Presented at Short Course X on Exploration for Geothermal Resources, organized by UNU-GTP, GDC and KenGen, at Lake Bogoria and Lake Naivasha, Kenya, Nov. 9-Dec. 1, 2015. 1 Kenya Electricity Generating Co., Ltd. OVERVIEW OF GEOTHERMAL SURFACE EXPLORATION METHODS Leakey Ochieng Geothermal Development Company P.O. Box 17700-20100, Nakuru KENYA lochieng@gdc.co.ke ABSTRACT Geothermal surface exploration invariably entails a multi-geoscientific process, which are holistically aimed at defining the geometry and characteristics of the geothermal system prior to drilling. The scientific disciplines commonly involved are geology, geochemistry, and geophysics. Geological approach generally aims at understanding the various lithologies, volcanological evolution, structural controls, and hydrological regimes of the system. Geophysical exploration helps in determining the geometry (shape, size and depth) of the heat sources, reservoir and cap rock. It also aims at imaging structures that are responsible for the geothermal system, and delineating the areal extent of the geothermal resource. The most commonly used geophysical methods are electromagnetic/electric, gravity, magnetics and seismics. These methods ultimately depend on the various intrinsic properties of rocks such as resistivity/electrical conductivity, density, magnetic susceptibility, elastic moduli/velocity respectively. Geochemical exploration relies mostly on sampling and analysis of water, steam and gas from the thermal manifestation in order to characterize the fluids, estimate equilibrium reservoir temperature, determine the origin, evaluate mixing scenarios, determine the suitability of the fluids for the intended use and locate recharge areas and direction of fluid flow. Additional geochemical studies entails soil diffuse degassing measurements aimed at identifying gas leakages that usually mimic active faults and structures. 1. INTRODUCTION Geothermal energy has become a viable alternative and sustainable source of energy in many countries. The energy is commonly manifested on the terrestrial surface in the form of fumaroles, hot springs, geysers, steaming grounds and altered grounds. The economically usable geothermal energy is that which occurs close to the earth’s surface where it can be tapped by drilling wells up to 3,000 m below the earth’s surface. Such shallow heat sources are in most cases attributed to volcanic activity, which are commonly associated with plate boundaries, which is reminiscent of the East African Rift system and other geodynamic environments. The essential components of a geothermal system include; heat source, permeable reservoir, cap rock and recharge regime. Ideally, multiple geoscientific disciplines such as geophysics, geology and geochemistry are commonly employed in the geothermal exploration, in order to define the aforementioned components.