For earth scientists, a wide range of geophysical, geo-chemical and geological
surveying methods exist for geothermal energy investigations. For each of these
methodologies, there is a typical physical/chemical property to which the technique
is sensitive to. For geophysics, location of a geothermal reservoir may be
determined by use of seismic velocity, electrical conductivity, magnetic or/and
gravity methods. Effects of exploitation of a geothermal reservoir can be
monitored using micro-seismic, micro-gravity, geo-chemical and
temperature/pressure techniques. Though these may require complex methodology
and relatively advanced mathematical treatment in interpretation, much
information may be derived from simple qualitative assessment of the survey or
monitoring data. Often many of these methods are used in combination to obtain a
plausible inference. At the interpretation stage, ambiguity arising from the results
of one survey may often be removed by consideration of results from a second
survey method. This article provides a general introduction to the most important
methods of geophysical exploration that have been employed at Olkaria geothermal
field, Kenya. The occurrence of surface manifestations in the country’s rift valley
regions encouraged various people to carry out various geophysical investigations
to establish the subsurface structure with a view of establishing its geothermal
potential. Various levels of success have been achieved with each of the
techniques. The activities resulted in the construction and commissioning of
Africa’s first geothermal power plant at Olkaria, with a 45 MW capacity, between
1981 and 1985. Changes in technology saw the deployment of modern
geophysical techniques that included transient electromagnetics (TEM) and
magnetotellurics (MT) which made it possible for shallow and deep conductors to
be accurately imaged and thus more accurate geothermal models developed.