Evaluation of Physical Methods in Geothermal Exploration of Rifted Volcanic Crust

Abstract

Geothermal exploration by physical methods has been applied in Iceland for almost 50 years using a wide variety of exploration techniques. Resistivity surveys have been shown to be the most powerful methods, especially TEM measurements and head on resistivity profiling. Methods like dipole dipole and AMT/MT have serious disadvantages in interpretation and are therefore not applied, except that the latter is used for deep crustal prospecting. Temperatures gradient measurements in shallow holes are quite useful when the near surface rocks are of low permeability. Gravity measurements are useful to predict major structures such as fault planes and high density bodies. Aeromagnetic surveys are mainly sensitive to high temperature alteration at shallow depth as well as major structures like caldera faults. This information is often included in other data like resistivity and gravity maps. Seismic prospecting methods are seldom used. They are relatively expensive and provide usually only indirect information about geothermal parameters. Recent seismic noise studies in Iceland indicate than this method might become important in the future.