The 1984 Northern Sumatra earthquake occurred with a
moment magnitude
The moment magnitude scale (MMS; denoted explicitly with or Mw, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. It was defined in a 1979 pape ...
of 7.2 on November 17 at 06:49 UTC. The epicentre was located off the coast of
Sumatra, near the island of
Nias
Nias ( id, Pulau Nias, Nias language: ''Tanö Niha'') (sometimes called Little Sumatra in English) 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, ...
, where building damage was reported. This earthquake could be strongly felt in parts of Northern Sumatra, including
Padang
Padang () is the capital and largest city of the Indonesian province of West Sumatra. With a Census population of 1,015,000 as of 2022, it is the 16th most populous city in Indonesia and the most populous city on the west coast of Sumatra. Th ...
and
Medan
Medan (; English: ) is the capital and largest city of the Indonesian province of North Sumatra, as well as a regional hub and financial centre of Sumatra. According to the National Development Planning Agency, Medan is one of the four mai ...
. The
focal mechanism 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
The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and the surrounding ocean and extends northwest to include the Indian subcontinent and the adjacent waters. It was formed by the fusion of the Indian an ...
and the
Eurasian Plate
The Eurasian Plate is a tectonic plate that includes most of the continent of Eurasia (a landmass consisting of the traditional continents of Europe and Asia), with the notable exceptions of the Indian subcontinent, the Arabian subcontinent and ...
. 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 planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
along the
Great Sumatran fault
The Indonesian island of Sumatra is located in a highly seismic area of the world. In addition to the subduction zone off the west coast of the island, Sumatra also has a large strike-slip fault, the Great Sumatran Fault also known as Semangko ...
. 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 ...
,
1833,
1861
Statistically, this year is considered the end of the whale oil industry and (in replacement) the beginning of the petroleum oil industry.
Events
January–March
* January 1
** Benito Juárez captures Mexico City.
** The first stea ...
,
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
File:2000 Events Collage.png, From left, clockwise: Protests against Bush v. Gore after the 2000 United States presidential election; Heads of state meet for the Millennium Summit; The International Space Station in its infant form as seen from S ...
and
2002.
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
Northern Sumatra Earthquake, 1984
November 1984 events in Asia
1984 disasters in Indonesia