Listen to the Corecasts about NZ's and Japan's earthquakes.
For a healthy diversion, this stuff is scientific.
12 March 2011
06 March 2011
Earthquakes and the moon: should we worry?
Borrowed from: http://drquigs.com/
I will expand on this section over the next couple days so please stay posted.
I will expand on this section over the next couple days so please stay posted.
Here are a couple points.
1. No one has predicted the recent earthquakes in Canterbury. Vague quotes about dates of 'increased' activity plus or minus several days, without magnitudes, locations, and exact times do not constitute prediction. Consider this: Ken Ring's probability of getting a prediction correct based on perigee/apogee new moon/full moon for 2010 was 63%. That's 230 out of 365 days that fall on some day that he would argue influences earthquake activity. For days that combine several factors of new moon/perigee etc. he missed out on several predictions and NOTHING unusual happened on those days. (i.e. Jan 30th, Feb 14th, Feb 27th, Mar 29, June 14th, Jul 12, Aug 10, and so on for his liberal interpretation of the aftershock sequence). This does not constitute 'prediction'. It is opportunistic and meaningless self promotion during a time of national crisis.
2. Consider your chances of getting a 'prediction' correct given this unscientific defintion of prediction. On average, New Zealand gets ~330 earthquakes of M4-4.9 every year, 26 M5-5.9s / yr, 2 M6-6.9s / yr, and 1 M 7-7.9 every 3 years (see stats on Geonet). If unspecific about magnitude and location, then your chances of 'predicting' an earthquake that is likely to be locally felt and recorded is >90% (based on the simplified method of assuming each earthquake occurs on a different day, which isn't the case, but you get the picture). This of course goes up during the recovery phase following a major earthquake like our 7.1 where the occurrence of large events is high. So far we have had 203 earthquakes > 4 in the Canterbury region close to the 7.1 rupture in the 6 months since Sept 4th. So one's chances of 'prediction' are actually quite high, aren't they?
3. If we had been specifically predicting large earthquakes (M>6) on the faults near Christchurch that ruptured in September 4th and Feb 22nd using the moon over the last several thousand years, we would have been wrong many thousands of times, with a success rate of "zero", even invoking the broad criteria cast by invoking all of the possible moon scenarios listed above.
4. There is no correlation between the largest aftershocks in the Darfield earthquake aftershock sequence and diurnal tides. Some of our largest earthquakes have occurred near high tide and some near low. More statistically robust calculations will appear here in the future.
5. Consider implementation of this 'predictive' strategy. Should we evacuate an area every time the moon is on its closest approach, is full or new, is moving rapidly, is at its maximum declination or is crossing the equator? Imagine the fear and frustration of such an approach, particularly given the unspecified times, locations, and magnitudes of the supposed 'imminent' events. Without a basic understanding of how faults generate earthquakes, where the faults are, at what stage they are at in the seismic cycle, and how they have been affected by prior activity, where should we evacuate and where should we go to? This would require several evacuations a month of 'unspecified areas' to other 'unspecified areas'. This is ludicrous.
*By the way, earthquakes occur when the stress acting on a fault exceeds the yield strength of said fault. It is much easier to break the crust along pre-existing faults than to create new faults in intact bedrock from earthquakes. Consider shards of glass lying in a box, when you push on one side do the shards not slide by each other on pre-existing faults or do they break internally? Sometimes faults are blind (don't reach the surface) and sometimes they break through a younger surface, which gives the appearance of creating a 'new' fault line. This is not almost certainly not a 'new' fault, but rather a previously unidentifed fault beneath the surface.
6. Since humans first looked into the sky and felt the effects of earthquakes, they have wondered if the moon and planets are in some way responsible for major earthquakes. As early as 1897, scientists began to pose hypotheses about moon-earth earthquake connections and test them in honest and rigorous way. After all, the moon still gets earthquakes in the absence of plate tectonics, so perhaps there is some validity to this claim. While some astrologers may feel isolated from the scientific community, this shows a true lack of appreciation for all of those dedicating significant effort to this issue. Many of these findings from studies comparing earthquake catalogues to tides have been published in high quality journals such as Science (e.g., Cochran et al., 2004) and some scientists have argued based on statistical data from global earthquakes for an influence of tides on earthquake activity under certain circumstances, such as beneath the oceans and within active volcanoes. Some scientists have even argued for a small correlation (perhaps an increased earthquake likelihood of 0.5-1%) between smaller, shallower continental earthquakes and 'solid earth tides' (changes in the shape of our planet due to the gravitational pull of the moon) - see http://www.ipgp.fr/~lalmetiv/metivier_etal_epsl2009.pdf. This is peer-reviewed but controversial research; it does not make it so, but it has undergone scrutiny and will continue to do so. This is the scientific process.
Typical earthquake-induced stress changes are about 100 to 1000 times greater than those induced by the tides. Earthquake induced stress increases are also constant, that it until the breaking of the rock alleviates that stress, while tidal stress changes occur in brief intervals related to the moon's elliptical orbit about the earth. There is significant evidence to suggest that the tidal oscillations are too brief and too weak to trigger major earthquakes. So the redistribution of stress related to our 7.1 mainshock and resultant aftershocks is undoubtedly the dominant control on our aftershock sequence, not the moon or planetary alignment. I won't be going anywhere in late March, but I will always be willing to engage in scientific discussion and debate if it appears in an open and honest format.
In the midst of a crisis, however, I feel quite strongly that the time is not yet right.
05 March 2011
Ken Ring can’t predict earthquakes either - by David Winter
Borrowed from http://sciblogs.co.nz/the-atavism/2011/03/01/ken-ring-cant-predict-earthquakes-either/
The New Zealand media have done a remarkably good job of covering the
Christchurch earthquake. TV, newspapers and radio have all struck the
difficult balance between the country’s desperate need to understand
what happened on the 22nd and how people are coping with the right that
each victim the quake has to privacy in such a terrible time. The media
have also shown great restraint with respect to one particular story.
Ken Ring, the astrological weather forecaster, claims to have predicted
the earthquake. I think Ring, with all his calculations and post-hoc
explanations, is the very embodiment of what Richard Feynmann called “cargo cult science”
– someone who does some of the things scientists do, but fails in the
most defining characteristic by not honestly testing his theories
against data. I’ve had a little fun at his expense before,
but, really; as much as it makes me sad that we live in a world in
which Ken Ring can sell his weather forecasts and appear as an “expert”
on anything in the media, the worst thing his almanac does is take money
from people. In the wake the earthquake Ken Ring has done something much more serious. While thousands of people are devastated by a natural disaster, and terrified about what might happen next, Ken Ring claims to have predicted the earthquake of the 22nd and that a much worse one is due in March. So, let’s do what Ring fails to and test his methods against reality.
If Ring had really made an isolated and specific prediction that a destructive earthquake would strike Christchurch on February the 22nd then he might be worth listening to. His claim revolves around this post from his website a little more than a week before the event. Here’s the quotes he’d like you to pick out from that post:Christchurch earthquake. TV, newspapers and radio have all struck the
difficult balance between the country’s desperate need to understand
what happened on the 22nd and how people are coping with the right that
each victim the quake has to privacy in such a terrible time. The media
have also shown great restraint with respect to one particular story.
Ken Ring, the astrological weather forecaster, claims to have predicted
the earthquake. I think Ring, with all his calculations and post-hoc
explanations, is the very embodiment of what Richard Feynmann called “cargo cult science”
– someone who does some of the things scientists do, but fails in the
most defining characteristic by not honestly testing his theories
against data. I’ve had a little fun at his expense before,
but, really; as much as it makes me sad that we live in a world in
which Ken Ring can sell his weather forecasts and appear as an “expert”
on anything in the media, the worst thing his almanac does is take money
from people. In the wake the earthquake Ken Ring has done something much more serious. While thousands of people are devastated by a natural disaster, and terrified about what might happen next, Ken Ring claims to have predicted the earthquake of the 22nd and that a much worse one is due in March. So, let’s do what Ring fails to and test his methods against reality.
The window of 15-25 February should be potent for all types of tidal action, not only kingtides but cyclone development and ground movement.You might quibble that the Christchurch quake, at magnitude 6.3, was about 5 times less powerful than the M7 event he’d predicted – but I don’t think anyone in Christchurch wants to argue about how strong their quake was. On the face it, it really does look like an amazing coincidence: Ring predicted a quake and it happened. But there is more to it than that, I’ve been through his site and Ring has also predicted earthquakes for, at least, the 24th of September, the 1st and 7th of October the first week in November, the 20th to the 27th of January, the 1st to the 5th and 19th to the 25th of March and the 17th of April. In fact, in one post, giving him the +/- one day he needs in order to claim he predicted the February 22nd quake , he paints more than half of the time between the start of January and the end of March as earthquake risk:
Over the next 10 days a 7+ earthquake somewhere is very likely
You can add a fair few false negatives to those false positives. In October he claimed the aftershock sequence would die down, missing the major rumble on boxing day and several times he declared that it was unlikely Christchurch would be face another major quake (tragically wrong).
Thanks to the way our brains work, we generally struggle to evaluate theories of causation and claims of prediction fairly. We are too impressed by occasional “hits” and tend to forget the many “misses” which outweigh them. If we want to be rigorous, how should we react to hearing about Ring’s “hit” given the litany of “misses” I list above? As it happens there is a theorem for that. Bayes theorem is one of the most important little pieces of maths going around, because it tells us how to update our beliefs about a given question in light of new evidence, and that’s exactly what we should be trying to do if we want to lead a skeptical life. It is maths, but it’s not too scary. I’m the sort of person that loses contact with scientific papers as soon as ‘Σ’s and ‘∫’s start turning up, so you know if I’m writing this , you can follow it. Before we start, we need to define a couple of terms. Let’s call P(KR) the probability Ken Ring can predict earthquakes and P(Prediction) the probability that Ken Ring would have successfully predicted this earthquake. From that we want to calculate how probable the claim “Ken Ring can predict earthquakes” is given his successful prediction, well call that P(KR|Prediction). Once we have those defined it’s just a little 3rd form algebra:
| P(KR|Prediction) = | P(Prediction|KR) * P(KR) |
| P(Prediction) |
Now, when we put the numbers in like so…
| P(KR|Prediction) = | 0.9 * 0.5 |
| 0.6 |
Skeptics are often accused of being closed minded for sticking to scientific orthodoxy in the light some piece of evidence or other: “If you would just let this evidence stand by itself you’d see my theory is true!”. Assessing any evidence by itself, without our background of knowledge on a topic, is not being open minded – it’s being willfully ignorant. When we want to compare one theory to another we should use all the evidence available to us, and that includes what we know about how the world works. Ring thinks earthquakes happen when the moon makes its closest approach to the earth (called perigee) and around full and new moons. This next sentence really pains me, but here goes. His theory is not 100% lunacy. The phases of the moon have no effect on the earth, but the position of the moon in its orbit just might. As every schoolchild knows, the moon exerts a tidal force on the planet and there really are “land tides”, tiny swells and lulls in the crust of the earth analogous to the ocean’s tides, that ebb and flow through the day. It’s just possible that a fault that has been loading up with pressure for hundreds of years is more likely to give way when then moon is close and the tidal forces are stronger. But think about that for even a second and the problem becomes clear. Even if the moon is sometimes the straw that breaks the camels back at a particular fault, you couldn’t use the moon to predict an earthquake unless you already new a fault was about to go, i.e., the moon could only predict earthquakes when you could already predict an earthquake!
Ken Ring get’s a bit touchy about scientists dismissing his theories out of hand, so let’s look at some data. I actually asked Ring for some help with this, but he is yet to answer my email. Luckily, since the September 4th earthquake Paul Nicholls from Canterbury University has been plotting the intensity of the aftershock sequence. He’s also plotted the two lunar cycles Ring thinks are responsible for the strength of earthquakes: the lunar distance and the moon’s phase. In many ways, this is the data-set in which we are most likely to find support for Ring’s ideas. We know for a fact that the faults around the Canterbury plains are going to be under stress while the land sorts itself out after the upheaval in September. If the moon really was pushing already loaded faults past their breaking point we’d expect to see it in this data. Usually the most important statistical test you can perform on a data-set is having a look at it. This is Paul’s plot from last night, the slimmer of the two waves on the top represents moons orbit (troughs are perigee, the point Ring thinks is most dangerous) and the larger is the moon’s phase (the troughs are new moons).
If you can see any correlation between either of the lunar cycles you’re doing a lot better than me. I decided to dig a littler further, and plot the intensity of each day’s activity against each of the lunar cycles. First the phases of the moon. Remember, Ring thinks new and full moons are the most dangerous, so we expect a curved relationship higher at either end of the x-axis. We find no such thing (in fact, if anything, it’s more dangerous between the new and the full moon):
How about the distance between the earth and the moon? This is the one that makes just a little scientific sense:
This time the relationship at least goes the right way, the quakes seem to be, on average, more powerful when the moon is close. In fact, when you put this data into a model that factors in the general tailing off in earthquake activity following the initial quake, the distance between the moon and the earth is a statistically significant variable with regard to the energy released. And there lies an incredibly important point. “Statistically significant” means unlikely to happen if the null hypothesis (in this case “the moon doesn’t effect earthquakes at all”) was true, it doesn’t mean the result is “powerful”, “meaningful”, or even “capable of explaining a great deal of the variation in the data”. As is often the case, we didn’t really believe our null hypothesis to start with, so it’s no surprise a large data-set found a significant relationship. But the actual effect of the moon is tiny, it explains about 2% of the variation in the data. The feebleness of the moon as a predictor is obvious when you look at the graph – there are plenty of days when the moon is close and there was not much energy released and, equally, there’s a whole lot of days when the moon was far away and there were still magnitude 5 quakes. The moon might well be having an effect on intensity of earthquakes from day to day, but if it can barely explain any of the variance in this data-set, one that was almost designed to test Ring’s theories in the best light, how could it predict an earthquake? It can’t.
Let’s get back to our calculation, last time we started with P(KR) at 50%. I hope you’ll agree, having seen the data, that Ken Ring’s methods are not the least bit plausible. I going to be outrageously generous and say there’s a one in one thousand chance that he can predict earthquakes, so let’s plug that into Bayes Theorem, remembering to update P(Prediction) for this new value too:
| P(KR|Prediction) = | P(Prediction|KR) * P(KR) |
| P(Prediction) | |
| = | 0.9 *0.001 |
| (0.9*0.001)+(0.3*0.999) |
The people of Christchurch desperately need information. In the next few weeks they want to know if they’ll have to face the terror of last Tuesday again and once they city has pulled itself back up they’ll want to understand the future risks for the city. In a climate of such desperation people have a duty to provide only verifiable information and to explain that information’s limitations. That’s exactly what scientist from GNS and Canterbury University have done when they’ve spoken to the media. Ken Ring, who lambasted GNS for scaring people with a “knee jerk” comment that a magnitude 6 aftershock could be expected after the September earth quake, has not lived up to that duty and I really hope no one takes him seriously.
01 March 2011
Hooray for the Wizard
Wizard gives his take on the Earthquake
Click the link above.
The Christchurch Wizard dishes out some sensible advice to his fellow Cantabrians - including not to listen to Ken Ring and his 'crackpot lunatic' theories.
At last, the media, and scientists, catch up
Scientists back John Campbell
Copied directly from source, click link above to see source:
Copied directly from source, click link above to see source:
Scientists back Campbell in Moon Man quake prediction row
Last night, self-styled commentator Ken Ring claimed he had correctly predicted the Christchurch earthquake of February 22.
And he told TV3's John Campbell that another quake will strike on March 20.
Dr Mark Quigley, Senior Lecturer in Active Tectonics and Geomorphology at Canterbury University:
No one has predicted the recent earthquakes in Canterbury.
Vague quotes about dates of 'increased' activity plus or minus several days, without magnitudes, locations, and exact times do not constitute prediction.
This is opportunistic and meaningless self promotion during a time of national crisis.
Consider implementation of this 'predictive' strategy. Should we evacuate an area every time the moon is on its closest approach, is full, or new, or is moving rapidly?
Imagine the fear and frustration of such an approach, particularly given the unspecified times, locations, and magnitudes of the supposed 'imminent' events.
Without a basic understanding of how faults generate earthquakes, where the faults are, at what stage they are at in the seismic cycle, and how they have been affected by prior activity, where should we evacuate and where should we go to? This would require several evacuations a month of 'unspecified areas' to other 'unspecified areas'. This is ludicrous.
Since humans first looked into the sky and felt the effects of earthquakes, they have wondered if the moon and planets are in some way responsible for major earthquakes. As early as 1897, scientists began to pose hypotheses about moon-earth earthquake connections and test them in honest and rigorous way. After all, the moon still gets earthquakes in the absence of plate tectonics, so perhaps there is some validity to this claim.
Many of these findings from studies comparing earthquake catalogues to tides have been published in high quality journals such as Science (e.g., Cochran et al., 2004) and some scientists have argued based on statistical data from global earthquakes for an influence of tides on earthquake activity under certain circumstances, such as beneath the oceans and within active volcanoes. Some scientists have even argued for a small correlation (perhaps an increased earthquake likelihood of 0.5-1%) between smaller, shallower continental earthquakes and 'solid earth tides' (changes in the shape of our planet due to the gravitational pull of the moon). This is peer-reviewed but controversial research; it does not make it so, but it has undergone scrutiny and will continue to do so. This is the scientific process.
Typical earthquake-induced stress changes are about 100 to 1000 times greater than those induced by the tides.
Earthquake induced stress increases are also constant, that it until the breaking of the rock alleviates that stress, while tidal stress changes occur in brief intervals related to the moon's elliptical orbit about the earth. There is significant evidence to suggest that the tidal oscillations are too brief and too weak to trigger major earthquakes. So the redistribution of stress related to our 7.1 mainshock and resultant aftershocks is undoubtedly the dominant control on our aftershock sequence, not the moon or planetary alignment.
I won't be going anywhere in late March.
Matt Gerstenberger - Geological Hazard Modeller; David Rhoades - Geophysical Statistician, both of GNS Science
Validation of an earthquake prediction methodology is a notoriously tricky undertaking.
Unfortunately it is not as simple as taking a single prediction, whatever that may be, and comparing it to what occurred.
It may be that a particular method has some bits of useful information in it, enough that it may get the prediction correct one out of every five times, or one out of every 100 times, or maybe, one out of every 10,000 times.
For a prediction to be useful it must be understood where in this range the method falls. If it is correct 1-in-10,000 times, or is wrong much more often than it is correct, it will be of little help and a random guess will do just as well.
A significant body of research has been directed at the idea that earthquakes may be predictable based on tidal information. While some of the studies have shown that there may be some level of correlation between the occurrence of earthquakes and tides, the correlation is low enough so that a prediction based on it would be correct only a small proportion of the time and would be wrong much more often than it is correct.
Dr John Beavan, Crustal Dynamics Geophysicist at GNS Science:
As Mark [Quigley] points out, vague assertions of increased earthquake likelihood are not useful.
But we should not be too dismissive of earthquake/tidal links in certain circumstances. (I'm referring to the stresses induced in the solid earth by the tides due to the moon and sun - (anyone who suggests that the planets have an influence is talking nonsense). As well as the tides induced directly in the solid earth, the ocean tides load the Earth and cause additional stresses, particularly close to coastlines.
We are quite happy these days to allow that Coulomb stress changes on the order of 1 bar due to a major earthquake can influence the locations of aftershocks, and can act as a trigger for future earthquakes adjacent to the original quake.
Though I emphasise that we can say nothing about the specific timing of such earthquakes.
Tidal stresses are only an order of magnitude or so lower than this, so it is reasonable to suggest that tidal stresses could have an influence on faults that are already stressed close to their breaking point.
Many studies were conducted and published in the 1970s and 1980s that looked for a connection between earth tides and earthquakes. These almost uniformly gave negative results, or results that were perhaps positive but very close to the noise level.
One could hypothesize that the Earth's crust in the Canterbury region has been so stressed by the September quake that the tiny stresses induced by the tides could have an influence on the times of aftershock occurrence. This is a testable hypothesis, as it could be applied to all the aftershocks recorded so far to see if the effect shows up in the timing of those aftershocks.
Dr Marc Wilson, Senior Lecturer in Psychology at Victoria University:
We have something of a pre-disposition to try to find explanations for things that happen, and much more so for bad things, than good.
Why? Bad things can kill us, where good things (no matter how good) have a much less final benefit!
This is one of the reasons news media tend to focus on bad stuff - because that's what we want to know about, so we can seek to prevent it in the future. We are really quite well adapted for making connections between apparently unrelated things that might help us avoid getting, in evolutionary terms, eaten.
The downside is that sometimes we make the wrong connections, but hey, wouldn't it be worse to GET eaten than make a fool of yourself crying wolf?
Of course, there's not much we can actually do about things that we REALLY don't have any control over. This makes most people very uncomfortable (and some more than others) so we look for ways to deal with that discomfort. One way to do this is to find 'causes' that we CAN point to, to explain bad stuff. This is one of the reasons that conspiracy theories develop - the fact that stuff sometimes just happens is less comfortable than being able to point to some shadowy evil conspiracy!
So, this explains why people try to predict the future (or secure the services of those, ahem, practitioners that purport to). We've done it forever, and will continue to do so. It helps us from living with the uncertainty and stress that comes from worrying about when things will happen. Where it can be counterproductive, though, is when the security we get from 'knowing' that nothing bad is going to happen prevents us from taking reasonable precautions or makes us complacent.
"My personal opinion? Find comfort where you can get it, BUT... I'd trust science over most sources, and I'd still make sure that I do those things that I CAN control (earthquake proofing those things I can, making sure my earthquake kit is well-stocked, etc.)
And he told TV3's John Campbell that another quake will strike on March 20.
Mr Ring is best-known for his weather predictions, based on lunar cycles.
And even though his track record in that department has been comprehensively debunked, he fronted on Campbell Live with his theories, and new prediction, about the Canterbury disaster.
Some will find Mr Ring's foray into pseudo-mystical seismology offensive.
Certainly, Mr Campbell ran out of patience - and, some said, common courtesy - as he interviewed Mr Ring.
The adverserial nature of the interview saw a public backlash in favour of Mr Ring, who enjoys majority support according to some online polls (whose self-selecting nature is, admittedly, about as scientifically valid as Mr Ring's theories).
The Science Media Centre has reacted to the brouhaha not by critiquing Mr Campbell's etiquette, but by asking experts to give their evaluation of Mr Ring's lunatic approach.
Here some excerpts (warning, if you prefer talkback philosophy to science, stop reading now):
And even though his track record in that department has been comprehensively debunked, he fronted on Campbell Live with his theories, and new prediction, about the Canterbury disaster.
Some will find Mr Ring's foray into pseudo-mystical seismology offensive.
Certainly, Mr Campbell ran out of patience - and, some said, common courtesy - as he interviewed Mr Ring.
The adverserial nature of the interview saw a public backlash in favour of Mr Ring, who enjoys majority support according to some online polls (whose self-selecting nature is, admittedly, about as scientifically valid as Mr Ring's theories).
The Science Media Centre has reacted to the brouhaha not by critiquing Mr Campbell's etiquette, but by asking experts to give their evaluation of Mr Ring's lunatic approach.
Here some excerpts (warning, if you prefer talkback philosophy to science, stop reading now):
Dr Mark Quigley, Senior Lecturer in Active Tectonics and Geomorphology at Canterbury University:
No one has predicted the recent earthquakes in Canterbury.
Vague quotes about dates of 'increased' activity plus or minus several days, without magnitudes, locations, and exact times do not constitute prediction.
This is opportunistic and meaningless self promotion during a time of national crisis.
Consider implementation of this 'predictive' strategy. Should we evacuate an area every time the moon is on its closest approach, is full, or new, or is moving rapidly?
Imagine the fear and frustration of such an approach, particularly given the unspecified times, locations, and magnitudes of the supposed 'imminent' events.
Without a basic understanding of how faults generate earthquakes, where the faults are, at what stage they are at in the seismic cycle, and how they have been affected by prior activity, where should we evacuate and where should we go to? This would require several evacuations a month of 'unspecified areas' to other 'unspecified areas'. This is ludicrous.
Since humans first looked into the sky and felt the effects of earthquakes, they have wondered if the moon and planets are in some way responsible for major earthquakes. As early as 1897, scientists began to pose hypotheses about moon-earth earthquake connections and test them in honest and rigorous way. After all, the moon still gets earthquakes in the absence of plate tectonics, so perhaps there is some validity to this claim.
Many of these findings from studies comparing earthquake catalogues to tides have been published in high quality journals such as Science (e.g., Cochran et al., 2004) and some scientists have argued based on statistical data from global earthquakes for an influence of tides on earthquake activity under certain circumstances, such as beneath the oceans and within active volcanoes. Some scientists have even argued for a small correlation (perhaps an increased earthquake likelihood of 0.5-1%) between smaller, shallower continental earthquakes and 'solid earth tides' (changes in the shape of our planet due to the gravitational pull of the moon). This is peer-reviewed but controversial research; it does not make it so, but it has undergone scrutiny and will continue to do so. This is the scientific process.
Typical earthquake-induced stress changes are about 100 to 1000 times greater than those induced by the tides.
Earthquake induced stress increases are also constant, that it until the breaking of the rock alleviates that stress, while tidal stress changes occur in brief intervals related to the moon's elliptical orbit about the earth. There is significant evidence to suggest that the tidal oscillations are too brief and too weak to trigger major earthquakes. So the redistribution of stress related to our 7.1 mainshock and resultant aftershocks is undoubtedly the dominant control on our aftershock sequence, not the moon or planetary alignment.
I won't be going anywhere in late March.
Matt Gerstenberger - Geological Hazard Modeller; David Rhoades - Geophysical Statistician, both of GNS Science
Validation of an earthquake prediction methodology is a notoriously tricky undertaking.
Unfortunately it is not as simple as taking a single prediction, whatever that may be, and comparing it to what occurred.
It may be that a particular method has some bits of useful information in it, enough that it may get the prediction correct one out of every five times, or one out of every 100 times, or maybe, one out of every 10,000 times.
For a prediction to be useful it must be understood where in this range the method falls. If it is correct 1-in-10,000 times, or is wrong much more often than it is correct, it will be of little help and a random guess will do just as well.
A significant body of research has been directed at the idea that earthquakes may be predictable based on tidal information. While some of the studies have shown that there may be some level of correlation between the occurrence of earthquakes and tides, the correlation is low enough so that a prediction based on it would be correct only a small proportion of the time and would be wrong much more often than it is correct.
Dr John Beavan, Crustal Dynamics Geophysicist at GNS Science:
As Mark [Quigley] points out, vague assertions of increased earthquake likelihood are not useful.
But we should not be too dismissive of earthquake/tidal links in certain circumstances. (I'm referring to the stresses induced in the solid earth by the tides due to the moon and sun - (anyone who suggests that the planets have an influence is talking nonsense). As well as the tides induced directly in the solid earth, the ocean tides load the Earth and cause additional stresses, particularly close to coastlines.
We are quite happy these days to allow that Coulomb stress changes on the order of 1 bar due to a major earthquake can influence the locations of aftershocks, and can act as a trigger for future earthquakes adjacent to the original quake.
Though I emphasise that we can say nothing about the specific timing of such earthquakes.
Tidal stresses are only an order of magnitude or so lower than this, so it is reasonable to suggest that tidal stresses could have an influence on faults that are already stressed close to their breaking point.
Many studies were conducted and published in the 1970s and 1980s that looked for a connection between earth tides and earthquakes. These almost uniformly gave negative results, or results that were perhaps positive but very close to the noise level.
One could hypothesize that the Earth's crust in the Canterbury region has been so stressed by the September quake that the tiny stresses induced by the tides could have an influence on the times of aftershock occurrence. This is a testable hypothesis, as it could be applied to all the aftershocks recorded so far to see if the effect shows up in the timing of those aftershocks.
Dr Marc Wilson, Senior Lecturer in Psychology at Victoria University:
We have something of a pre-disposition to try to find explanations for things that happen, and much more so for bad things, than good.
Why? Bad things can kill us, where good things (no matter how good) have a much less final benefit!
This is one of the reasons news media tend to focus on bad stuff - because that's what we want to know about, so we can seek to prevent it in the future. We are really quite well adapted for making connections between apparently unrelated things that might help us avoid getting, in evolutionary terms, eaten.
The downside is that sometimes we make the wrong connections, but hey, wouldn't it be worse to GET eaten than make a fool of yourself crying wolf?
Of course, there's not much we can actually do about things that we REALLY don't have any control over. This makes most people very uncomfortable (and some more than others) so we look for ways to deal with that discomfort. One way to do this is to find 'causes' that we CAN point to, to explain bad stuff. This is one of the reasons that conspiracy theories develop - the fact that stuff sometimes just happens is less comfortable than being able to point to some shadowy evil conspiracy!
So, this explains why people try to predict the future (or secure the services of those, ahem, practitioners that purport to). We've done it forever, and will continue to do so. It helps us from living with the uncertainty and stress that comes from worrying about when things will happen. Where it can be counterproductive, though, is when the security we get from 'knowing' that nothing bad is going to happen prevents us from taking reasonable precautions or makes us complacent.
"My personal opinion? Find comfort where you can get it, BUT... I'd trust science over most sources, and I'd still make sure that I do those things that I CAN control (earthquake proofing those things I can, making sure my earthquake kit is well-stocked, etc.)
28 February 2011
Ken Ring Moon Man Wrong
Is Ken Ring saying, or is he not, that everyone should get out of Canterbury on 20 March? Why don't any scientists agree with him? If there's no quake, should we say he was wrong? He predicts so many that he gets a few right (the odds are he'll get about 30% right, as he's predicting so many); beforehand he says they are not predictions, merely opinions. After the fact, if a quake occurs, he claims he predicted it; if it does not, he falls back on saying they were just opinions. If we left town every time he said there'd be a quake we'd only be in town three out of four weeks a month.
Read the quoted authors below; they explain it way better than I ever could. Then forward this on to your friends.
If you want to go straight to the sources, here they are:
Sci Blogs
Dr Mark Quigley
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Disclaimer: I have only copied and pasted the text below in case if I just posted the links, people couldn't be bothered clicking on them. If you are the author of either and are offended, I will remove the quoted text. I just want people to read what you've written.
Read the quoted authors below; they explain it way better than I ever could. Then forward this on to your friends.
If you want to go straight to the sources, here they are:
Sci Blogs
Dr Mark Quigley
---
Disclaimer: I have only copied and pasted the text below in case if I just posted the links, people couldn't be bothered clicking on them. If you are the author of either and are offended, I will remove the quoted text. I just want people to read what you've written.
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