These numbers come from a consensus reached after a number of seismology
stations report their data. In general, depth is harder to pinpoint than
horizontal location. Another thing to keep in mind is that these do not
occur at points, but rather along planes that may be kilometers long and
decameters high (as well as being angled and twisted somewhat).
The horizontal distance from a station can be deduced from a number of
factors, such as the relative arrival times of the s- and p-waves, the
crust structure (geological layers), pulse spreading, etc. Three
stations reporting their "distance to the epicenter" can be used to
"triangulate" the epicenter -- actually by plotting three overlapping
range circles rather than three overlapping bearings. Depth must be
inferred from phase inversions, geological structures, etc. My
background, by the way, is not seismology but it includes the
hydrological equivalent -- passive sonar analysis at sea -- in which
analogous considerations are taken into account.
Jim
kilopascal wrote:
>
> 2001-03-03
>
> >From the following website:
>
> http://www.msnbc.com/news/537200.asp
>
> The depth of the quake went from 40 km to 33 miles (53 km). Next report it
> will be 40 miles. Where do these numbers come from?
....
--
James R. Frysinger University/College of Charleston
10 Captiva Row Dept. of Physics and Astronomy
Charleston, SC 29407 66 George Street
843.225.0805 Charleston, SC 29424
http://www.cofc.edu/~frysingj [EMAIL PROTECTED]
Cert. Adv. Metrication Specialist 843.953.7644
