Following the methods of reconnaissance surveys in 1967 and 1968, more than 600 microearthquakes were recorded in Iceland in 1970. Most of these were located at or near geothermal areas. In most regions, only three days of recording at each site yielded a rate that was relatively constant (within a factor of three) over the three summers. The spatial correlation between geothermal areas and microearthquake activity proposed by Ward and Björnsson (1971), was strengthened by the discovery of microearthquake zones at three geothermal areas previously thought to have insignificant microearthquake activity. Significant seismic activity can be overlooked in reconnaissance monitoring of microearthquakes if determination of magnitudes is neglected. At two of the newly discovered seismic zones in central Iceland, microearthquake activity was much higher in 1970 than in previous years. Magnitudes of these events were comparable to those on the Reykjanes Peninsula. This suggests that tectonism may extend across central beland in connection with a broad band of post-glacial volcanics. Microearthquakes appear to migrate throughout a geothermal area on the Reykjanes Peninsula.