The convergence on this part of the boundary is highly oblique and the strike-slip component of the plate motion is accommodated along the right-lateral Great Sumatran fault.

[4] This earthquake has been regarded as anomalous, in comparison to other Sunda megathrust events, due to the small amount of observed shaking compared to the scale of the triggered tsunami.

More recent estimates give a range of epicentres, including some located on a shallow part of the megathrust, although the uncertainties remain large.

Martin et al. (2019) give their preferred location as just west of Simeulue, coincident with a major barrier to rupture propagation along the megathrust caused by a ridge associated with a fracture zone on the subducting plate.

Observations of the amplitude of Rayleigh and Love waves from recorded seismograms have been used to estimate a seismic moment (M0) of 2.5×1028 for periods in the range 100–160 seconds (6–10 MHz), equivalent to Mw  of 8.2.

[1] In 2004 the S'mong is credited with saving the lives of many people on Simeulue and neighbouring Nias as inhabitants ran to higher ground following the earthquake.

The maximum observed inundation was 2–3 km (1.2–1.9 mi) at Lakubang on the southern coast of Simeulue and a maximum estimated run-up in the range 7–15 m (23–49 ft) based on reports of the loss of coconut palms on the small island of Pulau Wunga off northwestern Nias.

The tsunami earthquake resulted in an anomalously low shaking intensity of IV–V (European macroseismic scale) compared to the instrumentally determined moment magnitude of 8.2–8.4.