Chile Earthquake

Update 2 | Summary
Posting Date: March 3, 2010, 12:00:00 PM

Four days after the devastating Mw8.8 earthquake struck off of Chile’s central coast, communications and access are slowly being reestablished to the remote towns and villages in the hardest-hit regions of Bio Bio and Maule. With a fuller understanding of the scope of destruction, officials have reported that as much as 80% to 90% of some towns in the epicentral region have been destroyed in the quake, reduced to rubble by violent ground shaking or, in coastal villages, overwhelmed by tsunami waves that arrived half an hour later.

In the inland town of Curico, 100 km (60 miles) northeast of the epicenter, most of the mud and wood buildings in the historic town center have been damaged, with some destroyed. According to Curico’s mayor, a hospital building suffered severe structural damage and is likely to collapse. At least 85 people were killed in the colonial city of Talca, 200 km from the epicenter, where the old town center was badly damaged and the main hospital partly collapsed. Significantly, reports from Talca indicate that newly built homes survived intact. In Constitución, a coastal fishing town less than 60 km from the epicenter, the entire seafront and town center was destroyed, and more than 350 people lost their lives either from collapsed buildings or by the subsequent tsunami, according to local media. Wooden homes in the hills, elevated beyond the tsunami’s reach, are among the only ones left standing.

Some 110 km (70 miles) south of the epicenter in Concepción, Chile’s second largest city, widespread looting broke out amid fears of food and water shortages. As many as 14,000 troops have now been deployed to the region to stop the disorder and begin distributing much needed aid. Meanwhile, rescuers continue to search for residents trapped in the ruins of a 15-story apartment building that had toppled onto its side. Questions have been raised about why such a new building, opened only last June, failed so catastrophically.

Chile’s capital of Santiago, 325 km (200 miles) from the epicenter, has fared much better. Santiago’s airport has reopened and is allowing a limited number of flights, and businesses have started to resume operation. Thousands of modern mid-rise and high-rise buildings in the capital withstood the earthquake without structural damage, thanks to a strict building code. On the other hand, there are several instances of mid-rise apartment buildings that, while still standing, have suffered structural damage sufficiently severe to require their demolition.

In Chile today, masonry (reinforced, confined, or unreinforced) is the predominant construction type, accounting for roughly 60% of residential buildings and more than 40% of commercial buildings. Wood frame is fairly common for residential construction as well, accounting for about 20% of the residential building stock. Concrete, which is typically used for mid- to high-rise apartments, accounts for approximately 15% of residential structures. About one third of commercial buildings use reinforced concrete, while steel construction accounts for about 15%. Industrial buildings are typically steel or light metal.

Although Chile’s building code is strong, it refers primarily to loads and not detailing. The detailing of connections is generally based on the American Concrete Institute standard (ACI-318 Spanish version), and it is up to the construction engineer of record to abide by it. While the building code is a national one, construction practices can vary significantly from company to company.

The earthquake downed many bridges and opened huge crevices in the main highway from Santiago to Concepción, which is still accessible only by four wheel drive vehicles. Roads throughout the region have suffered significant damage; many of these are reported to be insured. Damage to infrastructure, including ports, will extend significantly the interruption of business operations of Chile’s lucrative wine and salmon industries. Up to one fifth of Chile's copper-mining capacity was halted after the quake, but has since resumed.

The death toll from the earthquake stands at just under 800, but is expected to continue to rise, and hundreds of thousands have been left homeless. For the survivors, some of whom continue sleeping outside for fear of aftershocks, a primary concern is access to water and medical services. Field hospitals have been set up and aid is beginning to flow more freely. The Chilean government has requested international assistance from the United States as well as the United Nations.

The AIR earthquake team continues to analyze the available information on the parameters of this event and AIR will be sending a post-disaster survey team to affected areas. Additional information will be made available to NewsAlert subscribers as warranted.

Additional Information on AIR’s Loss Scenarios

The range of losses covered by the five scenarios posted on ALERT on Saturday, February 27—less than 24 hours after the event—were chosen in order to capture the considerable uncertainty that existed—and still exists—in the actual parameters of this event. To get a sense of this uncertainty, Table 1 below shows the estimated epicentral locations, focal depths and moment magnitudes published by various local and international seismological agencies as of today, more than 5 days after the earthquake occurred. At the time AIR published its scenarios on ALERT, the available data was somewhat different, with published focal depths ranging from 24 to 35 km and with epicentral locations varying by more than 60 km.

Table 1.  Published Earthquake Parameters (as of March 3, 10:00 AM GMT)

Notes: UCSC – University of Chile Seismological Centre; EMSC – European-Mediterranean Seismological Centre; GFZ – German Research Centre for Geosciences; USGS – United States Geological Survey

Even now, the rupture length for this earthquake remains uncertain. Inverse wave modeling techniques indicate a rupture length of about 400–450 km. Aftershocks, however, have occurred within an area that extends over 500 km or more. These differences make clear that consensus on the parameters of this earthquake has not yet been reached; indeed, it may never be reached, though there may be some further convergence.

Table 2 below presents the parameters used to model the five selected scenarios published on Saturday, February 27. The greatest uncertainty is typically not in the magnitude (for which we used the USGS reported value of Mw8.8), but rather in the rupture length and location. Note that in Table 2 the “Center of Rupture” does not represent the epicenter of the event, but rather the location of the center of modeled rupture plane. The epicenter may in fact be located anywhere along the fault rupture or at either end.

Given the large magnitude of the event, it can be expected that variations in the location and fault rupture characteristics would change significantly the estimated losses. For example, losses for modeled events whose rupture is located closer to Santiago will be larger due to the concentration of exposures there. Furthermore, even if the geometry of the rupture area is known, other sources of uncertainty—in particular the complex radiation pattern of long- and short-period seismic waves and the strength of radiation across the fault—can have a significant impact on the damage pattern for low-, mid-, and high-rise buildings.

Table 3 provides, for each Scenario, AIR modeled insurable loss ratios by sub-CRESTA zone within the impacted area, or damage footprint, for combined residential, commercial/industrial and automobile exposures. These represent the ratio of modeled losses to insurable properties (properties that are eligible for insurance, whether or not they are actually insured) divided by the total value of insurable properties. For easy orientation, maps of these zones can be found at: https://www.cresta.org/index.php/map-viewer

Table 3. Modeled Damage (Loss) Ratios by Sub-CRESTA Zone for Insurable Properties (Combined Residential, Commercial/Industrial, Automobile)

Note, again, that AIR's insured loss estimates reflect:

• Insured physical damage to property (residential, commercial/ industrial, auto), both structures and their contents
• Business interruption losses
• Demand surge—the increase in costs of materials, services, and labor due to increased demand following a catastrophic event

They do not reflect:

• Losses to uninsured properties
• Losses to infrastructure (AIR is aware that many highways in Chile are insured and placed in the facultative market; they are not included, however, in AIR’s industry exposure database and are therefore not modeled.)
• Losses from non-modeled perils, including fire-following, tsunami and landslide
• Losses from loss adjustment expenses

AIR will be dispatching a post-disaster survey team to areas of Chile impacted by this event later this month. In the meantime, additional useful information and damage photos can be found at the following links:

http://www.emol.com/especiales/2010/fotos_AD/terremoto_chile_aereas/index.htm
http://www.emol.com/especiales/2010/fotos_AD/terremoto_chile_aereas/index.htm

Update 2 | Downloads
Posting Date: March 3, 2010, 12:00:00 PM