Evidence for two possible relationships between observable surface deformation and geothermal activity

Abstract

During September of 1967 a large increase in the activity of a previously small geothermal field in south-western Iceland was accompanied by an earthquake swarm which lasted eight days. It is shown here, both from field observations and from the results of precise distance measurements made on a network of permanent benchmarks established soon after the seismic events, that the accompanying surface faulting shows the correct relationships with the local tectonics to be secondary shearing of the type found associated with large strike-slip faults elsewhere in the world. Vertical angle measurements on the same network of bench-marks are compared with corresponding measurements from the highly productive geothermal field at Wairakei, New Zealand, to show that the Icelandic field deforms more readily to the removal of geothermal fluids than does the New Zealand one. From this it is suggested that measurements of surface deformation in the immediate vicinity of a producing geothermal field could provide information on the gross permeability of the deep aquifers, and thus suggest how the field would behave under high discharge rates (such as would be encountered during economic exploitation).