Seismicity

Question 1

What is an earthquake

Answer 1

When there’s a small build up of stress in the earths rocks. When stress is suddenly released parts of Earth experience intense shaking lasts few sec- few min

Question 2

What is the focus of an earthquake

Answer 2

Point where pressure release occurs

Question 3

What depths are a shallow, intermediate and deep focus?

Answer 3

Shallow -0-70km
Intermediate -70-300km
Deep - 300-700km deep

Question 4

What type of focus causes the greatest damage?

Answer 4

Shallow

Question 5

What is the place on the earth called above the focus

Answer 5

Epicentre and receives highest amount of energy

Question 6

How are seismic waves measured

Answer 6

With a seismometer recorded on seismograph

Question 7

What types of seismic waves are there?

Answer 7

Primary waves
Secondary waves
Surface waves (love and Raleigh)

Question 8

How are primary waves characterised

Answer 8

Fastest, move earth back and forth in compressional motion

Move through solids and liquids

Question 9

How are secondary waves characterised

Answer 9

Half the speed of p waves.move in sideways/perpendicular shaking earth at right angles to direction of travel.
Can’t move through liquids.do more damage than p waves

Question 10

How are surface waves characterised

Answer 10

Slowest travel near to ground surface. Most destructive.
Include love waves - ground move up and down
Raleigh waves - complex heaving/rolling motion

Question 11

What is the magnitude of an earthquake

Answer 11

The amount of energy released by the event usually measured on Richter scale

Question 12

Describe the Richter scale

Answer 12

Logarithmic scale
Each unit 10 fold increase in strength and 30fold increase in energy.It’s an objective measurement based on scientific readings from seismographs

Question 13

Describe the modified mercalli scale

Answer 13

Measures the intensity and impact of event
12 point scale level 1-12
Uses observations to measure effects

Question 14

Examples of primary effects of earthquakes

Answer 14

Ground shaking
Death and destruction
People being buried by collapsing buildings
Fires

Question 15

Secondary effects of earthquakes

Answer 15

Soil liquefaction
Landslides and avalanches
Tsunamis
Effects on people and built environment

Question 16

What is soil liquefaction

Answer 16

When soils with a high water content lose their mechanical strength and behave like a fluid after been violently shaken. Surface appears dry but water comes to top by cracks. Creates soil volcanoes . Buildings can “sink”

Question 17

Long term effects of earthquakes

Answer 17

Higher unemployment 
Repair and reconstruction (months/years)
Longer term illness 
Trauma and grief (months(/year recover )
Loss of farmland and food production 
Emergency building can become permanent

Question 18

What causes earthquakes

Answer 18

They originate along faults where part of the crust is being forced to move in opposite directions. They can get stuck and forces continue building up stress eventually they are released as large amounts of energy- seismic waves

Question 19

Distribution of earthquakes

Answer 19

Broad uneven belts
Found around plate boundaries
Most powerful- destructive plate
At conservative marked by a series of faults
Some on old fault lines away from boundaries

Question 20

What is a tsunami

Answer 20

Giant sea waves generated by shallow focus underwater earthquakes (mostly) or volcanic eruptions, underwater debris slides and large landslide into the sea

Question 21

Causes of tsunamis

Answer 21

Generated by seismic activity NOT by wind

Caused by ocean floor earthquakes or submarine volcanic eruption

Question 22

Characteristics of tsunamis

Answer 22

• Very long wavelength
• Low wave height - deep water
• Travel quickly- greater than 700km/hr
• When reach shallow water rise rapidly in height and slow
• first sign is wave trough in front of tsunami and reduction in sea level - drawdown

Question 23

Effects of tsunamis depend on

Answer 23

Height of waves and distance travelled 
Length of event that caused tsunami
Extent to which warnings were given 
Coastal physical geography 
Coastal land use and population density

Question 24

Hazard definition

Answer 24

Something that’s a potential threat to human life or property

Question 25

What are tectonic hazards

Answer 25

Hazards caused by movement of tectonic plates eg earthquakes, volcanoes, tsunamis

Question 26

Tsunami warning systems

Answer 26

-Rely on earthquake detection systems
-Tsunami warning centres all around world eg USAs national oceanic and atmospheric administration (NOAA) in Alaska and Hawaii
They rely on good communication systems , early warnings give people time to evacuate

Question 27

Prediction of earthquakes - no reliable way to accurately predict when one will occur but they use such methods

Answer 27

• Seismic records- patterns of earthquakes
• Radon gas emissions - released from rocks when fractured
• Ground water- water levels may rise or fall deformation of the ground
• Remote sensing
• low frequency electromagnetic activity

Question 28

Protection for earthquakes eg In places such as Japan (prone to earthquakes)

Answer 28

• buildings and fire resistant, better evacuation routes
  Designed to withstand earthquakes eg use strong materials like reinforced concrete or building foundations that absorb an earthquakes energy.
  Construction laws eg Japan and US - strict in recent years so newer buildings protected

Question 29

How else can buildings be made earthquake resistant

Answer 29

Made single story as more resistant to ground shaking eg in Kobe
Having a soft story at the bottom designed to collapse

Question 30

How else are towns protected against earthquakes

Answer 30

There’s smart meters to prevent fire in earthquakes - shut down gas supplies in earthquake.
Land use planning identifies area of city most at risk and seeks to locate vulnerable land uses eg schools and hospitals away from high risk areas

Question 31

How are buildings protected against tsunamis

Answer 31

Designed with raised,open foundations and made of strong material eg concrete
In Japan they have tsunami walls built around settlements but not always effective