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Geography Tectonics > Seismicity > Flashcards

Seismicity Flashcards

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1
Q

Causes of Earthquakes

A

Earth’s rocks are subjected to forces that tend to bent, twist or fracture them they deform. These stresses cause earthquakes

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2
Q

Seismic waves

A

Waves emanating from the focus

  • body waves
  • surface waves
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3
Q

Body waves

A

Travel in all directions through the body of the earth

  • P waves
  • S waves
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4
Q

Surface waves

A
  • Do not travel through the earth, travel along paths parallel to the earths surface.
  • They cause up and down and side to side movements.
  • Slower than S waves
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5
Q

Seismometers

A

An instrument used to record seismic vibrations to create a seismograph.
-P waves arrive before S waves

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6
Q

Richter scale

A
  • Scale of earthquake size
  • Measures the amplitude of a wave
  • Tenfold increase for each number
  • Uses computers and advanced technology
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7
Q

Moment magnitude

A
  • No maximum or minimum
  • Measures the total energy released by an earthquake
  • Includes area of the faults rupture and the slippage along the fault
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8
Q

Mercalli scale

A
  • Asses the intensity of ground shaking and building damage over large areas
  • Applied after the earthquake
  • Surveys
  • Subjective
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9
Q

What happens during an earthquake

A
  • Shaking
  • Ground rupture (along the fault line)
  • Fire (secondary effect as power lines e.t.c rupture)
  • Landslide and debris/rock fall
  • Liquification
  • Aftershocks
  • Tsunami
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10
Q

Liquefaction

A

A process that occurs in water saturated unconsolidated sediment, sand and soil flows rather than remains solid.

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11
Q

Aftershocks

A
  • Further earthquakes

- May make it dangerous for a rescue effort to be made

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12
Q

Tsunamis

A
  • Giant ocean waves
  • Generated when a body of water is disturbed
  • Waves amplify as they reach the coast
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13
Q

Short term effects of earthquakes

A
  • Ground shaking causes damage
  • Schools destroyed
  • Immediate death and injury
  • shocked, hungry and homeless people
  • Landslides
  • Liquefaction
  • damage to power stations
  • Panic, fear and hunger
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14
Q

Medium term effects of earthquakes

A
  • Fire
  • Education suspended
  • Bodies not buried, and long term disabilities from injuries
  • NGO’s provide supplies
  • -Flooding
  • Power cuts
  • Civil disorder
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15
Q

Long Term effects of earthquakes

A
  • High unemployment
  • repair of infrastructure
  • Long term lost generation
  • Trauma and grief
  • Pre fab homes may become permanent
  • Loss of farmland
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16
Q

Long term forecasting

A
  • Paleo seismology, studies pre historic earthquakes, and they have recurrence intervals, Long term forecast can be made.
  • Seismic gaps, an area along a fault where no earthquakes have occurred recently
17
Q

Short term predictions

A
  • Precursor event may signal an earthquake is coming
  • Ground uplift and tilting
  • Foreshocks
  • Water levels in wells drop or raise
  • Emission of radon gas
  • Strange animal behaviour
18
Q

Equipment used to measure earthquakes

A
  • Levelling
  • Laser reflector
  • Seismometer
  • Gravity meter
  • Strain meter
  • Water table level
  • Radon gas sensor
  • Satellite surveying
19
Q

Human induced earthquakes

A

–Hoover Dam construction (600 earthquakes)
-Toxic waste injected into hazardous waste disposal wells in 1960’s
-Nuclear testing in Nevada
(Due to increasing fluid pressure in the rocks which reactive older faults)

20
Q

Mitigating earthquake hazards

A
  • Strict building codes (California)
  • Stepped profile of buildings
  • Bracing
  • deep foundations
  • steel framed buildings e.t.c
21
Q

1986 San Fran Earthquakes

A
  • Richter scale 7.1
  • Killed 40 people
  • Strict building codes
22
Q

1986 Armenia Earthquakes

A
  • Magnitude 6.9
  • No earthquake proof buildings
  • 25,000 killed
23
Q

P waves

A
  • P waves, travel with a velocity dependent of the elasticity of the rock, moves via compression, very like a sound wave
  • Less destructive
24
Q

S waves

A
  • S waves, shear waves or secondary waves, travel with a velocity dependent on the rigidity and density of the rock, shear a material or change its shape (Love waves shake side to side and Rayleigh waves shakes up and down)
  • More damaging
  • Don’t travel through liquids

Geography Tectonics (11 decks)

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