Sismordia - Seismology at Concordia

Two conversations of interest to polar seismology...

2009-04-26T08:06:00.001Z

During the afternoon of the last day of the European Geophysical Union meeting in Vienna, I had two very interesting conversations, one with a member of the IRIS-PASSCAL polar team, and the other with a friendly glaciologist I knew from Concordia.

The polar team at IRIS-PASSCAL have done all the development and part of the deployment of the American experiments in Antarctica for the International Polar Year. Their station designs are first rate, and their success rate for last season makes me envious (23 out of 24 stations deployed worked perfectly, sending state of health data over satellite links). We exchanged design details, and did some troubleshooting for some of the instruments at Concordia. One very interesting, motivating and helpful conversation!

Just afterwards, I bumped into a glaciologist from LGGE in Grenoble, who I met for the first time at Concordia, two years ago. We got talking about the ice structure around Dome C (quite a lot is known thanks to the EPICA ice core), and how it may influence the seismic data we record up there. He gave me a good overview of how compaction works, and suggested some people who might know more about the mechanical properties of the various ice layers, their density and possibly their wavespeeds. This might help us figure out how to correct for the ice-signal on or recorded seismograms.

Just an example of how putting a bunch of scientists and technical people in a conference center together can turn out to be hugely profitable, often in unpredictable ways.

Earth's core less anisotropic than we thought?

2009-04-20T08:52:00.001Z

One of the reasons for installing seismic stations in Antarctica is to improve our knowledge of the Earth's inner core. It would seem - from the data currently available - that seismic waves that propagate through the inner core parallel to the Earth's rotation axis (polar paths) are faster than those that propagate perpendicular to the Earth's rotation axis (equatorial paths). This speed difference implies the inner core is anisotropic, with a N-S fast axis.

This conclusion is based on a large number of equatorial paths, and only a small number of polar paths, most of which come from earthquakes in one particular region (South Sandwich islands) recorded in Alaska. Data from new stations in Antarctica are expected to increase the number of polar paths available, and improve our understanding of the inner core.

At EGU this morning, I heard one of the first talks on the inner core that actually uses data from newly deployed Antarctic stations:

D. Leykam, H. Tkalčić, and A.M. Reading : Core structure reexamined using new teleseismic data recorded in Antarctica: Evidence for, at most, weak cylindrical seismic anisotropy in the inner core (Abstract).

The data are from the SSCUA stations, deployed near Mawson station. The PKP(bc-df) measurements made on these data are all between 0 and 2 seconds, and imply that if there is N-S oriented anisotropy in the inner core, this anisotropy must be weak (and specifically, much weaker than implied by the South Sandwich data). Indeed, the weak anisotropy hypothesis seems to be consistent with all data except those from South Sandwich.

Should we therefore dismiss anisotropy in the inner core? Possibly. But before doing so we need more data and measurements from other Antarctic stations (the CASE-IPY and Concordia stations will contribute some of these data), and we need to understand why the PKP(bc-df) measurements from South Sandwich events are so large.

European Geophysical Union meeting

2009-04-19T20:14:00.001Z

Just a quick note from Vienna, where I'm presenting some research that has absolutely nothing to do with Antarctica (yes, there is indeed life outside the frozen continent).

Are there any other geobloggers here at EGU?

Back in from the cold

2009-01-19T07:08:00.001Z

Hello everyone,

I hope you've not been too worried by the lack of summer campaign
posts this year. The mission has been pretty tough going, and I've
not had much time to post.

I have just got back to civilization again, and plan to rest for the
remainder of this week before getting back to the university grindstone.

Thank you to those who have commented on the few posts I did write,
or who have contacted me up there.

PS: In the photo, I'm atop a 45 meter tower, with Concordia base in
the background. The sight from up there is stunning!

Merry Christmas everyone!

2008-12-25T20:33:00.002Z

Wishing you all a very merry Christmas, hopefully as merry as ours
was...

The evening started with champagne and strawberry wine apéritif, then went on to a gargantuan dinner (carpaccio, snails, salmon tagliatelle, poire wiliam sorbet, capriolo with potato gratin, nougat mousse) and an evening of dancing.

Maybe the dinner, maybe the alcohol, maybe the dancing, I'm not sure what it was, but I ended up sleeping until well into the afternoon the next day, completely missing another gargantuan meal for Christmas lunch !!

This is going to be a short post, as tomorrow is our first field visit to the CASE stations (no such thing as Boxing Day out here...). We leave in the morning, and shall stay out the whole day. We have finished preparations, and are all getting an early night to be fit and ready for tomorrow.

Merry Christmas everyone!

Gearing up for Christmas...

2008-12-23T20:52:00.001Z

Two days to Christmas, and the nose is still firmly to the grindstone. It looks like we might finally be centering in on the problem with the datalogger, and that it might be caused by a faulty component. A replacement is being sent to us via another person from my lab, who is leaving France to come here on December 30th. We are keeping our fingers crossed that they will both arrive ok.

Christmas seems to be a big affair out here. We have two trees covered with tinsel in the dining room (trees?? on the Antarctic plateau?), and plenty of foil-based decorations strewn on the walls and dropping from the ceiling, accumulating static electricity and zapping every other person than walks by. Someone has decided that Christmas music should be played during meals... personally, I think that is going a bit too far...

We are going to have a special Christmas dinner tomorrow night. We are supposed to stop work at 4pm, in order to get ourselves washed and prettified for the evening (the cooks have requested that we be smartly dressed, which given the effort they are putting into making the dinner is only fair). We start with an apéritif at 7:30 (we have been strongly encouraged to attend - maybe that means they will break out the last of the Champagne ??), then go on to dinner and a Christmas Eve party.

I'm charging my camera batteries this evening so as to be able to send you pictures of the event. For now you will have to make do with this picture of me walking back from the seismic shelter (the yellow blob in the background). The sky is blue and featureless, the snow is white, featureless and flat, and there is a lot of both. That's Dome C for you: nothing as far as the eye can see... spectacular!

A data logger with a problem

2008-12-22T20:14:00.002Z

You may recall from my descriptions of the seismic observatory at Concordia in last year's blog posts, that we have two seismometers down there, each connected to a different data logger. Both have worked reasonably well over the course of 2008, considering the conditions they run in (those of you who have kept up to date with http://case.u-strasbg.fr know this already).

However, on December 10th, for no apparent reason, one of the data loggers (a Q4120) stopped working. We have been trying to deal with the problem remotely (i.e. sitting warmly in our lab at the base, and working over a wireless connection to the seismology shelter that is 1km away) since we got here on the 18th, but have had little success. Last Saturday, the machine decided it no longer wanted to talk to us over the network, so we strolled over to the shelter (err... trudged would be more appropriate in my case, I'm not yet fully acclimatized to the altitude) to try to fix the problem. To no avail.

It was obvious that we would not be able to fix the recording system at the shelter, and that it needed to be brought back to the lab. However, carrying it over that distance by hand was not a viable proposition, so we simply prepared it for transport and left it there, knowing we would have to come back with some transport system to pick it up.

The route to the seismic shelter goes past several other scientific shelters, including one in which the air is continually filtered and its composition measured. Because of this particular experiment, we are not permitted to take a vehicle along the route, and so (in all but exceptional circumstances) have to carry equipment to and from our shelter on foot, either in backpacks or on sledges.

We went back to the shelter this morning, in order to pick up the faulty data logger. The photo above was taken this morning, and shows the Q4120 being pulled along by a volunteer Sherpa, a glaciologist by the name of Bruno who is much better acclimatized than either my colleague Maxime or myself. The data logger is now sitting on a table our the lab at the base, with all its innards visible, and cables strung across the room to various other bits of equipment. We have made some small progress to getting it working again, thanks mainly to valuable suggestions from our colleagues in Europe and the the manufacturer himself, but we're not finished yet!

PS: I must still have been over-tired when writing yesterday's post. Of course the picture in that post is not of Mount Ross (which is on Kerguelen Island in the sub-Antarctic) but of Mount Erebus, on Ross Island in Antarctica.

Sunday insomnia

2008-12-21T20:22:00.001Z

Days of the week swiftly loose their meaning when you are cut off from the rest of the world. Just as we try to keep a normal 24 hour daily schedule, we also try to keep a normal weekly schedule. Sundays are set up to be a day of rest: breakfast is from 8 to 10 am instead of from 7 to 8 am on weekdays, the evening meal is a buffet of the previous week's left-overs to give the cooks a half-day off duty.

It is very hard to stop working during a summer campaign, as there is a great deal to do in the limited time we have up here. It is common for most people to work 7 days a week, with the only change being a slightly later start on Sundays. Although this rhythm cannot be sustained eternally, most of us try to keep it up for the 4 to 6 weeks of our campaigns.

However, if you add to this situation fatigue caused by insufficient adaptation to altitude, by sickness, or simply by lack of sleep, then you can end up in trouble, as I found out to my expense this morning.

After lying awake from 2 to 5 AM unable to get back to sleep, I thought I would get up and start my day. I've not had a decent night's sleep since arriving here. This morning, instead of doing something harmless - like doing some TaiChi or Yoga, or simply browsing the comic book collection in the common room - I decided that I should get started on some of the work that had been buzzing around my brain all those hours.

On a Sunday morning... At 5 AM... After fewer than 3 hours sleep...

Well, the obvious happened, and I messed up. I was overly confident in my abilities, did not take enough care to check all the premises of the line of thought I was pursuing, and eventually made a big mistake. It was not an extremely serious mistake, and it was corrected easily enough later in the day, but it did lead to the loss of about 10 hours of secondary data from the only working seismometer at the CCD observatory. Not the end of the world, granted, but I should have known better!

Lesson to be learned: lack of oxygen, lack of sleep and excess confidence are a disastrous combination! I shall have to work hard on the third element in the next few days, at least until I develop a regular and restorative sleeping pattern.

PS: The image is of Mount Ross, taken from the airport at McMurdo.

First full day at work

2008-12-19T20:55:00.001Z

We all know it takes a while to get used to the conditions up here at Dome C, so we gave ourselves a good... err... 36 hours rest and planning time before getting down to the nitty-gritty stuff.

Yesterday we spent the day reviewing the status of both the CCD observatory station and the autonomous CASE field stations, and digging up lots of information that somehow never made it to Strasbourg. We had a number of surprises, some good, some less good, but by the end of the day we had an adequate mental picture of the current status and the work ahead.

Today we have worked on improving the radio connection to the CASE stations, and updating the firmware on the Q330 acquisition system at the observatory station. I shall spare you the technical details (they are being written up for our collaborators back home) and just say we should see the results of these changes in the next day or so.

The snow and ice around Concordia are flat for as far as the eye can see, which makes for poor photographic opportunities. In order to spice things up a bit, I've posted above a picture I took on the flight from Christchurch to McMurdo, in which you can see a stunning mountain range framed by the C-130's window.

What surprised me was the sharpness of the features, with the mountain crests standing out like knife edges. In some places we could see huge glaciers snaking their way down from the crests, with sets of curved crevasses showing the direction of flow. The excellent visibility made for a superb show, which went a long way to easing the boredom of the noisy 7 1/2 hour flight!!

Jet lag and then some !

2008-12-18T08:05:00.003Z

Greetings from Concordia!!

We arrived safe and sound last night, in the aircraft shown above (a very comfortable DC3). The journey to get here has been long and tiring (3.5 days of flying), with a lot of waiting around between planes and little sleep, but it has been otherwise uneventful. There are a great many people here this year who were also here last year, which made for a good reunion.

We are now happily installed at Dome C. It will take a few days to get over the jet lag (we've changed time-zones so often in the past four days we're totally confused) and to get used to the altitude (sleeping is difficult, any physical activity makes my head spin right now) and the 24 hour sunlight.

Dome C hasn't changed much from last year: it's still as flat and white as ever! Little has changed at Concordia base itself either, except that women now have a proper toilet they can use, and no longer have to rely on buckets: hooray for civilization !!

I should go start my day now. A quiet one as far as work goes, as it is important not do overdo things for the first few days. My task for the day: figure out where everything has moved to during the winter, and what the status of all our instruments is.

Stopover in Hong Kong

2008-12-15T08:18:00.006Z

Having been traveling now for a little over 24 hours, we have now completed the second of the six legs of the trip that will take us to Concordia. There are 7 of us on this trip, though only 2 from Strasbourg. We met up at the airport in Paris, and shall travel as a group all the way to Concordia.

The voyage has been good so far, with a comfortable aircraft and good weather for our morning walkabout in Hong Kong today. This year's impressions of Hong Kong reflect those I had a year ago: a very disturbing place by virtue of the juxtaposition of poverty and squalor with luxury and modernity.

Three of us have come back to the airport early, leaving the others to explore more widely. In the lounge we have been given access to thanks to IPEV, we are enjoying comfortable armchairs, internet, food, and even the access to showers. We are stocking up on comfort for the next two legs of the trip: another long haul flight to Auckland, then on to Christchurch.

Next update from New Zealand!

30kg for six weeks

2008-12-13T13:05:00.008Z

Less than one day left, and I have just finished packing my bags for 6 weeks in Antarctica. All the cold weather gear is supplied by IPEV (the French polar institute) and should be waiting for me in Christchurch NZ. I go through Paris, Hong Kong and Auckland to Christchurch, then fly to McMurdo, and then on to Concordia, so there will be no seasick posts from the Astrolabe this year - yay! The rest of the stuff I am taking is shown below:

And here is what it all packs down to:

Not bad, eh? It all weighs in at under 30kg (of which 9kg are scientific material we shall need in the first two weeks at Concordia): so whoever said girls cannot travel light should think again.

To be perfectly honest, I'm not quite finished packing: I am still missing the warm socks I got during last year's trip and my pocket knife, both of which are probably in my office. At least I hope they are, for I don't much fancy leaving without them!

PS: Found the socks. Still no knife...

PPS: Phew! Finally found the knife! It was at home after all...

Sunday Seismometer digest

2008-12-12T20:23:00.003Z

Just a quick post to announce the appearance of the Sunday seismometer digest, a pdf version of the Sunday Seismometer series.

Heads up

2008-12-12T14:25:00.006Z

Hello everyone!

Yes, I'm still here... although you would be pardoned for thinking
I'd dropped off the planet somewhere... I can't believe it has been
three months since I last posted anything!

Just a quick heads up to let you know I'm off to Antarctica again,
and leaving this Sunday. This year's trip won't be quite the
adventure it was last year, as I know what I'm getting into this time
round! I shall keep you posted...

In the meantime, in keeping with the current Wordle craze, here is
one of the projects that has kept me from blogging over the past
three months (my latest contribution to the technical literature in
seismology).

Any guesses on the topic of this paper??

Sunday Seismometer #12

2008-09-07T11:07:00.000Z

Rocard (1958)

From last week's prototype, let's move on to a more useful set of instruments, designed specifically to detect nuclear explosions in the context of Comprehensive Test Ban Treaty monitoring.

They are named after Professor Yves Rocard, the physicist who started to develop detection seismology in France in the 1960s, and who founded the division of the French Atomic Energy Commission (CEA) that is in charge of geophysical studies and activities associated with monitoring and the environment (LDG).

The Rocard is a classical electromagnetic seismometer, with a 1s natural period and electronic amplification. Rocard instruments were in operation at the Welschbruch station not far from Strasbourg.

Sunday Seismometer #11

2008-08-31T01:00:00.000Z

Peterschmitt (1950)

Continuing our mini-series on electromagnetic seismometers (see the Galitzine and Press-Ewing posts), here is a seismometer you are unlikely to see anywhere else. The Peterschmitt was designed and built in Strasbourg in 1950, where it was in use until 1975.

This admittedly ugly looking beast is a prototype classical electromagnetic seismometer (you can see its coils on the near side, very similar to those on the Galitzine instrument) combined with a galvanometer. It has a natural period of 1s, and its amplification is provided by a resistance bridge. The most interesting feature of this instrument is its original inbuilt calibration system.

The design of this instrument is attributed to Elie Peterschmitt, who was recruited by Strasbourg in 1937, took charge of the Strasbourg historical seismological station as well as the stations of Besançon and Bagnères de Bigorre, and later helped develop the European-Mediterranean Seismological Center (EMSC).

On batteries and aeroplanes

2008-08-28T06:47:00.001Z

Earlier this week I wrote about space-crafts with thermostatic skins, implying this kind of technology could prove to be useful for temperature control in low-power autonomous seismic stations in the Antarctic. Here is another technological achievement that may be of some use.

The BBC reported over the weekend that a UK-built solar-powered and unmanned plane, the Zephyr-6, had stayed aloft for more than three days, running though the night on batteries it had recharged during the day.

The Zephyr weighs 30kg and flies at an altitude of over 60,000 feet. Its power derives from solar power generated by paper-thin amorphous silicon solar arrays glued over the aircraft's wings. This power is stored in a new type of lithium-sulphur battery.

A lot of effort has gone into power storage and light-weighting the systems. Lithium sulphur is more than double the energy density of the best alternative technology which is lithium polymer batteries. Mr Kelleher, Qinetiq (UK defense and research firm)

These batteries are made by the Sion Corporation:

The custom built Li-S battery pack was designed and assembled by SION Power and consisted of 576 cells built into a battery configuration of 12 cells in series and 48 in parallel. The battery utilized SION’s unique, high specific energy Li-S cells (350 Wh/kg). At ~10 kg, the Li-S battery pack was carefully engineered to minimize total pack weight.
In addition to providing flight power, the battery pack supplied power to a special
internal pack heating system to maintain the batteries at 0oC throughout the cold nights. Sion press release.

The Sion battery data-sheet is available here: sion_product_spec.pdf.

The usefulness of this kind of battery for our stations in Antarctica would depend on its adaptability to long-duration low-power applications, and on its performance at low temperatures. Yet another thing to look into this fall!

Funky thermostat film for spacecrafts

2008-08-26T07:03:00.001Z

You may remember that keeping our antarctic instrumentation at a constant and not-too low operating temperatures is a major challenge. Some time ago I posted about the heating / insulation strategy we implemented in last year's prototype stations. I'm planning to write a short piece on how that strategy worked out in the next couple of weeks.

The subject of today's post is an innovation in thermostat technology that has just been presented at the 236th American Chemical Society' National Meeting in Philadelphia, and that was brought to my attention by the BBC News website.

Spacecraft have a serious problem with temperature regulation, as they operate in blazing sunlight, in the cold shadow of the Earth, or in even more extreme conditions closer or further away from the Sun. As operating conditions vary, so does the amount of heat generated by the onboard electronics.

For large spacecraft, [temperature control] is done with mechanical louvers—basically glorified window blinds—that open and close to allow in or reflect heat. But as satellites get smaller, these systems get too heavy and bulky. - Prasanna Chandrasekhar of Ashwin-Ushas, an American tehnology firm

Chadrasekhar and his team have developed a "skin" that can be placed on a spacecraft to actively control the amount of heat that it radiate by controlling its emissivity.

Polymers in the skin change their emissivity when electricity is applied to them, retaining heat in cold conditions and radiating it away in hot ones. That leads to an active temperature control that can be maintained with very little power.

The skin is just a few tenths of a millimetre thick, has been tested to withstand the rigours of the vacuum and temperature extremes of space, and can be bent and cut to fit craft of any shape without losing its properties.

Would such material be useful in Antarctic conditions, which are much less extreme than those experienced in outer space ? The answer will depend on the amount of energy required to power the emissivity-regulating skin.

Energy is a serious problem in Antarctica given the duration of the winter night. Should the new skin system be as low power and low-cost as announced at the conference, then its use in Antarctica may well be possible. We shall be keeping a lookout for updates on this product!

Sunday Seismometer #10

2008-08-23T23:25:00.001Z

Press-Ewing (1953)

Some 40 years after the Galitzine electromagnetic innovation, the same principles of operation are put to work in the Ewing-Press seismograph, built at the Lamont Geological Observatory of Columbia (now the Lamont-Doherty Earth Observatory) by Maurice Ewing and Frank Press.

In the photo below you can see the vertical Press-Ewing instrument on display at the Strasbourg Seismological Museum. It was in use in Strasbourg from 1963 to 1975.

It is an electromagnetic seismograph, coupled with a galvanometer, and has a natural period that can be selected and fixed up to 30s. Recording was optical, on photographic paper. The glass ball you can see on the near side of the instrument reduces the effect of variations in atmospheric pressure on the seismograph recordings, using the Archimedes principle.

This seismograph and its horizontal counterparts are very well adapted for the recording of surface waves. In 1957-58, Press-Ewing instruments were deployed in 125 locations around the globe to establish the World-Wide Standardized Seismograph Network, the first global earthquake monitoring system.

Sunday seismometer #9

2008-08-17T01:00:00.002Z

Galitzine (1910)

All the seismographs we have discussed up to now (Reuber-Paschwitz, Reuber-Ehlert, Wiechert horizontal and vertical, Mainka, Vicentini, 19-Ton, Mintrop) have been mechanical, with either mechanical or optical recording. Today's instruments, built by Galitzine in St Petersburg (Russia) in 1910, are the first examples of electromagnetic seismometers.

In the above photograph of the vertical Galitzine (mass 10 kg, period 24 s) you can see the new element of this seismometer: the coil placed at the end of the pendulum's rod. This coil oscillates in a magnetic field, and creates an electric induction current which can be measured using a galvanometer.

A copper plate, fixed on the same rod as the coil, oscillates in the field of a second magnet and provides damping via a Foucault current.

The horizontal instrument (above, mass 7 kg, period 12 s) works using the same principle. The object placed in front of the seismometer is a galvanometer that is equipped with a mobile frame and a mirror for optical recording.

The Galitzine instruments amplify Earth motion in two successive stages: an electromagnetic amplification (the galvanometer mirror rotates more than the pendulum oscillates) followed by the optical amplification caused by the distance between the galvanometer mirror and the recording medium.

Sunday seismometer #8

2008-08-10T01:00:00.001Z

Mintrop (built sometime after 1910)

From the very large (last week's 19-ton seismograph) to the relatively small : the Mintrop portable horizontal seismograph.

The Mintrop is an odd instrument, that measures horizontal motion using a damped inverted pendulum with a horizontal rotation axis. Its relatively small mass is coupled with a vertically oscillating mirror and an optical recording system.

Given the delicate nature of the recording system, the Mintrop must have been rather difficult to install. It is considered to be one of the first portable field instruments, and was used for early prospection studies by German oil companies.

Quake Catcher Network

2008-08-06T08:50:00.003Z

Thanks to Julian over at Harmonic Tremors whose post about last Tuesday's M5.4 earthquake brought the Quake-Catcher Network to my attention again (I originally read about it on Geology News and Highly Allochthonous earlier this year, but did not have time to blog about it).

The Quake-Catcher Network is a collaborative initiative run jointly by Stanford and UC Riverside that aims to use acceleration detectors present in most modern laptops to form a low-cost strong motion seismic network.

Laptop users can download a client program that sits and monitors the motion of their laptops, sending information to the Network when any strong signals are detected. If strong signals are detected by many nearby laptops at the same time, the Network knows an earthquake is happening.

Laptops continuously move with the people who use them. So how does the Quake Catcher Network know where the laptop is? Users can give precise locations (using a GoogleMaps widget) of where they use their laptops most often. To choose between these locations, and also to deal approximately with undefined locations, the Network uses the laptop's current IP address. Nifty!!

As correct time is essential for earthquake location (just ask any observational seismologist or seismic network manager), the Network also checks the laptop's clock to make sure it is on time.

I have just signed up as a Quake-Catcher laptop client. The sign up procedure is completely painless (at least it was on my mac). Quake-Catcher uses a system called BOINC to interact with your computer. This is the same system used by other distributed computing projects you may have heard about, such as SETI@home or LHC@home.

Quake-Catcher aims to become a global strong-motion network, but it can only do so with your help. The more laptops connect to the system, the better. The accuracy of Quake-Catcher detections depends on the number of users located in any given region, so if you want your contribution to Quake-Catcher to be really useful, you should urge your friends, families and colleagues to sign up.

Another Antarctic Earthquake

2008-08-04T08:00:00.000Z

In November of last year I wrote about an unusually large earthquake (M 5.8) that had occurred close to Casey Station in Antarctica. Earthquakes of this magnitude are rare in East Antarctica, except, it seems, in the Casey region...

Indeed, on July 23rd of this year, another large earthquake (M 5.3) occurred in the same region. The following image is from the USGS and shows the position of this event as an orange star.

This event was recorded on seismometers all over Antarctica. As examples, I have plotted the recordings of vertical ground velocity for this earthquake at stations CASY (Casey), MAW (Mawson) and PSP02 (a POLENET temporary station near South Pole).

The numbers under the station names on the above plot are distances in km from the earthquake. As you can see, the earthquake was well recorded even at distances over 2000 km.

We often say that the Antarctic plateau is virtually a-seismic, meaning there are few if any earthquakes. As you can see for this Casey event, it would be hard to miss an earthquake larger than M5 virtually anywhere on the continent. Smaller events may still be missed, however, and we do not have enough seismic stations in Antarctica (yet) to be sure that they do not occur.

Sunday seismometer #7

2008-08-03T01:00:00.002Z

Great Pendulum or "19-Tons"

In the last Sunday seismometer post on the Vicentini seismograph, we mentioned that in order for a seismograph to overcome the friction caused by a purely mechanical recording system, it needs a large mass.

The Vicentini instruments actually have the smallest masses (100 kg for the horizontal and 50 kg for the vertical) of the mechanically recorded seismographs we have described so far. The Mainka instrument has a 450 kg mass, the Wiechert horizontal instrument has a 1-ton (1000 kg) mass, and the Wiechert vertical instrument has a mass of 1.2 tons.

The largest mass of all the seismometers in the Strasbourg museum is that of the Great Pendulum: an impressive 19 tons (that is 19 000 kg)!

Its construction was started before the First World War (1910), when the Strasbourg Observatory was part of Germany. The idea was to build an instrument that would be similar to one installed in Göttingen, a 17-Ton seismograph. After the war, Strasbourg became French, and it was the French director of the Observatory, Edmond Rothé, who completed the construction of the Great Pendulum in 1925.

The mass itself is essentially made up of scrap metal from the War, including 12 tons of axles from military trucks and 2 tons of weapon parts.

The 19-Ton has a natural period of 2 seconds, and records both the horizontal directions of motion, like the Wiechert horizontal instrument. Also like the Wiechert, its motion is damped by air pistons.

The smoked paper recording system was abandoned in 1970 in favor of galvanometric recording. In 1987 the recording system was changed once again to digital recording using displacement detectors.

The 19-Ton instrument is still in working order today, and is a great favorite with visitors to the Strasbourg Seismology Museum.

Summer vacation is over

2008-08-02T14:08:00.000Z

With the end of July came the end of my much needed summer vacation. I took three weeks off last month in order to rest, recoup and recharge after this year's travels (7 weeks in Antarctica, and 4 weeks in the Sub-Antarctic islands).

I spent the time mostly sleeping, lazing on the beach, and swimming. This solar recharge should help me find the energy for the coming academic year: five research projects including the second year of CASE-IPY, teaching, and observatory work.

Here is a GoogleEarth image of my summer hiding spot:

While I was still on vacation, Kim posted about a great initiative to federate and publish geological maps from all over the world. The initiative is called OneGeology, and a new version of its portal will officially be launched next week. The current portal is already very easy to use. The image below is a larger scale GoogleEarth image of my summer hiding spot, in which the geologic units from the BRGM 1:1.5M geological map of Europe have been imported from OneGeology.