How does a tsunami originate? From the earthquake to the coast, what factors can aggravate it?

Not all earthquakes at sea cause tsunamis, nor do all tsunamis originate from an earthquake. An earthquake like the one that generated alerts across the Pacific Ocean this Wednesday only occurs when certain factors coincide to generate this massive movement of marine waters. Typically, it must be a major earthquake whose epicenter (the projection on the surface of its underground origin) is on the seafloor or not far from the coast. Furthermore, the earthquake mechanism must generally cause this gigantic surge of water, because there is a rupture of the seabed, with a sudden vertical thrust from the ocean floor. That is, the earthquake must occur underwater, releasing significant energy in a vertical movement, so that the crust pushes the column of water above it up or down.

When to sound an alert?

The initial surge generates waves that propagate at high speed through the ocean, up to 800 kilometers per hour (almost 500mph) in the open sea. But seismic waves travel much faster than tsunamis, so once a major earthquake like the one that struck Wednesday on Russia’s Kamchatka Peninsula has occurred, warning systems can predict the behavior, direction, and arrival of the phenomenon with enough time to alert the population. Specifically, in the Pacific region, many countries have extensive experience dealing with tsunamis, such as Japan, the United States, and Chile, allowing them to react very quickly. The Pacific Tsunami Warning Center advanced its projections shortly after the earthquake, predicting waves of up to three meters on the coasts of Russia, Ecuador, and the Hawaiian Islands. In the latter, the first waves were measured at over one meter in height on the island of Hilo, after the tsunami traveled some 5,000 kilometers (3,106 miles) from its origin.

Is there danger on the high seas?

In the deep ocean, tsunamis have lengths of hundreds of kilometers and heights of only a few meters, making them imperceptible. Therefore, it is often said that mariners on the high seas will normally not notice a tsunami when it passes beneath the hulls of their ships. However, as it approaches the coast, the speed decreases and the wave height increases, sometimes exceeding 30 meters. Therefore, the real danger is decided in the last few kilometers, when the tsunami generated by an earthquake leaves the deep ocean and reaches the coast, where the geomorphology of the coastline is crucial in dissipating its force or aggravating its intensity.

How strong was the earthquake?

The 8.8 magnitude Kamchatka earthquake is one of the 10 largest recorded worldwide since 1900, according to the U.S. Geological Survey. It is the worst since the tragic 9.0 magnitude earthquake in Tohoku, Japan, in 2011, which triggered the Fukushima tsunami that devastated its nuclear plant.

Was such an earthquake expected?

Wednesday’s quake is the latest in a 10-day sequence of earthquakes off the coast of the Kamchatka Peninsula. Before Wednesday’s earthquake, 50 other aftershocks greater than magnitude 5.0 were recorded, including one measuring 7.4 on July 20, according to the U.S. Geological Survey. On July 30, 24 aftershocks greater than magnitude 5.0 were detected, including one measuring 6.9.

Why is Kamchatka moving?

The Earth’s outer layer is divided into enormous tectonic plates that fit together like pieces of a puzzle. The earthquake occurred in a highly seismically active region, where the Pacific Plate slides beneath the North American Plate. In the Kamchatka Peninsula region, the Pacific Plate is moving northwest at a rate of about eight centimeters per year, making it one of the fastest converging boundaries in the world, according to the U.S. Geological Survey. A magnitude 9.0 earthquake occurred there in 1952, with an epicenter located just 30 kilometers (18.6 miles) from Wednesday’s. Since then, the plate has moved almost six meters. In 1923, another major earthquake, measuring 8.4, struck the Russian peninsula. The U.S. agency believes that Wednesday’s 8.8 quake filled “any small gap” between the rupture of 1923 and that of 1952.

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