[S-GD02] Crustal Deformation

[SGD02-P11] Rheology Structure Derived from Multiple Earthquakes and GNSS Data in Sumatra, Indonesia

*Satrio Muhammad Alif^1,4, Kuo-En Ching¹, Takeshi Sagiya², Irwan Meilano³, Ruey-Juin Rau¹ (1.National Cheng Kung University, Taiwan, 2.Nagoya University, Japan, 3.Institut Teknologi Bandung, Indonesia, 4.Institut Teknologi Sumatera, Indonesia)

Keywords:Earthquake, GNSS, Postseismic Deformation, Rheology, Sumatra, Viscosity

Multiple M>7 earthquakes occurred in the Sunda subduction zone, Sumatra since 2004. Several postseismic deformation studies have been conducted without considering the combination of all earthquakes and the GNSS data before 2004. By improving the flaws of those previous studies, we propose robust rheology structure that could be utiliized as velocitiy correction in the earthquake potential study in Sumatra. We calculate velocitiy difference between recent GNSS velocities and pre-2004 velocities to be utilized as the observation in modeling the structure in Sumatran rheology, consisting earth layer model and the viscosity of the asthenosphere. This velocity difference is calculated on the interpolated grid point to overcome the lack of a common station between those two time periods. Rheology structure was modeled using VISCO1D, incorporating a spherically stratified elastic-viscoelastic medium to to the stresses generated by an earthquake. Prior to estimate the best rheology, we evaluated the coseismic source models of the 2004 M9.2 Aceh, the 2005 M8.6 Nias, the 2007 M8.4 Bengkulu, and the 2010 M7.8 Mentawai earthquakes to see which one better fit the observation. Best earth model in the Sumatra is the earth model consists of three layers: lithosphere, asthenosphere with the best viscosity of 1.0 x 10¹⁸ Pa s, and the upper mantle with the fixed viscosity of 1.0 x 10²⁰ Pa s. The estimated uncertainty of the viscosity, which was propagated from the observation uncertainties, was ranging from 0.7 x 10¹⁸ Pa s to 2.0 x 10¹⁸ Pa s. The majority of the remaining velocity residuals were within their uncertainties, whereas the rest of them exhibited the persistent northwestward motion, most likely due to rheology model simplification.