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How do earthquakes activate landslides?
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landslide
This 1995 landslide at La Conchita, a coastal town in California, swept away a hillside road and destroyed a number of houses.
Earthquakes activate landslides primarily by imposing short-term shear stresses on slopes. These stresses can exceed the shear strength—the internal resistance to movement—of the materials forming the slope, such as rock, debris, or soil.12
The mechanism of activation can occur in several ways:
- Direct Mechanical Disturbance: The intense shaking caused by earthquake waves can mechanically disturb slope materials, particularly those with a loose or open sediment fabric, causing them to weaken.2
- Liquefaction: Earthquake shock can trigger liquefaction in certain substrates, such as weakly cemented silt or loess. This process turns solid ground into a fluid-like state, leading to complex lateral movements known as spreads.2
- Mobilization of Debris: Strong ground motions can cause large volumes of rock or debris to detach and fall. In some cases, these falls trap air, facilitating rapid, high-velocity flows such as rock or debris avalanches.2
By destabilizing the balance between gravitational forces and the material's inherent strength, earthquake-induced shocks serve as a primary trigger for mass movement events.12