Seismic Activity and Its Management

What Seismic Activity and Its Management covers

Seismic activity and its management is examined in Unit A2 1, Physical Processes, Landforms and Management. It covers the nature of a seismic event, seismic waves: P, S and L waves, seismic shaking and its impacts, liquefaction, tsunamis, attempts to predict seismic events, preparing for seismic activity and responding to seismic activity and evaluating the response.

The 8 subtopics

Each one has its own page.

• The nature of a seismic eventFocus and the epicentre of an earthquake and magnitude and the intensity of an earthquake.Open →
• Seismic waves: P, S and L wavesThree types of seismic wave, P wave and S wave.Open →
• Seismic shaking and its impactsSeismic shaking and socio-economic impacts of a major earthquake.Open →
• LiquefactionMechanism by which liquefaction occurs and sand boils and lateral spreading.Open →
• TsunamisHow an earthquake generates a tsunami and what happens to a tsunami as it approaches the coast.Open →
• Attempts to predict seismic eventsEarthquake forecasting and earthquake prediction, seismic gap theory and record of attempted earthquake predictions.Open →
• Preparing for seismic activityWhat preparation means when prediction is impossible: aseismic design, the engineering used on large buildings, retrofitting, enforced building codes, land-use planning and tsunami defence.Open →
• Responding to seismic activity and evaluating the responseThe first hours and the critical seventy-two, the priorities of the following weeks, what long-term recovery involves, and the problems international aid brings as well as solves.Open →

What you need to know

Answer each one before you reveal it.

Take Seismic Activity and Its Management further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Focus vs Epicentre

  Focus: the point underground where an earthquake originates. Epicentre: the point on the surface directly above it.

• Liquefaction vs Tsunami

  Liquefaction: saturated sediment losing its strength and behaving as a liquid when shaken. Tsunami: a sea wave generated by displacement of the ocean floor.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What actually happens when an earthquake occurs?

   Model answer

   Two blocks of rock that have been locked together along a fault suddenly slip past each other. Plate movement has been steadily loading the rock with stress, and because friction prevents the fault from sliding freely the rock deforms elastically, storing the strain like a bent spring. When the accumulated stress exceeds the frictional resistance the fault ruptures, the rock snaps back towards its original shape, and the stored energy is released as seismic waves that radiate outwards through the Earth. This build-up and sudden release is called elastic rebound.

2. 2

   Distinguish between the focus and the epicentre of an earthquake.

   Model answer

   The focus, or hypocentre, is the point underground where the rupture begins and from which the seismic waves are released. The epicentre is the point on the Earth's surface directly above the focus. The distinction matters because damage depends on distance from the focus: a shallow focus puts the surface close to the source and produces intense local shaking, whereas a deep focus of the same magnitude produces weaker shaking spread over a wider area.

3. 3

   How are earthquakes classified by focal depth, and where does each type occur?

   Model answer

   Shallow-focus earthquakes have foci within about 70 km of the surface and occur at all margin types, including constructive, conservative and collision margins where there is no descending slab. Intermediate-focus earthquakes have foci from about 70 to 300 km deep and deep-focus earthquakes from about 300 to 700 km, and both are confined to destructive margins because only there is cold, brittle lithosphere carried down into the mantle. Shallow-focus events are much the most common and cause the great majority of damage.

4. 4

   Why does a shallow-focus earthquake usually cause more damage than a deeper one of the same magnitude?

   Model answer

   Because seismic waves lose energy as they travel, spreading out and being absorbed by the rock they pass through. A focus 10 km below a city delivers waves that have travelled only a short distance, so they arrive with high amplitude and shake the ground violently over a small area. A focus 300 km deep delivers waves that have already dissipated much of their energy before reaching the surface, so the shaking is weaker, though it is felt across a much wider region.

5. 5

   What is an aftershock, and why do aftershocks matter for management?

   Model answer

   An aftershock is a smaller earthquake following the main shock on the same fault or nearby, caused by the readjustment of rock to the new stress distribution. Aftershocks can continue for weeks or months, becoming less frequent over time, and occasionally one is nearly as large as the main event. They matter because they collapse buildings already weakened by the main shock, killing rescuers and survivors, they trigger further landslides, and they force repeated evacuation of shelters, so search and rescue and damage assessment must be carried out under continuing risk.

6. 6

   Distinguish between the magnitude and the intensity of an earthquake.

   Model answer

   Magnitude measures the energy released at the source, so a given earthquake has only one magnitude, calculated from the amplitude recorded on seismographs. It is measured on a logarithmic scale, so each whole step upwards represents about a thirty-fold increase in energy released. Intensity measures the strength of shaking and the damage experienced at a particular place, so a single earthquake has many intensity values, high near the epicentre and decreasing outwards. Intensity is what determines the human impact, and it depends on ground conditions and building quality as well as on magnitude.

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Six ways to work the same material.

Seismic Activity and Its Management revision questions

What does Seismic Activity and Its Management cover in CCEA A-Level Geography?

8 subtopics: the nature of a seismic event, seismic waves: p, s and l waves, seismic shaking and its impacts, liquefaction, tsunamis, attempts to predict seismic events, preparing for seismic activity and responding to seismic activity and evaluating the response. Each one has its own page with questions and model answers.

How is Seismic Activity and Its Management organised?

By the CCEA 3910 specification, subtopic by subtopic, so it matches the order you are taught it in.