Seismicity

Question 1

What is the definition of an earthquake

Answer 1

• when there is a slow build up of stress within the rocks, there is a sudden release where parts of the surface experience an intense shaking motion that lasts between a few seconds and a few minutes

Question 2

What is the focus

Answer 2

• the point within the crust where the pressure release occurs

Question 3

What are the different depths that the focus can be located at

Answer 3

• shallow: 0-70km deep- greatest damage
• intermediate: 70-300km
• deep: 300-700km

Question 4

What are fault lines

Answer 4

• cracks in the earth which are small

Question 5

What are seismic waves

Answer 5

• parts of the crust are forced to move in opposite directions
• huge masses get stuck but the force of them continues
• building up stress
• strain overcomes friction and the rocks move
• releasing large amounts of energy
• energy is transferred to surrounding rocks travelling through Them as seismic waves

Question 6

Seismic shock waves characteristics

Answer 6

• highest level of energy at the focus

- energy decreases as the waves spread outwards

Question 7

What is the epicentre

Answer 7

• the place on the earths surface immediately above the focus
• receives highest amount of energy
• potentially hazardous location

Question 8

How are seismic waves measured

Answer 8

• seismometer

- tell us the internal structure of the earth

Question 9

What are the three main types of seismic waves

Answer 9

• primary
• secondary
• surface

Question 10

What are primary seismic waves

Answer 10

• fastest and move earth backwards and forwards

- travel better in liquids and solids

Question 11

What are secondary seismic waves

Answer 11

• travel half the speed of p waves
• move sideways
• shake the earth at right angles to the direction of travel
• cannot move through liquids
• do more damage than p waves

Question 12

What are surface waves

Answer 12

• travel the slowest
• nearest to the ground
• most destructive
• love waves- make the ground move up and down
• Raleigh waves- complex rolling motion

Question 13

Distribution of earthquakes

Answer 13

• not evenly distributed
• broad uneven belts
• majority of earthquakes relate to plate movement
• found along plate boundaries
• most powerful- destructive plate margin: frequent shallow to deep focus
• constructive: submarine often distant to people
• conservative: series of faults

Question 14

How is human activity the cause of some earthquakes

Answer 14

• minor earthquakes
• building large reservoirs- water puts pressure on the rocks
• deep mining work

Question 15

What is the magnitude

Answer 15

• amount of energy released by an event

- measured on the Richter scale

Question 16

What is the Richter scale

Answer 16

• logarithmic scale
• ## each unit represents a 10 fold increase in stress and a 30 fold increase in release of energy

Question 17

What is the seconds scale used to measure earthquakes

Answer 17

• mercalli scale
• measures intensity of the event and the impact
• 12 point scale
• level1- detected but felt by few people
• level12- total destruction

Question 18

What is the frequency

Answer 18

• • varies between seismically active regions

Question 19

What are aftershocks

Answer 19

• follow on from the main event and May last for months afterwards
• generated from the earth settling back after the disruption
• some are significant

Question 20

What is the initial effect of an earthquake

Answer 20

• ground shaking

- how sever depends on the magnitude

Question 21

What are the consequences from this initial effect

Answer 21

• people are buried under buildings

- many more dying in fires, chaos and confusion

Question 22

What does the earthquake depend on for how sever it will be

Answer 22

• magnitude and depth
• geological conditions
• distance from epicentre
• population density
• time of day
• design and strength of buildings

Question 23

What are some secondary effects of an earthquake

Answer 23

• soil liquefaction: soils with high water contents lose their mechanical strength and start to become like a fluid
• landslides: slope failure as a result of the shaking: further deaths and injury
• tsunamis: giant sea wave generated by a shallow/0-focus underwater earthquake

Question 24

What are the long term effects of an earthquake

Answer 24

• higher unemployment as not all businesses recover
• repair of build pings may take months or years
• longer term illness/lower life expectancy
• loss of farmland and food production
• permanent disruption to natural drainage patterns

Question 25

What is a tsunami

Answer 25

• giant sea wave
• generated by seismic activity
• caused by ocean floor earthquakes

Question 26

Characteristics of a tsunami

Answer 26

• open seas- long wavelength and a low wave height and they travel really quickly
• on reaching shallow waters they rise rapidly in height

Question 27

When a tsunami reaches the land the effects will depend on

Answer 27

• height of the wave and the distance it has traveled
• length of the event
• extent to which warnings were given
• coastal physical geography
• coastal landuse and population density

Question 28

What are the methods used to try and predict an earthquake

Answer 28

• seismic records: studying patterns of earthquakes and using them to predict the next one: seismometer
• radon gas emissions: radon is an inert gas that is released from rocks such as granite at a faster rate when they are fractured or deformed
• ground water: deformation of the ground can cause water levels to rise or fall

Question 29

Examples of protection from earthquakes

Answer 29

• better evacuation routes
• fire resistant buildings
• building strategies such as only having one story buildings
• keep supplies on slate such as water and blankets and food - land use planning to identify the places at most risk and move them
• some insurance companies are willing to dedicate earthquake damage control

Question 30

How do people protect from earthquakes

Answer 30

• making buildings more resistant
• raising public awareness
• improving earthquake prediction.

Question 31

Give examples of a building which has been lrotected by an earthquakes

Answer 31

• shorter buildings: Shake less
• open areas where people can assemble if evacuated, a.so avoids the domino effect
• steel frames which can sway during earth movement
• raids so the services can get there easily