Feed aggregator

ACT names 8 winners of $2m funding to roll-out 2MW solar-integrated battery storage across 600+ homes and businesses.

A startling number of solar households think the best use of their investment is to feed power to the grid. Education is needed.

Coalition and Labor fudge on commitments to ARENA, with vote on funding cuts looming next week.

Slash subsidies or back 100% renewables? Australia's Coalition parties at odds over whether to support or oppose wind and solar.

Free movement between the US and Mexico - the hottest of topics in the 2016 US presidential campaign - is not just a human issue.

HUGE FIND: The oldest fossils known to date have been discovered in 3.7 billion-year-old rocks in Greenland by an Australian-led team of researchers.

A look at Kenya's fast-growing crocodile farm industry, which is enjoying a big rise in demand for the animal's meat, led by China.

Of the many devastating pictures to come out of central Italy after last week’s deadly earthquake, the clock tower of Amatrice standing defiantly amid the rubble of the town has become an iconic image.

The clock tower was reportedly built in the 13th century and its solid stance defies us to understand how this remarkable structure has evaded destruction at least twice in the past 800 years.

But perhaps surprisingly, it’s not unusual for tall, ancient structures to survive earthquakes.

Unlikely survivors Nepal’s Dharawara tower in 2013, before it was destroyed in the 2015 earthquake. KATHMANDU NEPAL FEB 2013, CC BY-SA

Similar towers are relatively commonplace in Italy and part of the country’s charm. The town of San Gimignano, about 200km from the centre of the Amatrice earthquake, has 14 towers that date as far back as the 12th century – and have consequently survived many earthquakes big and small. Other towers can be seen in Alba in northern Italy.

Further afield, a memorable image of the Izmit earthquake in Turkey in 1999 was of the tower of the Golcuk Mosque standing forlornly among the ruins.

Photos from the 1906 San Francisco earthquake show a slender tower and an array of chimneys standing in the rubble of the city.

In many instances, however, the towers fall, as happened to the Dharahara tower during the magnitude-7.8 Nepal earthquake in April 2015.

Why do some of these slender icons survive repeated earthquakes and others fall? An article in The Economist suggested that the clock tower was better constructed than the surrounding buildings, pointing out that it even survived better than a modern school and hospital. The L'Aquila experience suggests that this is probably one part of the story.

However, the reality is more complex. Other factors can and do contribute to the resilience of buildings.

On shaky ground

It is very likely that the clock tower’s survival was influenced by the relationship between the frequency of the earthquake waves and the natural resonance of the building. To understand why, we have to consider how earthquakes interact with buildings.

Earthquakes generate seismic waves that pass through the ground. Like ocean waves, they have peaks and troughs. The frequency of the wave is related to its “period” – the time taken for one complete waveform (including a peak and a trough) to pass.

A building has a natural period that causes it to vibrate back and forth. Think of a child on a swing – a swing with short ropes will complete a full cycle much more quickly than a long swing.

The same is true of buildings with different heights. A building is effectively an upside-down pendulum and taller buildings have longer natural periods of oscillation (swinging back and forth).

The ground also has a preferred period at which it oscillates. Soft sediment in a river valley will oscillate over longer periods, and hard bedrock over shorter ones.

High-frequency (short period) earthquake waves are therefore amplified in bedrock, such as the site of Amatrice, and are the dominant frequency radiated by small to moderate and shallow earthquakes such as last week’s.

Low-frequency (long period) earthquake waves are amplified in sediment and form a greater part of the seismic energy radiated by larger earthquakes, such as the Tohuku earthquake in Japan and the Nepal quake that felled the Dharahara tower.

When the resonant frequency of the ground coincides with the resonant frequency of the building, the structure will undergo its largest possible oscillations and suffer the greatest damage. The rigidity and distribution of mass along the height of a building also have a big effect on the likely damage sustained in a given earthquake, as this governs the way the induced forces are distributed.

You can try this for yourself by experimenting with a broom handle and a 30cm ruler. Held vertically, the top of the broom handle will do little if you vigorously shake its base with small movements, whereas the ruler will oscillate under the same shaking.

Slow the shaking down and the handle will begin to whip back and forth while the ruler settles down. Place a large mass on the end of either the ruler or the broom handle and the characteristics will change.

The concept is beautifully demonstrated in a video by Robert Butler of the University of Oregon.

A resonant problem

Of course, real structures and real earthquakes are far more complex. Real structures have many natural frequencies, and earthquakes vibrate across a spread (or spectrum) of frequencies.

Destruction occurs when any of a buildings’s natural frequencies coincide with any of the dominant frequencies of the earthquake. In some situations, there may be just a few structures that avoid this dangerous combination, such as the clock tower at Amatrice, or the chimneys of San Francisco.

The characteristics of shaking at Amatrice have not yet been published, but it is highly likely that the tower is standing not only because it was built well in the first instance, but also because it is just the right size and shape to survive the frequency of shaking that occurs during Italy’s moderate-magnitude earthquakes.

This process is equally important in other regions. The magnitude-6.8 Myanmar earthquake on August 24 damaged many historic temples in the Irrawaddy Valley, but none appears to have collapsed. These high-but-squat structures are susceptible to high-frequency shaking, whereas the passage of earthquake waves through alluvium is likely to have amplified mainly low-frequency earthquake waves.

Notably, much of the damage to the temples seems to have occurred as a result of the collapse of recent cheap “restorations”.

Building practices are extremely important in mitigating the effect of shaking on buildings. Modern buildings are commonly fitted with devices to reduce the effects of resonance. Engineered solutions are available to retrospectively enhance the performance of unreinforced masonry buildings, with little impact on their aesthetics.

In Italy, this retrofitting needs to be done as quickly as possible before the next earthquake. This will be a costly exercise. Even apparently resilient medieval towers may require retrofits, because they have commonly accumulated a degree of damage.

However, Italy is a globally important cultural and tourism hub, and her earthquake-prone buildings, like those in Myanmar, are part of our collective heritage. Italy should not be left to struggle alone with the management of earthquake-prone building hazards.

The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond the academic appointment above.

Most scientific experts agree that data from the initial trial badger culling areas in Gloucestershire, Somerset and Dorset do not justify further extension of culling (Scientists criticise badger cull extension, 31 August). In ignoring this advice, and extending culling to five new areas, the government risks not only wasting much money but also giving farmers false hope that the approach will contribute to reducing TB in cattle. The initial trial areas were set up to test whether free-range shooting could be done humanely and at the same time reduce badger populations by at least 70% – the figure previously established as the level needed to achieve a significant reduction in TB in cattle.

The government was able to announce last year that it had achieved its culling targets, but only because they were based on unrealistically low badger population estimates – not on the central or best estimate value, but on the lowest bound value of the statistical margin of error around this estimate. This was simply a fudge. In none of these exercises did it achieve a 70% reduction based on the most likely population estimate.

Continue reading...

A drug that destroys the characteristic protein plaques that build up in the brains of patients with Alzheimer's is showing "tantalising" promise, scientists say.

Some of the world’s earliest life forms may have been captured in squiggles found in ancient rocks from Greenland.

My friend Chris Leyland, who has died of cancer aged 62, was that rare breed – a farmer for whom people mattered as much as the livestock in his care. In his native Northumberland, his most recent achievement was securing a future for the unique, 800-year-old Chillingham breed of wild cattle. Appointed park manager at Chillingham Castle in 2005, Chris used his farming expertise to double the herd numbers to more than a hundred today, by reversing decades of decay in their habitat.

But he will be best remembered by the Northumberland farming community as leader of a campaign that led to the creation of Bell View, a visionary approach to the housing and care of old people in Chris’s home town of Belford.

Continue reading...

George Purcell, 15, joins local outcry after charity buys historic farm’s land and sheep, but not its farmhouse or outbuildings

A teenage farmer has accused the National Trust of endangering farming for future generations by acquiring a piece of land in the Lake District, which has sparked an outcry in the area over fears it could end an agricultural tradition going back thousands of years.

Fifteen-year-old George Purcell, who began farming Herdwick sheep with his parents when he was 11, said the National Trust’s actions had put the future of farming in the Lake District in jeopardy.

Continue reading...

Barry Gardiner has warned the prime minister that any delay risks the UK being sidelined in influencing future action on climate change

Labour has warned Theresa May that the UK must hurry up and ratify the Paris climate deal before the year is out or risk being sidelined in influencing future action on global warming.

Writing to the new prime minister, Barry Gardiner said that the Brexit vote in June meant it was also vital that the UK demonstrated its continued commitment to international efforts to cut greenhouse gas emissions.

Continue reading...

Ambitious Great Elephant Census finds nearly one-third of continent’s largest elephants were wiped out between 2007-14, largely due to poaching for ivory

Poaching has driven a huge decline in Africa’s savanna elephants with almost a third (30%) wiped out between 2007 and 2014, the first ever continent-wide survey of the species has found.

Around 144,000 animals were lost over a seven-year period in 15 African countries, declining at a rate of 8% a year. The population across those countries today stands at 352,271 elephants.

Continue reading...

More than 30% of the water sources on our planet are being over-exploited, in many cases to near exhaustion. World Water Week brings together experts and innovators from around the world to develop solutions for a sustainable water future

• This year World Water Week takes place in Stockholm, 28 Aug to 2 Sept, and takes the theme of Water for Sustainable Growth

Continue reading...

Joan Rose, a microbiologist who has won the world’s most prestigious water prize, is both depressed and optimistic at progress to make water fit to drink

• World Water Week - in pictures

In May 2000, around half of Walkerton’s 5,000 residents fell severely ill and seven people died when cow manure washed into a well. The extent of the water pollution in the small Canadian town was concealed from the public, people drank from their taps and the result was ruined lives.

For academic microbiologist Joan Rose, who has observed water pollution outbreaks around the world, it was the worst that she had ever experienced.

Continue reading...

Wet spring and sunny conditions pave the way for a spectacular display of colour, according to the Forestry Commission

Autumn could come as early as mid-September as a wet spring and sunny conditions pave the way for a spectacular display of colour, the Forestry Commission has said.

England’s wet spring saw rainfall 30% above average in the east and the south, data from the Met Office shows.

Continue reading...

Special review recommending steps needed to strengthen climate policies receives a mixed response

The Climate Change Authority has advised the Australian government to institute two emissions trading schemes and strengthen regulations in order to meet Australia’s 2030 emission reduction targets and to allow it to lift those targets in line with international climate change obligations.

The move is expected to put pressure on the new environment and energy minister, Josh Frydenberg, to strengthen Australia’s climate policies but it has received a mixed response.

Continue reading...

Over the past 70 years, the bird has become a global staple, and could be the key fossil evidence for human-influenced epoch

The domestic chicken is set to play an epoch-defining role for humanity, as its bones could become the key fossil evidence for the dawn of the age in which humankind came to dominate the planet.

On Monday, an expert group announced that a new geological epoch, the Anthropocene, should be declared. But the key to defining a geological age is finding global physical evidence of the transition that will be preserved for future geologists, and the chubby modern chicken eaten worldwide is a prime candidate.

Continue reading...