The 1977 San Juan earthquake, also known as Caucete earthquake, took place in the

province A province is an administrative division within a country or sovereign state, state. The term derives from the ancient Roman , which was the major territorial and administrative unit of the Roman Empire, Roman Empire's territorial possessions ou ...

San Juan San Juan, Spanish for Saint John (disambiguation), Saint John, most commonly refers to: * San Juan, Puerto Rico * San Juan, Argentina * San Juan, Metro Manila, a highly urbanized city in the Philippines San Juan may also refer to: Places Arge ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

, on 23 November at 06:26:26 AM. It measured 7.5 on the

moment magnitude scale The moment magnitude scale (MMS; denoted explicitly with or Mwg, 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. was defined in a 1979 paper ...

, and had a maximum perceived intensity of X (''Extreme'') on the

Mercalli intensity scale The Modified Mercalli intensity scale (MM, MMI, or MCS) measures the effects of an earthquake at a given location. This is in contrast with the seismic magnitude usually reported for an earthquake. Magnitude scales measure the inherent force or ...

. The earthquake caused fatalities and severe damage to buildings throughout the province, especially in the city of Caucete, where at least 65 people died. It also caused slight damage in the north of the

Greater Mendoza Gran Mendoza (Greater Mendoza) is the name given to the large urban conurbation around the city of Mendoza in Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area ...

metropolitan area. Its were felt as far away as Buenos Aires, where people were awakened that Wednesday by the tremor. People left their houses at dawn in panic at the Argentinian capital, located at to the east southeast.

Tectonic setting

San Juan Province lies in an area where the

South American plate The South American plate is a major tectonic plate which includes the continent of South America as well as a sizable region of the Atlantic Ocean seabed extending eastward to the African plate, with which it forms the southern part of the Mid ...

is affected by

flat-slab subduction Flat slab subduction is characterized by a low subduction angle (<30 degrees to horizontal) beyond the seismogenic layer and a resumption of normal ...

of the underlying

Nazca plate The Nazca plate or Nasca plate, named after the Nazca region of southern Peru, is an oceanic list of tectonic plates, tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru– ...

, the so-called

Pampean flat-slab The Pampean flat-slab is the flat slab subduction, low angle subduction of lithosphere, oceanic lithosphere beneath Northern Argentina. The Pampean flat-slab is one of three flat slabs in South America, the other being the Peruvian flat-slab and t ...

. The very shallow angle leads to a much greater degree of coupling between the subducting and overriding plates. The increased coupling leads to shortening of the crust of the South American plate, causing active

thrust tectonics Thrust tectonics or contractional tectonics is concerned with the structures formed by, and the Tectonics, tectonic processes associated with, the shortening and thickening of the Crust (geology), crust or lithosphere. It is one of the three main ...

and rapid uplift, forming the

Sierras Pampeanas The Sierras Pampeanas (also called Central Sierras or Pampas Sierras) (English: Pampas Mountains) is a geographical region of Argentina. The Sierras Pampeanas are a chain of mountains that rise sharply from the surrounding pampa region of N ...

. The Pie de Palo range is one of the active structures, interpreted to be controlled by major

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. I ...

s. The overall structure has been interpreted as both thin-skinned and thick-skinned.

Earthquake

The earthquake consisted of two sub-events, separated by about 20 seconds, treated by some seismologists as foreshock and mainshock. The observed

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 ...

was reverse faulting, on a north–south trending structure. From the mainshock alone, it was not possible to decide whether the fault responsible dipped to the west or east. Analysis of the

aftershock In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in Epicenter, the same area of the Mainshock, main shock, caused as the displaced Crust (geology), crust adjusts to the effects of the main shock. Large earthq ...

sequence suggests that two separate faults moved during the earthquake, the earlier event on a segment to the north and the later one to the south. The fault segments have been interpreted as both alternating west and eastward-dipping faults or as an east-dipping fault in the hanging-wall of a larger west-dipping fault. There was no

surface rupture In seismology, surface rupture (or ground rupture, or ground displacement) is the visible offset of the ground surface when an earthquake rupture along a Fault (geology), fault affects the Earth's surface. Surface rupture is opposed by buried rup ...

associated with the earthquake and it is an example of a

blind thrust earthquake A blind thrust earthquake occurs along a thrust fault that does not show signs on the Earth's surface, hence the designation "blind". Such faults, being invisible at the surface, have not been mapped by standard surface geological mapping. Sometim ...

on thrust faults underlying the Pie de Palo range.

Damage

There was widespread damage in San Juan Province. The towns of Bermejo and Caucete were particularly badly affected. Many houses constructed of

adobe Adobe (from arabic: الطوب Attub ; ) is a building material made from earth and organic materials. is Spanish for mudbrick. In some English-speaking regions of Spanish heritage, such as the Southwestern United States, the term is use ...

or unreinforced masonry were either badly damaged or destroyed and very large areas were affected by

liquefaction In materials science, liquefaction is a process that generates a liquid from a solid or a gas or that generates a non-liquid phase which behaves in accordance with fluid dynamics. It occurs both naturally and artificially. As an example of t ...

. More modern structures, built to earthquake resistant designs, in contrast showed little damage. At least 65 people were killed and a further 284 were injured. The extensive damage left many homeless, with estimates in the range 20,000 to 40,000. The area's wine industry was heavily impacted due to damage to both buildings and particularly wine storage tanks, reducing the wine storage capacity of the affected area by about 10 million litres.

References

External links

''Listado de Terremotos Históricos''
– Instituto Nacional de Prevención Sísmica * {{Earthquakes in 1977

1977 Events January * January 8 – 1977 Moscow bombings, Three bombs explode in Moscow within 37 minutes, killing seven. The bombings are attributed to an Armenian separatist group. * January 10 – Mount Nyiragongo erupts in eastern Zaire (no ...

Earthquakes in San Juan Province, Argentina San Juan, 1977 San Juan Earthquake, 1977 Buried rupture earthquakes November 1977 in South America

Tectonic setting

Earthquake

Damage

See also

References

External links