What caused 8.8 earthquake in Russia’s Kamchatka? Shallow reverse faulting, explained

A massive earthquake that originated in Russia’s Kamchatka has left the world shaken.

The 8.8 magnitude quake caused tsunami waves to hit Kamchatka, Severo-Kurilsk in the Pacific, Nemuro in Japan and Hawaii and Alaska in America.

“Today’s earthquake was serious and the strongest in decades of tremors," Kamchatka Governor Vladimir Solodov said on Telegram.

Experts are saying shallow reverse faulting is to blame for the quake.

But what is shallow reverse faulting? What do we know about it? When does it occur

Let’s take a closer look:

What is it?

First, let’s take a look at why quakes happen.

Quakes occur when there is a rapid movement of rocks underground.

This happens when there is a fracture or a zone of fractures between two blocks of rock.

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The rock can move either a few millimetres or thousands of kilometres.

When this happens quickly and rocks on one side of a fault slips against the other, it results in an earthquake.

This can happen at horizontally, vertically or at a random angle.

Scientists use the angle of the fault and the direction of the slip to determine what type of fault it is.

Faults are classified into four types – normal, reverse, strike-slip and oblique.

Normal fault

In a normal fault, the rock block above the fault moves down compared to the block below. This usually happens when the Earth’s crust is being stretched or pulled apart. You often find these faults in places like the western US Basin and Range area and near underwater mountain ridges.

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Reverse fault

In a reverse fault, the rock block above the fault moves up and over the block below. If the fault’s angle is very shallow, it’s called a shallow reverse fault.

These faults happen in places where the Earth’s crust is being squeezed or pushed together, like where one tectonic plate slides under another, such as in Japan.

Strike-slip fault

These faults move side to side, horizontally. They don’t move up or down.

If the block on the opposite side moves to the left when you look at the fault, it’s a left-lateral strike-slip fault. If it moves to the right, it’s a right-lateral strike-slip fault.

Oblique-slip fault

These faults move both up/down and side to side at the same time. So they show a mix of dip-slip and strike-slip movements.

What triggered this quake?

Experts think it was shallow reverse faulting along the along the Kuril-Kamchatka Arc that triggered this quake.

This means that the fault would have had to occur near the top of the Earth’s surface.

This happened because the Pacific Plate continues to move west-northwest to the North American Plate.

This happens very slowly – at an estimated rate of just 77 millimetres per year.

These types of quakes are more dangerous because the tremors reaches the surface faster and harder, causing more damage.

When a shallow reverse fault happens under the ocean, the seafloor suddenly lifts up. This pushes a huge amount of water, resulting a tsunami.

The waves move very fast across the ocean and can cause damage far away—even thousands of kilometers from the quake.

Which explains why there were evacuations in Japan including at the Fukushima nuclear plant, people were sent tsunami alerts in California, coastal residents were warned to move in the Philippines and Taiwan.

It also happens extremely quickly – leaving authorities not much time to prepare for a possible tsunami.

Why Kamchatka is vulnerable

Kamchatka and Russia’s Far East sit on the Pacific Ring of Fire, a geologically active region that is prone to major earthquakes and volcanic eruptions.

The quake was centered about 119 kilometers east-southeast from the Russian city of Petropavlovsk-Kamchatsky, which has a population of 180,000, on the Kamchatka Peninsula. Multiple aftershocks as strong as 6.9 magnitude followed.

The quake at 8:25 am Japan time had a preliminary magnitude of 8.0, Japanese and U.S. seismologists said.

The US Geological Survey later updated its strength to 8.8 magnitude and a depth of 20.7 kilometers.

With inputs from agencies