30 May, 2006

Earthquake in Java

When they first heard news of Friday's earthquake in Java, many people's first reaction was undoubtedly to wonder if this latest event is in any way related to the Boxing Day 2004 quake. Here's some information on Friday's earthquake, courtesy of the National Earthquake Information Center (more specifically, here):

This image shows both the earthquake's location and a beachball-like symbol, known as a focal mechanism, which indicates the type of fault generating the earthquake. More in this in a minute, but first lets look at the same information for the Boxing Day Earthquake (full summary here).

You should ignore the magnitude, which was actually 9.0 - the automatic system which generates this information estimates magnitudes from the amplitude of seismic waves of a particular type and frequency, which are saturated (can’t get much bigger) for very large earthquakes and hence lead to an under-estimate.

The Boxing Day tsunami was caused by a rupture of the subduction megathrust at the boundary between two tectonic plates, just off the Indonesian coast. This is obvious from the fact that the hypocentre (point of first rupture) is very close to the Sunda trench, which is where the megathrust breaks the surface. It is also obvious from the focal mechanism, which is an idealised plan view of the movement associated with the earthquake, divided into compressional (solid areas of the beachball) or dilational (white) zones. This distribution is constructed by combining the directions of first motion, compared to the direction of the source, received by the global seismometer network; this will vary depending on the relative position of the station. The dividing lines between the solid and white zones represent the two possible fault planes along which this motion occurred - movement along either of these planes can produce the same focal mechanism (for slightly more detail, see here or here). The focal mechanism for the Boxing Day 2004 earthquake is a thrust fault - there is a compressive zone in the centre of the beachball which shows that shortening of the crust is occurring along either a very steep, or very shallow, thrust plane. Because we know it was at a subduction zone, it's probably the latter (the megathrust is normally shallowly dipping - see my previous post on subduction zones).

However, looking back at the information for Friday's earthquake, you can see that it is located much further away from the trench, in the forearc region of the overriding plate. Also, the focal mechanism is completely different; the pattern of compression and dilation implies horizontal strike-slip along a vertical fault plane. This indicates that this earthquake did not occur at the megathrust on the plate boundary.

However, things start to get interesting if we look at the relative motion across this boundary, which, as the figure below indicates, is generally oblique to the trend of the Sunda Trench. In contrast, the motion at the subduction megathrust (as indicated by the Boxing Day focal mechanism, and the focal mechanism of the 28th March earthquake in the adjacent section of the subduction zone) is almost exactly perpendicular to that trend. It seems that motion along the megathrust cannot account for all of the relative plate motion. However, the 'left-over' motion (see inset) can be accommodated by events like Friday's earthquake, if we assume a NW-SE-trending fault.

This phenomenon - different parts of the plate motion being taken up by separate sets of faults - is known as strain partitioning, and is very common in regions of oblique subduction. Thus the two events can be viewed as complementary - the strike slip fault in the forearc region is taking up the component of plate motion that the subduction thrust does not. The Boxing Day earthquake did not directly cause Friday's earthquake, but a study of its focal mechanism clearly requires events like it.

27 May, 2006

Viva'd out

Last week I finally managed to break the back of all my marking and, most importantly, the viva-ing. I've ended up doing much more than I expected, mainly because I rather foolishly agreed to cover for the single person in the department who is taking this whole lecturer strike seriously, more than doubling my workload at a stroke. The powers that be are paying me extra for this, but at several points in the last week or so I've wondered whether it was really worth the lost weekends and evenings.

The vivas themselves were an interesting experience. I have to confess to feeling a slight discomfort with the whole thing; here I was, passing judgement on the efforts of people I don't feel much older than, with my opinion having equal weight to that of the other, much more experienced marker. I did worry that they might chafe a bit at the situation, but that didn't seem to be a problem. For my part, it was interesting to see how the second markers focussed on different things in the vivas themselves. Some concentrated on narrrow technical issues, others on more general interpretation stuff - there was almost as much variety here as in the how the students coped. On that side of things, there was surpises both pleasant and unpleasant: it was great when they came in well-prepared, and showed a much better understanding than you expected, it was less good when they came in and threw random keywords together in the hope that some glimmer of sense would emerge (in much the same manner that many of them seemed to have written their reports).

As well as all of that, I also had to give a double lecture last Friday, ironically to the same third year who I have been viva-ing. It was also the last lecture of the semester for them (and hence for some, their last lecture ever), so there was a definite 'end of term' atmosphere which probably didn't do much for their attention spans. Still, hopefully I did enough to ensure they ended on a medium.

Anyway, I can't complain about not having anything to do at the moment, that's for sure, and my self-indulgent vanity projects (to wit, this blog) have suffered as a result. Hopefully I'll get back to having some spare time soon.

17 May, 2006

Pre-empting your own whitewash

I'm having real trouble understanding Tony Blair's speech to the CBI last night, where he declared nuclear power was 'back on the agenda with a vengeance'. The pro-nuclear spin is hardly surprising given the noises coming from the government lately, but given that the soon-to-be-published Energy Review was already expected to recommend building new nuclear power stations, why so publicly confirm the suspicion that the conclusion was preordained from the start? Surely this is not the best way to convince people.

I have two theories on this: one is that this is all a big softening up exercise, where the government threatens to build 50 (just a number pulled out the air) new nuclear power stations and exploits the sigh of relief when they then decide to build 10 or so as part of an integrated switch over to more sustainable energy sources. The other is that Blair has got to the stage where he thinks that any massively unpopular decision is the brave and right thing to do, regardless of logical or rational arguments to the contrary. Thus we'll all hate him but he'll be vindicated in the history textbooks of the future (which is where he always seems to be looking).

I'm fervently hoping for the former, but the fact that before the speech a Downing St spokesman rather disparagingly predicted "despairing shrieks of outrage" strongly suggests that the latter may be much closer to the truth. Which is a shame - I'm not going to deny that I'm rather unconvinced about the potential for nuclear to solve any of our environmental or energy security problems, but I'm in full agreement with David Osler, who actually does favour it but concludes:

But none of that should preclude a rational debate on the pros and cons of nuclear power. It's just a shame Blair is trying to bounce a reluctant populace into accepting a given outcome in advance.

Hear hear.

16 May, 2006

EU emissions trading in trouble

It seems the EU emissions trading scheme, launched to great fanfare last year, is in a bit of trouble (so the Guardian and Independent report). The idea was simple(ish): emitters of carbon dioxide covered by the scheme (power companies, cement factories, etc.) were given an emissions quota. If they did not use it all, they could sell the excess to firms whose emissions were too high; if those who exceeded their quota did not buy in extra rights, they would be fined. Hence cutting emissions is rewarded by making a profit from selling your spare emissions rights, rather than having to buy in extra ones. But all has not gone according to plan (all the quotes below are from the Guardian):

Officials involved in planning the first phase of the scheme, the results of which were announced yesterday, stand accused of being grossly overgenerous in issuing polluting permits to 12,000 European power plants and industrial installations, responsible for more than half of the EU's carbon dioxide emissions. The results showed that industrial sites in many member countries produced much less pollution last year than they were allocated - sending the fledgling market in carbon permits through the floor.

Obviously, if everyone can easily meet their targets, the system is unworkable because the emissions rights are effectively worthless. And it seems this is exactly what is happening. Of course, there's always an excuse:

European officials defended the scheme, blaming the mild winter in early 2005, soaring energy prices leading to reduced output, early use of clean technology and even the rain (promoting more hydro-power).

But you have to suspect the real reason is effective lobbying by the industries concerned for allocations way into the 'safe zone', where the targets could be met without much pain. Lots of talk in the right ears about 'stifling economic growth' would have done the trick. That's not really a criticism of them, by the way - more of those in charge of the scheme for not taking their whining with a pinch or five of salt. If they're really serious about this, the EU should adopt the approach used by my funding council when I applied for fieldwork costs - they ask how much we needed, then cut it in half. That would encourage a little bit of creativity.

Worst of all, of course, is the performance of our fair country - despite our demanding - and getting - a last-minute 20 million tonne increase of our quota, it seems we still managed to overshoot. You could argue that we were actually getting in to the spirit of the thing by having a quota in the right ballpark (rather than us being too incompetent to meet even a stupidly lax target), but a little fact belies this:

The UK government is considering asking for an increase in pollution permits for British industry in the next phase.

And this lot accuse Cameron of being a fair-weather environmentalist? Meh.

15 May, 2006

Algae and earthquake precursors

An interesting report from the BBC last week:

Concentrations of the natural pigment chlorophyll in coastal waters have been shown to rise prior to earthquakes.

These chlorophyll increases are due to blooms of plankton, which use the pigment to convert solar energy to chemical energy via photosynthesis.

This is based on an article by Singh et al. [doi] in Advances in Space Research, the current issue of which seems to be devoted to the use of satellite remote sensing for studying and predicting natural hazards such as earthquakes. The authors claim that you can detect a rise in sea surface temperature just before large coastal earthquakes. The blooms observed in this study are, they say, result from an increased flow of heat energy from the ocean to the atmosphere, enhancing the upwelling of cold, nutrient rich water and fuelling a boom in the growth of photosynthetic algae.

This is all very interesting, but what is unclear in the paper is the reason so much heat energy is being released prior to the earthquake, which is itself releasing accumulated strain energy. And, looking at the paper, I'm not really sure the relationship is quite as clear-cut as is claimed. The figure below is from their paper, which shows the amount of upwelling measured at three localities in the month in which an earthquake was recorded. The peaks can be linked to increased concentrations of chlorophyll, as measured by satellite. The dark vertical lines mark the date of the earthquake.

As you can see, there are a number of peaks in each of these plots, not just the one associated with an earthquake. In all but perhaps the last case the peak preceding the earthquake doesn't seem to have a significantly different magnitude to all the others, and the timing of the earthquake seems quite variable - in one case it coincides with the peak, in another it is ten days afterwards.

You may beg to differ, but I'm rather unconvinced by this. It seems on a par with other proposed earthquake precursors like low frequency EM fluctuations (on which there are also some papers in this issue of Space Science Research) - not only is it not clear how they work, but the supposed precursor signals are not obviously distinguishable from background. Sadly, I don't think we'll be using satellite data to reliably forecast earthquakes just yet.

09 May, 2006

When experiments go bad

Via Pharyngula via Evolving Thoughts comes this rather entertaining write-up of a physics experiment by a clearly disgruntled physics undergraduate.

The slightly sarcastic tone rather reminds me of my Cell Biology practicals way back in my first year of undergrad Natural Sciences. I generally finished these in a slightly bad mood –they were on a Friday afternoon, and my timetable was so crammed that I got there an hour after most people, forcing me to miss lunch and finish late (and hence miss valuable pub time). Also, the experiments rarely worked; most of them were quite complicated and fiddly (one I particularly remember was trying to get bacteria to take up foreign DNA) so there were myriad ways in which things could go awry. And that’s without considering the perverse bloody-mindedness which inhabits most biological things when they are placed in a lab environment. Being a tad perfectionist I found this quite frustrating, and through the year my write-ups became increasingly sarcastic as I analysed the large number of ways in which I may have been let down by the experimental procedure, the equipment or my own competence.

Strangely, my cynical tone didn’t really affect my marks. I found out why near the end of the year: I finally got an experiment to work exactly right, prompting a full chorus of hallelujahs at the end of my write-up. In response, my lab supervisor wrote that I had done well even on the many experiments which didn’t work right, because I had always tried to understand the failures (apparently my asides also made him laugh – something I can appreciate now I too get dumped with piles of marking).

In hindsight, he was right: you can sometimes get as much out of a failed experiment as a successful one. Failure certainly forced me to think a lot more about how exactly the things I was testing were supposed to work, in order to work out why they didn’t. Perhaps that’s why I aced the lab exam at the end of the year…

05 May, 2006

Marking madness

My (very) small band of semi-regular browsers might have noticed a slight drop in posting frequency over the last couple of weeks. This has not only been due to the first inklings of semi-nice weather drawing me away from the keyboard (although they haven't helped); I'm also completely snowed under marking undergraduate mapping projects. This is a rather time-consuming affair: each one consists of field slips, notebooks, an interpretative map and a report, which you have to constantly cross-refer between to check the interplay between observations and interpretations (is a strange interpretation due to a mistaken observation, or just poor extrapolation from sparse data?). I've never had to mark this sort of thing before, so am finding it even more slow going. In fact, I've been more than a little perturbed about the lack of guidance I've got - these things were effectively dumped on my desk and I was told, "Go mark". Given that these projects form a sizeable percentage of the students' final year mark, it's important to get them right, and I worry that my inexperience may cause difficulties (it's also yet another example of me being given responsiblities seemingly far beyond those you'd expect for my present position or salary, but that's actually a minor irk in this case, as I can see the experience will improve my teaching). I was reassured by the fact that they were being double-marked, and that the students would also have a viva, or oral exam, to help assess their performance.

Yes, I was reassured - until I found out yesterday who is doing the vivas.



I'm not sure what's more scary: the thought that the department trusts me with such things, or the thought that it's more because they can't get anyone else to do them.

03 May, 2006

Lascar volcano erupts

The picture below shows Lascar volcano in Chile erupting two weeks ago (from here)

Not amazing newsworthy – the eruption only vented stream and ash - except for the fact that this is only six weeks or so after people from my lab were up on the slopes of Lascar collecting samples. Not me of course – strangely, whilst my boss is too busy to lecture or mark, he can find time between all those meetings for jollies to South America. Maybe it’s the double standards that angered the volcano god…