Israel-Iran conflict: Iran hit by 5.1 earthquake near missile hub, prompts speculation of underground nuclear testing

A 5.1 magnitude earthquake rattled Iran early on June 21, striking 37 kilometers southwest of Semnan at a shallow depth of 10 kilometers. Though Iran’s state media reported no casualties and described the damage as minimal, the tremors stirred unease beyond geological explanations. With the region already on edge from Israeli airstrikes, the quake’s proximity to Iran’s strategic military zone quickly became a catalyst for speculation over possible nuclear activity.

The earthquake coincided with escalating hostilities between Iran and Israel, a conflict that began on June 13. Israeli strikes have targeted several critical Iranian facilities, including the nuclear sites at Natanz, Isfahan, and Fordo, while Tehran has launched missile responses. The seismic event's shallow depth and proximity to Semnan—a site known for its missile and aerospace infrastructure — fueled speculation on social media that the tremors might not be entirely natural.

Underground nuclear detonations are known to trigger seismic events, often mimicking the characteristics of earthquakes. The US Geological Survey (USGS) notes that such tests can displace tectonic structures, resulting in localized seismic activity. However, these man-made quakes typically register lower magnitudes than the blast itself and are confined to a relatively small radius.

Seismologists distinguish nuclear blasts from natural quakes through wave analysis. Natural earthquakes produce both primary (P) and secondary (S) waves, whereas nuclear explosions are dominated by P-waves. Additionally, the waveforms and energy dispersal patterns in artificial quakes diverge significantly from those of tectonic origin.

Iran, situated along the Alpine-Himalayan seismic belt, experiences frequent seismic activity. The country records over 2,000 earthquakes annually, with 15 to 16 exceeding magnitude 5.0. Data from 2006 to 2015 documented nearly 96,000 quakes nationwide, underscoring Iran’s inherent vulnerability to natural tremors.

Earlier this year, a similar situation unfolded during a four-day conflict between India and Pakistan in May. Tremors in Pakistan had prompted fears of nuclear testing, but those were dismissed following detailed seismological analysis.