Chile’s Earthquake Resilience is an Iterative Process

January 24, 2022 / 3 min read

Chile occupies 6,435 km of coastline on the west coast of South America along the Circum-Pacific Belt, which is popularly known as the Ring of Fire, thanks to its active volcanoes and frequent earthquakes. The country sits on the South American plate and is bordered on the west by the Nazca plate, which is subducting beneath the Chilean coastline. Chile experiences earthquakes often and some can be extremely strong. One was the most powerful ever recorded, as estimated by the USGS—the M9.5 Valdivia earthquake of May 1960.

About half of the structures in Chillán, the provincial capital, were destroyed by the first shock and many more succumbed to the aftershocks

Two decades before that catastrophic event, on January 24, 1939, another powerful earthquake struck the country’s richest agricultural region, Nuble Province, about 400 km (249 miles) south of the national capital, Santiago. The M7.8 Chillán earthquake occurred without any discernable foreshocks at 11:32 p.m., local time, when most of the population was in bed. The epicenter was approximately 32 km (20 miles) north of Chillán, and the earthquake is believed to have occurred within the subducting Nazca plate as a normal fault event (Beck et al. 1998). Destruction extended across an area of about 45,000 km² (26,097 square miles).

The unreinforced masonry cathedral in Challan's central square — Figure 1. The unreinforced masonry cathedral in Chillán’s central square was destroyed by the earthquake in 1939. (Source: Archivo Histórico de Concepción)

About half of the structures in Chillán, the provincial capital, were destroyed by the first shock and many more succumbed to the aftershocks; about a quarter of the population was killed. Moments later about 95% of the homes in Concepción—one Chile’s largest cities—were destroyed as shaking reached it. Power was cut, water supply was seriously affected, fires broke out and burned for days, and the tramway system was put out of service for weeks. Because of the late hour in which the earthquake struck and the lack of forewarning the number of casualties was high. Estimates vary widely, but it is likely that approximately 10,000 people were killed, 60,000 were injured, and 100,000 were left homeless.

Martial law was declared following the Chillán earthquake and the army was sent to prevent looting and oversee rescue attempts. The Red Cross directed effective relief efforts and thanks to the mild winter that followed there were few post-earthquake casualties. The nation’s first building regulations to improve the performance of structures had been introduced in the 1920s following a series of devastating quakes. The buildings destroyed by the Chillán earthquake were of unreinforced masonry construction and predated those measures, but reconstruction after the 1939 quake was governed by them. Significantly, the government founded the Corporación de Fomento de la Producción de Chile (Production Development Corporation, CORFO) to foster economic growth and support recovery.

Chillan's rebuilt cathedral from the 1950s — Figure 2. Chillán’s cathedral was rebuilt in the 1950s with earthquake resistance as the primary consideration. It survived the M8.8 Maule earthquake in 2010 with just a few broken windows. (Source: USGS))

Authorities in Chile have learned from each major disaster, introduced new measures, and improved public education. Seismic building codes were enhanced significantly following the Valdivia earthquake in 1960, for example, and were updated again following the M8.8 Maule earthquake in 2010 that wreaked destruction in southern and central parts of the country. In that quake thousands of adobe buildings crumbled, and even some engineered buildings adhering to modern construction practices did not escape damage. And following the inadequate warning of the devastating tsunami that followed the quake in 2010, agencies were strengthened and protocols were developed for a common response.

Today, Chile has an excellent reputation for earthquake resilience, but this has taken a century to develop. It is often repeated that earthquakes don’t kill people, collapsing buildings do. Today’s building codes in Chile are designed to ensure that new structures can survive even an M9.0 earthquake; they may crack or tilt to the point where they are declared unfit for use, but they must not collapse. Such measures have saved countless lives. The M8.1 Iquique Earthquake in 2014 and the M8.3 Central Chile earthquake and tsunami in 2015, for example, claimed 6 and 15 lives respectively.