[time-nuts] OT: NZ Christchurch member

[Bob Bownes]

The last 'modern' seismometers I worked with  (as an undergrad in the
early 80's) were all three axis laser interferometry based. I'm sure
they've gotten a bit better since then.

Not only could we pick up a shuttle launch from 1,400 miles away, we
could pick up frat parties from across town on the old strain gauge
monster at the top of the hill. :)

It was one of my first exposures to filtering actually.

As your friend said, 'Richter' is not actually used by seismologists
anymore, they use the moment magnitude scale for larger quakes, which,
while similar, is different. It's more about energy released than
about motion.

Back to your regularly scheduled discussion.

Bob


On Fri, Feb 25, 2011 at 11:09 AM, jimlux <jimlux at earthlink.net> wrote:
> On 2/25/11 7:55 AM, Poul-Henning Kamp wrote:
>>
>> In message<AANLkTikVLp0FMTrm8waFFAD9voHXc8oEo2ZJiCpniQKQ at mail.gmail.com>,
>> "Wil
>> liam H. Fite" writes:
>>
>>> Me:  You're saying that the Richter is a poor predictor of surface
>>> disruption?
>>
>> For damage assement you really need a vector-version of richter,
>> vertical does a lot more damage than horizontal on average.
>>
>
>
> Yes.. I doubt anyone still uses the torsion seismometer Richter used,
> although more modern scales (moment magnitude, etc.) still relate back (e.g.
> they set the calibration to match for some notional set of events)..
>
> That way, people have an idea... A Magnitude 3 earthquake within a few tens
> of km of me will be noticeable, if it's quiet. A magnitude 4 will be very
> noticeable, and a 5 will be exciting. A 6 will wake you up in the middle of
> the night.  I'd compare it to something like Mohs hardness, except actually
> with a quantitative basis.  (People who work with material properties like
> hardness use other scales anyway)
>
> It's a "roughly quantitative" measure of energy release, in the same sense
> that kilotons are for explosions. It's like that whole "cup of gasoline:
> dynamite" comparison.. it's the rate of energy (e.g. power) that creates the
> qualitative difference between running my camping stove and blasting.
>
> We do the same thing in time-nuttery.. we use log scales to talk about
> performance.. dBc/Hz for phase noise, and really, just the exponent to talk
> about ADEV.  (nobody gets excited about the difference between 1.1E-13 and
> 1.5E-13... but the difference between 1E-11 and 1E-15 is worth talking
> about)
>
> Maybe we should start promulgating dBallan?
>
> And maybe get an SI unit... The "Allan", although since the fractional
> frequency error is dimensionless....
>
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