The study examines the Osaka Plain and the Kyoto and Nara basins, a metropolitan region of approximately 15 million people overlying an extensive groundwater system exceeding 3,000 square kilometres. Intensive extraction from the 1920s through the 1960s lowered water levels by as much as 30 metres and produced more than 2 metres of cumulative subsidence across much of the area. Groundwater regulation introduced in the early 1960s was followed by multi-decadal recovery, while most subsidence stabilised by the mid-1970s. Because the region has retained measurable deformation during this recovery, it offers a rare opportunity to examine how groundwater reinflation reshapes the surface of a major urban basin.

Interferometric synthetic aperture radar observations formed the spatial backbone of the analysis. The researchers processed 293 Sentinel-1 images acquired from December 2016 through December 2021 and combined them with co-located global navigation satellite system measurements, producing vertical and east-west displacement fields at 10-metre resolution. The mapped vertical rate averaged 4.0 plus or minus 2.5 millimetres per year across the region, with local values reaching 12 millimetres per year. Rather than changing gradually, uplift was divided into broad domains, often larger than 100 square kilometres, separated by boundaries less than 100 metres wide. Such sharp transitions indicate that underground structures exert a first-order control on the deformation.

Mapped faults coincide with several of the largest contrasts. Across the east-dipping Uemachi reverse fault in the Osaka Plain, average uplift reached 6 to 7 millimetres per year on its eastern, hanging-wall side but only 3 to 4 millimetres per year to the west. A similarly abrupt change follows the Ujigawa Fault in the Kyoto Basin. The average difference in uplift rate across the major structures was approximately 6.5 millimetres per year. By contrast, bedrock along the western margin of the Osaka Plain rose by only 0 to 1 millimetre per year, implying that a substantial component of the inland motion was associated with basin-scale processes rather than regional tectonic uplift alone.

Groundwater observations reveal a matching pattern. The researchers analysed groundwater-head changes from 44 monitoring wells screened at depths between 10 and 561 metres, using records extending from 1985 to 2025 where available. All 31 evaluated wells in the Osaka Plain recorded net rises, but average increases were 0.3 metres per year on the eastern, upstream side of the Uemachi Fault and 0.1 metres per year on the western, downstream side. The contrast persisted in individual records: eight of nine wells west of the fault experienced a marked decline between 1991 and 1998, associated with large-scale underground construction, whereas no comparable decline appeared in the eastern wells. The asymmetry is consistent with a fault acting as a hydraulic barrier and promoting groundwater accumulation on its upstream side.

The Kyoto Basin provides another natural test. Across 12 wells with records from 2000 to 2023, heads north of the Ujigawa Fault rose by an average 0.54 metres per year, while those south of it increased by only 0.01 metres per year on average; several southern wells continued to decline. The largest observed recovery occurred at well NKY, where the level rose 23.4 metres between 2000 and 2010, corresponding to approximately 2.3 metres per year. Across major faults in the combined dataset, upstream wells rose by roughly 0.30 metres per year and were associated with about 6.0 millimetres per year of uplift. Downstream wells rose by about 0.06 metres per year alongside roughly 2.2 millimetres per year of uplift. Although the spatial agreement alone does not establish causation, it is consistent with a mechanical linkage between groundwater recovery and surface movement mediated by faults.

The researchers then compared three classes of elastic deformation model: slip on a shallow fault, tensile opening at depth and distributed volumetric expansion within an aquifer. A fault-slip model could reproduce the direction of vertical motion across the Uemachi Fault, but it necessarily predicted strong east-west convergence that the observations did not contain. Shallow reverse-fault creep was therefore rejected as an adequate explanation. Aquifer-expansion models, by contrast, reproduced both the amplitude and spatial pattern of vertical uplift and the accompanying horizontal deformation in fault-bounded areas around the Uemachi and Arima-Takatsuki structures and in the Nara and Oji regions. The results do not uniquely establish the mechanism, but they show that shallow elastic expansion of recovering aquifers is physically consistent with the observations.

Model sensitivity placed the dominant deformation sources at depths shallower than about 500 metres. This constraint was strongest along the sharp edges of uplifting domains; broad, nearly uniform uplift provided much less information about source depth. Deeper aquifers may still contribute, but the fitted geometry indicates that they were unlikely to be the principal source of the observed motion. The models simplify the geology by assuming spatially uniform mechanical properties and do not explicitly represent groundwater flow, layered aquitards or lateral variations in permeability. Nevertheless, the agreement with both vertical and horizontal motion supports elastic expansion of fault-bounded aquifers as a plausible mechanism. A simple pressure-to-strain estimate also produces several millimetres of annual uplift, matching the scale of the satellite observations.

Fault effects may evolve through time. Within the Arima-Takatsuki Fault Zone, a wedge-shaped area now rising by as much as 10 millimetres per year had subsided rapidly after the 1995 Kobe earthquake, with rates of minus 5 to minus 10 millimetres per year observed from 1998 to 2010. At well IKD, groundwater declined at an average 0.16 metres per year from 1998 to 2012 before reversing to a rise of 0.23 metres per year through 2019. A nearby well outside the rapid-uplift zone showed no equivalent reversal, instead recording a steady 0.07 metres per year of increase from 1997 to 2025. One plausible explanation is that coseismic and early postseismic damage increased fault-zone permeability, allowing trapped groundwater to drain, whereas subsequent healing reduced permeability and allowed water to accumulate again. The available observations cannot uniquely distinguish this explanation from other changes in fault properties.

The high-resolution deformation data may also reveal faults absent from conventional maps. In the Nara Basin, a 12-kilometre-long, northeast-trending boundary less than 100 metres wide separates fast uplift from slower deformation, yet it does not coincide with a mapped surface fault. Its pronounced linearity and high angle to the basin drainage are difficult to explain through lithological heterogeneity alone, and independent borehole evidence supports a subsurface discontinuity in the area. The findings have practical implications for cities pursuing managed aquifer recovery: ending excessive extraction can allow sustained reinflation, but the resulting uplift may be spatially uneven rather than uniform. The study therefore supports considering fault-controlled groundwater connectivity when anticipating differential movement of infrastructure and planning land use in urban basins.

Subject of Research: Fault-associated groundwater recovery and land uplift in Greater Osaka, Japan

Article Title: Rapid urban land uplift enhanced by crustal faults during groundwater recovery

Article References: Fukunishi, S., Kearse, J., Kaneko, Y., & Barbot, S. (2026). Rapid urban land uplift enhanced by crustal faults during groundwater recovery. Communications Earth & Environment, 7(1), Article 761. https://doi.org/10.1038/s43247-026-03915-z

Image Credits: AI Generated

DOI: 10.1038/s43247-026-03915-z

Keywords: groundwater recovery, urban land uplift, crustal faults, land subsidence, Greater Osaka, InSAR, aquifer deformation, hydraulic barriers, GNSS, pore pressure, Rapid, urban

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