Ted --

I don't know anything about the specific sensors used in this experiment,
but I know a little about high-speed instrumentation.  Piezoelectric or
piezoresistive devices are sometimes used to detect rapidly changing forces
which, when connected to a mass, can give acceleration.  Also, strain gages
can be pretty fast.  I've heard of people measuring strain to several
megahertz using these techniques.

Another approach is to suspend a mass on the end of a conductive fiber.
When high accelerations occur, the fiber will stretch and correspondingly
its resistance will change.  Measuring the change in resistance will give
an indication of acceleration.  Some methods even allow the fiber to break
in the process.

And if you attach the mass to the end of a relatively long but
much-less-massive bar, strain (compression) waves will travel down the bar
and can be picked off by high-speed strain gages located along the bar.  By
placing a number of strain gages on the bar, you can get a time-domain
reading of the change in force at the end of the bar.  Then sample the
strain gages all at the same time with sample-and-hold circuits and read
out the results at your leisure.

-- Karl

At 07:18 PM 12/11/99 -0500, you wrote:
>Does anyone know any more about these accelerometers, the instrumentation,
>and in particular what kind of sampling rate they wanted to get the fine
>structure of the subsurface geology?  If you wanted resolution to 1 mm
>you'd need about 1300 samples in 0.014 sec or about 92,000 samples/sec.
>How do you design an accelerometer which will report 100,000 times per
>second as it records accelerations between 0 and 1000 Gs?  Strong motion
>indeed!


_____________________________________________________________________

Public Seismic Network Mailing List (PSN-L)