Fixing the cracks in disaster mitigation

Key text

On 17 October 1989, an earthquake measuring 7.1 on the Richter scale rocked the United States city of San Francisco. The Loma Prieta earthquake, as it became known, killed 68 people and brought more than 24,000 homes crashing down.

This was certainly a disaster, but a relatively minor one compared to what hit Izmit, Turkey on 17 August 1999. That earthquake, registering 7.4 on the Richter scale, took the lives of at least 17,100 people and flattened 300,000 homes.

Why would two earthquakes of similar magnitude have such different impacts? Timing had something to do with the difference in casualties – the San Francisco earthquake occurred in the afternoon, when relatively few people were at home. In Izmit, many people were sleeping and could not escape their collapsing apartments.

But the main reason was that San Francisco was more prepared. In San Francisco, most houses, offices, sports stadiums, roads and bridges had been built to resist earthquakes, and emergency services were ready to lend assistance throughout the city. In Izmit, many buildings had been poorly constructed, and it was mostly these that collapsed. There was no real emergency plan: thousands of people made homeless by the quake had nowhere to go and little access to medical services. Diseases such as typhoid and hepatitis quickly became killers.

The lessons from these two examples are clear: long-term planning can greatly reduce the impact of earthquakes, and it is most needed in developing countries.

Related site: Earthquakes kill nearly 90,000 in 2005 Summarises the deaths and fatalities resulting from earthquakes in 2005. (PhysOrg.com, USA)

Developed versus developing

A quick glance at death rates shows the massive fault line that separates developed and developing countries in their capacity to withstand earthquakes. Clearly, developing countries need to make improvements in their preparedness for earthquakes and other disasters.

Year	Location	Intensity (Richter scale)	Death toll
Developing countries
2006	Java	6.3	5,800
2005	Kashmir-Pakistan	7.6	87,000
2004	Indian Ocean and tsunami	9.2	229,000
2003	Bam-Iran	6.6	27,000
2001	Gujarat-India	7.9	30,000
1976	Tangshan-China	8.2	242,000
Developed countries
2004	Chuetsu-Japan	6.9	39
1995	Great Hanshin-Kobe, Japan	7.2	6,400
1994	Northridge-Los Angeles, USA	6.7	60

Counteracting earthquakes

Perhaps the most obvious way of reducing the effects of earthquakes is to establish urban centres away from earthquake-prone areas, but this is much easier said than done. Some of the world's great cities – Tokyo, Yokohama, Jakarta, Los Angeles, Mexico City and Santiago, to name only a few – are sited right on the edge of tectonic plates, where earthquakes are most likely (Box 1: What is an earthquake?). Moving them somewhere safer isn't feasible.

Huge reductions in the effects of earthquakes are still possible in such cities – if they are prepared for the worst. Improved building standards help enormously. The main reason for the high death tolls in the recent earthquakes in Iran and Pakistan was the failure of buildings. In Bam, located about 1000 kilometres southeast of Tehran in Iran, most of the houses in the city were built with mud bricks: when these collapsed, thousands of people suffocated to death. In the Kashmiri–Pakistan disaster, an estimated 60 per cent of buildings in urban areas were made of un-reinforced solid concrete block masonry and more than 60 per cent of these collapsed, crushing and burying their inhabitants.

Effects of earthquakes

The effects of earthquakes can be classified as either direct or secondary. Direct effects are those caused by the shaking and deformation of the ground: the most dangerous consequence is the collapse of buildings, bridges and elevated roadways. The secondary effects of earthquakes might include tsunamis, which can devastate large areas of low-lying areas, as well as fire, landslides and avalanches. The Indian Ocean tsunami is a dramatic example of a secondary effect: more recently, another earthquake-triggered tsunami in July 2006 claimed more than 500 lives in Java. A small earth tremor may have contributed to a landslide in the Philippines in February 2006 that killed more than a thousand people.

How do earthquakes affect buildings?

The direct effects of earthquakes can damage buildings in several ways. They can cause the ground underneath to fail, thereby undermining foundations. This is particularly likely on unstable land, such as in areas that have been reclaimed from the sea. The huge Minato Mirai development in Yokohama, Japan, for example, is built on land reclaimed from Yokohama Bay. This land is expected to liquefy – turn to mud – in the event of a large-magnitude earthquake. To help counter this, the foundations of the buildings built there go through the landfill and are anchored firmly to the basement rock beneath.

Earthquakes can also rock a building to the point at which it collapses. All buildings vibrate at a natural frequency. This frequency varies from building to building, depending on characteristics such as the design and the construction materials used, but typically it's high in small buildings, such as most houses, and lower in taller buildings. Earthquakes cause most damage to a building when the frequency of the ground movement caused by the earthquake is similar to the building's natural frequency. When this happens the two are said to be in resonance, which means that the shaking caused by the earthquake complements and intensifies the natural shaking of the building. If they were not in resonance, the natural shaking of the building would tend to counteract the shaking of the earthquake. Perhaps the most striking example of this effect was seen in a 1985 earthquake in Mexico City, which was particularly severe on buildings about 20 stories high, while smaller and taller buildings tended to survive.

Better buildings

Knowledge of earthquake-resistant design has increased dramatically in recent decades – although many of the principles have been known for centuries (Box 2: Cultural monuments). The United States, which has the research capacity and a significant earthquake risk, has led the way. Thousands of structures throughout the country have been fitted with instruments to record the responses of those structures to earthquakes and other disturbances. This and other information has been used to improve building codes with the aim of ensuring that all new buildings are capable of surviving major earthquakes. Older buildings have been retrofitted to improve their earthquake resistance. But improved building codes are useless if they are not enforced.

Techniques

Engineers have developed many techniques for reducing the impacts of earthquakes on buildings and other structures. For example, 'damping' devices that act like car shock-absorbers can be installed to counteract the resonance effect: they absorb some of the kinetic energy of the earthquake and turn it into heat energy.

During a high-intensity earthquake, buildings will 'deform', which means that the materials from which they are constructed are bent and twisted as force is applied. The ability of a structure to accommodate large deformations without a significant loss of strength is known as ductility. Buildings built with ductile materials, such as steel and reinforced concrete, are better able to withstand the extreme forces of an earthquake than non-ductile or brittle materials, such as unreinforced masonry.

Another technique (among many) that engineers recommend to increase earthquake resistance is the use of bracing frames to help counteract the lateral forces imposed by seismic waves. Tall buildings should also be wide at the base and have most of their weight in the lower floors. Japan's tallest building, the Landmark Tower, is a good example of this.

But better information doesn't always produce better results. Many recently constructed houses in San Francisco's expensive Marina District collapsed during the Loma Prieta earthquake because they were built on reclaimed land. Large sections of elevated concrete freeway collapsed during the Great Hanshin earthquake, even though they were supposed to be earthquake-resistant.

Planning to plan ahead

Despite some notable failures, most developed countries generally have good systems for the design of building codes and monitoring their implementation. Developing countries are often not so well organised or resourced and often have great difficulty coping in the aftermath of disasters such as earthquakes, droughts, hurricanes and floods. Large numbers of people are suddenly without shelter and the systems of food and water supply and waste disposal break down: the result can be famine, malnutrition and disease. The process of development can be set back for years, even decades, meaning that poverty is perpetuated and the population remains vulnerable to further disasters.

Related site: Natural disaster management Provides information on disaster management and Australia's response to emergencies. (Global Development, Australia)

Better planning and construction need not cost huge sums of money. In some of the towns affected by India's Gujarat earthquake, authorities were caught in a bind. They felt they could not allow reconstruction without putting in place proper plans and establishing building standards, so the reconstruction process was slow to start. Some villagers – with the aid of local assistance agencies – took matters into their own hands, strengthening the traditional mud, stick and grass houses, called 'bungas', by adding cement to the mud. This low-cost solution might have been put into effect sooner if planners had already thought of it. In other areas, villagers distrusted the new concrete houses built on their behalf and chose to continue to live in tents.

A simple lesson can be learned from such experiences. Planning is best done prior to a disaster, so that when the disaster strikes, communities are prepared. Not only will they cope better with the initial shock and immediate after-effects, they will also be able to start rebuilding much sooner – not only their houses and other infrastructure, but also their lives. Introducing effective planning, and implementing the plans, might take a shake-up, but it could save hundreds of thousands of lives in the future.

Related Nova topics:

Calculating the threat of tsunami

Looking for clues to our mineral wealth

Box 1: What is an earthquake

An earthquake occurs when suddenly-released energy moves through the earth in the form of seismic waves. These waves radiate out from the site of energy release (the hypocentre) and, at the earth's surface, are felt as a shaking or displacement of the ground.

What causes them?

Most major earthquakes are natural events. The outermost shell of the earth, called the lithosphere, is divided into ten major and many minor tectonic plates ('tectonic' is a derivative of a Greek work meaning 'to construct and destroy'). These plates are about 100 kilometres thick and 'float' on top of another layer called the asthenosphere. Most major earthquakes occur on and adjacent to the boundaries between plates. The plates move constantly – if slowly – against each other, creating stresses that build up over time. An earthquake occurs when these stresses are suddenly released; the resultant seismic waves radiate in all directions, including towards the earth's surface.

Location, location, location

Location plays a very large role in the potential for an earthquake disaster, with the most vulnerable sites lying along the boundaries of tectonic plates. The majority of the world's earthquakes occur on the Pacific Rim of Fire, which lies on the boundary of the Pacific plate and runs from New Zealand in the southwest, up through the Solomon Islands, New Guinea and the Philippines to Japan, and eastwards across the northern Pacific to Alaska and down the west coast of Canada, the United States, Central and South America. The Indonesian archipelago is also highly susceptible to earthquakes, as are the Himalayan Mountains, which have formed at the boundary between the Eurasian and Indian tectonic plates.

Not all earthquakes occur along the tectonic plate boundaries, however. The earthquake in Gujarat, India, in 2001 is located well away from the nearest plate boundary, and its cause is not well understood. The entire continent of Australia is in the middle of a tectonic plate, with no part of it near a major plate boundary. Australia should therefore be reasonably safe from big earthquakes, but they still occur from time to time. Since 1900, 17 earthquakes with magnitudes greater than 6 have been recorded. In 1989 an earthquake registering 5.6 on the Richter scale killed 13 people in Newcastle, most of them in a single building that collapsed.

Human activities such as mining and the build-up of large masses of water behind dams can also cause earthquakes, although these are usually relatively minor in scale.

Related sites

• Plate tectonics (Nova: Science in the news, Australian Academy of Science)

• Earthquake science explained (United States Geological Survey)

• Plate tectonics, the cause of earthquakes (Nevada Seismological Laboratory, USA)

• Seismic deformation (Nevada Seismological Laboratory, USA)

• Indian Gujarat earthquake, 26 January 2001 (Global Education, Australia)

Box 2: Cultural monuments

One of the most inspiring photographs taken in the aftermath of Turkey's 1999 Izmit earthquake shows the beautiful Golcuk mosque. Built in the 14th century, it appears completely undamaged by the earthquake, its 50-metre-high minaret still pointing towards the heavens, while the modern city around has almost completely turned to rubble.

The ability of this mosque to withstand the devastating earthquake owes more to its architect, Mimar Sinan, than it does to divine intervention. Other, more modern mosques collapsed or were otherwise damaged in the earthquake.

But not all the great monuments of the world are proving as resistant as the Golcuk mosque. For example, an earthquake in Egypt in 1992 damaged up to 150 cultural heritage sites. Around the world, many thousands of cultural sites are vulnerable to damage, both natural and man-made. Yet they form an important part of the planet's cultural wealth and there is increasing concern for their loss and deterioration. To safeguard cultural heritage sites against natural disasters, governments and communities can develop disaster plans that might include disaster mitigation, structural reinforcement and restoration works.

Related sites

• Earthconsultants.com
  • Seismic vulnerability screening of the Suleymaniye mosque in Istanbul, Turkey
  • Earthquake damage in Afganistan
  • Seismic vulnerability screening of the Roman Colosseum

• Earthquakes threaten obelisks of culture (Boloji.com, USA)

• Methodology for strengthening and repair of earthquake damaged monuments in pagan Burma (United Nations Educational, Scientific and Cultural Organization)

• Iran: Glimmers of hope in Bam (United Nations Educational, Scientific and Cultural Organization)

Activities

• Global Education (Australia)
  • Natural disasters teaching activities – a series of 11 activities looking at disaster preparedness, emergency relief and response.

• Xpeditions (National Geographic, USA)
  • Dealing with disasters – students study potential natural hazards in their community and discuss community preparation and response.
  • The impact of natural hazards around the world – students investigate the negative consequences of natural hazards and learn to prepare for them.
  • Natural disasters – exploring plate tectonics – introduces students to the concept of plate tectonics and the natural disasters that can occur when plates shift.

• Microsoft, USA
  • How do earthquakes affect buildings? – students simulate earthquakes of different magnitudes online and see how they affect buildings.

• Discovery School, USA
  • Landslides – a lesson plan for landslides and other hazards.
  • Constructing earthquake-proof buildings – explores different materials, shapes and design options for buildings.
  • Earthquakes: Getting ready for the big one – students investigate different types of earthquake waves and consider building substrate and construction in preparation for an earthquake.

• Cable News Network (USA)
  • Lesson plan: Indonesian earthquakes – students locate areas of earthquake activity, conduct research on disaster prevention and design an education program.

• United States Geological Survey
  • A model of three faults – students observe fault movements on a model of the Earth's surface.
  • How much bigger is a magnitude 8.7 earthquake than a magnitude 5.8 earthquake? – students calculate the difference in strength between earthquakes of different magnitudes.
  • Word search puzzles – a series of nine word search puzzles of words related to earthquakes.

• The Franklin Institute (USA)
  • A journey to the center of the Earth – a website created by students that contains earth science facts and activities.

• Digital Library for Earth System Education (USA)
  • Living in earthquake country – explores seismic waves, earthquake prediction, earthquake magnitude and intensity, and the damage caused by earthquakes.
  • Evidence for plate tectonics – students investigate the evidence for plate tectonics.

• Introducing and Demonstrating Earthquake Engineering Research in Schools (University of Bristol, UK)
  • Explore a 3D model – students experiment with simple sine waves to make the complex wave forms of earthquakes.
  • Natural frequency experiments – students investigate natural frequency using plasticine balls and wire.
  • Resonance experiment – students use plasticine balls and wire to investigate resonance.
  • Inelastic deformation experiments – students investigate inelastic deformation using a coat hanger.

• Faultine: Seismic science at the epicentre (Exploratorium, USA)
  • Liquefaction – students investigate what happens to sandy or fine-grained soils during an earthquake.
  • Seismic slinky – students use a slinky to model earthquake waves.
  • Highway seismograph – students make a seismograph in a moving car.

• Daily Lesson Plan (New York Times, USA)
  • Feeling vulnerable – students examine the connection between global poverty and natural disasters.

Further reading

• May-August 2006
• January-April 2006
• September-December 2005

• Being prepared (by Le Huy Ngo)
• Breaking the cycle (by Didier Cherpitel)

Useful sites

• What is an earthquake?
  Provides information about earthquake science with an Australian focus.
  http://www.ga.gov.au/urban/factsheets/earthquakes.jsp

• Recent earthquakes measured by Geoscience Australia
  Provides up-to-date records of earthquake activity.
  http://www.ga.gov.au/bin/listQuakes

Faultline: Seismic science at the epicenter (Exploratorium, USA)

Provides information on major earthquakes in the past and the science of earthquakes. Also includes sections on earthquake prediction, engineering of buildings, useful graphics and photos. Has an American perspective.
http://www.exploratorium.edu/faultline/index.html

United States Geological Survey

• Latest earthquakes – last 7 days
  Shows the location of recent earthquakes around the world.
  http://earthquake.usgs.gov/eqcenter/

• Building safer structures
  Provides information about building monitoring during earthquakes.
  http://quake.wr.usgs.gov/prepare/factsheets/SaferStructures/

• Saving lives through better design standards
  Explains how an understanding of earth movement leads to improved building standards.
  http://quake.wr.usgs.gov/prepare/factsheets/BetterDesign/

Resistant buildings (Introducing and Demonstrating Earthquake Engineering Research in Schools, University of Bristol, UK)

Explains how buildings vibrate during earthquakes and how they can be protected or strengthened to resist earthquakes.
http://www.ideers.bris.ac.uk/resistant/resist_home.html

Earthquake engineering (National Information Service for Earthquake Engineering, University of California, USA)

Includes sections on the causes of damage by earthquakes and earthquake-resistant design and construction.
http://nisee.berkeley.edu/bertero/html/table_of_contents.html

Australian Broadcasting Corporation

• Adobe house (Catalyst, 18 May 2006)
  Describes an Australian researcher's work using string, bamboo and wire to reinforce mud brick houses.
  http://www.abc.net.au/catalyst/stories/s1640933.htm

• Earthquakes, tsunamis and volcanoes (Ask and Expert)
  Provides a series of questions and answers about natural disasters.
  http://www.abc.net.au/science/expert/realexpert/earthquakes/

Disaster risk reduction begins at school (United Nations World Disaster Reduction Campaign)

Provides information about the 2006-2007 World Disaster Reduction Campaign and other campaigns since 2000.
http://www.unisdr.org/eng/public_aware/world_camp/2006-2007/wdrc-2006-2007.htm

World Disasters Report 2005 (International Federation of Red Cross and Red Crescent Societies, Switzerland)

Reports on the latest trends, facts and analysis of recent crises, focusing on the role of information in disasters
http://www.ifrc.org/publicat/wdr2005/index.asp

Glossary

frequency. A measure of how frequently a wave goes up and down (oscillates) or the number of waves passing by in a second. A hertz is a unit of frequency – 1 oscillation per second; a kilohertz (kHz) is 1000 hertz – 1000 oscillations per second; a megahertz is 1 million hertz – 1 million oscillations per second. For more information see Sound properties and their perception – pitch and frequency (The Physics Classroom, USA).

intensity. Measures the strength of shaking produced by an earthquake at a certain location. Intensity is determined from the effects on paople and structures. Intensity isusually measured in the Modified Mercalli intensity scale (Association of Bay Area Governments, USA).

magnitude. The severity of an earthquake is determined by its magnitude and intensity. The magnitude of an earthquake is a measure of the amount of energy released by the seismic event that caused it. Its intensity is its capacity to cause damage at a given point on the earth's surface. Thus, there is usually one value for an earthquake's magnitude but many measures of its intensity – depending on factors such as the distance of a given point from the earthquake's hypocentre.

Richter scale. A scale for measuring the magnitude or size of an earthquake. The scale relates to the energy released by an earthquake and is determined from the logarithm of the amplitudes (heights) of the seismic waves recorded at seismograph stations on the Earth's surface. See also magnitude and intensity. For more information see The severity of an earthquake, Measuring the size of an earthquake and Magnitude intensity comparison (United States Geological Survey).

The largest recorded earthquake, measuring 9.5 on the Richter scale, occurred in Chile in 1960. Seismologists have devised several other scales of measuring the magnitude of earthquakes, although the Richter scale remains the main scale used by the media to inform the public about earthquake size. For more information about the earthquake in Chile see Great Chile earthquake of May 22, 1960 (National Geophysical Data Center, USA).

seismic waves. Waves that transmit the energy released from movement of the Earth's crust. Primary waves (P-waves) are longitudinal waves that shake the ground in the direction of the wave. Secondary waves (S-waves) are shear waves that shake the ground perpendicular to the direction of travel. For more information see What is seismology? (Michigan Technological University, USA).

shear strength. The maximum stress a material will bear when it is twisted or otherwise deformed without stretching or compression.

tectonic plates. The Earth's surface is made up of huge tectonic plates that have moved very slowly during geological history, and continue to move, thus changing the position of continent and oceans. The plates are about 100 kilometres thick and move at a rate of about 1-12 centimetres per year. See also continental drift. For more information see Plate tectonics (Looking for clues to our mineral wealth, Australian Academy of Science).