Seismic Events Near Sinabang, Indonesia: Geological Context and Recent History

The region surrounding Sinabang on Simeulue Island lies within one of the world's most active subduction zones. The Indo-Australian Plate converges with the Sunda Plate at rates of approximately 5–6 cm per year, driving megathrust earthquakes along the Sunda Trench. This tectonic setting produces frequent large-magnitude events, with hypocenters commonly occurring at depths between 20 and 40 km. On 6 April 2010 at 22:15 local time, a magnitude 7.8 earthquake struck 75 km east of Sinabang at a depth of 31 km. The event occurred near the same segment of the subduction interface that had ruptured five years earlier. On 28 March 2005, a magnitude 8.6 earthquake took place 78 km west-southwest of Singkil, only 33 km from the 2010 epicenter. Both shocks released substantial strain along adjacent portions of the plate boundary. These two events illustrate the segmented nature of the Sunda megathrust. The 2005 rupture extended roughly 400 km along strike and generated a modest tsunami that affected nearby coastlines. The 2010 event, while smaller, further stressed neighboring fault patches and contributed to ongoing afterslip and viscoelastic relaxation in the region. Post-seismic studies indicate that the combined sequence altered the stress state across the central Sumatran margin, influencing the timing of subsequent smaller earthquakes. Historical records document additional great earthquakes in the vicinity, including the 1861 event and the 2004 Sumatra-Andaman earthquake immediately to the north. Paleoseismic evidence from coral microatolls confirms recurrence intervals of 200–300 years for magnitude-8+ ruptures on this portion of the trench. Modern geodetic measurements from GPS networks show continued interseismic locking, underscoring the potential for future large events. Monitoring by regional seismic networks provides real-time detection and early-warning capabilities, reducing potential casualties from ground shaking and associated tsunamis. Continued research into fault coupling and slip deficits remains essential for refining hazard assessments in this rapidly deforming tectonic environment.

References

USGS Earthquake Catalog
Global Centroid Moment Tensor Project
Scientific literature on Sunda Trench tectonics