D - Earthquakes Flashcards
What is the focus of an earthquake?
It is the point within the Earth where seismic stress (tension or compression) is suddenly released.
What is the epicentre of an earthquake?
The point on Earth’s surface directly above the focus.
How do shallow-focus earthquakes differ from deep-focus earthquakes?
Shallow-focus quakes occur closer to the surface (often <70 km deep), while deep-focus quakes can originate hundreds of kilometers below ground.
Name two primary seismic wave types and their characteristics.
Primary (P) waves travel fastest and move through solids and liquids by compressing and expanding the ground; Secondary (S) waves move sideways, cannot travel through liquids, and often cause more structural damage.
What are Love waves and Rayleigh waves?
They are surface waves formed from P- and S-waves reaching the surface. Love waves move the ground sideways, while Rayleigh waves move it up and down.
Why are surface waves (Love and Rayleigh) often the most destructive?
They travel slowly near the surface and produce large ground displacements, causing significant damage to buildings and infrastructure.
How can subduction zones produce very deep earthquakes?
As the oceanic plate subducts into the mantle, it stays brittle at depth, causing deep-focus quakes up to about 700 km below the surface.
Why are earthquakes at mid-ocean ridges typically small?
Because the brittle faults there extend only a few kilometers before magma upwelling and new crust formation occur, limiting quake magnitude.
What human activities can trigger earthquakes away from plate boundaries?
Large dam construction, mining, fracking, and nuclear weapons testing can induce seismic activity.
List two primary hazards of earthquakes.
Ground shaking and surface rupture (or ground failure).
Name a secondary hazard that can result from earthquake activity.
Soil liquefaction, landslides, mudflows (lahars), or tsunamis.
How might earthquakes lead to landslides?
Seismic shaking destabilizes slopes, triggering rockfalls, debris flows, or large-scale slope failures.
What is liquefaction and why is it dangerous?
It occurs when water-saturated soil temporarily loses strength under shaking, causing buildings or structures to sink or tilt.
What are some impacts of ground shaking on communities?
Loss of life, building collapse, disruption of utilities, and potential fires from broken gas lines or damaged electrical infrastructure.
How do hazard-event profiles (frequency, magnitude, areal extent, etc.) help in understanding earthquakes?
They allow comparison of different hazard events, guiding preparedness, risk assessment, and response strategies.
