Iceland geophysical networks

The geophysical observational network in Iceland for studying crustal processes and plume/ridge activity consists of following main components:

• A 3-component digital seismic network of 38 stations spread over Iceland with highest concentration in areas of high seismic and volcanic risk, having various seismometer bandwidths. The system evaluates automatically small earthquakes for hypocenter location and magnitudes in real-time. In a semi-real-time it evaluates also for fault plane solutions and moment magnitudes. It evaluates automatically of the order of ten thousand earthquakes per year, and can cope with evaluating in near-real-time 1000-1500 earthquakes per day. The sensitivity of the system is down to magnitude 0 in the lowland areas, but down to magnitude 1-2 in the highland areas. All automatic evaluations are qualified and corrected manually, before putting them into database. The basic function of the system is to retrieve and to evaluate an almost continuous row of information carried by microearthquakes, information which is used for analyzing the state and possibly the outbursts of activity in the seismic and volcanic regions. Advanced software and 1 ms time accuracy in the waveform data makes it possible to map faults and fault instability at depth with a high accuracy. Although it is not the basic function of the system, it is also used for recording and storing information about distant earthquakes or teleseisms, providing information about structure to a large depth. An alert system provides automatic alerts about activity based on predefined parameters.

• A seven station network of 1-component analog seismic stations in the highlands.

• Volumetric strainmeters providing continuous digital data are operated in 7 boreholes in the South Iceland seismic zone (SISZ), linked to the SIL center.

• Continuous high accuracy GPS measurements for recording crustal deformation are in operation at five sites in the SISZ and at one site in Southeast Iceland, and four are in preparation in the North Iceland seismic zone.
• Continuous monitoring of conductuctivity by MT methods is carried out at two sites in Southwest Iceland, one of these linked to the SIL center.

• Continuously recording gravimeters are in operation at two sites in the SISZ, linked to the SIL center.

• Extensive information about deformation has been collected during the past decades, which are a very significant part of the infrastructure. Most significant are 600 points of repeated high accuracy GPS deformation measurements since 1986 and also high accuracy repeated geodimeter measurements from the last three decades. Information about deformation based on repeated SAR images exist for the last 5 years for a few sites.

• Measurements of water level in boreholes or pressures in closed systems are made by electrical or hydrothermal power companies. Significant and continuous row of these measurements can be made accessible.

Information of all the abovementioned observations, waveform data, parameter data and results of various high level evaluation will be made accessible for research by HOTSPOT.