On 27 February 2010 at 03:34 UTC−03:00, a 8.8 megathrust earthquake struck off the coast of the Maule Region of central Chile. One of the most powerful earthquakes ever recorded, it lasted approximately three minutes and was felt across six Chilean regions, home to roughly 80 percent of the country's population. The earthquake, which became known in Chile as the 27F earthquake (Spanish: Terremoto del 27F), was the largest to hit the country since the magnitude 9.5 1960 Valdivia earthquake and the strongest worldwide since the 2004 Indian Ocean earthquake.
The earthquake triggered a tsunami with wave heights reaching up to 24.1 m (79 ft) that devastated several coastal towns in south-central Chile, causing the most severe damage at Constitución. Tsunami warnings were issued across 53 countries, and waves caused damage as far away as California and Japan. The disaster resulted in 525 confirmed deaths and 25 missing persons, left approximately 370,000 homes damaged, and generated a nationwide blackout affecting 93 percent of the Chilean population. Economic losses were estimated at US$15–30 billion. President Michelle Bachelet declared a state of catastrophe and deployed the military to the worst-affected areas.
Location/epicenter
According to the USGS, the epicenter of the earthquake was about 3 km (1.9 miles) off the coast of Pelluhue, a town in the Maule Region. This is about 6 km (3.7 miles) west of the village of Chovellén, 15 km (9.3 miles) southwest of the town of Pelluhue and at a point approximately 100 km (62 miles) away from the following four provincial capitals: Talca (to the north-east), Linares (to the east), Chillán (to the south-east) and Concepción (to the south). Chile's Seismological Service located the quake's epicenter at about 34 km (21 miles) off the coast of Ñuble Region in the Biobío Region. This is 60 km (37 miles) north of Concepción and 170 km (110 miles) south-west of Talca.
Seismology and geology
The earthquake took place along the boundary between the Nazca and South American tectonic plates at a location where they converge at a rate of 80 millimetres (3.1 in) a year. This earthquake was characterized by a thrust-faulting focal mechanism, caused by the subduction of the Nazca plate beneath the South American Tectonic Plates. The end-regions of the rupture zone coincided with the Andean oroclines of Maipo (33° S) and Arauco (37° S). This has been interpreted as suggesting a link between upper plate (South American plate) structure and rupture length.
Chile has been at a convergent plate boundary that generates megathrust earthquakes since the Paleozoic era (500 million years ago). In historical times the Chilean coast has suffered many megathrust earthquakes along this plate boundary, including the strongest earthquake ever measured, the 1960 Valdivia earthquake. More recently, the boundary ruptured during the 2007 Tocopilla earthquake in northern Chile.
The segment of the fault zone which ruptured in this earthquake was estimated to be over 700 km (430 mi) long with a displacement of almost 10 meters, or 120 years of accumulated plate movement. It lay immediately north of the 1,000 km (620 mi) segment which ruptured in the great earthquake of 1960. Preliminary measurements show that the entire South American plate moved abruptly westward during the quake. A research collaborative of Ohio State and other institutions have found, using GPS, that the earthquake shifted Santiago 28 cm (11 in) to the west-southwest and moved Concepción at least 3 metres (10 ft) to the west. The earthquake also shifted other parts of South America from the Falkland Islands to Fortaleza, Brazil. For example, it moved Argentina's capital of Buenos Aires about 2.5 cm (0.98 in) to the west. Several cities south of Cobquecura were also raised by up to 3 meters. The maximum recorded peak ground acceleration was at Concepcion, with a value of 0.65 g (6.38 m/s2).
The locality of Tirúa south of Concepción recorded a 180 cm (71 in) uplift relative to sea level as a result of the earthquake. This is the highest known uplift of the coast resulting from the earthquake. This uplift made a large islet emerge at the mouth of Lebu River.
Compared with past earthquakes
This was the strongest earthquake affecting Chile since the magnitude 9.5 1960 Valdivia earthquake (the most energetic earthquake ever measured), and it was the strongest earthquake worldwide since the 2004 Indian Ocean earthquake and until the 2011 Tōhoku earthquake. It is tied with the 1906 Ecuador–Colombia and 2025 Kamchatka earthquakes as the sixth strongest earthquake ever measured, approximately 500 times more powerful than the 7.0 Mw earthquake in Haiti one month prior in January 2010.
Aftershocks
An aftershock of 6.2 was recorded 20 minutes after the initial quake. Two more aftershocks of magnitudes 5.4 and 5.6 followed within an hour of the initial quake. The USGS said that "a large vigorous aftershock sequence can be expected from this earthquake". By 6 March UTC, more than 130 aftershocks had been registered, including thirteen above magnitude 6.0.
Shortly after the mainshock seismologists installed a dense network of seismometers along the whole rupture area. This network captured 20,000 aftershocks in the 6 months after the mainshock and shows a detailed picture of the structure of the Chilean margin. Seismicity is focused in the depth range of 25–35 km (16–22 mi) and in a deeper band of between 45 and 50 km (28 and 31 mi) depth. Around 10,000 aftershocks occurred in the region of two large aftershocks in the Pichilemu region.
A 6.9-magnitude offshore earthquake struck approximately 300 kilometers southwest of, and less than 90 minutes after, the initial shock; however, it is not clear if that quake was related to the main shock. A separate earthquake of magnitude 6.3 occurred in Salta, Argentina, at 15:45 UTC on 27 February, at a depth of 38.2 km (23.7 mi); two people were injured and one died in Salta. This earthquake was followed on 1 March at 06:32 UTC by a magnitude 4.9 aftershock. Four other earthquakes above M5.0, some possible aftershocks, also occurred near the border in Argentina following the Chile earthquake; a magnitude 5.0 earthquake occurred in Mendoza on 28 February, a M5.3 earthquake in Neuquen and a M5.2 in San Juan on 2 March, and a M5.1 quake in Mendoza on 4 March.
Another strong earthquake occurred on 4 March, at 22:39 UTC in Antofagasta in northern Chile, with a magnitude of 6.3.
Minor quakes generated by the main one could be felt as far away as São Paulo, Brazil, located about 3,000 km (1,900 mi) away from Concepción. Since the major earthquake, and as of 15 March, at least four to forty >M5.0 earthquakes have been recorded daily in the vicinity of the main earthquake, including four above magnitude 6.0 between 3 and 6 March.
On 5 March, two aftershocks above M6.0 were reported. The first was a 6.3-magnitude off the coast of the Biobío Region. The second was near the epicenter of the original quake at 08:47 local time with a magnitude of 6.6.
On 11 March, the March 2010 Chile earthquake (magnitude 6.9, treated by some as an aftershock of the February 2010 earthquake) was reported, followed quickly by further aftershocks measuring 6.7 and 6.0. The epicenter of the 6.9 quake was in Pichilemu, O'Higgins Region.
On 15 March, two aftershocks of the February 2010 earthquake were reported, one at magnitude 6.2 at 08:08:28 local time offshore Maule, and another at magnitude 6.7 with the epicenter located offshore the Biobío Region, near Cobquecura, at 23:21:58 local time. This tremor was followed by two minor aftershocks, one occurring 45 minutes later, measuring M5.5. No tsunami was reported and there were no tsunami warnings issued.
On 17 March, at 14:38:37 local time, an earthquake of magnitude 5.2 was recorded in Aisén, in Southern Chile. Another magnitude 5.2 earthquake was recorded in Los Lagos the next day. On 26 March, at 10:52:06 local time, a magnitude 6.2 earthquake hit the Atacama region, in Northern Chile.
The Biobio Region of Chile had strong aftershocks of this earthquake. The first one was a magnitude 6.7 MW earthquake that struck off the coast of Biobío, Chile, at 23:21 on 15 March 2010 at the epicenter, at a depth of 18 kilometres (11 mi). The second earthquake struck on land in the region at 22:58 (UTC) on 2 April 2010 at 5.9 MW and at a depth of 39 km (24 mi). The third struck on 10:03 (UTC) on 23 April 2010 at 6.2 MW. The Pacific Tsunami Warning Center said that historical data indicates that this quake would not generate a tsunami but still advised of the possibility. On 3 May, at 19:09 a magnitude 6.4 MW earthquake struck off Biobío, Chile, at the epicenter, at a depth of 20 km (12 mi). The epicenter was 55 km (34 mi) south of Lebu. On 14 July 2010, another 6.5 magnitude earthquake occurred in the area.
2011 aftershocks
On 2 January at 17:20:18 local time, a 7.1 magnitude aftershock occurred 70 km (43 mi) northwest of Temuco, Chile. On Lautaro, Cañete, Nueva Imperial, Traiguén and Carahue the quake was felt at intensity VI (Strong) of the Mercalli intensity scale. In Temuco it was perceived at intensity V (Moderate). In Talcahuano, Concepción, Chillán, Osorno and Valdivia it shook at intensity IV (Light). According to the USGS the earthquake's epicenter was located on the ground, east of the coastal town of Tirúa in the Araucanía Region. However, according to the University of Chile's Seismological Service, the seismic event was located 134 km (83 mi) off the coast of Tirúa, measuring a magnitude 6.9 ML. The University of Chile also reported that the localities that received the strongest shaking (VI) were Curanilahue, Lebu and Tirúa. In Concepción, Talcahuano and Temuco it was felt at intensity V, and in Chillán and Valdivia at intensity IV.
A magnitude 6.2 Mw aftershock struck the coast of Biobío, Chile at a shallow depth of 15.1 km (9.4 mi) on 1 June 2011 at 08:55 local time (12:55 UTC). It was centered just offshore Arauco Province near a moderately populated area, with most structures in its vicinity reported to be resistant to earthquake shaking. Strong shaking registering at VI on the Mercalli intensity scale was felt in Lebu, just 7 km (4.3 mi) south of the epicenter, lasting for approximately one minute. Some residents in coastal areas panicked and evacuated their homes. The earthquake was followed by a moderate magnitude 5.1 Mw tremor that occurred about 52 minutes later to the northeast of the main shock epicenter at an estimated depth of 26.9 km (16.7 mi). Initial estimates from the USGS placed its intensity at a magnitude of 6.4 Mw.
Geophysical impact
Seismologists estimate that the earthquake was so powerful that it may have shortened the length of the day by 1.26 microseconds and moved the Earth's figure axis by 2.7 milliarcseconds (about 8 cm). Precise GPS measurement indicated the telluric movement moved the entire city of Concepción 3.04 metres (10.0 ft) to the west. The capital Santiago experienced a displacement of almost 24 centimetres (9.4 in) west, and even Buenos Aires, about 1,350 kilometres (840 mi) from Concepción, shifted 4 centimetres (1.6 in). It is estimated that Chile's territory could have expanded 1.2 square kilometres (0.46 sq mi) as a result.
The earthquake also caused seiches to occur in Lake Pontchartrain to the north of New Orleans, United States, located nearly 7,500 kilometres (4,700 mi) from the epicenter of the quake. In Antarctica a series of icequakes were triggered by the 2010 earthquake in Chile.
Damage and casualties
People were found dead after the earthquake struck, mostly under buildings and inside cars. Many people were also seriously injured. Most injuries were reported in Santiago and Maule.
According to an Associated Press Television News cameraman, some buildings collapsed in Santiago and there were power outages in parts of the city. A fire was reported in a chemical plant on the outskirts of Santiago and caused the evacuation of the neighborhood. Santiago's International Airport seemed to have been damaged and the airport authority closed off all flight operations for 24 hours from around 12:00 UTC. On Sunday, 28 February, Ricardo Ortega, head of the Chilean Air Force, said commercial airline services had been partially re-established and aircraft were being allowed to land in Santiago.
Santiago's national Fine Arts Museum was badly damaged and did not reopen until 9 March 2010. An apartment building's two-story parking lot collapsed, wrecking 68 cars. According to one health official, three hospitals in Santiago collapsed, and a dozen more south of the capital also suffered significant damage.
In Valparaíso, a tsunami wave of 1.29 m (4 ft 3 in) was reported. The port of Valparaíso was ordered to close due to the damage caused by the earthquake. The port started to resume limited operations on 28 February. In Viña del Mar, a touristic city and part of Greater Valparaíso, several buildings were structurally damaged, principally in the district Plan de Viña.