1861 Sumatra earthquake

Background

The island of Sumatra lies on the convergent plate boundary between the Indo-Australian plate and the Eurasian plate. The convergence between these plates is highly oblique near Sumatra, with the displacement being accommodated by near pure dip-slip faulting along the subduction zone, known as the Sunda megathrust, and near pure strike-slip faulting along the Great Sumatran fault. The major slip events on the subduction zone interface are typically of megathrust type. Historically, great or giant megathrust earthquakes have been recorded in 1797, 1833, 1861, 2004, 2005 and 2007, most of them being associated with devastating tsunamis. Smaller (but still large) megathrust events have also occurred in the small gaps between the areas that slip during the larger events, in 1935, 1984, 2000 and 2002.

Damage

Villages along the seaward side of the Batu Islands were devastated. The combined effects of the earthquake and tsunami caused several thousand fatalities.

Characteristics

Earthquake

There is evidence of coseismic uplift of Nias, with exposure of reefs and rock piers. There were six major aftershocks over the next seven months, the last of which, on 27 September caused a damaging tsunami. Based on studies of coral growth patterns, researchers have demonstrated that the 1861 event was the culmination of a 32 year long "slow-slip" seismic event, rendering it the longest known example of such a sequence ever recorded.

Tsunami

At least 500 km (310.7 mi) of coastline were affected by the tsunami with run-ups of up to 7m (23 ft) recorded on the southwest side of Nias.

References

References

1. Tsunami Laboratory. "Destructive historical tsunamis at the western coast of Sumatra".
2. Newcomb, K.R.. (1987). "Seismic history and seismotectonics of the Sunda Arc". Journal of Geophysical Research.
3. Natawidjaja, D. H.. (2006). "Source parameters of the great Sumatran megathrust earthquakes of 1797 and 1833 inferred from coral microatolls". Journal of Geophysical Research.
4. Wei-Haas, Maya. (2021-05-28). "An earthquake lasted 32 years, and scientists want to know how".
5. Pappas, Stephanie. (2021-05-26). "The Longest Known Earthquake Lasted 32 Years".
6. (2022). "Gempa Nusantara: A Database of 7380 Macroseismic Observations for 1200 Historical Earthquakes in Indonesia from 1546 to 1950". Bulletin of the Seismological Society of America.