Earthquakes

Question 1

Give a description of earthquakes

Answer 1

Earthquakes have a spatial distribution in linear belts/clusters. They occur anywhere along plate boundaries and dd boundaries, 90% occur along plate boundaries

Question 2

What are earthquakes?

Answer 2

A sudden movement of the earths crust

Question 3

What is the depth of shallow, intermediate earthquakes and deep earthquakes?

Answer 3

Shallow (<70km depth)

Intermediate (70-300km)

Deep (>300)

Question 4

Why do some earthquakes occur away from boundaries?

Answer 4

Reactivation of old fault lines

Question 5

Longer pressure builds up…

Answer 5

…stronger the earthquake

Question 6

Where do rocks obtain the strength?

Answer 6

Interlocking and cementation of grains or crystals of which they are built

Question 7

What are earthquakes meander using?

Answer 7

A seismograph

Question 8

What do high peaks and troughs show on a seismograph?

Answer 8

Worse or more violent earthquake

Question 9

How many violent earthquakes does the world experience on average each year?

Answer 9

20-50

Question 10

What is the magnitude of a earthquake measured on?

Answer 10

A Richter scale

Question 11

What is the scale of the Richter scale?

Answer 11

0-9

Question 12

On a Richter scale, and earthquake measured at 6 is how many times greater than a quake measured at 5?

Answer 12

Ten times more powerful

Question 13

What instrument is used to measure the effects of the quake on people?

Answer 13

A Mercalli scale

Question 14

How many degrees of severity are present on a Mercalli scale?

Answer 14

12 degrees of severity

Question 15

What scale, abbreviated as Mw, is preferred for measuring earthquakes?

Answer 15

The moment magnitude scale

Question 16

What does the Mw use to base the severity of the earthquake?

Answer 16

Total moment release of the earthquake

Question 17

What is moment?

Answer 17

Moment is the product of the distance a fault moved and the force required to move it

Question 18

What is a logarithmic scale?

Answer 18

It means for every whole number you go up on the magnitude scale, the amplitude of the ground motion recorded by the seismograph goes up in tens

Question 19

What are the magnitudes 1 and 8 power equivalent to?

Answer 19

1- 6 ounces of TNT exploding

8- 6 million tonnes of TNT exploding

Question 20

What are shock waves?

Answer 20

Energy released by and earthquake

Question 21

What is the focus?

Answer 21

Where shockwaves are released from

Question 22

What is the epicentre?

Answer 22

The point on the surface directly above the focus where the waves are felt the strongest

Question 23

What are P waves?

Answer 23

P waves or primary waves are compression waves
They move the fastest
Compress the rock in front of them and elongate behind it (to and fro)
That can move through solids liquids and gas

Question 24

What are S waves?

Answer 24

Secondary S waves or shear waves, undulate causing an up and down and side to side motion as they roll through the earth
They can only move through a solid
Do more damage than P waves

Question 25

P and S waves travel through the interior of the earth so therefore they are...

Answer 25

Body waves

Question 26

What are L waves?

Answer 26

The surface L waves are the surface waves whose motion is restricted to near ground surface Travel more slowly than S waves

Question 27

There are two types of L waves, what are they called and there properties?

Answer 27

Love waves- vibrate at Rift angles to the direction of transmission but have no vertical displacement Rayleigh waves- have both vertical and horizontal movement in a vertical plane pointing in the direction of the transmitted wave

Question 28

Where is the point of maximum displacement of shock waves?

Answer 28

The focus

Question 29

In what year were 4 kinds of seismic waves detected?

Answer 29

1909

Question 30

Seismographs close to the epicentre picked up waves doing what?

Answer 30

P and S waves close to the epicentre moving slowly and further away P waves and S waves were moving faster

Question 31

When these shock waves meet different rock densities, what happens to the waves?

Answer 31

They are reflected and refracted

Question 32

If shock waves pass through denser rocks they?

Answer 32

Speed up

Question 33

When shock waves pass through less dense rocks they?

Answer 33

Slow down

Question 34

From the MOHO, was was detected?

Answer 34

Slower waves had travelled from the focus of the earthquake through the upper layer of the crust but, by contrast foster waves have passed through denser material in the earths core, this denser material speeded up the waves and deflected them

Question 35

So what was suggested about the earths crust due to the MOHO?

Answer 35

The change in density from 2.9g/cm3 to 3.3g/cm3 marked the boundary between the earths crust and the mantle below

Question 36

What does MOHO stand for?

Answer 36

The Mohorovicic discontinuity

Question 37

Later a shadow was found in a area between 105o and 142o, why could they not detect shock waves from within?

Answer 37

Shock waves had passed from a liquid to a solid, this S waves would stop and P waves would be refracted, this was effectively the boundary between the mantle and the core

Question 38

What are the primary earthquake effects?

Answer 38

- collapsing buildings - falling debris - roads, bridges collapsing - shock and panic - broken gas pipes - loss of water supply - loss of medical supplies - damaged communications - Broken water mains - power lines destroyed - ports destroyed - poor quality housing flattered - shock waves and ground shaking

Question 39

What are the secondary effects of a earthquake?

Answer 39

- fires - landslides and avalanches - tsunamis - diseases - economic losses - soil liquefaction - fear of future tectonic events - homelessness

Question 40

The scale of a earthquake disaster depends on...

Answer 40

- strength of the earthquake - depth of focus - nature of bedrock - building design - population distribution - wealth of country

Question 41

How do humans cause earthquakes?

Answer 41

- Rocky Mountain in Denver Colorado, injected into underlying rocks during 60's. Minor earthquakes occurred in a previously earthquake free zone, 1962-1965 700 minor quakes - underground nuclear testing, 1968, 120,000 tone bombs in Nevada triggered 30 minor earthquakes - Hoover dam, as lake filled underlying rocks were adjusted and increased over 40 km3 of water and 6000 minor earthquakes in 10 years