Sunda megathrust


The Sunda megathrust is a fault that extends approximately 5,500 km from Myanmar in the north, running along the southwestern side of Sumatra, to the south of Java and Bali before terminating near Australia. It is a megathrust, located at a convergent plate boundary where it forms the interface between the overriding Eurasian plate and the subducting Indo-Australian plate. It is one of the most seismogenic structures on Earth, being responsible for many great and giant earthquakes, including the 2004 Indian Ocean earthquake and tsunami that killed over 230,000 people. The Sunda megathrust can be divided into the Andaman Megathrust, Sumatra Megathrust and Java Megathrust. The Bali-Sumbawa segment is much less active and therefore does not have the "megathrust" term associated with it.

Tectonic setting

The subducting plate consists of two protoplates, the Indian and Australian plates. Similarly, the overriding plate consists of two microplates, the Sunda and Burma plates. The relative motion of the subducting and overriding plates varies slightly along strike due to these complexities but is always strongly oblique. The strike-slip component of the oblique convergence is accommodated by displacement on the Great Sumatran fault, while the dip-slip component is taken up by the Sunda megathrust.

Megathrust geometry

The Sunda megathrust is curviplanar, forming an arc in map view and, at least in Sumatra, increasing in dip from 5°-7° near the trench, then increasing gradually from 15°-20° beneath the Mentawai Islands to about 30° below the coastline of Sumatra.

Earthquakes

At this plate boundary, earthquakes occur along the Sunda megathrust and within both the subducting and overriding plates. The largest earthquakes are generated when the megathrust itself ruptures. Studies of both recent and historical earthquakes show that the megathrust is segmented. The largest earthquakes occur on separate 'patches' along the megathrust surface, with smaller events occurring at the boundaries between these patches. The rupture area of the 1861 event appears to be very similar to that for the 2005 event, suggesting that it can be regarded as a repeat event. The 2007 event is interpreted to be a partial failure of the rupture area of the 1833 event.
The 2004 earthquake ruptured an enormous segment of the megathrust surface. Research into evidence for previous events of this size suggests that they are rare, with two candidate earlier events occurring soon after AD 1290–1400 and AD 780–990. The Java-Bali segment of the megathrust does not appear to be associated with great earthquakes, possibly due to mainly aseismic slip.

List of Sunda megathrust earthquakes

This table lists Sunda Megathrust quakes with magnitudes of 7 or greater, or any known to have caused deaths. Historic records before 2004 are incomplete.
Date/Time‡LocationCoordinatesFatalitiesMagnitudeCommentsSources
1797-02-10just north of Siberut, Mentawai islands3008.4See 1797 Sumatra earthquake
1833-11-2550 km NE of North Pagai, Mentawai islands"numerous victims"8.8–9.2 MwSee 1833 Sumatra earthquake
1861-02-16Nias9058.5Caused major tsunami. See 1861 Sumatra earthquake.
1907-01-04 05:19just west of Simeulue2,1888.2–8.4Tsunami earthquake that caused a tsunami that devastated Simeulue and Nias, see 1907 Sumatra earthquake
1935-12-28 02:35just west of the Batu Islands7.7See 1935 Sumatra earthquake
1984-11-17 06:49Between Nias and the Batu Islands7.2See 1984 Northern Sumatra earthquake
2000-06-04 16:2870 km NNW of Enggano Island467.9See 2000 Sumatra earthquake
2002-11-02 01:268 km north of Simeulue Regency37.3See 2002 Sumatra earthquake
2004-12-26 00:5850 km north of Simeulue Regency229,0009.3 Mw See 2004 Indian Ocean earthquake
2005-03-28 16:09Bangkaru, Banyak Islands1,3038.6 Mw See 2005 Nias–Simeulue earthquake
2007-09-12 11:10125 km SW of Bengkulu258.4 Mw See September 2007 Sumatra earthquake
2007-09-12 23:49:04 UTC205 km NW of Bengkulu-7.9 Mw See September 2007 Sumatra earthquake
2007-09-13 03:35:26 UTC165 km SSW of Padang-7.0 Mw See September 2007 Sumatra earthquake
2008-02-20 08:36:35 UTC310 km SSE of Banda Aceh37.4 Mw
2008-02-25 08:36:35 UTC160 km SSW of Padang7.2 Mw
2009-09-30 10:16:1045 km WNW of Padang6,2347.6 Mw See 2009 Sumatra earthquakes
2010-04-06 22:15:02 UTC215 km SW of Medan62 injuries7.8 Mw See April 2010 Sumatra earthquake
2010-05-09 05:59:42 UTC215 km SSE of Banda Aceh-7.2 Mw
2010-10-25 14:42:22 UTC240 km W of Bengkulu435 & 100 missing7.7 Mw See 2010 Mentawai earthquake and tsunami