Surface deformation caused by the unrest during 2002-2006 of the Changbaishan volcano in China

The Changbaishan volcano is recognized as one of China's most potentially dangerous active volcanoes. In response to the unrest event of 2002, GPS technology was utilized to monitor the surface deformation it induced. However, the understanding of the volcano's dynamics and the intricacies of GPS data at the time were limited, which affected the quality of the conclusions. For example, the commencement of GPS observations followed the escalation of seismic activities, leading to the loss of some deformation information. Moreover, observational noise in the GPS coordinate sequences introduced oscillations in the evolution of deformation characteristics. To overcome these limitations, we have developed an advanced GPS data processing methodology. This includes the establishment of a meticulous three-tier control network, the employment of high-precision geophysical models in GAMIT/GLOBK software, the creation of a volcanic regional reference frame, and the formulation of a sophisticated motion model for monitoring stations. With these approaches, we have captured the maximum surface deformation caused by the unrest and have re-evaluated the volume change (25.95x 106 m3/year) of the magma chamber based on Mogi model, yielding results that significantly surpass the mean of previous estimates of 8.58 x 106 m3/year and enhancing our understanding of the magma chamber's dimensions. Additionally, the surface deformation following the unrest displayed a pattern of continuous decay, which is in contrast to the seismic activity that initially rose and then declined, peaking notably after the surface deformation's peak. Considering the geological context of the volcano's formation, we have also provided an extensive dataset of GPS velocity fields. We have preliminarily discussed the possible relationship between the subduction of the Pacific Plate and the unrest in 2002, as well as the recent low-level unrest in 2021, acknowledging that this hypothesis requires further confirmation through stress modeling related to the disturbances. The deformation data resulting from the unrest, as well as the background deformation caused by plate subduction presented in this study, provide essential data constraints for the construction of subsequent stress models.