Earthquake!

[Shiny_Bottom_1]

Oh brother, now comes the onslaught of dismissive comments about earthquakes not being up to scratch.

Trust me Roger...5.2 was plenty enough for me. I love extreme weather where I can sit at home watching the blizzards outside, but an Earthquake isnt something I can sit back on my bean bag and think I want more.

[jethro]

http://www.sciencedirect.com/science?_ob=A...3752097c8075163

http://www.springerlink.com/content/4ut8121v071p0223/

http://www.ngdc.noaa.gov/seg/geomag/faqgeom.shtml

http://swdcwww.kugi.kyoto-u.ac.jp/igrf/anime/index.html

[The PIT]

Actually I wouldn't be surprised if the gravitational pull of the moon did trigger the odd quake. Look at it this way the fault is fully stressed ready to go it just needs a small trigger. Moon comes along shifts the crust slightly and bingo it's enough for the fault to release it's stress.

As for Global warming causing it well I've got another theory. Some Government official has dumped a load of Birds suffering from Bird Flu into a deep hole. The decayed mass of these chickens lubricated the fault and whammo. So it's all done to the HN51 bird flu virus. You've read it here first.

[alumact]

If anyone in interested into a more thorough explanation of what is contained there then please ask. As will be the same case for today's event, once picked the phase data is organised according to station and distance/time from the header downwards. Only in the case of severe anisotropy in the crust would this differ. Most of the phases relate to P-arrivals, with usually about 33% S-arrivals. The others relate to the peak to peak amplitude picked on the waveforms to determine the magnitude of the event. I have kept the amplitudes as determined at the time, but the back-catelogue of earthquakes (f.e the Dudley event) has been relocated with a 3-D model of seismic P- and S- velocity. The models used to provide the locations of say, todays event are 1-D models, that may be rather inaccurate. This is particularly true for eastern and southern England where there is little constraint from wide angle refraction profiles, because simply none have ever been shot in this area. Most of the 1-D models used to locate events in the UK are derived from refraction profiles shot in the 1970s (LISPB, Bamford et al.).

So there is still much work to be done. The largest errors in earthquake location are associated with depth. You can alter the depth alot but not affect the travel-time much, but change its spatial position in x and y it will.

Your posts are very interesting and precise!

Are you a geophysical researcher?

I'm a student of geophysics at Catania's University and I hope to graduate this year.

Ps: sorry, but I don't speak English very well yet!

[The PIT]

Apparently an old fault zone (that has been dormant for hundreds of millions of years) is to blame for the quake: -

http://www.dur.ac.uk/news/newsitem/?itemno=6226

Shame that there isnt more info on this though.

Apparently the area used to be a lot more active many moons ago and it's been quiet until Yesterday hence the idea the fault has re-activated.

[The PIT]

Interesting to view monitoring season at the time.

http://www.quakes.bgs.ac.uk/helicorder/heli.html

[Schnee]

Has there been any reported aftershocks yet?

[Bobby]

Global warming causing earthquakes? No wonder so many are sceptical when people come up with stuff like that! In my humble opinion, complete and utter nonsense of the highest degree. And anything to do with the weather/atmosphere at that. An average 0.7c warming of the atmosphere struggles to raise even soil temperatures by a small fraction of a degree, nevermind past many miles of thick rock.

I think it's plausible though that the Moon could have some effect on earthquakes by causing "tides" on the magma like we get in the oceans. Not too far fetched I don't think but I don't know if it's actually a correct theory or not. Just plausible.

Edited February 28, 2008 by Magpie

[The PIT]

Has there been any reported aftershocks yet?

Go to link I posted and quick hunt around the website will give you the answer. Last I looked two.

[mackerel sky]

Your posts are very interesting and precise!

Are you a geophysical researcher?

I'm a student of geophysics at Catania's University and I hope to graduate this year.

Ps: sorry, but I don't speak English very well yet! :huh:

Hi - yes I am indeed. I have an undergraduate degree in Geophysics and a masters degree in Exploration Geophysics. I then worked for 6 years as an exploration seismologist for an oil & gas exploration contractor before returning to do the PhD - which I need to finish up fast as I've accepted a job as an interpretation Geophysicist with another oil & gas exploration contractor - though this is more to do with potential fields (gravity and magnetics).

Send me a personal message if you want any advice (career wise or anything else) and best of luck!

Some basic facts. The earth has more of a forcing on the moon than it on us; the tides are caused by both the sun and the moon in combination. If the affect of the moon on the atmosphere is minimal; then its going to be less on the liphosphere. True that ocean and water movement causes stresses; but we must not forget what the real driving convective processes are.

I'll wait for mackerel sky for his views.

My views are that is a nonsense! There are very small tidal "moonquakes" on the moon itself as result of the Earth's gravitational influence which is much stronger, but not in the opposite direction - if there was any minor influence it would probably be beyond detection capabilities of the instrumentation - smaller than ambient noise! "Moonquakes" are if anything more akin to some of the many small (unfelt) earthquakes that occur in parts of western Scotland and to a lesser extent the lake district (typically less than a magnitude ~ 1) that generate thrust type focal mechanisms as a result of glacial unloading or isostatic rebound. Shallow small-scale gravity driven crustal flexure.

Edited February 28, 2008 by mackerel sky

[mackerel sky]

It also strikes me that it could be related to magma movement deep underground, possibly pushing against a weak point.

One of the ideas which my work complements is the idea that Tertiary magmatism associated with the break-up of the Atlantic may explain the pattern of seismicity as seen in around the edges of the Irish Sea (the East Irish Sea basin directly overlies it, which you might expect if underplate caused inital uplift in the area and exhumation of deeper buried rocks, only to later be eroded to re-estabilish isostatic equilibrium - in fact the exhumation is probably responsible for this area being a gas producing provence today in Morecambe Bay). Strangely, Ireland itself is virtually aseismic. One of the last things I want to do and integrate the 3-D models of seismic velocity I've developed is (if possible) generate stress tensors for the well constrained earthquakes from the past 25 years and see how well this fits. Heres an abstract I for something I presented at the AGU meeting a year last December which might shed some light on what I've just said:

Abstract

For the past three decades crustal studies of the British Isles have been restricted to the interpretation of 2-D seismic reflection and refraction profiles, mostly aquired offshore. The British Geological Survey (BGS) seismic monitoring network has grown substantially over the past twenty years to a density and quality unprecedented for an aseismic region. Recently, this has made it possible to undertake teleseismic studies to image the seismic velocity of the mantle via 3-D tomography and 1-D receiver functions for the crust and uppermost mantle. Whilst the British Isles can be considered an aseismic region by world standards, the BGS network typically records 40 local events of over 2.0 on the local magnitude scale every year. Irrespective of an intra-plate setting, the width of seismogenic zone is exceptional, ranging from the surface to in excess of 30 kilometres depth despite no surface ruptures ever having been observed. For the first time we utilise these locally generated seismic events within the BGS digital catalogue recorded over the past two decades to produce a model of seismic P- and S- velocity to depths of 70 km beneath England, Wales and the Irish Sea at an unmatched resolution. A high quality subset of over 1,000 local events and 18,000 arrival times has been extracted from the entire digital catalogue. This has been used to relocate the events with a 1-D seismic P-velocity model extracted from a regional 2-D model derived by extrapolation of wide-angle refraction profiles. The initial locations and 1-D model have been simultaneously updated and refined using VELEST to produce a consistent set of station corrections for the BGS network which is in good agreement with known geology. The updated locations and 1-D model acts as the reference model for a 3-D tomographic model developed with the SIMULPS inversion code. Our 3-D model will compliment teleseismic and controlled source studies which demonstrate seismic anomalies thought to be associated with the emplacement of magmatic underplate beneath the East Irish Sea. We note that the earthquakes are distributed around the edges of this high velocity and high density body which suggests that they may be related of loading on the crust.

Edited February 28, 2008 by mackerel sky

[alumact]

Hi - yes I am indeed. I have an undergraduate degree in Geophysics and a masters degree in Exploration Geophysics. I then worked for 6 years as an exploration seismologist for an oil & gas exploration contractor before returning to do the PhD - which I need to finish up fast as I've accepted a job as an interpretation Geophysicist with another oil & gas exploration contractor - though this is more to do with potential fields (gravity and magnetics).

Send me a personal message if you want any advice (career wise or anything else) and best of luck!

Thanks for info! :huh:

If I'll need you, I send you a personal message!

[PersianPaladin]

My views are that is a nonsense! There are very small tidal "moonquakes" on the moon itself as result of the Earth's gravitational influence which is much stronger, but not in the opposite direction - if there was any minor influence it would probably be beyond detection capabilities of the instrumentation - smaller than ambient noise! "Moonquakes" are if anything more akin to some of the many small (unfelt) earthquakes that occur in parts of western Scotland and to a lesser extent the lake district (typically less than a magnitude ~ 1) that generate thrust type focal mechanisms as a result of glacial unloading or isostatic rebound. Shallow small-scale gravity driven crustal flexure.

Thanks for that m-s.

:huh:

[Roger J Smith]

I'm surprised to read that somebody studying in the field has not come across this perspective in the literature. Especially valid for regions where strong tidal differentials in the shallow ocean region must be a factor (mass shifting on and off the formations involved).

But I will research a list of perhaps the 20 or 30 greatest earthquakes in modern history going back to perhaps the 1755 Lisbon quake which I notice happened three days before new moon, and see whether that small sample shows any bias towards lunar cycle or not.

I have also read somewhere in the distant past the opinion that a larger than average number of major earthquakes happen in winter in each hemisphere, and this is postulated to be because of larger atmospheric variations and tidal forces at full moon causing stress on the crust.

So watch this space for a list and an analysis of the dates. If somebody else wants to post a list, so much the better, then it will eliminate my subjective bias, although I will be going for the 30 quakes that caused the most damage in terms of casualties as a good indication.

[mackerel sky]

I'm surprised to read that somebody studying in the field has not come across this perspective in the literature. Especially valid for regions where strong tidal differentials in the shallow ocean region must be a factor (mass shifting on and off the formations involved).

Not in the journals I read. Its better to focus on the main issue at hand rather than be lead into voodoo territory and dubious cul-de-sacs of research. Whilst there may be something in it, you wouldn't give it any lip service because the potential influence is so minor. Does the general public care about earthquakes that aren't felt? Of course not.

[PersianPaladin]

Not in the journals I read. Its better to focus on the main issue at hand rather than be lead into voodoo territory and dubious cul-de-sacs of research. Whilst there may be something in it, you wouldn't give it any lip service because the potential influence is so minor. Does the general public care about earthquakes that aren't felt? Of course not.

I think calling it "voodoo" is a tad harsh perhaps.

I'm sure there is some sort of affect, although as you say most likely minor. Although the pull of the earth on the moon may inadverdantly be causing a more long-term affect on the earth in terms of geo-magnetic disturbance; we just don't know. Kind of like a feedback force....?

[PersianPaladin]

I seem to have a worried feeling that anamolously strong earthquakes are becoming more frequent these days. Indeed; the last near 5.0 earthquake was only back in 2002, a notable one affected Folkestone and now this.

Somebody also sent me a graph a while back showing a sharp worldwide increase in quakes above 6.0 magnitude since 1960....I can't find the link anymore. Is there any truth to this?

[The PIT]

If more earthquakes occur in winter perhaps it's due to the lucubration of the fault. Water penetrating down allowing it move more freely. If that's the case you would expect less quakes in late spring and early summer as the stresses have been released. Probably complete nonsense though.

[Roger J Smith]

My remarks were more about major earthquakes around the world than British earthquakes.

I have been looking at various lists and these do seem skewed towards the winter half-year in each hemisphere (actually a lot of late autumn and early spring dates more than mid-winter) and the new and full moon dates. Further analysis to follow.

Check the list given on the website livescience.com, which includes 21 great earthquakes. Of these, I see 14 that are in the winter half-year (including one in the southern hemisphere in late May) and 7 that are in the summer half-year. There seems to be a clustering of dates before and after the midwinter period, suggesting possibly that these seasons of rapid atmospheric transition are particularly stressful for the earth's crust.

My analysis of lunar dates is a little less revealing because some of the earthquakes in the list do not have precise dates and I am not sure about the pre-Gregorian dates quoted, old style or new style. From what I can see there is some clustering around new moon more than full moon, but as I would have expected, a more random scatter. I would expect more of a stress at northern max in the northern hemisphere, and this coincides with full moon only in December.

Probably the seasonal concept has more merit than the lunar month concept, but I still think the lunar dates are not entirely random for this process. In any case, I understand that the release of these stresses takes place over different time scales that can range from months to hours, so precise forcing concepts would be somewhat of a moot point in some cases.

As for British earthquakes, these are so weak on the global scale that they might not follow this sort of seasonal variation at all. One place where there is some connection to lunar cycles and earthquakes is New Brunswick in eastern Canada, which is prone to moderate tremors and has the world's largest tidal ranges offshore in the Bay of Fundy. You would have to think that tidal ranges would come into play when earthquakes are in shallow sedimentary layers near the coast, the stresses of that great mass of water moving around must be considerable.

Edited February 28, 2008 by Roger J Smith

[mackerel sky]

I seem to have a worried feeling that anamolously strong earthquakes are becoming more frequent these days. Indeed; the last near 5.0 earthquake was only back in 2002, a notable one affected Folkestone and now this.

Somebody also sent me a graph a while back showing a sharp worldwide increase in quakes above 6.0 magnitude since 1960....I can't find the link anymore. Is there any truth to this?

Gah, will people stop misquoting the magnitudes! Dudley is now apparently a 5.0, when it was a 4.7. Folkestone was a 4.2. I gave all the phase data for the Dudley event, and it has the amplitude in the header, as determined from the phase data. Indeed the peak-to-peak amplitude determined from the horizontal components of some of the stations is there.

With it being a logarithmic scale, the differences are substantial! Note that the preliminary magnitude given by the BGS was 5.3, that was adjusted to 5.2, as I said - until all the waveform data is available and can be picked at leisure, if you like, then the magnitude and location was likely to change a little.

Voodoo was a bit harsh. One the main interests in seismology at the minnute is understanding intra-plate earthquakes and the UK is no exception to this case. The UK is subject to crustal shortening as a result of ridge-push from the Atlantic and Africa's collison with Eurasia. The biggest enigma is probably the New Madrid events in central USA, which I haven't got the time to go into right now. But as result it is no suprise that principal stress in the UK is NW-SE, given ridge-push and N-S collision. Most of the main (old) faults in the UK are orientated SW-NE. Hence most of the larger earthquakes occuring on faults, such as the Church Stretton/Welsh Borderland faults, Highland Boundary Fault, Menai Straits Fault system are strike-slip as they are anti-parallel. Must go as my wife is fetching a pizza on the way home.

Must remember of course that there have been many felt earthquakes in the UK in regions of mining. These are easy to diagnose of course, if not at least they have a very different source signature to natural events.

My remarks were more about major earthquakes around the world than British earthquakes.

Sorry Roger, I'll try to digest what you've said better.

Edited February 28, 2008 by mackerel sky

[The PIT]

What is the difference between the European Macroseismic scale and the Richter scale by the way???

[Paranoid]

A lot of UK earthquakes seem to occur at night or early morning, is there a reason for this or is it just coincedence?

[Mammatus]

A lot of UK earthquakes seem to occur at night or early morning, is there a reason for this or is it just coincedence?

Yes there is a reason

[osmposm]

Yes there is a reason

um....and the reason is....??

(assuming it to be true)

[Roger J Smith]

Betcha it isn't any of the following:

(a) Moon only out at night

(.b.) daytime earthquakes mistaken for traffic

(.c.) most earthquakes in winter and night longer than day

(d) earthquakes secretive and don't like the light

(e) earthquakes produced by Dick Cheney's earthquake machine and he only works afternoons which is night in UK

Edited February 29, 2008 by Roger J Smith