Internal Landform Processes (Tectonic Processes)
Senior 2 · Geography and Environment
Internal Landform Processes (Tectonic Processes)
Lesson 4 of 4
18 min
On the morning of 3 February 2008 an earthquake struck under Lake Kivu. In Rusizi District a church collapsed, and at least 30 people died in Rwanda and the DRC together. Earthquakes cannot yet be predicted, but their effects can be reduced by knowing where they happen and how buildings and people should respond. Western Rwanda lies in one of Africa's most earthquake-prone zones, so this is not a distant topic.
An earthquake is a sudden shaking of the ground caused by the release of energy in the Earth's crust. Rocks on either side of a fault are locked together by friction while stress builds up. When the stress becomes greater than the friction, the rocks slip suddenly, and the stored energy spreads out as seismic waves.
A seismometer detects the waves and a seismograph records them as a zig-zag line (a seismogram).
The 2008 Lake Kivu earthquake had a magnitude of 5.9. How many times larger was its recorded ground motion than that of a magnitude 3.9 tremor?
The energy difference is far larger: about 32 × 32, or roughly 1,000 times.
Earthquakes are concentrated along plate boundaries: the Pacific Ring of Fire (Japan, Chile, Indonesia), the belt from the Mediterranean through the Himalayas, the mid-ocean ridges, and the East African Rift, including the Lake Kivu region and Rwanda's western districts.
Reducing the damage: build with reinforced frames and follow building codes; avoid building on steep, loose slopes; hold drills in schools; and during shaking, drop, cover and hold on under a strong table, away from windows, then move to open ground.
Tip
Memory hook. Focus is underground; epicentre is "upon" the surface (the Greek epi means "on"). Magnitude = energy (one number per earthquake); intensity = effects (different at every place).
Solution: the focus is the point underground where the rock breaks; the epicentre is the point on the surface directly above it.
Solution: a seismograph.
Solution: 6 − 4 = 2 steps; 10 × 10 = 100 times.
Solution: it lies along the Albertine Rift, where the crust is being pulled apart along active faults.
Solution: any two of: strong, well-built classrooms; regular drills; teaching "drop, cover and hold on"; keeping exits clear; agreeing on an open assembly point.
Summary
Sources and credits
The worked example and practice items are written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
