory because its offshore environment allows scientists to compare processes beneath the seafloor with signals measured on land and at sea. Seismic waves, seafloor mapping, geodetic measurements, and models of fault motion can reveal different aspects of the plate boundary. Each method has limitations: seismic imaging can blur small structures, geodetic observations may average behavior over broad areas, and models depend on assumptions about the fault’s geometry and friction. Combining these approaches is therefore essential for separating robust patterns from apparent connections.

The study’s message is not that incoming plate structure is irrelevant. Rather, it suggests that its effect is indirect, filtered through the complex physical conditions of the subduction interface. This distinction could influence how scientists interpret earthquake forecasts and hazard maps. A visible feature on the oceanic plate should not automatically be treated as a reliable marker of a locked patch, a slow-slip zone, or a future rupture boundary. More realistic assessments will need to integrate geology, fault mechanics, fluids, temperature, and the timing of past deformation.

For the public, the research offers a reminder that earthquake science is increasingly precise but not yet simple. The absence of a straightforward structural fingerprint does not remove the seismic threat at the Guerrero gap, nor does it predict when a major earthquake might occur. Instead, it highlights why the most dangerous faults require detailed, multidisciplinary monitoring. By showing that slip variability cannot be explained directly by incoming plate structure alone, the researchers provide a more nuanced framework for understanding how Mexico’s subduction margin stores and releases tectonic energy.

Subject of Research: Slip variability and incoming plate structure at the Guerrero gap offshore Mexico

Article Title: Limited direct links between slip variability and incoming plate structure at the Guerrero gap offshore Mexico

Article References: Acquisto, T., Bécel, A., Cruz-Atienza, V.M. et al. Limited direct links between slip variability and incoming plate structure at the Guerrero gap offshore Mexico. Commun Earth Environ (2026). https://doi.org/10.1038/s43247-026-03796-2

Image Credits: AI Generated

DOI: 10.1038/s43247-026-03796-2

Keywords: Guerrero gap, Mexico, subduction zone, tectonic slip, earthquake science, incoming plate structure, megathrust, slow-slip events, seismic hazard