Obtaining broadened-band data out of short period, analog seismometers
Although short period seismic stations are well suited for observing and locating micro-earthquake activity,
larger magnitude earthquakes carry much information of the source processes and path properties in the
long-period signals. Recent advances in seismological instrumentation have permited many observatories around
the world to update/complement their short-period stations with modern broad-band instruments, capable of
observing even the 12 hour period earth-tide related motions.
For earthquake research institutes in developing countries, upgrading the network to such instruments is not
a simple matter, since there are not enough founds available for research. Here in we presented the results
of an old dream made reality: extending the response of short period instruments and packing the information
into narrow-band analog telemetry.
The solution consisted on passively modiffy the response of 1-Hz seismometers to extract the longer-period
signals from the original records, modulate them into another sub-carrier band, and mix the new signal with
the original short-period information. With such strategy, we obtain two different windows: a high frecuency
window (1-35 Hz) used for microseismic studies, and a long period window (1-35 secs) used to observe larger
regional and teleseismic events.
In March 16, 2004 we installed on the field our first two-window vertical instrument, and actually we are
working in our first two-window, three component station to be deploy in the near future. As for today, we
present the results of two-months of "extended-band" seismological observation in western Colombia.
Key words: Seismological instrumentation, analog telemetry, long-period station, Western
UNIVERSIDAD DEL VALLE, Observatorio Sismológico del SurOccidente - OSSO