Chile earthquake, 16th September 2015: Impact Forecasting update

by Artemis on September 17, 2015

Overnight there has been a major magnitude 8.3 earthquake just off the coast of Chile. The quake has damaged regions of Chile, particularly coastal areas where a tsunami was recorded. Insurance and reinsurance industry exposure is unknown at this time.

Tsunami warnings have also been given for other countries around the Pacific, including California. However the height of waves further from the epicenter will be unlikely to cause much inundation. At this time the USGS has said there is a 52% chance of an economic impact of between $100m and $1 billion, with an 18% chance of the damage costing greater that $1 billion.

It is extremely early to be making any estimate of insurance costs, or impact to the reinsurance market, however the early reports suggest significantly lower damage levels than the last major Chile quake in 2010

The ShakeMap from the USGS is below and an update from Impact Forecasting, the catastrophe modelling team of reinsurance broker Aon Benfield, can be found further down the page:

Chile 8.3 earthquake, 16th September 2015 Chile 8.3 earthquake ShakeMap, 16th September 2015

A major magnitude-8.3 earthquake struck just off the coast of central Chile on Wednesday evening, triggering a series of tsunami waves that came ashore in Chile and elsewhere across parts of the Pacific Ocean. As of this writing, at least five people were confirmed dead and 20 others were injured as officials continue to survey impacted coastal areas that sustained damage from the ground shaking and tsunami inundation. More than one million people were evacuated along the Chilean coastline, Easter Island and the archipelago Juan Fernandez as residents sought safety and higher ground in the immediate aftermath of the event. Preliminary reports suggested that the level of damage was significant in some areas, but not as catastrophic as the February 27, 2010 magnitude-8.8 event.

The USGS-registered main tremor struck at 7:54 PM local time (22:54 UTC) with an epicenter located 46 kilometers (29 miles) west of Illapel, Chile and 229 kilometers (142 miles) north-northwest of the capital city of Santiago, Chile at a shallow depth of 25.0 kilometers (15.5 miles). Several strong aftershocks were recorded in the hours after the primary shock, with at least 18 registered at magnitude-5.0 or greater in intensity. One aftershock was measured at magnitude-7.0, while others were registered with magnitudes 6.7, 6.5, 6.4, 6.4, 6.3, 6.2, and 6.1 respectively. Additional strong aftershocks were expected in the coming days and weeks.

Immediately after the first earthquake occurred, the Pacific Tsunami Warning Center (PTWC) declared a Tsunami Warning for the entire coastline of Chile and Peru, and a Tsunami Watch for the U.S. state of Hawaii. Later, the agency issued tsunami advisories for New Zealand, Fiji, Ecuador, Solomon Islands, and the U.S. state of California. Tsunami waves of varying heights were recorded or expected across almost the entire Pacific Ocean.

This was the strongest earthquake to strike anywhere in the world thus far in 2015, and was widely felt across South America. Parts of Peru, Argentina and even as far away as Sao Paolo, Brazil – located 2,100 miles (3,380 kilometers) on the other side of the continent – felt shaking.

Event Details
Early reports suggested that some of the heaviest damage occurred in the coastal cities of Coquimbo, Tongoy, Concon, and Los Vilos. Each of the towns reported extensive damage and flooding from tsunami waves. The Chilean government has already declared the areas to be catastrophe zones and the military were sent to prevent any threats of looting. Coquimbo’s mayor cited major flood damage in the port city, which saw waves as high as 15.6 feet (4.75 meters) rage inland that damaged the port, the fishing wharf and much of downtown. In Tongoy, reports indicated that tsunami inundation reached the downtown area and destroyed a preschool, a police station and part of a health clinic. Officials in the inland town of Illapel noted that adobe homes had completely collapsed and that landslides and rockfalls were commonplace. Similar photos were seen in the town of La Serena, where walls and the ceiling collapsed at a shopping mall.

In the capital of Santiago, buildings swayed and residents rushed out of buildings. Initial reports did not indicate major structural damage, though there was significant indoor content damage as stored items fell to the ground. The tremor occurred in the middle of rush hour traffic when many residents were on roads.

Extensive damage to infrastructure was being reported especially in the northern half of the country as a result of severe buckling, debris from landslides, and coastal flooding. Chile was supposed to celebrate its national holiday on Friday, September 18, a time when families traditionally get together. Because of the holiday, many schools were already closed for vacation, and many Chileans were already traveling. Given the infrastructure damage, local media reported that public transport between Santiago and locales to the north had been cancelled and it was expected that many residents will be stranded.

The electrical grid was also affected as nearly 250,000 customers were without electricity, including the entire town of Illapel and 95 percent of the town of Coquimbo. Some cities reported no drinking water.

Operations were suspended at two major copper mines operated by Codelco and Antofagasta PLC that generate annual capacity of more than 600,000 tonnes. The airport in Santiago was temporarily closed, though no damage to the facility was cited.

Despite the damage reports, the overall scope was not as catastrophic as initially feared. One key reason may be that the government has since mandated that all new buildings must be able to withstand a magnitude-9.0 earthquake. It also instituted a new tsunami warning system that was activated for the first time during the September 16 event.

It is worth noting that since Chile is located in a highly seismic region, the government has a long-established set of strict building codes. A brief look at Chile’s building code history indicates that the first seismic codes were established as far back as 1935. The 1972 version of the building code was revised following the magnitude-7.8 earthquake that struck in 1985, though those updates first went into effect in 1993. The 1985 code was later updated in 1996 and 2003. As of 2010, it was estimated that approximately three percent of recently built buildings were not up to the current building code. However, newly built ‘essential’ facilities do conform to the current code. Overall, about 30 percent of the total buildings in Chile are designed and based on older versions of the building code.

The most predominant construction types are masonry (reinforced, confined, or unreinforced), and approximately 60 percent of residential buildings and 40 percent of commercial buildings are of this type. Other residential construction types are based on wood frame, which account for nearly 20 percent of the building stock. For highrise apartments, contractors typically use concrete; while 33 percent of commercial buildings are built using reinforced concrete. Steel construction is used in about 15 percent of commercial structures. Industrial buildings are typically built using steel or light metal.

Seismological Recap
According to preliminary information from the United States Geological Survey (USGS), an estimated 11 million people were exposed to earthquake shaking rated at intensity four or greater on the Modified Mercalli Intensity (MMI) scale. In the city of Santiago, with a population of more than 4.8 million, residents were estimated to have been exposed to shaking rated at MMI 5.

The earthquake occurred as a result of thrust faulting on the interface between the Nazca and South American tectonic plates in central Chile. The following earthquake summary has been provided by the USGS:

The September 16, 2015 magnitude-8.3 earthquake west of Illapel, Chile, occurred as the result of thrust faulting on the interface between the Nazca and South America plates in central Chile. At the latitude of this event, the Nazca plate is moving towards the east-northeast at a velocity of 74 mm/year with respect to South America, and begins its subduction beneath the continent at the Peru-Chile Trench, 85 kilometers to the west of the September 16 earthquake. The size, location, depth and mechanism of this event are all consistent with its occurrence on the megathrust interface in this region.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Events of the size of the September 16, 2015 earthquake are typically about 230×100 kilometers in size (length x width).

Chile has a long history of massive earthquakes, including the 2010 M8.8 Maule earthquake in central Chile, which ruptured a ~400 kilometer long section of the plate boundary south of this 2015 event (and to the south of the Juan Fernandez Ridge, which enters the trench immediately south of the 2015 earthquake). This subducton zone also hosted the largest earthquake on record, the 1960 M9.5 earthquake in southern Chile. Over the century prior to the September 16, 2015 earthquake, the region within 400 kilometers of this event has hosted 15 other M7.0+ earthquakes.

Historical Context
This was the strongest earthquake to strike Chile since a magnitude-8.8 occurred on February 27, 2010. That event left catastrophic damage throughout the country, with Chile’s National Institute of Statistics indicating that at least 1.5 million homes were damaged – including more than 500,000 of which were listed as destroyed. Beyond the excessive shaking from the tremor, the event triggered 8.0-meter (26.2-feet) high tsunami waves in parts of the cities of Los Cambuchos, Coronel, Concepcion, Dichato, and Constitucion. At least 500 people were killed. The event caused economic losses of USD30 billion (2010 USD), and insured losses of USD8.5 billion (2010 USD).

According to the USGS, a magnitude-8.8 earthquake is 3.2 times bigger than a magnitude-8.3 earthquake on a seismogram and 5.6 times stronger in terms of energy release.

The strongest earthquake ever recorded on Earth happened in Chile on May 20, 1960. The magnitude-9.5 event reportedly shook for almost 10 minutes and caused devastating damage throughout the country while tsunami waves damaged areas all across the Pacific Ocean. At least 5,000 people were killed.

Financial Loss
It remains far too early to provide an economic loss projection for the event. However, the USGS has preliminarily estimated that 52 percent chance of losses being between USD100 million and USD1.0 billion. The agency also cites that there is an 18 percent likelihood of economic damages exceeding USD1.0 billion, and a 29 percent chance of economic losses being less than USD100 million. For background, the USGS uses a computer simulation model that is designed to rapidly and automatically take into account the differences in proximity to populated areas, the depth of the earthquake, and building standards to provide initial analysis to governments and emergency management officials.

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