Earthquake Protection Systems_8 doc

5.7 Turning Reconstruction into Future Protection In the aftermath of the earthquake, the replacement of destroyed buildings and thereconstruction of a damaged community present a signifi

regions.26Small-scale production technologies are proving increasingly ful in building material manufacture in developing regions.27

success-Choice of building materials for use in reconstruction should largely reflect thepolicy of preference for local production Designs for new construction should

be determined by the materials available rather than trying to introduce newforms and materials Designs incorporating brick infill walls may be inappropriate

in areas where stone is normally used and plentifully available, for example.Reconstruction designs should largely respect the existing traditional buildingforms, materials and architectural style of the region As far as possible, as argued

in Section 5.5, control over the design and construction of buildings should beleft to the owners and the member of the community that use them

5.7 Turning Reconstruction into Future Protection

In the aftermath of the earthquake, the replacement of destroyed buildings and thereconstruction of a damaged community present a significant opportunity to makethe new community safer against a possible repetition of the disaster some time

in the future After a major disaster, the replacement of possibly large sections

of a town and the rehabilitation of a significant percentage of the townspeoplegive an opportunity to bring about changes that will reduce the impact of thenext earthquake

Changes are possible after a disaster where they would not be possible hand Funds are available, everyone is aware of the hazard and generally agreed

before-on the need for protectibefore-on, the political climate is sympathetic and there are ical opportunities to push through change where it is needed But the window ofpolitical opportunity and the period of availability of financial assistance are usu-ally short The key to making maximum use of the opportunity is pre-planningand an awareness of how best to achieve mitigation within reconstruction activ-ities The post-disaster emergency period is not usually the best time to makecrucial decisions concerning the long-term future of a city, and yet experiencehas shown that many reconstructions are planned rapidly, immediately after theevent, with little studied consideration of what contributes most to future safety.There are at least five important considerations that affect reconstruction plan-ning and the policies that are likely to be most effective in bringing about futuresafety:28

polit-1 The return period of the earthquake

2 Pre-existing plans for the future development of the city – including seismicrisk studies for future protection

26 As practised in the reconstruction programmes of Iran (1990), Yemen (1982) and Ecuador (1987).

27 Spence and Cook (1983), UNCHS (1990).

28Aysan et al (1989).

3 Profile of the communities affected, including the economic basis and culturalpreferences of the various groups affected.

4 The scale of the disaster

5 The resources available for reconstruction

Of these only the last two factors are unknown before the earthquake ness planning should establish the longer term aims of a mitigation programme

Prepared-in general, so that Prepared-in the event of a major earthquake, the reconstruction can

be channelled towards well-established mitigation aims rather than having toimprovise a new strategy plan

The way the reconstruction is carried out can have a major effect on thefuture safety in addition to what is reconstructed – the process is as important

as the end product Social and economic recovery of the affected ties and the reduction of the overall vulnerability of the city to the impact

communi-of future earthquakes require integrated and comprehensive policies covering

a wide range of activities A major reconstruction offers the opportunity to duce comprehensive mitigation measures into the ongoing processes of planning,administration and construction It also provides the impetus to channel financialresources where they are needed and prompts a political willingness to implementpolicies

intro-Political pressures for rapid recovery should take second place to systematicstudies of long-term needs The emphasis should be placed on creating the eco-nomic building blocks, the cultural continuity and the spatial framework for futuredevelopment rather than on construction showpieces Institutionalising reforms

in the building industry and construction process will be more important in thelong run than building an instant earthquake-proof town

5.7.1 Reconstruction after Earthquakes with Long Return Periods

It is obviously important to capitalise on the opportunities, funds and incentivespresent after an earthquake to improve the building stock and restore public con-fidence However, unless the opportunity is also taken to instigate much longerterm protection measures and to carry the lessons beyond the areas immediatelyaffected by the earthquake, stronger reconstruction may not be a very effectiveway of reducing future earthquake losses The risk of future earthquake lossesvaries considerably from place to place Return periods for earthquakes strikingthe same place twice are usually considerably longer than the lifetimes of indi-vidual buildings, and in areas of long return period, the construction of strongerbuildings has a sense of “closing the stable door after the horse has bolted” Thereturn periods of high intensities from shallow-depth, near-field events in mostsites across the world can usually be counted in centuries In eastern Turkey, an

area of relatively high seismicity, for example, the area affected twice by a aging earthquake (I
VII) within 100 years is only 2% of the high-risk areas Insouthern Italy the return period of damaging earthquakes at any particular loca-tion within the Apennine region is less than once in 350 years Most earthquakesoccur in areas which have not recently experienced a destructive event.

dam-In most locations in the world, where high intensities have a long returnperiod, using a reconstruction programme to make a place safer against a futureearthquake should mean planning long-term strategic developments for the cityrather than short-term upgrading Long-term strategies that should be consideredinclude:

• Using the reconstruction to maximise long-term economic development forthe region

• Controlling future urban land-use patterns in the reconstruction to minimiserisk

• Structuring the morphology, street layout and landownership in the tion to improve urban safety and density of development

reconstruc-The immediate reaction of most city authorities after a disaster is to rebuilddamaged buildings in strong, earthquake-resistant construction This is a naturalreaction, but its effect may be largely symbolic and psychologically reassuringrather than an effective method of reducing the losses from future earthquakes.Major monuments may last hundreds of years, but ordinary residential buildingstock in a city may have a lifetime of 30 to 100 years depending on pressures

of development, housing markets and fashions of housing style

5.7.2 Historical Reconstruction and Present-day Risk

The end results of the reconstruction-into-protection process are of special tance to the study of mitigation as are the examples of recent reconstruction policyand their intended results It is possible to look at examples of towns that wererebuilt after historical earthquakes that are now, many years later, facing up tothe threat of a repetition of a destructive event (See the boxes on the followingpages.) Studies of urban seismic risk in Noto in western Sicily, destroyed, relo-cated and rebuilt after a massive earthquake in 1693, and of Bursa in westernTurkey, repeatedly damaged by large-magnitude earthquakes and considerablyrebuilt after the destructive event in 1855, and also of Quetta, in northern Pak-istan, reconstructed after the earthquake of 1935, give insights into the long-termnature of earthquake protection from decisions implemented in the aftermath Thecase study of Mexico following the destructive earthquake of 1985, provides atwentieth-century comparison

impor-Reconstruction case study Noto, Sicily,

an eighteenth-century reconstruction

The city of Noto today The older stone masonry palazzi of the historic centre

(back-ground) are being abandoned in favour of new reinforced concrete villas seen in the foreground

After the earthquake that destroyed their city and killed an estimated 3000 people

in 1693, the citizens raised considerable sums to rebuild their city safely 29 After extensive public debate, the decision was finally made to relocate the city from its ruined site to a new location over 10 kilometres away where it could be laid out along the latest principles of city planning The new city layout, along wide streets and punctuated by a series of Baroque architectural monuments, provided an urban framework within which the townspeople could rebuild their family houses.

Most rebuilt in the grand style, building large and strong Italianate palazzi in

dressed stone to replace the vulnerable timber-framed or rubble houses of the ancient town.

Now, 300 years on, the town council is again facing up to the threat of a return of a destructive earthquake, forecast with a return period of between 200 and 1000 years Apart from the civic and religious monuments, less than 1%

of the building stock now at risk was built as part of that eighteenth-century reconstruction 30 The rest of the buildings were built in subsequent centuries, replacing the older buildings as they deteriorated, infilling vacant blocks and

29 Tobriner (1982).

30Coburn et al (1984b).

expanding onto areas surrounding the city And the few remaining

eighteenth-century palazzi, so much more robust and earthquake resistant than the buildings

they originally replaced, are now, after years of gradual deterioration, among the most vulnerable of the existing buildings – in 1997, part of the dome

of Noto’s cathedral suddenly collapsed without assistance from any earth tremors.

The policies of the eighteenth-century reconstruction for which today’s tion have cause to be grateful in making the city safer against the next earthquake are the strategic decisions on relocation, replanning and restructuring the local economy made at the time For example:

popula-• The relocation of the city away from its ancient defensive site onto a site closer

to the rich agricultural plains and a secure water supply ensured the prosperity

of the townspeople subsequently leading to a continual upgrading of building quality.

• The choice of site on a firm, travertine hilltop – one of the flattest rock sites in the region – reduced the potential for landslide and slope failure that claimed many lives in the old city in the 1693 earthquake.

• The rationalisation of the city’s street layout with wider avenues and lower densities of housing has made the streetscape safer and more accessible to emergency services, than if it had been rebuilt on the old site.

Reconstruction case study Bursa, western Turkey,

a nineteenth-century reconstruction

The extending suburbs of Bursa in 1985 The direction of expansion can have a big effect on the city’s future earthquake risk

The earthquake of 1855 that damaged the historical city of Bursa, once the capital of the Ottoman Empire, destroyed revered monuments, including sev- eral of the main trading bazaars, and caused serious fires that consumed sections of the residential areas in the city The reconstruction that followed was chiefly funded from Istanbul, the nation’s capital, and consisted of wide- scale restoration of the monuments and a resettlement of the population 31 Many feared another earthquake, even stronger, and it is reported that morale among the townspeople was low The protection measures included the sepa- ration of houses and the use of masonry instead of timber frame for buildings where possible Tall minarets were demolished as a hazard to the population Rocks were cleared from the slopes above the city to reduce the risk of future rockfalls.

For the city of Bursa today, again affected recently by the 1999 Kocaeli earthquake, hazard analysis shows that there is a relatively high level of seismic hazard in the area A ‘seismic gap’ close to the city has been identified by seismologists, which may indicate the likely location of a large earthquake in the near future 32 Detailed seismic risk analysis of the modern city shows that the major contribution to the present-day seismic risk has little to do with the earlier reconstruction There is little evidence in today’s city of the changes in the building stock that occurred following the earthquake The buildings built before 1920 now constitute only 3% of the building stock However, some of the reconstruction activities of 1855 have had an impact on the subsequent risk of the city The population reduction after the 1855 earthquake reduced the regional importance of the town, which limited its nineteenth-century growth This was reversed in the 1950s when a major industrialisation of the Mar- mara Sea region included car factories and major investment in Bursa, and caused a very rapid growth in the city The city continues to grow at well above the average rate for Turkish cities and its centre has retained its his- torical siting on the firm rock hillside of Uluda˘g Mountain Losses in future earthquakes will be highly influenced by the direction of expansion of the city suburbs in years to come Expansion out onto the alluvial plains could mean significantly higher earthquake losses in a future earthquake than if the sub- urbs continue to expand along the rock mountainside or onto firmer ground nearby 33 Building quality and engineering design will be important in reducing future losses but the main potential for earthquake losses will be the older twentieth-century buildings The reconstruction project to make Bursa safer in

1855 had little concept of the massive changes that Bursa would undergo a century later.

31 Kuran (1986).

32 Coburn and Kuran (1985).

33 Akbar (1989).

Reconstruction case study Quetta, Pakistan,

an early twentieth-century reconstruction

Reinforced masonry is a resilient and cost-effective way of building in earthquake areas ‘Quetta bond’, first developed after the 1935 earthquake in northern Pakistan,

is still in use today

Quetta is one of the major cities of Pakistan, with a key military significance In

1935 it suffered a major earthquake which destroyed almost every building in the city and many surrounding villages and claimed an estimated 20 000 lives 34

34 Jackson (1960).

Because of its strategic position, relocation was considered impossible, and the seismologists’ report pointed out that as a result of the energy released

in the earthquake of 1935, Quetta could expect to be safe from another such event for some time 35 The national government ordered instead that the city should be rebuilt on earthquake-resistant principles, and a building code was drawn up, which was in many respects a forerunner of modern codes 36

General regulations were specified governing the shape, height and spacing and materials of buildings For important buildings, a system of steel frames with brick infill panels was specified; brick masonry buildings were to be built according to a new bonding system which incorporated concrete ring beams and vertical reinforcement (later known as Quetta bond) 37 For the poor, various systems using timber frameworks clad in lightweight materials were proposed, and the heavy mud roofs which had caused so many deaths were banned Reinforced concrete frame construction was not recommended, as it required too high a level of skilled work.

For a time this code was effectively enforced throughout the city But the following decades brought war, then independence, then a mounting and still critical refugee problem It was impossible to maintain the tight controls on build- ing which were possible in the years following the earthquake Over the years since the earthquake the population has grown more than five-fold; pressure on space has made the demand for higher buildings irresistible; the timber required for the cheaper code buildings is now unobtainable; and the municipal engineer

is too preoccupied with public health problems to be concerned with control of building standards 38

Today the vast majority of the population live in unauthorised buildings of poor masonry materials, extremely vulnerable to earthquakes; even in the city centre buildings of reinforced concrete are constructed with no proper provision for earthquake forces The recurrence of the 1935 event today would without any doubt be a disaster on a much larger scale than before.

Quetta’s experience demonstrates that the introduction of a building code alone will not be sufficient to ensure future standards of protection; a continuing awareness of the earthquake risk, a degree of public control over building, and above all the economic means to pay for protection are all needed if protection

is to be effective.

35 West (1935).

36 Quetta Municipal Building Code (1940).

37 Spence and Cook (1983).

38 Spence (1983).

Reconstruction case study Mexico City, a late twentieth-century

reconstruction

Strengthening of an existing reinforced concrete frame building by the addition of steel cross-bracing One of a large number of public buildings in Mexico City strengthened this way following the 1985 earthquake

Mexico City has suffered three damaging earthquakes since 1957, each with a level of ground motion strong enough to cause structural failure and collapse

in some of its weaker buildings The earthquake in 1985 resulted in the highest level of damage in the city’s history: over 600 buildings collapsed and more than

7000 people were killed The high levels of damage were as much due to the poor quality of building in the 1960s and 1970s as they were to the fact that this was the strongest shaking to hit the city this century The particular characteristics

of the ground conditions in the city – built on a deep and ancient drained lake bed – make it likely to experience strong ground motions much more often than most other cities elsewhere Any distant earthquake occurring up to 400 km away from the city may cause the saturated weak soils below the city to amplify the shaking A damaging level of ground motion may be generated in this way every

15 years or so The effects are, however, highly localised, and earthquake motions repeatedly damage the same area within the city – the area around the historic centre in which about 1.5 million of the 19 million inhabitants of the city live.

In Mexico City, the short return period of the earthquake and the characteristic patterns and repetition of damage in the same locations make mitigation through reconstruction an important priority This has been well appreciated by the authorities in charge of structuring the reconstruction Mitigation measures taken after the earthquake included:

• a large-scale programme of reinforcement of several hundred government buildings, schools, hospitals and other structures;

• a massive public housing reconstruction programme which has gone far beyond replacement of earthquake-damaged buildings to upgrade poor-quality and vulnerable housing in the city centre;

• a complete revision of the urban master plan for the city, including a rezoning

of the city, proposals for decentralisation and reductions in allowable densities;

• a programme of renovation, strengthening and reuse of historical buildings;

• an urban upgrading programme to revitalise the city centre, to regenerate economic and environmental conditions and reduce vulnerability of the com- munities most at risk;

• the revision of seismic building codes, enforcing a considerable increase in earthquake resistance of engineered buildings.

5.7.3 Exporting Improvements beyond the Reconstruction Area

It is seismically probable that the areas most likely to be hit by the next quake are areas outside those badly damaged in the last earthquake, but probablywithin the same seismic region To make a significant impact in the losses fromearthquakes in the region as a whole, the reconstruction can be used to promotemitigation activities outside the damaged areas, into zones where the likelihood

earth-of an earthquake is equally severe, but perhaps on a shorter timespan The tradiction here is that, while the actual risk may be higher, the immediacy ofearthquake danger is not so obvious to the general public in the areas whichhave not experienced an earthquake recently, and the incentives and opportuni-ties for the occupants of those areas to carry out disaster mitigation activitiesmay also be much less

con-The fringes of earthquake-affected regions are often important and fruitful areas

to instigate earthquake protection projects, both because the population tends to

be very aware of the recent, nearby earthquake and because the areas are stillunder threat from future earthquakes

In general, any reconstruction aiming to instigate mitigation measures againstfuture events should aim to export its lessons to areas with significant future risks.39

39 The 1999 earthquake in Kocaeli Province, Turkey, triggered considerable earthquake mitigation activity in neighbouring Istanbul Province in the years immediately following.

5.7.4 Relocation of a Badly Damaged Community

Severe damage to any settlement almost always gives rise to suspicion thatthe damage is due to poor ground conditions, localised active faults or somesite-specific hazard A reduction in earthquake risk, it may be argued, could beachieved by resiting the community on a safer site, and the justification of futureearthquake protection is often advanced for relocating a town or village Problemswith relocating settlements in a reconstruction were discussed in Section 5.5 Thecosts of relocating almost any sizeable established settlement will be prohibitiveand unlikely to be justifiable in earthquake protection terms If it is possible toinfluence locational planning, the opportunity should be taken to introduce land-use modifications within the damaged settlement Urban planning measures forprotection are discussed in Section 6.3 Better protection can usually be providedmore cost-effectively by stronger design and construction standards of buildings

on the existing site Upgrading design and construction standards and buildingstock management are discussed in Chapter 6

The conclusions that can be drawn from this are that in order to make a icant impact in the losses from earthquakes, mitigation measures have to targetthe long-term reduction of vulnerability for the wider city, aimed at improvingnot only the existing and future building stocks but also the general living stan-dard of the communities at high risk and the decentralisation of the vital urbanfunctions

signif-5.7.5 Deconcentration of Cities and Services

The dispersal of elements at risk over a wider area to make them a more difficulttarget to hit is a key strategy in mitigation planning Reconstruction after anearthquake is a good time to instigate deconcentration measures Deconcentrationmay involve reduction in densities, dispersal of elements and restructuring roadlayouts Practical measures to decentralise urban areas on a regional basis may

be accelerated by the impact of an earthquake The principle of restructuring risk

by compartmentalising utility sectors, and spreading elements at risk, such asbuildings, industry or services, around the city is a valuable one, and one thatcan be widely applied The full range of deconcentration measures possible, toreduce densities, regulate urban form and protect utilities, is described in moredetail in Section 6.4

Further Reading

Aysan, Y and Oliver, P., 1987 Culture and Housing after Earthquakes: A Guide for

Future Policy Making on Housing in Seismic Areas, Disaster Management Centre,

Oxford Polytechnic, Headington, Oxford OX3 0BP, UK.

Comerio, M., 1998 Disaster Hits Home: New Policy for Urban Housing Recovery,

Uni-versity of California Press, Berkeley, CA.

Cuny, F., 1983 Disasters and Development , Oxford University Press, Oxford.

Davis, I., 1978 Shelter after Disaster , Oxford Polytechnic Press, Oxford.

NCEER, 1989 Proceedings of Conference on Reconstruction After Urban Earthquakes:

An International Agenda to Achieve Safer Settlements in the 1990s, September 1989,

National Centre for Earthquake Engineering (NCEER) at University of Buffalo, Red Jacket Square, Buffalo, New York, USA.

6 Strategies

for Earthquake

Protection

6.1 Creating a Safe Society

As described in Chapter 2, everyone is a stakeholder in the likely losses from

an earthquake and has an interest in earthquake protection, from individuals

to companies, professional risk managers, financiers and government agencies

If you live in an earthquake area, your safety depends on the strength of thebuildings you spend your time in and the precautions you take in your dailylife Companies can protect their operations and their staff by minimising thevulnerability of buildings, equipment and contents Risk managers can transferand manage their risk by buying insurance National governments take the lead

in setting building codes, safety standards and establishing a safety culture.Previous chapters have been concerned with the event of an earthquake andwith the emergency which a damaging earthquake causes They have discussedhow to act in that emergency, and how to prepare for it The following chaptersare principally concerned with strategies for making the community safer in theevent of an earthquake and defining the roles that various groups may play inbringing about earthquake protection These groups include:

• individuals and community groups

• private corporations or organisations

• urban authorities

• national governments

• international aid and development organisations