April 2012 intra-oceanic seismicity off Sumatra boosted by the Banda-Aceh megathrust

Area of Science:

• Geophysics
• Tectonics
• Seismology

Background:

• Large earthquakes typically occur at tectonic plate boundaries.
• Intraplate earthquakes, especially offshore, are rare and poorly understood.
• The 2012 Wharton basin earthquakes were unusually large strike-slip events in an intra-oceanic setting.

Purpose of the Study:

• To investigate the cause of the 2012 Wharton basin earthquakes.
• To understand the relationship between megathrust earthquakes and intraplate deformation.
• To analyze the role of stress transfer and mantle dynamics in triggering intraplate events.

Main Methods:

• Analysis of the 2012 Wharton basin earthquakes and their aftershocks.
• Coulomb stress change calculations to model stress transfer.
• Investigation of viscous relaxation in the asthenospheric mantle.

Main Results:

• The 2012 earthquakes were linked to stress changes from the 2004 Aceh and 2005 Nias megathrust earthquakes.
• These stress changes promoted strike-slip faulting on pre-existing planes.
• Viscous relaxation in the mantle explains the time delay between megathrust and intraplate events.

Conclusions:

• Megathrust earthquakes can trigger offshore intraplate earthquakes through stress transfer.
• Mantle dynamics play a crucial role in the timing of intraplate seismic events.
• The findings offer insights into plate tectonics and the evolution of the India-Australia plate system.