1965 Valparaíso earthquake and El Cobre dam failure

The Valparaíso earthquake (also known as the La Ligua earthquake) of 1965 struck near the city of La Ligua in the Valparaíso Region, Chile, about 140 km from the capital Santiago on Sunday, March 28 at 12:33 p.m. (UTC−03:00). The Mw  7.4-7.6 temblor killed an approximate 400 people and caused damages amounting to some US$1 billion (adjusted for inflation).[1][2] Many of the deaths were from El Cobre, a mining location that was wiped out after a series of dam failures caused by the earthquake spilled mineral waste onto the area, burying many people. Death toll from the earthquake is comparable to the magnitude 8.8, 2010 Maule earthquake.

1965 Valparaíso earthquake
UTC time1965-03-28 16:33:16
ISC event858940
USGS-ANSSComCat
Local dateMarch 28, 1965 (1965-03-28)
Local time12:33 pm CST (UTC-03:00)
Magnitude7.4-7.6 Mw
Depth70.0 km
Epicenter32.522°S 71.233°W / -32.522; -71.233
TypeNormal (Intraplate)
Areas affectedChile
Total damage$125 million USD (1965 rate)
Max. intensityIX (Violent) to X (Extreme)
TsunamiNone
LandslidesYes
ForeshocksMw 6.2-6.4
AftershocksYes
Casualties400-500 dead

The shock was so powerful that it could be felt throughout the country and even across the continent to the Atlantic coast of Argentina.[3]

Earthquakes are frequent in Chile as it lies in the so-called Pacific Ring of Fire, where many of the world's active volcanoes and seismic activities are concentrated at. Off the coast of Chile, the Nazca Plate subducts beneath the South American Plate along the Peru-Chile or Atacama Megathrust, producing large earthquakes including the 1960 Chilean earthquake which had a magnitude of 9.5-9.6 on the moment magnitude scale.[4]


Earthquake

On the 22nd of March the same year, a magnitude 6.2-6.4 earthquake rocked the coastal town of Los Vilos at a depth of 48.8 km, slightly north of the epicenter for the mainshock.[5] It has been interpreted as a foreshock of the March 28 quake, although both events were on separate fault planes. The foreshock had a thrust mechanism, different from the mechanism of the mainshock.[6] Whether the 22 March quake was a true foreshock or the seven day time separation was sheer coincidence may never be determined. The earthquake nucleated about 72 km beneath the community of La Ligua with a magnitude of 7.4 on the moment magnitude scale. Focal mechanism of this earthquake suggests normal faulting likely within the slab of the Nazca Plate rather than on the subduction zone interface of the megathrust.[7]

Impact

The maximum intensity of the earthquake has been estimated at IX (Violent) on the mercalli intensity scale, shaking severity for this earthquake would result in cataclysmic impact for the affected regions.[6] The earthquake inflicted serious damages to adobe and unreinforced masonry buildings. Over 21,000 housed collapsed and 70,000 had to be repaired. Houses made of hollow concrete units were especially severely affected, cracks appeared due to the lack of bonding between bricks and the concrete fillings, shear failure, and damages to beams.[8]

At the time it had struck, many Chileans had just finished preparing their lunch means or returned from church services. This may have reduced the anticipated death toll because many churches had collapsed from ground motions, and there were very few instances of conflagrations.

In Salamanca and Illapel, over 100,000 people were left homeless. The Department of Illapel reported more than 90% of homes had been damaged, and a hospital was completely destroyed. Adding that "Only facades of the houses remain standing.".

Valparaíso reported 25 deaths and 40% of its buildings damaged from the earthquake.

At Santiago, the shock knocked out electricity and stirred panic in many neighborhoods. Four persons died from the temblor, including a woman who fell to her death after jumping off the second floor of a hospital and another during a stampede to race for the exit at a racetrack after a grandstand collapsed, while ten were injured.[9][3] An estimated 2,000 homes were badly damaged in the capital.

Additional casualties were reported at Llay-Llay, where four people had died, two each in La Laguna and Quilpue, and one each in San Felipe, Colina, Melon, Olmue and Ventanas. Three deaths were from Vina Del Mar when a wall fell on those victims.[3]

Aftershocks

Records of aftershocks are sparse due to the poor instrumentation quality at the time, very few moderately-sized events were recorded.

Chile mining disaster

Severe liquefaction from the earthquake resulted in the failure of 17 tailing dams, the most severe of which, affected the town of El Cobre, killing hundreds of residents and workers. Tailing dams failing because of seismic activities were a known risk to surrounding communities as seen in previous events. Many of these incidents were a result of liquefaction with flow failure, slope instability and quake-related deformations or overtopping and flow failure. Similar instances of sand tailing dams failing were also observed during earthquakes in 1981, 1985, 1997, and 2010.[10]

1965 Central Chile mining disaster
Date28 March 1965 (1965-03-28)
LocationChile
Coordinates32.639°S 71.162°W / -32.639; -71.162
TypeTailing dam failures
CauseEarthquake + Liquefaction
OutcomeTailings from the failures travelled downstream and buried the town of El Cobre.
Deaths350-400

El Cobre dam failure

Two dams belonging to the El Soldado mine released 350,000 and 1,900,000 cubic meters of debris respectively, and traveled 12 km downstream which destroyed the town of El Cobre, in La Calera, burying it under three feet of muck.[3][11] About 60 to 70 farmhouses and cottages were swept away by the cascading debris flow. Many of the casualties were miners and peasants who were mining for copper. The death toll stands between 350 and 400, although the official figure is at 247.[3]

Aftermath

In the immediate hours of the quake, cabinet ministers met with the President of Chile, Eduardo Frei Montalva. The Ministers of Public Works and Defence were taken to the affected town of Llay-Llay to survey the damage extent and plan the rescue and recovery efforts. The Chilean Army was called in for aid to mobilize the arrival of tents and makeshift kitchens to those who had lost their homes. Government officials and military chiefs were also involved in the distribution of food, water, and medical aid.[12]

Legacy

This tragedy, along with the 1960 earthquakes was one of the reasons for the formation of the National Office of Emergency of the Interior Ministry which oversees natural disasters and rescue efforts in Chile. Prior to the disaster, there had not been any formal organization to coordinate any rescue and recovery efforts, mainly because local officials and residents have endured many of the frequent earthquakes in the area.[12]

The dam failures marked a series of changes to the civil engineering and mining community, and the design of tailing dams. Upstream tailing dams were opted for other means such as downstream tailings sand, rock-fills, and earth dams despite the higher costs.[13]

See also

References
  1. "Significant Earthquake CHILE: CENTRAL". NGCD. Retrieved 6 Dec 2020.
  2. Reuters Staff (28 Feb 2010). "Factbox: Chile has history of big earthquakes". Reuters. Retrieved 6 Dec 2020.
  3. "Earthquake Toll Heavy in Chile; Village Buried". The Desert Sun. Archived from the original on 29 March 1965. Retrieved 5 Dec 2020.
  4. Ruiz, Madariaga, Sergio, Raúl (February 2018). "Historical and Recent Large Megathrust Earthquakes in Chile". Tectonophysics. 733: 37–56.
  5. "M 6.2 - offshore Coquimbo, Chile". US Geological Survey. Retrieved 6 Dec 2020.
  6. Malgrange, Deschamps, Madariaga, M., A., R. (1981). "Thrust and extensional faulting under the Chilean coast: 1965, 1971 Aconcagua earthquakes" (PDF). Geophysical Journal International. 66: 313–331.CS1 maint: multiple names: authors list (link)
  7. Felipe Leytona, Javier Ruizb, Jaime Camposa, Edgar Kausel (June 2009). "Intraplate and interplate earthquakes in Chilean subduction zone:A theoretical and observational comparison" (PDF). Physics of the Earth and Planetary Interiors. 175: 37–46 – via Elsevier Science Direct.CS1 maint: multiple names: authors list (link)
  8. M. Astroza, F. Andrade, M.O. Moroni (2017). "CONFINED MASONRY BUILDINGS: THE CHILEAN EXPERIENCE" (PDF). 16th World Conference on Earthquake.CS1 maint: multiple names: authors list (link)
  9. admin (29 March 2014). "El Día reported on the strong earthquake on March 29, 1965 leaving extensive damage and fatalities". El Día. Retrieved 6 Dec 2020.
  10. Villavicencio, Espinace, Palma, Fourie, Gabriel, Raúl, Juan, Andy (April 2014). "Failures of sand tailings dams in a highly seismic country". Canadian Geotechnical Journal. 51.CS1 maint: multiple names: authors list (link)
  11. "Chronology of major tailings dam failures (from 1960)". WISE Uranium Project. 20 Nov 2020. Retrieved 6 Dec 2020.
  12. Kennedy, Will C. "ORGANIZATIONAL ACTIVITY AND THE MILITARY IN DISASTER OPERATIONS IN CHILE IN A 1965 EARTHQUAKE: A HISTORICAL CASE STUDY" (PDF). University of Delaware. Retrieved 6 Dec 2020.
  13. Valenzuela, Luis (15 December 2015). "Design, construction, operation and the effect of fines content and permeability on the seismic performance of tailings sand dams in Chile" (PDF). Obras y proyectos revista de ingeniería civil. 19: 6–22.
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