Seismic Hazards in the Sinabang Region of Indonesia

The area surrounding Sinabang on Simeulue Island lies within one of the most active subduction zones on Earth. The Indo-Australian plate converges with the Eurasian plate along the Sunda megathrust at rates of approximately 5–6 cm per year, generating repeated large-magnitude earthquakes and associated tsunamis. This tectonic setting has shaped the seismic history of the region for centuries, with great earthquakes occurring at intervals of decades to centuries. Instrumental records since 2000 document three notable events near Sinabang. On 2 November 2002, a magnitude 7.4 earthquake struck 50 km northwest of the town at a shallow depth. This event was followed on 26 December 2004 by the magnitude 9.1 Sumatra-Andaman Islands earthquake, whose rupture extended to within 58 km of the 2008 epicenter. The sequence continued with another magnitude 7.4 shock on 20 February 2008, located 56 km northwest of Sinabang at a depth of 26 km and occurring at 08:08 local time. These earthquakes illustrate the segmented behavior of the Sunda megathrust. The 2004 event released strain accumulated over centuries across a rupture length exceeding 1,200 km, producing widespread coseismic deformation and a devastating tsunami. The 2002 and 2008 events, though smaller, occurred in the same northern segment and likely represent triggered or complementary slip on adjacent patches of the plate interface. Depths around 26 km place these ruptures within the seismogenic zone where frictional locking gives way to stable sliding at greater depths. Ongoing convergence ensures continued seismic hazard. Post-2004 afterslip and viscoelastic relaxation have altered stress on nearby faults, increasing the probability of future moderate-to-large events. Paleoseismic studies of coral microatolls and coastal sediments confirm that similar sequences have repeated in the past, underscoring the need for sustained monitoring and preparedness in coastal communities of Simeulue and northern Sumatra. References
USGS Earthquake Catalog (events 2002–2008)
Global CMT Project moment tensor solutions
Sunda megathrust convergence rates from GPS studies (published literature)