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Tier 2 grant to Asst Prof Wei Shengji for study of megathrust ruptures close to Singapore

13 Aug 2019

Megathrust earthquakes are the most powerful and destructive earthquakes. These cataclysmic events cause the ground to shake and generate tsunamis, posing a great threat to society. When they wreak havoc they not only damage property and infrastructure, but most importantly, human life, with casualties reaching apocalyptic proportions of tens to hundreds of thousands in a single event, as well as hundreds of billions of dollars in economic losses. The majority of the seismically active regions where megathrusts occur are very densely populated; for example, the Sumatran region, home to about 50 million people, has been the world’s most active seismic area in the last two decades, releasing more than 50% of global seismic energy in the 21st Century despite occupying less than 4% of Earth’s surface.

Here in Singapore we may feel at safe distance from such disasters, but several of the recent Sumatran earthquakes were also felt in Singapore, where high-rise buildings may be vulnerable to future, closer Sumatran megathrust earthquakes. At least one anticipated future great earthquake has been forecast along the section of the megathrust that lies closest to Singapore, but more research is needed to understand the severity of shaking that could occur. The size of the 2004 and 2005 Sumatran megathrust ruptures was limited, and the reason why may hold a clue to the mechanisms of a future earthquake.

With this new Tier 2 grant, Asst Prof Shengji will first study the geometry and structure of the barrier beneath Simeulue Island that limited the ruptures of the 2004 and 2005 Sumatran earthquakes, by using data from 200 transportable seismometers and global seismic networks. Then he will use advanced computer simulations of earthquakes to create a better rupture scenarios of plausible future events. With the better understanding of how earthquake ruptures propagate and terminate that will come out of this research, better earthquake and tsunami risk assessment and hazard preparation will be possible. And we will be a few steps closer to better prepare Singapore for a future mega-earthquake from the Mentawai seismic gap, which is closest subduction zone to Singapore and have not ruptured from more than 150 years.

Images of the study area. (a) Seismicity and tectonic setting of the study area. Background seismicity from 1960–2010 are shown as purple circles. The rupture areas of the 2004 (Mw9.2), 2005 (Mw8.7), 2002 (Mw7.2) and 2008 (Mw7.4) earthquakes are displayed as color contours. The green and red stars indicate the epicenter of the 2004 and 2005 events, respectively. Global Centroid Moment Tensor (GCMT) solutions of Mw>5.5 earthquakes are shown as purple beach-balls. The black line across the Simeulue island gives location of the profile shown in Fig. 2. Black dashed lines are the depth contour of slab from Slab2 model at every 20km. The upper inset shows the larger area of Sumatran subduction zone with recent great earthquake ruptures (color patches) on the megathrust. The Mentawai seismic gap is highlighted. (b) Enlarged map of the Simeulue island, the coseismic uplift produced by the 2004/05 earthquakes are shown as contour lines. The proposed seismic stations to be installed on the island are displayed as red triangles.   

 

By Wei Shengji and Anna Lagerstroem