The 1984 Northern Sumatra earthquake occurred with a
moment magnitude of 7.2 on November 17 at 06:49 UTC. The epicentre was located off the coast of
Sumatra
Sumatra () is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the list of islands by area, sixth-largest island in the world at 482,286.55 km2 (182,812 mi. ...
, near the island of
Nias
Nias (, Nias: ''Tanö Niha'') is an island located off the western coast of Sumatra, Indonesia. Nias is also the name of the archipelago () of which the island is the centre, but also includes the Batu Islands to the southeast and the small ...
, where building damage was reported. This earthquake could be strongly felt in parts of Northern Sumatra, including
Padang
Padang () is the Capital city, capital and largest city of the Indonesian Provinces of Indonesia, province of West Sumatra. It had a population of 833,562 at the 2010 CensusBiro Pusat Statistik, Jakarta, 2011. and 909,040 at the 2020 Census;Bad ...
and
Medan
Medan ( , ) is the capital city, capital and largest city of the Indonesian Provinces of Indonesia, province of North Sumatra. The nearby Strait of Malacca, Port of Belawan, and Kualanamu International Airport make Medan a regional hub and multi ...
. The
focal mechanism
The focal mechanism of an earthquake describes the Fault (geology)#Slip.2C heave.2C throw, deformation in the Hypocenter, source region that generates the seismic waves. In the case of a Fault (geology), fault-related event, it refers to the ori ...
corresponded to
reverse faulting.
Tectonic setting
The island of Sumatra lies on the
convergent plate boundary
A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a ...
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
In geology, a fault is a Fracture (geology), planar fracture or discontinuity in a volume of Rock (geology), rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust (geology ...
along the
Great Sumatran fault
The Great Sumatran fault, also known as Semangko fault, is a large strike-slip fault running the entire length of the island of Sumatra. This Indonesian island is located in a highly seismic area of the world, including a subduction zone off th ...
. The major slip events on the subduction zone interface are typically of
megathrust
Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate is forced underneath another. The earthquakes are caused by slip along the thrust fault that forms the contact between the two plates. These interplate earthqu ...
type. Historically, megathrust earthquakes have been recorded in
1797
Events
January–March
* January 3 – The Treaty of Tripoli, a peace treaty between the United States and Ottoman Tripolitania, is signed at Algiers (''see also'' 1796).
* January 7 – The parliament of the Cisalpine Repu ...
,
1833
Events January–March
* January 3 – The United Kingdom reasserts British sovereignty over the Falkland Islands in the South Atlantic Ocean.
* February 6 (January 25 on the Greek calendar) – Prince Otto Friedrich Ludwig of Bavaria arr ...
,
1861
This year saw significant progress in the Unification of Italy, the outbreak of the American Civil War, and the emancipation reform abolishing serfdom in the Russian Empire.
Events
January
* January 1
** Benito Juárez captures Mexico Ci ...
,
2004
2004 was designated as an International Year of Rice by the United Nations, and the International Year to Commemorate the Struggle Against Slavery and Its Abolition (by UNESCO).
Events January
* January 3 – Flash Airlines Flight 60 ...
,
2005
2005 was designated as the International Year for Sport and Physical Education and the International Year of Microcredit. The beginning of 2005 also marked the end of the International Decade of the World's Indigenous Peoples, Internationa ...
and
2007
2007 was designated as the International Heliophysical Year and the International Polar Year.
Events
January
* January 1
**Bulgaria and Romania 2007 enlargement of the European Union, join the European Union, while Slovenia joins the Eur ...
, 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
Events
January
* January 7 – Italian premier Benito Mussolini and French Foreign Minister Pierre Laval conclude an agreement, in which each power agrees not to oppose the other's colonial claims.
* January 12 – Amelia Earhart ...
, 1984,
2000
2000 was designated as the International Year for the Culture of Peace and the World Mathematics, Mathematical Year.
Popular culture holds the year 2000 as the first year of the 21st century and the 3rd millennium, because of a tende ...
and
2002
The effects of the September 11 attacks of the previous year had a significant impact on the affairs of 2002. The war on terror was a major political focus. Without settled international law, several nations engaged in anti-terror operation ...
.
The deformation velocity in the offshore Sumatra fore-arc region is estimated to be 19 mm/yr along N45° near the equator, with compression being the dominant deformation.
The 1984 earthquake occurred in the same gap as the 1935 event.
Characteristics
The earthquake was caused by a rupture of the subduction interface. The
focal depth was about 27 km and the fault plane
dipped at 12°. This earthquake contained mainly a down-dip convergence but also a right-lateral displacement.
[
]
See also
* List of earthquakes in Indonesia
References
External links
*
{{Earthquakes in Indonesia
Earthquakes in Indonesia
Earthquakes in Sumatra
Northern Sumatra Earthquake, 1984
November 1984 in Asia
1984 disasters in Indonesia