Scientists identified earthquake faults in Sichuan, China

Only last summer research published by earth scientists in the international journal Tectonics concluded that geological faults in the Sichuan Basin, China “are sufficiently long to sustain a strong ground-shaking earthquake, making them potentially serious sources of regional seismic hazard.”

An international team of scientists including Dr. Alexander Densmore (Institute of Hazard and Risk Research, Durham University), Dr. Mike Ellis (Head of Science for Climate Change at the British Geological Survey) and colleagues from research institutes in Chengdu, carefully mapped and analysed a series of geologically young faults that cross Sichuan Province like recently healed scars.

The team mapped the densely populated Sichuan Basin and adjacent mountains using what is known as ‘tectonic geomorphology’. This technique can demonstrate significant changes in ground movement over time, such as observations of offset river channels, disrupted floodplains, abnormally shaped valleys and uplifted landscape features. These subtle signals of deformation, when combined with the ability to measure the age of the disfigured landscapes (using cosmogenic nuclides that bombard the Earth from all corners of the universe), produced surprising results.

The recent earthquake in Sichuan occurred under some of the steepest and most rugged mountains in the world, the Longmen Shan: the Dragon’s Gate Mountains. This dramatic range, steeper than the Himalayas, is the upturned rim of the eastern edge of Tibet, a plateau that has risen to 5 km in response to the slow but unstoppable collision of India with Asia that began about 55 million years ago and which continues unabated today.

Two long faults in particular, running almost the entire length of the Longmen Shan, showed clear evidence of slip during the last few thousands, and in some cases hundreds, of years. The rates of slip varied between fractions of mm per year to possibly many mm per year. Millimetre by millimetre, the Longmen Shan are being sliced and displaced much like salami. One of these faults is likely to be the one that gave rise to the 7.9 magnitude earthquake that has now caused 22,069 fatalities. Exactly why the Longmen Shan are here is a mystery. Unlike the Himalaya, which form the southern boundary of Tibet and whose faults chatter continuously with small earthquakes, faults in the Longmen Shan, remnants perhaps of geological events hundreds of millions of years ago, have historically only produced earthquakes up to magnitude 6.

Geomorphological evidence, described in the Tectonics paper, suggests that the mapped faults are very steep with dominantly lateral or strike-slip displacements taking place over time scales of thousands to hundreds of thousands of years. This contrasts with shorter-term measurements using Global Positioning Systems which suggest a greater proportion of thrust or shortening displacement than lateral displacement. The observations of seismologists at the BGS suggest both things: more thrust in the SW, nearer the epicentre, and more strike-slip toward its direction of propagation, the NE.

Global Earthquake Fatalities Expected To Rise This Century

Earthquake expert and geological sciences Professor Roger Bilham of the University of Colorado at Boulder says unprecedented human fatalities from earthquakes will occur around the globe in the coming century unless significant earthquake-resistant building codes are implemented.

Bilham, who has worked extensively in the Himalaya, anticipates that the death toll from the May 12 magnitude 7.9 Sichuan Province earthquake in China may exceed 50,000 based on previous similar earthquakes in urban settings. According to May 16 reports by the Associated Press, the event damaged or destroyed 4 million apartments and homes and thousands of schools.

Bilham said there were 43 “supercities” on Earth with populations from 2 million to more than 15 million in 1950, but there are nearly 200 today. Roughly 8 million people have died globally as a result of building collapses during earthquakes in the past 1,000 years. A four-fold increase in the annual death toll from earthquakes between the 17th and 20th centuries is linked to increased urbanization, he said.

Half the world’s supercities now are located near potential future magnitude 7.5 earthquakes, said Bilham, who is also a fellow of the Cooperative Institute for Research in Environmental Sciences. By the year 2025 more than 5.5 billion people will live in cities — more than the entire 1990 combined rural and urban population. While large earthquakes over magnitude 7.5 have for the most part spared the world’s major cities in the last century, this pattern will not persist indefinitely, he said.

“After the Earth Quakes,” a 2006 book authored by the U.S. Geological Survey’s Susan Hough and Bilham and published by Oxford University Press, looks at the collision between global urban construction and earthquake destruction.

Geosciences Professor Measuring Aftershocks of China Earthquake

Professor and students study seismic activity of critical area near China’s largest hydroelectric dam.

Just 40 minutes before the May 12 earthquake measuring 7.9 on the Richter scale struck the Sichuan province in Central China, a Texas Tech University professor of geosciences had arrived in Beijing, only 960 miles away.

Hua-wei Zhou, professor of petroleum geophysics and seismology, was about to start work for the National Natural Science Foundation of China to monitor smaller earthquakes by the Three Gorges reservoir, 250 miles east of the Sichuan earthquake epicenter.

Now, Zhou is leading a team of six graduate students to deploy 60 seismometers to the Three Gorges area. The team hopes to record aftershocks that will help reveal the structure of the Earth’s crust in this area. Though there is no reported damage to the hydroelectric dam in Three Gorges by the killer earthquake in Sichuan, Zhou said it is imperative to study the safety of the dam during an earthquake.

Failure of the dam could result in one of the worst disasters in history, as more than 75 million people live downstream of the dam, and the floodplain surrounding the Yangtze River is used for growing much of the country’s food.

Zhou said the destructive earthquake occurred on the Longmenshan fault, which has many historic earthquakes greater than magnitude 7, which is capable of widespread, heavy damage. The last one occurred in 1933.

“While the Sichuan earthquake is a major human tragedy, the situation could have been even worse considering that the city of Chengdu, with a population of 4 million, is just 60 miles away from the epicenter,” Zhou said. “First, Chengdu is on the footwall side of the northeast-trending Longmenshan fault, and the footwall side usually has much less damage than the hanging wall side. Second, the northeast-trending fault and northeast rupture direction put most rupture energy away from the city of Chengdu and its population.

“However, the region near and to the northeast side of the fault will suffer a lot, though that region has much smaller population density than Chengdu.”

Another large earthquake occurred in 1973 on the nearby Xianshuihe fault to the southwest, he said.

“In 1986 I spent two months in the field studying that fault with several colleagues,” he said. “The main driving force of all these earthquakes is the collision of the Indian and Eurasian plates that pushes the mountains against the Sichuan basin.”

Funding to study earthquake region

A major research consortium has just started to investigate the causes of devastating earthquakes in south-east Asia.

The research team, led by the National Oceanography Centre, Southampton (NOCS), are surveying the region struck by the 2004 and 2005 Sumatran earthquakes and tsunami to determine how the structure of major faults affects the size of large earthquakes.

The team has been awarded more than £2m by the Natural Environment Research Council (NERC) to carry out the research, which will combine data recorded during the earthquakes with new observations of the seafloor and sub-seafloor plate boundary zone.

The project will provide critical information about what happened during the Sumatran earthquakes, and whether similar events might have happened in the past. This will have important implications for understanding the risk from future earthquakes both in Sumatra and elsewhere.

All plate boundaries are divided into segments – sections of fault that are distinct and behave differently from one another. Barriers between these segments often limit how far a particular earthquake ruptures. But it is not known what determines whether an earthquake ruptures only a single segment, staying relatively small, or jumps across the barriers between segments to become a major event.

“The Sumatran earthquakes provide a unique framework to tackle this problem”, explains Dr Tim Henstock, a NOCS geophysicist at the University of Southampton and Principal Investigator for the project. “The southern boundary of the major 2004 earthquake – the southernmost point at which the fault slipped – stopped the rupture, and therefore limited the earthquake magnitude, but we don’t yet know why this boundary is there, nor how it controls the earthquake rupture process.”

The project aims to understand this behaviour, and was designed to combine observations of the earthquakes with measurements of the faults beneath the seafloor, linking the dynamics of the rupture to the static structure of the plate boundary. The study will collect many different geophysical and geological datasets around the earthquake rupture barriers exploring different properties at many different scales. The data will improve understanding of the shape of the two tectonic plates and the properties of the sediments and fluids within them, all of which influence how an earthquake propagates along a fault.

A complementary experiment on land installed instruments on Sumatra and the islands overlying the plate boundary zone in April 2008. They will record waves from earthquakes all over the world to image deep into the subduction system and will show which faults are currently most active.

The 130-day shipboard programme started this week, using the German R/V Sonne. Dr Mike Webb from NERC said, “This is the largest exchange of marine facilities that we have ever undertaken. As well as providing an excellent platform for this important study, we hope the project will demonstrate the expanding cooperation between European research fleets. Because the Sonne is already working in the area, this exchange is logical and more efficient.”

Earthquake Engineering Conference

Experts on earthquake engineering and simulation will meet at the Sacramento Convention Center May 18-22 for the fourth decennial Geotechnical Earthquake Engineering and Soil Dynamics conference, organized by the American Society of Civil Engineers.

Conference topics will address how soils and the structures built on them behave during earthquakes, and how dams, levees, bridges, tunnels and other structures can be engineered to withstand earthquake damage. Sessions will range from basic research to specific case histories and new technologies for preventing earthquake damage.

Plenary speakers include Professor Thomas O’Rourke, Cornell University, on “Earthquake Engineering for Complex Geotechnical and Lifeline Systems”; Professor Raymond Seed, UC Berkeley, on “Seismic Evaluation of Levees”; and Bruce Kutter, professor of civil and environmental engineering at UC Davis, who will discuss modeling studies of the Bay Area’s BART tube tunnel.

There will also be demonstrations of equipment for earthquake engineering research, including ground-shaking trucks and UC Davis’ large geotechnical centrifuge. The equipment show will be held on the afternoon of Tuesday, May 20, at the UC Davis Center for Geotechnical Modeling, part of the George E. Brown Jr. Network for Earthquake Engineering Simulation (NEES) funded by the National Science Foundation.

The meeting is organized by the Geo-Institute of the American Society of Civil Engineers (ASCE). Ross Boulanger, professor of civil and environmental engineering at UC Davis, is chair of the conference organizing committee.

Conference registration is available online at News reporters interested in attending the meeting should contact Joan Buhrman at ASCE for details on press registration.

Studies confirm greenhouse mechanisms even further into past

The newest analysis of trace gases trapped in Antarctic ice cores now provide a reasonable view of greenhouse gas concentrations as much as 800,000 years into the past, and are further confirming the link between greenhouse gas levels and global warming, scientists reported today in the journal Nature.

They also show that during that entire period of time, there have never been concentrations of carbon dioxide and methane as high as the current levels, said Edward Brook, an associate professor of geosciences at Oregon State University, and author of a Nature commentary on the new studies.

“The fundamental conclusion that today’s concentrations of these greenhouse gases have no past analogue in the ice-core record remains firm,” Brook said in the report. “The remarkably strong correlations of methane and carbon dioxide with temperature reconstructions also stand.”

The latest research, done by members of the European Project for Ice Coring in Antarctica, extend the data on trace gases back another 150,000 years beyond any studies done prior to this, Brook said. Ultimately, researchers would like to achieve data going back as much as 1.5 million years.

The tiny bubbles of ancient air trapped in polar ice cores have been used to provide records of trace gases in the atmosphere at distant points in the past, and better understand the natural fluctuations that have occurred, largely as a result of cyclical changes in Earth’s orbit around the sun.

“These natural cycles that occur on the order of tens or hundreds of thousands of years can help us understand both the forces that have controlled and influenced Earth’s climate in the past, and the implications of current changes on future climate” said Brook, who is co-chair of an international group that organizes global studies in this field.

According to the data, the current levels of primary greenhouse gases – those that are expected to cause global warming – are off the charts.

The concentration of carbon dioxide is now a bit more than 380 parts per million, compared to a range of about 200-300 parts per million during the past 800,000 years. The current concentration of methane is 1,800 parts per billion, compared to a range of about 400-700 parts per billion during that time.

In every case during that extended period, warm periods coincide with high levels of greenhouse gases. Of some interest, the latest studies are showing that the temperature increases have been even more pronounced during the most recent 450,000 years, compared to several hundred thousand years prior to that.

“It appears there may even be very long term natural cycles that have operated on much longer periods of 400,000 years or more,” Brook said. “We still have quite a bit to learn about these past cycles and all the forces that control them.”

Most of the time during the past 800,000 years, the Earth has experienced long, cooler periods about 80,000 to 90,000 years long, which eventually lead to ice ages. Those have been regularly interrupted by “interglacial” periods about 10,000 to 20,000 years long that are considerably warmer – this is the stage the Earth is in right now. Abrupt climate changes on much shorter time scales are also possible, researchers believe, possibly due to shifts in ocean circulation patterns or other forces.

Scientists are continuing to search for the optimal sites in Antarctica that will allow them to take the ice core records back even further, Brook said.

Ice cores reveal fluctuations in the Earth’s greenhouse gases

The ice core boring at Dome C in Antarctica shows that the curves for the temperature and the greenhouse gases carbon dioxide and methane follow each other over the past 800,000 years -- with few deviations. (See arrows) - Credit: Professor Thomas Blunier, Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen
The ice core boring at Dome C in Antarctica shows that the curves for the temperature and the greenhouse gases carbon dioxide and methane follow each other over the past 800,000 years — with few deviations. (See arrows) – Credit: Professor Thomas Blunier, Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen

Ice cores from Antarctica show both the lowest atmospheric content of CO2 (carbon dioxide) and fast changes in the content of CH4 (methane) measured over the past 800,000 years. Knowledge about the relationship between greenhouse gases and the temperature in the Earth’s climate history will help scientists develop models of future climate changes.

The results obtaines in the framework of the European Project for Ice Coring in Antarctica (EPICA) run by a consortium of 10 European Nations among them the Niels Bohr Institute at University of Copenhagen are being published in two articles in the respected scientific journal Nature.

An ice core drilled through the three-kilometre-thick ice cap at the EPICA Dome C Station in the middle of Antarctica reveal the climate 800,000 years back in time – through eight glacial periods and eight interglacial periods. The glacial periods last 100,000 years on average, and the warm interglacial periods – such as the one we are now in – last an average of 10,000 years.

The ice is formed by snow falling year after year and which, with time, is compressed to form a thick ice cap. The ice contains atmospheric air, and the annual layers provide information about the climate in the years in which the snow fell. The mix of water isotopes in the ice reveals the temperature, and analyses of the entrapped air show the atmospheric content of gases such as carbon dioxide and methane.

Extremely low CO2 content

“The temperature curve over the past 800,000 years matches the CO2 curve beautifully – during glacial periods in which the climate is cold, there is less CO2 in the atmosphere,” says Professor Thomas Blunier from the Centre for Ice and Climate at the Niels Bohr Institute, University of Copenhagen. He explains that when it is cold there is less plant growth, and so there are fewer plants to absorb the CO2 from the air, while more CO2 is absorbed in the oceans, so the final calculation is a low CO2 content in the atmosphere during glacial periods. This produces a lower greenhouse effect, and leads to an even colder climate.

However, the new results show that during the glacial period that occurred between 650,000 and 750,000 years ago, the CO2 level was extremely low – lower than any previous measurements have indicated. It happened twice in this period, while the temperature was not lower than during other glacial periods.

Drop in sensitive greenhouse gases

Methane, CH4, is a another important greenhouse gas and a sensitive indicator of climate changes and temperature fluctuations. Methane is formed by microorganisms and escapes from natural gas reservoirs. The biggest discharge from nature comes from bacteria in marsh areas which contribute 70 per cent of the air’s methane content, while the remainder comes mostly from wild animals.

Analyses of the ice cores from Antarctica show that the curve for methane matches the temperature curve – when the climate is cold, there is less methane in the atmosphere. The measurements indicate a strong relationship between the atmospheric methane content in relation to the Earth’s path around the Sun as well as the inclination and direction of the Earth’s axis. They find evidence for an increasing strength of the monsoon circulation in the tropics over the past 400,000 years.

For the first time, scientists have now produced a complete set of data showing measurements of methane going back 800,000 years. The new measurements from the EPICA Dome C ice cores show also that some climate changes are happening faster than those resulting from the long-term cycles in space. About 770,000 years before now, scientists have identified rapid changes in the amount of both CO2 and CH4 in the atmosphere. These are very fast changes which have occurred within just a few decades. The dramatic changes indicate that climate changes can take place very quickly. Similar changes took place about 40,000 years ago during the last glacial period.

Today, emissions from nature only account for a small amount of the methane found in the atmosphere. Current concentrations are 124 per cent higher than in previous periods, and this is largely due to domestic animals, agriculture and fossil fuels, so the high level is indirectly the result of man’s activities. The concentration of CO2 is 28 per cent higher than before the Industrial Age. And which process might this trigger”

By analysing historical climate data, scientists will be able to better predict the climate-produced consequences of global warming.

Scientists aim to unlock deep-sea ‘secrets’ of Earth’s crust

RRS James Cook
RRS James Cook

Scientists from Durham University will use robots to explore the depths of the Atlantic Ocean to study the growth of underwater volcanoes that build the Earth’s crust.

The Durham experts will lead an international team of 12 scientists aboard Britain’s Royal Research Ship (RRS) James Cook which will set sail from Ponta Delgada, San Miguel, in the Azores, on 23 May 2008.

During the five-week expedition they will use explorer robots to map individual volcanoes on the Mid-Atlantic Ridge tectonic plate boundary – which effectively runs down the centre of the Atlantic Ocean – almost two miles (3km) below the surface of the sea.

They will then use another robot, called ISIS, to collect rock samples from the volcanoes which will be dated using various techniques to shed more light on the timescales behind the growth of the Earth’s crust and the related tectonic plates.

As tectonic plates – formations that make up the Earth’s shell – are pulled apart by forces in the Earth, rocks deep down in the mantle are pulled up to fill the gap left behind. As the rocks rise they start to melt and form thousands of volcanoes on the sea floor which eventually cluster into giant ridges.

The ridges along the Mid-Atlantic Ridge plate boundary are each about the size of the Malvern Hills and contain hundreds of individual volcanoes.

Principal investigator Professor Roger Searle, in the Department of Earth Sciences at Durham University, said, “The problem is that we don’t know how fast these volcanoes form or if they all come from melting the same piece of mantle rock.

“The ridges may form quickly, perhaps in just 10,000 years (about the time since the end of the last Ice Age) with hundreds of thousands of years inactivity before the next one forms, or they may take half-a-million years to form, the most recent having begun before the rise of modern humans.

“Understanding the processes forming the crust is important, because the whole ocean floor, some 60 per cent of the Earth’s surface, has been recycled and re-formed many times over the Earth’s history.”

Professor Searle’s team will include scientists from the National Oceanography Centre Southampton, the Open University, the University of Paris and several institutions in the USA.

They will date the volcanoes using radiometric dating (which measures the radioactive decay of atoms) and by measuring the changing strength of the Earth’s magnetic field through time as recorded by the natural magnetism of the rocks.

Co-investigators on this project are Professors Jon Davidson and Yaoling Niu of Durham University’s Earth Sciences Department, and Dr Bramley Murton of the National Oceanography Centre, Southampton.

The work is funded by a grant from the Natural Environment Research Council, which also owns and operates the RRS James Cook.

A cruise blog will be available at the Classroom@Sea website.

Hot climate could shut down plate tectonics

With locked crust, Earth could become another Venus

A new study of possible links between climate and geophysics on Earth and similar planets finds that prolonged heating of the atmosphere can shut down plate tectonics and cause a planet’s crust to become locked in place.

“The heat required goes far beyond anything we expect from human-induced climate change, but things like volcanic activity and changes in the sun’s luminosity could lead to this level of heating,” said lead author Adrian Lenardic, associate professor of Earth science at Rice University. “Our goal was to establish an upper limit of naturally generated climate variation beyond which the entire solid planet would respond.”

Lenardic said the research team wanted to better understand the differences between the Earth and Venus and establish the potential range of conditions that could exist on Earth-like planets beyond the solar system. The team includes Lenardic and co-authors Mark Jellinek of the University of British Columbia in Vancouver and Louis Moresi of Monash University in Clayton, Australia. The research is available online from the journal Earth and Planetary Science Letters.

The findings may explain why Venus evolved differently from Earth. The two planets are close in size and geological makeup, but Venus’ carbon dioxide-rich atmosphere is almost 100 times more dense than the Earth’s and acts like a blanket. As a result, Venus’ surface temperature is hotter than that of even Mercury, which is twice as close to the sun.

The Earth’s crust — along with carbon trapped on the oceans’ floors — gets returned to the interior of the Earth when free-floating sections of crust called tectonic plates slide beneath one another and return to the Earth’s mantle. The mantle is a flowing layer of rock that extends from the planet’s outer core, about 1,800 miles below the surface, to within about 30 miles of the surface, just below the crust.

“We found the Earth’s plate tectonics could become unstable if the surface temperature rose by 100 degrees Fahrenheit or more for a few million years,” Lenardic said. “The time period and the rise in temperatures, while drastic for humans, are not unreasonable on a geologic scale, particularly compared to what scientists previously thought would be required to affect a planet’s geodynamics.”

Conventional wisdom holds that plate tectonics is both stable and self-correcting, but that view relies on the assumption that excess heat from the Earth’s mantle can efficiently escape through the crust. The stress generated by flowing mantle helps keep tectonic plates in motion, and the mantle can become less viscous if it heats up. The new findings show that prolonged heating of a planet’s crust via rising atmospheric temperatures can heat the deep inside of the planet and shut down tectonic plate movement.

“We found a corresponding spike in volcanic activity could accompany the initial locking of the tectonic plates,” Lenardic said. “This may explain the large percentage of volcanic plains that we find on Venus.”

Venus’ surface, which shows no outward signs of tectonic activity, is bone dry and heavily scarred with volcanoes. Scientists have long believed that Venus’ crust, lacking water to help lubricate tectonic plate boundaries, is too rigid for active plate tectonics.

Lenardic said one of the most significant findings in the new study is that the atmospheric heating needed to shut down plate tectonics is considerably less than the critical temperature beyond which free water could exist on the Earth’s surface.

“The water doesn’t have to boil away for irrevocable heating to occur,” Lenardic said. “The cycle of heating can be kicked off long before that happens. All that’s required is enough prolonged surface heating to cause a feedback loop in the planet’s mantle convection cycle.”

The research was supported by the National Science Foundation and the Canadian Institute for Advanced Research.

Chilean volcano captured blasting ash

Chile's Chaiten Volcano is shown spewing ash and smoke into the air for hundreds of km over Argentina's Patagonia Plateau in this Envisat's Medium Resolution Imaging Spectrometer (MERIS) image, acquired on 5 May 2008. - Credits: ESA
Chile’s Chaiten Volcano is shown spewing ash and smoke into the air for hundreds of km over Argentina’s Patagonia Plateau in this Envisat’s Medium Resolution Imaging Spectrometer (MERIS) image, acquired on 5 May 2008. – Credits: ESA

Chile’s Chaiten Volcano is shown spewing ash and smoke (centre left of image) into the air for hundreds of km over Argentina’s Patagonia Plateau in this Envisat image acquired on 5 May 2008.

The 1000 m-high volcano had been dormant for thousands of years before erupting on 2 May, causing the evacuation of thousands. Chaiten Volcano is located in southern Chile 10 km northeast of the town of Chaiten on the Gulf of Corcovado.

Envisat’s Medium Resolution Imaging Spectrometer (MERIS) instrument processed this image at a resolution of 1200 m.

Satellite data can be used to detect the slight signs of change that may foretell an eruption. Once an eruption begins, optical and radar instruments can capture the lava flows, mudslides, ground fissures and earthquakes.

Atmospheric sensors onboard satellites can also identify the gases and aerosols released by the eruption, as well as quantify their wider environmental impact.

To boost the use of Earth Observation (EO) data at volcanic observatories, ESA has started to monitor volcanoes worldwide within the Agency’s Data User Element programme.

The Globvolcano project, started in early 2007, will define, implement and validate information services to support volcanological observatories in their daily work by integration of EO data, with emphasis on observation and early warning.