In an average year, we would expect about 20 quakes exceeding magntiude 7.0, so naturally the news media got rather excited as to whether the two quakes were linked. Had the Samoan quake caused the Sumatra quake? I spent quite a while on Wednesday evening talking to various print and broadcast journalists by telephone and on Skype, and was chauffeured down to London at 4am on Thursday to do a live interview on GMTV just after 6am. Some journalists also cottoned on to a magnitude 5.8 quake in Peru nine hours after the Sumatra quake, and looked for a link between all three...

The answer is that the events are most unlikely to be linked. Look at the map below: the epicentres of the Samoan and Sumatra quakes are more than 7500 km apart, and they are not even on the same plate boundary. The Samoan quake occured in what is popularly called the 'Ring of Fire' This (almost) circles the Pacific ocean, and is a system of trenches where the Pacific ocean floor is being subducted (pushed down below) continents or island arcs, running from New Zealand, northwards past Tonga (where the ocean floor is being subducted westwards, and hence the Samoan quake), thence onwards to the Philippines, Japan, Kamchatka, Alaska and down the west coast of the Americas to Chile. The magnitude 5.8 Peru quake was on the 'Ring of Fire' too, where the ocean floor is being subducted east below South America) and was entirely unremarkable because we expect three or four quakes exceeding magitude 5.0 somewhere in the world every day. Melting processes in subductioin zones, not directly related to earthquakes, feed the volcanoes that give the 'Ring of Fire' its name. An earthquake happens when strain that has built up over decades or centuries is released by the sudden, violent, slippage of a fault. The most that can be said is that a distant quake might be capable of precipitating a quake that was going to happen soon anyway. It certainly cannot cause one that was not fairly imminent.

Strictly speaking, the Sumatran quake was not on the 'Ring of Fire', despite what you may read or hear in many new reports, but was caused by the same sort of process. Here, the Indian ocean floor is being subducted northeastwards below Sumatra and Java. It was a large quake further along this plate boundary that caused the 26 December 2004 Indian ocean tsunami that claimed nearly 300,000 lives, and a smaller (magnitude 7.7) quake just offshore of Java that caused a smaller tsunami in July 2006.  There was a very intelligent report about many of these issues on the BBC's Newsnight on Thursday.

The epicentres of the Sumatran (on the left) and Samoan (on the right) quakes.  They are more than 7500 km apart, and a very complex system of tectonic plate boundaries lies between. [Map made in Google Earth]

Attention now must focus on rescue efforts, but I hope it will subsequently switch to enquiries into why buildings in Padang were not better able to withstand the shaking caused by the earthquakes. It seems that hospitals and schools collapsed. These are buildings with large rooms, and hence large extents of unsupported roofs and ceilings, but it is well known how to make such structures earthquake resistant. All too often, it turns out that seismic building codes have been flouted. I have blogged previously about shoddy school buildings in regions at risk from earthquakes, for example in the magnitude 7.9 quake in Sichuan, China on 12 May 2008 . Fortunately the local time when the quake struck Padang was after 5 pm, so presumably the schools were fairly empty - but not so the hospitals.

Take it further

Volcanoes, earthquakes and tsunamis   ⁸

Teach Yourself Volcanoes, Earthquakes and Tsunamis by David Rothery
published by Hodder Education

About the author

Dave Rothery is a volcanologist and planetary scientist at the Open University. His current research includes studying volcanic eruptions on the Earth and characterising planetary surfaces, especially Mercury.

Subscribe to Dave Rothery's posts

 

Like those, this tsunami was caused by an undersea earthquake, at a subduction zone where one tectonic plate is being pushed down below another. In this example, the floor of the Pacific ocean is being pushed westwards below the Tonga island arc. Plates do not slide past each other smoothly. Instead, strain builds up until the deformation is relieved in a major jerk. In this case, the 'jerk' began at a relatively shallow depth of about 18 km, and the seafloor above it was probably jolted upwards by several metres. This sudden displacement caused a series of waves on the sea surface, which became higher and steeper when they ran ashore. Local reports speak of waves reaching more than 5 metres above sealevel and rushing 100 metres inland.

Unlike the situation in the Indian ocean back in 2004, the Pacific ocean has a pretty good tsunami warning system, and evacuation of Samoa's capital, Apia, did occur although I am not sure whether this was achieved before any tsunami waves were likely to hit it, because the earthquake was so close by that the waves would arrive in less than an hour. Also the earthquake happened so early in the day, just before 7am local time, that many people may not have been aware of the situation.

Students of the Open University short course Volcanoes, earthquakes and tsunamis , which is supported by the book Teach Yourself Volcanoes, Earthquakes and Tsunamis will doubtless soon be discussing the issues and implications raised by this event. There are many current news reports, and already a rather good entry on Wikipedia.

Samoan region of the Pacific ocean
[data courtesy of US Geological Survey]

Earthquakes in the Samoa region in the 24 hours before the time stated at the top (there were none in the previous week). The largest blue square locates the epicentre of the magnitude 8.0 quake that caused the tsunami. The others are smaller aftershocks.  Samoa is the group of islands north of the earthquake swarm, Tonga lies to the south, and the outlying islands of the Fiji group are visible near the western edge of the map. The map covers a 10 by 10 degree block, approximately 1000 km across. Data courtesy of USGS.

Take it further

Volcanoes, earthquakes and tsunamis

Teach Yourself Volcanoes, Earthquakes and Tsunamis by David Rothery
published by Hodder Education

About the author

Dave Rothery is a volcanologist and planetary scientist at the Open University. His current research includes studying volcanic eruptions on the Earth and characterising planetary surfaces, especially Mercury.

Subscribe to Dave Rothery's posts

 

While we were planning and filming an ambitious item for Bang Goes the Theory in which an 'action man' type-figure dubbed mini-Dallas is sent up to the "edge of space" by a balloon, there was a lot of discussion among the Bang gang about whether or not we could claim to be reaching 'space', and also whether Joseph Kittinger had really "parachuted from space" after his balloon ascent to 102,800 feet (31,333 metres) in 1960.

We got our mini-Dallas to pretty much the same height, but I’m afraid that the answer has to be ‘no’ in both cases, even though the sky looks gratifyingly black in our remarkable camera shots.

Mini Dallas from Bang Goes The Theory.
[image © copyright BBC]

It’s pretty obvious if you think about it. Kittinger and mini-Dallas were both carried up by a balloon, and a balloon only goes up if it (plus its 'astronaut' payload) is on average less dense than the air that it displaces. That’s how buoyancy works.

There must still be air – albeit very tenuous – at the height reached by the balloon, otherwise it could not float.

There is not a vacuum at the height reached by these extreme balloons, but the pressure is very low. In fact it is about one-hundredth of the pressure at sea-level. This means that 99% of the atmosphere’s mass is below, and only 1% of the mass of the atmosphere is above.

However, that does not mean that mini-Dallas was 99% of the way to the top of the atmosphere, because the atmosphere becomes more and more tenuous with height. If you look at this diagram that shows how atmospheric temperature varies with height, you will see that 30,000 metres is only about halfway to the top of the stratosphere, and that there are layers called the mesosphere and the thermosphere above that!

Temperature variation with height in the Earth’s atmosphere. The warming with height in the stratosphere and thermosphere are because the air molecules are warmed by absorption of ultraviolet and other radiation from the Sun

Temperature variation with height in the Earth’s atmosphere. The warming with height in the stratosphere and thermosphere are because the air molecules are warmed by absorption of ultraviolet and other radiation from the Sun.

There is actually no definite boundary that marks the top of the atmosphere, but eventually it becomes so completely tenuous that for practical purposes it can be regarded as ‘space’. But where is this limit?

Well, I did some web searching, and I came up with this. Satellites can orbit 200 km above the Earth, free of any appreciable atmospheric drag. Clearly at 200 km, you are in ‘space’ (the International Space Station orbits at 320-347 km). Lower orbits down to about 160 km are possible, but there is too much drag for these to be stable.

The US government refuses to recognise a definition of where space begins, perhaps because it prefers to keep its option open.

However the Fédération Aéronautique Internationale recognises 100 km as the lower limit of space, whereas an encyclopedia of international law suggests 80 km as a practical limit between ‘air space’, potentially reachable by an aircraft, and ‘outer space’.

However you look at it, sadly 30,000 metres or 30 km is less than half way there, but it was a bold effort nonetheless.

Find out more

John Zarnecki looks back over fifty years of space exploration

Visit The Planets & Beyond

Consider The Open University course Planets: an Introduction

About the author

Dave Rothery is a volcanologist and planetary scientist at the Open University. His current research includes studying volcanic eruptions on the Earth and characterising planetary surfaces, especially Mercury.

Subscribe to Dave Rothery's posts

 

There was an interesting item in programme two of Bang Goes the Theory. The story is that cows produce a lot of methane (which is a more potent greenhouse gas than carbon dioxide), but that insects make protein without releasing methane to the atmosphere. So, to do our bit towards saving the planet from global warming, why don’t we eat insects "and other creepy-crawlies" instead?

Presenter Liz then offers various insect delicacies to her three co-presenters, of which Dallas is at first reluctant to partake. Eventually, he concedes that he likes to eat prawns, and wonders why he is freaking out at the thought of eating something that Liz agrees is ‘essentially a prawn’. Was she right? Read on!

Why some foods revolt us is a complex issue. As I watched for the first time, I too was thinking "go on, I bet you’d eat a prawn, so why not a scorpion or a cricket?" - but that is not actually good logic when you look into it.

Insects and prawns may appear similar, but they are not very closely related. They both have segmented external skeletons and jointed limbs, placing them in the same Phylum (the Arthropoda), but they are in different divisions - Classes - of that Phylum. Insects constitute the Class Insecta, whereas prawns belong to the Class Crustacea.

The flash-fried scorpions that we see Liz cooking belong to a third arthropod Class, the Arachnida (of which spiders are familiar members), and are definitely not insects - despite any impression that the programme my leave to the contrary. Millipedes and centipedes form two other Classes of Arthropoda.

Turning to what non-vegetarians more familiarly eat - for example haddock, chickens and sheep - these belong to three different Classes of the Phylym Chordata. Thus a prawn, a scorpion and a locust are no more closely related to each other than a haddock is to a chicken and a sheep. No problem there, you might think. If you’d eat one, you’d probably eat the other.

Sea squirt - pass the ketchup?
[Image Open University, made available under a Creative Commons BY-NC-SA Licence]

But what about a frog, from the Class Amphibia, would you eat that? Or a sea squirt (Class Ascidiacea)? Both are Classes of the Phylum Chordata. The latter are probably eaten in China, but the majority of westerners would refuse them. Yet both are just as closely related to chickens as prawns are to scorpions, and as chickens are to sheep.

On the other hand, few westerners would eat dog, and I’m unaware of vulture being on the menu anywhere in the world, yet these are far more closely related to sheep and chickens than prawns are to scorpions. Then there are the molluscs; even people who love oysters or Coquille St Jacques (Phylum Mollusca, Class Bivalvia) would probably retch at the thought of eating slugs (Phylum Mollusca, Class Gastropoda).

My conclusions after all this are: One, scorpions aren’t insects; Two, what animals you are willing to eat has little to do with what they are related to.

Find out more

Discover how to start studying biology with The Open University

About the author

Dave Rothery is a volcanologist and planetary scientist at the Open University. His current research includes studying volcanic eruptions on the Earth and characterising planetary surfaces, especially Mercury.

Subscribe to Dave Rothery's posts

 

"There has been a magnitude 6.3 earthquake to the north of Rome, but no news yet of casualties," says the BBC World Service radio news at 03:30 as I drive to Luton airport for a flight to Amsterdam. By the time I am in a Dutch taxi heading for my meeting at the European Space Agency my phone is ringing demanding a blog.

Earthquakes in Italy are not unusual. The whole region is riddled with faults as a result of the tectonic collision between Africa and Europe.

Today's quake at 01:32 GMT was moderately large but more significantly shallow - its depth is preliminarily estimated at only 10 km - so the shaking that it caused at the surface was large. I see from the news that 27 are confirmed dead, and I expect the death toll will rise.

Italian colleagues who arrived today from Rome and Padova for the same meeting as me felt the quake for themselves. My colleague from Rome was already awake, and according to him his house shook for 20 seconds. His wife was still in bed, but was awoken.
Here's a map of the location with the intensity of ground shaking.

Thousands of homes have been damaged. I wait to learn how many schools have collapsed, which is a common cause of tragedy because classrooms have large and often inadequately supported roofs. Fortunately this time the quake struck at night while the schools were empty.

About the author

Dave Rothery is a volcanologist and planetary scientist at the Open University. His current research includes studying volcanic eruptions on the Earth and characterising planetary surfaces, especially Mercury.

Subscribe to Dave Rothery's posts

 

I'm not a particle physicist, and for many years it has seemed to me that chasing after the ever more complex and abstruse families of fundamental particles was likely to be a never-ending struggle (perhaps I ought to refresh myself by studying the OU's modestly titled How the Universe Works that deals with fundamental particles and cosmology). However, if the LHC is able to create the so-called Higgs boson (the particle that imparts mass to matter) then that will be a tremendous step forward. On the other hand, if it does not find it, then decades of physics will need to be re-thought, and that will be a good thing too. Only by finding out the truth can science advance.

Don't hold your breath. I'd be suprised if any results are available soon. In the meantime, enjoy the BBC's Big Bang Day (the link leads you to where various rather surprising people comment (very well) on why they think this is important), and also the Hadron Rap!

About the author

Dave Rothery is a volcanologist and planetary scientist at the Open University. His current research includes studying volcanic eruptions on the Earth and characterising planetary surfaces, especially Mercury.

Subscribe to Dave Rothery's posts

 

Earthquakes on 12 May 2008.
[Map courtesy of United States Geological Survey]

After seeking out some other basic information on this event, I wrote some quotes for the British media, disseminated by the excellent Science Media Centre. I explained how the quake had been both large and relatively shallow (which probably accounted for the violence of the ground motion and the extent of the damage) and explained that the quake was a consequence India's plate tectonic collision with Asia, which is squeezing Tibet eastwards over the Sichuan Basin. On the next day, I was pleased to find that some of my material had been used by The Times. 'So, Tibet fights back' posted one wag in the on-line comments section.

That made me smile, but  the earthquake was, of course, a terrible tragedy. The official death toll has now exceeded 65,000, making it a close rival to the cyclone that recently hit the Irrawaddy delta in Burma. Fortunately, the Chinese rescue and relief effort seems a good deal more effective than what the Burmese government has managed to do, even though hampered by contunuig aftershocks - smaller than the initial quake, but big enough to collapse already-damaged buildings.

Today's map shows yet another in a the long series of aftershocks in the same region.

Earthquakes on 27 May 2008.
[Map courtesy of United States Geological Survey]

What really depresses me though is the disproportionate loss of life among school children. This is such a common story in many parts of the world; schools are built with inadequate resilience to earthquake shaking, not through ignorance but through corruption. I discussed this in my book Teach Yourself  Volcanoes, Earthquakes and Tsunamis, which forms the basis of the Open University's Volcanoes, Earthquakes and Tsunamis short course:

School buildings have often proved unstable in earthquakes. They are built at the public expense, usually as a result of competitive tendering with the construction firm that offered the cheapest deal being given the contract. Without conscientious enforcement of seismic building codes tragedy can ensue, as at San Giuliana di Puglia in 2002 where poor-quality masonry walls and a heavy reinforced concrete roof contributed to the collapse of the school. Following this event, the Italian government ordered an evaluation of the seismic vulnerability of all public buildings, such as schools and hospitals. Similar lessons were learned in Venezuela when two schools, built in contravention of the local seismic building code, collapsed as a result of a M7.0 earthquake on 9 July 1997 killing 46 students. In Algeria a M6.8 quake on 21 May 2003 left 122 schools in need of rebuilding. School-house tragedy was avoided in this case because the quake happened after the end of the school day, though 2287 other people died. However a M6.4 earthquake in eastern Turkey on 1 May 2003 brought down the roof of a school dormitory, killing many children as they slept. A subsequent survey found that none of the local schools accorded with the 1998 Turkish Seismic Code, and the blame for this was placed on lack of resources to supervise building works, and on poorly-trained architects and engineers. A similar story is likely to emerge concerning the collapse of school buildings during the Kashmir earthquake of 2005.

The same lessons keep being learned, and then ignored. In the next edition, I can foresee that I'll be adding in a damning comment about Chinese flouting of building codes.

Take it further

Volcanoes, earthquakes and tsunamis

Teach Yourself Volcanoes, Earthquakes and Tsunamis by David Rothery
published by Hodder Education

About the author

Dave Rothery is a volcanologist and planetary scientist at the Open University. His current research includes studying volcanic eruptions on the Earth and characterising planetary surfaces, especially Mercury.

Subscribe to Dave Rothery's posts

 

I didn't get much sleep on Sunday night. NASA's Phoenix lander was due to land in the arctic wastes (68 degrees N) of Mars, and what with staying up late to watch podcasts and then waking up in the wee small hours to see the first images I was rather bleary-eyed for Bank Holiday Monday. As a geologist on the Beagle2 project I've experienced the pain when your lander heads down towards the surface and is never heard from again, so I was immensely pleased that Phoenix made it.

Phoenix suspended by its paracute, as it floated down towards the martian surface.
Image courtesy of NASA/JPL/University of Arizona)

Phoenix landed in a flat wasteland of 'patterned ground', traversed by inresecting grooves marking out a polygonal pattern that is well-known on Earth where there is ice at a shallow depth below the surface. One of the main tasks of  Phoenix will be to use its 8 ft long robotic arm to dig for this ice so it can be analysed to look for traces of life.

A colour view from Phoenix, all the way to the horizon. The patterning of the ground is obvious.
[Photo courtesy of NASA/JPL-Caltech/University of Arizona)

About the author

Dave Rothery is a volcanologist and planetary scientist at the Open University. His current research includes studying volcanic eruptions on the Earth and characterising planetary surfaces, especially Mercury.

Subscribe to Dave Rothery's posts