Seismic Events in Western Sumatra: The 2007 Padang Earthquake and Regional Context

Western Sumatra lies along the Sunda megathrust, where the Indo-Australian plate subducts beneath the Eurasian plate at rates of approximately 5–6 cm per year. This tectonic setting produces frequent large earthquakes and has generated a well-documented history of megathrust ruptures, including the great 2004 Indian Ocean event and the 2005 Nias earthquake. The segment offshore of Padang and Bengkulu has experienced repeated strain release in the past two decades. On 13 September 2007 at 03:35 UTC, a magnitude 7.0 earthquake struck 153 km SSW of Padang at a depth of 22 km. The event occurred within the aftershock zone of a larger sequence that began the previous day and was felt across West Sumatra. One hundred sixty-eight days later, on 25 February 2008, a magnitude 7.2 earthquake occurred 164 km WSW of Sungai Penuh, approximately 55 km from the 2007 epicenter. Both events are consistent with thrust faulting on or near the plate interface. These earthquakes form part of an ongoing cluster that has redistributed stress along the Mentawai segment. Historical records and paleoseismic studies indicate that the region has hosted multiple great earthquakes with recurrence intervals of roughly 200–250 years. The 2007–2008 activity did not produce a tsunami of regional significance, yet it underscores the persistent seismic hazard facing coastal communities in West Sumatra. Continued monitoring by regional seismic networks shows that moderate aftershocks persist, although the rate has declined since 2008. Updated hazard assessments incorporate these events into probabilistic models that forecast a substantial likelihood of future magnitude 8+ ruptures along adjacent locked portions of the megathrust.

References

USGS Earthquake Catalog (events 200709130335 and 200802250000)
Global Centroid Moment Tensor Project
Subarya et al., 2006, Nature (Sunda megathrust geometry)