Why the tsunami caused by the megaterremoto of Russia has not caused more damage

Street with bricks and a car — Photo foot, The only considerable material damage so far occurred on the coast of the Kamchatka Peninsula, in East Russia.

- Author, Writing
- Author's title, BBC News World
1 hour

It has been one of the strongest earthquakes ever registered, but has not caused the tsunami catastrophic that many feared.

When the earthquake 8.8 shook east of Russia at 11:25 local time on Wednesday (23:25 GMT on Tuesday) the fears in the coastal populations of the entire Pacific.

Millions of people were evacuated, thinking of the devastating tsunamis of December 26, 2004 in the Indian Ocean and Japan in 2011, both triggered by earthquakes of similar magnitude.

Although it has caused some damage, the new tsunami has been much less severe.

So what caused the earthquake and tsunami, and why was the latter as destructive as it was feared at the beginning?

What causes a megaterremoto?

Kamchatka's remote peninsula is found in the so -called Pacific Fire belt, named for the large number of earthquakes and volcanoes that occur in that area.

The upper layers of the Earth are divided into sections called tectonic plates, which move with respect to others.

The Pacific Fire belt is a convergence of these plates that extends around the world's largest ocean.

According to the British geological service, 80% of the world's earthquakes occur throughout this ring.

Tsunami alert poster in Peru — Photo foot, Several Latin American countries, including Chile and Peru, are found in the Pacific Fire belt.

In front of the coast of the Russian Peninsula, the Pacific plaque moves to the northwest to about 8 cm per year, which is equivalent to twice the speed at which your nails grow, but it is a fast rhythm in tectonic terms.

There comes into contact with another smaller plate, called Eyotsk Microplaca.

The Pacific plaque is oceanic, which means that it is composed of dense rocks and tends to sink below the microplack, less dense.

As the Pacific plate sinks towards the center of the earth it is heated and begins to melt, disappearing in practice.

But this process is not always fluid. Often the plates can be looked as they touch each other, dragging down the upper plate.

This friction can be accumulated for thousands of years, but then suddenly released in minutes, generating what is known as a megaterremoto.

Destroyed city in Indonesia in 2004 — Photo foot, In December 2004, a tsunami caused by a megaterremoto swept the coast of Indonesia and neighboring countries.

“When we think of earthquakes, we tend to imagine an epicenter as a small point on the map. However, earthquakes of this magnitude, the failure has broken along hundreds of kilometers,” explains Stephen Hicks, a professor of environmental seismology at the University College of London.

“It is this huge amount of displacement and surface of the failure that generates such a high seismic magnitude,” he remarks.

The greatest earthquakes recorded in history – including the first three in Chile, Alaska and Sumatra – were all of this type.

And the Kamchatka Peninsula is prone to this type of earthquakes of great magnitude.

In fact, in 1952 another earthquake of magnitude 9.0 shook an area located less than 30 km from the epicenter of today's earthquake, according to the US Geological Service (USGS).

Why was the Tsunami as destructive as other previous ones?

The sudden movement displaces the water on the tectonic plates, and that displacement can travel to the tsunami coast.

In an open sea, a tsunami can move at more than 800 km/h, approximately the same speed of a commercial plane.

Under these conditions, the distance between the waves is very long and their reduced height: they rarely exceed one meter.

But, when approaching shallow waters near the coast, the tsunami slows down, usually between 30 and 50 km/h.

The distance between the waves is shortened and its height increases, which can generate a kind of water wall upon reaching land.

However, a very strong earthquake does not necessarily guarantee that the resulting tsunami is especially high or penetrating in an inland.

This Wednesday's earthquake generated waves of up to 4 meters in some areas of eastern Russia, authorities reported.

These, however, do not approach the waves of tens of meters that were observed in the Tsunami of December 26, 2004 in the Indian Ocean, or in Japan in 2011.

“The wave height is also influenced by the shape of the seabed near the coast and by the geography of the land where it impacts,” explains Professor Lisa McNeill, an expert in tectonics at the University of Southampton.

McNeill adds that “these factors, together with population density in the coastal area, determine how serious the impact is,” he added.

The first reports of the US Geological Service indicated that the epicenter of the earthquake was at a relatively low depth: about 20.7 km under the earth's surface.

This can cause greater displacement of the seabed and, therefore, generate larger tsunami waves, although it is difficult to know with certainty in such a short time since the event occurred.

“It is possible that Tsunami models have used a conservative estimate on the depth of the earthquake,” Hicks told the BBC.

If the earthquake occurred at a depth 20 kilometers greater than the one believed, “that would have considerably reduced the magnitude of the tsunami waves,” he said.