2010 Chile earthquake

The 2010 Chile earthquake and tsunami occurred off the coast of central Chile on 27 February 2010, at 03:34:12 local time. It had a magnitude of 8.8 on the moment magnitude scale, with intense shaking lasting for about three minutes. It was felt strongly in six Chilean regions that together make up about 80 percent of the country's population. According to the United States Geological Survey the cities experiencing the strongest shaking—VIII on the Mercalli intensity scale —were Concepción, Arauco, and Coronel. According to Chile's Seismological Service, Concepción experienced the strongest shaking at MM IX. The earthquake was felt in the capital Santiago at MM VII or MM VIII. Tremors were felt in many Argentine cities, including Buenos Aires, Córdoba, Mendoza, and La Rioja. Tremors were felt as far north as the city of Ica in southern Peru. It is the largest earthquake to hit Chile since the 1960 Valdivia earthquake. A 2014 study contended that water pressure built up between the two plates had been the catalyst.
The earthquake triggered a tsunami which devastated several coastal towns in south-central Chile and damaged the port at Talcahuano. Tsunami warnings were issued in 53 countries, and the wave caused minor damage in the San Diego area of California and in the Tōhoku region of Japan, where damage to the fisheries business was estimated at ¥6.26 billion. The earthquake also generated a blackout that affected 93 percent of the Chilean population and which went on for several days in some locations. President Michelle Bachelet declared a "state of catastrophe" and sent military troops to take control of the most affected areas. According to official sources, 525 people lost their lives, 25 people went missing and about 9% of the population in the affected regions lost their homes.
On 10 March, Swiss Reinsurance Co. estimated that the Chilean quake would cost insurance companies between 4 and 7 billion dollars. The rival German-based Munich Re AG made the same estimate. The losses to the economy of Chile caused by the earthquake are estimated at US$15–30 billion.

Location/epicenter

According to the USGS, the epicenter of the earthquake was about off the coast of Pelluhue, a town in the Maule Region. This is about west of the village of Chovellén, southwest of the town of Pelluhue and at a point approximately away from the following four provincial capitals: Talca, Linares, Chillán and Concepción. Chile's Seismological Service located the quake's epicenter at about off the coast of Ñuble Region in the Biobío Region. This is north of Concepción and 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 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 and Arauco. This has been interpreted as suggesting a link between upper plate structure and rupture length.
Chile has been at a convergent plate boundary that generates megathrust earthquakes since the Paleozoic era. 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 long with a displacement of almost 10 meters, or 120 years of accumulated plate movement. It lay immediately north of the 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 to the west-southwest and moved Concepción at least 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 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.
The locality of Tirúa south of Concepción recorded a uplift relative to sea level as 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, 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 M_w 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 and in a deeper band of between 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 ; 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 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 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 M_W earthquake that struck off the coast of Biobío, Chile, at 23:21 on 15 March 2010 at the epicenter, at a depth of. The second earthquake struck on land in the region at 22:58 on 2 April 2010 at 5.9 M_W and at a depth of. The third struck on 10:03 on 23 April 2010 at 6.2 M_W. 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 6.4 M_W earthquake magnitude struck off Biobío, Chile, at the epicenter, at a depth of. The epicenter was 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 northwest of Temuco, Chile. On Lautaro, Cañete, Nueva Imperial, Traiguén and Carahue the quake was felt at intensity VI of the Mercalli intensity scale. In Temuco it was perceived at intensity V. In Talcahuano, Concepción, Chillán, Osorno and Valdivia it shook at intensity IV. 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 off the coast of Tirúa, measuring a magnitude 6.9 M_L. The University of Chile also reported that the localities who received the strongest shaking 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 M_w aftershock struck the coast of Biobío, Chile at a shallow depth of on 1 June 2011 at 08:55 local time. 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 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 M_w tremor that occurred about 52 minutes later to the northeast of the main shock epicenter at an estimated depth of. Initial estimates from the USGS placed its intensity at a magnitude of 6.4 M_w.