1960 Valdivia earthquake: Wikis

  
  

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El Gran Terremoto de Valdivia (The Great Earthquake of Valdivia)
Date 22 May 1960 (1960-05-22)
Magnitude 9.5 Mw[1]
Depth 33 km
Epicenter location Cañete
Countries or regions affected Chile
Casualties 2231, 3000, 5700[2] or 6000[3]

The 1960 Valdivia earthquake or Great Chilean Earthquake (Spanish: Gran terremoto de Valdivia) of 22 May 1960 is to date the most powerful earthquake ever recorded, rating 9.5 on the moment magnitude scale.[1] It occurred in the afternoon (19:11 GMT, 14:11 local time) and its resulting tsunami affected southern Chile, Hawaii, Japan, the Philippines, eastern New Zealand, southeast Australia, and the Aleutian Islands in Alaska.

The epicenter was near Cañete (see map) some 900 km (435 miles) south of Santiago, although Valdivia was the most affected city. It caused localised tsunamis that severely battered the Chilean coast, with waves up to 25 metres (82 ft). The main tsunami raced across the Pacific Ocean and devastated Hilo, Hawaii. Waves as high as 10.7 metres (35 ft) were recorded 10,000 kilometres (6,000 miles) from the epicenter, and as far away as Japan and the Philippines.

The death toll (and rate) and monetary losses arising from such a widespread disaster can never be precisely known. Various estimates of the total number of fatalities from the earthquake and tsunamis have been published, with the USGS citing studies with figures of 2231, 3000, or 5700 killed,[2] and another source uses an estimate of 6000 dead.[3] Different sources have estimated the monetary cost ranged from 400 million to 800 million US dollars[2] (or 2.9 to 5.8 billion in 2010 dollars, adjusted for inflation.)

Contents

Earthquake development

Global seismic release from 1906 to 2005, the graph shows that almost 25% of the energy was concentrated in the Great Chilean Earthquake alone.
A Valdivia street after the earthquake of 22 May 1960
The town of Riñihue flooded during the Riñihuazo.

The Great Chilean Earthquake came after a smaller earthquake in Arauco Province at 06:02 on 21 May 1960. Telecommunications to southern Chile were cut off and President Jorge Alessandri cancelled the traditional ceremony of the Battle of Iquique memorial holiday to oversee the emergency assistance efforts. The government was just beginning to organize help to the affected region when the second earthquake occurred at 14:55 UTC on 22 May in Valdivia.

The second earthquake affected all of Chile between Talca and Chiloé Island, more than 400,000 square kilometers (154,440.9 sq mi). Coastal villages, such as Toltén, disappeared. Later studies argued that the earthquake actually had 37 epicenters through a 1,350 km (839 mi) north-south line that lasted from 22 May to 6 June.[4] At Corral, the main port of Valdivia, the water level rose 4 m (13 ft) before it began to recede. At 16:20 UTC, an 8 m (26 ft) wave struck the Chilean coast, mainly between Concepción and Chiloe. Ten minutes later another wave measuring 10 m (33 ft) was reported.

Hundreds of people were already reported dead by the time the tsunami struck. One ship, El Canelo, starting at the mouth of Valdivia River sank after being moved 1.5 km (1 mi) backward and forward in the river; its mast is still visible from the road to Niebla.[4]

A number of Spanish-colonial fortifications were completely destroyed. Soil subsidence also destroyed buildings, deepened local rivers, and created wetlands in places like the Río Cruces and Chorocomayo, a new aquatic park north of the city. Extensive areas of the city were flooded. The electricity and water systems of Valdivia were totally destroyed. Witnesses reported underground water flowing up through the soil. Despite the heavy rains of 21 May, the city was without a water supply. The river turned brown with sediment from landslides and was full of floating debris, including entire houses. The lack of potable water became a serious problem in one of Chile's rainiest regions.

The earthquake did not strike all the territory with the same strength; measured with the Mercalli scale tectonically depressed areas suffered heavier damages. The two most affected areas were Valdivia and Puerto Octay near the northwest corner Llanquihue Lake. The overall picture of damages showed that Puerto Octay was the center of a north-south elliptical area in the Central Valley where the intensity was at its highest if not counting the Valdivia Basin. East of Puerto Octay in a hotel in Todos los Santos Lake piles of plates were reported to have remained in place.

Two days after the earthquake Cordón Caulle, a volcanic vent close to Puyehue volcano, erupted.Other volcanoes may also have erupted, but none were recorded due to the lack of communication in Chile at the time. The relatively low death toll in Chile (estimated at 6,000) is explained in part by the low population density and by buildings being built taking into account that the region is very active geologically. Other possible reasons include a high number of wooden houses and that coastal towns also tended to be located on higher ground, following a pre-Hispanic tradition.[citation needed]

Tectonic interpretation

The earthquake was a megathrust earthquake resulting from the release of mechanical stress between the subducting Nazca Plate and the South American Plate. The focus was relatively shallow at 33 km, considering that earthquakes in northern Chile and Argentina may reach depths of 70 km. Subduction zones are known to produce the strongest earthquakes on earth as their particular structure allows more stress to build up before energy is released. Geophysicists consider it a matter of time before this earthquake will be surpassed in magnitude by another. The earthquake's rupture zone was 800 km long, stretching from Talca (35° S) to Chiloé Archipelago (43° S). The rupture velocity has been estimated as 3.5 km per second.[5] On 27 February 2010 at 03:34 local time an 8.8 magnitude earthquake occurred just to the north (off the coast of the Maule region of Chile, between Concepción and Santiago).[6] This quake was reported to be centered approximately 22 miles (35.4 km) deep and several miles off shore.

Natural disasters triggered

Landslides

The earthquake triggered numerous landslides, principally in the step glacial valley of the southern Andes. Within the Andes most landslides occurred on forested mountain slopes around the Liquiñe-Ofqui Fault. Some of these areas remain sparsely vegetated while others have naturally developed more or less pure strands of Nothofagus dombeyi. These landslides did not cause many fatalities nor significant economical losses because most of the areas were uninhabited with only minor roads. One landslide did however cause destruction and alarm following its blockage of the outflow of Riñihue Lake (see Riñihuazo).

Tsunami

Map showing the travel time of the Tsunami across the Pacific and beyond. Contours are at one hour intervals.

Earthquake induced tsunamis affected southern Chile, Hawaii, Japan, the Philippines, eastern New Zealand, south east Australia and the Aleutian Islands. Some localised tsunamis severely battered the Chilean coast, with waves up to 25 metres (82 ft). The main tsunami crossed the Pacific Ocean at a speed of several hundred km/h and devastated Hilo, Hawaii, killing 61 people, allegedly due to their failure to heed warning sirens. Hilo's position in the bay caused a cumulative bounce of tsunami waves far more destructive to Hilo than to other more exposed areas of Hawaii. Tsunami waves as high as 10.7 metres (35 ft) were recorded 10,000 kilometres (6,000 miles) from the epicentre, several as far away as Japan and the Philippines.

Riñihuazo flood

During the Great Chilean Earthquake, several landslides west of Tralcán Mountain blocked the outflow of Riñihue Lake (39°45′00″S 72°30′00″W / 39.75°S 72.5°W / -39.75; -72.5). Riñihue Lake is the lowest of the Seven Lakes chain and receives a constant inflow from the Enco River. The blocked San Pedro River, which drains the lake, passes through several towns and the city of Valdivia before finally reaching Corral Bay.

Because the San Pedro River was blocked, the water level of Riñihue Lake started to rise quickly. Each meter the water level rose was equivalent to 20 million cubic meters, which meant that 4800 million cubic meters of water would release into the San Pedro River (easily overpowering its flow capacity of 400 cubic meters (14,126 cubic feet)) if it rose above the final, 24-meter-high dam. This potential disaster would have violently flooded all the settlements along the course of the river in less than five hours, and had more dire consequences if the dam suddenly broke.

About 100,000 people lived in the affected zone.Plans were made to evacuate Valdivia, and many people left. To avoid the destruction of the city, several military units and hundreds of workers from ENDESA, CORFO, and MOP started an effort, called the Riñihuazo, to control the lake. Twenty-seven bulldozers were put into service, but they had severe difficulties moving in the mud near the dams, so dykes had to be constructed with shovels. The work was not restricted to the lake; drainages from other parts of the Seven Lakes were also dammed to minimize the flow into Riñihue Lake. These dams were removed later, with the exception of Calafquén Lake, which still retains its dam.

By 23 June, the main dam had been lowered from 24 m (79 ft) to 15 m (49 ft), allowing 3000 million cubic meters of water to leave the lake gradually, but still with considerable destructive power. The team was led by ENDESA engineer Raúl Sáez.

Cordón Caulle eruption

Eruption of Cordón Caulle following the 1960 Valdivia earthquake

On 24 May, 38 hours after the main shock of the 1960 Valdivia earthquake, Cordón Caulle begun a rhyodacitic fissure eruption. Being located between two sparsely populated and isolated Andean valleys, the eruption had few eyewitnesses and received little attention by local media, preoccupied with the huge damages and losses caused by the earthquake.[7] The eruption fed a 5.5 km long and N135° trending fissure where 21 individual vents have been found. These vents produced an output of about 0.25 km3 DRE both in form of lava flows and tephra. The eruption ended on 22 July.

Consequences and response

Creation of emergency committee

After the 1960 Valdivia earthquake a committee was formed to solve problems caused by the earthquake. However this committee was not dissolved afterward and in 1974 it became ONEMI (Spanish acronym for National Emergency and Information Office) when it acquired by law independent status as governmental office.

Urban impact in Valdivia

It has been estimated that about 40% of the houses in Valdivia were destroyed, leaving 20,000 people homeless. The most affected structures were those built of concrete, which in some cases collapsed completely due to lack of earthquake engineering. Traditional wooden houses fared better and were in many places left uninhabitable but without collapse. Houses built upon tectonically elevated areas suffered considerably less damage compared to those on the lowlands. Many city blocks with destroyed buildings in the city center remained empty until the 1990s and 2000s, with some of them still being used as parking lots. Some of these blocks before the earthquake had modern concrete buildings, built after the great fire of 1909. In terms of urban development Valdivia suffered the loss of the minor but significant Cau-Cau bridge, a bridge that has not been rebuilt. The other bridges suffered only minor damage. Land subsidence in Corral Bay improved navigability as shoal banks produced earlier by sediments from Madre de Dios and other nearby gold mines sunk and compacted.

The earthquake and the degradation to a provincial capital are seen in retrospect as the culmination of a long period of economic decline that begun with shifts in trade routes due to the expansion of railroads in southern Chile and the opening of the Panama Canal in 1911. Industrial activity in Valdivia, dominated by Germans, declined further due to human and capital migration after the earthquake. Facilities of several industries, such as the Anwandter brewery and the Rudloff shoe factory, were destroyed and activity eliminated.

In 1974 Valdivia lost its capital status to Puerto Montt when the military government of Chile reorganized the country's administrative divisions. Valdivia had previously been a first level administrative center since the 16th century. It regained its status in 2007 with the creation of the Los Ríos Region.

Previous and later earthquakes

There is evidence that a similar landslide and earthquake occurred in 1575.[8] This earthquake was of similar strength and also caused a Riñihuazo. According to Mariño de Lobera, corregidor of Valdivia in 1575, a landslide blocked the outflow of the lagoon of Renigua and several months later caused a flood. Mariño de Lobera states that while the flood killed many Indians, Spanish settlers waited on high ground until after the dam burst. This (the 1960) earthquake may be connected to the 2010 Chile earthquake.[9]

In popular culture

A 1969 episode of the U.S. television series Hawaii Five-O titled "Forty Feet High and it Kills!" referenced the tsunami that devastated Hilo in 1960.

Chilean novelist Isabel Allende included the 1960 Valdivia earthquake in The House of the Spirits.

See also

References

  1. ^ a b U.S. Geological Survey (7 March 2006). Historic Earthquakes - Chile - 1960 May 22 19:11:14 GMT- Magnitude 9.6: The Largest Earthquake in the World. Retrieved on 2007-01-09
  2. ^ a b c "The Largest Earthquake in the World - Articles". U.S. Geological Survey. http://neic.usgs.gov/neis/eq_depot/world/1960_05_22_articles.html. Retrieved 2007-01-11. 
  3. ^ a b "Emergency & Disasters Data Base". Centre for Research on the Epidemiology of Disasters (CRED). http://www.em-dat.net. Retrieved 2007-01-09. 
  4. ^ a b La Tercera Retrieved on 2008-01-14
  5. ^ Hiroo Kanamori and Jogn J. Cipar. Focal process of the great Chilean earthquake May 22, 1960 Physics of the Earth and Planetary Interiors. 1974.
  6. ^ "Tsunami After Deadly Earthquake Hits Chile". February 27, 2010. http://uk.news.yahoo.com/5/20100227/twl-tsunami-after-deadly-earthquake-hits-3fd0ae9.html. Retrieved 2010-02-27. 
  7. ^ Lara, L.E., Naranjo J.A., Moreno, H. Rhyodacitic fissure eruption in Southern Andes (Cordón Caulle; 40.5°S) after the 1960 (Mw:9.5) Chilean earthquake: a structural interpretation. Journal of Volcanology and Geothermal Research. vol 138. 2004.
  8. ^ Breve Historia de Valdivia. Editorial Francisco de Aguirre. 1971. http://www.buscalibros.cl/libros.php?c=226. 
  9. ^ [2010 Chile Earthquake Born in 1960?|http://news.nationalgeographic.com/news/2010/03/100302-chile-earthquake-earth-axis-shortened-day/]

External links

Coordinates: 38°14′S 73°03′W / 38.24°S 73.05°W / -38.24; -73.05








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