Quantifying seasonal poroelastic response induced by groundwater changes in GPS vertical displacement: a case study of Central Valley, California, USA

California has suffered several severe drought-flood abrupt alternation (DFAA) events over the past ~20 years, affecting non-linear variations in GPS position time series. Previous studies have demonstrated that hydrological loading plays an important role in seasonal surface uplift or subsidence beyond the large Central Valley Aquifer System (CVAS), California. However, GPS stations located on the CVAS are not only affected by hydrological loading but also by the groundwater-related poroelastic effect. In this study, we proposed a novel frame for poroelastic response based on an elastic half-space to quantify the contribution of poroelastic effects to seasonal variations in GPS displacement time series. Results show that for GPS stations beyond CVAS, the impact of poroelastic effect on GPS vertical displacement can be ignored due to the fact that hydrological loading deformation is 1–2 orders of magnitude larger than modeled poroelastic deformation. Whereas a significant and spatially widespread poroelastic response is observed for those GPS stations above CVAS and other possible aquifer systems. Moreover, the poroelastic deformation exhibits an in-phase and similar amplitude to the GPS vertical displacement corrected by hydrological loading deformation. More than half of all GPS stations show a positive value of the RMS reduction ratio after removing the modeled poroelastic effect, with an average of ~12%. In this case, only the pure elastic effect is considered for explaining the seasonal signals in the GPS vertical displacement may be inappropriate. Our work suggests that such a framework can describe a more complete spatial distribution of poroelastic response that encompasses the entire CVAS and would provide new geophysical insights into seasonal variation of GPS vertical displacement time series for those GPS stations located in large aquifer systems.