Earthquakes: primary and secondary effects
Two earthquakes of similar magnitude can produce completely different death tolls. The difference is rarely the shaking itself: it is the buildings, the ground, the warning and the money.
Part of your national curriculum
- Human and physical geography: Understand tectonic processes and hazards, including earthquakes and volcanic activity
- Geographical skills and fieldwork: Interpret and analyse a range of quantitative and qualitative data, including statistical data on trends and relationships between geographical phenomena
Lesson overview
What you'll learn in this lesson
Distinguish primary from secondary effects and explain why impacts differ between places.
Key learning points
- • How an earthquake works
- • Primary effects
- • Secondary effects
- • Why the same magnitude does different damage
This lesson at a glance
- 25 minutes
- 21 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 21
Visual introductionPicture this
Earthquakes: primary and secondary effects
Two earthquakes of similar magnitude can produce completely different death tolls. The difference is rarely the shaking itself: it is the buildings, the ground, the warning and the money.
In a nutshell
Distinguish primary from secondary effects and explain why impacts differ between places.
Learning cycle
Part 2 of 21
Learning cycle 1 of 2
Part 1 · How an earthquake works
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 21
Learn
How an earthquake works
Stress builds where plates lock, then releases suddenly. Energy radiates from the focus, the point underground where the rock breaks, and the point directly above on the surface is the epicentre. Shallow focus earthquakes lose less energy on the way up, so they shake the surface hardest. Magnitude on the moment magnitude scale is logarithmic: each whole number is roughly 32 times more energy.
Reset break
Part 4 of 21
Pause
That's sitting 1 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 5 of 21
Learn
Primary effects
Primary effects happen the moment the ground shakes: buildings and bridges collapse, roads crack, pipes and power lines break, and people are killed or injured by falling structures. These are direct, immediate and caused by the shaking itself.
Quick check
Part 6 of 21
Quick check
Part 7 of 21
Reset break
Part 8 of 21
Pause
That's sitting 2 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 9 of 21
Learning cycle 2 of 2
Part 2 · Secondary effects
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 10 of 21
Learn
Secondary effects
Secondary effects follow on: fires from ruptured gas mains, tsunami if the sea floor is displaced, landslides on steep saturated slopes, disease from broken sewers and contaminated water, homelessness, school closures and lost income. Secondary effects often kill more people and last far longer than the shaking, which is why they dominate a good answer on impacts.
Explore the idea
Part 11 of 21
Learn
Why the same magnitude does different damage
Compare a magnitude 7 in a high income country with one in a low income country. Building codes, enforced construction quality, emergency services, hospital capacity, insurance and early warning all reduce deaths. Population density, time of day, ground type (soft sediment amplifies shaking, a process called liquefaction) and distance from the epicentre matter too. Wealth is not the only factor, but it buys most of the protections.
Reset break
Part 12 of 21
Pause
That's sitting 3 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 13 of 21
Quick check
Part 14 of 21
Explore the idea
Part 15 of 21
Worked example
Worked answer: explain why deaths from earthquakes are usually higher in lower income countries (6 marks)
Buildings are often constructed without enforced aseismic codes, so unreinforced concrete and masonry collapse onto occupants during the primary shaking (2). Emergency response is slower because there are fewer trained search and rescue teams, less heavy equipment and damaged roads, so people trapped in rubble die before they are reached (2). Hospitals are already stretched and may themselves collapse, and broken water and sewer pipes spread disease in temporary camps, adding secondary deaths in the weeks afterwards (2). Each pair of marks is one developed chain, not two separate statements.
Reset break
Part 16 of 21
Pause
That's sitting 4 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 17 of 21
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Challenge round
Part 18 of 21
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
____ effects happen the moment the ground shakes: buildings and bridges collapse, roads crack, pipes and power lines break, and people are killed or injured by falling structures.
____ effects often kill more people and last far longer than the shaking, which is why they dominate a good answer on impacts.
Challenge round
Part 19 of 21
Game · Recall cards
Why can oceanic crust sink beneath continental crust?
Card 1 of 4
Mastery quiz
Part 20 of 21
Marked quiz
End of lesson quiz: Earthquakes: primary and secondary effects
4 questions, marked with the reasoning shown. No timer.
1. Why can oceanic crust sink beneath continental crust?
2. Which is the strongest single piece of evidence for sea-floor spreading?
3. What does slab pull describe?
4. Why is Hawaii volcanic despite sitting far from a plate margin?
Lesson round-up
Part 21 of 21
Lesson round-up
Ready when you are
Quiz score
Not sat
Games
Not played
Points this lesson
0
Best run
0 in a row
Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?
Ask LunaPart 1 of 21 · Watch & discover
How this is going
- Not looked at yet
Understand tectonic processes and hazards, including earthquakes and volcanic activity
- Not looked at yet
Interpret and analyse a range of quantitative and qualitative data, including statistical data on trends and relationships between geographical phenomena