PLATE TECTONICS
Study Figure 1, a photograph of an area in northern Pakistan after a recent earthquake. Using Figure 1 only, comment on the evidence that suggests that an earthquake has recently taken place. (7 marks)
It is clear that an earthquake has recently taken place for a number of reasons. In the
foreground piles of rubble lay where the houses once stood which infers that the
earthquake tremors led the houses to collapse. There are also many tents present as well where local people may now be living as their houses may have collapsed.
In the background on the mountain side there is little vegetation compared with further up and the rock appears fresh as if a landslide caused by the earthquake cleared many of the vegetation and the top layer of the rock away. There are also quite a few trucks lined up on one of the streets which look like they would not naturally be there. They could be rescue trucks to help evacuate people out of the area or they could be transporting waste materials from the earthquake eg rubble away from the area. Also there appears to be extremely few people and animals present in the picture which could infer that the animals have fled and the people have been evacuated away from the area due to the earthquake.
Your mark ____
Examiners mark: 7
Mark scheme
Level 1: simple listing of features from the photograph such as landslides, tented community, military lorries etc. with no commentary on any aspect. 1-4
Level 2: commentary on the nature of the evidence as seen. Some sophistication of description, and/or evidence of geographical thinking. 5-7
This photograph was taken in January 2006 following the October 2005 earthquake in Kashmir. There are signs of the original earthquake in the background . in the form of landslides of mud and rock (sandstones). The landslides are extensive, and very clear (whiteness). Large amounts of debris must have fallen into the valley below. There
is also evidence of tented communities. An implication has to be that many of the original houses in the settlement have been destroyed or are at risk; or there have been refugees into the settlement. On the other hand, several buildings seem to be upstanding; perhaps this settlement was not as badly damaged as others in the region?
There is evidence of some military presence . perhaps to act as rescuers, or to maintain order? Rubble in foreground?
Question 02
Describe how seismic waves and earthquakes can be measured. 8 marks
Candidate B
Seismic waves can be measured on a seismograph which records and locates the size of
seismic waves during an earthquake event. Seismographs can be used to help predict an
earthquake epicentre and they can also be used to help predict future earthquake events by determining which areas are most likely to suffer from structural damage, landslides and soil liquefraction. Seismographs measure the amplitude of the seismic waves by measuring the distance between movement of the instrument and the spring which has inertia in it. The degree of movement between the mass and the rest of the instrument helps geologists and scientists to accurately measure the magnitude and size of seismic waves. Earthquakes are measured on a Richter scale which records the magnitude of the event. The Richter Scale is logarithmic and so each unit represents a 10 fold increase in strength and a 30 fold increase in energy released. So, therefore a magnitude 7.1 earthquake is twice as big as a magnitude 6.9 event. Moreover earthquakes can be measured on a 12 point Mercalli scale which reflects the effects of an earthquake. The more severe the earthquake the more destructive the effects and the higher the score on the Mercalli scale. The scale however relies on individual interpretations of the effects of an event and not everyone will agree on its effects eg degree of ground shaking. Finally an earthquake can also be measured on the moment magnitude scale which is a more up-to-date way of measuring earthquakes by geologists. However the Richter Scale is still used to show the size of an earthquake for the public and mass media.
Your mark ____
Examiners mark: 8
Mark scheme
Level 1: simple references to the scales given above, increasing numbers of the scale, but without any precision in their use; or detailed explanation of one system only, including technology. 1-4
Level 2: recognition that there is more than one way in which to measure seismicity – by energy levels, or by impact, or by technology. Some detail is given of more than one system. Also credit commentary on usefulness if given when in this level. 5-8
Notes for answers
The magnitude of seismic waves and earthquakes is measured on two
scales. (a) The Richter scale is a logarithmic scale - an event measured at 7
on the scale has amplitude of seismic waves ten times greater than
one measured at 6 on the scale. The energy release is proportional to the magnitude, so that for each unit increase in the scale, the energy released increases by approximately 30 times. (b) The Mercalli scale measures the intensity of the event and its
impact. It is a 12-point scale that runs from Level I (detected by
seismometers but felt by very few people – approximately equivalent to 2 on the Richter scale) to Level XII (total destruction with the ground seen to shake - approximately 8.5 on the Richter scale).
Seismic records enable earthquake frequency to be observed, but these records only date back to 1848 when an instrument capable of recording seismic waves was first developed. Candidates may provide details of both scales. Detail of the equipment and technology used, such as seismographs, is also relevant. Credit elaboration of how the technology is used or works.
With reference to two seismic events you have studied from contrasting areas of the world, compare the ways in which earthquakes and their impacts have been managed. 10 marks
The Great Hanshin earthquake or KobeJapan earthquake took place on the 17th January
1995 in the early hours of the morning. The focus was 16km beneath the epicentre on AwajiIsland, 20km from Kobe. The tremors lasted 20 seconds. This earthquake was caused by the destructive plate margin where the heavier oceanic Pacific plate sank under the lighter continental plate, Eurasian plate, causing a subduction zone which eventually caused the earthquake. It measured 7.2 on the Richter scale. In total 6434 people lost their lives due to the earthquake and many thousands lost their homes. Many of these people lost their lives due to the poor living conditions in their wooden houses with most having very heavy lead roofs with up to 2 tonnes of weight on their roofs. In response to this much stricter building laws were introduced so that not as
many buildings would collapse if it were to happen again. Other measures implemented
included installing weights on top of high rise buildings to stop them swaying as much in
future earthquakes and reinforcing buildings with steel girders again for added support. All these ways of managing the impacts of the earthquake were quite easy for the Japanese government due to them being a developed country. However a similar earthquake but in a different part of the world had much larger impacts upon the country. The Gujarat earthquake in India in January 2001 was extremely devastating and one of the largest earthquakes in that region of the world for around a 100 years. It caused 20000 3 deaths and left around 1 million people homeless. Many died in the aftermath due to lack of resources whereas in the Kobe earthquake the Japanese were much better equipped to manage the hazard. However, the Indian government should be commended for them sending in thousands of troops to help with the clear up as well as food, medicine and tents for all the people affected, especially as all four hospitals in Bhuj collapsed. After the Gujarat earthquake there were fears of the spreading of diseases such as cholera and typhoid but due to the swift response of the Indian government this did not happen. However, around 20000 cattle died in the earthquake which severely affected the local people especially from an agricultural perspective. After the Kobe earthquake due to the country being more developed they were able to manage the impacts a little better than in India. Large sums of money were funnelled into research and other initiatives such as installing rubber on to the underside of bridges so they are less susceptible to collapse because during the earthquake a lot of the freeways and train tracks collapsed. Overall both earthquakes were extremely devastating but Japan were much better at recovering from the impacts even though their total damage costs were around 20 times higher larger (Kobe – 100 billion dollars; Gujarat – 4/5 billion dollars). I believe this is due to Japan being much more developed and having better plans for when earthquakes strike. Afterwards the Japanese also introduced particular days of the year dedicated towards earthquake safety and children at school have regular drills in how to act in an earthquake.
This shows how well the impacts have been managed by the Japanese. The rebuilding of the destroyed port very quickly also shows how well managed the impacts were.
Your mark ____
Examiners mark: 10
Mark scheme.
Level 1: simple statements of management which could apply to any earthquake hazard. No specific detail provided. 1-4
Level 2: specific statements of management strategies which can be clearly attributed to named areas and/or earthquakes access this level. Comparison must be clearly recognisable
for 7/8 marks. 5-8
Level 3: a fully developed answer, with good elaboration of the management strategy of two seismic events. A rounded answer with a full comparison of the two events. 9-10
Notes for answers
Management may take the form of prediction, prevention or protection.
Precise detail will depend on the case studies selected. The prediction of earthquakes is very difficult. Regions at risk can be identified through plate tectonics, but attempts to predict earthquakes a few hours before the event are unreliable. Such prediction is based upon monitoring groundwater levels, release of radon gas and unusual
animal behaviour. Fault lines such as the San Andreas can be monitored and local magnetic fields can be measured. Areas can also be mapped on the basis of geological information and studies of ground stability to produce a hazard zone map that can be acted upon by local and national planners.
Trying to prevent an earthquake is thought by most people to be impossible. This, however, has not stopped studies into the feasibility of schemes to keep the plates sliding past each other, rather than .sticking. and then releasing, which is the main cause of earthquakes. Suggestions so far for lubricating this movement have focused on using
water and/or oil.
Protection. Being prepared for an earthquake involves everyone from civil authorities to individuals. Protection can include any of the following:
Hazard-resistant structures: buildings can be designed to be seismic or earthquake-resistant (a great deal of detail can be given here)
Education: instructions issued by the authorities explain how to prepare for an earthquake by securing homes, appliances and heavy furniture, and getting together earthquake kits
Fire prevention: .Smart meters. have been developed which can cut off the gas if an earthquake of sufficient magnitude occurs
Emergency services: use of the emergency services in the event of an earthquake requires careful organisation and planning
Civilians are given first-aid training as trained medical personnel can take some time to arrive
The establishment of computer programs that will identify which areas the emergency services should be sent to first
Land-use planning: the most hazardous areas in the event of an earthquake can be identified and then regulated. Certain types of buildings such as schools and hospitals should be built in areas of low risk
Insurance: people are urged to take out insurance to cover their losses though this can be very expensive for individuals
Aid: most aid to developing countries has been emergency aid in the few days after the event - providing medical services, tents, water purification equipment, and search and rescue equipment. Aid over the longer term, to reconstruct the built environment and redevelop the economy, is much less readily available.
(10 marks)
'The hazards presented by volcanic and seismic events have the greatest impact on the world’s poorest people'. To what extent do you agree with this view? (40)
Answer 1.
Tectonic hazards such as earthquakes and volcanic eruptions occur across the surface of the globe, but many argue that they have the greatest impact on the poorest people – the inhabitants of LEDCs. However, there are many different factors which contribute to the severity of a tectonic event, both physical and human. Firstly I do not agree with this view because the severity of an event and the impact it has obviously depends on the magnitude of the event. For example, the Bandah Aceh earthquake of 26th December 2004 off the coast of Indonesia measured 9.1 on the Richter Scale whereas L’Aquila earthquake in Abruzzo, Italy of 2009 only measured 6.3R.
Volcanic eruptions also differ in explosivity. Mount Etna on Sicily erupted in 2008 with only Strombolian activity whereas the Soufriere Hills eruptions 1995-97 on Montserrat varied from Pelean to Plinean activity. Also obviously the type of event also determines the impact it has on people – rich or poor. With the L’Aquila earthquake the only primary effect it produced was ground shaking for 20 seconds whereas the Bandah Aceh earthquake was submarine and produced tsunami waves. There were several waves varying from 20m to 30m in height. This made the impact of the tsunami far more widespread as the waves travelled a great distance across the Indian Ocean affecting countries as far apart as South Africa and Indonesia, India and Burma.
Volcanic eruptions also come in different forms – volcanoes found on destructive
margins often lie dormant for long periods of time, then produce explosive and violent
eruptions of acidic lava, pyroclastic flows, ash and larger lava bombs. The eruptions on
Montserrat were of this nature. Constructive margins and hot spots produce gentle
eruptions of lava which are more continuous. Although on Etna on Sicily has uncertain
tectonic conditions and lies near a destructive margin, the eruptions here are of this nature.
Finally the length of the event also determines the severity of its impact. The Boxing Day
tsunami was thankfully short-lived as was the L’Aquila earthquake. However the Soufriere Hills complex on Montserrat erupted for 2 years and eruptions on Mount Etna are on-going. These three factors, magnitude, type and length do have a large effect on its impact. However I mainly agree with the view that human geography has the greatest impact on whether a tectonic event becomes a ‘natural disaster’. Mostly this is dependent on the level of economic development of a country.
Firstly the population density of the area as well as the land use and infrastructure determines the input of the event. The countries bordering the Indian Ocean are mainly LEDCs with many fishing communities living on the coast. The coastal geography in places like Thailand and Indonesia is low-lying. However, it is also densely populated often with mainly poorly built houses and poor roads and communications. This contributed to the destruction of the area by the tsunami and made it more difficult for remote communities to receive aid. The same is true for Montserrat as an LEDC (although it is a UK colony), the infrastructure was not of the same standard as is an MEDC – 50% of the water supply network was destroyed by the eruption and the capital Plymouth was covered in ash.
However the lack of roads and communications on other parts of the island made it again difficult to obtain aid. On the other hand, the medieval city of L’Aquila had good
communications by road and rail and although it was built on lake sediments which
amplified the shaking, aid was able to be delivered. or even, the major determinant of the impact of a tectonic event is the level of protection, prediction and preparation a country has against tectonic hazards. For example, Japan has an excellent tsunami warning system which can relay public warnings within 3 minutes of the seismic event. It has also built tsunami walls to aid tsunami shelters along the coast. As a consequence, a 30m tsunami in 2005 killed only 240 people. The Boxing Day tsunami killed an estimated 230000 people. One of the main reasons for this is that the countries bordering the Indian Ocean are LEDCs and so could not at that time afford a warning system. One has subsequently been installed.
On the other hand it is not just LEDCs which suffer from poor hazard management. A
Californian scientist commented of the L’Aquila earthquake ‘an earthquake of this