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This study analyzed time series data from six GPS stations within the Tatun Volcano Group (TVG), a long‐dormant volcanic system in northern Taiwan, using multichannel singular spectrum analysis to search for potential spatiotemporally correlated transient deformations. A notable cycle of transient deformation was identified from 2015 to 2020, characterized by ground subsidence and uplift of up to 10 mm, accompanied by asymmetric horizontal motions directed inward and outward toward Dayoukeng, the largest fumarole and hydrothermal area in TVG. Evidence from earthquake focal mechanisms and gas composition, along with preliminary source modeling, suggest that these transient phases were likely caused by the pressure change of shallow hydrothermal systems beneath Dayoukeng. Further analysis of time series data from three long‐operating GPS stations revealed similar patterns of transient motion in the area from 2006 to 2015, indicating that TVG has experienced cyclical deformation, akin to many other volcanic systems worldwide. Plain Language Summary: Monitoring ground deformation in volcanoes is crucial for understanding the underlying processes and providing early warnings of potential hazards. Previous geodetic studies of the long‐dormant Tatun Volcano Group (TVG) in northern Taiwan relied on sporadic data, leading to incomplete insights into its time‐varying deformation behavior. Continuous GPS, however, allows for accurate tracking of surface movements over time, including short‐term changes caused by intermittent volcanic activity. This first GPS study of TVG employed a method called multichannel singular spectrum analysis to identify transient signals in noisy data from six stations. Significant ground deformation was revealed between 2015 and 2020, with the ground sinking and rising by up to 10 mm, along with horizontal movements toward and away from Dayoukeng, a major steam vent area in TVG. This sinking is likely related to changes in the shallow hot water and steam systems beneath Dayoukeng, as suggested by anomalies in earthquake activity and surface gas composition. Additional GPS data from 2006 to 2015 revealed that TVG experienced recurring cycles of ground deformation, closely correlated with local seismic activity. Key Points: Data‐adaptive detection of transient deformation in noisy GPS time seriesCycle of ground deformation first detected in the Tatun Volcano area, where about 7 million people reside nearbyHydrothermal processes may have driven consistent spatiotemporal variations in seismicity and deformation in the Tatun Volcano area [ABSTRACT FROM AUTHOR]

Southwestern Taiwan exhibits multiple fold-thrust systems as a consequence of the interaction between the Philippine Sea Plate and the Eurasian Plate. A prominent geological feature of this region is the extensive layer of GuTingKeng mudstone, with a thickness of approximately 4 km, which serves as a source material for the formation of mud or shale diapirs. The 2016 Mw 6.4 Meinong earthquake, striking southwestern Taiwan at a depth of 15–20 km and inducing approximately 100 mm of uplift, has prompted investigations into the potential involvement of shallow structures (< 4 km) in this uplift. Recent studies have proposed that such shallow structures may have contributed significantly to the observed uplift during the earthquake. This study aims to elucidate the role of buried mud diapirs in the context of coseismic deformation. Here, we present a modeling approach that utilizes sill-like dislocations to simulate the deformation at the upper tip of the diapir. Our results indicate a vertical opening of approximately 60 mm at a depth of 1.4 km, which closely aligns with the spatial distribution of tomographic and gravity anomalies. We also examine how the coseismic stress changes induced by the Meinong earthquake can lead to a dilatational strain of about 1.2 microstrain within the shallow depth range of 0–4 km, resulting in extension within our modeled region. In contrast, the dilatational strain diminishes from 0.2 to − 1.2 microstrain at greater depths (4–8 km), implying compression in the subsurface beneath the diapir's top. This study discusses the potential mechanisms how fluid-rich and high-pressure mudstone may be deformed through coseismic process and how mud diapirs may contribute to additional deformation within the seismic cycle. [ABSTRACT FROM AUTHOR]