Topic 9. Hazardous Environments
9.1 Hazardous envi resulting from crustal (tectonic) movement
Global Distribution of Tectonic Hazards
Tectonic hazards include seismic activity (earthquakes), volcanoes and tsunamis.
Most Earthquakes occur in defined linear patters, generally follow plate boundaries.
Earthquakes
Where they occur?
Broad belts of EQ caused by convergent plate boundaries (collision
boundaries – Himalayas)
Narrower belts of EQ caused by divergent plate margins
Transform plate boundaries, California San Andreas fault line, narrow belt of
EQ
Hotspots -> Intra-plate activity (within plate), not at plate boundaries, isolated
plumes (magma chamber)
What is an Earthquake?
Series of vibrations/seismic (shock) waves from focus – point where plates
release tension or compression
Epicenter – Point on Earth surface right above focus of EQ
Large EQ followed by small tremors: Foreshocks then Aftershocks
Seismic waves travel along surface and through body of Earth
2 Types of Body waves (within Earth): Primary and Secondary waves
P-waves: Travel by compression/expansion, pass thru rocks, gases and liquids
S-waves: Side-to side motion, only passes thru solids
Unconsolidated sediments (sand) shake unpredictably -> more damage
Liquefaction - P-waves can turn solid sediment into fluids (quicksand)
Richter and Mercalli Scales
Richter scale -> logarithmic: EQ of 5.0 is 10 x more powerful than 4.0 (DC)
Magnitude scale – Measure amount of energy released
Mercalli scale -> Ground movement observations. Allows eyewitnesses to
provide info on how strong EQ was (LEDC)
Factors affecting severity of EQ’s
Strength and depth of EQ and num of aftershocks, shallow EQ more damage
Pop density – More damage to highly populated (more buildings) region
Type of Buildings – MEDC better EQ resistant buildings
Time of day - EQ during rush hour, night unprepared
Distance from epicenter – Closer to epicenter, greater damage
Nature of rocks – Unconsolidated material act as liquid (liquefaction)
Secondary hazards – Cause mudslides, tsunamis and fires
Economic development – Level of preparedness and effectiveness (tech,
health)
9.1 Hazardous envi resulting from crustal (tectonic) movement
Global Distribution of Tectonic Hazards
Tectonic hazards include seismic activity (earthquakes), volcanoes and tsunamis.
Most Earthquakes occur in defined linear patters, generally follow plate boundaries.
Earthquakes
Where they occur?
Broad belts of EQ caused by convergent plate boundaries (collision
boundaries – Himalayas)
Narrower belts of EQ caused by divergent plate margins
Transform plate boundaries, California San Andreas fault line, narrow belt of
EQ
Hotspots -> Intra-plate activity (within plate), not at plate boundaries, isolated
plumes (magma chamber)
What is an Earthquake?
Series of vibrations/seismic (shock) waves from focus – point where plates
release tension or compression
Epicenter – Point on Earth surface right above focus of EQ
Large EQ followed by small tremors: Foreshocks then Aftershocks
Seismic waves travel along surface and through body of Earth
2 Types of Body waves (within Earth): Primary and Secondary waves
P-waves: Travel by compression/expansion, pass thru rocks, gases and liquids
S-waves: Side-to side motion, only passes thru solids
Unconsolidated sediments (sand) shake unpredictably -> more damage
Liquefaction - P-waves can turn solid sediment into fluids (quicksand)
Richter and Mercalli Scales
Richter scale -> logarithmic: EQ of 5.0 is 10 x more powerful than 4.0 (DC)
Magnitude scale – Measure amount of energy released
Mercalli scale -> Ground movement observations. Allows eyewitnesses to
provide info on how strong EQ was (LEDC)
Factors affecting severity of EQ’s
Strength and depth of EQ and num of aftershocks, shallow EQ more damage
Pop density – More damage to highly populated (more buildings) region
Type of Buildings – MEDC better EQ resistant buildings
Time of day - EQ during rush hour, night unprepared
Distance from epicenter – Closer to epicenter, greater damage
Nature of rocks – Unconsolidated material act as liquid (liquefaction)
Secondary hazards – Cause mudslides, tsunamis and fires
Economic development – Level of preparedness and effectiveness (tech,
health)
