First Global Map of Rare Continental Mantle Earthquakes: A New Achievement in the Study of the Earth's Interior

Researchers at Stanford University have achieved a significant milestone in the field of seismology by creating the first global map of rare continental mantle earthquakes. This research is considered a major scientific breakthrough in understanding the structure and dynamics of the Earth's interior, particularly the mantle.

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¨     This study, published in the journal Science in February 2026, provides the first systematic global evidence of earthquakes originating deep within the continental mantle rather than within the Earth's crust.

¨     Traditionally, earthquakes were thought to originate primarily in cold, brittle crust or at subduction zones where oceanic plates plunge into the mantle.

¨     Confirming mantle earthquakes beneath continental interiors has long been challenging due to limitations in detection techniques and seismic interpretation.

¨     The new research introduces a waveform-based identification method that enables scientists to distinguish between crustal earthquakes and mantle earthquakes with greater accuracy and global consistency.

Key Findings of the Study

¨     Global distribution of mantle earthquakes: Continental mantle earthquakes occur worldwide, but they are spatially clustered rather than uniformly distributed.

¨     Their main concentrations have been identified below: the Himalayas in South Asia and the Bering Strait between Asia and North America.

¨     Depth and nature of mantle earthquakes: Unlike typical crustal earthquakes (≈10–29 km depth), mantle earthquakes occur at much greater depths, sometimes more than 80 km below the Moho (Mohorovicic discontinuity), the boundary separating the crust and mantle.

¨     New detection method: Researchers developed a method that compares two seismic waves: Sn waves, which travel from the upper part of the mantle, and Lg waves, which travel efficiently through the crust.

¨     Stronger Sn signals than Lg signals indicate earthquakes originate in the mantle, allowing scientists to distinguish between mantle and crustal earthquakes using waveforms alone.

¨     Using this method, researchers analyzed more than 46,000 earthquakes (since 1990) and confirmed 459 continental mantle earthquakes.

Significance of the Findings

¨     Aid in Observing the Earth's Interior: These findings provide direct global evidence of seismic activity within the continental mantle, reshaping long-held assumptions in geophysics.

¨     This provides a new direction for observing crust-mantle interactions, helping scientists understand how the Earth's layers function as an integrated system.

¨     Advances in Seismology: Although mantle earthquakes cannot cause serious damage to the surface because they occur too deep, studying them can help clarify how stress is transferred between the crust and mantle, which in turn can refine models of earthquake initiation in all layers.

¨     Guide Future Research and Monitoring: The clusters identified beneath the Himalayas, the Bering Strait, and other regions highlight priority areas for denser seismic networks and focused geophysical studies.

¨     The new waveform-based detection approach will enable the expansion of global seismic monitoring, especially in remote areas such as the Tibetan Plateau.

Earthquakes typically originate in the Earth's upper layer, the crust, or at plate boundaries. However, continental mantle earthquakes are extremely rare and occur deep below the Earth's surface, in the mantle region beneath the crust. Until now, limited information was available about these earthquakes, making it challenging for scientists to understand the Earth's internal behavior. A Stanford University research team used global seismic data and advanced analytical techniques to identify and study these deep earthquakes in detail. The resulting global map clearly depicts the location, depth, and frequency of continental mantle earthquakes. This helps to understand how Earth's internal stresses and thermal processes operate.

This discovery not only provides new insights into theories about the origin of earthquakes, but also contributes to understanding plate tectonics, the structure of the mantle, and the long-term evolution of continents. Furthermore, this study provides a strong scientific basis for future seismic risk assessment and understanding the impacts of deep earthquakes.

Earthquakes

¨     An earthquake is a sudden release of energy within the Earth that generates seismic waves, usually caused by movement of tectonic plates, faulting, or volcanic processes.

¨     Hypocenter/Focus: This is the location beneath the Earth's surface where an earthquake originates.

¨     Epicenter: This is the location directly above it on the Earth's surface.

¨     Earthquakes are recorded by instruments called seismographs. The records they make are called seismograms.

¨     The destructive power of an earthquake depends not only on its intensity but also on its location, distance from the epicenter, and depth. Shallow earthquakes are generally more destructive than deep earthquakes.

Earthquakes are divided into the following three zones based on the depth of the focus:

¨     Shallow Earthquakes: The epicenter is less than 70 km deep.

¨     Intermediate Earthquakes: Epicenter 70–300 km deep.

¨     Deep Earthquakes: Epicenter 300–700 km deep.

New Seismic Zone Map

¨     Recently, the Bureau of Indian Standards (BIS) released an updated seismic-hazard map of India by revising the Earthquake Design Code, 2025.

¨     The new map aims to guide building codes, infrastructure design, urban planning, and disaster preparedness, especially in rapidly urbanizing and seismically active areas.

Key features of the updated map

¨     A new category, Seismic Zone VI, has been added as the highest hazard category. Under this, the entire Himalayan arc is now placed in Zone VI, reflecting its very high tectonic activity and unruptured fault segments.

¨     Previously, India was divided into four zones: II (low), III (moderate), IV (high), and V (very high).

¨     Under the revised map, about 61% of India's land area now falls in moderate to high hazard zones (up from about 59% previously), and about three-quarters of the population lives in seismically active areas.