Faults focus groundwater recovery into rapid urban land uplift

Groundwater recovery is lifting parts of Greater Osaka, Japan, at rates as high as 12 millimetres per year, with abrupt changes often aligned along crustal faults. A study combining satellite radar, ground-position measurements and multi-decadal groundwater records found that faults appear to impede lateral groundwater flow, causing pressure and water levels to accumulate on selected sides of the structures. Elastic expansion of the recovering confined aquifers then raises the land above. The results suggest that urban land motion is not a smooth basin-wide rebound but a patchwork of sharply separated uplift domains strongly associated with the basin’s fault network.

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