3. What are the main hazards generated by seismic activity? Flashcards
(17 cards)
What is a shallow-focus earthquake?
Earthquake with a focus less than 70 km deep.
🔹 Most common and damaging due to proximity to the surface.
🔹 Often occur at destructive and conservative boundaries.
What is a deep-focus earthquake?
Earthquake with a focus between 70 and 700 km.
🔹 Less intense surface shaking but can be widespread.
🔹 Typically found in subduction zones (e.g. destructive boundaries).
What does the Richter scale measure?
Magnitude — the energy released by an earthquake.
🔹 Logarithmic scale (each whole number = 10× increase in amplitude).
🔹 Now largely replaced by the Moment Magnitude Scale (Mw).
What does the Moment Magnitude Scale (Mw) measure?
Measures total energy released, based on fault movement and rock rigidity.
🔹 Most widely used today, especially for large quakes.
What does the Modified Mercalli Scale measure?
Measures earthquake intensity — the impact on people and structures.
🔹 Roman numerals I–XII based on observed effects.
What landforms can earthquakes create?
🔹 Escarpments: steep slopes formed when land on one side of a fault drops.
🔹 Rift Valleys: formed at divergent plate boundaries (e.g. East African Rift) where crust stretches and collapses.
What is ground shaking?
Vibrations caused by seismic waves.
🔹 Can collapse buildings and infrastructure.
What is ground displacement?
The movement of the ground along a fault line.
🔹 Can rupture roads, pipelines, and communication lines.
What is liquefaction?
When saturated ground temporarily loses strength during shaking, behaving like a liquid.
🔹 Causes buildings and vehicles to sink or tilt.
How do earthquakes trigger landslides and avalanches?
Seismic shaking destabilises slopes, especially in mountainous or deforested regions.
🔹 Can bury settlements or block rivers, causing flooding.
How do earthquakes generate tsunamis?
Sudden uplift or downthrust of the sea bed displaces water.
🔹 Large tsunamis follow undersea earthquakes or landslides.
How can earthquakes cause flooding?
Dam failures, land subsidence, or tsunami backwash can lead to widespread flooding.
What were the tectonic causes of the 2011 Japan earthquake?
🔹 Destructive (convergent) boundary: Pacific Plate subducting beneath Eurasian Plate.
🔹 9.0 Mw, shallow-focus (30 km), 130 km offshore of Honshu.
What were the primary physical impacts of the Japan earthquake?
🔹 Up to 40.5m tsunami waves travelled 10 km inland.
🔹 Fukushima nuclear meltdown after power failure.
🔹 Honshu shifted 2.4m east; 400 km coastline dropped by 0.6m.
What were the tectonic causes of the 2010 Haiti earthquake?
🔹 Conservative boundary: Caribbean Plate and North American Plate.
🔹 7.0 Mw, shallow-focus (13 km), only 25 km from Port-au-Prince.
What were the primary physical and human impacts in Haiti?
🔹 230,000 killed, 300,000 injured, 2.3 million made homeless.
🔹 Cholera outbreak; 1300 schools, all hospitals destroyed.
🔹 Pancake building collapse due to poor construction.
What hazards occurred in both case studies?
🔹 Tsunamis (Japan’s was far more severe).
🔹 Aftershocks (Japan: up to Mw 8.0; Haiti: 50+ >Mw 4.5).
🔹 Liquefaction and ground shaking in both.
🔹 Landslides and disease outbreaks (notably cholera in Haiti).
