Geography - Earthquakes

Sydney Routley
Flashcards by , created over 4 years ago

A Level Geography Flashcards on Geography - Earthquakes, created by Sydney Routley on 04/04/2015.

Sydney Routley
Created by Sydney Routley over 4 years ago
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Question Answer
What is a earthquake? Plate movement cause by friction and pressure building up then suddenly releasing. This causes seismic waves that travel through the plate to the surface
What is the Focus? The point where the pressure is released. The ground ruptures at this spot, then seismic waves radiate outward in all directions.
What is the epicenter? The point on the earth's surface vertically above the focus of an earthquake.
Shallow earthquake? 0-70km deep These cause the most damage
Deep earthquake? 300-700km deep
Describe the Mexico City earthquake? Shallow Earthquake 1985 10,000 people died 50,000 injured 35% city destroyed
Describe the Iran earthquake? Shallow Earthquake 1990 35,000 died 100,000 injured 400,000 homeless
Describe the Tangshan earthquake? NOT associated with plate boundaries 1976 240,000 people killed 7.8 M initial quake, 7.1 M aftershock
Describe the Killari earthquake? Potentially caused by the building of a reservoir putting pressure on a fault India, Killari 1993 10,000 people died
What are the Primary Hazards of earthquakes? Seismic waves - Magnitude and Frequency Aftershocks
What is a seismic wave? a wave of energy that is generated by an earthquake that travels within the earth or along its surface causing buildings to collapse which kills
What is the aftershock? a small earthquake or tremor that follows a major earthquake which causes further damage to already weakened buildings
Secondary Hazards of an earthquake? Tsunamis Landslides Liquefaction Flooding - sometimes caused by burst water pipes Fire - caused by damaged gas+electrics
What is a Tsunami? Large sea waves generated by disturbance of the sea floor caused by earthquakes or submarine landslides. eg. Indonesia, Dec 2004
What is Liquefaction? Violent disruption of the ground causes it to become liquid-like due to increased pore water pressure which weakens the ground. Groundwater mixes with soil and comes through the newly formed cracks eg. 1989 San Francisco
What are landslides and avalanches? When slope failure occurs due to ground shking
What are the 3 types of seismic shock waves? P-waves S-waves Surface waves -> Love waves and Rayleigh waves
Whats a P-wave? Can travel through solids and liquids (mantle and core). The waves push and pull the earth in the same direction the earth is travelling. Fastest type of wave. High frequency.
Whats a S-wave? Can travel through solids only (mantle only). The waves move the earth at 90* to the direction of travel. These waves cause a lot of damage because of their shearing effect.
Whats a love wave? Can only travel through solids. They move the surface from side to side causing a lot of damage due to their shearing effect. Slowest waves.
Whats a Rayleigh wave? Can travel through liquids and solids. They move the surface in a low frequency rolling motion radiating from the epicenter
Define magnitude? Is the amount of energy released by the event and is usually measured on the Richter scale.
Physical factors effecting an earthquake? Distance from epicenter Depth of focus Time of Day Duration of shaking Magnitude of earthquake Geology of land
Human factors effecting an earthquake? Community preparedness Emergency relief services Economic + social structure of country Building design Gas and electricity supply Land use planning
How do you prepare for an earthquake? Modify the event -> Controlling physical variables and hazard resistant design Modify the vulnerability -> Prediction and Warning and community preparedness Modify the loss
How do you modify the event -> Controlling physical variables? Geophysical event - it can NOT be stopped Human induced earthquakes (eg. dam construction) could be prevented by consideration of the seismic hazard when siting the structure.
How do you modify the event -> Hazard-Resistant design? Aseismic designs Not possible to rebuild whole cities Economically developed nations and put in strict planning/building regulations - poor can't Aseismic designs expensive to replace and repair after a quake
What are some aseismic designs? Concrete counterweight - moves in the opposite direction to quake, power failure means it cant move Rubber shock absorbers - allows building to move with quake Cross bracing - allows the tower to twist easier
Define modify the vulnerability? The aim is to lessen the impacts of the earthquake by prediction and warning, community preparedness and land use planning
How do you modify the vulnerability -> Prediction and warning? Regional - use previous recorded data to pinpoint areas at risk (where) 'Gap theory' - predicts when a quake will happen based on how long the plates have been 'locked' short term - changing water levels and released radon gas
How do you modify the vulnerability -> community preparedness? General public - must have supplies, move under protective furniture, await rescue, first-aid training valuable as 'self help only' period crucial Emergency services - well organised, know where to deploy people in the area with disrupted transport routes and communication
Describe Tangshen earthquake? 1976 250,000 people died + 160,000 injured 16% above due to trying to escape 25% above due to heat, thirst + hunger Further 250,000 tried rescuing others Most survivors were under heavy furniture
Whats a tsunami? Giant waves caused by earthquakes under the sea. Out in the depths of the ocean, tsunami waves do not dramatically increase in height. But as the waves travel inland, they build up to higher and higher heights as the depth of the ocean decreases.
Describe a tsunami wave in open ocean? Very deep water High speed - 700km/h long wavelength - 200km small amplitude - 1m
Describe a tsunami wave closer to land? Shallower water Waves compress = energy more concentrated slower - 80km/h wavelength decreases - 20km amplitude increases - many meters
Hydrostatic effect? Debris in the water that kills being moved by the water
Hydrodynaimc effect? power in the wave destroying buildings and infastructure
Describe the Indonesian tsunami? 9.1 magnitude quake Sunda trench off SW coast Indonesia Australia plate subducted under Burma plate 20m slip along 1600km faultline epicenter 160kn offshore - focus 30km down