Managing Tectonic Hazards » Protection, Planning and Technology

Why protection and planning matter

We cannot stop an earthquake or an eruption. But we can reduce the damage they do. Remember from the last lesson that monitoring and prediction give warning, and that early warning systems give a few seconds or minutes. This lesson is about what is done before a hazard strikes so that fewer people are hurt.

There are three groups of methods: protection (making buildings and land safer), planning (deciding where and how people live and what they do in an emergency) and technology (warning devices and apps).

When you evaluate any method, ask four questions: what are its strengths, what are its weaknesses, how much does it cost, and who benefits? A method is sustainable here if it keeps people safe for the long term, can be paid for and maintained by the country itself, and does not harm the environment.

Key terms:

• Earthquake-resistant building: a building designed to stay standing, or at least not collapse, when the ground shakes.
• Retrofitting: adding earthquake protection to an older building that was not built with it.
• Hazard map: a map that shows which areas are at greatest risk from a hazard such as ground shaking, lava, lahars or tsunamis.
• Exclusion zone: an area where people are not allowed to live or enter because the risk is too high.
• Evacuation plan: an agreed plan of routes, meeting points and shelters so people can leave danger quickly.

Earthquake-resistant buildings

Most earthquake deaths happen because buildings collapse, not because the ground opens up. So the single most useful protection is a building that does not fall down. Engineers use five main ideas.

A fifth idea is a flexible frame. Steel and reinforced concrete bend a little without snapping, so the building sways instead of breaking. Rigid, unreinforced brick or stone walls can crack and fall.

Many older buildings are not safe. Retrofitting adds bracing, stronger foundations or shock absorbers to them. It is cheaper than rebuilding, but it still costs a lot, and each building needs its own survey.

Building codes and enforcement

Building codes are legal rules that say how strong new buildings must be. Japan has strict codes that were tightened in 1981, and modern Japanese buildings survive very strong shaking.

A code only works if it is enforced. That means inspectors check the plans and the finished building, and builders are punished for cutting corners. In some countries inspectors are few, corruption is a problem, or poor families build their own homes cheaply. Then the code exists on paper but buildings still collapse.

Land-use planning and hazard maps

Planners use hazard maps to decide where to build. Schools, hospitals and homes are kept away from the highest risk areas, such as unstable slopes, soft ground that turns to mud when shaken, river valleys that lahars follow, and low coasts that tsunamis flood. Land in dangerous zones can be used for parks, farming or car parks instead.

Hazard maps also show people which route to take out of danger. Their weakness is that they need detailed scientific survey work, and the land may be very valuable or already crowded with homes, especially in fast-growing cities in LICs.

Evacuation plans, exclusion zones, drills and education

• Evacuation plans: clear signs, safe routes and shelters mean a whole town can leave quickly. They are cheap but only work if people know them.
• Exclusion zones: on Montserrat in the Caribbean, about two thirds of the island, including the capital Plymouth, was closed off after the Soufriere Hills volcano erupted in the 1990s. The zone keeps people away from danger, but people lost homes, farms and their capital, and some who went back inside it in 1997 were killed.
• Drills and education: Japan holds national disaster drills every 1 September. Children learn to drop, cover under a table and hold on. This is cheap and saves lives in countries of any income, but people forget over time and many ignore warnings.

Protecting against lava and lahars

Lava moves slowly enough that some can be diverted or cooled. In 1973 on Heimaey in Iceland, huge pumps sprayed sea water onto a lava flow. The lava cooled, slowed and the harbour was saved. It was expensive and only works on slow, small flows. Walls and channels can steer lava away from towns, but they cannot stop a large eruption.

Lahars follow river valleys. Engineers build barriers and check dams across the valleys to trap mud and boulders. Channels and dams cost a lot and need to be cleared out regularly, but they protect towns and farmland downstream.

Technology: tsunami warning buoys and apps

Undersea earthquakes can cause tsunamis. Buoys on the surface connect to sensors on the sea floor that measure the pressure of the water above. If the pressure changes, a tsunami may be passing, and the buoy sends the signal by satellite. Warnings then go out by sirens, radio, television and phone apps. Apps can reach many people at once and cost users little, but they need a phone signal, power and a working warning centre behind them. A warning from a buoy can give minutes or hours, depending on how far the earthquake was. Buoys are expensive to build and maintain, and an earthquake right beside a coast leaves almost no time.

Evaluation: which approach saves most lives?

Approach	Strength	Weakness	Cost
Earthquake-resistant buildings	Stops the main cause of death	Only new or retrofitted buildings are safe	High
Hazard maps and land-use planning	Keeps people out of danger for good	Hard in crowded cities	Medium
Evacuation plans, drills, education	Cheap and works for everyone	People forget or ignore it	Low
Exclusion zones	Removes people from the danger completely	People lose homes and farms and may return	Medium to high (rehousing, compensation)
Lava and lahar barriers	Protects towns and farmland	Only works for small flows	High
Warning technology	Gives time to move to safety	Too little time near the source	High

LICs and HICs differ. HICs can afford strong buildings, retrofitting and expensive warning systems, and they can enforce the rules. LICs often have limited money, rapid city growth and many homes built without permission or checks, so they depend more on low-cost methods such as drills, education and evacuation plans, and on help from aid.

A judgement. Safer buildings save the most lives from earthquakes, because buildings cause most deaths. But no single method is enough. The best results come from combining strong buildings, good planning, and well-practised evacuation. For volcanoes, hazard maps and evacuation save most lives, because lava and ash cannot easily be stopped.

Exam-style question

Fig. 1.1 shows made-up data for two earthquakes of similar magnitude.

Feature	City A	City B
Magnitude	7.1	7.0
Buildings meeting earthquake codes	90%	15%
Deaths	40	6,000

(a) Identify one way a building can be made earthquake-resistant. [1 mark]

(b) Describe how a tsunami warning buoy works. [3 marks]

(c) Suggest why City B had many more deaths than City A. [3 marks]

(d) To what extent can protection and planning reduce the number of deaths from earthquakes? [6 marks]