Microseismicity in the Reykjanes Ridge, July, 1990: Hypocenter Distribution Derived from an OBS Array

We report hypocenter distribution derived from 24-day OBS array observation on the Reykjanes ridge, SW off Iceland. Our research area was between 62.5°N and 64°N, 150km along the ridge and 40km width. In this area, 18 OBSs were deployed with interval of 10-20km. The object of this experiment was to investigate detailed microseismicity in the area. In the observation period (July 2-26, 1990), about 800 earthquakes were recorded. We selected 444 earthquakes for hypocenter location, and 297 hypocenters were determined. In order to discuss the hypocenter distribution there, we selected 179 earthquakes whose errors are less than 5km. The epicenters are distributed along the ridge axis, with 5km width. Hypocenters seem to be distributed vertically. The focal depths are less than 12km below ocean bottom. Seismic activity is concentrated in space and time; two active swarms were observed (July 4 and 14).