How a seismometer works

Image from Wikimedia Commons. An old seismometer from Lick Observatory.

Earthquakes are a release of energy due to rock failing from the amount of stress and strain that are placed on it. This energy is released as a series of waves, or vibratory motion as the energy dissipates away from the source of the quake. Simplifying it a bit, there are S-waves, P-waves, Love Waves, and Rayleigh waves. Together, along with all the reflections and refractions that these waves can experience (due to what sort of material the wave encounters on its path) they generate a signal that can be measured. By measuring the signal and performing in depth analysis on it, geophysicists come up with ideas and theories about the specifics of what caused the earthquake.

One of the earliest seismic detection devices consisted of an ornate urn with copper balls that would fall off of the urn into the mouth of an awaiting toad (part of the ornate structure). Crude by today’s standard, but pretty brilliant considering that it was 132 AD. It provided a rough direction in which the quake originated.
Later designs incorporated a suspended mass that etched out a path on a lamp black coated drum with a stylus.(1) (lamp black – the soot from an oil lamp, almost pure carbon) It didn’t take long for paper and ink to take over the recording task.
With the advent of electronics, eventually seismographs consisted of a mass suspended on a pendulum structure, and a coil of wire moving in a magnetic field. The early ones used mechanical dampers in order to slow the movement if the mass. Failing to do so would result in the seismograph oscillating far beyond the time period of the quake and yield faulty data. (Remember, the mass is on a pendulum, and pendulums by their nature oscillate or swing back and forth.)

Enter the the torsion seismometer.

In 1925, Harry O. Wood and J.A. Anderson published a seismograph design that eliminated many of the problems with the pendulum siesmos.(2) It consisted of a wire under tension and a mass attached to one side of it. As the wave passed, the mass would swing back and forth along an arc beside the wire. In order to provide damping, magnets would counteract the movement and bleed off momentum from the moving mass. This design became the predominant tool for seismographs world wide. Highly sensitive, it had minimal resistance due to mechanical damping.

Years later, other designs came along, but in order to keep the seismological record consistent, the output of the newer gear had to be adjusted to match the sort of response that a Wood-Anderson seismograph would provide.

But that is only part of the problem.

How a quake is measured really depends on the structure of the crust, the type of gear measuring it, what size it was, and even what agency is doing the measuring. Here are a few of the scales listed in “Magnitude Scale and Quantification of Earthquakes” Hiroo Kanamori, 1983, Tectonophysics, 93.

ML Local magnitude, Richter (1935)
Ms Surface-wave magnitude, Gutenberg (1945a)
mB Body-wave magnitude, Gutenberg (1945b), Gutenberg and Richter (1956)
mb Short-period body-wave magnitude reported in “Earthquake Data Reports” and “Bulletin of International Seismological Center”
mbLg Lg-wave magnitude, e.g., Nuttli (1973)
MGR Magnitude used in Gutenberg and Richter (1954)
MR Magnitude used in Richter (1958)
MD Magnitude used in Duda (1965)
Mz Surface-wave magnitude determined from the vertical-component seismograms (e.g., Earthquake Data Reports)
Mv Surface-wave magnitude defined by Vanek et a!. (1962)
MJMA Magnitude scale used by the Japan Meteorological Agency
MM Moment magnitude by Brune and Engen (1969)
Mw Kanamori (1977)
ME Purcaru and Berckhemer (1978)
Mi Tsunami magnitude regressed against Mw ‘ Abe (1979)
Mc Coda (or duration magnitude), e.g., Bisztricsany (1959), Tsumura (1967), Real and Teng (1973)
MI Magnitude determined from intensity data and macro-seismic data, e.g., Nuttli and Zollweg (1974),
Nuttli et a!., (1979), Utsu (1979).
MK Kawasumi (1951).

A simple drawing for “Do It Yourself” building of a seismometer.

As you can see, there a lot of different scales. The ones that we see most often are Mw, M, and ML. mblg is used by IGN quite a bit. For the most part, they track along with each other in the mid scale, but at the low or high end they tend to diverge. Me was not mentioned in the list, but it figures prominently in trying to convert from one scale to the other… it’s the energy magnitude and is directly related to “A” which is the energy release in several of the formulas.
I’ll not bore you with the nitty gritty details about getting from one scale into another. I have been fighting this task for quite some time and have yet to find a reliable, reproducible method listed anywhere.

How I deal with energy release is to find a plot or published data by the agency that has the energy release and the magnitude listed, and then calibrating a conversion curve that matches what that agency uses. It’s a kludge, but it works and is stable across many quake reports within that agency. That’s the method that I used to come up with my cumulative released energy plots, which is different than using a canned formula published on a website. At least what I produce matches whatever methods the agency has adopted and has incorporated their adjustments.
Remember that “A” value that I mentioned? That’s the total energy of the quake. When spread across the fault face (where the fracture actually occurred) that will determine what the quake magnitude value is. (however it gets measured).
Some scales use the total amplitude of the trace movement; some measure the coda (how long it lasts). It’s part art, part science, and part nuanced thinking by some brilliant researchers.

GEOLURKING

1) Popular Mechanics Aug 1946
2) http://www.data.scec.org/Module/s3inset3.html
3) http://www.gps.caltech.edu/uploads/File/People/kanamori/HKtect83b.pdf

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121 thoughts on “How a seismometer works

    • You could always hijack their PA-system and have it play some highly annoying song at >110 dB. I think that after five relentless days of this, even they would eventually capitulate:

    • In that “Do It Yourself” image, those horseshoe magnets are typically Magnetron magnets. Very strong. Quite handy for securing a persons arms and legs to a steel bulkhead and daring them to try and get out.

      For those of you who have never heard of a Magnetron, they work via “crossed fields.” A high voltage potential at 90° to a strong magnetic field, with a series of resonant cavities around a central chamber. When the trigger pulse comes in, the electrons are forced into the central chamber and corkscrew spiral out at a frequency determined by the intensities of the fields and the size of the chambers.

      Using in a lot of radars, and in microwave ovens. In fact, the microwave oven controls the amount of heat that is produced from the duty cycle of the trigger pulses… this is akin to the Pulse Width and Repetition rate used in a radar. About the only thing missing is an antenna, pin diode setup, and a receiver/signal processor.

      Radars and Microwave Ovens share a common ancestry… usually attributed to a melted candy bar in a researcher’s pocket.

      Microwave Cooking

      Raytheon’s discovery of microwave cooking in 1945 was initially an accident, but its development, like so many others, can be credited to Percy Spencer. A candy bar in Spencer’s pocket began to melt as he stood in front of a magnetron tube that had been switched on. Intrigued, he placed kernels of popcorn in front of the tube, and they too popped. He then conducted a similar experiment with a raw egg, which exploded when the inside yolk cooked faster than the outside of the egg. Scientists familiar with magnetrons knew the tubes generated heat at the same time they radiated the microwave energy that made radar possible. Spencer was the first, however, to discover that one could cook food using microwave radio signals.

      http://www.raytheon.com/ourcompany/history/leadership/

        • Oh I definitely have one. I have have Ramen in two minutes and can run it off of the generator if needed. Meat – no way, other than a hotdog or corndog. Veggies… only if you stop and stir them regularly. Even though the carousel rotates you get uneven heating if you don’t. Other than that, our microwave is mainly used for defrosting stuff.

          Handy tip for those who really need to destroy CD’s in bulk. Microwave. 5 seconds and it’s done. Do it in the open cuz it’s gonna stink the high heaven and may cause a fire… but the CDs will be unreadable.

          • They are also useful for home schmelting:

            Standard Disclaimer: If you do try this at home (I recommend that you dont) have a fire extinguisher of the correct type to hand, turn off at the mains before opening the door (using a long stick) also im not sure what he built the “surround” for his crucible with; so do yr research kids… the fire was the result of oxygen getting to the very hot “surround”. Fire requires heat, fuel and oxygen, he might have got away with it if he’d closed the door after removing the molten tin…

  1. Nice simple post, good post. It is a good idea have “regular posts on diiferent things” (from the “que”) we are so much interested in. Thank you Lurk
    *all quiet on mid-western Iceland front, small swarm in Krýsuvik, else rather quet..*

    • Ya don’t need to go to school.

      According to some obscure company that derives their name from the Goddess of Victory… “Just do it!”

      I picked up an old project, and have become… perplexed.

      Quite some time ago, I made a short one year plot of CO2 concentration (ppm) vs Latitude. There was an odd spike in the levels at the high latitudes. My original intent was to look at average CO2 levels vs average water temperature at those latitudes and peek at the effect that the CO2 solubility might have in relation to water temp as the year went by.

      That big arsed spike seemed to be coincidental with Icelandic eruptions… even though the timing wasn’t exact. Vagaries in when magma degases, or such could affect the timing, so no big deal. Obviously the volcanic signature was going to mess with my original plan.

      Well, I’ve gone back and put older data in… back to 2009. It seems that spike happens every year, and looks to originate at the pole.

      The fun part?

      I havn’t got a freekin’ clue why it does that.

      It might have something to do with the orbit of the satellites, it might not. If it were an orbital artifact, it should be related in time to the precession of the orbit, not the same time every flipping year.

      So.. that still leaves me with the question. Why? Why does the atmosphere’s CO2 seem to originate at the pole?

      At the worst case, I was expecting it to originate from major metropolitan and industrial latitudes. But the pole?

      • North pole too, right? Not south pole. Seems related to land mass or (gulp) population density… some kind of gyre maybe?

        • North Pole, that’s Danzig (Gdansk) innit? If it’s South Pole it’s Krakow. I know Poles are full of gas, but surely not that much?

      • Industrial air pollution from the developed world is carried on the dominant wind currents up to the arctic. After settling onto the tundra, snow and ice it is absorbed into the food chain. The people and creatures there have some of the highest concentrations of toxins in their bodies of anywhere on earth. Likewise if the CO2 is carried northwards on warm currents as it cools, the air mass descends hence during winter months there may well be higher levels of CO2 towards the poles.

        • Its such a very nice explanation, Diana. I can’t think of anything else, except one thing.

          Curiously it really originated near the pole (much further north than Iceland) and in spring interestingly there is a second minor peak in early autumn. These are also the time when geomagnetic storms occur more often (around the equinoxes). Who know if increased geomagnetic activity causes either a spike in CO2 or some data artifact. However, it does not occur in south pole, so I guess this theory might hold false.

          Can also be something similar to the ozone hole, a seasonal phenomena. Whatever is, if it happens in north pole, is more likely to be caused by human pollution, because most of it occurs in northern hemisphere and is transported toward the pole. So I guess Diana is right on spot.

          By the way, EXCELLENT post Geolurk, it such a nice topic.
          And since I often forget to say so, I alo take the change that the recent posts by Carl were also excellent and pleasant to read.

      • The answer is simple. Fish and decomposition. As fish breath they releasy CO2, as things decompose, CO2…
        Here you have a large area of ocean, and ontop of that gulfstream. The output from the ocean is constant, but during the iced over months the CO2 and other gases are trapped under and in the ice. That is the “air” that you can see on ice diving movies.
        So as the ice melts all that juicy CO2 is released in one big spike.

  2. William Wallace, 13th/14th Century Scottish knight and landowner, evidently had a car.

    From “Brave Heart”:

    Too bad he didn’t have a “Boom Stick” like “Ash” Williams (Bruce Campbell) in Evil Dead… who fell to Earth in Medieval Europe along with his car. Well, not necessarily Europe, but Europe like.

    S-Mart™ 12 gauge shotgun

    • Whilst we are on the subject of Hollywood blunders…… Look at the clip above.. A young woman is holding a basket of potatoes……In Medieval Europe? Potatoes as a crop were not discovered until around 1536 when this crop was noticed (and I presume tasted by the Spanish soldiers) in the high Andes. They took a while to catch on but here’s an interesting fact for our Canary Island friends…Barrels of potatoes (patatas) were exported from Gran Canaria to Antwerp in November 1567 and from Tenerife via Gran Canaria to Rouen in 1574.
      There we have it. The first recorded export, growth and use of the humble Spud in Europe..

      • Very true! And it wasn’t until well after the Napoleonic wars that it caught on, at least in Northern Europe (all the countries around the Baltic including the German principalities). Up until then, grain was the predominant staple.

        • Potato complements our European diets and it is a very productive (weight per area) food. Also much easier to harvest than grain!
          Also potatoes grow easier even here in Iceland, you don’t need to do much, just toss some potatoes in early June and eat them in September.

          However grains can grow in even poorer soils and are a larger staple in our diets. From bread to pasta to breakfast cereals and cookies and to animal feed, grains are still our largest staple. By the way, in Iceland we also grow grain: rye, barley and oats.

          Diana: actually this is a topic that highly interests me 🙂

          There are many other food crops in the Andes that never made into our mainstream food. They might one day in the future. Tubers like oca or yacon or “grains” like quinoa.

  3. Thanks Lurking. Nice and simple with enough physics to nudge my brain cells into working order for the day.
    Microwave cooking? No way. Microwaves are good for heating up pre cooked meals and defrosting. Mine is used for heating milk in a cup for a cafe latte; drying my home grown herbs for the winter use, they stay nice and green; Steralising small items such as feeders for baby rescued birds and animals When making milky sauces I often cheat and I do cook those in the microwave. Boiled milk + flavourings ,salt ,pepper, mustard or what ever, in microwave until just boiling, then add cornflour mixed with cold milk. Stir and it quickly thickens. No fat, so slimming, as I am trying to keep weight down (As a treat I add a little butter). Cheese is added last also and maybe a quick minute or less back in microwave………
    However do not try to shortcut Hollandaise and other emulsified sauces.. There is no way but the classic hand whisked and bain marie for these. Also don’t try to make syrups, like chocolate ice cream topping.. the sugar content is to high and they will taste awful even if they don’t burn.
    …..You can tell I speak here with experience 😀 😀 Oh! And I only once tried to melt chocolate for cooking purposes and found nothing beats the bain marie for this .

    • I don’t own a microwave. I know they don’t leak but I used to work for a radio station many years ago and the engineer had skin cancer on his knuckles from “testing if the microwave transmitter was on.” This put me off them. Also I’ve never seen the point. If I want something de-frosted I get it out of the freezer in time. For those of you who say porridge tastes better if done in a microwave – it doesn’t. Microwave snacks are usually junk food. It often seems to take the same amount of time to microwave something as it would to heat it in/on a stove. 🙂

      • I don’t use a microwave at all. I am not fully sure if there are harmless effects, they might be, as well as they might not be.

        But one thing is sure: the vibration induced in molecules by microwave warming is totally different than that from normal heating. I reckon what that might do to some molecules. Because it is a very energetic radiation. UV is less energetic and it breaks down your DNA. I don’t want to think what microwave does to DNA and all the other molecules in live animals and plants that we eat.

        • Mentioned above (somewhere; by geolurking) was the guy (working in high energy radar) who had skin cancer on his hands from sticking them into the “path” to make sure the machine was on…

      • I agree with you there, my old one died with electricity problems, it is a letterbox now, great keeps he moisture out, living in the country box is 5km from the house, easy for the postie as well, put it on some branches so she can reach it from the car window, wound down of course, the one in use now is a friends, he uses it sometimes, I use it for defrosting the natural way and storing things in it, so the cats can’t get to it, yep

        • I had a video, I can’t find now, most likely deleted it, gave me the creeps, one of my grand daughters friends put a mobile phone in it, a person materialised before exploding, makes one think.

        • You could always get an electrically savvy freind to wire the door switch to an internal light run off of a battery.

          That would freak out your carrier.


          The unintended prank.

          While in Sasebo, the Fire Control techs were checking the target illuminator by shining it on the collimating tower. They slewed the antenna off axis and momentarily swept across the top of building where a maintenance guy on the balcony was carrying a box of dead flourescent bulbs he had just replaced. Suddenly, every one of them came on… in the box. Which he promptly dropped.

    • Oh! I like that one GeoLoco. Nice one! Thank you. I hope your day is good. Although at home I have work to do here on line, so I try hard to be strict with myself and set myself office hours! Time I stopped my coffee break and carry on.

    • What a Super dad. I bet that litle boy will grow up with ideas beyond the norm. If his toy train can do it…….?
      I am sad when I see Dads and Mothers who seem to be more intent on their mobile phones that actually having conversation with their children.
      Already in the UK we have a “problem” with English language exams in schools being “too difficult”.
      I am of the opinion that it is actually the kids who honestly do not know how to converse in an informed and imaginative way with each other let alone write down basic English correctly.

  4. Thanks for the explanation GeoLurking. I sorted it into the archives but will create a special hm “chapter” with posts with technical explanations once i am back home and got time, so these don’t get lost and people can re-read them.
    I did not have the slightest idea there are so many scales on the quantification of earthquakes.
    Does someone feel he/she is up to writing a post about this? Lurking?
    It would also be interesting which scale is used on the most common site we regularly check.
    And another one about the different waves, how the start existing and what effect they have and so on.
    Here are a few links:
    http://www.geo.mtu.edu/UPSeis/magnitude.html
    So people see what is a mayor earthquake and what is not.
    The Richter scale : http://en.wikipedia.org/wiki/Richter_magnitude_scale
    MMS used by USGS: http://en.wikipedia.org/wiki/Moment_magnitude_scale

  5. Thanks for the post GeoLurking. I’m so glad there are people on here like you who can explain technical/science stuff to people like me. 🙂

  6. Hi All,
    Got back from Naples on Monday, but have just caught up, fascinating posts, thanks Peter Nathan, Geo n’ Carl 😀
    I especially enjoyed Peter’s article, controversial, but well worth publishing; kudos to Carl. It has been a long time coming, I can remember the ruminations on schlow schlip scheismicity (couldn’t resist, sorry) from the early days here and even when I was lurking over on Jon’s blog.
    Naples was wonderful and crazy, the first thing you learn is how to cross the road Neapolitan Style, you have to keep in your mind that the lunatics on Knackered old Vespa loaded down with crates of vegtables or the rest of the family DON’T want to hit you (it would delay thier arrival at where ever it is they are going in such a screaming hurry!!!) Identify a half gap, even a quarter gap in the traffic and go for it; they will either swerve or (reluctantly) slow down for you, repeat with each lane of traffic until you are acroos… Follow a native the fist few times until you are confident 🙂
    We managed to visit Vesuvius and the Solfatura, as well as Herculaneum and Pompeii, which both have thriving modern equvalents!!! More of that another time though x

      • A bit of disinhibitation certainly helps 🙂 The biggest danger is returning to England, the traffic is on the other side of the road, and using the Naples technique here means you are likely to get run over… People seem to think that this will get them to thier destination quicker…
        Will put together a post if people are interested; can’t promise pictures as good as Spica’s, but maybe first in an occaisional series about “tourist” volcanoes?

  7. Before anyone comments about the strain plot at Hekla.. There has been a technical glitch so don’t read anything untoward into it!

  8. This isn’t the same Merapi Volcano that erupted in 2010 and is a decade volcano. MARAPI (spelled differently) is a separate and independent volcano, also located in Indonesia.

    Marapi is the most active volcano in indonesia.

  9. Thanks GeoL for a very informative post, that someone totally unscientific like me, found pretty easy(ish) to understand…thanks also for that picture from the Braveheart film, it is one of my favourite films, have watched it at least 10 times and never noticed the car in the background..

  10. OT Rant.

    I drive. Being mobile is one of my strong points… being able to solve an equipment problem out in the field is the other. The brunt of my time is getting to and from the site. Being short a tech, I got dispatched to a site well out of my normal area, and when I finished, I was tired, had a clear schedule, and figured that I could grab a bite to eat before heading home.

    Miss the turn for the entrance… okay I’ll use the side entrance on the cross street. Nope. Exit only. Alright, circle block. Next street. One way. Next street. One way. ??? Next street. One way. Okay. Not playing your games. I”m off to the next town. Now I sit enjoying my meal, and the city planners for that town can KMA. I wonder if other people are as likely to just head out rather than play their street games.

    Oh well, so they missed a sale.

    • Sounds like most towns in Britain. There is a town near me that I never visit unless I have to (lots of local government offices there) because I always get lost in the horrendous one-way system. It is so bad a local band made a song about trying to find a way round the town. Often one-way systems are necessary in medieval streets but it makes driving anywhere new a bit of a headache until you know the layout.

      • our national capital comes to mind on that one, there are only a few places where I go to and I know the way, to find a different way or area at your peril, but the roads are excellent

        • City planners got mad here.. .. must be too much stardust in the air … after all them Hollywood ones over here .. One small single-lane one-way street changing directions overnight (had driven that one several times over past weeks before). Found out the hard way, coming front-to-front with … two ladys … *that was a doh moment**

    • Oh darn, the links seem to be to the mobile version of YouTube (m in the address). Sorry if that doesn’t work. Anyway was a completely unimportant OT “fun” comment.
      Have a good night. And a save drive for Lurking.

  11. So, I turned fifty yesterday. Today, the lovely people at work left my present on my desk for me. A bottle of wine? No. A voucher for a massage and a pampering? No. A fist sized lump of Scottish Biotite Granite? Yessirreee.

      • Hi manofhemoors, another person who is younger than me…drat! Sounds like an excellent birthday gift….wine you will buy for yourself if you really want it, a voucher for massage and pampering,,the same….but ” A fist sized lump of Scottish Biotite Granite” is something well “special” to mark the occassion…Happy Belated birthday wishes xx

        • the Spanish news has just reported on thehuge amount of rainfall and total flooding in the parts of the UK… hope all our UK residents here are OK…and are keeping safe.

          • OK here as we are on a small hill. Other places near the local rivers have flooded and some disruption to traffic. It did stop raining for a while earlier today but then we had another torrential downpour. Nice rainbow before it hit us though 😀 .
            <<<<<<<<< Is just looking for a DIY Ark kit on ebay.

          • Yes large rainfall totals from a system that moved North from the Azores.
            Some called it Child of Nadine, as a large area of moist tropical air broke away from the Tropical storm. It then got to the UK where it became blocked and so sat stationary over the UK giving some large rainfall totals. A respite now till the Weekend but long term it looks like rain will remain very much in the forecast. I do have live images of the flooding on floodwarn and leeds is one place where it is still very much a problem.
            A strong jet stream is not helping the UK and its pretty much been a dire summer.
            interestingly the 2hpa (statosphere temperature) between 25n and 25S has been close to the minimum temperature set over a number of previous years, in Setember it has dipped below minimum. No volcanos of signifigance to cause this. probably more to do with space weather, which includes sun spots and CME activity. Perhaps i will during a quiet period do a little about global weather and Volcanos and submit to Carl and if he feels relevant could be posted here. Hurricane / tropical storm Activity has been a little strange this year with two storms, Micheal and Nadine close to the Azores. perhaps they were drawn to Bob El Heiro. Thats just humour and not serious.

          • Your rain has reached us and is happily dumping on me.
            I discovered earlier today what happens when torrential deluge and opposing 24m/s wind gusts meet a high speed train.
            3 things seem to happen:
            1. The electrical engines are bloody strong on those trains, didn’t loose a km of speed.
            2. You could hear the engines as they roared as the driver compensated for the 90km of extra air friction and heavy rain to blast through it all as it motored down the railway in 280km per hour. You never hear them normally.
            3. Even a rather hefty lump of steel train moves a bit in the gusts. Have never seen so many green people. At every stop there where people stumbling off the train to talk to the Porcelein Godess in the bushes. Personally I slept like a baby.

            Personaly I take rain as a personal insult. I really wish I lived in a nice dessert.

          • “Slept Like a Baby”

            Then you sir, are a squid. Only non-squids loose their lunch when confronted with a slow swaying motion. I developed the ability to sleep through Motor Generator sets being swapped over in the next compartment, pumps going on/offline, missile magazine operations, and damn near slept through a missile launch three decks up… but I did actually wake up for a few moments when that happened.. then happily back off to Z-land.

          • Here in NE Oregon we now have a dry, warm wind, saw a UH-1 head over the hill
            with a 500gal. Bucket for fire ops… But I hear they have handle on it..
            Happy birthday, MM, I’m pushing 60 myself, Remember my personal motto:
            “You may grow old but you don’t have to grow up.”

          • On the subject of noisy machinery. Back in my DC7 co-Piloting days I could sleep though
            just about anything waiting for a fire. Aircraft starting,taking off all while I’m dozing in the pilot’s shack one thing gets my attention: Even today, a bell, siren, or klaxon gets my attention. My wife bought an alarm clock for me when I got back from fire fighting.
            wound it up set the alarm, and i was comfortably dozing away when it went off.
            Sounded exactly like the engine fire bell on a DC7. I woke up.
            She took it back to the store…
            Before I threw it in the Ocean…

        • In the Canary Islands, they have warned us of the tail of tropical storm nadine since last week, but so far, apart from some strong winds (which Spica will verify)…in Tenerife we are still completely sunny, dry and warm…. the Spanish mainland however is a different kettle of fish

          • Having said that earlier, just popped outside, there is a rather, exceptinally strong wind blowing outside this evening, maybe (doubt it though) there could be some sort or storm on it-s way to Tenerife (hope not because my nephew has just arrived for a holiday here),

        • Saga Car insurance… expensive. Saga Holidays refused my husband a place as he is a little younger than me (Well! By 20 years ) so as I am not into stair lifts or chairs that throw you back onto your feet, (yet)They can get stuffed as far as I am concerned.

          • I think that the Saga people are obviously losing a lot of business by their petty rules….if I was in charge there, I would welcome any booking from anyone…I am sorry but yes, I can see the point that they don´t want unruly teenagers mixing in with their elderly (is that what you call people like me these days) holiday makers, but surely then can see that someone who is the partner of a 50+ person and over 25 or 30 years old, is not going to wreck the holiday for the rest….like a lot of companies, they are complacent and are not looking at the bigger picture…the economic crisis is effecting a lot of companies, and they really need to move with the times if they are to survive….you cannot afford to turn away business in this day and age

          • Sounds like they have missed how todays “slightly less young teenagers” are.
            My mother goes to Ibiza every winter to party… Since she finds any place designed for elderly vehemently obnoxious with lame music and that they are inevitably run by moroons who dote the elderly. Also, general lack of nightclubs in elderly places play a certain role in it. My mother turns 80 this year.
            Me and my brother flat out refuses to visit since we get outpartied and need a second vacation to recouperate from the visit.
            I hope I will have that kind of energy when I get less young. I doubt it.

      • what! are you saying that if I join Saga (have only been 50 since May this year) I can get 10 years taken off my look! Diana,send me the link so that I can sign up–I haven´t got the same problem as you, my husband is 2 years older than me, does that get us a bigger discount?? 🙂

          • yeah, i thought it sounded to good to be true–haven´t yet tried to chase bears in Swedish Lapland, but am sure that would be an invigorating holiday experience for the Saga “over 50´s”….just need to make sure they get to taste that wonderful Reindeer Salami …In fact I am seriously thinking my next holiday should be to visit one of the Scandanavian countries, I just love the marinated salmon with dill sauce (which my Swedish/Finnish friend makes for me every Christmas), and all the other specialities that the Scandi´s do so well…..never have tried Swedish Lapland Bear though… 🙂

          • That and eating frog cakes in Skelleftea. I think lounging in hammocks, staring into the distance whilst eating bilberries and cloudberries is my recipe for “youthful good looks”.
            Oh, and having a wife who is exactly 10 years younger.

    • Think about it. Halloween is coming, and the standard Charlie Brown Great Pumkin’ episode is just around the corner. The missive from Charlie Brown when all the kids are yammering about what they got from Trick or Treating… “I got a rock.”

      How many of us would prefer the rock? Especially the Biotite Granite!

      • Cheers all. My manifesto for the future is, to quote a very smart English rocknroller, to “ride upon a five mile tide of surprise and oblivion”. The granite was certainly a surprise…the oblivion came courtesy of Rioja later in the evening.

  12. @ Peter Cobbold,
    Have just re-read yr article,
    Does yr theory account for the giant collapses: el Golfo, el julan and the semi collapse of San Andreas? If rock is uplifting and moving laterally due to relaxation I guess that would maybe work… the Orotava collapse on Tenerife might also fit this model… Over the long term these compression/ relaxation quakecycles could have eventually pushed the pre collapse edifices past thier angle of repose; “the swarm that broke the mountains back.”
    Disclaimers: 1: Schtandard daily Fail. 2: Controversial; but worth a mention.

    • Schteve, I dont think so because the erupted mass is above the sedimentary layer which seems to be relatively immune to eq swarms. I see the sedimentary layer as insulating the shallower erupted mass from tectonic loading and hence from fracturing. So the tendency to mass wasting in big slides would have another cause that the hypothesis does not cover. The GPS motion might accumulate over many swarm cycles but I think it would be insignificant compared with the effect of erupting fresh lava. Fresh eruptions might well preferentially follow the swarm-weakened zones so dictating the star shape. But the link with that and wasting in big slides is not obvious. There is a paper by Scheidegger (?) on Lanzarote (?) who found a statistical bias towards rock fracture planes being oriented WE – that might be relevant to your idea, I’ll try to find it.
      Cheers, Peter

      • Mornin’ Peter,
        To quote my well thumbed copy of Caracedo’s Canarian Volcanoes IV :
        “The existence of a triple rift system on El Hierro has favoured the concentration of eruptions at the centre of the island, increasing it’s height and progressively leading to gravitational instability. When combined with the tensional forces of dyke injection at the axes of the rifts this has triggered several lateral collapses…”
        It seems to me that the “standard” model of giant collapses as quoted doesn’t rule out your theory, which is what I was getting at with my original question (in a backwards roundabout kinda way 🙂

  13. back to work will have time in a few days to look at all the posts I missed, the weather is fine and warm, got to make hay while the sun shines or so it says

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