Question

Which of the following describes liquefaction? A. the stopping of S-waves by Earth's molten outer core B. ice melting during an earthquake to cause flooding C. seismic waves shaking sediment, causing it to become more liquid like D. rivers diverted by the motion of earthquake flooding

Short answer

Option C: Seismic waves shaking sediment, causing it to become more liquid-like, describes liquefaction.

Step-by-step solution

Understand the Term 'Liquefaction'

First, we need to understand what the term 'liquefaction' means in the context of earthquakes and geological processes. Liquefaction refers to a process where saturated or partially saturated soil substantially loses strength and stiffness in response to an applied stress, often from earthquake shaking, which causes it to behave like a liquid.

Analyze Answer Choices

We have four options: (A) stopping of S-waves by Earth's molten outer core, (B) ice melting during an earthquake, (C) seismic waves shaking sediment, causing it to be more liquid-like, and (D) rivers diverted by earthquake motion. We must match the correct definition of liquefaction to these choices.

Eliminate Incorrect Options

We can immediately eliminate option (A) because it refers to wave behavior in the Earth's mantle, not liquefaction. Option (B) involves ice melting, which is unrelated to soil behavior and liquefaction. Option (D) describes a scenario involving water flow changes, not soil behavior.

Identify the Correct Option

Option (C) specifically describes seismic waves shaking sediment and causing it to become more liquid-like, which aligns perfectly with the definition of liquefaction. Thus, (C) is the correct description of liquefaction.

Key concepts

Seismic Waves

Seismic waves are energy waves generated during an earthquake. These waves are integral to understanding how earthquakes cause damage. Classified mainly into two types, they are known as primary waves (P-waves) and secondary waves (S-waves). Each type carries different characteristics and impacts the Earth's crust differently.

The main properties of these waves are:

• P-Waves: These are compressional waves moving parallel to the wave direction. They travel fastest through the Earth and can move through solids, liquids, and gases.
• S-Waves: Also known as shear waves, they move perpendicular to the wave direction. S-waves are slower than P-waves and can only move through solid materials.

Understanding these seismic waves is crucial because they directly influence phenomena like liquefaction. When a strong earthquake occurs, the seismic waves can shake the ground significantly. The shaking can disturb loose sediments and water-saturated soils, potentially causing the ground to act like a fluid, leading to liquefaction. Hence, seismic waves have a significant role in triggering liquefaction events.

Soil Behavior

Soil behavior during an earthquake is a critical factor that defines the extent of damage. Earthquakes impact soil properties, often leading to liquefaction in saturated soils. Liquefaction transforms firm soil into a more fluid-like state due to seismic waves' vibrations.

Several factors influence soil behavior during seismic activity:

• Soil Saturation: When soil is fully or partially saturated with water, it becomes more susceptible to liquefaction.
• Soil Composition: Soils with high sand content and loose structures are more prone to liquefaction. The less dense the soil, the higher the risk.
• Wave Characteristics: The intensity and duration of seismic waves also affect how soil behaves during an earthquake.

During liquefaction, the soil loses its strength and stiffness, causing structures to sink or tilt. This is why understanding soil behavior and its response to seismic waves is vital for earthquake-resistant construction and planning.

Earthquake Shaking

Earthquake shaking is the ground movement caused by the passage of seismic waves. It is responsible for most of the damage observed during an earthquake, affecting buildings, roads, and infrastructure. The intensity of shaking varies based on several factors:

1. Magnitude of the Earthquake: Higher magnitude earthquakes release more energy, resulting in more intense shaking. This is often the precursor to soil liquefaction. 2. Distance from the Epicenter: The closer a location is to the earthquake epicenter, the stronger the shaking experienced. 3. Local Geological Conditions: Areas with loose, water-saturated soils experience more severe shaking, heightening the risk of liquefaction.

Earthquake shaking can lead to ground deformation and failure, including landslides and liquefaction. In liquefaction, as described earlier, the shaking causes a build-up of water pressure within the soil, making solid ground behave like a liquid. This can have catastrophic effects on infrastructure. Understanding the dynamics of earthquake shaking helps in designing better structures and mitigating the risks associated with these natural events.