Seismicity of the Reykjanes Peninsula 1971–1976

Abstract

The Reykjanes Peninsula Oblique Rift, a segment of the mid-Atlantic plate boundary, connects the Reykjanes Ridge to the rift zones of Iceland. The axis of the deformation zone of the plate boundary can be traced as a rather narrow epicentral zone of earthquakes that is highly oblique to the spreading direction of the North America Plate with respect to the Eurasia Plate. The seismicity of the area is episodic. Active periods with a duration of about a decade are separated by more quiet periods of one to two decades. Our observation period spans a good part of an episode that began in 1967 and ended in 1975. Nine earthquake swarms illuminate a 50 km long segment of the plate boundary. The epicentral zone cuts obliquely across the fissure swarms of the volcanic systems of the Peninsula. Geothermal areas are preferentially located at the intersection of the fissure swarms with the seismic zone. Outside the intersections with the seismic zone the fissure swarms show very low seismicity. The tectonic characteristics gradually change along the plate boundary segment, from being similar to those of a spreading segment in the western part to being more like a transform zone in the eastern part. This is seen in the type of earthquake sequences, maximum magnitude, and type of faulting.