Geol. 1403/Cook ch.8

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GEOL
Chapter 8
earthquakes
updated 2 years ago by Devalon_N_Burk
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geology, science
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1

The earth's magnetic field originates by ____.

weak electrical currents associated with fluid motions in the outer core.

2

When an earthquake occurs, energy radiates in all direction from its source. The source is also referred to as ____.

focus

3

Which one of the following statements is correct?

a) P-waves travel through solids; S-waves do not

b) P and S waves travel through liquids, but P-waves do not travel through solids.

c) S-waves travel through solids and P-waves travel through liquids.

d) P and S waves travel through liquids, but S-waves do not travel through solids.

S-waves travel through solids and P-waves travel through liquid

4

____ have the highest velocities.

primary (P) waves

5

What is true regarding tsunamis?

They occur in the open ocean, wavelengths are many miles or kilometers apart and wave heights are only a few feet.

6

The amount of destruction caused by earthquake vibrations is affected by ____.

design of structures, intensity and duration of vibrations, and the nature of the surface material.

7

On a typical seismogram, ____ will show the highest amplitudes.

surface waves

8

Major earthquakes are often followed by somewhat smaller events known as ____.

aftershocks

9

The ____ magnitude scale is a measure of the energy released. It does not directly measure the extent of building damage.

Richter

10

The instrument that records earthquake events is termed a ____.

seismograph

11

____ is the maximum possible damage design on the Mercalli scale.

XII

12

The position on earth's surface directly above the earthquake source is called the____.

epicenter

13

The mechanism by which rocks store and eventually release energy in the form of an earthquake is termed ____.

elastic rebound

14

Overall, this type of seismic wave is the most destructive.

surface wave

15

Approximately how much more energy is released in a 6.5 Richter magnitude earthquake than in one with 5,5 magnitude?

30 times

16

P-waves ____.

are faster than S-waves and surface waves

17

The Mercalli Scale is a scale from ____.

I to XII that rates the structural damage due to an earthquake.

18

The distance between a seismological recording station and the earthquake source is determined from the ____.

arrival times of P and S waves.

19

The Richter magnitude of an earthquake is determined from the ____.

amplitude of the surface waves

20

What best characterizes tsunamis?

They have relatively small amplitudes compared to their very long wavelengths.

21

The ____ earthquake was accompanied by extensive fire damage.

San Francisco, 1906

22

___ refers to the tendency for a foundation material to lose its internal cohesion and fail mechanically during earthquake shaking.

liquefaction

23

The record of an earthquake obtained from a seismic instrument is a(n) ____.

seismogram

24

Most of our knowledge about earth's interior comes from ____.

seismic waves

25

Which one of the following statements about the crust is not true.

a) it is the thinnest of the major subdivision

b) it is the thickest where prominent mountains exist

c) ocean crust is enriched in potassium, sodium, and silicon

d) continental rocks are compositionally different than oceanic rocks.

oceanic crust is enriched in potassium, sodium, and silicon

26

The dense core of earth is thought to consist predominantely of ____.

iron

27

The lithosphere is defined as ____.

a rigid layer of crustal and mantle material

28

The average composition of the oceanic crust is thought to approximate that of ____.

basalt

29

The average composition of the continental crust most closely approximated that of ____.

granite

30

T/F - Tsunamis are caused by sudden displacement of large volumes of seawater.

true

31

T/F - The Richter earthquake magnitude scale is based on the total amount of energy released by the earthquake.

true

32

T/F - The epicenter of an earthquake is on the surface of the earth directly above the focus.

true

33

T/F - Unconsolidated, water-saturated soils or sediments provide good foundation materials for buildings and other structures.

false

34

T/F - Oceanic crust is mainly basaltic in composition; the mantle is more like the igneous rock periodotite in chemical composition.

true

35

T/F - Continental crust is generally thicker than oceanic crust.

true

36

T/F - The crust and mantle are solids; the inner core is thought to be solid.

true

37

T/F - the mantle is composed mainly of metallic iron with small amounts of magnesium silicate minerals.

false

38

T/F - Earthquakes result from the sudden release of elastic strain energy previously stored in rocks surrounding a zone of fault movement.

true