The heart of the fault zone

Posted on October 6, 2007 by Chris Rowan

For all that we currently know about earthquakes and faulting, seismology remains primarily a descriptive science. We can tell where an earthquake occurred, and how powerful it was, but we still don’t understand why some ruptures trigger failure over a large section of a fault, and others do not. Plate tectonics allows us to predict the overall motion across a fault zone, and even the type of faulting that is needed to accommodate it, but we can’t predict whether that motion will be expressed by a single large earthquake or dozens of little ones.
A large part of the problem is that we don’t know much about what faults are like where it really matters: although many large faults break and deform the Earth’s surface, the initial rupture in an earthquake always occurs several kilometres below, where increased temperatures and pressures make rocks behave somewhat differently that they do in the part of the fault we can see and touch. Geophysical techniques can tell us roughly where the fault zones are, but lack the resolution to tell us much about a feature which may only be tens of metres across. Which is why the rocks pictured below are so important: they were collected from 3 km below the surface, right in the heart of the San Andreas Fault.

SAFOD.jpg

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Categories: earthquakes, geology, tectonics

What’s your Sputnik moment?

Posted on October 4, 2007 by Chris Rowan

A couple of years ago, I was talking on the phone with my Mum. Nothing so unusual about that, you might think (unless you’re thinking that was the last time I talked to her, in which case I assure you I’m not quite that feckless) – except that she was sitting at home in the UK, and I was standing in the middle of a field in rural New Zealand, chatting to her on my mobile phone.
What’s quite awe-inspiring about this, when you think about it, is that people who emigrated to New Zealand in the 1960s will tell you that you that they were effectively cut off from the family they left behind in Britain; letters could take weeks or months to arrive, and telegrams were short and too expensive for most. Step forward 40 years, and I was able to travel in their footsteps to the opposite side of the globe, and still engage in a real-time conversation with the folks back home. Such are the scale, and pace, of the changes wrought by satellite technology.

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Categories: general science

Out of the ice age, into the asteroid shower

Posted on October 3, 2007 by Chris Rowan

21,000 years ago, at the peak of the last glacial, ice sheets covered most of Western Europe and North America; by 10,000 years ago, a warming climate had melted them away. Records from ice and sediment cores all agree that the ice’s retreat back to its strongholds in the Arctic Circle was not smooth, but jerky: the Greenland temperature record, calculated from oxygen isotope variations in the GISP2 ice core, indicates that episodes of more rapid warming and cooling were superimposed on the longer-term warming trend. Particularly prominent is a 1,500 year period between about 13,000 and 11,500 years ago, known as the Younger Dryas, when the mean annual temperature abruptly dropped to levels more typical of the Last Glacial Maximum.

Greenlandtemp.png

There is evidence that the Younger Dryas cooling, and much of the other shorter-term variability seen earlier in the last deglaciation, are related to fluctuations in the strength of the thermohaline circulation, due to sudden additions of meltwater to its North Atlantic source region. But some scientists, such as Richard Firestone of the Lawrence Berkeley National Laboratory, have been wondering if the particular severity of the Younger Dryas cooling might be the result of a more exotic cause: an asteroid or comet exploding above North America 12,900 years ago.

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Categories: climate science, geochemistry, geohazards, paper reviews, past worlds, planets, Pleistocene

ID out in Britain’s educational cold, but what of South Africa?

Posted on October 1, 2007 by Chris Rowan

Good news for those of use who believe that what little British schoolchildren get taught in science classes nowadays should actually vaguely resemble science – here’s some choice quotes from some new guidelines (hat-tip to the Panda’s Thumb) regarding the treatment of intelligent design and creationism in science lessons:

Creationism and intelligent design are sometimes claimed to be scientific theories. This is not the case as they have no underpinning scientific principles, or explanations, and are not accepted by the science community as a whole. Creationism and intelligent design therefore do not form part of the science National Curriculum programmes of study.

Any questions about creationism and intelligent design which arise in science lessons, for example as a result of media coverage, could provide the opportunity to explain or explore why they are not considered to be scientific theories and, in the right context, why evolution is considered to be a scientific theory.

Any resource should be checked carefully before it is used in the classroom. If resources which mention creationism or intelligent design are used, it must be made clear that neither constitutes a scientific theory.

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Categories: antiscience

Highly Allochthonous needs YOU!

Posted on October 1, 2007 by Chris Rowan

September is obviously an auspicious month for starting geology blogs: Brian’s celebrated its first anniversary last week, and over the weekend Highly Allochthonous turned two. I’ve come a long way since my first post, and even since this time last year; I certainly did not expect to be marking this anniversary as a member of Scienceblogs (a fairly minor one to be sure, but I still think it’s pretty cool). So who knows what next year will bring – I can only hope that I continue to improve as a writer, and that people keep on reading and commenting.
By way of a retrospective this year, I thought that this would be a good time to consider what, if anything, I should submit for this year’s Science Blogging Anthology. However, since I find self-assessment rather difficult, I thought that I might prevail on you – the readers – to help me out. I’d like to know what you’d consider to be my best posts from the past nine months. Consider it a birthday present – and, as it was my actual birthday on Friday too, a virtual replacement for those beers y’all would be buying me if we were on the same continent.
As a starting point, here are a few posts which either seemed particularly popular, or that I was particularly proud of:


However, if you enjoyed something else I’ve written better, please let me know what, and (if possible) why. This may seem like just a big ego-stroking exercise for yours truly, but at these times I like to look forward as well as back; I’m also thinking about where to take this blog in the future, and your opinions matter (even if I reserve the right to completely ignore them…one captain on a ship and all that). So if you have any general comments or suggestions, this is the place to make them known, as well.

Categories: bloggery