Earthquakes and tsunamis

Question 1

What is an aftershock

Answer 1

An aftershock is a smaller earthquake that occurs after a previous large earthquake, in the same area of the main shock.

Question 2

What is an earthquake?

Answer 2

a sudden violent shaking of the ground, typically causing great destruction, as a result of movements within the earth’s crust or volcanic action.

Question 3

What is an Epicentre?

Answer 3

the point on the earth’s surface vertically above the focus of an earthquake.

Question 4

What is the Elastic Rebound Theory?

Answer 4

an explanation for how energy is spread during earthquakes. As rocks on opposite sides of a fault are subjected to force and shift, they accumulate energy and slowly deform until their internal strength is exceeded.

Question 5

What is a faultline?

Answer 5

line determined by the intersection of a geological fault and the earth’s surface

Question 6

What is a focus?

Answer 6

The location where the earthquake begins (underground). The ground ruptures at this spot, then seismic waves radiate outward in all directions.

Question 7

What is a magnitude?

Answer 7

a number that characterizes the relative size of an earthquake.

Question 8

What is a mega thrust?

Answer 8

A sudden slip along a fault between a subducting and an overriding plate, resulting in a major earthquake.

Question 9

What is the Mercalli Scale?

Answer 9

a twelve-point scale for expressing the local intensity of an earthquake, ranging from I (virtually imperceptible) to XII (total destruction).

Question 10

What is a minor shock?

Answer 10

an earthquake that occurs before a larger seismic event (the mainshock) and is related to it in both time and space.

Question 11

What is the Richter Scale?

Answer 11

A logarithmic scale used to express the amount of energy released by an earthquake. Its values typically fall between 0 and 9

Question 12

What is a seismic wave?

Answer 12

a wave of energy that is generated by an earthquake or other earth vibration and that travels within the earth or along its surface.

Question 13

What is a seismograph?

Answer 13

an instrument that measures and records details of earthquakes, such as force and duration.

Question 14

What is a tsunami?

Answer 14

giant waves caused by earthquakes or volcanic eruptions under the sea.

Question 15

2) Why do Earthquakes happen?

Answer 15

Firstly, they can be linked to explosive volcanic eruptions; they are in fact very common in areas of volcanic activity where they either proceed or accompany eruptions.

Secondly, they can be triggered by Tectonic activity associated with plate margins and faults. The majority of earthquakes world wide are of this type.

Question 16

What is the origin of an earthquake?

Answer 16

The origin of the earthquake the focus.

Since this is often deep below the surface and difficult to map, the location of the earthquake is often referred to as the point on the Earth surface directly above the focus. This point is called the epicentre.

Question 17

What determines the extent of the damage caused?

Answer 17

The strength, or magnitude, of the shockwaves determines the extent of the damage caused.

Question 18

What two main scales exist for defining the strength?

Answer 18

Two main scales exist for defining the strength, the Mercalli Scale and the Richter Scale.

Question 19

What is meant by: ‘Earthquakes are three dimensional events’?

Answer 19

the waves move outwards from the focus, but can travel in both the horizontal and vertical plains.

Question 20

What are tectonic earthquakes?

Answer 20

Tectonic earthquakes are triggered when the crust becomes subjected to strain, and eventually moves.

The theory of plate tectonics explains how the crust of the Earth is made of several plates, large areas of crust which float on the Mantle.

Since these plates are free to slowly move, they can either drift towards each other, away from each other or slide past each other. Many of the earthquakes which we feel are located in the areas where plates collide or try to slide past each other.

Question 21

What does the theory of plate techniques explain?

Answer 21

The theory of plate tectonics explains how the crust of the Earth is made of several plateslarge areas of crust which float on the Mantle.

Since these plates are free to slowly move, they can either drift towards each other, away from each other or slide past each other. Many of the earthquakes which we feel are located in the areas where plates collide or try to slide past each other.

Question 22

Which theory explains the process of these earthquakes?

Answer 22

The process which explains these earthquakes, known as Elastic Rebound Theory