Published on: 09-Jun-2015
Sabah earthquake banner.jpg
Map of earthquake epicentres in Sabah over the past
century, based upon recordings made by seismographs around the world. Data source from USGS (http://earthquake.usgs.gov/) and ISC (http://www.isc.ac.uk/)
Destructive earthquakes in easternmost Malaysia have been very uncommon historically, note scientists from the Earth Observatory of Singapore (EOS) at Nanyang Technological University (NTU Singapore).
In the past century, Sabah has experienced only three earthquakes greater than Friday’s magnitude 6.0. In 1923 and 1976, magnitude 6.3 and 6.2 earthquakes occurred about 100 km to the southeast. In 1951, a magnitude 6.1 earthquake occurred about 50 km to the north.
Professor Kerry Sieh, Director of the Earth Observatory of Singapore at NTU, said: "All of us at the Earth Observatory and at NTU extend our deepest condolences to the families and friends of the victims of this unusual natural disaster."
"Unlike Sumatra, Nepal, Taiwan and Japan, which straddle fast-moving tectonic plate boundaries, Sabah is not a place well-known for destructive earthquakes, so Friday’s destructive earthquake came as quite a surprise,” added Prof Sieh, a renowned geologist who developed new ideas and techniques to understand the recurrence of earthquakes and fault behaviour that changed how scientists study earthquakes.
“But this event has drawn our attention to the fact that they do occur there. Seismic recordings from around the world, measurements of ground deformation from orbiting satellites, and analysis of Sabah’s mountainous topography are now helping us understand what happened and why."
A quick initial exploration of the records of past earthquakes by the Earth Observatory scientists indicates that within a 300-km radius of the recent epicentre, there have been just four earthquakes equal to or greater than magnitude 6 in the past century, and none larger than 6.3. In comparison, Indonesia’s Sumatra has experienced in the past 15 years over a hundred earthquakes with magnitudes greater than or equal to 6, with 14 of these having magnitudes between 7 and 9.2.
Seismological recordings indicate that last week’s earthquake was caused by sudden slippage along a fault about 10 km in size and centred a little over 10 kilometres beneath the Earth’s surface, south of Mount Kinabalu.
During the rupture of the fault, the Earth’s crust around the fault stretched nearly a metre, northwest to southeast. The Earth Observatory scientists anticipate that analysis of satellite observations will show that the block northwest of this fault moved down relative to the block southeast of the fault, probably by about 20 centimetres. These numbers are very small compared to the several metres of shortening and metres of uplift during Nepal’s much larger, magnitude 7.8 earthquake in April.
A cursory inspection of the mountainous topography of this part of Sabah suggests that the fault that ruptured during the earthquake is part of a system of faults that courses nearly 200 km from northeast to southwest across this part of Sabah. The earthquake of 1951 may have occurred on the northern portion of this system of faults.
Prof Sieh, who is also the AXA-Nanyang Chair in Natural Hazards, said this tragic event illustrates a problem faced by many who live in South and Southeast Asia: How do individuals, communities and governments deal effectively with geological hazards that occur very, very infrequently but have potentially tragic, even devastating consequences?
As the Asian region is a hotbed of seismic activities, key areas where the Earth Observatory scientists have been studying over the past few years include Nepal, Indonesia’s Sumatra, Myanmar and China’s Yunnan province, where large earthquakes have occurred in the last few years.
Figure 1. Map of earthquake epicentres in Sabah over the past century, based upon recordings made by seismographs around the world. The dates indicate the years of the four largest earthquakes.
Figure 2. The type of fault that slipped during the Sabah earthquake is what geologists call a “normal” fault. The blocks on opposite sides of the fault move past each other suddenly during the earthquake, with one block dropping relative the other. In the case of the recent earthquake, the size of the fault was about ten kilometres on a side and slippage was about a metre. It is not known whether the fault broke all the way to the Earth’s surface during the earthquake.
Figure 3. Expected deformation pattern above the fault that ruptured in the Sabah earthquake.
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About Earth Observatory of Singapore (EOS)
The Earth Observatory of Singapore (EOS) is Singapore’s main hub for conducting research on geohazards, focusing on tectonics, tsunamis, volcanoes, sealevel and climate change in and around Southeast Asia. The Observatory’s mission is to understand these natural hazards and pass this information on to exposed communities, so that they might adapt to these environmental challenges.
The Earth Observatory of Singapore, an autonomous institute of Nanyang Technological University, is one of five Research Centres of Excellence funded by the Ministry of Education and National Research Foundation.
For more information, visit www.earthobservatory.sg
About Nanyang Technological University
A research-intensive public university, Nanyang Technological University (NTU) has 33,000 undergraduate and postgraduate students in the colleges of Engineering, Business, Science, Humanities, Arts, & Social Sciences, and its Interdisciplinary Graduate School. It has a new medical school, the Lee Kong Chian School of Medicine, set up jointly with Imperial College London.
NTU is also home to world-class autonomous institutes – the National Institute of Education, S Rajaratnam School of International Studies, Earth Observatory of Singapore, and Singapore Centre on Environmental Life Sciences Engineering – and various leading research centres such as the Nanyang Environment & Water Research Institute (NEWRI), Energy Research Institute @ NTU (ERI@N) and the Institute on Asian Consumer Insight (ACI).
A fast-growing university with an international outlook, NTU is putting its global stamp on Five Peaks of Excellence: Sustainable Earth, Future Healthcare, New Media, New Silk Road, and Innovation Asia.
The University’s main Yunnan Garden campus has been named one of the Top 15 Most Beautiful in the World. NTU also has a campus in Novena, Singapore’s medical district.
For more information, visit www.ntu.edu.sg
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