1933 Sumatra Earthquake

The 1933 Sumatra earthquake or Liwa earthquake affected southern Sumatra, Indonesia, on 25 June at 04:54 WIB. The earthquake had an estimated surface-wave magnitude () of 7.5–7.7 and occurred at a shallow depth of . It was caused by slip along a section of the seismically active Great Sumatran fault. The earthquake caused damage and hundreds of deaths in Kaur and Liwa. At least 788 people were reported killed, although the death toll may have been in the thousands. Aftershocks followed, including one that caused additional fatalities. The mainshock also triggered a nearby volcanic eruption at Suwoh two weeks later, killing many people.

Tectonic setting

The west coast of Sumatra is dominated by the Sunda megathrust; a long convergent boundary where the Australian plate subducts beneath the Burma plate and Sunda plate at a rate of per year. Convergence along this plate boundary is highly oblique, severely deforming the overriding Sunda plate. This deformation is accommodated by strike-slip motion along the Great Sumatran fault; a long strike-slip fault system located on the island of Sumatra. The fault is divided into about 20 segments. Slip along the fault is not uniform; in northern Sumatra, it moves at per year; the central segments slip at per year, and in the south, is at per year. The Great Sumatran fault was the source of the 1994 Liwa and 1995 Kerinci earthquakes. It produced its largest earthquake during the 1943 Alahan Panjang sequence; measuring  7.8.

Earthquake

The earthquake occurred on 25 June at 04:54 WIB with a surface-wave magnitude of 7.5 or 7.7. It was caused by a strike-slip rupture on the southern section of the Great Sumatran Fault. It had an epicenter southeast of the Semangko segment and north of the Kumering segment.

The distribution of damage suggest most of the long Kumering segment ruptured during the earthquake. An analysis of the aftershocks suggest the rupture extended for at least on the southern portion of the segment. The earthquake initiated at the southeastern end of the Kumering segment and propagated northwestward. The southern extent of the rupture remains unclear and may have extended southwards onto the northern Semangko segment. Five aftershocks were recorded, two of which were located and northwest of the epicenter, respectively. A secondary branch away from the main strand of the Great Sumatran Fault may have also ruptured. The 1933 earthquake epicenter was located close to that of the 6.8 earthquake in 1994.

Between 1933 and 1994, no earthquakes of magnitude 6.0 or larger were recorded on the aforementioned portions of the Great Sumatran Fault. H. P. Berlage reported ground fissures in Negeri Ratu and near the Wai Uluhan river, located apart. However, Berlage did not specify the fissures at these locations formed a continuous feature or provide any details of offset in the ground. At Negeri Ratu, he documented a "mole track" rupture that appeared in the flat plain. These observations were made along the Kumering sement and may represent surface rupture caused by the earthquake.

Damage

Destruction was widespread along an area between Lake Ranau and Suwoh, coinciding with the approximate length of the Kumering segment rupture. The earthquake had a maximum Modified Mercalli intensity of VIII–IX (''Severe–Violent''). Many buildings and other infrastructures in the western portion of southern Sumatra were damaged. Damage in Sebarus, a village in Lampung, was so severe that it forced all of its residents to leave. In Pasirah, every home was destroyed and rice fields were ruined, while in Liwa and Banding Agung, all of its buildings were razed. Landslides were widespread, seen in the Barisan Mountains. Large fissures and ground subsidence were reported from Kota Agung to Makaka. On Lake Ranau, at the entrance of the Wai Warduk river in Kotabatu, a "co-seismic flood wave" inundated ten paddy fields by up to .

At least 424 deaths were reported in Kaur, South Bengkulu, while another 364 people died in Liwa. At least 50 people were badly injured in addition to 600 others with minor injuries. The total number of fatalities is not known and may be in the thousands, although the National Geophysical Data Center earthquake database only attributed 76 deaths with the event. An early statement by Reuters said at least 20 Europeans were among the 60 people dead which they later retracted. Officials took strong measures to ensure food, medication and hygiene was adequate.

An aftershock on June 26 also caused several fatalities in Bengkulu. Two weeks after the mainshock, geothermal activity at Suwoh increased, and a series of phreatic eruptions occurred, causing ash to fall on settlements. The eruption was rated a 4 on the Volcanic explosivity index and also caused many deaths. It ejected of tephra which blanketed the region.

See also

* List of earthquakes in 1933
* List of earthquakes in Indonesia

Notes

References

Sources

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External links

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{{Earthquakes in Indonesia

1933 earthquakes
Earthquakes in Indonesia
Earthquakes in Sumatra
1933 in the Dutch East Indies
West Lampung Regency
History of Lampung
20th-century volcanic events
VEI-4 eruptions
Bengkulu
Strike-slip earthquakes
Landslides in Indonesia
1933 disasters in Asia
1933 disasters in Oceania
20th-century disasters in Indonesia
20th century in Sumatra
June 1933 in Asia