Reconnaissance geophysics to locate major faults in clays

Trial surveys using resistivity, seismic refraction and electromagnetic techniques have been carried out at two potential research sites on Jurassic clays. A previously unknown major fault has been detected at Down Ampney and mapped during the main survey to a precision of 5 to 10 metres by resistivity profiling using a Schlumberger array, optimized from pre-existing data and model studies. The fault is identified by a strong characteristic signature which results from the fault displacement and a zone of disturbance within the clay. This method is rapid, provides high resolution and permits immediate field interpretation