Chile Earthquake

First Posting | Summary
Posting Date: February 27, 2010, 5:00:00 AM

A great earthquake struck the coast of Chile today at 6:34 UTC. Initially estimated at moment magnitude (Mw) 8.3 and later revised to Mw8.8 by the USGS, the quake occurred at the boundary between the Nazca and South American plates about 325 km southwest of the capital Santiago (est. pop. 5.3 million). Focal depth has been estimated at 35 km. At least four aftershocks of Mw6 or higher have already occurred, the largest at Mw6.9. It is in the very early aftermath of this event and telephone and power lines have been cut over a large area, making communications difficult and information scarce. Reports coming out of the capital seem to suggest that structural damage to newer buildings there is not significant; in the historic center, a church has reportedly collapsed and other buildings damaged. Strong shaking was reported throughout the city and the true extent of the damage will become clearer once damage surveys and building inspections get underway. The shaking sent crowds into the streets of the capital and was felt as far away as Argentina, on the other side of the Andes. An earthquake of this magnitude is likely to have caused considerable damage in towns closer to the epicenter. Fortunately, the area closest to the epicenter is relatively sparsely populated, but there may be significant damage in Concepción (est. pop. 300,000) and Chillan (est. pop. 170,000), which lie 115 km and 100 km to the south of the epicenter, respectively. Reported fatalities already exceed 50 and that number is likely to increase. Lying as it does along a major plate boundary, Chile is no stranger to large earthquakes. The largest ever recorded earthquake—a Mw9.5 event—occurred just off of Chile's southern coast in 1960. That event produced a destructive tsunami that affected countries as far away as Japan and the Philippines. Today's quake triggered a tsunami alert across the Pacific and sea-level readings indicate that one occurred; its impact, however, is still unknown. Today's event is Chile's largest since the Mw8.0 1985 Valaparasio/Santiago earthquake, which killed nearly 200 people and destroyed 140,000 homes. Closer to today's epicenter, a Mw7.6 earthquake shook the cities of Concepción and Chillan in 1939. Most of the city of Chillan was flattened in that event while in Concepción, many buildings, homes, churches, and schools were destroyed. Chile has a long history of building code evolution, beginning in 1928. Most recently, a year after the 1985 event, the government of Chile asked the Chilean Institute of National Standards to revise the previous (1972) building codes to incorporate the findings of the damage observations from the Valaparasio/Santiago earthquake. The revised codes were officially released in 1993 and represented a significant advance over the 1972 code. Indeed, because of the frequency with which large earthquakes affect the country—a Mw7 and higher event at least once every five years—there is high earthquake awareness in the country. As a result, Chile has more stringent building codes than its neighbors, superior construction quality, and possibly the most highly engineered building inventory in Latin America. This will undoubtedly help mitigate the damage. The age of the affected building inventory, however, will play a significant role. Today, the majority of buildings in Chile are of reinforced, confined, or unreinforced masonry construction. In general, most residential buildings are of confined masonry construction, which is unreinforced masonry surrounded by a thin reinforced concrete shell. Newer masonry structures in Chile are typically more slender and have a reinforced beam-column system, which is designed to maintain the structural integrity of the building during an earthquake. Commercial and mid- to high-rise apartments are typically either of reinforced-concrete construction with shear walls or of reinforced-masonry construction. Industrial buildings are typically of steel or light-metal construction. Once again, it is in the very early aftermath of this event, whose parameters may yet change as reports continue to come in from seismic networks around the world. The AIR earthquake team is collecting and analyzing the available information for input into the AIR Earthquake Model for Chile. AIR clients will be notified when results are available.

First Posting | Downloads
Posting Date: February 27, 2010, 5:00:00 AM