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I N F O R M A T I O N

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Earthquake in

Saturday 27 February 2010 Magnitude = 8.8 at 6.34 GMT

Version 1 of 3 March 2010

The Seismic Hazard Facts Assessment Bureau  On Saturday 27 February 2010 at 6.34 GMT (3.34 local time) a very high magnitude (Mw 8.8 – source USGS) struck the region of Maule in central Chile for Nuclear Facility (Figure 1). Located at 35.85 ° south latitude and 72.72 ° west longitude, its focus was Safety (BERSSIN) of around 6 km offshore from the coastal city of Constitución. Its depth is estimated at the French Institute around 35 km (USGS). for Radiological  The quake set off a that crossed the Pacific. It severely damaged the coastal Protection and regions of Chile where an amplitude of around 2 to 3 metres was observed (2.34 m Nuclear Safety measured at according to the NOAA). The tsunami reached 1.50 m in , 4 m in the Marquesas Islands, 3 m in the Samoan Islands and 2 m along the coasts of (IRSN) conducts Sakhalin Island (Russia). research and assessments on the  The cities of Chillan, Concepción and Talcaà, within a 100-kilometre area, experienced external hazard the most violent tremors. The capital city of (325 km northeast of the epicentre) also shook for nearly a minute and a half and was significantly damaged. The posed by event had a very broad impact, affecting populations in a radius spanning several in high- hundred kilometres (Argentina, Uruguay, Paraguay, Brazil). risk facilities.  After 36 hours, 164 aftershocks with a magnitude of over 4.5 were recorded, 90 of which occurred during the first 24 hours. The strongest aftershock was measured 6.9 and struck an hour and a half after the main shock. More aftershocks are expected in the coming weeks.

 According to the latest report issued by the authorities on 3 March 2010, the earthquake killed 795 people and destroyed or significantly damaged 500,000 homes. It also caused very significant damage to the infrastructure in the region (schools, hospitals and artwork), thus affecting 2 million people.

 The earthquake occurred in a zone where the seismic hazard is known to be high. Chile's awareness of the hazard and its adoption of earthquake-resistant construction standards helped limit destruction and loss of human life, which could have been much greater given the magnitude of the quake and the relatively high population density in this zone.

Figure 1: Location of the earthquake CONTACT: in Chile on 27 February 2010 IRSN/BERSSIN and its Christophe Clément/Hervé aftershocks during Jomard the following two +33 (0)1 58 35 76 65 days. +33 (0)1 58 35 73 78 [email protected] [email protected]

www.irsn.fr

3 March 2010 1 I N F O R M A T I O N

Seismotectonic context

Chile is located in the southern part of the mountain range, which was formed by the sliding (or 1) of the Pacific Plate () beneath the . The length of the subduction zone (several thousand kilometres) and the rate of convergence between the two plates (8 cm/year in the WSW-ENE direction) result in frequent and violent earthquakes in the region. The sliding of the two plates leads to an accumulation of elastic energy along the fault plane until the rupture threshold is reached. Rupture and the resulting movement are responsible for earthquakes. The greater the accumulated energy and the longer the fault area affected by the rupture, the more violent the quake. The 1960 earthquake (Mw 9.5) affected 1,000 km of the subduction plane; it remains the most powerful earthquake recorded to date.

The epicentre of the 27 February 2010 earthquake is located between the 1960 rupture zone and the rupture zone for the Valparaiso 1906 and 1985 earthquakes (Figure 2). The affected region (Concepción) had not experienced a significant earthquake since 1835 and was therefore considered a seismic gap 2 by several seismologists ( e.g. Campos et al., 2002; Ruegg et al., 2009).

The aftershocks on the Chilean coast are geographically distributed over approximately 600 km from North to South (Figure 1). This distribution highlights the maximum extension of the fault plane affected by the main shock. Its size is consistent with the magnitude of 8.8, calculated by seismological recordings around the world.

(1) Process during which the tectonic plate with the highest density slides beneath the plate with the lowest density.

(2) A seismic gap refers to a region known to be seismic, but where no earthquakes have occurred for a significant period of time and where, consequently, the accumulation of strain on the faults makes the occurrence of the “next earthquake” more probable.

Figure 2: Rupture zones of the main subduction earthquakes in Chile (Ch. Vigny, ENS).

As part of its research on evaluating seismic hazard, the IRSN has been working for several years with seismological researchers at the University of Chile in Santiago (notably through the Sub-Chile research project funded by the French National Research Agency). Based on this collaboration, the IRSN has contributed to studies characterising site effects in the sedimentary basins of Santiago and Valparaiso.

Following the earthquake of 27 February 2010, the IRSN has been asked by the International Associated Laboratory (LIA) “Montessus de Ballore” to participate in a post-seismic campaign of seismological and geodetic measurements. This laboratory brings together research teams from France (CNRS-INSU/IPGP/ENS) and Chile (University of Chile).

03 March 2010 2 I N F O R M A T I O N

Impact on nuclear facilities

In Chile , according to the press release by the Chilean Nuclear Energy Commission (CCHEN: http://www.cchen.cl ) the two reactors at the nuclear research centres of La Reina and Lo Aguirre, located close to the capital and around 350 km from the epicentre, were operating when the earthquake occurred. The two reactors were stopped by the automatic shutdown system. Preliminary investigations at the site confirmed shutdown. They also established that there was no damage that could compromise nuclear safety and ruled out any possibility of radiological exposure of facility personnel or the general public. Only a few windows and drinking water pipes were damaged, without any impact on nuclear safety. An in-depth inspection of the site is ongoing. In Argentina , the closest nuclear power plant is located in Embalse, around 900 km northwest of the epicentre (Figure 1). It is a 600-MWe pressurised heavy water reactor, in operation since 1983. There is also a nuclear research reactor at located 600 km southeast of the epicentre. Considering the significant distances between the earthquake’s epicentre and these facilities and the attenuation of seismic waves in the ground, no significant effect is expected in these facilities. The only reported effects in the surrounding cities are low- intensity tremors causing no damage (III and IV on the Modified Mercalli Intensity Scale, source: USGS). In Japan , the Japan Meteorological Agency (JMA) launched a tsunami alert with predicted wave heights of 3 metres along the coasts. On 1 March 2010, a memorandum by the Nuclear and Industrial Safety Agency (NISA) to the International Atomic Energy Agency (IAEA) reported that were observed at seven sites on the eastern coast of Japan where nuclear power plants are located. A maximum rise in sea level of 1 m was measured at the Fukushima Daiichi site, and a maximum drop of 1.2 m was measured at the Tokai No. 2 site. The memorandum noted that this series of waves did not have any impact on the safety of these facilities, given the measures taken to protect the them against tsunamis and storm surges.

Summary  A major magnitude-8.8 earthquake struck the Andean subduction zone in central Chile on 27 February 2010. The epicentral area was located just north of the 1960 earthquake rupture zone (M 9.5). No significant quakes had occurred in this area since 1835, increasing the probability of a major earthquake.  Given the considerable size of the fault that ruptured, the earthquake caused significant damage along several hundreds of kilometres. According to the provisional death toll, there were nearly 800 victims, half of them in Concepción, Chile’s second largest city. Loss of human life and significant damage to buildings and infrastructure were reported in other locations, including the capital city of Santiago, 350 km northeast of the epicentre.  The earthquake set off a tsunami that crossed the . Loss of human life and severe damage occurred along Chile’s coasts and on Chilean islands, where wave height surpassed 3 m in some places. Elsewhere, no victims or severe damage were reported.  Two nuclear research reactors close to Santiago were automatically shut down. Inspections at these sites confirmed that there was no damage that could compromise nuclear safety. The tsunami had a low amplitude in Japan and did not affect the nuclear power plants on the eastern coast.

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