Earth Science

The Global Positioning System has completely revolutionised how geologists study the deformation of the Earth. If you leave a GPS receiver in a fixed location for days, months and years, it is precise enough to measure motions on the millimetre scale, allowing us to track strain building up across active faults, and even the incremental drift of the tectonic plates themselves across the Earth’s surface. But on the 26th December 2004, stations across a sizeable slice of the Earth’s surface suddenly found themselves being jerked around a bit more rapidly. The plots below are from stations in southern India and northern Taiwan, respectively. If you are thinking that date sounds a bit familiar, you’d be right: that jerk is the signal of the massive magnitude 9.3 earthquake that ruptured a 500 km length of the Sunda Trench off the coast of Indonesia on Boxing Day 2004, and unleashed a devastating tsunami. What’s impressive is that we are seeing permanent deformation of the crust due to motion on a fault (what is known as coseismic deformation) an extremely long way away. As we can see on the map below, the Indian GPS station IISC is some 2,300 miles away, and the Taiwanese station TNML is 3,600 miles away, from the Sunda Trench. And yet, even at that distance, the Sumatra-Andaman earthquake shifted the land beneath these points about a centimetre – a little less for the Taiwan, a little more for India. The figure above also compares the actual motion observed with GPS (black arrows) with predictions from a model of the Boxing Day rupture (grey arrows). What this figure doesn’t show is the predicted coseismic deformation at places not occupied by GPS stations. Fortunately, a paper just published in the Journal of Geophysical Sciences contains a much nicer visualisation of the output of a similar model. This model – rather mind-blowingly – indicates that the Sumatran-Andaman earthquake rupture directly deformed a sizeable fraction of the Earth’s surface, including Africa, Arabia, the eastern half of Asia, and most of the Americas. Paul Tregoning and his co-authors have gone on to calculate the cumulative coseismic deformation resulting from all 15 magnitude 8 or greater earthquakes that have occurred since the turn of the millennium on the Earth’s surface. Unsurprisingly, the big three earthquakes in this period – the Sumatra-Andaman, the magnitude 9.1 Tohoku earthquake in March 2011, and the magnitude 8.8 Chilean earthquake in February 2010 – are the major contributors, but the smaller ones fill in some gaps in the southwest Pacific. Modelled global coseismic deformation due to all M 8+ earthquakes since 2000, from Tregoning et al., 2013 Basically, outside of western Europe and the Arctic Circle, pretty much the entire surface of the planet has been shifted at least a millimetre or two by an earthquake since the turn of the millennium. And this has real world consequences. The interiors of the Earth’s tectonic plates are generally assumed to be rigid and undeforming, and are used as a fixed reference point for measuring deformation at the plate boundaries. The red arrows in the figure above show exactly how much you’d be wrong if you are assuming that for a given point on the Earth’s surface. Even when you’re a long way from a plate boundary, coseismic deformation from distant, large earthquakes is causing your ‘fixed’ reference point to be not so fixed. Spooky tectonic action at a distance, indeed. References Corné Kreemer, Geoffrey Blewitt, William C. Hammond, & Hans-Peter Plag (2006). Global deformation from the great 2004 Sumatra-Andaman Earthquake observed by GPS: Implications for rupture process and global reference fram Earth, Planets, Space, 58 (2), 141-148 Tregoning, P., Burgette, R., McClusky, S., Lejeune, S., Watson, C., & McQueen, H. (2013). A decade of horizontal deformation from great earthquakes J

In the drive to climate-proof cities, we can't just focus on buildings. Social infrastructure is just as important, says sociologist Robert Sampson

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Some people believe the Intergovernmental Panel on Climate Change (IPCC) is a small, unified body composed of the best scientists who make proclamations on lots of things.That isn't really true. The actual IPCC is a tiny UN group, around a dozen people, but the bulk of the data is compiled by unpaid (well, unpaid by the UN) scientists who participate in working groups that argue over the science - it is not without some flaws. They use geographical and gender parameters for participation so a working group may not have the best scientists in the world, some will have been chosen because they needed to meet a cultural quota - and they still get to be heard. --> read more

Temperatures in central China are 10 to 14 degrees Fahrenheit hotter today than they were 20,000 years ago - an increase two to four times greater than many scientists previously thought. read more

…me, apparently. Even though I didn’t know I’d been nominated until I was notified on Twitter: #bbpBox_334328305673187328 a { text-decoration:none; color:#B30000; }#bbpBox_334328305673187328 a:hover { text-decoration:underline; } Congrats to @Allochthonous for “Best Physics, Astronomy, or Earth Science Post”: http://t.co/em4cxUTWcl about 10 hours ago via webReplyRetweetFavorite @SciSeeker ScienceSeeker Check out the announcement on the ScienceSeeker blog for full details and links to the winning posts in other categories; there’s some good – award winning! – reading there. My winning entry was my response to the verdict in the L’Aquila trial, where I argued that earthquake safety is about door locks, not fire alarms: in other words, whatever the dubious merits of the trial and conviction itself, it highlights a worrying focus on short-term warnings (which we can’t do) at the expense of long-term preparedness (which we can do, at least in theory).

A comprehensive study of the behaviour of ice sheets in a warming world suggests that the ocean will rise less than feared this century

We all know that the Earth is in constant motion, rotating beneath our feet, but new research in Nature Geoscience reveals that the center of the Earth is out of sync with the rest of the planet and is frequently speeding up and slowing down.Associate Professor Hrvoje Tkalcic from the ANU College of Physical and Mathematical Sciences and his team used earthquake doublets to measure the rotation speed of Earth’s inner core over the last 50 years and discovered that not only did the inner core rotate at a different rate to the mantle – the layer between the core and the crust that makes up most of the planet’s interior – but its rotation speed was variable. --> read more

Experiments on iron's behaviour at extreme pressure may help explain why seismic waves' speed through Earth's core is affected by their direction

Rather than Draconian measures to cut emissions, which will impact people in various regions and economic spheres unfairly, a better solution may be to simply keep places cooler on hot days, which will reduce fuel needed for air conditioning.And outer space can help, Stanford researchers say. They designed an entirely new form of cooling structure that cools even when the sun is shining - by reflecting sunlight back into the chilly vacuum of space. --> read more