STRESS PERTURBATION ALONG SUMATRA ISLAND DUE TO THE OCCURRENCES OF MEGA-EARTHQUAKE (MW > 8)

• Main Author: Taufiq Rafie, Muhammad
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/36516
• Institution: Institut Teknologi Bandung

The perturbation of principle stresses orientation can be addressed to the occurrences of mega-earthquakes which altered the stress condition in the earth’s crust. Therefore, fault parameters, i.e. type, orientation, and slip, are crucial to infer the variation of the crustal in-situ stress field in spatial and time. Sumatra Island has a high seismic activity due to its close location to the subduction zone between the Indo-Australian and Eurasian plates as well as the existence of the Great Sumatran Fault (GSF). According to the historical seismicity of Sumatra Island, there were three mega-earthquakes Mw > 8: (1) 2004 Sumatra-Andaman earthquake Mw ~9.0, (2) 2005 Nias-Simeulue earthquake Mw ~8.6 and (3) 2012 off the west coast of Sumatra earthquake Mw ~8.6. In addition, there are 652 focal mechanisms data Mw 5 and focal depth < 250 km from 1976 to 2017. This catalog was compiled from Global Centroid Moment Tensor (GCMT) and the International Seismological Centre (ISC) bulletin. Those data were used in stress inversion to retrieve the evolution of principal stress orientations due to the existance of mega-earthquakes using iterative joint stress inversion method. To better understand the correlation between the variation of principal stresses and the slip of the three mega-earthquakes Mw > 8, we model the static Coulomb Failure Stress (?CFS). Our results showed remarkable changes of maximum principle stress orientation after mega-earthquakes, especially in the corner of thw Northern Sumatra Island (perturbed by ~30°) and in the vicinity of the Nias Island (perturbed by ~16°). In addition, the models of stress transfer showed good correlation between the distribution of aftershocks and increased Coulomb stress area. Our observations, i.e. ?CFS models and the orientations of principle stress axes, suggest that these parameters could be used as the first approach to analyse the stress level and, hence, its seismic hazard potential. Furthermore, this study could be extended for analyzing the mechanism of the stress rotation after mega-earthquakes in the Sumatra Island.