Knowledge Organiser: Tectonic Hazards

Lithosphere — Earth's rigid outer layer, divided into tectonic plates
Subduction — oceanic plate forced beneath continental plate at destructive margin
Focus — underground origin point of earthquake energy release
Epicentre — surface point above the focus
Vulnerability — susceptibility to harm (poverty, building quality, terrain, governance)
Preparedness — actions taken before a hazard to reduce impact
Pyroclastic flow — fast-moving superheated gas, ash and rock (up to 700 km/h)
Lahar — volcanic mudflow; continues years after eruption

Magnitude 8.8 Mw — one of the largest ever recorded
Destructive margin: Nazca Plate subducting under South American Plate
~550 deaths; $30 billion damage; 2 million displaced
Tsunami hit coastal towns (Constitución, Dichato)
Low deaths due to: strict building codes since 1960, GDP ~$10,000, effective governance
$8.4 billion reconstruction plan; largely complete within 3–4 years

Magnitude 7.8 Mw — 32× less energy than Chile
Collision margin: Indian Plate colliding with Eurasian Plate
~9,000 deaths; $10 billion damage (~50% of GDP); 2.8 million displaced
600,000+ houses completely destroyed; UNESCO heritage sites collapsed
High deaths due to: unreinforced brick/stone buildings, GDP ~$700, remote terrain, limited services
Recovery extremely slow; families still in temporary shelters 3 years on

Bigger magnitude ≠ more deaths — vulnerability is the key variable
Always compare Chile (HIC) and Nepal (LIC) with specific statistics; alternative LIC example: Haiti 2010 (7.0 Mw, ~316,000 deaths — covered fully in Natural Hazards Overview topic)
Three margin types: Destructive (earthquakes + volcanoes), Collision (earthquakes only), Conservative (earthquakes only)
Volcanoes also form at hotspots (Hawaii) and constructive margins (Iceland)
Level 3 answers need: named case study + specific evidence + supported judgement about WHY
CLEVER framework: Context → Location → Effects → Vulnerability → Emergency response → Rebuilding

Confusing focus and epicentre: The focus is underground where energy is released; the epicentre is directly above it on the surface — use both terms correctly in describe questions
Saying all plate margins cause volcanoes: Collision margins only produce earthquakes, not volcanoes — volcanoes need subduction or constructive margins (or hotspots)
Using one case study without comparison: AQA tectonic questions reward comparison — always use Chile (HIC, 8.8 Mw, ~550 deaths) AND Nepal (LIC, 7.8 Mw, ~9,000 deaths) to explain why development matters
Describing effects without explaining causes: Don't just list "buildings collapsed" — link to the specific vulnerability (unreinforced stone buildings in Nepal, GDP ~$700) to explain WHY the impact was severe

Tectonic Hazards, Knowledge Organiser