Earthquake and tsunami hazards
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Flip to reveal answersDefine the focus of an earthquake.
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All 12 Flashcards — Earthquake and tsunami hazards
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Question
Define the focus of an earthquake.
Answer
The point **underground** where the rock ruptures and the earthquake begins.
Question
Define the epicentre.
Answer
The point on the **surface** directly above the focus.
Question
Magnitude vs intensity?
Answer
**Magnitude** = the energy released (moment-magnitude scale); **intensity** = how strongly the shaking is felt at a place, which falls with distance.
Question
Why does focus depth matter?
Answer
A **shallow** focus causes far more violent surface shaking and damage than a deep focus of the same magnitude.
Question
What is a tsunami?
Answer
A series of large sea waves caused when an undersea earthquake (or landslide) suddenly **displaces the seabed and water column**.
Question
Name four secondary earthquake hazards.
Answer
**Tsunamis, landslides, liquefaction and fires** - knock-on hazards triggered by the shaking.
Question
What is liquefaction?
Answer
Saturated, soft ground loses strength and behaves like a **liquid** when shaken hard, so buildings sink, tilt or collapse.
Question
How does secondary-hazard severity change with distance?
Answer
Most (landslides, liquefaction, fires) **weaken** with distance from the epicentre; a **tsunami** is the exception and stays destructive far away.
Question
Why do magnitude and frequency vary by place?
Answer
Mainly the **plate margin**: subduction (destructive) zones give the largest, most frequent quakes + tsunamis; constructive margins give smaller, shallow quakes.
Question
What can trigger quakes far from a plate margin?
Answer
**Human triggers** - filling large reservoirs, or deep fluid extraction/injection - can set off earthquakes away from any margin.
Question
Why did Haiti 2010 kill far more than Tohoku 2011?
Answer
Despite being a smaller quake, Haiti hit a poor, densely built city with weak buildings and no preparedness - **vulnerability**, not geophysics, drove the toll.
Question
What does a top [10] Examine answer on impacts need?
Answer
Two named events compared, two+ developed geophysical factors with data, a weighing of geophysics vs vulnerability, and a clear judgement.
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Full study notes for Earthquake and tsunami hazards
Topic 10.2 hub
Geophysical hazard risks
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