OVERLAPPING RIFT-ZONE SEGMENTS AND THE EVOLUTION OF THE SOUTH ICELAND SEISMIC ZONE

The South Iceland seismic zone is a 20-60 km-wide (north-south) and up to 70 km-long zone of north and north-northeast trending Holocene arrays of en echelon tension fractures. These fracture arrays are related to dextral strike-slip faults buried by Holocene lava flows. In this zone, major destructive earthquake sequences occur at intervals of 45-112 years, the largest events reaching magnitude 7 (Ms). We propose that this seismic zone is located between overlapping rift-zone segments (spreading centers), where the eastern segment has been propagating to the south during the past 3 Ma. We made a finite element study of this configuration with the segments modeled as mode I cracks loaded in tension. The results suggest that the South Iceland seismic zone in general, and the north and north-northeast trending dextral faults in particular, develop in response to the shear stresses generated between the rift-zone segments.