Tidal motion found to influence Antarctic subglacial seismicity

first_img Scientists pioneer wireless sensors to explore little known glacier phenomenon This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Image: National Science Foundation (Phys.org) — An American team of researchers has concluded that a period of rapid-succession small earthquakes in Antarctica over a several month span back in 2002-2003 was likely due to a glacier passing over some rough terrain and its periodic nature likely came about because of the impact of ocean tides. The team has published a paper describing their observations and conclusions in the journal Nature Geoscience. Explore further More information: Motion of an Antarctic glacier by repeated tidally modulated earthquakes, Nature Geoscience (2012) doi:10.1038/ngeo1555AbstractBetween debris-laden glacial ice and bedrock, basal seismicity can develop that yields information about bed properties1, stress distribution, outburst flooding, and crevassing and calving. Basal seismicity in response to glacial motion is linked to variations in both stress and lubrication of bedrock by water and till. Here we analyse data from the Transantarctic Mountains Seismic Experiment array in 2002–2003 to investigate seismic behaviour at David Glacier, a large outlet glacier that drains 4% of East Antarctica’s ice sheet into the Ross Sea. We identify about 20,000 seismic events that are larger in magnitude and duration than typical for glacial sources and repeat at regular intervals of about 25 min. These events are consistent with stick–slip behaviour of debris-laden ice moving over a single obstacle of rough bedrock, modulated by relatively small stress changes from the ocean tides. In the years before and after the interval of repeating events, seismic events with irregular and generally longer intervals were detected at the same location, and are consistent with combined stick–slip and continuous sliding of the subglacial interface. We suggest that the observed transitions in seismicity patterns capture the dynamic behaviour of the ice stream, and that—despite lower ice-flow velocities—sliding in the stick–slip regime enhances subglacial erosion.center_img There are a lot of seismic sensors in Antarctica, continuously monitoring the continent and its movements. Scientists have found over the years that glaciers tend to produce small earthquakes as they move over rocky protrusions. Such activity is generally random and irregular and for that reason a series of small earthquakes occurring beneath David Glacier roughly every twenty five minutes, for several months, stood out.The researchers note that small earthquakes that occur due to glacial movement generally come about as a result of stick-slip action. The glacier encounters an obstacle that causes part of it to slow or stop until the momentum of its mass is enough to overcome the obstacle, at which point it suddenly lurches forward, causing the ground to shake a little bit. Normally such actions occur without any discernible pattern. With David Glacier however, the stick-slip shaking, recorded by the Transantarctic Mountains Seismic Experiment array under the glacier in East Antarctica (which drains into the Ross Sea) was so predictably periodic that it warranted further research.The team identified 20,000 small earthquakes during the time frame, all coming within about 25 minutes of each other. By comparing the seismic data with other glacier slip-stick recordings, they confirmed that the shaking was due to the glacier moving over something below, rather than conditions beneath the surface of the land mass. Then they noted that the periodicity of the earthquakes matched up with ocean tides, which made sense, because scientists already know that glaciers tend to slow a very small amount during high tide (because of buoyancy) and speed up at low tide. That they say, accounts for the regularity of the earthquake activity during the time period under study.The researchers say their findings indicate that tidal activity likely plays a role in other glacial areas as well and suggest that it might play an additional unknown role as global warming causes a rise in sea levels around the world. Journal information: Nature Geoscience © 2012 Phys.org Citation: Tidal motion found to influence Antarctic sub-glacial seismicity (2012, August 20) retrieved 18 August 2019 from https://phys.org/news/2012-08-tidal-motion-antarctic-sub-glacial-seismicity.htmllast_img read more

Philippine Airlines PAL is on a mission to enha

first_imgPhilippine Airlines (PAL) is on a mission: to enhance its passenger experience to the level expected of high-end operators sought out by flyers seeking the best. To that end, PAL has reconfigured its A330s flying between Manila and Sydney and Melbourne, among other international destinations. Signature Luxury Travel & Style flew Manila to Sydney with PAL this month, and can confirm the airline is on track to compete with the big guns with its business-class offering.The 18-seat business class cabin is set up in a 1-2-1 configuration in a grey-blue colour scheme with mood lighting and 18.5-inch (47-centimetre) touch screens. The Thompson Vantage XL seats have an ample width of just under 60 centimetres. When in their flat-bed position, the seats stretch out to 200 centimetres. The seat-adjustment panel is conveniently positioned on the divider between the two seats, which are far enough apart to allow for a roomy seatside storage area. As well as a flat space big enough for a laptop, gadget charging and other items, the storage area has an additional shelf to keep personal items secure, including the L’Occitane-stocked inflight bag provided. The reading lamp has three levels of brightness and slippers are provided.Seats feature the Pneumatic Comfort System, which allows passengers to adjust the firmness to their preference. The seat cushion and back also adjust according to the passenger’s weight and pressure on the seat, such as during take-off.“The seat is quite firm when you first sit down but after a few minutes it inflates beneath you and increases the comfort factor,” says Signature Luxury Travel & Style feature writer Joanna Tovia. “It’s a big step up from the last time I flew Philippine Airlines business class; it’s really moving in the right direction to become a five-star airline.”Tovia suggests bringing your own noise-cancelling headphones, however, as those provided are adequate but nothing special. The wine and champagne on offer are exceptional – the champagne is Charles Heidsieck Brut Reserve from Reims, France – and the menu fuses Filipino flavours with contemporary tastes.The aircraft is equipped with Wi-Fi, and the service is warm, friendly and efficient. PAL has also upgraded its premium economy and economy cabins on these planes.last_img read more