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Quartz may be key to understanding quakes

March 19, 2011
Courtesy of Royal Holloway, University of London
and World Science staff

The com­mon min­er­al quartz may be be­hind earth­quakes, moun­tain build­ing and oth­er de­forma­t­ions of the Earth’s crust, accord­ing to a new stu­dy.

The study in the West­ern U.S. showed that the areas where the Earth’s crust has the most quartz al­so suf­fer the most fre­quent de­forma­t­ions, which can in­clude earth­quakes or lead to them, re­search­ers said.

Quartz, the pri­ma­ry com­po­nent of beach sand, is not only the most com­mon but the “weak­est crus­tal min­er­al,” said geo­phys­i­cist Mar­ta Pérez-Gussinyé of Roy­al Hol­loway, Un­ivers­ity of Lon­don, a co-author of the stu­dy. The study, pub­lished in the re­search jour­nal Na­ture, sug­gests that quartz may hold the key to the per­sist­ent zones of weak­ness along which the Earth’s con­ti­nents de­form.

The find­ings were based on a sur­vey of gra­vity, heat-flow mea­sure­ments and the speed of un­der­ground en­er­gy waves known as seis­mic waves.

“The key to our dis­cov­er­ies has been to de­vise new ways to jointly an­a­lyze many geo­phys­i­cal da­ta sets that were pre­vi­ously an­a­lyzed sep­a­rate­ly,” said Pérez-Gussinyé. “This, in com­bina­t­ion with the US-array seis­mic ex­pe­ri­ment, which has en­abled us to ob­tain an im­age of the Earth’s sub­sur­face at a 70-km lat­er­al spac­ing over the whole sur­face of the Un­ited States, has been de­ci­sive to de­ci­pher the rel­a­tive abun­dance of quartz in the crust.”

Places where quartz “is most abun­dant… ex­perience re­peat­ed cy­cles of de­forma­t­ion dur­ing Earth’s his­to­ry,” she added.


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The common mineral quartz may be behind earthquakes, mountain building and other deformations of the Earth’s crust, acording to a new study. The study in the Western U.S. showed that the places where the Earth’s crust has the most quartz also suffer the most frequent deformations, which can include earthquakes or lead to them, researchers said. Quartz, the primary component of beach sand, is not only the most common but the “weakest crustal mineral,” said geophysicist Marta Pérez-Gussinyé from Royal Holloway, University of London, a co-author of the study. The research, published in the research journal Nature, suggests that quartz may hold the key to the persistent zones of weakness along which the Earth’s continents deform. The findings were based on a survey of gravity, heat-flow measurements and the speed of underground energy waves known as seismic waves. “The key to our discoveries has been to devise new ways to jointly analyze many geophysical data sets that were previously analyzed separately,” said Pérez-Gussinyé. “This, in combination with the US-array seismic experiment, which has enabled us to obtain an image of the Earth’s subsurface at a 70-km lateral spacing over the whole surface of the United States, has been decisive to decipher the relative abundance of quartz in the crust.” Places where quartz “is most abundant… experience repeated cycles of deformation during Earth’s history,” she added.

Man’s best friend may provide more than just faithful companionship. A new study shows people who owned and walked their dogs were 34 percent more likely to meet U.S. federal benchmarks on physical activity. The results show that promoting responsible dog ownership could help many Americans get healthier, said Michigan State University epidemiologist Mathew Reeves, who led the study. Surprisingly, he found that the dog walking itself didn’t account for the whole increase in physical activity among dog walkers. Fewer than half of Americans currently meet recommended levels of leisure-time physical activity, he noted. “Walking is the most accessible form of physical activity available to people,” said Reeves, whose study appears in the current issue of the Journal of Physical Activity and Health. “Obviously you would expect dog walkers to walk more, but we found people who walked their dog also had higher overall levels of both moderate and vigorous physical activities,” he added. “There appears to be a strong link between owning and walking a dog and achieving higher levels of physical activity, even after accounting for the actual dog walking.” Using data from the Michigan Behavioral Risk Factor Survey, an annual health survey conducted by the U.S. Centers for Disease Control and Prevention and the Michigan Department of Community Health, Reeves and collaborators found that not only did owning and walking a dog affected people’s amount of walking and was associated with greater activity overall. Dog-walkers generally walked about an hour longer per week than people who owned dogs but didn’t walk them. The study analyzed the amount of leisure-time physical activity a person gets; examples include sports participation, exercise conditioning and recreational activities such as walking, dancing and gardening. Public health benchmarks call for at least 150 minutes of such activity a week. “There is no magic bullet in getting people to reach those benchmarks,” Reeves said. “But owning and walking a dog has a measurable impact.” He also pointed out the social and human/animal bond aspects of owning a dog that has been shown to have a positive impact on quality of life. And since only about two-thirds of dog owners reported regularly walking their dogs, Reeves said dog ownership represents a opportunity to increase participation in walking and overall physical activity. “The findings suggest public health campaigns that promote the responsible ownership of a dog along with the promotion of dog walking may represent a logical opportunity to increase physical activity,” he said.