Iran Rocked by 5.1-Magnitude Earthquake: A Nation on Fault Lines
By John Heffernan
June 20, 2025
At 9:19 p.m. local time today, a 5.1-magnitude earthquake struck 37 kilometers southwest of Semnan, Iran, at a shallow depth of 10 kilometers, according to the United States Geological Survey (USGS). The tremor, felt across parts of northern Iran, rattled homes and sent residents into the streets, though no immediate reports of casualties or significant damage have emerged. As seismologists analyze the event, this quake serves as a stark reminder of Iran’s precarious position atop some of the world’s most active fault lines—a geological reality that has shaped the nation’s history with devastating consequences.
Today’s Earthquake: A Wake-Up Call
The epicenter of today’s quake lies in a seismically active region near Semnan, a city of over 150,000 people in northern Iran. The shallow depth amplified the shaking, categorized as “light” on the Modified Mercalli Intensity scale, though its effects may have been felt beyond the mapped shake area. Local authorities, including the Semnan crisis management agency, deployed rescue teams to assess potential damage to infrastructure, particularly in rural areas where older buildings are vulnerable to even moderate quakes.
This event follows a 4.5-magnitude quake near Qom on June 20, 2025, which raised concerns due to its proximity to the Fordow nuclear facility. While today’s quake near Semnan appears unrelated to nuclear sites, it underscores Iran’s ongoing challenge: preparing for seismic hazards in a country where earthquakes are a daily occurrence. On average, Iran experiences one earthquake per day, with 2735 quakes of magnitude 4 or higher recorded within 300 kilometers of the country over the past decade.
As a journalist who has covered natural disasters across the globe, I’ve seen how earthquakes expose not just geological faults but societal ones—crumbling infrastructure, lax building codes, and economic constraints. Iran, with its rich history and resilient people, faces these challenges acutely. Today’s quake, though moderate, prompts a deeper look at the fault lines beneath Iran and the catastrophic events that have defined its seismic past.
A History of Major Earthquakes in Iran
Iran’s location on the Alpine-Himalayan seismic belt, where the Eurasian, Arabian, and Indian tectonic plates collide, makes it one of the most seismically active countries in the world. Since 1900, earthquakes have claimed at least 126,000 lives and caused billions in economic losses. Below is a timeline of some of Iran’s most significant quakes, drawn from historical records and modern data:
- April 10, 1972 – Ghir Karzin Earthquake (Magnitude 7.1): This quake in southern Iran killed 5,074 people, leveling villages around Ghir Karzin. Its shallow depth and proximity to populated areas amplified the destruction.
- September 16, 1978 – Tabas Earthquake (Magnitude 7.8): One of Iran’s deadliest modern quakes, it killed 15,000 people and destroyed the eastern desert town of Tabas. The quake was associated with 75 kilometers of thrust faulting, with a maximum vertical displacement of 35 centimeters.
- June 21, 1990 – Manjil-Rudbar Earthquake (Magnitude 7.4): Striking the Caspian regions of Gilan and Zanjan, this disaster killed 40,000–50,000 people, injured 60,000, and left 500,000 homeless. Nearly all buildings in the Rudbar-Manjil area were destroyed, with damage felt as far as Tehran.
- May 10, 1997 – Eastern Iran Earthquake (Magnitude 7.3): This quake near the Afghan border killed 1,567 people in rural areas, highlighting the vulnerability of remote communities.
- December 26, 2003 – Bam Earthquake (Magnitude 6.6): Devastating the historic city of Bam, this quake killed 31,000 people and flattened ancient mud-brick structures, including the iconic Arg-e Bam citadel. Economic losses reached an estimated $9 billion.
- August 11, 2012 – Tabriz Twin Quakes (Magnitudes 6.4 and 6.3): These quakes near Tabriz killed 250 and injured 2,000, striking a mountainous region near Azerbaijan and Armenia.
- April 16, 2013 – Iran-Pakistan Border Earthquake (Magnitude 7.8): The strongest quake in Iran in 40 years, it killed 34 in Pakistan and caused minor damage in Iran due to its deep origin.
- November 12, 2017 – Iran-Iraq Border Earthquake (Magnitude 7.3): Centered between the High Zagros and Mountain Front Faults, this quake killed hundreds and injured thousands, with significant destruction in western Iran.
These events, among others, illustrate Iran’s long history of seismic devastation. Historical records also document ancient quakes, such as the 855 AD Rey earthquake (magnitude ~7.1) and the 958 AD Taleghan quake (magnitude ~7.7), which caused widespread destruction near modern-day Tehran.
Fault Lines: The Geological Culprits
Iran’s seismic activity stems from its position at the convergence of multiple tectonic plates. The Arabian Plate moves northward at 2–3 centimeters per year, colliding with the Eurasian Plate in southwestern Iran, while the Indian Plate exerts pressure from the southeast. This tectonic interplay has created the Zagros fold and thrust belt, a 1,600-kilometer-long zone of extreme seismic activity where the Arabian and Iranian plates overlap.
Key fault systems driving Iran’s earthquakes include:
- Zagros Fault System: Spanning southwestern Iran along the Persian Gulf and the Iran-Iraq border, the Zagros hosts numerous active faults, including the High Zagros Fault and Mountain Front Fault. The region has recorded 25,000 quakes in the past 11 years, mostly small but occasionally moderate to large, like the 2017 Iran-Iraq quake. The Zagros Mountains, formed by this collision, are a hotspot for shallow, destructive quakes due to their proximity to population centers.
- North Tehran Fault: Running beneath Tehran, this fault has produced historical quakes, including the 312–280 BC Rey quake (magnitude ~7.6) and the 1830 Damavand quake (magnitude ~7.1). Paleoseismological studies suggest a recurrence interval of about 3,800 years for major events, but smaller quakes, like the 2020 Damavand event (magnitude 5.1), keep the capital on edge.
- Mosha and Taleghan Faults: Located near Tehran, these faults have triggered significant historical quakes, such as the 958 AD Taleghan event. They contribute to the capital’s high seismic risk, with Tehran’s 16 million residents living atop six main and 60 minor fault lines.
- Makran Subduction Zone: In southeastern Iran, the Arabian Plate subducts beneath the Eurasian Plate, causing shallow and occasional deeper quakes. This zone is less active but capable of producing significant events.
- Herat Fault: Extending into Afghanistan, this dextral transform fault influences eastern Iran’s seismicity, contributing to quakes like the 1997 eastern Iran event.
- Secondary Faults in Kerman Province: Recent studies using Landsat 8 data have mapped 123 fault segments in central-east Iran, many previously unidentified. These “secondary” faults, though less active, can produce strong quakes, as seen in the 2003 Bam disaster.
The collision energy in these fault zones is released through earthquakes or mountain-building, with shallow quakes (less than 50 kilometers deep) being particularly destructive due to their proximity to the surface. Iran’s fault systems create a mix of compression, shear, and overthrust faults, resulting in diverse earthquake types and widespread seismic risk. Over 90% of the country lies in an active seismic zone, making preparedness a national imperative.
Looking Ahead: Can Iran Prepare?
Today’s quake near Semnan, while moderate, highlights the urgency of addressing Iran’s seismic vulnerabilities. Tehran, with its dense population and aging infrastructure, is particularly at risk. A 2020 study ranked it among the top 20 global megacities for earthquake risk, citing its proximity to active faults and poorly constructed high-rises. The city’s fire department has identified 129 dangerously unsafe buildings, but progress on retrofitting is slow.
Economic challenges and corruption have hindered enforcement of building codes, a problem exacerbated by the construction boom of the 1990s, when high-rises sprouted across Tehran with little regard for seismic standards. Rural areas, reliant on mud-brick homes, fare even worse, as seen in Bam’s collapse. Yet, there is hope. Seismologists are mapping previously unknown faults, and public awareness campaigns are teaching residents to secure homes and prepare for quakes.
As I write this, aftershocks may still be rattling Semnan, and scientists are likely poring over data to pinpoint the fault responsible. Each quake, even a moderate one, adds to our understanding of Iran’s restless geology. But knowledge alone isn’t enough. Iran must invest in resilient infrastructure, enforce stricter building codes, and empower communities to withstand the inevitable. The earth beneath Iran will keep trembling—it’s up to its people and leaders to ensure the nation stands firm.
John Heffernan
