Seismological evidence for Lateral magma intrusion during the July 1978 deflation of the Krafla volcano in NE-Iceland

Abstract

The July 1978 deflation of the Krafla volcano in the volcanic rift zone of NE-Iceland was in most respects typical of the many deflation events that have occurred at Krafla since December 1975. Separated by periods of slow inflation, the deflation events are characterized by rapid subsidence in the caldera region, volcanic tremor and extensive rifting in the fault swarm that transsects the volcano. Earthquakes increase in the caldera region shortly after deflation starts and propagate along the fault swarm away from the central part of the volcano, sometimes as far as 6 5 km. The deflation events are eted as the result of subsurface magmatic movements, when ma from the Krafla reservoir is injected laterally into fault swarm to form a dyke. In the July 1978 event magma was injected a total distance of 30 km into the northern fault swarm. The dyke tip propagated with the velocity of 0.4-0.5 m/sec during the first 9 hours, but the velocity decreased as the length of 'the dyke increased. 'Combined with surface deformation data, these data can be used to estimate the cross sectional area of the dyke and the driving pressure of the magma. The cross sectional area is variable along the dyke and is largest in the regions of maximum earthquake activity. The average value is 1200 m2. The pressure difference between the magm ervoir and the dyke tip was of the order of 10-40 bars and did not change much during the injection.

Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland

“…We calculate the stress and strain due to a dyke segment opening in a similar manner and superpose them on the estimated tectonic contributions. Assuming a linear relationship between stress and strain, we then calculate the strain energy potential using equation (2). When inferring the path of preferred dyke propagation, we assume also that the dyke depth, with respect to sea level, is the same for all strikes tested.…”

Interaction between Transform Faults and Rift Systems: A Combined Field and Experimental Approach

“…In fact, it is well-known that, at the tip of an advancing dyke, tensile stresses can increase due to magma injection (Rubin and Pollard, 1988;Rubin, 1992) and exceed the Coulomb failure threshold, triggering earthquakes in the brittle crust (Brandsdóttir and Einarsson, 1979;Einarsson and Brandsdóttir, 1980;Feigl et al, 2000;Cattin et al, 2005). The effects of magmatic pressure at an advancing dyke have already been explored in several papers by field data, numerical modeling, and analog experiments (review in Rivalta et al, 2015, and reference therein).…”

The January 1998 Earthquake swarm at Axial Volcano, Juan de Fuca Ridge: Hydroacoustic evidence of seafloor volcanic activity

“…Gaps in the distribution of seismicity associated with the intrusion of a magma dike have also been observed at Krafla [Einarsson and Brandsdottir, 1980] and Kilauea Volcanoes [Rubin and Gillard, 1998]. Rubin and Gillard [1998] concluded that dikes propagating into regions of low ambient differential stress are likely to produce no seismicity at the magnitude 1 level or above.…”