Why earthquakes are more common in places like Vanuatu

A severe earthquake has shaken Vanuatu, causing extensive damage throughout the capital.

Although seismic activity is relatively common in the region, Tuesday’s earthquake is considered one of the strongest in recent years.

Here’s what you need to know:

What happened?

At 12:47 p.m. AEDT, a magnitude 7.3 earthquake struck near Vanuatu’s capital Port Vila.

According to the United States Geological Survey (USGS), the quake occurred 30 kilometers west of the city at a depth of 57 kilometers.

Dan McGarry, a journalist in Port Vila, described the quake as a “violent, high-frequency tremor” that lasted about 30 seconds.

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Shortly thereafter, the U.S. Tsunami Warning System issued a tsunami warning, but it was later canceled.

Several buildings and roads have collapsed or been damaged, and videos on social media show vehicles being crushed by falling debris.

Witnesses have reported serious landslides near Port Vila.

Where is Port Vila?

Vanuatu is an archipelago in the South Pacific, about 1,750 kilometers east of Australia.

Port Vila is located on the south coast of Efate Island.

What is the death toll?

McGarry said police at the scene confirmed that at least one person died in the earthquake.

“It was a violent earthquake, more violent than I have ever experienced in my 21 years of living in Vanuatu,” he said.

“A police officer confirmed there was at least one death and I saw a mass triage for the injured being set up at the hospital.”

There are fears that more deaths and injuries could be reported.

Is this considered a major earthquake?

Yes.

Magnitude refers to the size of an earthquake and those with a magnitude greater than seven are considered strong.

The measurement is expressed in whole numbers and decimal fractions, and each increase in the whole number represents a tenfold increase in the amplitude.

Fabio Capitanio, associate professor at Monash University’s School of Earth Atmosphere and Environment, said the strength of Tuesday’s earthquake was “comparable to the Mt St Helens explosion in 1980”.

“Events of similar magnitude are associated with a risk of tsunami, but the historical record shows that tsunamis occur rarely, as appears in this case,” he said.

“The damage associated with such high-energy earthquakes is expected to be extensive, even though this area has little seismic damage.”

How common are earthquakes in Vanuatu?

Earthquakes occur relatively frequently in the island nation.

According to the USGS, 24 earthquakes of magnitude seven or greater have been recorded over the past century within 150 miles (250 kilometers) of Tuesday’s epicenter.

The largest recorded event in the region was a magnitude 7.9 earthquake in December 1950.

Why do earthquakes occur more frequently in some areas?

It depends on where the Earth’s tectonic plates meet.

The Earth’s surface is broken into massive slabs of rock, forming seven large and eight small plates.

Most boundaries between plates are hidden beneath the planet’s oceans, the USGS explains.

“Tectonic plates probably developed very early in Earth’s 4.6 billion year history and have been drifting on the surface ever since – like slow-moving bumper cars that repeatedly clump together and then separate again.”

As the plates move, they occasionally get stuck as they brush past their neighbors.

When the plates overcome friction, sudden slip occurs and an earthquake occurs.

For this reason, tremors occur more frequently in areas along plate boundaries than in areas located in the middle of a plate.

Vanuatu, for example, lies on the seismically active Ring of Fire – a belt where several tectonic plates abut the Pacific plate.

It is also known as the Circum-Pacific Belt.

The area where the Australian and Pacific plates meet – where Tuesday’s earthquake struck – is one of the most seismically active regions in the world.

Why do earthquakes sometimes trigger tsunamis?

You may have noticed that tsunami warnings are sometimes issued after earthquakes.

That was certainly the case on Tuesday and earlier this month in California following a magnitude 7.0 earthquake.

The National Oceanic and Atmospheric Administration says some large earthquakes can trigger tsunamis.

“The energy of such an earthquake can cause the sea floor to suddenly rise or sink,” it said.

“This sudden vertical shift of the seafloor typically triggers a tsunami.”

However, Adam Pascale, chief scientist at the Seismology Research Center’s Earthquake Observatory, said not all large-magnitude earthquakes triggered tsunamis.

“(This is) due to reasons such as the depth of the earthquake and the orientation of the fault rupture,” he said.