Bhutan Earthquake Horror: More Danger Ahead? Why Shallow Earthquakes Cause Greater Damage
On September 8, 2025, a magnitude 4.2 earthquake struck Bhutan at a shallow depth of 10 kilometers, sending ripples of concern through the Himalayan nation. While this quake caused no reported casualties or significant damage, its shallow nature raises critical questions about Bhutan’s vulnerability to seismic events and the potential for more destructive quakes in the future. This blog explores why shallow earthquakes like this one are particularly dangerous, the unique risks Bhutan faces, and whether more danger lies ahead.
Why Shallow Earthquakes Are More Dangerous
Earthquakes occur when tectonic plates shift along fault lines, releasing pent-up energy. The depth of an earthquake’s hypocenter—the point where the rupture begins—plays a significant role in its destructive potential. Shallow earthquakes, defined as those occurring at depths of less than 70 kilometers, are far more dangerous than their deeper counterparts for several reasons:
Stronger Ground Shaking: Seismic waves from shallow earthquakes travel a shorter distance to the surface, retaining more energy. This results in intense ground shaking that can cause significant structural damage. In the case of the September 8 quake, its 10-kilometer depth amplified the shaking felt at the surface, though its moderate magnitude limited widespread destruction.
Increased Likelihood of Aftershocks: Shallow earthquakes often trigger aftershocks, as the crust adjusts to the initial rupture. The National Center for Seismology (NCS) noted that the September 8 quake’s shallow depth increases the likelihood of aftershocks, which could compound damage if structures are already weakened.
Liquefaction and Landslides: In regions with soft soils or steep terrain, shallow quakes can trigger liquefaction—where saturated soil behaves like a liquid—or landslides. Bhutan’s mountainous landscape, crisscrossed by rivers and prone to heavy monsoon rains, heightens the risk of landslides, which can devastate villages and infrastructure.
Bhutan’s Seismic Vulnerability
Bhutan’s location in the Himalayan Mountains makes it one of the most seismically active regions in the world. The country sits along the boundary where the Indian tectonic plate collides with the Eurasian plate, driving the Himalayas upward and generating frequent earthquakes. This tectonic setting, combined with Bhutan’s unique geography and infrastructure, amplifies its vulnerability:
Active Fault Lines: The Main Frontal Thrust (MFT) and Main Himalayan Thrust (MHT) are major fault systems running along Bhutan’s southern border. These faults are capable of producing earthquakes exceeding magnitude 8, as evidenced by a historical M8.1 quake in 1714 that caused widespread destruction.
Historical Precedents: Bhutan has experienced significant earthquakes in the past, including a magnitude 6.1 quake in 2009 that killed 11 people and damaged over 5,000 homes. Paleo-seismic studies indicate that even larger events, like the 1714 quake, are possible, underscoring the region’s high seismic risk.
Challenging Terrain: Bhutan’s rugged, mountainous terrain complicates disaster response and recovery. Remote villages are difficult to access, and landslides triggered by earthquakes can block roads and rivers, leading to flooding or isolation.
Vulnerable Infrastructure: While urban areas like Thimphu and Paro follow strict building codes, many rural homes are constructed with traditional materials like mud and timber, which are less resistant to seismic shaking. The government has promoted confined masonry construction to improve seismic resilience, but implementation remains uneven.
The September 8, 2025 Earthquake: A Wake-Up Call
The recent magnitude 4.2 earthquake, centered 23 kilometers northeast of Samdrup Jongkhar, was followed by a smaller 2.8 magnitude quake later the same day. Although these events were minor, they serve as a stark reminder of Bhutan’s seismic hazards. The shallow depth of the 4.2 quake, combined with its location in seismic zones IV and V—the most active zones per the Indian Seismic Code—highlights the potential for more significant events.
No major damage was reported, but the quake’s proximity to the Main Frontal Thrust raises concerns. Historical data suggests that Bhutan experiences an average of 39 earthquakes per year with a magnitude of 4 or higher within a 300-kilometer radius, with a magnitude 7.1 quake striking near Thimphu on January 7, 2025. These frequent tremors indicate that the region’s faults are active and capable of producing larger, more destructive quakes.
Is More Danger Ahead?
The September 8 quake, while minor, underscores the need for vigilance. Several factors suggest that Bhutan could face more significant seismic events in the future:
Long Seismic Gap: Paleo-seismic studies indicate that Bhutan’s last major earthquake occurred in 1714, with an estimated magnitude of 8.1–8.6. The absence of a major quake in recent centuries suggests that stress may be building along the MFT, potentially leading to a large rupture.
Regional Seismic Activity: Recent earthquakes in neighboring regions, such as a magnitude 7.1 quake in Tibet on January 7, 2025, and a devastating magnitude 7.7 quake in Myanmar in March 2025, highlight the active tectonic environment surrounding Bhutan. These events, felt across South Asia, demonstrate the far-reaching impacts of Himalayan quakes.
Climate-Induced Risks: Climate change exacerbates Bhutan’s seismic risks. Glacial Lake Outburst Floods (GLOFs), triggered by glacial melt, can be worsened by earthquakes, leading to catastrophic flooding. Landslides and flash floods, already common due to heavy monsoon rains, could be triggered by even moderate quakes.
Preparing for the Future
Bhutan has taken steps to mitigate earthquake risks, but challenges remain. The Department of Geology and Mines (DGM) operates 223 earthquake intensity monitoring stations to assess damage and guide response efforts. The government is also working with the GovTech Agency to improve real-time seismic data dissemination. However, gaps in disaster preparedness persist:
- Strengthening Infrastructure: Expanding the use of earthquake-resistant construction techniques, especially in rural areas, is critical. The 2020 Seismic Hazard and Risk Assessment Report identifies high-risk urban centers
