# Q1D · Discuss in detail the three causes resulting in earthquakes with neat sketches.

Subject: Disaster Management

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/dm/#tee/papers/paper-2023-07-05/q1d

Canonical: https://deep-learning-study-room.vercel.app/read/dm/tee/papers/paper-2023-07-05--q1d/

Actual older TEE paper · 100 marks · Q1 compulsory; any four of Q2–Q7

### Q1D. Discuss in detail the three causes resulting in earthquakes with neat sketches. [5 marks]

#### Answer

**Definition.** An earthquake is ground shaking caused by a sudden release of stored energy in the Earth. Most destructive earthquakes result from sudden slip on a fault, sending out seismic waves.

## Build the idea one step at a time

1. The outer rigid Earth is divided into **tectonic plates**. Their slow relative movement loads rocks with stress.
2. A **fault** is a fracture or zone of fractures along which rock blocks can move. Friction can temporarily lock the blocks.
3. The rocks deform and store elastic energy. When stress exceeds the resistance to slip, the fault moves suddenly. This is the elastic-rebound explanation.
4. Energy travels outward as **seismic waves**. These cause shaking at the surface. The waves carry the released energy; they are not the original tectonic cause.

Swipe across the diagram to read its labels ↔

![Focus, epicentre and a slipping fault](https://deep-learning-study-room.vercel.app/dm/fig/earthquake.46adac0128.svg)

Diagram: Focus, epicentre and a slipping fault. Labels: Focus, epicentre and a slipping fault | Focus, epicentre and a slipping fault | Fault plane | Epicentre: surface above focus | Focus: rupture begins within Earth | Surface | Waves spread from the source; shaking effects vary with local conditions.

Focus is inside the Earth; epicentre is the surface point directly above it. Fault rupture can extend far beyond the starting point.

| Word | Meaning |
| --- | --- |
| Focus / hypocentre | The point inside the Earth where rupture begins. |
| Epicentre | The point on the surface vertically above the focus. |
| Focal depth | Vertical distance from the surface to the focus. |
| Foreshock / mainshock / aftershock | Smaller preceding event, largest event in a sequence, and subsequent events; “foreshock” is usually identified retrospectively. |

Swipe across the diagram to read its labels ↔

![Three plate-boundary movements](https://deep-learning-study-room.vercel.app/dm/fig/boundaries.8b6b55444b.svg)

Diagram: Three plate-boundary movements. Labels: Three plate-boundary movements | Three plate-boundary movements | Convergent | Divergent | Transform | Separation / rising material | Compression | Extension | Shear

Convergent: move together. Divergent: move apart. Transform: slide past.

Most earthquakes result from sudden fault slip releasing stored strain. Volcanic processes, collapse and certain human activities can also generate earthquakes; seismic waves are the released energy travelling outward, not the underlying tectonic cause.

## Three plate movements that build stress

1. **Convergence.** Plates move together, causing compression, subduction or collision. Locked faults can release stored energy suddenly.
2. **Divergence.** Plates separate and the crust extends. Faulting associated with extension can generate earthquakes.
3. **Transform motion.** Plates slide past one another. Friction can lock parts of a fault until stress overcomes resistance and slip occurs.

#### Illustrative application · A classroom earthquake illustration

A fault begins to rupture below ground at the focus. The surface point vertically above it is the epicentre. Waves spread outward and shake buildings; the damage also depends on local ground and construction. Use the labelled diagram in the earthquake chapter to connect these terms.