KEY TERMS

Question 1

abyssal plains

Answer 1

very flat areas that make up most of the ocean floor

Question 2

bathymetric map

Answer 2

a map of the seafloor created from the measurement of water depths.

Question 3

continental arc

Answer 3

a line of volcanoes sitting on a continental plate and aligned above a subducting oceanic plate near a deep sea trench.

Question 4

continental drift

Answer 4

the hypothesis developed in the early 20th century that states that the continents move about on the surface.

Question 5

convergent plate boundary

Answer 5

a location where two lithospheric plates come together

Question 6

divergent plate boundary:

Answer 6

a location where two lithospheric plates spread apart.

Question 7

echo sounder

Answer 7

a device that uses sound waves to measure the depth to the seafloor.

Question 8

epicenter

Answer 8

he point on the Earth’s surface directly above an earthquake’s focus, which is the place where the ground breaks.

Question 9

fault

Answer 9

a fracture along which there has been movement of rock on one or both sides

Question 10

hotspot

Answer 10

plume of hot material that rises through the mantle and can cause volcanoes

Question 11

intraplate activity

Answer 11

geologic activity such as volcanic eruptions and earthquakes that takes place away from plate boundaries.

Question 12

magnetometer

Answer 12

instrument that measures the intensity of a magnetic field

Question 13

mid-ocean ridge:

Answer 13

the location on the seafloor where magma upwells and new seafloor forms. Mid-ocean ridges are the dominant feature of divergent plate boundaries found in the oceans.

Question 14

Pangaea

Answer 14

in early geologic time, a supercontinent that incorporated almost all the landmasses on Earth.

Question 15

plate

Answer 15

a slab of the earth’s lithosphere that can move around on the planet’s surface.

Question 16

plate boundary

Answer 16

a location where two plates interact.

Question 17

plate tectonics

Answer 17

the theory that the Earth’s surface is divided into lithospheric plates that move on the planet’s surface. The driving force behind plate tectonics is mantle convection.

Question 18

seafloor spreading

Answer 18

the mechanism for moving continents. The formation of new seafloor at spreading ridges pushes lithospheric plates on the Earth’s surface.

Question 19

subduction

Answer 19

the sinking of one lithospheric plate beneath another.

Question 20

subduction zone

Answer 20

the area where two lithospheric plates come together and one sinks beneath the other.

Question 21

transform plate boundary

Answer 21

the type of plate boundary where two plates slide past one another.

Question 22

trench

Answer 22

a deep hole in the seafloor where subduction takes place. Trenches are the deepest places on Earth.

Question 23

anticline

Answer 23

A fold that arches upward, in which the older rocks are in the center and the younger rocks are at the outside.

Question 24

compression

Answer 24

Stresses that push toward each other. This causes a decrease in the space a rock takes up.

Question 25

confining stress:

Answer 25

The stress due to the weight of material above a buried object. Confining stress reduces volume but causes no deformation.

Question 26

deformation

Answer 26

The change of shape that a rock undergoes when it has been altered by stresses. Also called strain.

Question 27

elastic deformation

Answer 27

A strain that temporarily alters the shape of rocks.

Question 28

elastic rebound theory

Answer 28

The theory that earthquakes occur when rocks break and snap back to their original position after being deformed elastically until they cannot deform anymore.

Question 29

epicenter

Answer 29

The point on the earth’s surface that lies above an earthquake’s focus

Question 30

fault zone

Answer 30

A network of related faults.

Question 31

fracture

Answer 31

Cracks or breaks in rocks caused by stress.

Question 32

focus

Answer 32

he point where rocks rupture during an earthquake.

Question 33

fold

Answer 33

A bend in a set of rocks caused by compression

Question 34

joint

Answer 34

A break in rock caused by stresses along which there is no movement.

Question 35

liquefaction

Answer 35

Clay, silt, and sand saturated with water become like quicksand, lose their strength and behave more like a liquid than a solid.

Question 36

Mercalli intensity scale

Answer 36

This scale measures the effects of earthquakes seen on the land surface and felt by humans. It measures from I-XII.

Question 37

moment magnitude scale

Answer 37

This is a logarithmic scale that measures the total energy released by an earthquake. An increase of one integer indicates a 30-fold increase in energy released. An increase of two integers indicates a 1,000-fold increase in energy released.

Question 38

monocline:

Answer 38

A bend in a set of rocks that causes them to be inclined relative to the horizontal.

Question 39

normal fault:

Answer 39

A fault in which the rocks above the fault plane, or hanging wall, move down relative to the rocks below the fault plane.

Question 40

plastic deformation:

Answer 40

A strain that permanently alters the shape of rocks.

Question 41

primary waves (P-waves)

Answer 41

P-waves are body waves that are the first to arrive at a seismometer because they are the fastest. P-waves are longitudinal waves that travel through solids, liquids, and gases.

Question 42

retrofitting: