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Resources for 1.7 Global Earthquakes
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The earth has four major layers: the inner
core, outer core, mantle and crust. The
crust is made up of hard rock, mainly
granite. The mantle is mainly molten lava
on which the crust is floating. The core is
mostly iron, with the outer core being
liquid and the inner being solid. The hot,
liquid mantle is continually moving due to
convection currents caused by the heat
radiating out from the core. The crust and
the top of the mantle make up a skin on
the surface of our planet. This skin is not all in one piece – it is made up of many pieces like a
jigsaw puzzle covering the surface of the earth. These puzzle pieces are slowly moving around,
sliding past one another and bumping into each other. The movement of the plates is caused by
the convection currents in the molten magma. These puzzle pieces are called tectonic plates,
and the edges of the plates are called the plate boundaries.
Plate Boundaries
These plates are always moving. That is why most of
the earthquakes and volcanoes are found near or on
the plate boundaries. Earthquakes usually occur along
faults, which are weak points in the crust. The plate
boundaries are made up of many faults, and most of
the earthquakes around the world occur on these
faults. Sometimes the blocks of rock on either side of a
fault abruptly shift to a new position in just a few
seconds. This sudden release of energy sends out
waves, which are felt on the surface as an earthquake.
Resources for 1.7 Global Earthquakes
A process known as Elastic
Rebound Theory can be
demonstrated with a green
twig or branch.
Holding both ends, the twig
can be slowly bent. As it is
bent, energy is built up within
it. A point is reached when
the twig suddenly snaps.
As it snaps the energy is
released and this is known as
an earthquake.
The edges of the plates are
rough and they get stuck while
the rest of the plate keeps
moving. This builds up strain
or tension around plate edges.
The plates often rub together,
pull apart, collide or dive
under one another.
Since they are all moving, they rub against each other in some places (like the San Andreas Fault
in California), or sink beneath each other in others (like the Peru-Chile Trench along the western
border of South America), or spread apart from each other (like the Mid-Atlantic Ridge in the
Atlantic Ocean). As the motion continues, the strain builds up to the point where the rock
cannot withstand any more bending. The rock breaks and the two sides move. An earthquake is
the shaking that radiates out from the breaking rock. These movements cause global
earthquakes and can also cause volcanoes to erupt.
Volcanic earthquakes are far less common than Tectonic ones. They are triggered by the
explosive eruption of a volcano. When extraordinary levels of pressure develop with a volcano,
the resultant explosion can produce an earthquake of considerable magnitude. When Krakatoa,
in Indonesia, exploded in 1883, the explosion was heard over 5000km away in Australia. The
shockwaves produced a tsunami, (a series of large sea waves) one of which was over 36m high.
The majority of earthquakes are tectonic ones. When there are sudden movements in the
various layers of the earth, crust or mantle, concentric waves are produced. These waves are
known as seismic waves and are of three types; Primary Waves (P-Waves), Secondary Waves (SWaves) and Surface Waves (L-Waves). When the underground rock snaps, shock waves radiate
out in all directions. The underground origin of an earthquake is called the focus or hypocentre.
The point at which an earthquake is seen on the surface is called the epicentre.
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Resources for 1.7 Global Earthquakes
Plate boundaries are placed into three categories:
constructive or divergent, destructive or convergent
and conservative or transform plate boundaries.
Constructive or divergent plate boundaries move
apart creating new land. Most of these are in the
middle of the ocean, although the Great Rift Valley
in Africa is also spreading. Hot rock is coming up
from the middle of the earth like an ongoing
volcanic eruption. The lava comes up and pushes
the ridges apart, one running North-South is what has formed the mid-Atlantic Oceanic ridge.
The destructive or convergent plate boundaries are colliding with each other. As the collision
takes place, the heavier, oceanic plate can subduct, or goes under, the lighter, continental plate
and is absorbed into the mantle beneath. This is happening along the west coast of South
America. When there is a continent near the edge, the sea
floor always goes underneath because it is denser and the
continent floats on the top. This is called subduction.
Friction prevents the down-going plate from sliding under
smoothly. As it descends it drags against the overlying plate,
and eventually the crust of the overlying plate fractures,
shifts or crumples, causing frequent earthquakes. Ocean
crust of the Pacific Plate is descending under eastern NZ. The land has splintered into long blocks
separated by major faults. Movement on these long faults has produced several earthquakes of
magnitude 7 or greater, such as, the 1855 Wairarapa earthquake.
The Ring of Fire surrounding the Pacific basin represents the subduction edge of the Pacific
plate. This causes a lot of molten lava to rise to the surface and the presence of active volcanoes
along the Pacific Rim. These volcanic eruptions cause frequent earthquakes. 80% of all recorded
earthquakes are taking place around the edge of the Pacific Plate, including New Zealand, Papua
New Guinea, the Solomon Islands, Vanuatu, Japan, Canada, USA and South America.
There is a major converging boundary north of India where the subcontinent of India pushes
against Asia. Neither plate can go under because they are too light and thick so both plates are
buckling, throwing up the Himalayas and all the mountain chains through central Asia. This
results in several earthquakes occurring in this region.
The conservative or transform plate boundaries slip or slide past each other. It is similar to a
converging boundary because edges get caught, tension builds up and then it releases suddenly,
causing an earthquake. An example is the San Andreas Fault in California. The Pacific Plate and
the North American Plate, are both moving in a roughly north-westerly direction, but one is
moving faster than the other. The San Francisco area is subjected to hundreds of small
earthquakes every year as the two plates grind against each other. Haiti is on the northern
border of the Caribbean plate, a transform boundary. But the southern edge of the Caribbean
plate is subducting under the South American plate, as are the Cocos and Nazca plates. This is
what has caused the 2010 Chilean earthquake, and in 1960 the same area experienced the
strongest earthquake ever recorded.
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Resources for 1.7 Global Earthquakes
Japan March 2011
The effects of the earthquake and subsequent tsunami that hit Japan could stay with the people
caught up in the natural disaster for the rest of their lives. Cars, ships and buildings were swept
up by a huge wall of water that was created when the earthquake, which measured at 8.9
magnitude, hit the north-east of the
country. Yukiko, from Tokyo, described the
experience as being "really scary", adding
buildings were shaking with increasing
violence. Professor Lorraine Sherr said
people's lives are changed forever
whenever a tsunami or an earthquake hits.
The expert noted: "Surviving, living through
trauma, panic or injury affect people
forever." The immediate reaction, would
be the importance of information, support
and community connectedness in helping people cope in the short term and with longer term
adjustment. The tsunami caused a number of nuclear accidents: meltdowns at three reactors in
the Fukushima Daiichi Nuclear Power Plant complex, and the associated evacuation zones
affecting hundreds of thousands of residents. Residents within a 20 km radius of the Fukushima
Daiichi Nuclear Power Plant and a 10 km radius of the Fukushima Daini Nuclear Power Plant
were evacuated. Japanese National Police Agency report confirmed 15,867 deaths, 6,109
injured, and 2,909 people missing across twenty regions. Japanese Prime Minister Naoto Kan
said, "In the 65 years after the end of World War II, this is the toughest and the most difficult
crisis for Japan." Around 4.4 million households in north eastern Japan were left without
electricity and 1.5 million without water.
Christchurch 2011
The February earthquake caused widespread damage across Christchurch, especially in the
central city and eastern suburbs, with damage to buildings and infrastructure already weakened
by the 4 September 2010 earthquake and its aftershocks. Significant liquefaction affected the
eastern suburbs, producing around 400,000 tonnes of silt. In total, 185 people were killed in the
earthquake, making it the second-deadliest natural disaster recorded in New Zealand (after the
1931 Hawke's Bay earthquake).
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Resources for 1.7 Global Earthquakes
Over half of the deaths occurred in the six-storey Canterbury Television (CTV) Building, which
collapsed and caught fire in the quake. The government declared a state of national emergency,
which stayed in force until 30 April 2011.
In the immediate moments following the quake, rescue and response was offered by ordinary
citizens and those emergency services on duty. They were supported by NZ Police, Fire Service,
Defence Force and many other agencies and organisations. Christchurch Police were helped by
staff from around the country, along with 300 Australian Police, bringing the total officers in the
city to 1200. The police from Australia were used for non-rescue tasks such as traffic control,
general policing duties and to prevent looting.
The scale of the disaster meant many people went some
days without official contact, so locals in neighbourhoods
and streets were encouraged to attend to those around
them. The Christchurch Student Army willingly donated
time and labour to help shovel silt and mud out of many
elderly residents’ driveways. This showed empathy for
fellow human beings.
Water provision was worked on by companies and
contractors, while Fonterra provided milk tankers to bring in water, the NZ Army provided
desalination plants, and bottled supplies were sent in by volunteer companies. Waste water and
sewerage systems had been severely damaged. Over 2000 port-a-loos and 5,000 chemical toilets
from throughout New Zealand and overseas were brought in. Community cooperation was
important at this difficult time and communal laundries were set up in water affected suburbs.
Portable shower units were also established in the eastern suburbs. People had to face months
of indignity and inconvenience of using these communal public facilities if their own homes were
affected by the loss of water and sewer supply.
Haiti 2010
Thousands of traumatised Haitians remained without food
and shelter following the 2010 earthquake. Mental health
experts said the psychological effects of the disaster could
take months to fully emerge. The people of Haiti – already
worn down by conflict, cyclone, hunger and floods – were
vulnerable to an outbreak of mental-health disorders that
the country's poor health system could not begin to cope
with. Aid
agencies were working to minimise some of the risks
that could lead people to suffer post-traumatic shock
syndrome (PTSD). "To prevent lasting mental injury people need shelter, warmth, a meaning to life,
things to do – and as fast as possible," said Mark
Brayne, a psycho-therapist specialising in individual
and collective trauma. "After the tsunami in 2004
many people were not able to see or bury their dead
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Resources for 1.7 Global Earthquakes
because of panics over public health issues, but actually the rituals of death are hugely
important to how we cope with grief and death, and you can cause enormous damage by
preventing people doing that." He said that in the immediate aftermath of a disaster people are
focused on self-preservation and taking care of their families, and although they experience
intense grief, shock and anxiety, PTSD can take six months to show itself.
Friends and family are what gets people through, and in a tight-knit place like Haiti, we have to
be careful about imposing western understandings. People will feel shock and pain but there will
also be resilience." Poverty may be endemic but social support is deep in Haitian culture. The
country has a strong sense of mutual responsibility among extended families and communities
or "lakou" – a system where people work co-operatively while still living in individual properties.
The distinctively Haitian tradition, along with the dominance of the Catholic faith, forms a tightmeshed social net through which few can slip. Children are especially vulnerable to trauma, and
several projects in trouble spots around the world have shown remarkable success by helping
them cope through play – especially using drawing to express themselves.
Unicef provided "recreation kits" to Haiti. Patrick McCormick, an emergencies communication
officer for the UN children's organisation, said: "The worst thing for children in natural disasters
isn't just the damage that they see around them, but also when they sit around and have
nothing to do. It ramps up anxiety and despair, and that's what does even more damage.
The 2004 Indonesian earthquake causing the Boxing Day tsunami.
The earthquake was caused by
subduction and triggered a series of
devastating tsunamis along the coasts
of most land masses bordering the
Indian Ocean, killing over 230,000
people in fourteen countries, and
flooding coastal communities with
waves up to 30 metres high.
Indonesia was the hardest-hit
country, followed by Sri Lanka, India,
and Thailand.
This disaster prompted a worldwide humanitarian response.
The world community donated more than $14 billion (2004
US$) in humanitarian aid. Relief agencies reported that onethird of the dead were children. This was a result of the high
proportion of children in the populations of many of the
affected regions and because children were the least able to
resist being overcome by the surging waters. Oxfam reported that as many as four times more
women than men were killed in some regions because they were waiting on the beach for the
fishermen to return and looking after their children in the houses.
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Resources for 1.7 Global Earthquakes
States of emergency were declared in Sri Lanka, Indonesia, and the Maldives. A great deal of
humanitarian aid was needed because of the widespread damage to the infrastructure and
shortages of food and water. Disease epidemics were of special concern due to the high
population density and tropical climate of the affected areas. The main concern of humanitarian
and government agencies was to provide sanitation facilities and fresh drinking water to contain
the spread of diseases such as cholera, diphtheria, dysentery, typhoid and hepatitis A and B. In
the days following the tsunami, significant effort was spent in burying bodies hurriedly for fear
of disease.
In an addition to the large number of local
residents, up to 9,000 foreign tourists (mostly
Europeans) enjoying the peak holiday travel
season, were among the dead or missing. They
were affected by the holiday being cut short and
the loss of loved family members and friends.
Since the media coverage of the event was so
extensive, many tourists cancelled vacations and trips to that part of the world, even though
their travel destinations may not have been affected. Countries in the region appealed to
tourists to return, pointing out that most tourist infrastructure is undamaged. However, tourists
were reluctant to do so for psychological reasons. Even beach resorts in parts of Thailand which
were completely untouched by the tsunami were hit by cancellations.
China April 2013
China had a powerful earthquake on 20 April 2013. Rescue
workers had to use dynamite and heavy equipment to get
through roads blocked by landslides to reach remote village
areas. Bad weather and powerful aftershocks contributed to
delays. At least 188 people died in the quake and more than
11,500 others were reported injured. Those made homeless
also had trouble receiving food or water. Landslides blocked
access to aid trucks and prevented some of the casualties from
being brought out. This greatly added to the stress and trauma. The hill villages, where poor
farmers grow rice, vegetables and corn on terraced plots, were hit the hardest by the
earthquake. Food supplies and crops for sale have been severely affected. Many of the collapsed
buildings were schools and nurseries, leading to increased suffering for the remote communities
and especially the children of the villages. Many are worried it will take months or years to
repair the devastated region which was hit by another earthquake 5 years earlier.
People around the world need to prepare for future earthquakes by individually having
insurance policies and emergency plans of action for their homes and families. Community
groups should have civil defence emergency plans and many councils need to spend money on
strengthening buildings to meet earthquake standards. Many world population settlements are
very established in quake zones around the world and are unlikely to be relocated. Therefore
plans must be made to minimise future earthquake effects on people.
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