Analysing the gravity variations due to groundwater storage and sea level changes in the Indian Oceanic region

Abstract

Sri Lanka has been recognised as one of the places with the lowest gravitational measurement on Earth. However, the factors contributing to this phenomenon remain largely unexplored. The study examined the impact of Groundwater Storage (GWS) and fluctuations in sea level on regional gravitational anomalies by utilising satellite-based remote sensing data. An analysis of Gravity Recovery and Climate Experiment (GRACE) and Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) models, along with gravity data from the International Centre for Global Earth Models (ICGEM), CG-6 terrestrial gravity readings, Bureau Gravimétrique International (BGI) terrestrial and marine gravity data, and Global Land Data Assimilation System (GLDAS) hydrological information was conducted to discern how the redistribution of mass resulting from hydrological and oceanographic activities influences gravity across terrestrial and oceanic regions. The investigation spanned the timeframe from 2018 to 2022 and employed methodologies including kriging interpolation, Pearson correlation, and time series regression to identify spatial and temporal trends. The results unveiled important statistical connections among gravity anomalies and sea level indicators. The correlation coefficient of gravity to sea surface height (SSH) was R² = 0.6183, and it registered R² = 0.6029 against sea level anomaly (SLA), which suggests that more than 60% of gravity variations could be attributed to ocean mass redistribution. This connection of gravity to groundwater storage percentile (GWSP) was even stronger and reached R² = 0.7577, validating that groundwater changes are an important determining factor that acts upon gravity in the surveyed region. Long-term gravity observation results from high as well as low gravity sites proved overall stability defined by small fluctuations that could represent climatic action or small tectonic activity. This study revealed the potential of satellite methods to monitor gravity variations resulting from mass changes in very large and remote areas. It offered useful information about regional gravity anomalies of Sri Lanka without recourse to expensive ground survey, and it enriched general knowledge about geophysical and hydrologic processes.