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UTC time | 1977-11-23 09:26:26 |
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ISC event | 690743 |
USGS-ANSS | ComCat |
Local date | 23 November 1977 |
Local time | 06:26:26 |
Magnitude | 7.5 Mw , [1] 7.4 Ms [2] |
Depth | 15 km (9.3 mi) [1] [3] |
Epicenter | 31°07′08″S67°50′20″W / 31.119°S 67.839°W [1] [3] |
Type | Reverse |
Max. intensity | MMI X (Extreme) |
Casualties | 65 deaths |
The 1977 San Juan earthquake, also known as Caucete earthquake, took place in the province of San Juan, Argentina, on 23 November at 06:26:26 AM. It measured 7.5 on the moment magnitude scale, [1] and had a maximum perceived intensity of X (Extreme) on the Mercalli intensity scale.
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 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 1,000 km (620 mi) to the east southeast.[ citation needed ]
San Juan Province lies in an area where the South American Plate is affected by flat-slab subduction of the underlying Nazca Plate, the so-called Pampean flat-slab. 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 and rapid uplift, forming the Sierras Pampeanas. The Pie de Palo range is one of the active structures, interpreted to be controlled by major thrust faults. [4] The overall structure has been interpreted as both thin-skinned and thick-skinned.
The earthquake consisted of two sub-events, separated by about 20 seconds, treated by some seismologists as foreshock and mainshock. [5] The observed focal mechanism 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 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. [6] 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. [7]
There was no surface rupture associated with the earthquake and it is example of a blind thrust earthquake on thrust faults underlying the Pie de Palo range. [8]
There was widespread damage in San Juan Province. The towns of Bermejo and Caucete were particularly badly affected. Many houses constructed of adobe or unreinforced masonry were either badly damaged or destroyed and very large areas were affected by liquefaction. 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. [9]
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. [9]
The 1944 San Juan earthquake took place in the province of San Juan, in the center-west area of Argentina, a region highly prone to seismic events. This moderate to strong earthquake destroyed a large part of San Juan, the provincial capital, and killed 10,000 of its inhabitants, 10 percent of its population at the time. One third of the province population became homeless. It is acknowledged as the worst natural disaster in Argentine history.
Two earthquakes hit the Italian regions of Molise and Apulia on 31 October at 10:32:58 (UTC) and 1 November at 15:09:00 (UTC). The shocks had magnitudes of 5.9 and 5.8 Mw respectively. Most of the victims were killed and injured when a school collapsed in the town of San Giuliano di Puglia: 26 of the 51 schoolchildren died, together with one of their teachers. In particular, none of the nine children in the school's 4th Year survived.
Caucete is a department in the eastern part of the San Juan Province of Argentina, which is predominantly a landscape of mountains, and many plantations. It contains the popular Shrine of the Difunta Correa.
Striking southern Italy on 8 September, the 1905 Calabria earthquake had a moment magnitude of 7.2 and a maximum Mercalli intensity of XI (Extreme). The first major earthquake of the 20th century, it severely damaged parts of Lipari, Messina Province and a large area between Cosenza and Nicotera and killed between 557 and 2,500 people.
The El Tigre Fault is a 120 km long, roughly north-south trending, major strike-slip fault located in the Western Precordillera in Argentina. The Precordillera lies just to the east of the Andes mountain range in South America. The northern boundary of the fault is the Jáchal River and its southern boundary is the San Juan River. The fault is divided into three sections based on fault trace geometry, Northern extending between 41–46 km in length, Central extending between 48–53 km in length, and Southern extending 26 km in length. The fault displays a right-lateral (horizontal) motion and has formed in response to stresses from the Nazca Plate subducting under the South American Plate. It is a major fault with crustal significance. The Andes Mountain belt trends with respect to the Nazca Plate/South American Plate convergence zone, and deformation is divided between the Precordilleran thrust faults and the El Tigre strike-slip motion. The El Tigre Fault is currently seismically active.
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The 1992 Murindó earthquake occurred on October 18 at 15:11 UTC with an epicenter in the Department of Chocó, northern Colombia. The shallow magnitude 7.2 earthquake struck northwest of the town of Murindó, killing ten and injured more than a hundred. Thirty-three municipalities were severely damaged.
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