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Mw 6.4 Earthquake Strikes Western Sumatra

13 Aug 2017

A map indicating the location of today’s Mw 6.4 earthquake relative to the other earthquakes that have occurred along the Sunda megathrust fault since 2000. The location of the “seismic gap” is also indicated (Source: Aron Meltzner, 2017)

A moderate earthquake struck western Sumatra near Bengkulu on 13 August 2017 at approximately 12pm (Singapore time). According to the United States Geological Survey (USGS), the magnitude-6.4 earthquake occurred off the southwestern coast of Sumatra at a depth of about 36 kilometres (km).

Based on the preliminary information provided by USGS, this Mw 6.4 quake originated deep within the Sunda megathrust fault – the same fault that generated major earthquakes in 2004, 2005, 2007, and 2010.  The Sunda megathrust is the plate-boundary fault between the Indo-Australian and Sunda plates. It extends approximately 5,500 km from Myanmar, forming an arc around the Indonesian islands of Sumatra, Java, and Bali, ending near Australia.

Although today's earthquake originated from the same fault that has caused major tsunami-related earthquakes in the past, we do not expect this earthquake to trigger a widespread tsunami risk along the western coast of Sumatra, due to its moderate magnitude and deep hypocentre.  

The Sunda megathrust fault, however, remains a significant risk for Sumatra. The epicentre of today’s earthquake was located at the eastern edge of the same fault section that ruptured in 2007, causing a magnitude-8.4 earthquake. It was located far away, however, from the “seismic gap” between the rupture patch of the 2005 and 2007 megathrust earthquakes.

This seismic gap, which is located approximately 600 km away from Singapore, is a portion of the Sunda megathrust fault that has not ruptured for more than 180 years. The last ruptures can be dated back to 1797 and 1833 AD. If the fault were to rupture at the seismic gap, it could easily generate an earthquake with a magnitude of 8.5 or larger, with considerable tsunami waves along the southwestern coast of Sumatra Island.