From: stead@skadi.CSS.GOV (Richard Stead)
Newsgroups: sci.geo.geology
Subject: Re: Seismic Data
Date: 27 Jan 93 19:55:52 GMT

In article <1993Jan27.160412.8415@unocal.com>, stgprao@st.unocal.COM (Richard Ottolini) writes:
> The original questioner was probably interested in obtaining a seismogram
> like they show on TV news or in a museum- a single channel, 24 hours a
> day.  This is something well within the capacity of a hobby seismometer
> or public data center.

I disagree.  It doesn't take very many requests to completely jam a data
circuit.  For example, if you offered all data from a typical single-component
broad-band instrument at 40Hz sampling, about 400 1-hour segment requests a
day would jam a typical 56kb link.  It is not well within the capacity of
a public data center.  Until T1 is pretty common everywhere, you won't
see seismic data offered publicly this way.  This is exactly why internet
access to seismic data is controlled.

Compression would only help a little - only the periods of noise compress
very well, the signal does not compress very well and that's usually what
people want.  What would likely help the most is some sort of multicasting -
a station that wanted to share its data would set up a multicast server
that remote sites could subscribe to.  I could imagine an X-program that
would know how to subscribe, and then pop up a display to show the seismogram
running continuously across the window.  This would not allow access to
past data, but another multicast service could be one that automatically
sent only event segments to all subscribers, which a client on the subscriber's
system would simply write to disk for later when the user would decide if
to delete it or not.

> Seismic data *is* available through the InterNet.  Access and format is tailored
> toward people studying scientific problems.  For example, one might make a

Absolutely.  CSS is probably foremost in this area.  All access is controlled
(to use CSS, a user must have a DARPA research contract, an agreement with
CSS, or DARPA's blessing), but we have moved to a data center concept where
all data exchange is via networks.  We have friendly front-end programs that
allow users to tailor their request and immediately get their data without
human intervention, except in the case of off-line data.

> request to a network for an hour's worth of data during a given earthquake,
> and a day or so later these are retrieved from offline storage and put into
> an ftp file.  Most of these sites are not set up to handle general public

Or sites like CSS where we currently have about 50 Gb of archive data on-line
and immediately accessible.  Also, our stations are set up with continuous
diskloops and network servers that allow near-real time waveform retrieval.
However, supporting our restricted user community and the ongoing operations
here already taxes our communications heavily (and we have multiple T1 and
64kb links).  We could not support access to seismic data for the general
public, (nor is it in our mission to do so).

> requests.  Read the publications of the seismic professional societies- AGU,
> BSSA, to learn about these sites.  They were discussed at last Decembers AGU
> meeting and will be at the May meeting.

Yes, this is the "open station" concept.  These are stations and data centers
open to any seismologist, but not generally available to all parties.  CSS
does not count, since we are not open to any seismologist.


(These are my opinions only - not DARPA or CSS)
--
Richard Stead
Center for Seismic Studies
Arlington, VA
stead@seismo.css.gov