1984 Northern Sumatra earthquake
Encyclopedia
The 1984 Northern Sumatra earthquake occurred on November 17, 1984 at 06:49 UTC. The epicenter was located off the coast of Sumatra
, near the island of Nias
. It was an Mw
7.2 earthquake
. Building damage was reported in Nias island. This earthquake could be strongly felt in parts of Northern Sumatra, including Padang
and Medan
. The focal mechanism
corresponded to reverse faulting.
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
. 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.
depth was about 27 km and the fault plane dipped at 12°.
Sumatra
Sumatra is an island in western Indonesia, westernmost of the Sunda Islands. It is the largest island entirely in Indonesia , and the sixth largest island in the world at 473,481 km2 with a population of 50,365,538...
, near the island of Nias
Nias
Nīas is an island off the western coast of Sumatra, Indonesia. Nias is also the name of the archipelago, containing the Hinako archipelago....
. It was an Mw
Moment magnitude scale
The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...
7.2 earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
. Building damage was reported in Nias island. This earthquake could be strongly felt in parts of Northern Sumatra, including Padang
Padang, Indonesia
Padang is the capital and largest city of West Sumatra, Indonesia. It is located on the western coast of Sumatra at . It has an area of and a population of over 833,000 people at the 2010 Census.-History:...
and Medan
Medan
- Demography :The city is Indonesia's fourth most populous after Jakarta, Surabaya, and Bandung, and Indonesia's largest city outside of Java island. Much of the population lies outside its city limits, especially in Deli Serdang....
. The focal mechanism
Focal mechanism
The focal mechanism of an earthquake describes the inelastic deformation in the source region that generates the seismic waves. In the case of a fault-related event it refers to the orientation of the fault plane that slipped and the slip vector and is also known as a fault-plane solution...
corresponded to reverse faulting.
Tectonic setting
The island of Sumatra lies on the convergent plate boundaryConvergent boundary
In plate tectonics, a convergent boundary, also known as a destructive plate boundary , is an actively deforming region where two tectonic plates or fragments of lithosphere move toward one another and collide...
between the Indo-Australian Plate
Indo-Australian Plate
The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and surrounding ocean, and extends northwest to include the Indian subcontinent and adjacent waters...
and the Eurasian Plate
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...
. 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
Sunda megathrust
The Sunda megathrust is a fault that extends approximately 5,500 km from Myanmar in the north, running along the southwestern side of Sumatra, to the south of Java and Bali before terminating near Australia...
, and near pure strike-slip faulting along the Great Sumatran fault
Great Sumatran fault
The Indonesian island of Sumatra is located in a highly seismic area of the world. In addition to the subduction zone and the associated Sunda Arc off the west coast of the island, Sumatra also has a large strike-slip fault, the so-called Great Sumatran Fault, running the entire length of the island...
. 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
1797 Sumatra earthquake
The 1797 Sumatra earthquake was the first in a series of great earthquakes that ruptured part of the Sumatran segment of the Sunda megathrust. It caused a damaging tsunami that was particularly severe near Padang, where a 150-200 ton English ship was driven 1 km inland up the Arau...
, 1833
1833 Sumatra earthquake
The 1833 Sumatra earthquake occurred on November 25, 1833, about 22:00 local time, with an estimated magnitude in the range Mw= 8.8–9.2. It caused a large tsunami that flooded the southwestern coast of the island. There are no reliable records of the loss of life, with the casualties being...
, 1861
1861 Sumatra earthquake
The 1861 Sumatra earthquake occurred on February 16, 1861. It was the last in a sequences of earthquakes that ruptured adjacent parts of the Sumatran segment of the Sunda megathrust. It caused a devastating tsunami which led to several thousand fatalities. The earthquake was felt as far away as the...
, 2004
2004 Indian Ocean earthquake
The 2004 Indian Ocean earthquake was an undersea megathrust earthquake that occurred at 00:58:53 UTC on Sunday, December 26, 2004, with an epicentre off the west coast of Sumatra, Indonesia. The quake itself is known by the scientific community as the Sumatra-Andaman earthquake...
, 2005
2005 Sumatra earthquake
The 2005 Sumatra earthquake, referred to as the Nias Earthquake by the scientific community, was a major earthquake on 28 March 2005, located off the west coast of northern Sumatra, Indonesia. Approximately 1300 people were killed by the earthquake, mostly on the island of Nias...
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
1935 Sumatra earthquake
The 1935 Sumatra earthquake occurred at 02:35 UTC on 28 December 1935. It had a magnitude of Mw = 7.7 and a maximum felt intensity of VIII on the mercalli intensity scale. It triggered a minor tsunami.-Tectonic setting:...
, 1984, 2000
2000 Sumatra earthquake
The 2000 Sumatra earthquake struck at 23:30 local time on June 4, 2000 off the coast of southern Sumatra, Indonesia with a magnitude of 7.9 Mw. The United States Geological Survey reported 103 fatalities, in addition to 2,174 injured people...
and 2002
2002 Sumatra earthquake
The 2002 Sumatra earthquake occurred at 01:26 UTC on 2 November. It had a magnitude of 7.3 on the moment magnitude scale with an epicenter just north of Simeulue island and caused three deaths...
. 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 focalHypocenter
The hypocenter refers to the site of an earthquake or a nuclear explosion...
depth was about 27 km and the fault plane dipped at 12°.