Seismic History of West Sumatra: The 2008 M7.2 Earthquake and Regional Context

West Sumatra, Indonesia, lies along one of the world's most active tectonic boundaries, where the Indo-Australian Plate subducts beneath the Eurasian Plate along the Sunda Trench. This subduction zone generates frequent large earthquakes, with the region near Sungai Penuh and Padang experiencing significant seismic events in recent decades. The area's geology features a combination of megathrust faults offshore and the Great Sumatran Fault onshore, contributing to both deep and shallow seismicity. On 25 February 2008 at 08:36 local time, a magnitude 7.2 earthquake struck 164 km west-southwest of Sungai Penuh at a depth of 25 km. This event occurred within a cluster of strong shaking that affected the Mentawai Islands and adjacent coastal areas. The moderate depth allowed for noticeable ground motion across parts of West Sumatra, though detailed damage reports remained limited compared to larger regional quakes. This 2008 earthquake followed a sequence of major events in 2007. On 12 September 2007, a magnitude 7.9 quake occurred 87 km southwest of Sungai Penuh. The following day, 13 September, a magnitude 7.0 event struck 153 km south-southwest of Padang. These three earthquakes, all within roughly 100 km of one another, highlight the segmented nature of the subduction interface in this portion of the Sunda Trench. The proximity suggests stress transfer along adjacent fault patches. Historically, the broader Sumatra region has produced some of the largest recorded earthquakes, including the 2004 magnitude 9.1 event farther north. The 2007–2008 sequence near Sungai Penuh represents a continuation of strain release along the Mentawai segment of the megathrust. Updated monitoring by global seismic networks confirms ongoing activity in this zone, with aftershock patterns typically aligning with the plate interface geometry. The combination of thrust faulting offshore and strike-slip motion along the Sumatran Fault creates a complex seismic environment. Depths around 25 km, as seen in the 2008 event, commonly correspond to the locked portion of the subduction zone where elastic strain accumulates between great earthquakes. Continued GPS measurements in the region indicate ongoing convergence rates of approximately 5–6 cm per year.

References

USGS Earthquake Catalog Global CMT Project Indonesian Meteorological, Climatological, and Geophysical Agency (BMKG) reports