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Gravity signals rapidly show true size of giant quakes

Researchers develop a new speedy approach to estimate the true size of very large earthquakes.

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Researchers have developed a new approach to estimate the true size of very large earthquakes.

At present, scientists use seismic waves from a rupture to work out the scale of the event.

But a new analysis of the Tohoku earthquake in Japan in 2011 shows that changes in gravity can give more rapid information.

This method could have accurately estimated that magnitude 9 tremor in minutes, not the hours actually taken.

As Japan’s largest recorded earthquake, the Tohoku event is probably best remembered for the huge tsunami it unleashed.

As well as killing around 12,000 people it triggered the meltdown of three nuclear reactors at the Fukushima Daiichi power plant.

Image copyright Getty Images Image caption The 330-tonne trawler Kyotomaru was swept 500 metres inland by the tsunami in 2011

Experts believe that the quake was caused by the rupture of a stretch of the subduction zone associated with the Japan Trench, which separates the Eurasian Plate from the downward-sliding Pacific Plate.

Initial estimates of magnitude by Japan’s meteorological agency indicated it was a 7.9 tremor. Three hours later, this was corrected to 8.8. Eventually the Tohoku quake was upgraded to 9.1 magnitude.

These estimates are based on seismic waves generated by the earthquake which travel through the Earth and are recorded on seismometers all over the world.

Scientists look for what are termed P-waves as the fastest way to deduce what is happening in an event. These travel at around 7-8km per second.

However, French researchers have been looking at the possibility of using small shifts in gravity to estimate scale.

Large tremors can cause perturbations in the Earth’s gravitational field – and as these signals travel at the speed of light, they open up the possibility of much more rapid detection of quake magnitude.

Up to now, gravitational signals have been difficult to detect above the seismic noise, but the French research team developed their model to analyse the Tohoku event using data recorded with broadband seismometers located some 1,000 to 2,000km from the quake.

“As soon as you have the location and origin time of the earthquake, you know when the seismic waves will arrive at good quality stations inland,” said lead author Dr Martin Vallée, from the Paris Institute of Earth Physics.

Image copyright USGS Image caption A map showing the intensity of shaking due to the 2011 quake

“And if you look to see a gravity signal before the arrival time of the seismic waves, if you can see this, it really means you have a large event. If you cannot see it you will be in a magnitude 8.5 or below.”

According to the authors, this method of analysis would have reliably detected that the Tohoku quake was greater than magnitude 9 within three minutes of the origin time.

This could have had major implications especially for the tsunami that followed it.

“Knowing that a quake is very large a few minutes after is not very useful for the areas that are directly affected because the seismic waves will already have affected the area,” said Dr Vallée.

“But it is for the tsunamis which often arrive half an hour after an earthquake, they are much slower than the seismic waves, and here you have some time to react. It is very useful.”

At present, the research team say that the ideal places to test the method are in locations that have had an earthquake greater than magnitude 9 in recent centuries, such as the Cascadia region of the US and Canada.

Looking ahead, the scientists believe that with refinement, their method of analysing gravity signals could allow more rapid detection of the size of smaller events.

“It will be really important if in the future we have instruments that can measure the signal and are more sensitive,” said Dr Vallée.

“We will be able to apply the same analysis to smaller earthquakes, and when I say smaller I mean magnitude 7 or 8 which in fact are very large and can destroy a lot.”

The study has been published in the journal, Science.

Using gravity signals for early warning?

Image copyright Getty Images

by Jonathan Amos, BBC Science Correspondent

It’s not possible to predict earthquakes but it is possible to issue alerts once a major event is under way.

And for those not living directly above the point of rupture, but some distance away, such warnings can give people vital seconds to prepare.

These systems – they have them in places like Japan and Mexico – work on the basis of detecting the different arrival times of seismic waves.

So-called P-waves are less destructive vibrations that run ahead of the far stronger and more damaging S-waves. But neither move as swiftly as the changes that become apparent in the gravity field once a quake has moved a great mass of rock inside the Earth.

If you could practically harness this signal in an early warning system then it could provide just a few seconds more grace for the surgeon to lift their scalpel away from a patient’s organ or for the driver of a packed commuter train to slow down.

However the gravity signal is very subtle and it will be challenging to make use of it in all but the very largest events. On average there is only about one “great quake” of magnitude 8 or higher a year. But there is hope the technologies can be improved.

This new research came out of discussions surrounding the detection of gravitational waves from black hole mergers in space.

That technique had its doubters for a long while but eventually proved its worth. Even if a gravity signal cannot be woven into an early warning system, just knowing the true scale of a quake much faster will be important information for first responders.

Science & Environment

RemoveDebris: Space junk mission prepares for launch

A spacecraft that will test the best methods to clean up space debris is nearing completion.

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A mission that will test different methods to clean up space junk is getting ready for launch.

The RemoveDebris spacecraft will attempt to snare a small satellite with a net and test whether a harpoon is an effective garbage grabber.

The probe has been assembled in Surrey and will soon be packed up ready for blast off early next year.

Scientists warn that the growing problem of space debris is putting spacecraft and astronauts at risk.

It is estimated that there are about half a million pieces of man-made rubbish orbiting the Earth, ranging from huge defunct satellites, to spent rocket boosters and nuts and bolts.

Any collisions can cause a great deal of damage, and generate even more pieces of debris.

The RemoveDebris mission is led by the Surrey Space Centre at the University of Surrey.

The assembly of the spacecraft, which is about the size of a washing machine, has taken place at Surrey Satellite Technology Ltd (SSTL) and is almost complete.

Dr Jason Forshaw, project manager on the RemoveDebris team, said: “RemoveDebris will be one of the world’s first missions in this area…. We have technologies on here that have never been demonstrated in space before.”

Image copyright Max Alexander Image caption The spacecraft has been assembled in the UK and will soon be packed up for launch

The spacecraft will first head for the International Space Station on a resupply rocket.

It will then be unpacked by astronauts before being launched from the orbiter to begin its experiments.

RemoveDebris has its own space junk on board – small satellites. It will release one of these into space and then will use a net to recapture it.

It will also fire a small harpoon at a target plate to see if the technology can accurately work in the weightless environment.

It will finally test future de-orbiting technology. As the orbiter descends to Earth it will deploy a 10sq m sail, which will change the spacecraft’s speed and ensure it burns up as it enters the atmosphere.

“It will prevent the spacecraft from becoming space junk itself,” explained Dr Forshaw.

The hope is that the technology-testing mission, which has cost £15m, will lead to larger clean-up efforts.

“People are starting to realise the significance of space junk and the problem it presents,” Dr Forshaw said.

Image copyright RemoveDebris Mission Image caption The spacecraft will establish whether a net could ensnare a small satellite

Scientists estimate that there are about 7,500 tonnes of rubbish in space and we are reaching a critical point. .

Dr Hugh Lewis, senior lecturer in aerospace engineering at the University of Southampton, said: “For some people, space debris is one of these things that is out of sight, out of mind.

“But from my perspective it is one of the worst environmental catastrophes that we have encountered.”

Even very small pieces of junk can do a great deal of damage.

Last year a loose fleck of paint is thought to have caused a crack in a window on the International Space Station.

Image copyright ESA Image caption Last year a small piece of debris chipped a window on the International Space Station

The largest pieces, though, present a pressing problem.

In 2012, a European satellite called Envisat, the size of a double decker bus, suddenly stopped working.

Since then it’s been circling the Earth, threatening other key satellites in its path.

Dr Lewis explained: “The biggest pieces of space debris have huge amounts of mass in them. If they were to be hit by something, they would release all that mass in the form of thousands and thousands of more fragments.”

More debris, could lead to more collisions – a cascade effect known as the Kessler syndrome. The fear is that space could eventually become inoperable.

“The environment provides us with really important services – like navigation, timing, communications, weather forecasting and so on,” Dr Lewis added.

“The worst case scenario is probably the loss of some vital satellites… it would mean stepping back probably decades in terms of our technology we take for granted on Earth.”

Image copyright Hugh Lewis Image caption It is estimated that there are about half a million pieces of space junk the size of a marble or larger

The European Space Agency is now looking at how larger satellites like Envisat can be destroyed – but cleaning up space piece by piece will be difficult and extremely expensive.

International space guidelines suggest that satellites should de-orbit themselves after 25 years – but it is difficult to ensure everyone plays by the rules.

Some experts are also concerned that the new push to launch small satellites (known as cubesats) in increasingly large numbers could add to the problem.

Martin Pointer from SSTL said: ” Space junk is definitely a concern for us. As more and more satellites are put up – especially some of the constellations of small satellites – the likelihood of collisions is much greater.

“I think it’s our responsibility to ensure we don’t cause more junk in space and find ways of either removing those at the end of life or for mitigating against problems.”

Follow Rebecca on Twitter.

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Science & Environment

River departed ‘before Indus civilisation emergence’

One of the world’s earliest urban civilisations thrived in the absence of a big Himalayan river, a new study finds.

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Further light has been shed on the emergence and demise of one of the earliest urban civilisations.

The Indus society came to prominence in what is now northwest India and Pakistan some 5,300 years ago thanks in large part to the sustenance of a long-lost Himalayan river.

Or so it was thought.

New evidence now indicates this great water course had actually changed its path and disappeared before the Indus people had even settled in the region.

That they lacked the resource offered by a big, actively flowing river will come as a surprise to many; the other early urban societies of the time, in Egypt and Mesopotamia, certainly benefitted in this way.

The new research was led from the Indian Institute of Technology Kanpur and from Imperial College London.

Image copyright NASA/USGS Image caption Infrared satellite imagery picks out the distinctive sediments of the ancient channel Image copyright S.Gupta Image caption Remnant of a street in the urban centre of Kalibangan

The group’s scientists do not disagree that the Bronze Age settlements would have needed a good water supply, but argue that this requirement could have been met instead by seasonal monsoon rains that still collected and ran through the valley abandoned by the old river.

“Our paper clearly demolishes the age-old river-culture hypothesis that assumed that the disappearance of the river triggered the demise of the Harappan civilisation,” said IITK’s Prof Rajiv Sinha.

“We have argued that while large rivers have important connections with ancient societies, it is their departure that controls their stabilisation rather than their arrival.

“This has clearly been demonstrated by the large difference in age data between the demise of the river (8,000-12,000 years ago) and the peak of mature civilisation (3,000-4,000 years ago),” he told BBC News.

Prof Sinha and colleagues report their findings in this week’s Nature Communications journal.

Image copyright A.Carter/Birkbeck, University of London Image caption A collection of mineral grains that helped trace the origin of the palaeo-river

They have examined afresh the course of what is referred to as the Ghaggar-Hakra palaeo-channel, from satellite data and from field investigations.

Much of the archaeology of Indus cities, such as Kalibangan and Banawali, is scattered along this old river course.

The team shows the relict valley to be the former trace of today’s big Sutlej River, which must have abruptly changed course – as many Himalayan rivers are prone to do.

“They tend to switch on 100-year timescales,” explained Prof Sanjeev Gupta from Imperial College.

“But because the Sutlej became incised in its new course, it never switched back and that left the paleo-channel protected. That allowed, I believe, the Indus communities to flourish because they were saved from devastating floods.

“Some of their sites were actually built in the palaeo-channel itself and that makes no sense if there was a big raging Himalayan river there at the time because these people would have been wiped out.”

Image copyright S.Gupta Image caption Broken pieces of Indus pottery exposed at the surface at Kalibangan

Dating of the sediments in the palaeo-channel was done using a technique known as optically stimulated luminescence.

It reveals that the initial abandonment of the valley by the Sutlej River commenced after about 15,000 years ago, with complete “avulsion” to its present course shortly after 8,000 years ago.

Prof Gupta said the Indus people were competent engineers and so would have been able to manage their water needs, potentially even accessing underground supplies. But precisely how they operated in these circumstances of reduced water possibilities was now really a question for the archaeologists to answer, he added.

“What is clear though is that this culture had a diverse landscape and they were able to adapt to it,” he told BBC News.

Prof Rita Wright is an anthropologist at New York University and unconnected to the new research.

She said it represented a “major building block” in our understanding but stressed also that it concerned just a part of the region occupied by Harappan society.

“It is focused primarily on a single area in northwest India, [but] enormously important.

“In contrast to the Indus Valley, it presents (and provides evidence for) a very different water ecology. No denying that water was one of the major resources in the Indus, so here we have evidence for significant differences between the Indus valley alluvial plain and the Ghaggar monsoon-driven water system.”

Image copyright NASA/USGS Image caption Indus civilisation urban settlements were spread across what is now NW India and Pakistan Image copyright Spl Image caption The Harappan site at Mohenjo-daro, Pakistan. It was built on the banks of the Indus River

Prof Gupta has written a longer account of the research which can be read here.

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos

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Trophy hunting removes ‘good genes’ and raises extinction risk

Hunting animals with the biggest horns, tusks or manes could lead to extinction, according to a study.

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Hunting animals that stand out from the crowd because of their impressive horns or lustrous manes could lead to extinction, according to a study.

Research predicts that removing even 5% of high-quality males risks wiping out the entire population, for species under stress in a changing world.

Animals prized by trophy hunters for their horns, antlers or tusks usually have the best genes, say UK scientists.

Removing these could push a species over the edge, they warn.

There is intense global debate over trophy hunting. Some argue that it should be banned or restricted, while others say it can provide valuable revenue for conservation.

Dr Rob Knell of Queen Mary, University of London, who led the research, said the assumption that so-called selective harvesting is not especially threatening to a population of animals does not take into account recent work.

”Because these high-quality males with large secondary sexual traits tend to father a high proportion of the offspring, their ‘good genes’ can spread rapidly, so populations of strongly sexually selected animals can adapt quickly to new environments,” he said.

”Removing these males reverses this effect and could have serious and unintended consequences.”

Human hunting is different from natural predation in that big-game trophy hunters target large animals, usually males.

They may be awarded prizes for killing animals with exceptionally large antlers, horns or manes.

And illegal poaching of animals such as elephants for the ivory trade also targets animals with the biggest tusks.

Using a computer simulation model, the scientists were able to predict the impact of selectively targeting males on the basis of their secondary sexual traits.

”If the population is having to adapt to a new environment and you remove even a small proportion of these high quality males, you could drive it to extinction,” said Dr Knell.

”You’re removing the genes from the population that would otherwise allow the population to adapt.”

In the past, human hunting has led to the extinction of many animals, from the zebra-like Quagga, which was once common in Southern Africa, to the Tasmanian tiger of mainland Australia and Tasmania.

Hunting is still legal in many countries; trophy hunting takes place over a larger area in Sub-Saharan Africa than is conserved in national parks.

In the US and Canada, there is also a lucrative trophy hunting industry, for the likes of deer and big-horn sheep.

Some argue that revenue from trophy hunting can support conservation efforts and local livelihoods.

The scientists said age restrictions that allow males to breed before being removed could reduce the impact of trophy hunting.

This is already recommended with some species, such as lions.

“When properly regulated trophy hunting can be a powerful force for conservation which is why we’re suggesting a different management approach as opposed to calling for a ban,” said Dr Knell.

The study is published in Proceedings of the Royal Society B: Biological Sciences.

Follow Helen on Twitter.

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