Magnitude 5.6 Earthquake in Silicon Valley
 

There was a magnitude 5.6 earthquake last night on the Calaveras fault in the East San Jose foothills, epicenter about 10-15 miles east of my apartment. I was just settling in to watch [i]It's the Great Pumpkin, Charlie Brown[/i] [which came on at 8pm], and a few minutes in, it felt as if my upstairs neighbor [a nice but somewhat heavy-set fellow] had started stomping around heavily ... times 50. That initial rumbling is apparently due to the [url=http://en.wikipedia.org/wiki/Seismic_wave]p-wave[/url] component of the shock, which travels faster than the more-rolling s-wave, which in my case arrived a few seconds later. I quickly went out onto the back patio - not from fright, since I've experienced decent-sized quakes before [though this was the strongest we've had since I moved to California in 1999 - strongest in these parts since the '89 Loma Prieta quake, in fact] and it was all over in about 10 seconds - but rather to watch the water slosh back and forth in the community pool. The last sensible quake we had here a couple years ago was a 4.5 and caused a sloshing amplitude of just 2-3 inches, last night's was closer to a foot, so I guessed "about five-and-a-half." Pretty close!

Using the well-known rule of thumb [cf. the above Wikipedia page] for earthquake shock arrival times:
[quote]A quick way to determine the distance from a location to the origin of a seismic wave less than 200 km away is to take the difference in arrival time of the P wave and the S wave in seconds and multiply by 8 kilometers per second[/quote]
... and estimating roughly 2 seconds delta-T gives 16km, which is again pretty close to the actual distance 'twixt my abode and the reported epicenter. Shaky scientific reasoning, to be sure. ;)

[QUOTE=ewmayer;117455]There was a magnitude 5.6 earthquake last night on the Calaveras fault in the East San Jose foothills, epicenter about 10-15 miles east of my apartment. I was just settling in to watch [i]It's the Great Pumpkin, Charlie Brown[/i] [which came on at 8pm], and a few minutes in, it felt as if my upstairs neighbor [a nice but somewhat heavy-set fellow] had started stomping around heavily ... times 50. That initial rumbling is apparently due to the [url=http://en.wikipedia.org/wiki/Seismic_wave]p-wave[/url] component of the shock, which travels faster than the more-rolling s-wave, which in my case arrived a few seconds later. I quickly went out onto the back patio - not from fright, since I've experienced decent-sized quakes before [though this was the strongest we've had since I moved to California in 1999 - strongest in these parts since the '89 Loma Prieta quake, in fact] and it was all over in about 10 seconds - but rather to watch the water slosh back and forth in the community pool. The last sensible quake we had here a couple years ago was a 4.5 and caused a sloshing amplitude of just 2-3 inches, last night's was closer to a foot, so I guessed "about five-and-a-half." Pretty close!

Using the well-known rule of thumb [cf. the above Wikipedia page] for earthquake shock arrival times:

... and estimating roughly 2 seconds delta-T gives 16km, which is again pretty close to the actual distance 'twixt my abode and the reported epicenter. Shaky scientific reasoning, to be sure. ;)[/QUOTE]

Fun times :D

I was there for the '89 quake, I remember being a bit freaked out by the main quake, but kind of enjoying the aftershocks.

[quote=ewmayer;117455]...the community pool. The last sensible quake we had here a couple years ago was a 4.5 and caused a sloshing amplitude of just 2-3 inches, last night's was closer to a foot, so I guessed "about five-and-a-half." Pretty close!

Shaky scientific reasoning, to be sure. ;)[/quote]
:lol:
Yes. Without knowing the distance of the 4.5 quake or the depth
of either, even knowledge of the relationship between sloshing
amplitude and strength of the quake makes "one more on the
Richter scale" a lucky guess.
I imagine direction relative to fault line comes into play as well.
I think Sri Lanka copped the Boxing day tsunami off Sumatra much
worse than Bangla Desh did was down to the direction being
perpendicular to the fault line.

[QUOTE=davieddy;117468]:lol:
Yes. Without knowing the distance of the 4.5 quake or the depth
of either, even knowledge of the relationship between sloshing
amplitude and strength of the quake makes "one more on the
Richter scale" a lucky guess.[/QUOTE]

Yes, any such extrapolation was only justified if yesterday's quake was at a similar distance as the earlier 4.5 - which turned out to be the case although I couldn't have known it at the time, obviously. OTOH the assumption of yesterday's being stronger based on it feeling stronger at my locale was not totally unjustified, since for a 4.5-or-weaker to feel stronger, we would have had to have been essentially right atop the rupture site, which is statistically improbable. [Though not impossible, since the San Andreas fault runs through the coastal hills just a few miles W of where I live. The Hayward and Calaveras faults run roughly || to the SAF, but are on the opposite side of the valley.]

"It's 'one stronger', isn't it?" -- Nigel Tufnel, famous geologist.

Anyway, admit it: you're just jealous of my pulling-numbers-out-of-my-butt quake postdiction skills. ;)

Yeah, I felt the earthquake.

Gee :>

And I was kinda freaked out when a 5.8 hit Roermond in 1992 (which is about 150 km from where I live, so pretty much 3.0 was left at where I live).
Of course, that one hit in the middle of the night, and it was my first earthquake. (And the last one I hope)

That one was at a 17km depth, and didn't do too much damage.

Isn't it so that the whole area you live in is bound to have a very major earthquake in the near future?

[QUOTE=michaf;117485]Isn't it so that the whole area you live in is bound to have a very major earthquake in the near future?[/QUOTE]

Not sure what the latest doomsday predictions of the USGS are, but historically the San Andreas or one of its branches has a major rupture [magnitude ~7] every century or so. I expect it's likely we'll have another 6+ in the next 20 years.

However, the *really* big quakes along the US west coast, the magnitude > 8 ones, are in an area whose danger many people don't know about: The pacific northwest, in particular the population centers of Seattle and Vancouver. The problem is that these monster quakes are infrequent enough [last one was in [url=http://en.wikipedia.org/wiki/Cascadia_Earthquake]1700[/url], it was recently confirmed that the Japanese have detailed historical records of a massive tsunami caused by that one] that there is no modern-historical record. The whole Seattle and Vancouver area was built up in blissful ignorance of these massive recurring quakes. There have been such quakes in the general area [viewed at large] in living memory [in particular the 1964 alaska quake, magnitude ~9], but none has happened to be near a major population center.

The richter scale is ~ log[sub]10[/sub](amplitude) but the energy rises a factor of 1000 when richter scale rises 2 values, so the Richter scale is ~ log[sub]sqrt(1000)[/sub](energy) ~ log[sub]32[/sub](energy).

[URL="http://en.wikipedia.org/wiki/Richter_magnitude_scale"]http://en.wikipedia.org/wiki/Richter_magnitude_scale[/URL]

[URL="http://science.howstuffworks.com/earthquake5.htm"]http://science.howstuffworks.com/earthquake5.htm[/URL]

[URL="http://www.ux1.eiu.edu/~cfjps/1300/magnitude.html"]http://www.ux1.eiu.edu/~cfjps/1300/magnitude.html[/URL]

[quote=ATH;117532]The richter scale is ~ log[sub]10[/sub](amplitude) but the energy rises a factor of 1000 when richter scale rises 2 values, so the Richter scale is ~ log[sub]sqrt(1000)[/sub](energy) ~ log[sub]32[/sub](energy).

[/quote]
Not sure if you glimpsed my post (which I deleted swiftly) but it
was on this topic.

In my book, "energy" is proportional to amplitude^2 so when log[sub]10[/sub](amplitude) rises by 2, energy rises by a factor of 10,000.

Since "decibel" refers to log(energy) why didn't Richter conform
to this previously established convention?

David

[quote=ewmayer;117471]
"It's 'one stronger', isn't it?" -- Nigel Tufnel, famous geologist.
[/quote]
I think this answers my last post.


[quote]
Anyway, admit it: you're just jealous of my pulling-numbers-out-of-my-butt quake postdiction skills. ;)[/quote]

I'm quite proficient in this respect myself:lol:

BTW If Richter meant log (intensity) then an increase of sloshing amplitude
by a factor of SQR(10) would be "one stronger".

[QUOTE=davieddy;117534]Since "decibel" refers to log(energy) why didn't Richter conform to this previously established convention?[/QUOTE]

IIRC decibel [as applied to acoustics] multiplies the sound energy [actually the power-per-sq-meter, I believe, since the total energy and power depend on the areal extent of the acoustic front] by a factor of 10, so that scale also has an arbitrary constant factor mixed in. I don't think there is a "standard" convention in this respect - for an example of yet-another-and-completely-different logarithmic multiplier, look at astronomical magnitudes.

In one way, expressing earthquake magnitude as log10(amplitude) actually makes prefect sense, since the shaking you feel is proportional to wave amplitude, not total-energy-release. But again, it all comes down to picking one's arbitrary logarithmic multiplier.

[quote=ewmayer;117554]IIRC decibel [as applied to acoustics] multiplies the sound energy [actually the power-per-sq-meter, I believe, since the total energy and power depend on the areal extent of the acoustic front] by a factor of 10, so that scale also has an arbitrary constant factor mixed in.[/quote]
The factor of 10 here isn't "arbitrary". It follows from the bog standard
definition of the prefix "deci".

[QUOTE=davieddy;117562]The factor of 10 here isn't "arbitrary". It follows from the bog standard definition of the prefix "deci".[/QUOTE]

The choice of *scaling* is arbitrary - but as you note, once one has chosen a scaling, the resulting unit *naming* is not. I was referring to the former, not the latter.

I still think log base 32 is a load of bollocks.

[QUOTE=davieddy;117571]I still think log base 32 is a load of bollocks.[/QUOTE]

Decimal fascist. :mad:

[quote=ATH;117532]The richter scale is ~ log[sub]10[/sub](amplitude) but the energy rises a factor of 1000 when richter scale rises 2 values, so the Richter scale is ~ log[sub]sqrt(1000)[/sub](energy) ~ log[sub]32[/sub](energy).

[/quote]

Is "Richter" case sensitive here?
I guess now that the factor of 1000 is an empirical observation.
I am having difficulty squaring this with intensity(W/m^2) being
proportional to amplitude^2.

David

[quote=ewmayer;117554]
In one way, expressing earthquake magnitude as log10(amplitude) actually makes prefect sense, since the shaking you feel is proportional to wave amplitude, not total-energy-release. But again, it all comes down to picking one's arbitrary logarithmic multiplier.[/quote]

One big thing in favour of using intensity(W/m^2) instead of
amplitude is conservation of energy.

[quote]
Originally Posted by [B]ewmayer[/B] [URL="http://www.mersenneforum.org/showthread.php?p=117554#post117554"][IMG]http://www.mersenneforum.org/images/buttons/viewpost.gif[/IMG][/URL]
[I]IIRC decibel [as applied to acoustics] multiplies the sound energy [actually the power-per-sq-meter, I believe, since the total energy and power depend on the areal extent of the acoustic front] by a factor of 10, so that scale also has an arbitrary constant factor mixed in.[/I]
[/quote][quote=davieddy;117562]The factor of 10 here isn't "arbitrary". It follows from the bog standard
definition of the prefix "deci".[/quote]
deci=10^-1, deca (or deka) = 10^1
IIRC, bels were inconveniently large in some situations, so dBs were used. Makes sense considering it was originally used ([I]inter alia[/I]) to measure S/N on standard telephone lines. Also the use of dB implies a ratio, rather than an absolute value (of course, sometimes the baseline reference value is 0).

No, the baseline reference can't be 0... sheesh. Too much typing, not enough thinking.

[QUOTE=davieddy;117652]One big thing in favour of using intensity(W/m^2) instead of amplitude is conservation of energy.[/QUOTE]

Depends on one's POV - personally, during an earthquake, I'm more concerned about whether my house is going to fall down on top of me than whether total seismic energy is being conserved - but I'm probably just weird that way.

OTOH geologists obviously do care very much about total energy release and where that energy winds up going.

The folks at the USGS did say that this latest quake along the normally-quiete Calaveras fault increases the chance of a major quake along the nearby Hayward fault, due to strain displacement - but only by a small percentage, relative to the previously estimated ~25% odds of a major quake along the Hayward in the next 25 years:

[url]http://seismo.berkeley.edu/hayward/probabilities.html[/url]

The above answers michaf's earlier question: yes, it seems likely we're gonna have another big one in the next few decades:
[quote]A new probability report was released in 2003 by Working Group '02. This report concludes that the Bay Area faces a 62% probability of an M6.7 or larger earthquake over the next 30 years (2003-2032).[/quote]

===

[i]Aside:
While I don't question the overall probability, I am skeptical of the claimed uncertainty of 10%, which seems ludicrously low to me. Obviously it's possible that no such quake occurs in the given time frame, which instantly gives a much-larger -62% negative uncertainty, and similarly if such a quake does occur, we get a +38% uncertainty. Maybe I'm misunderstanding what they mean by "+-10%", it's probably something like the one-sigma confidence interval of their computer models - but as with weather prediction, that ignores "the uncertainty in the uncertainty," i.e. there are many assumptions built in such complex-systems models, if one proves significantly wrong, all your earlier uncertainty estimates are right out the window.[/i]

[quote=ewmayer;117471]
Anyway, admit it: you're just jealous of my pulling-numbers-out-of-my-butt quake postdiction skills. ;)[/quote]

Could you address these skills to the "fact" that a quake
with 32 times greater energy release produces waves with
a peak amplitude 10 times greater (power 100 times greater)?

The word "coupling" comes to mind.

PS Brainwave(?): isn't power freqency dependent as well?
If so perhaps bigger quakes have lower frequency.
Yes intensity proportional to density*wavespeed*(amplitude*frequency)^2

[QUOTE=ewmayer;117664]
[i]Aside:
While I don't question the overall probability, I am skeptical of the claimed uncertainty of 10%, which seems ludicrously low to me. Obviously it's possible that no such quake occurs in the given time frame, which instantly gives a much-larger -62% negative uncertainty, and similarly if such a quake does occur, we get a +38% uncertainty. Maybe I'm misunderstanding what they mean by "+-10%", it's probably something like the one-sigma confidence interval of their computer models - but as with weather prediction, that ignores "the uncertainty in the uncertainty," i.e. there are many assumptions built in such complex-systems models, if one proves significantly wrong, all your earlier uncertainty estimates are right out the window.[/i][/QUOTE]

If the quake doesn't fall into the 30 year time-frame, the probability could of course still have been 62%. The time-frame just happend to be entirely in the other 38%.

But still, it's a very major chance anyway you look at it. I'm glad to live in Holland, albeit much of that is below sealevel. (Flooding is the only major disaster that can strike Holland afaik)

[QUOTE=michaf;117704]But still, it's a very major chance anyway you look at it. I'm glad to live in Holland, albeit much of that is below sealevel. (Flooding is the only major disaster that can strike Holland afaik)[/QUOTE]I'm just across the sea from Holland and although above sea level, not a long way above sea level. Luckily, I'm well in-land.

Neither of us is in a particularly seismically acitive zone, so only small earthquakes (though over the last thousand years or so they have just about reached Richter 5 in the fault that lies in the English channel near Dover) and no volcanoes.

However, in terms of tornados per square meter per second, southern England is the most likely place in the world to encounter them (I've seen two myself, and have been within 50km of several more) and The Netherlands is the second most likely.

We occasionally get massive tsunamis. One around 10k years ago caused massive damage all over the North Sea. There are places in Scotland where beach material was carried many kilometers inland. That tsunami was caused by a landslip off the Norwegian coast. If the south western quarter of La Palma falls into the sea, as it's very likely to do in the fairly near future, we should be ok as we're protected by England and northern France, but I certainly wouldn't want to be anywhere near Bristol, South Wales or southern Eire. (Or in Florida, for that matter, as the waves would stand a good chance of washing over the entire peninsular from east to west.)

Although, by definition, we don't get hurricanes over here, storms with hurricane-strength winds are not that uncommon. I've experienced two since 1987.

Asteroid strikes can hit essentially anywhere...


Paul

[quote=davieddy;117703]
If so perhaps bigger quakes have lower frequency.
[/quote]

Yes. I expect energy is proportional to the volume of stressed rock,
and volume is proportional to wavelength^3.
In fact one could argue that the maximum strain in a wave
(~amplitude/wavelength) was determined by the maximum strain
in the ground prior to the quake, which suggests wave intensity
might be independent of energy of quake at an appropriate distance
away (likely to be proportional to wavelength).

This is truly "seat of the pants" physics:smile:

[QUOTE=xilman;117713]However, in terms of tornados per square meter per second, southern England is the most likely place in the world to encounter them (I've seen two myself, and have been within 50km of several more) and The Netherlands is the second most likely.[/QUOTE]Incidentally, my parents live in the Derbyshire village of Breaston. (As did I, until I left for Oxford.)

Breaston was struck by a tornado on my mother's birthday (24th September) this year. It missed my parents' house by well under a kilometre.

Paul

[quote=ATH;117532]The richter scale is ~ log[sub]10[/sub](amplitude) but the energy rises a factor of 1000 when richter scale rises 2 values, so the Richter scale is ~ log[sub]sqrt(1000)[/sub](energy) ~ log[sub]32[/sub](energy).

[/quote]

This is saying energy^2 proportional to amplitude^3, other things being
equal.

My deliberations are trying to explain this qualitatively.

David

[QUOTE=xilman;117713]
However, in terms of tornados per square meter per second, southern England is the most likely place in the world to encounter them (I've seen two myself, and have been within 50km of several more) and The Netherlands is the second most likely.
[/QUOTE]

Eeks :)
First time I hear that...
Is there a difference in strength between hurricanes and tornados, or is it the same words for the same phenomenon?

[quote=michaf;117752]Eeks :)
First time I hear that...
Is there a difference in strength between hurricanes and tornados, or is it the same words for the same phenomenon?[/quote]

They are different phenomena. Search for each and you will find a wealth of information.

I did some searching after xilman's post, because I had always thought that "tornado alley" in the central US had the most frequent occurance of tornados in the world. He may be right on the per unit area per sec qualification, but everything I've read indicates that most of these are not particularly dangerous tornados. The really destructive ones are generally found in tornado alley, with the strongest (class F5) having wind speeds of greater than 260mph. I've lived in "tornado alley" all my life, but have never actually seen a tornado (but have seen the effects of several).

[QUOTE=bsquared;117753]He may be right on the per unit area per sec qualification, but everything I've read indicates that most of these are not particularly dangerous tornados. The really destructive ones are generally found in tornado alley, with the strongest (class F5) having wind speeds of greater than 260mph.[/QUOTE]Quite true. We get a few F3 per annum but (AFAIK) never F5 strength.

However, we really do get 30 to 40 tornados each year, and in an area which is much smaller than tornado alley.

Paul

[quote=xilman;117762]

However, we really do get 30 to 40 tornados each year, and in an area which is much smaller than tornado alley.

Paul[/quote]

I don't doubt you ;) I just didn't know your area gets so many. Here is a nice site I found which talks about frequency and magnitude of tornados globally, focusing on the US: [URL]http://www.ncdc.noaa.gov/oa/climate/severeweather/tornadoes.html[/URL]

I would rather be in your situation: more likely to see the awesome and mysterious phenomena of a tornado without all the fuss and bother of potential mayhem and destruction...

[quote=ewmayer;117574]Decimal fascist. :mad:[/quote]
Especially when 32~SQR(1000):lol:

[quote=xilman;117762]Quite true. We get a few F3 per annum but (AFAIK) never F5 strength.

However, we really do get 30 to 40 tornados each year, and in an area which is much smaller than tornado alley.

Paul[/quote]

Calling Cambridge and its environs the UK's "Silicon Valley" is one thing.
Trying to compete with "Tornado Alley" is quite another. And as for
earthquakes, I don't think the English Channel is much competition
for San Andreas.

David:smile:

(St. Catz 1972)

Huygen's principle and earthquakes
 

Picture an earthquake size L just before it happens.

The typical wavelength is L, as is the diameter of
the "fault", so diffraction effects scale similarly.

Huygens would compute the amplitude as proportional to
area(L^2). And the energy is proportional to the volume (L^3).

So amplitude proportional to energy^(2/3).

Ernst/Paul/any other physicist out there like to
agree/disagree with this?

David

I don't think the above kind of analysis applies very well to quakes, for the following reasons:

- Energy release in a quake is proportional to length of fault rupture, which can be very large w.r.to the other relevant dimensions - for instance the great 1960 Chile earthquake had a rupture zone over 1000km long. For quakes this large, that also means it takes a significant time for the rupture to spread out from the original break location [the proverbial straw that broke the camel's back] in both directions along the fault, like a 2-way zipper. The resulting wavelength spectrum may thus be more determined by local fault-zone relaxation times than anything having to do with overall quake magnitude. [This also explains why local shaking amplitude scales typically far sublinearly with overall quake energy release.]

- On top of the above non-point-source aspect there may be a significant small-scale granular aspect, due to local asperities interacting with the propagating rupture, and all the vagaries of local fault geology and geography.

Any geologists around here?

[QUOTE=davieddy;117804]Calling Cambridge and its environs the UK's "Silicon Valley" is one thing.
Trying to compete with "Tornado Alley" is quite another. And as for
earthquakes, I don't think the English Channel is much competition
for San Andreas.

David:smile:

(St. Catz 1972)[/QUOTE]I never said the fault under the Channel was anything like as serious a cause of earthquakes as the SA fault. Quite the reverse.

However, Tornado Alley gets several hundred tornados per annum in an area which is perhaps a hundred times that of southern England. The latter gets 30 - 40 tornados esentially every year, and over a hundred every now and again.

Go dig out the records if you don't believe me.

Paul

[quote=ewmayer;117822]
Any geologists around here?[/quote]

I think we have enough variables as it is:lol:

David

[quote=ewmayer;117822]I don't think the above kind of analysis applies very well to quakes, for the following reasons:

- Energy release in a quake is proportional to length of fault rupture, which can be very large w.r.to the other relevant dimensions - for instance the great 1960 Chile earthquake had a rupture zone over 1000km long. For quakes this large, that also means it takes a significant time for the rupture to spread out from the original break location [the proverbial straw that broke the camel's back] in both directions along the fault, like a 2-way zipper. The resulting wavelength spectrum may thus be more determined by local fault-zone relaxation times than anything having to do with overall quake magnitude. [This also explains why local shaking amplitude scales typically far sublinearly with overall quake energy release.]

[/quote]

This line of argument would maintain that
"volume ~ L^3" was falsified by the example of a pencil.

When I said "picture an earthquake" I was expecting its
shape to remain the same when scaling by L. (I was
picturing a sphere of stressed rock not particularly close to the surface,
but the details shouldn't matter).

I was only trying to justify the genralization asserted in
Wikipedia as the reason for for "Richter = log32(energy)~log10(amplitude)+c".

But I do see that, since speed at which rupture propagates is
presumably comparable to wavespeed, the Huygen's Principle argument
is complicated.

David

Can I have some marks for ingenuity anyway? ;-)

Whatever the Chile quake of 1960 was deemed to be
on the Richter scale, I don't see how that value could be
particularly meaningful, for the reasons you stated.

David

Although we are in the "Lounge", I would like to point out that
we use Huygen's Principle to derive diffraction patterns, and that
these are intimately connected with Fourier analysis. So we are not
as "off topic" re prime searching as you might think.

[quote=xilman;117829]I never said the fault under the Channel was anything like as serious a cause of earthquakes as the SA fault. Quite the reverse.

However, Tornado Alley gets several hundred tornados per annum in an area which is perhaps a hundred times that of southern England. The latter gets 30 - 40 tornados esentially every year, and over a hundred every now and again.

Go dig out the records if you don't believe me.

Paul[/quote]

I didn't say you did say it.
Having lived in SE England for 57 years I have to say
I have never witnessed a tornado, although I have seen
numerous news bulletins on them. Occasionally the tornado
was 20 miles away.
How many others have been similarly (un)lucky here and
in Tornado Alley?

David

[QUOTE=davieddy;117890]How many others have been similarly (un)lucky here and
in Tornado Alley?[/QUOTE]

I spent most of my youth in Ohio - not sure if that's officially considered part of Tornado Alley, but it is in the wild-weather US Midwest. Never saw one touch down [on land - did see a spectacular waterspout, a.k.a. tornado-over-water on Lake Ontario one summer], but saw several funnel clouds, and had at least one a year touch down somewhere within a 20 mile radius. However, ones that caused widespread damage were relatively rare - maybe every decade within a 20-to-50-mile radius you'd get a trailer park destroyed[sup]*[/sup]. The most-famous killer tornado that hit Ohio in my lifetime was one of the 1974 [url=http://en.wikipedia.org/wiki/Super_Outbreak]super outbreak[/url] that [among other things] destroyed Xenia, Ohio.

I wonder if there could be a reporting bias at work here - in the US, tornados in Tornado Alley are so common that the news reporting thereof is roughly thus:

1) Funnel clouds [tornados that fail to fully coalesce and/or touch down] at best make the local news;
2) Tornados that touch down and cause at most modest property damage make the local news and maybe get a small 'pagefiller' mention in the national news;
3) Tornados that cause widespread property damage but cost no or very few lives make the national news and maybe get a small 'pagefiller' mention in the international news;
4) Only Tornados that level entire towns and kill tens of people, typically ones that are part of Super Outbreaks, make the international news in a meaningful way.

The fact that many non-Brits here apparently have never even heard of 'tornados in the UK' indicates to me that there may be a similar trend at work - since [acording to Paul] UK tornados rarely make it above the afore-defined step (2), news of them stays local and national.

=========

[sup]*[/sup][Aside: I have no explanation for the apparent predilection tornados have for trailer parks here in the US - is it part of as larger global 'shantytown' phenomenon?].

[QUOTE=ewmayer;117894]I spent most of my youth in Ohio - not sure if that's officially considered part of Tornado Alley, but it is in the wild-weather US Midwest. Never saw one touch down [on land - did see a spectacular waterspout, a.k.a. tornado-over-water on Lake Ontario one summer], but saw several funnel clouds, and had at least one a year touch down somewhere within a 20 mile radius. However, ones that caused widespread damage were relatively rare - maybe every decade within a 20-to-50-mile radius you'd get a trailer park destroyed[sup]*[/sup]. The most-famous killer tornado that hit Ohio in my lifetime was one of the 1974 [url=http://en.wikipedia.org/wiki/Super_Outbreak]super outbreak[/url] that [among other things] destroyed Xenia, Ohio.

I wonder if there could be a reporting bias at work here - in the US, tornados in Tornado Alley are so common that the news reporting thereof is roughly thus:

1) Funnel clouds [tornados that fail to fully coalesce and/or touch down] at best make the local news;
2) Tornados that touch down and cause at most modest property damage make the local news and maybe get a small 'pagefiller' mention in the national news;
3) Tornados that cause widespread property damage but cost no or very few lives make the national news and maybe get a small 'pagefiller' mention in the international news;
4) Only Tornados that level entire towns and kill tens of people, typically ones that are part of Super Outbreaks, make the international news in a meaningful way.

The fact that many non-Brits here apparently have never even heard of 'tornados in the UK' indicates to me that there may be a similar trend at work - since [acording to Paul] UK tornados rarely make it above the afore-defined step (2), news of them stays local and national.

=========

[sup]*[/sup][Aside: I have no explanation for the apparent predilection tornados have for trailer parks here in the US - is it part of as larger global 'shantytown' phenomenon?].[/QUOTE]I believe your conclusion about the newsworthiness of UK tornadoes is correct --- very few of them kill anybody or cause massive damage.

I suspect the shantytown phenomenon, as you term it, is related to the newsworthiness angle too. Shantytowns tend not to be physically robust and individual dwellings tend to be close together. Consequently, a tornado strike is more likely to cause more damage to more properties and to kill or injure more people in a shantytown than it would in a more prosperous area.

Paul

[quote=ewmayer;117894][sup]*[/sup][Aside: I have no explanation for the apparent predilection tornados have for trailer parks here in the US - is it part of as larger global 'shantytown' phenomenon?].[/quote]

I guess you see a caravan upsidedown more often than a house.

May I belatedly say how glad I am that you survived your recent
earthquake. I am sure the rest of the Forum would concur.

David

[quote=ewmayer;117894]
[Aside: I have no explanation for the apparent predilection tornados have for trailer parks here in the US - is it part of as larger global 'shantytown' phenomenon?].[/quote]

[URL]http://www.frankwu.com/tornado.html[/URL] :smile:

And more seriously:
[URL]http://www.newton.dep.anl.gov/askasci/gen99/gen99010.htm[/URL]

Which seems to support the news bias explanation.

[quote]...I spent most of my youth in Ohio...[/quote]
We did as well. We remember lots of tornadoes and have seen a few in action.

We now live in NC and have to deal with the occasional hurricane, which is worse in some ways, but at least gives you a warning.

Some opinions about trailer parks and tornadoes:

[url]http://ask.metafilter.com/26791/Trailer-parks-and-tornadoes[/url]

[SIZE=1]Gerbil1: How is a tornado and a divorce the same? Either way, somebody's gonna lose a trailer.
[/SIZE]

Can't resist.
Quiz show ("The Weakest Link* which I am watching ATM)
Q: The best point on a tennis racket with which to
hit the ball is called the what "spot"?
A: The G spot.

PS The guy just won:)

LOL - yes, few people know about *real* tennis sweet spot, probably due to its recent discovery, or perhaps because it sounds so similar to the sex-related one, or perhaps we're just such a sex-fixated culture composed of wannabe porn stars and the people who download them. But in any event, the tennis version was discovered by ATG female tennis player Steffi Graf, and retired men's great Stefan Edberg, in honor of which it is known [in unabbreviated form] as the "Graf-Edberg Spot."

[i]p.s.: Thanks for the glad-you-survived-the-quake sentiments, but seeing as this one was really quite modest AFA this area goes, if you have only a finite supply of remotely transmittable good karma, I beg you, save it for the next Big One.[/i]

[i]p.p.s.: I was momentarily tempted there to add a parting quip along the lines of "shake on it?", but I suppose that would be crass - real scary-earthquake survivors might well find fault with me.[/i]

[i]p.p.p.s.: I have on at least 2 occasions suggested to my buddies Larry Flax and Rick Rosenfield, co-CEOs of the California Pizza Kitchen chain of restaurants, to offer pizza with a choice of thin, thick and subducted crust, but for some reason they've never taken me up on it - I didn't even ask for trademark royalties. Stodgy old farts, no wonder [url=http://chart.finance.yahoo.com/c/my/c/cpki]their stock[/url] has been stuck in "random oscillation around a mean of $15" mode for the past decade. Time to shake up the business model, gentlemen![/i]

[quote=ewmayer;117915]LOL - yes, few people know about *real* tennis sweet spot, probably due to its recent discovery, or perhaps because it sounds so similar to the sex-related one, or perhaps we're just such a sex-fixated culture composed of wannabe porn stars and the people who download them. But in any event, the tennis version was discovered by ATG female tennis player Steffi Graf, and retired men's great Stefan Edberg, in honor of which it is known [in unabbreviated form] as the "Graf-Edberg Spot."

[/quote]

:lol:
Having googled "G spot" and been reminded that it was short
for "Grafenberg" I now appreciate the full humour of your post.

As Paul will testify, "real tennis" in England is a whole different
and ancient ball game.
I don't know when the term "sweet spot" was first applied to the
"centre of percussion", but the concept was understood long
before Graf and Edberg used their big rackets. Perhaps with
smaller rackets, the spot lay too near the rim or even outside it.
OTOH Cricket/baseball bats have been around a long time.

Huygens revisited
 

On reflection it is not obvious that increasing the
size of a given shape of earthquake is like increasing
the aperture of a hole in a diffraction experiment.
Back to square one re explaining
amplitude^3 proportional to energy^2:sad:

New Zealand's East Coast shaken by 6.8 Quake
 

[url=http://www.nytimes.com/reuters/world/international-newzealand-quake.html]New Zealand's East Coast shaken by 6.8 Quake[/url]
I see the famous "swimming pool magnitude gauge" was used successfully here as well:
[quote]Murray McPhail, who lives about 10 km from Gisborne, said he could see waves in his swimming pool as the quake shook.

"You could just about surf on it," McPhail told the NZ Press Association. "Stuff came out of cupboards, bottles fell off walls, ornaments fell."

A seismologist said the depth of the quake had limited damage and minimized any chance of a tsunami.[/quote]
...except in Mr. McPhail's swimming pool, apparently.

The quote about the quake depth raises an interesting issue for us backyard seismologists: We have rule-of-thumb methods for estimating quake distance [time between onset of initial rumbling and subsequent rolling, times 5 miles per second], magnitude [swimming pool water sloshing amplitude - we just need the right amplitude-vs-distance normalization] and direction [the ancient Chinese marbles-on-the-rim-of-a-a-bowl method], but none for estimating quake *depth*. Any ideas?

Rob G, were you shaken by the NZ quake?

[QUOTE=ewmayer;121128]Rob G, were you shaken by the NZ quake?[/QUOTE]

It was 8:55pm and my son woke up and came into the lounge announcing that his bed was shaking and that he had jumped under the doorway. My wife and I didn't notice a thing, and we were only 10ft away from him! May have had something do do with the drinks we had been having :whistle:

We thought he had just woken up from a dream until the 'breaking news' came on 10 minutes later.

We live half a mile from a huge rock quarry. While we are certain it is nothing like an earthquake, some of the explosive work there has been real surprising because there is no warning. At worst, however, the pictures on the wall rattle a little and that is about it.

We can't imagine a real earthquake. That would certainly be very freaky.

:unsure:

If one is native to an eq zone, it is fun to watch the non-natives freak when a small (or distant) quake happens.

True natives will return a seat-of-the-pants (or sole-of-the-foot) estimate, based upon the S and P waves. A handy thing if one is in bed (do I get out or stay put?)

One time I was walking along and saw non-natives stop stalk still in the open when one struck. I laid down a guess and had it within 0.5 magnitude and ~25km. (It was an aftershock occuring about 2-3 weeks later.)

[QUOTE=Uncwilly;121237]If one is native to an eq zone, it is fun to watch the non-natives freak when a small (or distant) quake happens.[/QUOTE]We get an analogous sort of reaction when visitors visit Oxford (and Cambridge) for the first time. Especially when they learn that New College, so called becauase it was the first one created after a gap of 65 years, was founded in 1379, so t's about 3 times as old as the US. My college, Exeter, was the one formed immediately before New College and dates from 1314.

I've visited a number significantly older places in the UK. Nottingham, for instance, has two thirteenth century pubs.


Paul

This is not really related to earthquakes, but imagine how much sway there is up on top of tall buildings.

[QUOTE=Xyzzy;121483]imagine how much sway there is up on top of tall buildings.[/QUOTE]

I was in a 12 story building during a fairly close 5.2 quake. It was the first building in Wellington built on the flexible rubber feet and stretching walls technology. The quake lasted for about 15 seconds but on the 10th floor it kept swinging on a couple of metres radius for about 5 minutes minutes before it stopped completely (extremely freaky!).

Can't imagine how much sway there would be on some of the skyscrapers.

[QUOTE=rgiltrap;121505]I was in a 12 story building during a fairly close 5.2 quake. It was the first building in Wellington built on the flexible rubber feet and stretching walls technology. The quake lasted for about 15 seconds but on the 10th floor it kept swinging on a couple of metres radius for about 5 minutes minutes before it stopped completely (extremely freaky!).

Can't imagine how much sway there would be on some of the skyscrapers.[/QUOTE]Current understanding is that when Los Angeles gets its "big one", most of the tall buildings in the downtown area will shed most of their glass windows.

[QUOTE=Uncwilly;121570]Current understanding is that when Los Angeles gets its "big one", most of the tall buildings in the downtown area will shed most of their glass windows.[/QUOTE]I kinda thought the meaning of "big one" was it's ability to make the buildings shed their ability to stay upright.

[quote=rgiltrap;121505]I was in a 12 story building during a fairly close 5.2 quake. It was the first building in Wellington built on the flexible rubber feet and stretching walls technology. The quake lasted for about 15 seconds but on the 10th floor it kept swinging on a couple of metres radius for about 5 minutes minutes before it stopped completely (extremely freaky!).

Can't imagine how much sway there would be on some of the skyscrapers.[/quote]
Is the application of critical damping difficult to achieve in practice?

[QUOTE=xilman;117898]I believe your conclusion about the newsworthiness of UK tornadoes is correct --- very few of them kill anybody or cause massive damage.

I suspect the shantytown phenomenon, as you term it, is related to the newsworthiness angle too. Shantytowns tend not to be physically robust and individual dwellings tend to be close together. Consequently, a tornado strike is more likely to cause more damage to more properties and to kill or injure more people in a shantytown than it would in a more prosperous area.

Paul[/QUOTE]Another one today and only a few miles from here ...

[url]http://news.bbc.co.uk/1/hi/england/cambridgeshire/7164235.stm[/url]

Paul

[QUOTE=retina;121571]I kinda thought the meaning of "big one" was it's ability to make the buildings shed their ability to stay upright.[/QUOTE]
There is a projected 6.5-7.2 projected for a particular fault that runs NW-SE south of the city. This is considered LA's "big one". An 8.0 or greater on the San Andreas will have less effect on the city proper. (Akin to NYC vs. east LI)

We had a 5.2 earthquake in England last night. Biggest
for 20 years, and I actually felt the earth move for the
first time in my life!
David

And there was the largest earthquake in Norwegean history with in the last few days.....

Right up near the "Noah's Ark" seed bank.

Read about the UK quake in this morning's paper - now we just need an outbreak of the limey tornados Paul mentioned, and we'll have enough "phenomena not usually associated with the UK" material to chew on for a while.

[QUOTE=Uncwilly;127162]And there was the largest earthquake in Norwegean history with in the last few days.....

Right up near the "Noah's Ark" seed bank.[/QUOTE]

I hope Noah's seed was undamaged...was any spilled that you know of?

5.4 in the Los Angeles area. Can't seem to get the site mentioned in this thread: [url]http://www.mersenneforum.org/showthread.php?t=6481[/url] to work.

I was home with my girlfriend when this most recent earthquake hit. I live near the coast in the South Bay, which is some distance south (and slightly west) of Los Angeles. We felt two or three fairly hard jerks at first and then a considerable amount of rolling motion. Initially, my concern was a glass covered large picture frame that hangs over the bed we were sitting upon. After looking at that and moving slightly away from it, we looked at the disposition of our cats (scared but not completely terrified) and then moved into a doorway. The event seemed to last 30 seconds or so. I am a native born Southern California resident and have been present for most of the earthquakes here but still felt more disturbed and uncomfortable than the motion alone warranted. After the motion ended, for several seconds I was unsure if it had in fact stopped; I had felt a bit of dizziness or motion sickness or some other heightened discomfort that I situationally slotted into that category.

All and all, this earthquake seems timed well to bring attention to: [URL="http://www.shakeout.org/"]http://www.shakeout.org/[/URL]
[quote]
The Great Southern California ShakeOut
November 12–16, 2008

The Great Southern California ShakeOut is a week of special events featuring the largest earthquake drill in U.S. history, organized to inspire Southern Californians to get ready for big earthquakes, and to prevent disasters from becoming catastrophes.

These activities are based on the ShakeOut Scenario, a realistic portrayal of what will happen in a southern San Andreas earthquake.
[/quote]

I live about 15 miles from the epicenter. We had a few random things fall from shelves, but no real damage. For us, it started with a couple little jerks, then a few hard jerks, then about 20-30 seconds of gentle rolling motion. The cell phone networks were out for about an hour afterward, and the Cal State Fullerton campus closed for the day. There was no structural damage, but a number of windows broken, ceiling tiles broken, etc., on campus. Here's a nice photo of an aisle in the library stacks. This is one of MANY for them to sort out...

Greg

[QUOTE=frmky;138622]There was no structural damage, but a number of windows broken, ceiling tiles broken, etc., on campus. Here's a nice photo of an aisle in the library stacks. This is one of MANY for them to sort out...
[/QUOTE]
Worst of all, the campus closing delayed the announcement of the factorization of 2,949+ :)