Tectonic and climate induced mass changes - competing signals in long term gravity signals

Several mountain ranges as Alps, Himalaya and Tibet are presently subject to uplift, as documented by GNSSvertical movement rates. Uplift occurs in response to climatic mass loss (deglaciation or hydrologic mass loss)or due to the dynamic forces (crustal compression or mantle inflow below uplifting crust). The uplift generates amass change, which produces a time variation of the gravity field. The deglaciation and changes in the subsurfacehydrologic budget, also generate a mass change, which sums to the tectonic change. Satellite remote sensingis useful in determining the shrinking outlines of glaciers, using both multispectral imaging as well as Radarobservations, thus allowing to determine the surface geometry change. The essential value for climate change andestimate of the hydrologic budget is though the total volume budget estimate, which requires also the thicknessvariation. Remote sensing catches the surface height changes, but these must be corrected for the crustal uplift. Thegeodetic measurements of the crustal dynamics of the Alpine and Himalayan mountain ranges in terms of heightand gravity changes, are therefore in close relation to the estimate of the climatic changes inducing glacier andhydrologic budget changes. We estimate the hydrologic and glacier signal for the Alps and Himalaya-Tibet, usingresults from remote sensing and subsurface hydrologic observations, where available (for the methodologicalrationale see Chen et al. 2018). We estimate the contribution of the dynamic uplift by direct observations ofGNSS. We find that the hydrologic and glacier gravity signal calculated at satellite heights of GRACE andGOCE are superposed to the tectonic signal, and discuss to which amount the signals can be resolved by gravitymeasurements. We compare the predicted signals with the satellite observations of GRACE and GOCE, findingthat the tectonic uplift signal is small relative to the expected glacier/hydrologic signals, but that it cannot beneglected. We define the requirements to future gravity satellites in order to make a significante contribution to thedetection of hydro-glacial mass changes and the separation of the tectonic signal.Reference:Chen W., Braitenberg, C., Serpelloni, E. (2018) Interference of tectonic signals in subsurface hydrologic monitor-ing through gravity and GPS due to mountain building, Global and Planetary Change, Volume 167, August 2018,Pages 148-159.