1960 Valdivia Earthquake: The Strongest Earthquake Ever Recorded

The 1960 Valdivia earthquake, also called the Great Chilean Earthquake, struck southern Chile on the afternoon of 22 May 1960. With a magnitude usually given as 9.5, it is the strongest earthquake ever recorded by instruments. Its shaking, the tsunami it generated and the landslides and volcanic eruption that followed devastated southern Chile, while the waves killed people as far away as Hawaii and Japan.

Background: a subduction zone

Chile lies along one of the most active plate boundaries on Earth. Off its coast, the oceanic Nazca Plate slides eastwards beneath the South American Plate at several centimetres a year. This process, called subduction, builds up enormous strain on the fault between the plates, which is released in great earthquakes known as megathrust earthquakes.

Southern Chile had experienced large earthquakes before, notably in 1575 and 1837. Later research on coastal sediments, published in 2005, showed that very large earthquakes have struck the region at intervals of roughly 300 years on average, with the 1575 event being the most similar predecessor to 1960.

The foreshocks and the main shock

The sequence began on 21 May 1960 with a powerful foreshock near Concepción, of magnitude around 8, which caused damage and casualties in that city. Further foreshocks followed the next day.

The main earthquake began at 15:11 local time on Sunday 22 May. Its epicentre lay near Lumaco, in the Araucanía region, and the rupture spread southwards along the plate boundary for roughly 1,000 kilometres, as far as the Chiloé archipelago and beyond. The ground shook for several minutes. Because the strongest shaking came in the afternoon and many people had already left damaged homes after the foreshocks, the death toll was lower than it might have been.

Cities and towns across a large part of southern Chile were damaged, including Valdivia, Puerto Montt, Osorno, Ancud and Castro. In Valdivia, wooden houses and brick buildings collapsed or tilted, and parts of the city and surrounding land sank by up to 2 metres, allowing rivers and the sea to flood low-lying districts.

The tsunami

The earthquake uplifted and lowered large areas of the seabed, generating a tsunami. Within minutes waves up to about 25 metres high struck parts of the Chilean coast, destroying fishing villages and ports and causing many of the deaths in Chile.

The tsunami then spread across the Pacific Ocean at the speed of a jet aircraft. About 15 hours after the earthquake it reached Hawaii, where waves of up to about 10 metres hit the waterfront of Hilo, killing 61 people despite warning sirens, partly because many residents did not understand or heed them. Around 22 hours after the earthquake, waves of several metres struck the coasts of Japan, killing about 140 people, especially in north-eastern Honshu. The Philippines, New Zealand, Australia and the west coast of the United States also recorded waves and damage.

Landslides, a dangerous lake and a volcano

The shaking set off thousands of landslides in the Andes. Three of them blocked the San Pedro River, the outlet of Lake Riñihue. As the lake level rose behind the blockage, engineers feared it would burst through and send a flood down the valley onto Valdivia, already badly damaged.

Under the direction of the engineer Raúl Sáez, hundreds of workers and soldiers dug channels through the landslide dams over about two months, lowering the blockage so that the water could escape in a controlled way. The episode, known in Chile as the Riñihuazo, is remembered as a major engineering success.

On 24 May, about two days after the main shock, the Cordón Caulle volcanic complex began a fissure eruption that lasted for weeks. Scientists generally regard it as triggered by the earthquake.

The human toll and relief

The number of deaths remains uncertain. Estimates range from about 1,000 to around 6,000, with figures of roughly 1,600 to 2,000 most commonly cited. About 2 million people, a large share of the population of southern Chile, lost their homes or had them damaged. The government of President Jorge Alessandri organised relief with substantial international aid, and the cost of damage in Chile was estimated at hundreds of millions of US dollars at 1960 prices.

The earthquake struck a region that was largely rural and relatively poor, with many communities reachable only by unpaved roads, ferries or small aircraft. Bridges, railways and ports were damaged, cutting off towns for days. The Chilean armed forces, the Red Cross and local volunteers organised shelters, field kitchens and evacuations, while aircraft brought food, medicine, tents and clothing.

Help arrived from many countries. The United States sent military transport aircraft, helicopters and field hospitals, and governments and charities across Latin America and Europe contributed money and supplies. In the following years the Chilean state set up reconstruction programmes for housing, roads and public buildings across the affected provinces.

The disaster also changed the economy of the region. Valdivia, once one of Chile’s leading industrial cities with river ports, shipyards and breweries, lost much of its industry and port activity because of the damage and the changed level of the land. Its recovery took many years, and the city’s relative economic importance declined.

In the countryside, coastal Mapuche communities and small farmers were among those worst affected, losing homes, boats, livestock and land that was flooded by the sea. Some coastal settlements were never rebuilt on their original sites.

By the numbers

Scientific significance and legacy

The Valdivia earthquake was a landmark for seismology. Instruments around the world recorded the Earth “ringing” for days after the shock. These free oscillations of the whole planet had been predicted in theory, and the 1960 earthquake provided the first clear observations, giving scientists new information about the Earth’s interior.

Together with the 1964 Alaska earthquake, the Chilean event helped scientists understand that the largest earthquakes occur on gently sloping faults where one plate dives beneath another. This understanding was a key part of the plate tectonics revolution of the 1960s.

The tsunami deaths in Hawaii and Japan also showed the need for better warnings. A United States seismic sea wave warning system based in Hawaii had operated since 1949, but international coordination remained weak. In 1965 countries around the Pacific established an international tsunami warning system under UNESCO’s Intergovernmental Oceanographic Commission.

In Valdivia, land that sank during the earthquake was permanently flooded, creating wetlands along the Cruces River that are now a protected nature sanctuary. Chile developed stricter building codes over the following decades, which helped limit deaths in later great earthquakes, including the magnitude 8.8 Chile earthquake of 2010.

Timeline

• 1960, 21 May: A magnitude 8-class foreshock strikes near Concepción.
• 1960, 22 May, 15:11 local time: The main earthquake begins near Lumaco; shaking lasts several minutes.
• 1960, 22 May: Tsunami waves devastate the Chilean coast within minutes.
• 1960, 23 May: The tsunami strikes Hilo, Hawaii, killing 61 people.
• 1960, 24 May: The tsunami reaches Japan, killing about 140; the Cordón Caulle eruption begins in Chile.
• 1960, May–July: Engineers drain Lake Riñihue to protect Valdivia.
• 1965: An international Pacific tsunami warning system is established.

Why it matters

The Valdivia earthquake is the benchmark for the most powerful earthquake ever measured. It caused great loss of life in Chile and across the Pacific, advanced the understanding of Earth’s structure and plate boundaries, and pushed nations to cooperate on tsunami warnings.