USGS Professonal Paper 1096 - IRIS

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"Seismometer component" is most generally
General information.--Every effort was made listed as Z for vertical, NS for horizontal in a
to discern the individual or organization in- north-south direction, and EW for horizontal in
lto] ~led wHb each station Statj ODS and networks an east-west direction. Conventionally) first
are listed under the operating organization, so motion is N and E on horizontal instruments, and
that contact can be made directly with that thus, when written as NS and EW, the first
organization for current information and answers letters imply a first-motion direction. When
to any questions. The records generally are the reverse orientation is known, the component
available from the station, except where the is listed as SN or WE. Unfortunately, the more
data are transferred to a data center. The conventional listing cannot imply absolutely
National 6eophysical and Suiar-Terrestrial Bata that the eoftVlentioft fof' first metien is £01
Center in Boulder, Colo. , is equipped to respond lowed. No mention is made of polarity changes
to data requests by supplying copies of the that have occurred during a station's operation.
records kept on file; the originals usually Orientations other than these are listed with
reside at the station.
their compass orientatioB. If the anly infarma
tion known is that there was a horizontal in-
The address and telephone number listed in strument, it is listed simply as horizontal.
most cases refer to the operating organization's
central location; sometimes this is the address "Seismometer T " is the free period of the
of a station. The different offices of the USGS seismometer, listeR in seconds. "Galvo Tg" is
are treated as separate organizations because the period of the galvanometer. For instrument
the responsibility is distinctly segregated. systems that do not use a galvanometer, the
The Telex number is listed when applicable. filter characteristics are given, either in
seconds or, where noted, in hertz (Hz).
Site information.--"Code" is the three- or
four-letter code aSSigned, either by NELS or the "Type record1ng" refers to tfie mode of
operator at each location. (The codes does not recording (Helicorder, Develocorder) or the type
GRang@ in the e~~ent of , challge in instrllmenta- of records (film, smoked ~a:Qer).
tion or controlling organization; however, a
location change of more than 1 kIn necessitates a Magnification of the record is measured at
new code.) As mentioned above, any code not the free period of the seismometer (T ) unless
assigned by NElS Hill be in parelltheses; if both noted nnder "Remarks ll as measured af another
assigned and local codes exist, they will both period. Though the magnification can often
be listed. The station name is generally the change, the stated magnifications refer to the
town closest to the station. Latitude and most common settings used for a system. High
longitude are listed in degrees and decimal noise level requires lower magnification; low
degrees. The four decimal places give the noise level allows higher magnification.
significance of minutes and seconds, but are not
always truly s1grnf1cant to that level. eOllver
Leaders imply no data a .. ailahle, er in the
sion to the four decimals was made from whatever case of Galvo Tg may indicate that a solid-state
form was supplied by the stations. "Elevation" amplifier with a filter is used instead of a
generally is the elevation of the seismometer. galvanometer.
Leaders em) 1ndicate no data. "lJa La opened"
is the date that the site was occupied and Listed under remarks is
..
a variety of data
started recording, regardless of which instru- about the particular station's instrumentation.
ment system was involved or which organization A station recorded ott-s1te noted as telemwas
responsible. "Date closed" is the date etered to another station or location. Newer
recording ceased or when the instruments were communications systems, however, now enable
removed. When no date, not even the year, could various types of transmissions such as microbe
found, the "Date closed" column is merely wave, radio, and liard-w1re; and these spec1al
noted "Closed." Foundation and geologic age are systems are not delineated from telemetering.
listed whenever this information was available. Particular standard-instrument networks such as
The information listed under foundation ranges WWSSN (World-Wide Standard Seismograph Network)
from formation and series names to generic and SRU (Selsm1c Research Observatory) are
descriptions.
noted.
Instrumentation.--Following the code, which "Timing system" refers to the clock used
is listed again in the instrumentation section, and how or if drift is checked. Virtually all
are type (make or design) of seismometer and, if currently operating stations now use the Nation-
Jisted , the mode] number: Most of tbe t)lpes a] Bureau Qf Standards broadcast WWV to check
listed are conventional enough to be readily times, or WWVB to record directly on the recidentified.
However, some makes may not be ords. In some cases the accuracy may be noted.
familiar; if further information is desired, it The NElS generally requires accuracy to a tenth
should be requested from the operating organiza- of a second.
tion.
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