Continental Mantle Earthquakes
Kartavya Desk Staff
Source: DTE
Subject: Geography
Context: A Stanford-led study has created the first global map of rare continental mantle earthquakes, identifying 459 such events worldwide.
About Continental Mantle Earthquakes:
What Are Continental Mantle Earthquakes?
• Continental mantle earthquakes are rare seismic events that originate deep within the Earth’s mantle beneath continental regions, rather than in the shallow crust where most earthquakes occur.
• Unlike typical crustal earthquakes (10–29 km depth), these quakes occur more than 80 km below the Mohorovičić discontinuity (Moho)—the boundary separating the crust from the mantle.
Where Do They Occur?
• The recent study found clustering beneath tectonically active regions such as:
• The Himalayan collision zone (Indian Plate subducting beneath the Eurasian Plate) The Bering Strait region
• The Himalayan collision zone (Indian Plate subducting beneath the Eurasian Plate)
• The Bering Strait region
• Such areas are marked by intense continental collision and lithospheric deformation.
How Do They Originate?
• Tectonic Stress Transfer: Stress from continental collision or crustal earthquakes may penetrate deeper into the mantle, triggering rupture.
• Subduction-Related Processes: In collision zones, the descending plate may retain brittle characteristics at greater depths.
• Thermal & Rheological Variations: Though the mantle is generally semi-solid and ductile, localized cooler or compositionally distinct zones may become brittle enough to fracture.
• Seismic Wave Identification: Scientists distinguished mantle quakes using differences between Sn waves (mantle-travelling) and Lg waves (crustal-travelling) in seismic waveforms.
How Are They Different from Crustal Earthquakes?
Feature | Crustal Earthquakes | Continental Mantle Earthquakes
Depth | 10–29 km | >80 km
Location | Within brittle crust | Deep mantle beneath continents
Surface Impact | Strong shaking possible | Minimal surface impact
Frequency | Common | Rare
Impacts and Significance:
• Limited Surface Damage: Due to great depth, these quakes typically do not cause significant surface shaking or destruction.
• Insight into Earth’s Interior: Provide new data on mantle structure and stress distribution beneath continents.
• Understanding Mountain Building: Regions like the Himalayas show how deep tectonic processes contribute to orogeny (mountain formation).