Global Distribution of Earthquakes

Earth scientists have determined that the global distribution of earthquakes is not random but follows a few relatively narrow belts that wind around Earth. Figure 9 illustrates the world distribution of earthquakes for a period of several years. Use the figure to answer questions 17 and 18.

1. With what Earth feature is each of the following earthquake belts associated?

Western and southern Pacific Ocean basin:______________________

Western South America:______________________________________

Mid-Atlantic Ocean basin:_____________________________________

2. The belts of earthquake activity follow closely the boundaries of what Earth phenomenon?

_____________________________________________________________________

The Earth Beyond Our View

The study of earthquakes has contributed greatly to Earth scientists' understanding of the internal structure of Earth. Variations in the travel times of P and S waves

as they journey through Earth provide scientists with an indication of changes in rock properties. Also, since S waves cannot travel through fluids, the fact that they are not present in seismic waves that penetrate deep into Earth suggests a fluid zone near Earth's center.

In addition to the lithosphere, the other major zones of Earth's interior include the asthenosphere, mantle, outer core, and inner core. After you have reviewed these zones and the general structure of the Earth's interior, use Figure 10 to answer questions 19-24.

3. The layer labeled A on Figure 10 is the solid, rigid, upper zone of Earth that extends from the surface to a depth of about (100, 500, 1,000) kilo-meters. Circle your answer.

a. Zone A is called the (core, mantle, lithosphere).

b. What are the approximate velocities of P and S waves in zone A?

P wave velocity:____________km/sec

S wave velocity:_____________km/sec

c. The velocity of both P and S waves (increases, decreases) with increased depth in zone A. Circle your answer. d. List the two parts of Earth's crust that are included in zone A and briefly describe the composition of each.

1)_______:_______________________________________

2) __________:_____________________________________

4. Zone B is the part of Earth's upper mantle that extends from the base of zone A to a depth of up to about (180, 660, 2,250) kilometers in some regions of Earth. Circle your answer.

a. Zone B is called the (crust, asthenosphere, core).

b. The velocity of P and S waves (increases, decreases) immediately below zone A in the upper part of zone B.

c. The change in velocity of the S waves in zone B indicates that it (is, is not) similar to zone A.

5. Zone C (which includes the lower part of zone A and zone B) extends to a depth of

_____________kilometers.

a. Zone C is called Earth's______________________

b. What fact concerning S waves indicates that zone C is not liquid?

_____________________________________________________

c. What is the probable composition of zone C?

6. Zone 13 extends from 2,885 km to about (5,100, 6,100) kilometers.

a. Zone D is Earth's ____________ __________

b. What happens to S waves when they reach zone D, and what does this indicate about the zone?

c. The velocity of P waves (increases, decreases) as they enter zone D. Circle your answer.

7. Zone E is Earth's _____________ ____________

a. Zone E extends from a depth of ______km to the________ of Earth.

b. What change in velocity do P waves exhibit at the top of zone E, and what does this suggest about the zone?

c. What is the probable composition of Earth's core?

8. Label Figure 10 by writing the name of each interior zone at the appropriate letter.

Earth's Internal Temperature

Measurements of temperatures in wells and mines have shown that Earth's temperatures increase with depth. The rate of temperature increase is called the geothermal gradient. Although the geothermal gradient varies from place to place, it is possible to calculate an average. Table 2 shows an idealized average temperature gradient for the upper Earth compiled from many different sources. Use the information in Table 2 to answer questions 25-29.