WP 2.4 Space and time variations in crustal stress using microearthquake  source information from the South Iceland seismic zone

Start date or starting event:


Lead contractor:





Objectives: Obtain stress tensor information for the SISZ, prior and after the June 2000 earthquakes, using source information from  microearthquakes.

Analyze dynamic source parameters in the SISZ during the whole operational period of the SIL-network.


Inputs: Source and ray path information from more than 100000 microearthquakes in the SISZ from the SIL-database at the Icelandic  Meteorological Office (IMOR).

Fault slip data collected in the field close to the fault traces of the June 2000 earthquakes and in the whole SISZ.

Methodology / work description:

Two different algorithms will be used to obtain the stress tensor in the SISZ using the  available microearthquake focal mechanisms.

Spectral Amplitude Grouping (SAG) will  be used to analyze the variations in the radiation patterns from  the microearthquakes.

Relocation of microearthquakes using cross-correlation techniques.

Statistical analysis of microearthquke source parameters during the entire period of the operation of the SIL-network.

The main focus of this work is to utilize the unique data set provided by the SIL-network prior (10 years), during and after the major earthquakes in June 2000. The uniqueness of the data is due to the low threshold level of the SIL-network (ML=0) and due to  the completeness of the routine analysis done in respect to source  information of the many small earthquakes. This together with the extensive geological mapping of the surface exposed fractures makes the available data unique for earthquake prediction research.

The stress regimes that prevailed in the SISZ area during the last 2-3 millions years will be reconstructed based on systematic  inversion of fault slip data, in order to be compared with the  present-day stress regimes obtained from focal mechanisms of the earthquakes.

The SAG method will be use as a preprocessor on the focal mechanisms data to obtain reliable short-term variations of the stress field.

Particular attention will be paid to the short-term variations of the stress state, as related to the propagation of microearthquakes along, and in the vicinity of the main faults. To this end, stress tensors will be computed within narrow 4-D (space-time window). In addition, Coulomb stress models will be established. The June 2000 earthquakes will be the primary target for such analysis.

The SAG method will be used to monitor variations in the crustal  stress during the period 1991 through 2001. The objective here is to utilize the differential characteristics of the SAG method to monitor changes in the stress field with high resolution, both in time and space. Other methods for the stress tensor estimates will  be used and the comparative results will be analyzed and presented.

Statistical properties of the source parameter estimates from the SIL-network will be analyzed   as well as their relations to the possible physical properties of the deformation processes.


Deliverables including cost of deliverable as percentage of total cost of the proposed project:


Estimates of the stress tensor in the SISZ during 1991 through 2001.

M12  Re  PU  0,7%


SAG analysis in the SISZ during 1991 through 2001.

M12  Re  PU  0,7%


Estimates of the stress regimes in the SISZ during the last 2-3  million years.


M12  Re  PU  0,7%


Results from statistical analysis of source parameters of the earthquakes in the SISZ during 1991 through 2001.


M12  Re  PU  0,7%


Stress changes based on microearthquake source information.

M24  Re  PU  1,2%



Milestones: Delivery of the above items at the date indicated.