Mexico City is particularly prone to earthquake damage because it is built on top of what ground material?

Mexico City is particularly prone to earthquake damage because it is built on top of what ground material?

• A. On top of bedrock
• B. On top of granite
• C. On top of water-saturated soil
• D. On top of silt

Answer: (D)

The key idea is how ground material influences how strongly earthquakes shake the surface. Soft, loose sediments that are water-saturated have low stiffness and low shear-wave velocity, so seismic waves are amplified as they move through them. In basins filled with these sediments, waves can get trapped and resonate, leading to stronger and longer shaking than you’d get over solid bedrock. Water in the pores reduces effective stress, which can even cause liquefaction and collapse in unconsolidated sediments. Mexico City sits on thick layers of ancient lakebed sediments, dominated by soft silt and clay that are often saturated with water. This combination makes the ground highly amplifying during earthquakes, producing the severe damage seen there. Bedrock would dampen shaking more, and granite isn’t the material present, while water-saturated soil is a factor, silt specifically captures the type of soft, fine-grained, waterlogged sediment driving the amplification.

The key idea is how ground material influences how strongly earthquakes shake the surface. Soft, loose sediments that are water-saturated have low stiffness and low shear-wave velocity, so seismic waves are amplified as they move through them. In basins filled with these sediments, waves can get trapped and resonate, leading to stronger and longer shaking than you’d get over solid bedrock. Water in the pores reduces effective stress, which can even cause liquefaction and collapse in unconsolidated sediments.

Mexico City sits on thick layers of ancient lakebed sediments, dominated by soft silt and clay that are often saturated with water. This combination makes the ground highly amplifying during earthquakes, producing the severe damage seen there. Bedrock would dampen shaking more, and granite isn’t the material present, while water-saturated soil is a factor, silt specifically captures the type of soft, fine-grained, waterlogged sediment driving the amplification.