Jökull - 31.12.2001, Page 90

Steinunn S. Jakobsdóttir et al.
UNIX
SIL
software
SIL Seismic Station Network 1991-2000
CPS- O
antenna
x25-card i/o-card
UNIX
SII.
software
Netcard xza-card
wvz
X25 modem

\25 nd
SIL center

A
Reykjavík
Reykjanes
£ Power- supply
! X25 net X25 modem
box
House
TFZ
.
NVZ
SIL station
P-wave velocity (km/s)
3 4 5 6 7
Barðarbunga
Gjáip VatnajökuM
Grímsfjall
▲
SIL velocity
model
EVZ
1991 - 1993
A 1994 - 1995
A 1996 - 1998
A 1998-2000
Figure 1. The SIL seismic station network 1991-2000. Also shown are the main tectonic features of Iceland.
SISZ is South Iceland Seismic Zone, TFZ is Tjörnes Fracture Zone, WVZ is Western Volcanic Zone, EVZ is
Eastern Volcanic Zone and NVZ is Northern Volcanic Zone. The box in the upper right corner shows schemat-
ically the components of a SIL seismic station. The velocity model used to locate earthquakes is shown in the
right bottom corner. The box to the left represents the SIL center in Reykjavík. - Myndin sýnir þróun SIL jarð-
skjálftamœlanetsins árin 1991-2000. Sýnd eru gos- og brotabelti landsins. SISZ er Suðurlandsbrotabeltið, TFZ
er Tjörnesbrotabeltið, WVZ er vestara gosbeltið, EVZ er eystra gosbeltið og NVZ er norðurgosbeltið. Kassinn
í efra horni til hœgri sýnir helstu þœtti SIL jarðskjálftamœlistöðvar. Hraðalíkan sem notað er við staðsetningar
á skjálftum er sýnt í neðra horni til hœgri. Kassinn til vinstri táknar SIL miðstöðina í Reykjavík.
The data acquisition is based on waveform analy-
sis and locations of the earthquakes. At every station
the data stream from the sensor is digitized and stored
in a ringbuffer on the hard drive of a PC-computer
at a nearby farm. The incoming signals, exceeding
some predefined threshold, are analyzed, the onset
time is determined and different parameters are cal-
culated, such as peak-to-peak amplitude, frequency
content, coherence and azimuth of the incoming wave
and a few additional parameters. All this information
is packed into 128b long messages and sent through a
communication link (mostly X.25) to a central com-
puter in Reykjavík.
Information from all stations is gathered in the
central computer and used to locate all possible earth-
quakes and estimate their magnitudes. For all loca-
tions passing a quality test, requests for waveform
data are sent out to the stations which are expected
to see the respective event. This means that an earth-
quake can already be referenced in the automatic bul-
88 JÖKULLNo. 51