New constraints on dike injection and fault slip during the 1975-1984 Krafla rift crisis, NE Iceland

Correlation of KH9 spy and SPOT5 satellite images, airphotos, digital elevation model differencing, electronic distance measurement, and leveling survey data is used to constrain the deformation resulting from the 1975-1984 Krafla rifting crisis. We find that diking typically extends to depths of 5 km, while the dike tops range from 0 km in the caldera region to 3 km at the northern end of the rift. Extension is accommodated by diking at depth and normal faulting in the shallowest crust. In the southern section of the Krafla rift, surface opening is 80% of the dike opening at depth. Over the 70-80 km length of the rift, the average dike opening was 4.3-5.4 m. From these estimates, we calculate the total geodetic moment released over the Krafla rift crisis, 4.4-9.0×10¹⁹ Nm, which is an order of magnitude higher than the seismic moment released over the same time period, ~5.8×10 ¹⁸ Nm. The total volume of magma added to the upper crust was 1.1-2.1×10⁹m³. This study highlights how optical image correlation using inexpensive declassified spy satellite and airphotos, combined with simple models of crustal deformation, can provide important constraints on the deformation resulting from past earthquake and volcanic events. Key Points Constrain sub-surface deformation in the 1975-84 Krafla rift crisis Investigate the interplay between dike injection and fault slip Improve our understanding of oceanic-rifting