Understanding The Lithosphere Rheology Of Sumatra Using GPS Data Obtained Through Earthquakes

Abstract

Crustal deformation and associated earthquakes are an integral part of the plate tectonics of Earth, especially in an active subduction zone like Sumatra. Alongside that, mantle rheology governs mantle’s dynamics, yet little is understood about how deformation is distributed at depth. Sumatra allows for a chance to investigate the post-seismic crustal deformation with its frequent and large earthquakes, thereby understanding lithosphere rheology. Utilizing time series data obtained from GPS stations and applying simple analytical logarithmic function, the average post-seismic time was set at 100 days for all the earthquakes. Using Maxwell’s viscosity equation, the asthenosphere beneath Sumatra is calculated to be at 5.53±1.14 × 10¹⁷ 𝑃𝒶𝑠. The asthenosphere viscosity estimated falls within the range of estimated values of other researches, which ranges from 3× 10¹⁷ 𝑃𝒶𝑠 to 1× 10¹⁹ 𝑃𝒶𝑠. The lithosphere rheology of Sumatra might be a result of a thick, viscoelastic slab overlaying a weak, low viscosity asthenosphere. Using the Burger’s model, an inelastic transient viscoelastic deformation of the crust and asthenosphere happen post-earthquake, allowing for a fast relaxation. Large uncertainties remain regarding lithosphere rheology and further research is needed to increase the understanding of subsurface post-seismic deformation.