The 1977 San Juan earthquake, also known as Caucete earthquake, took place in the
province
A province is almost always an administrative division within a country or sovereign state, state. The term derives from the ancient Roman ''Roman province, provincia'', which was the major territorial and administrative unit of the Roman Empire ...
of
San Juan San Juan, Spanish for Saint John, may refer to:
Places Argentina
* San Juan Province, Argentina
* San Juan, Argentina, the capital of that province
* San Juan, Salta, a village in Iruya, Salta Province
* San Juan (Buenos Aires Underground), ...
,
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
, on 23 November at 06:26:26 AM. It measured 7.4 on the
surface wave magnitude
The surface wave magnitude (M_s) scale is one of the magnitude scales used in seismology to describe the size of an earthquake. It is based on measurements of Rayleigh surface waves that travel along the uppermost layers of the Earth. This ma ...
scale, and had a maximum perceived intensity of X (''Extreme'') on the
Mercalli intensity scale
The Modified Mercalli intensity scale (MM, MMI, or MCS), developed from Giuseppe Mercalli's Mercalli intensity scale of 1902, is a seismic intensity scale used for measuring the intensity of shaking produced by an earthquake. It measures the eff ...
.
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, Argentina, Mendoza in Argentina. The 2001 Census estimated the population of Gran Mendoza as 848,660 making it the 4th largest urban conurbat ...
metropolitan area.
The effects of the earthquake 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-A ...
is affected by
flat-slab subduction
Flat slab subduction is characterized by a low subduction angle (<30 degrees to horizontal) beyond the
Nazca Plate
The Nazca Plate or Nasca Plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru–Chile Trench, of the Na ...
, the so-called
Pampean flat-slab
The Pampean flat-slab is the low angle subduction of 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 the Bucaramanga flat-slab.
It is ...
. 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 tectonic processes associated with, the shortening and thickening of the crust or lithosphere. It is one of the three main types of tectonic regime, ...
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 ...
. 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.
If ...
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 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 ...
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 the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock. Large earthquakes can have hundreds to thousand ...
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 associated with the earthquake and it is 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 ( ; ) 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 used to refer to any kind of e ...
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 the ...
. 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.
See also
*
List of earthquakes in 1977
This is a list of earthquakes in 1977. Only earthquakes of magnitude 6 or above are included, unless they result in damage and/or casualties, or are notable for some other reason. Events in remote areas will not be listed but included in statist ...
*
List of earthquakes in Argentina
This is a list of earthquakes in Argentina.
* Details are approximate for old events.
* Magnitude is measured in the Richter magnitude scale.
* Intensity is measured in the Mercalli intensity scale.
* Depth is given in miles.
1600-1899
20th c ...
1977
Events January
* January 8 – 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 (now the Democratic R ...