Iranian ‘nuclear weapons test’ was actually earthquake

Tremor struck about 50km south-west of Semnan last October

A satellite carrier is launched from the spaceport in Semnan. An earthquake struck near the Iranian city last year. AFP

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An earthquake that struck Iran last year was misreported as a covert nuclear weapons test amid rising global tension, seismologists said.

Researchers in the US studied seismic data after reports on social media sites and some news outlets suggested the magnitude-4.5 tremor on October 5 was connected to the country’s nuclear programme.

The quake occurred about 50km south-west of Semnan, an area in northern Iran that is home to the Shahroud missile plant, which builds solid-propellant ballistic missiles and has previously launched space vehicles into orbit.

But data suggested the rumble was a result of natural seismic activity along a gently sloping fault line where Earth’s crust was affected by the collision between the Arabian and Eurasian plates – ruling out any connection to human activity.

“Seismic waves carry information about the earthquake that produced them as they propagate around the planet,” said Benjamin Fernando, a Johns Hopkins seismologist who led the study, published in Seismica. "By recording the waves at different points on the Earth’s surface, we can work out what the properties of the source that produced them were."

“In this case, the source was what we call a reverse fault − a motion associated with the Earth’s crust being crushed as the Arabian and Eurasian plates collide. Nuclear tests have very different signatures, which are explosive.”

But reaction after the earthquake quickly suggested otherwise. The first post on X alleging it was nuclear test appeared only 27 minutes after it happened. Over the following hours the claims multiplied, with some posts sharing seismic data from another earthquake in Armenia earlier that day. Other posts linked the Iranian earthquake to a supposed seismic event in Israel the same evening.

One of the most widely shared social media posts claiming the earthquake was a nuclear test came from an account tied to Russian-supported disinformation campaigns, the researchers found. They said while it is difficult to confirm the disinformation was deliberate, the specialised use of seismology data on social media suggests the post was written by an expert.

Within hours, news reports with the claim began to appear worldwide. Indian English-language media were the most active in reporting the nuclear test claims, often referencing each other’s stories and citing incorrect seismic data. But the researchers also identified media reports from the US, Israel, Pakistan, Zimbabwe, France and the UK.

“There was a concerted misinformation and disinformation campaign around this event that promoted the idea this was a nuclear test, which is not something you often see happen with an earthquake,” said Mr Fernando. “This shows how geophysical data played an important role in a geopolitical crisis.”

By contrast, Iranian media generally described the event accurately as an earthquake. The reports drew on local expert commentary and more official seismic data than English-language reports.

The researchers recommended greater and faster collaboration among seismologists to quickly check facts, and correct false reports and misinterpretations of data.

“Scientific agencies could issue detailed reports swiftly to counter misinformation,” said co-author Saman Karimi, a Johns Hopkins geophysicist.

“Giving amplification to contents coming from verified scientific accounts could help reduce the misleading narrative. This can be done via partnership between social media platforms and trusted seismologists or agencies such as the US Geological Survey.”

Iran is one of the most seismically active countries in the world and crossed by several major faults that cover at least 90 per cent of the country, meaning earthquakes in the country are common and often destructive. Their impact can sometimes be felt in the UAE.

Since 1900, at least 126,000 people have died in Iran as a result of earthquakes.

Earthquakes with similar characteristics and magnitudes occurred in the same region in 2015 and 2018, according to the Comprehensive Test Ban Treaty Organisation, which monitors nuclear tests worldwide. Both were unrelated to nuclear activity.