Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
An earthquake is a sudden shaking or trembling of the Earth which lasts for a very short time, caused by disturbances deep inside the Earth's crust.
The outermost layer of the Earth, the crust, is not in one piece but is fragmented into several plates known as .
Earthquakes are primarily caused by the movement of these plates: when they brush past one another or collide, one plate goes under another, causing disturbances.
The boundaries of the plates are the weak zones where earthquakes are more likely to occur; these are known as or .
The point inside the Earth's crust where the earthquake originates is called the (or ).
The point on the Earth's surface directly above the focus is called the .
Tremors produce waves on the surface of the Earth called . These are recorded by an instrument called a .
The power of an earthquake is expressed in terms of a magnitude on a scale called the . It is a logarithmic scale, not linear.
A seismograph consists of a vibrating rod or a pendulum which begins to vibrate when tremors occur. A pen attached to the vibrating body records the seismic waves on a moving paper.
📐Formulae
💡Examples
Problem 1:
An earthquake of magnitude is recorded on the Richter scale. How many times more destructive energy does it have compared to an earthquake of magnitude ?
Solution:
The Richter scale is not linear. An increase of in magnitude means the earthquake has times more destructive energy. Since , the magnitude earthquake is times more powerful than the magnitude earthquake.
Explanation:
In the Richter scale, for every increase of unit, the amplitude of the waves increases by times, but the energy released increases by approximately (rounded to ) times. Therefore, a difference of units results in times more energy.
Problem 2:
Identify the primary parts of a seismograph and their function.
Solution:
- : Holds the instrument. 2. : Acts as a pendulum. 3. : Attached to the weight. 4. : Covered with paper.
Explanation:
When the Earth shakes, the drum moves with the ground, but the suspended weight (due to inertia) stays relatively still. This allows the pen to trace the movement of the ground (seismic waves) onto the paper on the rotating drum.