Jökull - 01.01.2020, Blaðsíða 60

Reviewed research article
The analog seismogram archives of Iceland:
Scanning and preservation for future research
Páll Einarsson and Sigurður Jakobsson
Institute of Earth Sciences, University of Iceland, Sturlugata 7, 101 Reykjavík
Corresponding author: palli@hi.is; https://doi.org/10.33799/jokull2020.70.057
Abstract — The history of seismography in Iceland began in 1909 with the installation of one horizontal
Mainka seismograph in Reykjavík. Following a period of intermittent operation, regular operation was initi-
ated in 1925 with the establishment of the Icelandic Meteorological Office. The number of stations increased
gradually over the following decades, and in the sixties, four stations were in operation. The number of perma-
nent stations proliferated following the Heimaey eruption in 1973 and during most of the eighties the number
of stations was 40–50. The first digital seismograph stations were installed in 1990 and the analog seismic
network was gradually replaced by digital stations over the next two decades. Between 1910 and 1920 the
number of seismograms grew to an estimated 300,000. A four-year project to make this record collection ac-
cessible on the internet has been initiated and funded. So far around 175,000 seismograms have been scanned
and the results are available and free for download on the open website seismis.hi.is. The seismograms are
scanned with a resolution of 300 dpi and presented on the website as jpg-, and png-file. The high-resolution
files are on the order of 4–8 Mb each. Digitization of the seismic traces has not been attempted since most
of the seismograms are from short-period instruments and the waveforms are already lost. In addition to nu-
merous teleseismic body-wave-phases, the record collection contains primary data from various tectonic and
magmatic events in Iceland during the last century. This includes eruptions of Hekla in 1947, 1970, 1980–81,
1991 and 2000, Surtsey in 1963–1967, Heimaey in 1973, Askja in 1961, Grímsvötn in 1934, 1983, 1998, and
2004, Gjálp in 1996, rifting episode at Krafla in 1975–1984, persistent seismic activity of the Bárðarbunga
and Katla volcanoes, numerous suspected subglacial magmatic events, earthquake swarms on the Reykjanes
Peninsula Oblique Rift and within the Tjörnes Fracture Zone, and earthquake sequences in the transform zones
of South and North Iceland and adjacent segments of the Mid-Atlantic Ridge.
INTRODUCTION
All over the world scientists are waking up to the real-
ity that valuable seismological data are being lost. Be-
cause storage is costly, large archives of analog data of
various nature are taken to the waste dumps (Richards
and Hellweg, 2020). The analog-to-digital revolution
and the large increase in storage capacities for digital
data has brought many benefits to the scientific com-
munity. Digital data are becoming readily available to
a large generation of scientists, allowing sophisticated
analysis and research, unthinkable before. This brings
with it the danger of forgetting and ignoring data sets
obtained in the pre-digital era. In several branches of
science it is essential to have long term data. This in-
cludes many branches of earth sciences. The natural
systems under investigation operate on time scales of
centuries and millennia, much longer than the time
periods of available digital data, including volcanic
systems, active seismogenic faults, climatic systems
(e.g., Sturkell et al., 2006; Sigmundsson et al., 2018).
For research in these fields, it is important to extend
the period of observation back in time as far as pos-
sible in order to appreciate the time-variability of the
systems. In earthquake seismology, this is done by
studying and interpreting 1) surface effects of pre-
historic and historic earthquakes, 2) old documents
JÖKULL No. 70, 2020 57