Seismic activity and rifting in the Krafla fault swarm in NE-Iceland

International Symposium on the Activity of Oceanic Volcanoes. Ponta Delgada, 4-9 August 1980.The Krafla volcano in the rift zone of NE-Iceland has been going through a series of inflation-deflation cycles since 1975. Magma accumulates beneath the volcano during slow inflation periods and is injected laterally into the Krafla fault swarm during deflation events. Each deflation event has a characteristic pattern of seismic activity. It typically begins with continuous volcanic tremor and the tremor amplitude is dependent on the rate of deflation. Earthquake activity increases shortly after the deflation starts and the epicentral area is soon extended from the caldera region, along the fault swarm to the north, the south or both. The propagation speed of the seismic activity is highest in the beginning, but decreases with decreasing deflation rate and increasing length of the epicentral zone. Typical speed is 0.5 m/s, but may reach values as high as 1.2 m/s. […].