Taiwan sits at the junction of the Ryukyu and Manila subduction zones, where a rapid convergence rate of ~90 mm/yr drives intense seismic and tsunami hazards. However, land-based geodetic networks provide insufficient resolution for monitoring offshore deformation. To address this, we have developed and deployed GNSS-Acoustic (GNSS-A) systems to monitor seafloor deformation. A total of six GNSS-A sites were established along the southern Ryukyu subduction zone near Taiwan, with three additional sites located near the northern tip of the Manila Trench. GNSS-A data in the southernmost Ryukyu margin reveal an eastward increase in convergence rate, from 92 mm/yr offshore Hualien to 123 mm/yr near the Gagua Ridge, indicating the potential to generate Mw 7.5–8.4 earthquakes. The 2024 Mw 7.3 Hualien earthquake ruptured a deep 70° east-dipping Longitudinal Valley fault and a 35° west-dipping offshore fault. At seafloor site ORY2, ~ 40 km east of the epicenter, we recorded coseismic displacements of 9.1±12.1 cm eastward and 12.3±11.4 cm southward motions, along with 52.9±13.5 cm uplift. These observations are consistent with coseismic dislocation modeling results. Additionally, multiple slow slip events on fault systems in eastern Taiwan appear to have preceded the 2024 Mw 7.3 Hualien earthquake.Offshore southern Taiwan, geodetic data reveal N–S-oriented extension in the Tainan Basin and NE–SW extension between the northern Manila Trench and the North Luzon Trough. These strain axes align with the focal mechanisms of the 1994 M 6.5 and 2006 Mw 7.0 earthquakes. Notably, deformation and seismicity patterns shift distinctly across the Eurasian Plate–South China Sea continent–ocean boundary near 20°N. Together, these integrated observations provide new insights into fault segmentation, strain accumulation, and regional seismic and tsunami hazards.

Continuous Global Navigation Satellite System observations provide important constraints on crustal deformation and a wide range of geophysical and environmental processes. Here we present a 15-year continuous GNSS dataset for Taiwan, comprising observations from more than 300 continuously operating stations distributed across the island and covering the period from 2010 to 2024. The dataset integrates observations from multiple agencies through a unified and internally consistent workflow that includes metadata handling, precise point positioning processing in the ITRF2020 reference frame, and systematic quality assessment, resulting in daily coordinate time series, station metadata, and associated quality metrics. Three key quality indicators, including data availability, satellite visibility, and the standard deviation of residuals from time-series modeling, are provided to support evaluation of station performance and the reliability of derived products. Instrumental and coseismic offsets are identified and recorded to support consistent and reproducible analyses. The dataset is archived in a version-controlled repository with complete metadata and detailed supporting documentation. This release represents a fixed dataset version to ensure reproducibility. The dataset provides a foundation for investigating crustal deformation, coseismic and postseismic deformation, hydrological loading effects, and other geodynamic processes in Taiwan.

Studying deep-seated catastrophic landslides is challenging due to their complex geological conditions, slow and imperceptible movements, limited real-time monitoring, and difficulties in accurately assessing sliding behavior. We examine slope instability in a deep-seated landslide-prone area located in Lantai, Taiwan, by analyzing the temporal evolutions of slope movement and rainfall. Using a non-invasive automatic monitoring system that integrates the Global Navigation Satellite System, seismic velocity changes derived from ambient noise interferometry, as well as rainfall and groundwater-level records, we investigate rainfall-induced accelerated slope deformation in 2015–2024. Our findings show that acceleration events are triggered when rainfall lasts over 30 h and cumulative rainfall exceeds 200 mm at the study site. Multiple sliding events show a consistent temporal sequence, in which rainfall triggers an immediate dv/v decrease of 2–4

We characterize the spatiotemporal patterns of ground deformation caused by an earthquake doublet: the September 17, 2022, ML 6.6 Guanshan and the September 18, 2022, ML 6.8 Chihshang earthquakes occurred on the Central Range fault, eastern Taiwan. We use geodetic data collected from continuous and campaign-mode GNSS stations, as well as two precise leveling routes to estimate coseismic displacements and invert for fault slip distributions. The ML 6.6 foreshock caused northwestward horizontal displacements and uplift reaching 200 mm and 170 mm, respectively, in the region between Chihshang and Taitung. Seventeen hours later, the ML 6.8 mainshock generated coseismic displacements about four times larger than the foreshock, with horizontal displacements exceeding 900 mm and vertical displacements of 800 mm in the area between Guanshan and Ruisui. The maximum horizontal and vertical coseismic displacements of the entire earthquake sequence exceed one meter. The epoch-by-epoch high-rate GNSS data reveal significant seismic shaking, with maximum displacement exceeding 600 mm and 1100 mm during the foreshock and mainshock ruptures, respectively, correlating with severe infrastructure damage near surface ruptures. The dense spatial coverage of networks allows us to map the largest surface deformation along the Yuli fault, a branch of the steeply west-dipping Central Range fault, as well as the associated pop-ups along the east-dipping Longitudinal Valley fault. This observation suggests a likely coseismic and/or postseismic slip along the Longitudinal Valley fault. Our slip model indicates a maximum slip of approximately 3 m at a depth of 4.5 km to the west of Yuli, primarily on the Central Range fault. The coseismic slip extends over 50 km along the fault with two asperities near the hypocenter and Yuli. In addition, the Longitudinal Valley fault is characterized by shallow slip, with a maximum of 0.85 m at depths of 0-3 km.

Abstract Unknown seismogenic structures lurking beneath convergent margins introduce substantial uncertainty in seismic hazard assessments. In northwestern Luzon, the Mw 7.0 Abra earthquake on 27 July 2022 highlights the seismic activity along an unmapped blind fault underneath the Cordillera Central. By integrating coseismic displacements constrained by radar satellite imagery and Global Navigation Satellite System, we image oblique coseismic slip at 11–22 km depth with peak slip of ∼1 m beneath the Philippine Fault Zone in northern Luzon. The southward propagation of coseismic slip and aftershocks terminated at a distance of 50 km from the northern end of the 1990 Luzon earthquake rupture, leaving a seismicity gap in between. Coulomb stress changes of reaching 2 bars are imparted at the shallow portions of the Vigan‐Aggao and Abra River faults, where the updated 100‐year seismic potential is increased to Mw 7.0–7.7, given the thick seismogenic layer of ∼30 km in northern Luzon.

Nearby faults interact with each other through stress fluctuation incurred by seismic rupture, aseismic slip, and viscoelastic flow in the lithosphere. Understanding fault interactions and their temporal variation under different geometry are critical to regional seismic hazard and risk assessments. However, the complex interplay between adjacent faults is often unclear due to insufficient observations of large earthquakes with prolonged recurrence intervals. The 2022 Chihshang earthquake sequence in eastern Taiwan provides unprecedented insights into the interaction between two head-to-head thrust faults during and after a major earthquake. The Chihshang sequence was initiated by an Mw 6.5 foreshock on 17 September, followed by an Mw 7.0 mainshock 7 km to the north and 17 hours later. Based on the coseismic displacements constrained by field survey, optical satellite images, interferometric synthetic aperture radar (InSAR) data, and a dense network of Global Navigation Satellite System (GNSS) measurements, we map the major coseismic rupture on the east-verging Central Range fault (CRF), and the secondary induced slip on the west-verging Longitudinal Valley fault (LVF). The induced slip on the LVF accounts for 9-15% of the total moment release (Mw 7.1). Before the Chihshang earthquake sequence, the seismic hazard along the CRF was much overlooked due to the high seismic activity of the LVF. The 2022 Chihshang earthquake sequence demonstrates for the first time that the CRF is capable of generating earthquakes of Mw 7. The early afterslip primarily took place on the downdip extension of the CRF at great depth, indicating a contribution of ductile deformation there. Incorporating historical earthquake records over the past 120 years, we demonstrate that a rupture on the CRF or LVF reduces the stress level on the other, causing periods of seismic quiescence and an out-of-phase moment release pattern over time between the two faults. These results not only illuminate the fault geometry at the plate suture zone of eastern Taiwan, but also revise the conventional view of the nearby fault interaction. Integrating geometric complexity and fault slip history among adjacent faults in future modeling is essential for assessing realistic seismic hazards in similar structural settings.

Nearby faults interact through stress changes induced by fault slip and viscoelastic flow. The process is, however, often elusive and can be geometry-dependent and time-variant. Here, we combine geodetic and field observations to characterize the interaction of two head-to-head, conjugate faults in eastern Taiwan during the 2022 Chihshang earthquake sequence. We map the coseismic slip on the Central Range fault and dynamically-triggered shallow slip on the Longitudinal Valley fault, which has been creeping interseismically. Overlapping of seismic and aseismic slip suggests that the Longitudinal Valley fault is capable of hosting a variety of distinct slip behaviors. Moreover, substantial slip on the Central Range fault suppresses Coulomb stress on the Longitudinal Valley fault, and vice versa, resulting in seismic bursts in an out-of-phase pattern on the two faults as seen in the hundred-year historical records. Such fault interaction implies the need for time-dependent seismic hazard reassessment for the complex fault system.

The southern Ryukyu subduction zone is one of the potential sources for tsunamigenic earthquakes. Despite a great seismic risk, the deformation pattern remains poorly known, primarily due to the absence of seafloor constraints. With GNSS‐acoustic measurements over years, we characterize the convergence rate across this margin growing from 92 mm/yr offshore eastern Taiwan to 123 mm/yr near the Gagua Ridge. The new data suggest the subduction interface is capable of hosting M w 7.5–8.4 earthquakes. The orientations of seafloor movement and P‐ axes in the Nanao Basin are both subnormal to the trench, notably deviate from the direction of plate convergence. By considering the combined effect of plate convergence and backarc rifting, different trends between the forearc convergence, P ‐axes, and seafloor movement may indicate some degree of slip‐partitioning. The trench‐parallel component is likely accommodated in part by earthquakes near Taiwan, lower plate deformation, and strike‐slip faults within the accretionary wedge.

Long-term seafloor geodetic measurements are important for constraining submarine crustal deformation near plate boundaries. Here we present an integrated analysis of a decade of GNSS/acoustic data collected at a site 60 km to the east of northeast Taiwan near the axis of the Okinawa Trough back-arc basin. We obtained a time-series of horizontal and vertical positions based on 18 measurements from 2009 to 2019. These data reveal a southeastward movement at a rate of 43 ± 5 mm/yr since 2012 with respect to the Yangtze Plate. The horizontal motion can be explained by the clockwise rotation of the Yonaguni Block and northern Central Range. In addition, the vertical displacement of the transponder array shows rapid subsidence of 22 ± 9 mm/yr from 2012 to 2019. The fast subsidence rate and negative free-air gravity anomaly in this region indicate that crustal thinning is compensated mainly by surface deformation rather than upward migration of the Moho. Taking into account the offset in 2012 owing to the replacement of the transponder array, the horizontal position time series of our site are best explained by two linear lines with a slope change in July 2013. The timing of the velocity change coincides broadly with a change in the nearby seismicity rate and dike intrusion 150 km away from the site. Our results highlight the potential of seafloor geodesy in assessing temporal changes in deformation near the spreading center of the Okinawa Trough, which cannot be one using data from onland GNSS stations.

To better characterize the vertical movements and the deformation behaviors across the plate suture of an arccontinent collision, we conducted annual repeated measurements on two precise leveling routes in a length of 34 and 37 km, respectively, across the middle part of the Longitudinal Valley in eastern Taiwan in 2004-2018. The 14-year-long results showed that the Longitudinal Valley fault (LVF) dominates the surface deformation: a) the middle LVF (Juisui fault) exhibited partially locked in the upper few kilometers, with a cumulative uplift rate of 9-10 mm/yr in a distance of 4 km; b) the southern LVF (Chihshang fault) showed a creeping behavior with a vertical rate of 24-27 mm/yr. In addition, we are able to characterize other features, including 1) tilting upward to the west in the eastern Central Range, suggesting activity on the west-dipping Central Range fault; 2) the hanging wall of the LVF showed tilting downward behavior to the east; 3) the Chimei fault, a suspected active fault, revealed active slip on the sub-vertical fault plane, that caused a vertical rate of 8-9 mm/yr. Putting the results under global ITRF system, the whole Juisui route was moving downward, supporting the notion that NNW subduction of the Philippine Sea plate starts around the latitude of the middle of the Longitudinal Valley. Finally, the co-seismic vertical deformation of the 2013 ML6.4 Juisui earthquake was characterized by tilting upward to the west, consistent with stick-slip on the deeper part of a west-dipping interface of the forearc basement.

Applications of low-cost single-frequency continuous GPS receivers for monitoring volcano and landslide activities as well as to complement dual-frequency receivers have been demonstrated to produce stable and accurate positioning. In studies of crustal deformation, the relative distance between monitoring stations may vary from several kilometers to tens of kilometers, hence the differential single-frequency observations cannot model the ionospheric delay or other distance dependent errors. The 55 low-cost single-frequency continuous stations have been deployed together with 52 continuous dual-frequency stations in southeastern Taiwan since 2008. All of the single-frequency stations have applied corrections using dual-frequency stations to eliminate the distance dependent errors. Comparing velocity estimates from 8 co-located, the differences in horizontal and vertical components are less than 3 mm/yr and 6 mm/yr, respectively. Our study shows that the combination of single- and dual-frequency GPS data can provide robust results to study the fault slip behavior on the Longitudinal Valley fault.

The paper presents an estimation of the Earth’s crustal motion from the continuous GPS data at 6 stations (MTEV, MLAY, DBIV, TGIV, SMAV and SLAV) in the Northwestern and at PHUT (Hanoi) station using GAMIT/GLOBK software. The absolute displacements of the Earth’s crust at 7 stations in the IGS14 frame are respectively: 34.10±0.71 mm/yr (DBIV), 34.31±0.65 mm/yr (PHUT), 34.51±0.75 mm/yr (SMAV), 34.55±0.80 mm/yr (MLAY), 34.80±0.72 mm/yr (TGIV), 34.93±0.99 mm/yr (SLAV) and 35.59±0.73 mm/yr (MTEV), in the southeastward with the azimuth range 104-108o. The Son La fault is a right-lateral slip fault with a shear amplitude of ~1.5 mm/yr. The Lai Chau-Dien Bien fault is a left-lateral slip fault with a shear amplitude of ~1.9 mm/yr. Although the absolute velocities at the DBIV, SMAV, SLAV, TGIV and MLAY stations are evaluated with the error <1 mm/yr, the relative displacement on the Ma River fault is of ~0.5 mm/yr, and it seems that we still do not have a reliable assessment of the slip rate on the Ma River right-lateral slip fault.

On 6 February 2018 at 23:50 local time, a Mw 6.4 earthquake struck eastern Taiwan. We characterize the instantaneous surface ground motion and the permanent displacement induced by this event from continuous GPS data and SAR images within a short time after the mainshock. We use high-rate GPS positioning techniques to obtain epoch-by-epoch positions peak ground displacement to assess potential seismic damage. The maximum coseismic GPS horizontal displacement of about 450 mm trending to the northeast is observed at the station HUAL located on the hanging wall of the Milun fault. The PEPU located on the footwall of the Milun fault shows a coseismic horizontal displacement of 280 mm trending to the southwest and a coseismic uplift of about 70 mm. Moreover, ascending and descending tracks of ALOS-2 and Sentinel-1 SAR images are processed to estimate coseismic surface deformation along the line-of-sight (LOS) toward the satellite. Then, wide coverage from east-west and uplift components of surface deformation is fulfilled by combining the LOS displacement from ascending and descending interferograms. The main deformation area revealed by both GPS results and D-InSAR interferograms is concentrated around the Milun and Lingding faults. Significant uplift on the footwall of the northern Lingding Fault implies that the Milun fault and an unknown westdipping fault close to the Lingding fault were triggered. Both the two nodal planes of the Mw 6.4 Hualien event could be different with the kinematic behavior of the Milun fault and Lingding fault. Thus we suggest that slip on multiple faults was triggered during the 0206 event.

Rock uplift on the Earth surface is a key observation for studies of tectonics and geodynamic processes. Geodetic measurements from Global Positioning System (GPS) and leveling are able to track vertical deformation over a wide range of spatial and temporal scale. Taiwan mountain belt is subject to a rapid uplift rate of 20 mm/yr as revealed by GPS and leveling measurements in previous studies. The extremely high rates motivate us to analyze a set of newly processed GPS and leveling data along a NW-SE transect across southern Taiwan by considering the effects of the earthquake-related deformation as well as hydrological and surface processes. Our estimates of rock uplift rates from GPS and leveling are from - 12 to + 14 mm/yr across the southern Central Range of Taiwan. Vertical velocity changes on the small spatial scale are primary related to fault locking in the seismic cycle. The large spatial feature showing the mean uplift rate of 6 mm/yr between the eastern Central Range and the frontal thrust faults can be explained by a large-scale pop-up structure assuming the depth of 15-20 km in the orogenic wedge and the horizontal shortening of 30 mm/yr. Our results draw attention to carefully study geodetic vertical deformation in the mountain belts and seek relevant causes.

We measured seafloor movement using a Global Navigation Satellite Systems (GNSS)/Acoustic technique at the south of the rifting valley in the western end of the Okinawa Trough back‐arc basin, 60 km east of northeastern corner of Taiwan. The horizontal position of the seafloor benchmark, measured eight times between July 2012 and May 2016, showed a southeastward movement suggesting a back‐arc opening of the Okinawa Trough. The average velocity of the seafloor benchmark shows a block motion together with Yonaguni Island. The westernmost part of the Ryukyu Arc rotates clockwise and is pulled apart from the Taiwan Island, which should cause the expansion of the Yilan Plain, Taiwan. Comparing the motion of the seafloor benchmark with adjacent seismicity, we suggest a gentle episodic opening of the rifting valley accompanying a moderate seismic activation, which differs from the case in the segment north off‐Yonaguni Island where a rapid dyke intrusion occurs with a significant seismic activity.

Groundwater is an important part of the precious water resources. As the fresh surface water resources become scarcer because of climate change, population growth, and industrial activities, more and more groundwater has been extracted to meet the demands of various water uses e.g. municipal, industrial, and agricultural. Excessive groundwater extraction leads to severe ground subsidence which compromises the safety of surface and underground infrastructures. Modelling the effects of groundwater extraction is vital to the management and sustainable use of groundwater. However, results of such modelling have to be validated with inputs such as the field survey of ground subsidence. Levelling and continuous global positioning system GPS receiver networks are routinely used to collect these field measurements. Unfortunately, these techniques have limitations in terms of areal coverage and density of survey marks and, as a result, subsidence hot spots can be easily missed out. In order to provide a comprehensive picture of subsidence to aid geotechnical modelling and to assess the effectiveness of measures used to mitigate ground subsidence, satellite imaging radar interferometry techniques interferometric synthetic aperture radar InSAR can be used to complement other deformation monitoring techniques. In this study, 20 Advanced Land Observing Satellite ALOS Phased Array L-band Synthetic Aperture Radar PALSAR images acquired from 31 December 2006 to 26 February 2011 were used to map the land displacement over the Choushui River Fluvial Plain CRFP, Taiwan. The GPS measurements acquired at 10 continuously operating reference stations CORS were used to refine the orbit error in the each differential interferogram obtained from each radar image pair. The displacement time series over the distributed scatterers and the persistent scatterers were analysed. Several subsidence bowls were identified in CRFP. A quantitative comparison was conducted to compare the radar measurements to the GPS measurements over 36 GPS CORS stations. Good agreement between both measurements was observed with coefficient of determination R2 of 0.97, absolute mean difference of 3.2 mm year−1, and standard deviation of 4 mm year−1. The InSAR-measured Line-of-Sight displacement and GPS-measured horizontal displacement were integrated to derive the vertical displacement map. Two displacement maps were generated using two ALOS-2 PALSAR-2 pairs acquired between 2015 and 2016. Similar subsidence patterns were found in the two maps compared to the 2006–2011 displacement rate map, suggesting the land over the same region might have continued to fall.