title: Seasonal Hydrological Loading in Southern Tibet Detected by Joint Analysis of GPS and GRACE.
abstract: In southern Tibet, ongoing vertical and horizontal motions due to the collision between India and Eurasia are monitored by large numbers of global positioning system (GPS) continuous and campaign sites installed in the past decade. Displacements measured by GPS usually include tectonic deformation as well as non-tectonic, time-dependent signals. To estimate the regional long-term tectonic deformation using GPS more precisely, seasonal elastic deformation signals associated with surface loading must be removed from the observations. In this study, we focus on seasonal variation in vertical and horizontal motions of southern Tibet by performing a joint analysis of GRACE (Gravity Recovery and Climate Experiment) and GPS data, not only using continuous sites but also GPS campaign-mode sites. We found that the GPS-observed and GRACE-modeled seasonal oscillations are in good agreements, and a seasonal displacement model demonstrates that the main reason for seasonal variations in southern Tibet is from the summer monsoon and its precipitation. The biggest loading appears from July to August in the summer season. Vertical deformations observed by GPS and modeled by GRACE are two to three times larger than horizontal oscillations, and the north components demonstrate larger amplitudes than the east components. We corrected the GPS position time series using the GRACE-modeled seasonal variations, which gives significant reductions in the misfit and weighted root-mean-squares (WRMS). Misfit (χ2 divided by degree of freedom) reductions for campaign sites range between 20% and 56% for the vertical component, and are much smaller for the horizontal components. Moreover, time series of continuous GPS (cGPS) sites near the 2015 Nepal earthquakes must be corrected using appropriate models of seasonal loading for analyzing postseismic deformation to avoid biasing estimates of the postseismic relaxation.
authors.affiliation: Hubei Subsurface Multi-Scale Imaging Key Laboratory, Institute of Geophysics &amp; Geomatics, China University of Geosciences (Wuhan), Wuhan 430074, China. zourong@cug.edu.cn.|Finnish Geospatial Research Institute FGI, Geodeetinrinne 2, Masala 02430, Finland. zourong@cug.edu.cn.
authors.forename: Rong
authors.initials: R
authors.lastname: Zou
authors.affiliation: Hubei Subsurface Multi-Scale Imaging Key Laboratory, Institute of Geophysics &amp; Geomatics, China University of Geosciences (Wuhan), Wuhan 430074, China. wangqi@cug.edu.cn.
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK 99775, USA. jeff.freymueller@gi.alaska.edu.
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Freymueller
authors.affiliation: Finnish Geospatial Research Institute FGI, Geodeetinrinne 2, Masala 02430, Finland. markku.poutanen@nls.fi.
authors.forename: Markku
authors.initials: M
authors.lastname: Poutanen
authors.affiliation: Hubei Subsurface Multi-Scale Imaging Key Laboratory, Institute of Geophysics &amp; Geomatics, China University of Geosciences (Wuhan), Wuhan 430074, China. caoxuelian@cug.edu.cn.
authors.forename: Xuelian
authors.initials: X
authors.lastname: Cao
authors.affiliation: Institute of seismology, China Earthquake Administration &amp; Hubei Earthquake Administration, Wuhan 430071, China. stellazch@gmail.com.
authors.forename: Caihong
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Institute of seismology, China Earthquake Administration &amp; Hubei Earthquake Administration, Wuhan 430071, China. whgpsyang@gmail.com.
authors.forename: Shaomin
authors.initials: S
authors.lastname: Yang
authors.affiliation: Hubei Subsurface Multi-Scale Imaging Key Laboratory, Institute of Geophysics &amp; Geomatics, China University of Geosciences (Wuhan), Wuhan 430074, China. phe@cug.edu.cn.
authors.forename: Ping
authors.initials: P
authors.lastname: He
keywords: GPS; GRACE; horizontal deformation; seasonal variations; vertical deformation