Revisited Mantle Structure beneath the Sunda Arc
About the Event:
Detailed P-wave velocity structure beneath the Sunda arc has been successfully imaged by applying a non-linear approach to seismic tomography and using the new data provided by the 2004–2005 Sumatra-Andaman great earthquake sequences. Nearly one million compressional phases from events within the Indonesian region have been used. These include the surface-reflected depth phasespP and pwP in order to improve the sampling of the upper-mantle structure, particularly below the back-arc regions. We have combined a high-resolution regional inversion with a low-resolution global inversion to minimize the mapping of distant aspherical mantle structure into the study region. The tomographic images indicate thatthe slab is folded at depth beneath northern Sumatra, exhibiting geometry similar to that of the volcanic arc and the trench at the surface. We envisagethat this fold plays a major role in the segmentation of the Sumatra megathrust, and may impede rupture propagation in the region. North of Andaman, significant slab material in the mantle transition zone is imaged for the first time, and we infer the presence of a major tear between the upper mantle and transition zone there. East of Sumatra, the tomograms depicta hole in the subducted slab in the upper mantle beneath eastern Java and suggest that a tear in the slab exists below the easternmost part of the Sunda arc, where the down-going slab is deflected in the mantle transition zone. In good agreement with previous studies, the properties of the deflected slab show a strong bulk-sound signature.In addition, we also observe a southward dipping feature below Bali depicted clearly by P- and S-wave images derived using similar ray path coverage. This feature is intriguing and in excellent agreement with local seismicity. The south-dipping feature in the back-arc region to the north of Bali has caused some tsunamigenic events. Following the great Andaman–Sumatran earthquake of 26 December 2004 with its attendant devastating tsunami, there have been calls for a tsunami early warning system for the Indian Ocean. Inferences from this study also urgently call for such an early warning system to mitigate tsunami hazards not only in the fore-arc, but also in the back-arc regions of Bali and small islands to the east.
About the Speaker:
Sri Widiyantoro is a professor of seismology at ITB, Bandung, Indonesia, where he has spent his academic career since 1987. He has frequently conducted research and study visits at prestigious universities overseas, including MIT and ANU, where he finished his Ph.D. program, and research institutions (e.g. Earthquake Research Institute, Tokyo University) to work with top scientists on collaborative research. His main research interest is in the field of seismology, particularly seismic tomographic imaging. His tomographic models have been published in various journals, including top journals like Science and Nature. Alongside his work on large-scale seismological problems, he has engaged actively in consultancy on oil, gas, and geothermal explorations related work in Indonesia, so that he can bring a very broad perspective to his science.
He has received recognition through many awards including the Doornbos Memorial Prize from the IUGG Committee on the Study of the Earth’s Deep Interior, the Habibie Award from the Habibie Center, the Science and Technology Award from the Indonesian Toray Science Foundation, and the Australian Alumni Award for Research and Innovation. He has been a Fellow of the Indonesian Academy of Sciences since 2011. He is currently Dean of Faculty of Mining and Petroleum Engineering, ITB, and was the President for the Indonesian Association of Geophysicists (2012-2014). Since 2015, he has been the Head of the Seismology Working Group of the National Center for Earthquake Study (PuSGeN) for updating the Indonesian seismic hazard maps that were published in 2017.