Managing Tectonic Hazards » Responses, Monitoring and Prediction

Primary responses: the first hours and days

When a tectonic hazard strikes, people and governments respond. Responses are split by timing. Primary responses happen immediately, during and just after the event. The aim is to save lives and stop further harm.

Key terms:

• Primary response: an immediate action taken in the hours and days after a hazard to save lives.
• Secondary response: a longer-term action taken in the weeks, months and years after, to recover and rebuild.
• International aid: help (money, supplies, equipment or trained people) given by other countries and organisations.
• NGO: a non-governmental organisation, a charity that is independent of government, such as the Red Cross.

Secondary responses: recovery and rebuilding

Secondary responses begin once the emergency is over and can last for years.

• Rebuilding homes, schools and hospitals.
• Restoring services such as water, electricity, roads and phone networks.
• Economic recovery: helping farms, shops and factories reopen so people have jobs and income again.
• Improved building codes: new rules so that buildings are made stronger next time, which is called 'building back better'.

LICs and HICs, and the role of international aid

The same earthquake can lead to very different responses. A country's wealth decides how fast and how well it can cope.

Response	Typically in an HIC	Typically in an LIC
Search and rescue	Trained teams with machinery and sniffer dogs, quickly on site	Few teams and little equipment; people often dig by hand; roads may be blocked
Medical care	Many hospitals, ambulances and helicopters	Hospitals may be damaged or full; shortage of doctors and medicines
Rebuilding	Paid for by government money and insurance; fast recovery	Slow, because there is little money; often depends on aid and loans
Building codes	Strict rules, mostly followed	Rules may be weak or not enforced, so rebuilt homes can stay unsafe

This is why international aid matters most for LICs. Other governments send rescue teams and supplies, and NGOs and the United Nations bring tents, medicines, food and money.

A response is sustainable if it reduces the risk for the future and does not rely on outside help for ever. Training local people and rebuilding to stronger codes is more sustainable than only handing out supplies.

Monitoring volcanoes

Monitoring means measuring changes in a hazard. A rising magma chamber gives warning signs, so scientists watch for them.

Technique	What it detects
Seismometers	Many small earthquakes as magma pushes through rock; more of them is a warning
Tiltmeters	The slope of the ground changing as it swells
GPS ground deformation	The ground surface bulging outwards by centimetres as magma fills the chamber
Gas sampling	Changes in gases such as sulphur dioxide leaking from the volcano
Thermal imaging	Heat rising in the crater or on the slopes
Satellites	Ground movement and heat over large or remote volcanoes, from space

How successful is it? Volcanoes usually give warning, so scientists can often say an eruption is likely and issue an alert level, and people can be moved out. Scientists can issue alert levels, and people living on the slopes can be moved out before the eruption. But monitoring is not perfect. It can tell us an eruption is coming, but not always the exact day, size or type. False alarms cost money and make people stop trusting warnings. Monitoring equipment and trained scientists are also expensive, so poorer countries may have fewer instruments.

Can earthquakes be predicted?

No. Prediction means saying exactly when, where and how big. For earthquakes this cannot yet be done. Scientists can only say where earthquakes are likely, not when. Here is why.

• Seismic gaps: a part of a fault that has not had a big earthquake for a long time may be building up stress. This shows where one is possible, but not whether it will happen next week or in 50 years.
• Foreshocks: small earthquakes sometimes come before a big one. But most small earthquakes are not followed by a big one, and nobody can tell in advance which is a foreshock.
• Animal behaviour: there are stories of animals acting strangely before earthquakes, but it has not been shown to work, so it is not reliable.

Early warning systems

An earthquake cannot be predicted, but once one has started it can sometimes be detected quickly. Fast P waves reach sensors first. A computer works out the size and sends an alert before the slower, more damaging S and surface waves reach people. This gives only seconds of warning, up to about a minute, depending how far away you are. It is not much time, but it is enough to stop trains, shut off gas, open fire station doors and let people drop, cover and hold on. Japan and Mexico both run systems like this. People close to the epicentre get little or no warning, because the waves reach them almost immediately.

Evaluation: what works best?

Monitoring and warning can reduce deaths only if people can act on them. Keep these evaluation points ready:

• Cost: instruments, satellites and alert networks are expensive; rescue teams and aid cost a lot too.
• Who benefits: people in rich countries and cities with systems; remote or poor communities benefit less.
• Sustainability: responses that build local skills and stronger buildings last longer than one-off aid.

Exam-style question

Fig. 1.1 shows made-up monitoring data for Volcano K over four weeks.

Fig. 1.1	Week 1	Week 2	Week 3	Week 4
Small earthquakes per day	4	12	40	95
Sulphur dioxide (tonnes per day)	300	700	1,600	3,500
Ground bulge (cm)	0	2	6	15

(a) Identify one instrument that could be used to measure the ground bulge. [1 mark]

(b) Describe how the monitoring data change over the four weeks. [2 marks]

(c) Explain why earthquakes are much harder to predict than eruptions. [3 marks]

(d) How far do you agree that international aid is the most important response after a major earthquake in an LIC? [6 marks]