[S21-P] Poster

[S21-P-02] Oceanic Lithosphere-Asthenosphere Boundary Estimated from Stress Dependent Deformation after the 2012 Indian Ocean Earthquake

^○Cecep Pratama¹, Takeo Ito¹, Takao Tabei², Ryohei Sasajima¹, Putra Maulida³, Irwan Meilano³, Joni Efendi⁴ (1.Nagoya University, Nagoya, Japan, 2.Kochi University, Kochi, Japan, 3.Bandung Institute of Technology, Bandung, Indonesia, 4.Geospatial Information Agency, Cibinong, Indonesia)

Plate tectonic constitutes of a strong lithosphere overlying weaker asthenosphere. Therefore, the structure of lithosphere-asthenosphere system is essential key element to understand evolution of the earth. However, the boundary between oceanic lithosphere and asthenosphere under ocean are remaining poorly understood. On April 2012, an exceptionally large earthquake release high stress beneath Indian Ocean (＆#62; 17 MPa in average) during Mw8.6 mainshock and Mw8.2 largest aftershock. This high stress released in wider area of oceanic plate and reached more than 1 MPa in several hundreds depth km of mantle. The 2012 Indian Ocean earthquake, which occurred in the oceanic plate, provide strong constraint of oceanic lithosphere-asthenosphere rheological structure beneath ocean. Here, we try to reveal rheological structure including water content of hot asthenosphere and thickness of cold lithosphere. The boundary between lithosphere and asthenosphere is assumed to be dry olivine in the lithosphere and wet olivine in the asthenosphere as suggested by Karato (2012). Therefore, we develop heterogeneous three-dimensional spherical earth finite element models. The models produce spatial-temporal evolution of stress dependent deformation after the 2012 Indian Ocean earthquake using power-law rheology based on a thermally activated flow law obtained by rock experiments. We propose a systematic grid search to obtain trade off between water content and thickness parameter by using Global Navigation Satellite System (GNSS) data mainly in Sumatra and surrounding Indian Ocean region. In addition, we also investigate a possible stress dependent postseismic deformation mechanism due to the 2012 Indian Ocean earthquake between viscoelastic relaxation, afterslip or multiple mechanisms.