Hazardous environments
9.1 Hazards Resulting from tectonic processes
Global distribution of tectonic hazards
● Include seismic activities, volcanoes and tsunamis
● Most of the world’s earthquakes occur in clearly defined linear patterns, which
usually follow plate boundaries
Earthquakes
● Broad belts of earthquakes are usually associated with subduction zones,
where dense oceanic plates subduct a less dense continental plate
● Narrow belts of earthquakes are associated with constructive (divergent)
plate margins, where new materials are formed and plates move apart
● Collision boundaries (convergent), such as the Himalayas are associated with
broad belts of earthquakes
● There appear to be occurrences of earthquakes related to the isolated plumes
of tectonic activity, known as hotspots
● Earthquakes are series of seismic waves that originate from the focus, the
point at which plates release their tension or compression suddenly
● The epicentre marks the point on the surface, immediately above the focus
● Large have foreshocks and aftershocks
● Aftershocks can be particularly damaging as the building has already been
weakened by the main shock
● Seismic waves are able to travel along the surface of the Earth and also
through the body of the Earth
● Two types of body waves occur(Earth’s interior) P-waves and transverse
S-waves
● P-waves travel by compression and expansion and are able to pass through
rocks, liquids and gases
● S-waves travel in a side-to-side motion and are able to pass through solids
but not liquids and gases as they have no rigidity to support sideways motions
● Seismic activity close to the epicentre showed slow-travelling P and S-waves,
by contrast, those further away from the shock showed faster-moving waves
● These shocks are reflected or refracted when they hit rocks with different
densities
● If the shock waves pass through denser rocks, they speed up
● If they pass through less dense rocks, they slow down
● When P and S-waves travel to the surface, they become surface waves
● Love waves cause the waves to go sideways
, ● Rayleigh waves cause the Earth to go up and down
● Surface waves often cause the most damage
● The nature of the rocks and sediment in the ground influenced the patterns of
shocks and vibration
● Unconsolidated sediment, such as sand, shakes in a less predictable way
than solid rocks, which makes the damage of the earthquake greater
● P-waves from earthquakes can turn solid sediment into fluids like quicksand,
disrupting sub-surface water conditions
● This is known as liquefaction and can wreck the foundations of large buildings
and other structures
Earthquakes and resultant hazards
Primary hazards
● Ground shaking
● Surface faulting
Secondary hazards
● Ground failure and soil liquefaction
● Landslides and rockfalls
● Debris flow and mudflow
● Tsunamis
Impacts
● Loss of lives
● Loss of livelihood
● Total or partial destruction of building structures
● Interruption of water supplies
● Breakage of sewage disposal systems
● Loss of public utilities such as electricity and gas
● Floods from collapsed dams
● Release of hazardous materials
● Fires
● Spread of chronic illness
Hazards
● Most earthquakes occur with little warnings in advance
● Some places like Japan and California have earthquake action plans and
information programmes to increase public awareness about what to do in an
earthquake
● Most problems are associated with damage to buildings, structures and
transport systems
, ● The collapse of the building causes many injuries and deaths and reduces the
effectiveness of emergency services
● Aftershocks shake the already weakened structures and they are longer
lasting and more frequent than the main tremors
● Some earthquakes involve surface displacements, which leads to the facture
of pipes and causes damage to the lines of communication
● The cost of repairing such fractures is considerable
● Earthquakes might cause other geomorphological hazards such as landslides,
liquefaction and tsunamis
Earthquakes and plate boundaries
● The movement of oceanic crust into the subduction zone creates some of the
deepest earthquakes recorded from 700 km below the ground
● When the cool oceanic crust slides into the hot fluid mantle, it takes time to
warm up
● As the oceanic crust sinks into the hot, fluid mantle, it bends, breaks and
causes earthquakes along the way
● However, by the time the crust has cracked, it has slipped several hundred of
km down into the mantle
● The chances of an earthquake increase over time if no earthquakes have
occurred in a while
● Plates move at a rate of 1.5 and 7.5 cm a year, however, a large earthquake
can move the plates by a few metres
● Many earthquakes are created due to the pressure created by moving plates
● This increases the stress on the rocks, the rocks deform and eventually give
up and snap
● The snapping releases energy and form an earthquake
● The size of an earthquake depends on the thickness of the descending slab
and the rate of the movement
● The strength of earthquakes is measured by the Richter Scale and the
Mercalli Scale
Richter scale:
● A numerical scale used to measure the magnitude of earthquakes
● It quantifies the amounts of seismic energy released by an earthquake by
measuring the amplitude of seismic waves recorded by seismographs
Mercalli scale:
● A subjective scale that measures the intensity of an earthquake based on
observed effects and damage at specific location s
● It provides a descriptive assessment of an earthquake’s impact on people,
buildings and the environment ranging from 1 (rarely felt) to 12 (total damage)
9.1 Hazards Resulting from tectonic processes
Global distribution of tectonic hazards
● Include seismic activities, volcanoes and tsunamis
● Most of the world’s earthquakes occur in clearly defined linear patterns, which
usually follow plate boundaries
Earthquakes
● Broad belts of earthquakes are usually associated with subduction zones,
where dense oceanic plates subduct a less dense continental plate
● Narrow belts of earthquakes are associated with constructive (divergent)
plate margins, where new materials are formed and plates move apart
● Collision boundaries (convergent), such as the Himalayas are associated with
broad belts of earthquakes
● There appear to be occurrences of earthquakes related to the isolated plumes
of tectonic activity, known as hotspots
● Earthquakes are series of seismic waves that originate from the focus, the
point at which plates release their tension or compression suddenly
● The epicentre marks the point on the surface, immediately above the focus
● Large have foreshocks and aftershocks
● Aftershocks can be particularly damaging as the building has already been
weakened by the main shock
● Seismic waves are able to travel along the surface of the Earth and also
through the body of the Earth
● Two types of body waves occur(Earth’s interior) P-waves and transverse
S-waves
● P-waves travel by compression and expansion and are able to pass through
rocks, liquids and gases
● S-waves travel in a side-to-side motion and are able to pass through solids
but not liquids and gases as they have no rigidity to support sideways motions
● Seismic activity close to the epicentre showed slow-travelling P and S-waves,
by contrast, those further away from the shock showed faster-moving waves
● These shocks are reflected or refracted when they hit rocks with different
densities
● If the shock waves pass through denser rocks, they speed up
● If they pass through less dense rocks, they slow down
● When P and S-waves travel to the surface, they become surface waves
● Love waves cause the waves to go sideways
, ● Rayleigh waves cause the Earth to go up and down
● Surface waves often cause the most damage
● The nature of the rocks and sediment in the ground influenced the patterns of
shocks and vibration
● Unconsolidated sediment, such as sand, shakes in a less predictable way
than solid rocks, which makes the damage of the earthquake greater
● P-waves from earthquakes can turn solid sediment into fluids like quicksand,
disrupting sub-surface water conditions
● This is known as liquefaction and can wreck the foundations of large buildings
and other structures
Earthquakes and resultant hazards
Primary hazards
● Ground shaking
● Surface faulting
Secondary hazards
● Ground failure and soil liquefaction
● Landslides and rockfalls
● Debris flow and mudflow
● Tsunamis
Impacts
● Loss of lives
● Loss of livelihood
● Total or partial destruction of building structures
● Interruption of water supplies
● Breakage of sewage disposal systems
● Loss of public utilities such as electricity and gas
● Floods from collapsed dams
● Release of hazardous materials
● Fires
● Spread of chronic illness
Hazards
● Most earthquakes occur with little warnings in advance
● Some places like Japan and California have earthquake action plans and
information programmes to increase public awareness about what to do in an
earthquake
● Most problems are associated with damage to buildings, structures and
transport systems
, ● The collapse of the building causes many injuries and deaths and reduces the
effectiveness of emergency services
● Aftershocks shake the already weakened structures and they are longer
lasting and more frequent than the main tremors
● Some earthquakes involve surface displacements, which leads to the facture
of pipes and causes damage to the lines of communication
● The cost of repairing such fractures is considerable
● Earthquakes might cause other geomorphological hazards such as landslides,
liquefaction and tsunamis
Earthquakes and plate boundaries
● The movement of oceanic crust into the subduction zone creates some of the
deepest earthquakes recorded from 700 km below the ground
● When the cool oceanic crust slides into the hot fluid mantle, it takes time to
warm up
● As the oceanic crust sinks into the hot, fluid mantle, it bends, breaks and
causes earthquakes along the way
● However, by the time the crust has cracked, it has slipped several hundred of
km down into the mantle
● The chances of an earthquake increase over time if no earthquakes have
occurred in a while
● Plates move at a rate of 1.5 and 7.5 cm a year, however, a large earthquake
can move the plates by a few metres
● Many earthquakes are created due to the pressure created by moving plates
● This increases the stress on the rocks, the rocks deform and eventually give
up and snap
● The snapping releases energy and form an earthquake
● The size of an earthquake depends on the thickness of the descending slab
and the rate of the movement
● The strength of earthquakes is measured by the Richter Scale and the
Mercalli Scale
Richter scale:
● A numerical scale used to measure the magnitude of earthquakes
● It quantifies the amounts of seismic energy released by an earthquake by
measuring the amplitude of seismic waves recorded by seismographs
Mercalli scale:
● A subjective scale that measures the intensity of an earthquake based on
observed effects and damage at specific location s
● It provides a descriptive assessment of an earthquake’s impact on people,
buildings and the environment ranging from 1 (rarely felt) to 12 (total damage)
