- Distinguish between the hypocenter and the epicenter of an earthquake.
The hypocenter is the actual origin of the earthquake. It is the point where rock slippage occurs along a fault. The epicenter is the point on the Earth’s surface that is directly above the hypocenter.
- At what depth do most earthquakes occur?
Most earthquakes occur at a depth of less than 70 kilometers (43 miles) below the Earth’s surface.
- Why don’t earthquakes occur below a depth of 700 kilometers (435 miles)?
Rock at these depths is under such pressure and is so hot that it deforms and flows rather than breaking.
- What key property of P and S waves allows geologists to determine the location of an earthquake?
P and S waves travel at different speeds. The difference between their arrival times is directly related to how far way the earthquake’s epicenter is.
- Why is it necessary to have three seismic receiving stations in order to accurately locate the epicenter of an earthquake?
The signal from one station situates the earthquake anywhere on a circle around the station. Signals from two stations narrows the location down to two locations where the signal circles from each station overlap. A third station’s signal is necessary so that the signal circles overlap at only one unique point.
- Distinguish between the Mercalli scale and the Richter scale.
The Mercalli scale is a qualitative scale based on intensity. It is based on a visual description of the damage caused by an earthquake. The Richter scale is a quatitative scale and is based in magnitude. The magnitude is determined by measuring the largest amplitude of the seismic waves.
- What are some drawbacks to using the Mercalli scale?
Since it is qualitative, there can be fair element of subjectivity in it. Factors such as building design, population density, and the nature of surface materials can have a great affect on the damage caused by an earthquake. In addition, the Mercalli Scale cannot be used on earthquakes that occur under oceans or in uninhabited areas.
- The magnitude scale is a logarithmic scale. What does this mean?
This means that for every number that you go up in the scale, the actual amplitude of the seismic wave has increased by 10.