USA Earthquake Depth & Damage Patterns Quiz
Shallow vs deep quakes; attenuation; basin amplification (10 questions).
USA Earthquake Depth & Damage Patterns Quiz: Quick Study Notes
Earthquakes are a powerful geological phenomenon, and their destructive potential is influenced by more than just magnitude. Understanding the interplay of earthquake depth, seismic wave attenuation, and local geological features like sedimentary basins is crucial for predicting and mitigating damage, especially in regions prone to seismic activity. This quiz explores these key factors as they relate to earthquake impacts in the USA.
Key Concepts
Typically occur within the upper 70 km of the crust. Hypocenter close to the surface, leading to more concentrated and intense shaking at the epicenter.
Occur at depths greater than 70 km, sometimes down to 700 km. Energy dissipates more over longer travel paths to the surface, resulting in less intense shaking.
The natural process where seismic wave energy decreases as it travels away from the earthquake source, due to geometric spreading and absorption by rocks.
Phenomenon where seismic waves entering a sedimentary basin slow down and increase in amplitude, leading to prolonged and stronger ground shaking.
Key Takeaways
- Shallow earthquakes (0-70 km) generally cause more severe local damage than deep earthquakes of the same magnitude.
- Seismic wave attenuation reduces the energy and amplitude of waves as they travel, diminishing impact over distance.
- Deep earthquakes experience greater attenuation due to longer travel paths to the surface.
- Sedimentary basins, filled with soft, unconsolidated materials, can trap and amplify seismic waves.
- Basin amplification leads to increased shaking intensity and duration, causing disproportionately high damage in urban areas built on such geology.
- Local geology (bedrock vs. sediment) is a critical factor in determining ground motion intensity, independent of epicentral distance.
Frequently Asked Questions
Why do shallow earthquakes cause more damage than deep ones?
Shallow earthquakes have their hypocenter closer to the Earth’s surface, meaning the seismic waves travel a shorter distance before reaching populated areas. This results in less attenuation (energy loss) and more concentrated, intense shaking compared to deep earthquakes of similar magnitude, whose energy dissipates over a longer travel path.
What is the primary factor that causes seismic wave attenuation?
The primary factor is the spreading out of seismic wave energy over an increasingly larger area as it travels from the source (geometric spreading). Additionally, some energy is absorbed and converted into heat as waves pass through rock formations.
How does a sedimentary basin amplify earthquake shaking?
When seismic waves encounter the boundary between hard bedrock and soft, unconsolidated sediments within a basin, they slow down. This reduction in wave speed is often accompanied by an increase in wave amplitude. Furthermore, the waves can become trapped and reverberate within the basin, prolonging the shaking duration and intensifying the ground motion.
Can basin amplification occur far from the earthquake’s epicenter?
Yes, basin amplification can significantly affect shaking intensity even at considerable distances from the earthquake’s epicenter. The local geological conditions of the basin itself are the key factor, not necessarily its proximity to the fault rupture.
What measures can be taken to mitigate earthquake damage in areas prone to basin amplification?
Mitigation measures include strict building codes requiring structures to withstand amplified shaking, retrofitting older buildings, conducting detailed seismic hazard mapping to identify specific areas of high amplification, and urban planning that considers geological conditions.
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