Task 1.1: Data collection

A very significant achievement within Task 1 is the increase of number of operating seismic stations. In the original application to EC, 12 SIL type seismic stations were requested, to be integrated in the SIL system in Iceland. The SIL system is an automatic acquisition and evaluation system for earthquake data, developed in Iceland during 1988-1995 as a part of an earthquake prediction research project of the Nordic countries, i.e. the so-called SIL project []. The cutting of the EC application for the PRENLAB project, however, did not permit any new stations according to our own evaluation. However, it showed to be possible to arrange funds from other sources to build 15 new permanent SIL stations. These stations are as other permanent stations of the SIL network available for the PRENLAB project and are of great significance for it. However, they do not fully complement what was asked for in the original application as they are not all at sites most preferable for the project.

Anyhow, since the start of the PRENLAB project in March 1996, the number of SIL stations in operation has increased from 18 to 33. The new stations are funded by Icelandic communities, hydrothermal and hydroelectrical power companies, civil defence funds, a private tunnel-digging company, the Icelandic Research Council, and indirectly by research groups carrying out tomographic studies, which can make use of the powerful SIL acquisition system. The largest supporter of this build-up project of the SIL system is IMOR.DG/the Icelandic Government, which besides contributions to the initial costs guarantees the operation cost of the system [44,,,].

Preparations are going on to install 5 new permanent SIL type stations in the area around Vatnajökull, i.e. central and SE Iceland, within short. The 1996 eruption in this area including the preparation stage was very well monitored by the SIL seismic system. This made it possible to obtain funds from the Icelandic State to operate 5 permanent stations around the area and thus to fill in a gap in the Icelandic seismological network. Two of these stations are in a very remote area and request special facilities for operation. It is planned that these stations will become operative and an integrated part of the SIL system during summer 1998.

Since summer 1996 to end August 1998, 29 extra digital broad-band stations are operated continuously at remote places not covered by the SIL system, mainly for collecting teleseismic data. This is a part of the Iceland Hotspot project, lead by Gillian Foulger, University of Durham. Among other participants are Princeton University, with Jason Morgan and Guust Nolet, and Bruce Julian of the U.S. Geological Survey, besides IMOR.DG. The waveform information from these stations will be included into the SIL evaluation processes, especially as concerns the local seismic activity. This is a significant addition to the data that according to the original plan can be approached for the PRENLAB project. As the Hotspot Project stations are operated at sites where we have only a few SIL stations they can provide us with a much more general overview about the stress conditions in the country as a whole than would be possible with the SIL system only [,]. Figure 2 shows the locations of the seismic stations operated in Iceland during the period

  

Figure: The available 3 component digital earthquake monitoring in Iceland. The Mid-Atlantic Ridge goes through Iceland from the Reykjanes Ridge along the South Iceland seismic zone (SISZ), the rift zones to the Tjörnes fracture zone (TFZ) in the north. The most destructive earthquakes occur in the transform zones, SISZ and TFZ. The outlines of the Iceland mantle plume at depth are shown in purple. The Iceland Hotspot project stations are operated during 1996-1998. Other stations are permanent. Some other seismological and hydrological monitoring stations are operated too.

of the later part of the PRENLAB project.

Besides the seismic networks the operation of borehole strainmeters is the most significant continuous monitoring within PRENLAB. 7 Sacks-Evertson volumetric strainmeters have been operated in boreholes in and near the South Iceland seismic zone (SISZ). This is in cooperation with the Carnegie Institution of Washington [5,,].

An alert system relating to activity in 30 areas within Iceland is in continuous operation. It is mostly based on the automatic evaluation of the seismological network. The purpose of it is to inform the seismologists instantly if there are changes in the seismic activity which might be a premonitory activity before larger earthquakes or volcanic eruptions. It also serves the purpose of making the data collection better, because sometimes it is necessary to take special actions when activity increases in some area. The functions of the alert system are gradually improved as a result of experience and outcome from the ongoing scientific research [6].