It is neither practically nor economically feasible to move an entire town or city located near or on faultlines, so what is being done to protect earthquake-prone cities and address earthquake-prone building stock?
An earthquake-prone building is defined as a structure that:
- will have its ultimate capacity exceeded in a moderate earthquake, and
- would be likely to collapse causing injury or death to persons in the building or to persons on any other property; or cause damage to any other property
Since a 7.1 magnitude earthquake struck in September 2010, Christchurch and its surrounding areas have experienced several subsequent major earthquakes. The earthquakes have had a devastating effect on the central city and the people of Christchurch and policy has changed in the aftermath to reduce the impact of any future disaster.
It is estimated there are potentially 7,600 buildings in Christchurch that are earthquake-prone. Before 2010, policy required earthquake-prone buildings to be strengthened to 33 per cent of the building code requirements for a new building. Post-2010, buildings need to be strengthened to 67 per cent of code.
Although the earthquake-prone buildings section of the policy primarily affects buildings constructed prior to 1976, the level of risk posed by buildings constructed as recently as a few years ago is now more widely appreciated.
All new buildings must be designed to withstand earthquakes and fully comply with the current Building Code requirements. An earthquake strengthening level under 100 per cent is not considered acceptable for any new building.
As mentioned, the level of risk posed by buildings constructed just a few short years ago is now more widely appreciated, in particular the inadequate performance of reinforced concrete structures due to deficient detailing.
NZI, one of the country’s leading insurers, says an ‘earthquake-risk building’ is any building that is assessed at being between 34 per cent and 67 per cent of New Building Standard. The risk of injury or death in an earthquake-risk building is lower than an earthquake-prone building but the risk of damage to the building remains high.
Although every building is different and needs to be assessed on its own merit regarding insurance cover, building owners need to consider the insurance implications if their building is identified as earthquake-prone.
The minimum changes likely to apply are:
- The basis of settlement on the building will move to Indemnity Value if it is currently insured on another basis. Indemnity Value is the value of the building to the insured at the time of loss, sufficient to place the insured back in the same financial position to that immediately prior to the loss.
- Seismic upgrade costs will be excluded from cover
One of the basic principles of insurance is to cover the actual financial loss of the insured. A building, once it has been identified as earthquake-prone will potentially have a lower value than it held previously due to the known financial liability on the owner to undertake seismic strengthening work.
Therefore, providing reinstatement cover for an earthquake-prone building would mean a substantial level of betterment which would not be aligned with covering the financial loss and putting the insured back in the same place as they were prior to the loss. This is why cover is restricted to Indemnity Value.
The Riverside Apartments is the latest development in Christchurch’s CBD to reach practical completion after nine months of reconstruction works. The works, designed by the Buchan Group, include code-specified structural strengthening, a new external façade, and upgrades to the apartment’s boutique rooms and have been rebuilt to earthquake-resistant standards after ground improvement and remediation was carried out on the site
“The building was stripped back almost to its bare concrete frame and re-levelled by compaction and jet grouting under the foundations. This is an important technique which ensures loose soils are reinforced to help correct the building’s structural foundations,” said Raylene McEwan, the Buchan Group’s Christchurch-based practice manager.
“This project shows it is physically possible and economically viable to repair earthquake damaged buildings, to bring them up to current building code requirements and return them to function rather than having to demolish and construct new in every case.”
Sitting on major, active fault lines, experts believe a major earthquake could hit Istanbul in the coming decades. Housing more than 14 million people, considering this eventuality is foremost in the government’s mind.
In 2012, they established a strategy known as Urban Transformation, an initiative to renew lower-income areas, reinvigorate shantytown settlements and construct earthquake-proof buildings.
This month, the Environment and Urban Planning Ministry updated its map of areas under the risk of collapse. In 2015, some 200,000 housing or business units are set for demolition in 170 districts. Last year, 12,000 buildings were demolished out of about 130,000. Istanbul’s risky areas in total house roughly 1 million people.
The majority of areas under risk are located on the city’s European side, which saw mass migration in the early 20th century and the construction of many makeshift buildings called “gecekondu” in haphazardly zoned areas, which are regarded as unlikely to survive in the event of an earthquake or a similar disaster. According to authorities, the relocation of those in areas under risk will create new and much safer settlements in the city called “reserve areas.”
Last year, the Headquarters for Earthquake Research Promotion, put the probability of metropolitan Tokyo being struck by a magnitude 7.0 quake within the next 30 years at around 70 per cent.
The Japanese government has estimated that the number of casualties and buildings destroyed could be halved from a predicted 23,000 and 610,000 respectively if local authorities adopt a new 10-year risk management plan.
The figures reflect the devastation caused by the magnitude 9.0 earthquake which hit the Tohoku region in March 2011.
The aim is to increase the proportion of buildings with earthquake-resistant features to 95 per cent by 2020 from an estimated 80 per cent in 2008.
With many residential areas crowded with wooden properties, particular focus is also being placed on fire-prevention measures, with requirements for authorities to speed up the installation rate of quake-sensitive electricity breakers which automatically stop the flow of electricity when they sense a strong temblor. More than 60 per cent of the fires reported after the Tohoku quake were caused by electrical appliances.
The 10 prefectures and 309 municipalities named as areas that could also suffer if a powerful earthquake strikes directly beneath the Tokyo area are being asked to finish their plans by 2024.
Each year, Southern California experiences as many as 10,000 earthquakes, though the majority of these are non-destructive.
The most recent was a magnitude 3.5 earthquake that occurred near the 46-mile-long Newport-Inglewood fault.
The fault has long been a concern for seismologists and government officials as it runs under some of the most densely populated areas of Southern California. After it caused destruction and killed more than 100 people in 1933, it forced changes in the state’s seismic building regulations.
Damage to school buildings caused by that quake led to major steps toward earthquake-resistant construction in the state. It was also one of the first faults covered by a state’s earthquake law prohibiting construction on active faults and requiring developers to perform studies identifying them.
As earthquakes become more and more prevalent around the world, design, strategies and laws will have to continue to evolve to ensure protection of buildings and lives.