Earthquake or nuclear test in Iran? Experts weigh in

On October 5, 2024, at approximately midnight, a 4.5-magnitude earthquake struck Iran, originating 50 kilometers from Semnan Province, southeast of Tehran, at a depth of 10 kilometers, according to the United States Geological Survey (USGS). Minutes later, a second, weaker tremor was reported in Israel. While earthquakes are common in the region due to Iran's location on major fault lines, the close sequence of these tremors, coupled with recent tensions between the two countries, sparked unusual speculation on social media.

Starting October 6, social media platforms were flooded with claims suggesting the Iran quake was not naturally caused but rather the result of a covert, underground nuclear bomb test, fueling widespread speculation.

Screenshots of X and Facebook posts claiming that the recent earthquake in Iran was the result of a nuclear test conducted by the country. (Source:X/Facebook/Screenshot)

Users shared screenshots of seismograms, claiming they were from the Iranian seismic event and suggesting that the readings indicated a nuclear test rather than an earthquake. The veracity of these seismograms remains unverified, as no experts have commented on them specifically.

Screenshots of X posts sharing the screenshots of a seismogram, claiming it shows recordings of a nuclear test conducted by Iran. (Source: X/Screenshot)

Some social media users claimed that earthquakes rarely occur in this region, speculating about the incident's proximity to the Fordow Fuel Enrichment Plant. Others pointed to the shallow depth of the seismic event as evidence that it was unlikely to be an earthquake.

Screenshots of X posts making additional claims about the depth, and location of the seismic event to term it a nuclear test-related seismic event. (Source: X/Screenshot)

These claims emerged amid heightened tensions following Iran's missile attack on Israel on October 1, 2024. Israeli Prime Minister Benjamin Netanyahu had vowed consequences, while Tehran warned that any Israeli retaliation would lead to "vast destruction." The situation intensified fears of an escalating conflict, with multiple reports suggesting Iran was "inching closer to a nuclear weapon."

However, experts maintain that the tremors exhibited characteristics typical of earthquakes, not nuclear test blasts.

What are experts saying?

When contacted by Logically Facts, the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), which operates a global International Monitoring System (IMS) to detect nuclear tests, directed us to their official X post (archived here). The organization stated that the "recorded waveforms are consistent with previous earthquakes in the northern region of #Iran."

Screenshot of the CTBTO X post noting that the recorded waveforms are consistent with previous earthquakes in the region. (Source: Screenshot/X)

Indian geoscientist CP Rajendran, an Adjunct Professor at the National Institute of Advanced Studies' School of Natural Sciences and Engineering told Logically Facts that the tremor was an earthquake, not a nuclear test.

"That was an earthquake of M 4.5 with a shallow focus of 10 km. The area is known for earthquakes, not very far from the location of the 1997 Izmit earthquake of M 7.5. The U.S. Geological Survey has analyzed the records and categorized it as an earthquake," Rajendran explained.

Regarding the waveforms, Rajendran clarified that they show characteristics typical of earthquakes, not nuclear test blasts. "The nuclear test blast will not show shear waves. The records of this earthquake exhibit both P and S waves typical of an earthquake," the senior geoscientist noted.

Rajendran provided official seismograms of the Iran earthquake from various locations, including Armenia, UAE, and Pakistan. "You can see different waveform phases like P, PP, S, SS, etc., which are typical of an earthquake. The Iranian event is a natural earthquake without any doubt," he stated.

Screenshot of the seismogram showing multiple recordings at various stations located in countries like Armenia, UAE and Pakistan sent by Rajendran. (Source: Screenshot/Rajendran)

For context, National Geographic explains that P-waves dominate explosion-triggered earthquake seismographs, while S-waves dominate naturally occurring earthquake seismographs. The Berkeley Seismology Lab concurs, noting that earthquakes generate ‘strong S-waves,’ while underground nuclear test seismograms ‘lack most of these waves and are dominated by P-waves.’

Rajendran also indicated that the viral seismogram purportedly showing the "Iran nuclear test" is unrelated to the actual Iran earthquake. Logically Facts could not verify the origin of this viral image.

Dr. Stephen Herzog, Professor of Practice at the James Martin Center for Nonproliferation Studies (CNS), told Logically Facts, "Iran is one of the most seismically active countries in the world, and the reported depth, wave patterns, and magnitude are consistent with earthquakes that commonly happen in Iran."

Herzog, who is also the academic co-chair of the Beyond Nuclear Deterrence Working Group, emphasized that discussions about a potential nuclear test were primarily social media speculation, not assessments from authoritative sources like the CTBTO or recognized national nuclear explosion monitoring authorities.

Logically Facts contacted the European-Mediterranean Seismological Centre (EMSC) for insight into the cause of the tremors. The EMSC is an international, non-governmental, and non-profit organization comprising 84 member institutes from 55 countries, dedicated to researching and providing information on earthquakes in the European and Mediterranean regions.

Remy Bossu, head of the EMSC, explained, “An explosion generates only compressional waves at its source, whereas an earthquake also produces shear waves. The ratio of compressional to shear waves can theoretically distinguish an explosion from an earthquake. However, the situation is often more complex due to the interfaces between the mediums the waves travel through, which can cause conversions between wave types.”

According to the USGS, nuclear explosions can trigger earthquakes and aftershocks, though these aftershock sequences are typically less intense than those from natural earthquakes of similar magnitude. The affected area is usually limited to within tens of kilometers from the explosion site.

Iran, situated in the Alpine-Himalayan seismic belt, is highly earthquake-prone, with over 96,000 earthquakes recorded between 2006 and 2015. In the month ending September 21, 2024, alone, 527 earthquakes were documented in the country.

Iran’s nuclear capabilities - What do we know?

Iran's nuclear facilities, including the Natanz and Fordow enrichment plants and the Arak heavy-water reactor, have long been subject to international scrutiny due to concerns about potential weapons development.

While Iran maintains its nuclear program is for peaceful purposes, past secrecy and enrichment activities have raised suspicions, leading to negotiations like the Joint Comprehensive Plan of Action (JCPOA) to limit its capabilities in exchange for sanctions relief.

Following the U.S. withdrawal from the accord in 2018, Iran accelerated uranium enrichment and has accumulated uranium that is near weapons grade level, raising concerns about its ability to produce bomb-grade material quickly, though developing a deliverable nuclear warhead would require additional time.

However, Dr. Herzog noted, "Iran is likely quite a bit further from the bomb than the short 'breakout time' calculation based on fissile material quantity and quality suggests. This is because it would need to conduct advanced weaponization work to carry out a nuclear test."

(Edited by Shreyashi Roy and Nitish Rampal)