| Abstract Submission No. | ABS-3.1-0131 |
| Title of Abstract | Postseismic Relaxation in Andaman Following the 2004 SumatrażAndaman Megathrust Earthquake |
| Authors | Nidhi Parashar*, Vineet K. Gahalaut, Joshi K. Catherine, M.S. Naidu, V Rajeshwara Rao |
| Organisation | CSIR-National Geophysical Research Institute; AcSIR |
| Address | Tectonic Geodesy group, CSIR-NGRI Hyderabad, Telangana, India Pincode: 500007 E-mail: nidhiparasharawr@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | The SumatrażAndaman subduction zone is one of the most seismically active plate boundaries, where the Indo-Australian Plate subducts obliquely beneath the Sunda Plate. This complex convergence produced the 2004 SumatrażAndaman megathrust earthquake (Mw 9.1), which ruptured ~1500 km of the Sunda Trench over ~10 minutes, generating a catastrophic tsunami that caused more than 200,000 fatalities. Owing to its large magnitude, this earthquake triggered long-lasting postseismic deformation across a broad region. Previous studies have modeled this deformation as afterslip, viscoelastic relaxation, or a combination of both. Far-field sites are generally well explained by viscoelastic relaxation, with afterslip dominating during the initial postseismic years, whereas near-field sites remain less well understood. In this study, we model the postseismic deformation at near-field sites in the Andaman and Nicobar Islands using VISCO1D, which incorporates a spherical, layered, compressible, self-gravitating, viscoelastic Earth model. We adopt a PREM-based Earth structure with a 62 km elastic lithosphere, underlain by a biviscous (Burgers body) asthenosphere and a Maxwell viscoelastic upper mantle. The coseismic rupture source is constructed using STATIC1D, incorporating both the 2004 (Mw 9.1) SumatrażAndaman and the 2005 (Mw 8.7) Nias earthquakes. We use continuous GPS measurements from sites on the Andaman and Nicobar islands. The model produces very good results for far field sites, consistent with the previous models, however the near field sites are not adequately explained, with the exception of Campbell Bay (CBAY) in the Nicobar Islands. The result enforces the fact that for a complex subduction zone such as Sumatra Andaman, lateral heterogeneity is required in the earth model to produce consistently good results in both near and far field sites. |
| Keywords | Postseismic, Viscoelastic, Sumatra-Andaman, Megathrust |