| dc.description.abstract | GPS position time series can be utilized as an efficient method for monitoring surface displacement changes over time. In general, these time series can capture various ground motions such as long-term variations, short-term transient displacement, offsets, and seasonal signals. Differentiating between these different signals within GPS time series is crucial for comprehending the underlying geophysical or environmental processes. In this study, we selected six GPS stations located in the Tatun volcanic group (TVG) in northern Taiwan from 2013 to 2021 to explore potential spatially and temporally correlated transient deformations. Initially, we removed the secular trend and offsets using the least square method and addressed missing data using the singular spectrum analysis imputation method proposed by Kondrashov and Ghil (2006). Subsequently, the multichannel singular spectrum analysis (MSSA) was applied to extract the common transient displacements across these stations. Our analysis revealed two distinct periods of transient motion between June 2015 and April 2020: vertical subsidence and horizontal contraction from June 2015 to October 2016, and vertical uplift and horizontal expansion from June 2015 to October 2016, likely associated with local volcanic activity. To validate our findings, we compared our results with a hydrothermal fluid activity model proposed by Pu et al. (2021), which relied on seismic data and the ratio of surface sulfur emission (S_t) to {
m CO}_2 at Dayoukeng fumarole from 2014 to 2017. We suggested that the notable increase in shallow normal faulting earthquakes and the S_t/{
m CO}_2 ratio between October 2015 and July 2016 might indicate the upward movement of volcanic fluids and gases. Therefore, we infer that our first transient period, characterized by vertical subsidence and horizontal contraction from June 2015 to October 2016, may correspond to the regional crustal decompression effect resulting from the substantial outflow of hydrothermal fluids and gases. Additionally, MSSA analysis of three long-operated GPS stations (back to ~2006) revealed similar patterns of ground uplift and subsidence in the TVG from 2008 to 2015, albeit with smaller amplitudes. Utilizing MSSA effectively analyzes the GPS time series in this region as a method for monitoring future volcanic surface activity characteristics. However, most GPS stations are concentrated in the western region, and the significant displacement at station YM03 in the eastern region may suggest potential surface deformation due to volcanic activity in the eastern region. | en_US |