Earthquake magnitude and orientation are the controlling factors in tsunami generation. It's not the vibrations, high frequency or otherwise, that cause the tsumani. It's the sudden displacement of mass in water (well, ok, you could argue that's a very low, 1-wavelength frequency signal, but that's getting away from the main point...).
Large enough earthquakes that have sufficent energy release to displace large quantities of mass will have very broad-spectrum vibrations anyway. High frequency earthquakes, will, by their nature, be small. And hence of very little tsunami-generating potential.
Tsunamis are caused by large quantities of mass moving and causing a displacment of water. This is most likely to be due to earthquakes, but also includes landslides or volcanic activity.
Purpose built seismometers can detect minute vibrations caused by the passage of seismic waves from an earthquake on the other side of the planet. The stations where they are based are specially constructed to isolate the seismometers from any sort of local environmental noise.
What will actually help with real-time tsunami warnings is faster and more accurate analysis of the triggering earthquake. Knowing the displacement that occurs along a fault means you can make a more accurate estimate of water displacement, and hence tsunami potential. From that point, you can model the propogation and size of a resulting tsunami, to allow better warnings to be distributed to shorelines. A magnitude 9 earthquake could occur underwater - but if it's a transverse fault, and the two side of the fault are moving past each other horizontally, then there's practically no chance of a tsunami being triggered.
Trying to analyse hard drive vibrations and is somewhat optimistic. For a start, seismometers have a very wide frequency-response range to vibrations, and are purpose-designed for this - the same can not be said for hard-drives.
While there are clearly many, many times more hard drives out there than dedicated seismic stations, the supposed benefit of having so much data would most likely be cancelled by the massively increased time required to extract any sort of useful signal. Especially from such a narrow frequency response, that cannot distinguish noise from signal (eg; a truck driving past your house, and actual seismic signals). And this is without even getting to the fact that tsunamis are vibrations in a liquid - when vibrations from tsunami reach your location, that's because the tsunami is already there.
This seems like a case of someone with technical knowledge/ability not grasping the physical science basics behind the actual problem. Someone's noticed that PC's have (very limited) vibration sensors in them, and jumped on the shared p2p bandwagon to solve the problem.
Improved tsunami warnings will come from improvments in dedicated seismic monitoring for early warnings of a potential tsunami in the local region near the earthquake. Followed by fast, accurate modelling of tsunami propogation, to allow reliable warnings to be sent to coastlines at greater distance. One of the problems with early warning systems for natural hazards, is that if they aren't accurate, then their effectiveness in the future is reduced.
Sending data from actual seismic monitoring stations to a p2p network might help with improved earthquake models. But the time-critical nature of the problem means that such analyses are probably better left to dedicated supercomputers or clusters.
Re:An upcoming shift of the magnetic poles?
on
Canada Loses North Pole
·
· Score: 5, Informative
Several writers have suggested that a "polar shift" may occur in the near future. While I'm not a geophysicist myself, perhaps that is what we are seeing: a reverse in polarity of the north and south magnetic poles.
For what it's worth, I am a geophysicist...
If by "polar shift", you mean a magnetic reversal, then one will happen, sooner or later. The main field appears to be weaking slowly at the moment. On the other hand, the actual location of the magnetic pole is continually shifting.
Another poster gave a link to http://www.pbs.org/wgbh/nova/magnetic/reversals.ht ml. If you look at some of the quicktime animations of a reversal in progress, you can see what happens to the field at the Earth's surface. The dominant feature of the current field is a dipole field - which is why the field can be nicely approximated to a bar magnet. As a reversal takes place, the dipole component of the field falls in strength, and quadrapole and then octopole features start to dominate - meaning there won't be an actual pair of poles.
The original poster said;
There's speculation that December's tsunami causing earthquake may have been one of the factors causing the pole to move more quickly than predicted.
This is mentioned in the original article. Although not impossible, I would tend to think it's pretty unlikely (but my speciality is seismology now, not geomagnetism). Big subduction zone earthquakes, which produce a significant vertical movement of mass, do affect the earth's moment of inertia. This leads to (small) changes in rotation speed and the orientation of the rotation pole. This is because the moment of inertia is dependant on the mass distribtion of the entire earth.
The magnetic field is produced in the liquid outer core. It's in constant motion. There's also a difference in the net rotation of the core relative to the rest of the earth, which causes a continual westward drift of the field. This means the poles are always moving. Ships have been measuring the declination between geographic and magnetic north for centuries - the movement of the magnetic pole isn't uniform.
Well well, just imagine a chunk of water floating inside a space station. Initially it'd be more or less spherical at rest. But once an astronaut pokes on it, it starts vibrating in many different modes...but its vibration eventually dies down, thanks to the air molecules surrounding the water bubble.
Basically the same thing is happening to the Earth. But in this case, the air (atmosphere) is thinner and there is nothing outisde (vacuum). So dumping the vibration energy takes time. Eventually the energy would turn into heat via friction, however.
This is a nice analogy, but it's not the air molecules surrounding the water bubble that are the dominant factor in attenutating the vibrations, but rather the internal dissaption of kinetic energy to heat through friction. A lump of water floating in a vacuum would still come to rest, but just very slightly slower.
These vibrations are called spherical harmonics, and are often compared to a bell ringing - it's only larger earthquakes with sufficient energy that produce observable normal and tesseral (I think - been a few years since I've done this) modes. These describe in-and-out, and up-and-down patterns of vibrations respectively.The great 1960 Chilean earthquake (biggest earthquake of the last 100 years) was the first earthquake large enough to produce spherical harmonics that could be seen with m a global seismometer network.
Spherical harmonic oscillations (the in-and-out normal modes) have also been observed on the surface of the Sun - leading to a branch of science called Helioseismology. As in the earth, analysis of these vibrations provides further constraints on the internal structure.
A few people have suggested that there are interactions between the atmosphere and the earth. One published theory said that the atmosphere could actually drive spherical harmonics, which is pretty much opposite to what you'd think intuitively. I seem to remember that this theory was shot down though.
Actually, it doesn't necessarily start at zero - it's a logarithmic scale so negative magnitudes are still meaningful, if not worth worrying about outside seismology research.
And as for 8 being the upper limit - one of the reasons that the Richter magnitude scale isn't actually used anymore is that it saturates at large magnitudes. In other words as earthquakes keep getting bigger, the richter scale doesn't really keep up - it under-reports the actual size. So an earthquake with a moment magnitude (see below) of 7.5 might have a comparable richter magnitude, but one with a moment magnitude of 8.5 or 9.0 might still only have a richter magnitude of 7.5 or 8.0.
Moment magnitudes are calculated from the area of fault surface that actually ruptures, how much it moves, and the rigidity of the surrounding rock. A fault can propagate over long horizontal distances (~1000 km in the Sumatran earthquake last year) but only down to a point where the crust is still rigid enough to crack. It's this factor that is the main control on upper earthquake size. Other wise the rupture could just keep spreading down. Then you could have stupidly large earthquakes like a magnitude 15 or 20 that would crack the earth in half. Well, not really.
Part of the reason is the the richter magnitude scale is a local magnitude - it's not actually giving the true energy release of an earthquake, but how bad it feels at some nearby point (corrected for distance). It's also a bit of a hold-over from the early days of seismology in California. When people started to realise that the are earthquakes outside California as well, the richter magnitude scheme fell out of favour.
Seismologists don't use the richter (local) magnitude scale anymore really. The reason it's still often reported in the news is that after alarge earthquake, reporters call up their local governmental Geological Survey for a size. If the seismologists then try to give the size in a modern, more accurate scale, the reporters tend to say "Moment magnitude? No one knows what that is - how big was it on the Richter scale?". So, even though it's generally out of date, it still manages to be somewhat self-perpuating.
Widely used by people in the geophysics field. It's open source, and for the basic linux user it can be a slightly fiddly to get up and running.
It's a collection of command line tools that generate postscript output. You can basically customise everything to your exact tastes, and re-use the scripts if you want consistent graphs and charts.
So what happens if all these time travellers materialise in the same location and time?
42.360007,-071.087870 is very precise - on the order of 10 cm if I've done my (very quick) sums right.
A good way to kill off any future time travellers.
But then, you'd like to think that anyone who's mastered time travel will realise this and appear at some offset location. Otherwise the outcome will surely be a catastrophic rift in the very fabric of space and time itself!
Like when one of the evil consoles uses a multitap attack to throw 4 controllers at once, only for one to bounce off the xbox - "projectiles have no effect".
The stronger than average n64 rumble pak brings back memories as well...
I do. Adobe Reader is the crappiest piece of shit there is. Slows, segfaults, VERY SLOW TO STARTUP.
Well, this might not help in terms of the web-browser plugin, but when you launch it directly, holding down the shift key stops all the plugins and extra bits and pieces from loading. (Not sure what they're actually for, but for your everyday, run-of-the-mill.pdf's, disabling them doesn't seem to make any difference).
Surely it would have to be included in the top pc fps releases of last year. At least it gave the illusion of being sightly non-linear at times, unlike the big name games. And it was much easier on the eye, without needing such top-end machine.
I'd much rather see an expansion pack for Far Cry than one for Doom 3 or Half-Life 2.
The seismic (geophysical) moho is the most common definition (and the one I would use most regularly), but the petrological moho is a valid description as well. I'm informed that it's the
"transition from crustal plagioclase bearing rocks to plagioclase-free olivine and pyroxene rocks".
When you think about it the seismic discontinuity has to be attibutable to some actual physical change in the earth.
I was once on a geological field trip to Cyprus, which has been upthrust a lot, to the point where some old moho is visible at the surface. Having heard this I was hoping for a big outcrop with a nice clear line running through it, so I could stand with a foot on either side of the moho for a picture. Unfortunately it didn't quite look like that.
Not being a geologist I grabbed a few nice looking pieces of rock to take home for paper weights. Alas the cleaning staff at the hotel threw these out, thus stealing my moho. Ah well.
Unlikely.
The Mohorovicic (Moho) discontinuity can be described in a few different ways - either where seismic veolocities have a marked discontinuity, or where a noticable chemical/mineralogical change occurs (can't remember what it is, I'm a geophysicist, not a geologist).
What it's not is a boundary between a nice solid crust floating on top of "firey liquid mantle". In fact more accurate terms are lithosphere and asthenosphere, rather than crust and mantle, which basically differentiate between rigid, colder material, and warmer, more ductile rock. The top of the mantle is still solid, but becomes increasingly ductile with depth. Various minerals reach melting point as you go down towards the Core-Mantle Boundary, but basically I think you have to get to the outer core before it's all liquid (mostly iron).
In terms of energies, the largest nuclear bomb ever detonated was about 55-60 megatonnes (depending on who you ask), in 1961 by the USSR. The energy released by the great 1960 Chilean earthquake (the largest recorded in the last 100 years) was equivalent approximately to a 2000 Mt bomb.
So, setting off a nuke at the moho might temporarily create a small spherical cavity which would probably collapse in on itself, and maybe create some melt, but it's doubtful it would come gushing to the surface as a raging plume of "liquid hot magma".
Besides, there have been plenty of underground nuclear tests, and none of those have resulted in a humungous volcano. As yet.
The USGS site at http://www.usgs.gov/ is probably a good place to find out more.
Slashdot Mirror
Earthquake magnitude and orientation are the controlling factors in tsunami generation. It's not the vibrations, high frequency or otherwise, that cause the tsumani. It's the sudden displacement of mass in water (well, ok, you could argue that's a very low, 1-wavelength frequency signal, but that's getting away from the main point...).
Large enough earthquakes that have sufficent energy release to displace large quantities of mass will have very broad-spectrum vibrations anyway. High frequency earthquakes, will, by their nature, be small. And hence of very little tsunami-generating potential.
Tsunamis are caused by large quantities of mass moving and causing a displacment of water. This is most likely to be due to earthquakes, but also includes landslides or volcanic activity.
Purpose built seismometers can detect minute vibrations caused by the passage of seismic waves from an earthquake on the other side of the planet. The stations where they are based are specially constructed to isolate the seismometers from any sort of local environmental noise.
What will actually help with real-time tsunami warnings is faster and more accurate analysis of the triggering earthquake. Knowing the displacement that occurs along a fault means you can make a more accurate estimate of water displacement, and hence tsunami potential. From that point, you can model the propogation and size of a resulting tsunami, to allow better warnings to be distributed to shorelines. A magnitude 9 earthquake could occur underwater - but if it's a transverse fault, and the two side of the fault are moving past each other horizontally, then there's practically no chance of a tsunami being triggered.
Trying to analyse hard drive vibrations and is somewhat optimistic. For a start, seismometers have a very wide frequency-response range to vibrations, and are purpose-designed for this - the same can not be said for hard-drives.
While there are clearly many, many times more hard drives out there than dedicated seismic stations, the supposed benefit of having so much data would most likely be cancelled by the massively increased time required to extract any sort of useful signal. Especially from such a narrow frequency response, that cannot distinguish noise from signal (eg; a truck driving past your house, and actual seismic signals). And this is without even getting to the fact that tsunamis are vibrations in a liquid - when vibrations from tsunami reach your location, that's because the tsunami is already there.
This seems like a case of someone with technical knowledge/ability not grasping the physical science basics behind the actual problem. Someone's noticed that PC's have (very limited) vibration sensors in them, and jumped on the shared p2p bandwagon to solve the problem.
Improved tsunami warnings will come from improvments in dedicated seismic monitoring for early warnings of a potential tsunami in the local region near the earthquake. Followed by fast, accurate modelling of tsunami propogation, to allow reliable warnings to be sent to coastlines at greater distance. One of the problems with early warning systems for natural hazards, is that if they aren't accurate, then their effectiveness in the future is reduced.
Sending data from actual seismic monitoring stations to a p2p network might help with improved earthquake models. But the time-critical nature of the problem means that such analyses are probably better left to dedicated supercomputers or clusters.
For what it's worth, I am a geophysicist...
If by "polar shift", you mean a magnetic reversal, then one will happen, sooner or later. The main field appears to be weaking slowly at the moment. On the other hand, the actual location of the magnetic pole is continually shifting.
Another poster gave a link to http://www.pbs.org/wgbh/nova/magnetic/reversals.ht ml. If you look at some of the quicktime animations of a reversal in progress, you can see what happens to the field at the Earth's surface. The dominant feature of the current field is a dipole field - which is why the field can be nicely approximated to a bar magnet. As a reversal takes place, the dipole component of the field falls in strength, and quadrapole and then octopole features start to dominate - meaning there won't be an actual pair of poles.
The original poster said;
This is mentioned in the original article. Although not impossible, I would tend to think it's pretty unlikely (but my speciality is seismology now, not geomagnetism). Big subduction zone earthquakes, which produce a significant vertical movement of mass, do affect the earth's moment of inertia. This leads to (small) changes in rotation speed and the orientation of the rotation pole. This is because the moment of inertia is dependant on the mass distribtion of the entire earth.
The magnetic field is produced in the liquid outer core. It's in constant motion. There's also a difference in the net rotation of the core relative to the rest of the earth, which causes a continual westward drift of the field. This means the poles are always moving. Ships have been measuring the declination between geographic and magnetic north for centuries - the movement of the magnetic pole isn't uniform.
This is a nice analogy, but it's not the air molecules surrounding the water bubble that are the dominant factor in attenutating the vibrations, but rather the internal dissaption of kinetic energy to heat through friction. A lump of water floating in a vacuum would still come to rest, but just very slightly slower.
These vibrations are called spherical harmonics, and are often compared to a bell ringing - it's only larger earthquakes with sufficient energy that produce observable normal and tesseral (I think - been a few years since I've done this) modes. These describe in-and-out, and up-and-down patterns of vibrations respectively.The great 1960 Chilean earthquake (biggest earthquake of the last 100 years) was the first earthquake large enough to produce spherical harmonics that could be seen with m a global seismometer network.
Spherical harmonic oscillations (the in-and-out normal modes) have also been observed on the surface of the Sun - leading to a branch of science called Helioseismology. As in the earth, analysis of these vibrations provides further constraints on the internal structure.
A few people have suggested that there are interactions between the atmosphere and the earth. One published theory said that the atmosphere could actually drive spherical harmonics, which is pretty much opposite to what you'd think intuitively. I seem to remember that this theory was shot down though.
Actually, it doesn't necessarily start at zero - it's a logarithmic scale so negative magnitudes are still meaningful, if not worth worrying about outside seismology research.
And as for 8 being the upper limit - one of the reasons that the Richter magnitude scale isn't actually used anymore is that it saturates at large magnitudes. In other words as earthquakes keep getting bigger, the richter scale doesn't really keep up - it under-reports the actual size. So an earthquake with a moment magnitude (see below) of 7.5 might have a comparable richter magnitude, but one with a moment magnitude of 8.5 or 9.0 might still only have a richter magnitude of 7.5 or 8.0.
Moment magnitudes are calculated from the area of fault surface that actually ruptures, how much it moves, and the rigidity of the surrounding rock. A fault can propagate over long horizontal distances (~1000 km in the Sumatran earthquake last year) but only down to a point where the crust is still rigid enough to crack. It's this factor that is the main control on upper earthquake size. Other wise the rupture could just keep spreading down. Then you could have stupidly large earthquakes like a magnitude 15 or 20 that would crack the earth in half. Well, not really.
Part of the reason is the the richter magnitude scale is a local magnitude - it's not actually giving the true energy release of an earthquake, but how bad it feels at some nearby point (corrected for distance). It's also a bit of a hold-over from the early days of seismology in California. When people started to realise that the are earthquakes outside California as well, the richter magnitude scheme fell out of favour.
Seismologists don't use the richter (local) magnitude scale anymore really. The reason it's still often reported in the news is that after alarge earthquake, reporters call up their local governmental Geological Survey for a size. If the seismologists then try to give the size in a modern, more accurate scale, the reporters tend to say "Moment magnitude? No one knows what that is - how big was it on the Richter scale?". So, even though it's generally out of date, it still manages to be somewhat self-perpuating.
Try GMT (Generic Mapping Tools) at http://gmt.soest.hawaii.edu/
Widely used by people in the geophysics field. It's open source, and for the basic linux user it can be a slightly fiddly to get up and running.
It's a collection of command line tools that generate postscript output. You can basically customise everything to your exact tastes, and re-use the scripts if you want consistent graphs and charts.
So what happens if all these time travellers materialise in the same location and time?
42.360007,-071.087870 is very precise - on the order of 10 cm if I've done my (very quick) sums right.
A good way to kill off any future time travellers.
But then, you'd like to think that anyone who's mastered time travel will realise this and appear at some offset location. Otherwise the outcome will surely be a catastrophic rift in the very fabric of space and time itself!
Like when one of the evil consoles uses a multitap attack to throw 4 controllers at once, only for one to bounce off the xbox - "projectiles have no effect".
The stronger than average n64 rumble pak brings back memories as well...
Well, this might not help in terms of the web-browser plugin, but when you launch it directly, holding down the shift key stops all the plugins and extra bits and pieces from loading. (Not sure what they're actually for, but for your everyday, run-of-the-mill .pdf's, disabling them doesn't seem to make any difference).
Speeds up the start up quite nicely.
Surely it would have to be included in the top pc fps releases of last year. At least it gave the illusion of being sightly non-linear at times, unlike the big name games. And it was much easier on the eye, without needing such top-end machine. I'd much rather see an expansion pack for Far Cry than one for Doom 3 or Half-Life 2.
grammar?
The seismic (geophysical) moho is the most common definition (and the one I would use most regularly), but the petrological moho is a valid description as well. I'm informed that it's the
"transition from crustal plagioclase bearing rocks to plagioclase-free olivine and pyroxene rocks".
When you think about it the seismic discontinuity has to be attibutable to some actual physical change in the earth.
I was once on a geological field trip to Cyprus, which has been upthrust a lot, to the point where some old moho is visible at the surface. Having heard this I was hoping for a big outcrop with a nice clear line running through it, so I could stand with a foot on either side of the moho for a picture. Unfortunately it didn't quite look like that.
Not being a geologist I grabbed a few nice looking pieces of rock to take home for paper weights. Alas the cleaning staff at the hotel threw these out, thus stealing my moho. Ah well.
Unlikely. The Mohorovicic (Moho) discontinuity can be described in a few different ways - either where seismic veolocities have a marked discontinuity, or where a noticable chemical/mineralogical change occurs (can't remember what it is, I'm a geophysicist, not a geologist). What it's not is a boundary between a nice solid crust floating on top of "firey liquid mantle". In fact more accurate terms are lithosphere and asthenosphere, rather than crust and mantle, which basically differentiate between rigid, colder material, and warmer, more ductile rock. The top of the mantle is still solid, but becomes increasingly ductile with depth. Various minerals reach melting point as you go down towards the Core-Mantle Boundary, but basically I think you have to get to the outer core before it's all liquid (mostly iron). In terms of energies, the largest nuclear bomb ever detonated was about 55-60 megatonnes (depending on who you ask), in 1961 by the USSR. The energy released by the great 1960 Chilean earthquake (the largest recorded in the last 100 years) was equivalent approximately to a 2000 Mt bomb. So, setting off a nuke at the moho might temporarily create a small spherical cavity which would probably collapse in on itself, and maybe create some melt, but it's doubtful it would come gushing to the surface as a raging plume of "liquid hot magma". Besides, there have been plenty of underground nuclear tests, and none of those have resulted in a humungous volcano. As yet. The USGS site at http://www.usgs.gov/ is probably a good place to find out more.