Stuff we linked to on Twitter last week

Posted on February 3, 2013 by Chris Rowan

A post by Chris RowanA post by Anne JeffersonA busy week for both of us this week – Anne had a stimulating few days at the ScienceOnline 2013 conference in North Carolina, while Chris tried to achieve something other than teaching prep. But, through all this, we still found some cool links to share with y’all.

Up-Goer 5

Volcanoes

Earthquakes

Planets

(Paleo)climate

Water

Environmental

General Geology

Interesting Miscellaney

Categories: links

Friday Focal Mechanism: the Himalayas’ long tectonic shadow

Posted on February 1, 2013 by Chris Rowan

A post by Chris RowanIt wasn’t the biggest seismic event of the week, but this shallow (15 km depth) magnitude 6.0 that shook the remote southeast corner of Kazakstan on Monday still caught my attention.

Location and (strike-slip) focal mechanism for Monday’s M6.0 earthquake in the Tian Shan Mountains, SE Kazakstan.

Located within the Tian Shan mountains, this earthquake is testimony to the profound and ongoing regional impact of the collision of India with Asia over the past 50 million years or so. This crash of continents has thrown up the Himalayas, and behind them raised the Tibetan plateau; but GPS measurements of deformation for this region show that even 500 kilometres further inland still, the northward motion of India is still being felt, pushing and squashing the Asian crust, raising the Tian Shan mountains – and causing this earthquake.

GPS measurements of deformation associated with collision between India and Asia. Motion vectors are relative to the non-deforming interior of Asia. Source: Gan et al., 2007.

This is a good example of how unlike plate tectonics in the strict sense the deformation of continental crust can be: rather than large, rigid chunks of crust which interact only at their edges, the ‘plate boundary’ between India and Asia stretches a long way into Asia. Rather than a single fault system, you have an entire region gradually absorbing India’s inward charge. But this event is interesting for another reason: the reported focal mechanism suggests that the rupture was due to strike-slip motion on a fault, either dextral strike slip on an northwest oriented fault (north-east side moving south-east) or sinistral strike-slip on a southwest oriented fault (northwest side moving southwest).

The two possible interpretations of the focal mechanism. Dextral strike slip on NW-SE fault, or sinistral strike-slip on a SW-NE fault.

Strike-slip is perhaps a bit of a surprise, since most earthquakes in this region seem to be on thrust faults accommodating north-south compression. These faults mostly appear to be following a northeast-southwest trend, which might suggest that we are seeing sinistral strike-slip on one these structures, as in the first possibility above. However, this implies some sort of lateral escape tectonics in this area, where rather than being all squashed and crumpled up to make room for India’s incursion, some of the Asian crust simply moves out of its way. This is clearly evident in eastward GPS vectors seen in eastern Tibet, but is not particularly compatible with the SW-NE trend of the GPS-derived motion in the Tian Shan. However, it turns out that about 200 km to the west, on the other side of Lake Issyk Kul, there is an 800 km-long, active, northwest-southeast trending dextral strike-slip fault, the Talas-Fergana Fault (TFF):

GPS velocity field for Tian Shan; motion vectors relative to stable Eurasia. TFF=Talas-Fergana Fault. Source: Zubovich et al., 2010.

Monday’s earthquake could therefore have occurred on a smaller but similarly oriented structure east of the Talas-Fergana fault (meaning that the first of the two possibilities suggested above is correct). Over 1000 km beyond the main collision front, the northern motion of India is causing deformation; and in the Tian Shan that deformation is being accommodated by N-S strike-slip faults as well as E-W thrust faults. Why is it doing it that way? I suspect it may have something to do with us being near the eastern edge of the Tarim Basin, which is thought to be a strong, rigid block that is not deforming very much. Based on the GPS velocities in the figure above, the Tarim block appears to transmit the stress from the Himalayas and Tibet further northwards into the Tian Shan than is possible in the weaker crust beyond its edges. Strike slip faults such as the Talas-Fergana fault, and possibly the fault that ruptured on Monday, are accommodating the difference. That’s continental tectonics for you: why use one fault when you can use whole different sets of faults at the same time?

Note:No promises, but I’m hoping to make this a quasi-regular feature again.

Categories: earthquakes, focal mechanisms, tectonics

The Up-Goer Five Challenge: now at Scientific American

Posted on January 28, 2013 by Chris Rowan

A post by Chris RowanAnne and I have continued to be blown away by the magnitude of the response to Anne’s original challenge to explain your scientific research using only a list of the thousand most commonly used English words. Ten Hundred Words of Science, the tumblr blog we created to manage and showcase the flow of submissions, has now got up to almost 300 responses, with more still arriving. In a post now up at the Scientific American Guest Blog about the whole memetic shebang, we highlight some of the more brilliant and creative examples, although that is but a small sampling of the riches on offer. Check it out here.

As a side note, I’ve noticed a curious bipolarity in reactions to the ‘Up-Goer 5’ phenomenon. Many are genuinely enthusiastic, but some are very dismissive indeed (check out a couple of comments on the Guest Blog post for some fairly typical examples). Partly this seems based on the mistaken idea that we’re arguing that you should actually lecture or write exclusively from the Up-Goer 5 lexicon*. Should you speak like this? No, of course not. The point of the challenge is to see if and how you could, and in the process discover the snarly, hand-wavy parts of the explanations we store in our head – the bits we mentally gloss over with ‘obviously’s and ‘clearly’s and basically ignore until we are trying to pass our wisdom onto others, and realise that they’re not really obvious or clear at all.

This, I believe, is where the challenge comes in: it forces you to take apart the linguistic engine of an explanation, and allows you to identify and remove the ugly bits of jargon that are clogging things up and inhibiting the spark of comprehension; and then, you can put it all back together again, creating a shiny new explanatory framework that enlightens the people you are trying to reach more smoothly. It’s a training aid, not something you use when performing. Although the results are fascinating – and fun.

*Seriously, people. Me, argue for abolishing virtually every word with more than two syllables? Preposterous!

Categories: public science, science education

Stuff we linked to on Twitter last week

Posted on January 27, 2013 by Chris Rowan

A post by Chris RowanA post by Anne JeffersonSince it seems much of the northern hemisphere is cold and snowy at the moment, here’s some good reading to curl up with a hot drink over. For those in the southern hemisphere: here’s some good brain food to distract you from gloating…

Volcanoes

Earthquakes

Planets

(Paleo)climate

Water

Environmental

General Geology

Interesting Miscellaney

Categories: links

Scenic Saturday: A Special Place and Time

Posted on January 26, 2013 by Anne Jefferson

A post by Anne JeffersonA few weeks ago, on an afternoon in London, I took in the Thames and then headed a few miles down river to Greenwich and the Royal Observatory, a prime attraction for map nerds around the world. Unfortunately, my visit was untimely, and the observatory was closing up for the day when we got there.

The Royal Observatory in Greenwich is THE home to Prime Meridian and Greenwich Mean Time (GMT), so I hope you’ll forgive me the terrible puns in the last paragraph. A telescope at the Royal Observatory precisely defines the Prime Meridian – the line of longitude at 0o 0′ 0″ from which all east-west distances are measured. Fittingly, the observatory is home to the extraordinarily precise chronometers which solved the “longitude problem” in the first place. “By international decree, the official starting point for each new day, year and millennium (at the stroke of midnight GMT as measured from the Prime Meridian)” occurs at the Royal Observatory.

Dim view of the Telescope building

Our view of the telescope building at the Royal Observatory

During the Observatory’s open hours, visitors can see the telescopes, historical exhibits, a planetarium, and a famous line on the pavement that separates the eastern and western hemisphere. Visitors arriving too late in the day to get inside are, however, still rewarded for the climb up the hill from the river. A green laser light shines forth along the meridian, streaming out of the observatory and across the Thames and London.

Greenlight from a hole near the roof a building

The green laser demarcating the Prime Meridian, issuing forth from a building on the grounds of the Royal Observatory. The pavement marking seen by daylight visitors is in the courtyard in front of this building.

As the sky darkens toward night, there’s a stunning panorama of lit up London to enjoy. [Click on the image below for a much larger view.]

City lights in a panorama of blackness

The view from the Royal Observatory, not long after sunset. From the left, you can see the Observatory building, and central London in the distance. Straight ahead is the Canary Wharf financial district and to the right is the O2 Millenium Dome. Just to the left of the O2 cuts the Prime Meridian, though you can’t see it in this picture. Click to very much embiggen.

As, arguably, the start of time and the center of space, it was totally worthwhile to visit the Royal Observatory – even in the dark. But Greenwich is a place that deserves more time and light than I could give it on this trip, so I’ll be back to take in the sights of this special place on some future journey.

Green laser line in the night sky marks the Prime Meridian, I'm underneath it.

The green laser light emanating from the Royal Observatory marks the path of the Prime Meridian as it encircles the world. My arms encircle my world – my daughter – who turned 6 years old today.

Categories: by Anne, general science, photos