Study on non-tectonic gravity effects in western Shandong

Earth's gravity field change is closely linked to the processes of strong earthquake preparation, occurrence, and post-seismic adjustment. However, the observed gravity changes often include non-tectonic effects such as ground subsidence and variations in groundwater levels, which significantly impact the study of the relationship between gravity changes and seismic activity. Therefore, effectively identifying and eliminating these non-tectonic gravity effects is crucial for accurately interpreting tectonic activities and enhancing the scientific validity of earthquake prediction. To address this issue, this study focuses on the gravity field changes in Western Shandong from October 2017 to October 2021. By integrating contemporaneous groundwater and vertical deformation data of Global Navigation Satellite System (GNSS), the study employs an infinite plane layer model to forward calculate non-tectonic gravity effects, ultimately extracting the residual gravity signals related to tectonic activities. The results indicate that significant gravity changes in Western Shandong are strongly correlated with declining groundwater levels and ground subsidence, with non-tectonic gravity effects reaching up to + 78.22 µGal, while the residual gravity changes remain within normal ranges. Furthermore, the study provides an in-depth analysis of the reasons behind the differences in gravity changes among shallow groundwater depression zones, deep groundwater depression zones, and bedrock areas, proposing corresponding correction methods. This offers operational correction workflow for eliminating non-tectonic gravity effects in similar regions.