Some videos of the earthquake that shook the Celebes Islands on September 28, 2018, followed by a tsunami, continue to trend.
According to , this catastrophe caused two thousand deaths and another five thousand missing. THE nature’s destructive power is undeniableespecially taking into account that the event “only” reached 5.1 on the moment magnitude (MW) scale, i.e. 7.5 on the old Richter scale.
Can you imagine what an earthquake with twice the magnitude would be like? It turns out that such an event is not purely hypothetical — happened not long ago.
Em 1960, in the Chilean province of Valdiviaa magnitude 9.5 earthquake went down in history as the strongest ever recorded by instruments.
This seismic event did not occur without warning. At six in the morning on May 21 of that year, several provinces in southern Chile were abruptly awakened by a violent shock.
This first earthquake caused 125 dead and destroyed a third of Concepciónthe capital of the province of the same name.
The neighboring city of Talcahuano — among other affected areas — was also largely devastatedalthough it would suffer an even greater disaster decades later, in 2010, due to a 8.8 MW earthquake and tsunami.
The Concepción earthquake lasted just over half a minute, but it was not the end. It just delayed what was yet to come.
The next day, at almost the same time, a new earthquake, slightly weaker, 7,1 MWwith an epicenter in La Araucanía, while the previous one had been in Biobío.
But, at 2:56 p.m., a third earthquake, also centered in the Araucanía region, reaching a magnitude of 7,8.
Despite the material catastrophe, the number of human casualties was limited because people had been evacuated from their homes since that morning. As a result, there were no more fatalities.
It seemed time to focus on organizing rescue efforts, debris removal and relief. Or so it was believed.
However, the Concepción earthquake was just a prologue of what would happen very shortly later, that same day, at 3:11 pm. This event impacted the previously mentioned regions, as well as The Rivers and The Lakes.
This earthquake was much stronger and, in fact, reached 9.5 MW (or maybe even more, as the instruments broke at that moment).
To make matters worse, instead of lasting 35 seconds, continued for 8 minutes. Seismologists now consider that it was a sequence of 37 earthquakes, triggered by a tectonic rupture in the subduction zone which extends from the Arauco Peninsula to the Taitao Peninsula.
The epicenters extended for approximately 1250 kilometers parallel to the coastaffecting an area of approximately 400,000 square kilometers.
It is not uncommon that catastrophic events occur in this part of the world, as it is where the Nazca Plate collides with the South American and Chiloé Plates. This causes the Nazca Plate to subduct beneath the others, generating friction that manifests as surface earthquakes and supports magma outflows through numerous volcanoes.
A intensity reached in 1960 was extraordinary. Scientists estimate that such events occur only once every three centuries, on average. To illustrate the magnitude, tectonic plates are normally considered to move about 9 centimeters per year, but on that day they moved 40 meters in an instant.
In fact, Valdivia is a coastal city, so it was only a matter of time before the Pacific Ocean reacted. First, there was a sudden 4 meter rise in sea level, causing damage to ships in the harbor, especially as the waters receded as quickly as they had risen.
But ten minutes later, a 8 meter wall of water appeared on the horizon, hitting the ground 150 kilometers per hour and destroying everything in its path.
Hundreds of people lost their livesthat moment, but the worst was yet to come. One second waveeven greater, with 10 meters high.
The magnitude of the tsunami meant that it also hit Hawaii, where waves of similar height killed 61 people in the city of Hilo. The event was also felt in distant places, such as Japan and the islands of Oceania.
In Valdivia, the effects were devastating, with the collapse of several Spanish fortresses from the viceregal era, 40% of the buildings and the river mouth becoming unusable for navigation.
To make matters worse, as the city was situated on land of river sedimentation and swamps, everything turned into a colossal swamp of mud when the sea receded.
Several nearby cities have disappeared from the mapwith thousands of dead, many missing and around 20,000 people affected. A ship was stranded a kilometer and a half from the coast, clearly demonstrating the tsunami power.
It is was the most destructive agentbut the chaos was joined by the firesos landslides — like Pelhueco, which buried an entire village with its 300 inhabitants — and volcanic eruptions, with the eruption of the Puyehue volcano. Even the inland water bodies created challenges for the population.
Lake Villlarica overflowed and several hills collapsed onto the floodgates of Lake Riñihue, blocking its flow. The lake’s water level continued to rise, threatening an icatastrophic flooding if the dam failed.
For this reason, the Chilean army and several companies had to carry out a colossal project around the clock to divert part of the water and connect the lake to other lakes to alleviate the situation.
Despite everything, the humanity continues to defy nature. The fact that the affected areas are located on the so-called Pacific Ring of Fire is not enough to deter occupation and they continue to be populated despite there was already a serious warning 443 years ago. In 1575, Valdivia suffered a large earthquake whose magnitude is unknown, but which is estimated to have been similar to that of 1960.
It also caused a tsunami and a similar incident to Lake Riñihue, when the Renigua lagoon overflowed and flooded the surrounding areas.
In reality, the Chile recorded hundreds of significant earthquakes from 1570 to 2015, 29 of which are considered serious. These include the aforementioned earthquakes of 1575 and 1960, the Valparaíso earthquake of 1730 and the Arica earthquake of 1868.
Teresa Oliveira Campos, ZAP //
