The Earth’s crust is a dynamic system of tectonic plates constantly grinding against one another, an interaction that periodically results in seismic events. People have long sought ways to understand and quantify the sudden, violent release of energy that we call an earthquake. This desire led to scientific methods that allow us to compare the severity of different quakes, confirming which one holds the record for the greatest recorded magnitude.
Defining Earthquake Magnitude
The scientific measurement of an earthquake’s size has evolved significantly. The older Richter Scale, developed in the 1930s, measures the amplitude of seismic waves recorded on a seismograph. While it works well for small-to-moderate earthquakes, it has a limitation known as “saturation.” For quakes above magnitude 7, the Richter Scale cannot accurately distinguish between the energy released, underestimating the power of the largest events.
Because of saturation, the scientific community now relies on the Moment Magnitude Scale (MMS or \(M_w\)) to measure large earthquakes. The MMS is a physically-based measurement that calculates the seismic moment. This moment is proportional to the area of the fault rupture, the amount of slip, and the rigidity of the Earth’s crust. This approach provides a more reliable and globally applicable estimate of the total energy released for massive events.
The Record-Holding Earthquake in History
The highest-magnitude earthquake ever instrumentally recorded is the Great Chilean Earthquake, which occurred on May 22, 1960. Also known as the Valdivia Earthquake, this event registered a magnitude of 9.5 on the Moment Magnitude Scale. Its power originated from a massive subduction zone where the Nazca Plate is being forced beneath the South American Plate.
The rupture zone along this continental boundary was estimated to be approximately 1,000 kilometers long. The localized effects in southern Chile were catastrophic, with severe ground shaking lasting for about ten minutes. Cities such as Valdivia and Puerto Montt experienced extensive damage, and approximately 40% of the buildings in Valdivia were destroyed or rendered uninhabitable.
Geological changes near the epicenter included significant land deformation. Portions of the Chilean coast subsided by one to 1.5 meters, while other areas experienced uplift. Landslides were common in the Chilean Lake District, and pressure changes triggered the eruption of the nearby Puyehue volcano two days later. The ground failure caused immense destruction, leaving an estimated two million people homeless.
Global Impact and Aftermath
The Great Chilean Earthquake’s most far-reaching consequence was the massive trans-oceanic tsunami it generated. The seafloor displacement created waves that sped across the Pacific basin, impacting coastlines thousands of miles away. Waves reaching up to 11 meters high struck the coast of Chile, destroying coastal towns like Puerto Saavedra.
The tsunami traveled approximately 15 hours to the Hawaiian Islands. Wave run-up reached 10.6 meters in Hilo Bay, causing significant damage and 61 fatalities.
About 22 hours after the earthquake, the waves arrived in Japan, destroying over 1,600 homes and resulting in 138 deaths, primarily on the northern Honshu coast. The disaster also reached the Philippines, where 32 people were reported dead or missing.
The global extent of the 1960 tsunami led to the creation of the International Tsunami Warning System of the Pacific.