Coping with hazards
- A wide range of approaches can be used to cope with tectonic hazards, but there are essentially three options; do nothing, adjust, or leave.
- Which option is chosen depends on a number of factors. These include the nature of the hazard, its frequency, its magnitude, population pressure in the location and the level of economic development.
- Volcanoes are easier to deal with, as there is usually some prior indication of an eruption. They also originate at a known, visible point that can be monitored. Earthquakes typically occur without warning and may have their focus anywhere on a long fault line.
- The level of development is significant, as it will influence the extent of capital investment (a deterrant to lleaving) and the level of available technology (an encouragement to adjust).
Earthquake risk assessment
- One reason for the increased destructiveness of earthquakes is that human populations have expanded into earthquake risk zones - especially those where earthquakes are infrequent but also violent - and that buldings and infrastructure are increasingly expensive and vulnerable.
- Where written records of earthquakes do not exist, geological and soil maps can be used to identify past earthquake activity. Once the geological record is understood, areas of special risk can be mapped. Areas of high risk include steep slopes, sensitive soils and low-lying coastal areas.
- Risk-assesment also has to take into account the nature of the settlement and its infrastructure. Medium-height buildings are more vulnerable than either tall or single-storey buildings. Masonry buildings are more vulnerable than wooden or steel-framed buildings, but wooden buildings are more prone to fire risk.
- The location of mains services (electricity, gas and water) may have an impact on potential damage.
- The size and design of roads, bridges, etc, will have a considerable impact on evacuation, emergency access and potential loss of life.
There are many possible indicators of imminent earthquake activity, but none has proved relliable. There are a number of key areas of research and monitoring;
- The P wave/S wave ratio drops prior to a large earthquake,
- Warning activity. The number of small earth tremors increases before a major shock. These are known as foreshocks and can be of different types.
- Water levels in wells rise or fall as the rocks are squeezed by the increasing strain before an earthquake.
- Radon levels in wells. This radioactive gas is squeezed out from rock pores by the build-up of strain.
- Levels of manganese, zinc, and copper in basaltic rock at a depth of 1000m increased by over 1000% before an earthquake and rapidly falls afterwards.
- Changes in the electrical properties of rock occur as increasing strain causes the crystals to rearrange their structures, in extreme cases this produces light displays.
- Ground deformation occurs as rocks are strained. This can be surveyed on the ground with laser ranging techniques or measured by accurate radar imagery from satellites. This method is still being developed and GPS systems are increasingly being used/
- Ununusal animal behaviour is often reported before earthquakes. It would be possible to monitor animal behaviour or identify the sensory cues they use and monitor these.
Volcano risk assessment
- Assessing the risk of volcanic eruption includes monitoring current levels of activity and mapping the evidence of destruction caused by previous eruptions.
- It is possible to modufy lava flows by damming, cooling (with water) snd bombing, but the only realistic approach to living with volcanoes is to avoid high-risk sites (e.g. lava and mudflow tracks) and to evacuate as necessary.
Planning for earthquakes
Regardless of the magnitude of the event, several things are true about damaging earthquakes;
- They occur without warning, and pre-event response activity is not possible.
- The probability of the event occuring during non-working hours is more than 3:1.
- Damage to sensitive communications systems will interfere with response management.
- Aftershocks are likely and will cause additional damage, interfere with response efforts, and cause unease among the population.
The key strategies to reduce the impact of earthquakes lie in the hands of governments, for example;
- Land-use zoning.
- Building regulations.
- Evacuation drills.
- Emergency service provision.
Government bodies such as the Federal Emergency Management Agency in the USA publish advice on how to prepare for and cope with events such as earthquakes.
- One way to evaluate different approaches to dealing with tectonic hazards is to subject them to cost-benefit analysis, a technique widely used in business and resource management.
- The marginal benefit of increasing investment in a given adjustment represents demand or the willingness to pay. This decreases with increasing effort or expenditure on hazard prevention. Marginal cost represents supply.
- The optimum exists when marginal costs and marginal benefits are equal.
- Such economic evaluations are useful, but the real impact of hazard events cannot be expressed in simple monetary terms.
- What is the 'value' of human life, for example? The Warsaw Convention places a value of $360,000 on each death, but how meaningful is this?
- It is also difficult to place monetary values on long-term or widespread reductions in environmental quality. How much is an attractive view worth, for instance?
- Because of environmental variability, different perceptions and imperfect knowledge about hazard potential, maximising the gain from investment in hazard strategies is rather optimistic.
- Much scientific research is being done to improve the accuracy and reliability of the methods used to forecast tectonic hazards. New approaches are beginning to emerge that may offer a more secure future.
- A new idea in earthquake prediction is to monitor how fast strain accumulates. Scientists measure the accumulation of strain along a fault segment each year, the time that has passed since the last earthquake along the segment, and how much strain was released in the last earthquake.
- Another new approach is to monitor electrical charges with satellites. As pressure builds before an earthquake, the oxygen modecules inside the rocks undergo chemical reactions, creating a positive electrical charge that radiates towards the earth's surface.
- New research to improve the prediction of volcanic eruptions is also underway. In Japan, attention focused on the temperature of escaping gases from volcanic vents. A research project on Mt Etna digitally collects geophysical information on seismic movements and transforms it into audible sound waves, which can be 'scored' as melodies. The resulting 'music' is analysed for patterns and used to identify similarities in eruption dynamics.
- It is hoped that this and other research will make the prediction of tectonic events, particularly earthquakes, more reliable. It is also hoped that new technology and materials can be used to improve the shock-proofing of built structures of all kinds,