1969 Sulawesi earthquake

The western coast of West Sulawesi was struck by a major earthquake on 23 February 1969 at 00:36 UTC. It had a magnitude of 7.0 Mw and a maximum felt intensity of VII on the Modified Mercalli intensity scale.[2] It triggered a major tsunami that caused significant damage along the coast of the Makassar Strait. At least 64 people were killed, with possibly a further 600 deaths caused by the tsunami.[1]

1969 Sulawesi earthquake
UTC time1969-02-23 00:36:58
ISC event812497
USGS-ANSSComCat
Local dateFebruary 23, 1969 (1969-02-23)
Local time08:56[1]
Magnitude7.0 Mw
Depth15.0 km (9 mi)
Epicenter3.201°S 118.904°E / -3.201; 118.904
FaultMajene Thrust
TypeThrust
Max. intensityVII
Tsunamiyes
Casualties664

Tectonic setting

Sulawesi lies within the complex zone of interaction between the Australian, Pacific, Philippine and Sunda Plates in which many small microplates are developed.[3] The main active structure onshore in the western part of Central Sulawesi is the left-lateral NNW-SSE Palu-Koro strike-slip fault that forms the boundary between the North Sula and Makassar blocks and was responsible for the destructive Palu earthquake in 2018.[4][5] According to the interpretation of GPS data, the Makassar block is currently rotating anticlockwise, with its northwestern margin showing convergence with the Sunda block across the Makassar Strait. The main structure in that part of Sulawesi is the offshore, north–south trending, moderately east-dipping Makassar Thrust, also known as the Majene Thrust.[6] The GPS data also support the presence of a seismically "locked" fault in the Makassar Strait.[4] Seismic reflection data from the Makassar Strait support the presence of active thrusting west of the Makassar block. The Majene/Kalosi fold and thrust belt is exposed onshore between Majene and Mamuju. The northern part of the Makassar Strait is interpreted as a foreland basin, with its subsidence caused by the loading of this active thrust belt.[7]

Earthquake

The earthquake had an estimated magnitude of 7.4 Ms,[1] later recalculated to be 7.0 Mw .[2] It was caused by movement on the Majene Thrust, which was also responsible for the 2021 Sulawesi earthquake 52 years later.[8]

Tsunami

The earthquake triggered a significant tsunami, with a maximum run-up of 4 m at Peletoang and 1.5 m at both Parosanga and Palipi.[9]

Damage

The city of Majene was particularly badly affected, with the foundations of four out of five of tile brick buildings suffering serious effects. Wooden buildings escaped with only minor effects, but unreinforced masonry walls were badly damaged. A number of bridges were damaged beyond repair.[1]

The tsunami caused local flooding, damaging banana plantations along the coast. Many wooden buildings were washed away by the waves. At Majene's harbour, the pier was seriously affected due to the effects of subsidence. Witnesses mention a "roaring sound" just before the tsunami.[9]

At least 64 deaths were reported, with one news story also mentioning another 600 deaths due to the tsunami. A further 97 injuries were also reported.[1]

References
  1. National Geophysical Data Center / World Data Service (NGDC/WDS): NCEI/WDS Global Significant Earthquake Database. NOAA National Centers for Environmental Information. (1972). "Significant Earthquake Information". NOAA National Centers for Environmental Information. doi:10.7289/V5TD9V7K. Retrieved 16 January 2020. Cite journal requires |journal= (help)
  2. ANSS. "Sulawesi 1969 : M 7.0 - Sulawesi, Indonesia". Comprehensive Catalog. U.S. Geological Survey. Retrieved 16 January 2020.
  3. ANSS. "Sulawesi 2018: M 7.5 - 70km N of Palu, Indonesia". Comprehensive Catalog. U.S. Geological Survey. Retrieved 28 September 2018.
  4. Socquet A.; Simons W.; Vigny C.; McCaffrey R.; Subarya C.; Sarsito D.; Ambrosius B.; Spakman W. (2006). "Microblock rotations and fault coupling in SE Asia triple junction (Sulawesi, Indonesia) from GPS and earthquake slip vector data". Journal of Geophysical Research: Solid Earth. 111 (B8): B08409. Bibcode:2006JGRB..111.8409S. doi:10.1029/2005JB003963.
  5. ANSS. "Sulawesi 2018: M 7.5 - 70km N of Palu, Indonesia". Comprehensive Catalog. U.S. Geological Survey. Retrieved 28 September 2018.
  6. Bellier, O.; Sébrier, M.; Seward, D.; Beaudoin, T.; Villeneuve, M.; Putranto, E. (2006). "Fission track and fault kinematics analyses for new insight into the Late Cenozoic tectonic regime changes in West-Central Sulawesi (Indonesia)". Tectonophysics. 413 (3–4): 201–220. Bibcode:2006Tectp.413..201B. doi:10.1016/j.tecto.2005.10.036.
  7. Bergman, S.C.; Coffield, D.Q.; Talbot, J.P.; Garrard, R.A. (1996). "Tertiary Tectonic and magmatic evolution of western Sulawesi and the Makassar Strait, Indonesia: evidence for a Miocene continent-continent collision". In Blundell, D.J.; Hall, R. (eds.). Tectonic Evolution of Southeast Asia. Geological Society, Special Publications. 106. pp. 391–429. doi:10.1144/GSL.SP.1996.106.01.25. ISBN 9781897799529. S2CID 140682113.
  8. "BMKG : Gempa Majene Merusak" (in Indonesian). Media Indonesia. Retrieved 15 January 2021.
  9. National Geophysical Data Center / World Data Service (NGDC/WDS): NCEI/WDS Global Significant Earthquake Database. NOAA National Centers for Environmental Information. (1972). "Tsunami Event Information". NOAA National Centers for Environmental Information. doi:10.7289/V5TD9V7K. Retrieved 16 January 2020. Cite journal requires |journal= (help)
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