What three general characteristics account for the density ...

[jake]

What three general characteristics account for the density differences among the concentric layers of Earth?

Question 2

Explain two measures of an earthquake's strength that are commonly used by seismologists.

[gasdhashg]

Answer to Question 1

Earth consists of three concentric layers: the core, the mantle, and the crust. This orderly division results from density differences between the layers as a function of variations in composition, temperature, and pressure.

Answer to Question 2

Intensity is a subjective or qualitative measure of the kind of damage done by an earthquake as well as people's reaction to it. Geologists use intensity as a rough approximation of the size and strength of an earthquake. The most common intensity scale used in the United States is the Modified Mercalli Intensity Scale. The intensity value given for each affected area is the maximum intensity that the earthquake produced for that area. The intensity scale provides geologists with a rough approximation of the location of the earthquake, the kind and extent of the damage done, and the effects of local geology on different types of building construction. Insurance companies still classify earthquakes on the basis of intensity.

If earthquakes are to be compared quantitatively, the Richter Magnitude Scale is used. It measures the amount of energy released and is independent of intensity. The Richter Magnitude Scale measures earthquake magnitude, which is the total amount of energy released by an earthquake at its source. It is an open-ended scale with values beginning at zero. Scientists determine the magnitude of an earthquake by measuring the amplitude of the largest seismic wave as recorded on a seismogram. Each whole number increase in magnitude represents a 10-fold increase in wave amplitude. Magnitude is now frequently given in terms of both Richter magnitude and another scale called seismic-moment magnitude.