3.1. Hazardous environments resulting from tectonic movement

Question 1

Define earthquakes

Answer 1

• the shaking/trembing caused by the sudden release of energy
• usually associated with faulting/breaking of rocks
• continuing adjustments of position results in aftershocsk

Question 2

Define focus/hypocenter

Answer 2

The point within the earth where faulting begins

Question 3

Define epicentre

Answer 3

The point directly above the focus on the surface

Question 4

Why do earthquakes occur?

Answer 4

• Occur along plate margins
• Plates move at a rate between 1.5cm and 7.5cm per year
• When plates move past/towards/away from each other, the movement is not smooth as friction causes the plate to get stuck => causes pressure to build up
• Energy waves then race rapidly from the focus causing commotion on the ground

Question 5

Elastic Rebound Theory

Answer 5

Explains how energy is stored in rocks:

• Rocks bend until the strength of the rock is exceeded
• Rupture occurs and the rocks quickly rebound to an undeformed shape
• Energy is released in waves that radiate outward from the fault

Question 6

2 types of body waves (wave that travel within earth’s interior)

Answer 6

• P Wave/Pressure wave/Primary wave
• S wave/Sheer wave/Secondary wave

Question 7

P Waves

Answer 7

• The fastest body waves
• These are compressional waves where the material movement is in the same direction as wave movement
• They travel through solids and liquids

Question 8

S Waves

Answer 8

• Slower than P-waves
• Travel with a sideway motion and move material perpendicular to wave movement thus making the ground move horizontally
• Travel through solids only
• Cause a lot of damage

Question 9

Mohorovicic Discontinuity - Moho

Answer 9

• Seismographs close to epicentre showed slow travelling P-waves and S-waves which contrasted with the faster moving P-waves and S-waes further away from the shock
• If the shock waves pass through the denser rocks, they speed up and vice versa
• S-waves don’t go through solid so stop at outer core
• Whereas, P-waves are refracted

Question 10

Types of seismic waves/surface waves (travels through crust)

Answer 10

• Slower than body waves
• Long/love waves (cause ground to move sideways)
• Rayleigh waves (cause ground to move up and down

Question 11

Impact of P-waves

Answer 11

Can turn solid sediments into fluids like quicksand by disrupting sub-surface water conditions. This is known as liquefaction or fluidisation

Question 12

Different types of fault

Answer 12

• Normal dip-slip faults: results from tension in crustal rocks pulling apart
• Reverse dip-slip faults: results from compression in the crust collision
• Strike-slip faults: results from crustal blocks sliding past each other

Question 13

Richter scale

Answer 13

• Measures magnitude of a tremor using seismometer which records data on seismograph
• Logarithmic scale (a size 2 s 10 times larger than 1)
• Less than 3: not felt
• 3-3.9: felt, little damage
• 4-4.9: some structural damage
• 5-5.9: losses in populated areas
• 6-6.9: large losses in urban area
• 7-7.9: serious building damage, major loss of life
• >8: total destruction

Question 14

Mercalli scale

Answer 14

• measures how much damage is caused by the earthquake based on observations (a result of surface shaking)
• measures intensity of earthquake by indicating the violence of the earth motion
• scale between 1 and 12

Question 15

Differences between Richter and Mercalli

Answer 15

• Richter measures strengths, Mercalli measures damage/effects
• Richter scale is based on scientific data, Mercalli is based on people’s observations
• Richter measured by seismometers, Mercalli measured by people
• Mercalli uses whole number, Richter uses numbers to one decimal place

Question 16

Physical factors affecting earthquake

Answer 16

• Magnitude of earthquake
• Time of the day - occur during rush hour can be more damaging
• Distance from epicentre - shorter => less energy is disspated
• Depth of focus (same as above)
• Type of rock and sediments - loose materials are more vulnerable to liquefaction
• Coastal locations are more vulnerable to tsunami

Question 17

Human factors affecting earthquake damage

Answer 17

• Population/population density
• Type of buildings
• Level of economic development for prediction and preparation

Question 18

Impacts of earthquakes

Answer 18

Primary hazard (ground shaking, surface faulting)

• loss of life
• total/partial destruction of infrastructure
• communications cut off
• economic depression
• blocked transport routes

Secondary hazard (liquefaction, landslides, rockfalls, tsunamis, debris mudflow)

• same as above

Question 19

Define tsunami

Answer 19

harbour wave in Japanese

Question 20

Causes of tsunami

Answer 20

• Sudden motion on the ocean floor.
• This sudden motion could be an earthquake, a powerful volcanic eruption, or an underwater landslide. The impact of a large meteorite could also cause a tsunami.

Question 21

Types of volcanic eruptions

Answer 21

• Icelandic lava
• Hawaiian
• Strombolian
• Vulcanian
• Vesuvian
• Plinian

Question 22

Iceland lava eruptions

Answer 22

• persistent fissure eruptions
• large quantities of basaltic lava build up vast horizontal plains
• formed Deccan Plateau and Columbia Plateau

Question 23

Hawaiian eruptions

Answer 23

• central activity
• runny,basaltic lava travels down the sides of the volcano in lave flows
• gases escape easily
• occasional pyroclastic activity

Question 24

Stombolian eruptions

Answer 24

• frequent gas explosions
• blast fragments of runny lava into air to form cones
• large quantities of pyroclastic rock
• white cloud of steam emitted from crater

Question 25

Vulcanian eruptions

Answer 25

• violent gas explosions blast out plugs of sticky or cooled lava
• fragments build up into cones of ash and pumice
• occurs when there is very viscous lava which solidifies rapidly after an explosion
• clears blocked vent ad spews large quantities of volcanic ash into atmosphere

Question 26

Versuvian eruptions

Answer 26

• powerful blast of gas pushing ash clouds
• more violent
• lava flows
• ash falls

Question 27

Plinian eruptions

Answer 27

• gas rushes up through sticky lava
• blasts ash and fragments into sky in a huge explosion
• immense clouds of gas and volcanic debris several km thick
• parts of volcano may be blasted away during the eruption

Question 28

Define pyroclastic flows

Answer 28

a fast moving current of high-density mix of hot lava blocks, pumice, ash and volcanic gas

Question 29

Define lava flows/bombs

Answer 29

streams of molten rock that pour or ooze from an erupting vent

Question 30

Define fire fountains

Answer 30

a continuous spray of disrupting magma through a vent to form a persistent fountain of magma above the vent

Question 31

Define lahars

Answer 31

A type of mudflow/debris flow composed of a slurry pyroclastic material, rocky debris and water

Question 32

How is lahar formed?

Answer 32

1. Rain brings soot and ash back to ground and this becomes a heavily saturated mudflow
2. Heat from volcanoes melts snow and ice - the resulting flow picks up sediment and turns it into a destructive lahar

Question 33

Earthquake/tsunami/volcanoes prediction

Answer 33

• seismometers to record swarms of tiny earthquakes
• chemical sensoring
• thermal sensoring
• animal behaviour
• lasers to detect swelling of waves