Seismic Hazards in Bengkulu, Indonesia: Subduction Zone Dynamics and Recent Major Events

Bengkulu lies on the southwestern coast of Sumatra, directly above the Sunda megathrust where the Indo-Australian plate subducts beneath the Eurasian plate at a rate of approximately 5–6 cm per year. This convergent boundary generates frequent large-magnitude earthquakes, with historical records documenting events exceeding magnitude 8. The tectonic setting features a locked interface that accumulates strain over decades to centuries, punctuated by sudden releases that produce both megathrust and intraslab seismicity. Two notable earthquakes illustrate ongoing activity in the region. On 4 June 2000, a magnitude 7.9 event struck 103 km south of Bengkulu at a shallow depth, producing intense ground shaking across southern Sumatra and triggering landslides in the Barisan Mountains. Roughly eight months later, on 13 February 2001 at 19:28 local time, a magnitude 7.4 earthquake occurred 102 km south-southeast of Bengkulu at a focal depth of 36 km. The epicenters lie only 52 km apart, indicating rupture within the same segment of the subduction interface. Both events released significant energy within the seismogenic zone, where brittle failure occurs between roughly 10 and 50 km depth. The 2001 shock, occurring at intermediate depth relative to the megathrust, likely involved intraslab deformation downdip of the main 2000 rupture area. Ground-motion recordings showed peak accelerations sufficient to damage unreinforced masonry structures common in rural Bengkulu Province. Long-term monitoring reveals that the Bengkulu segment experiences recurrence intervals of several decades for magnitude 7+ earthquakes, consistent with the high convergence rate. Paleoseismic studies of coral microatolls and coastal uplift further indicate that the broader Mentawai–Bengkulu region is capable of hosting magnitude 8.5–9.0 events when multiple adjacent patches rupture together, as occurred in 1833 and 1797. Current seismic hazard assessments classify the area as high risk, with design standards recommending structures capable of resisting peak ground accelerations exceeding 0.4 g. Ongoing GPS measurements detect continued locking along the plate interface, underscoring the potential for future large events.

References

USGS Earthquake Catalog (events of 4 June 2000 and 13 February 2001)
Global CMT Project focal mechanism solutions
Sumatra subduction zone parameters from McCaffrey (2009) and recent GNSS studies