Table 1.

List of surface-based geophysical methods commonly used in fractured rock. The extent and depth of the survey region and the resolution are all approximate ranges. The measured parameters can be derived directly from the acquired data. The recovered properties are obtained through processing and/or inversion of the acquired data.

Method	Lateral Extent of Survey Region (meters)	Depth of Survey Region (meters)	Resolution (meters)	Measured Parameters	Recovered Properties of Interest	Potential Fractured Rock Targets
Electrical Resistivity	1 to 100	1 to 100	0.5 to 10	Electrical potential from applied current	DC electrical conductivity	Fracture zones, Amendment monitoring
Ground Penetrating Radar	1 to 1000	1 to 50	0.1 to 10	Amplitude and arrival time of reflected EM energy	Dielectric constant at frequencies of 1MHz to 1GHz	Major fractures, fracture zones, transport in fractures
Electro-magnetic induction	1 to 10000	1 to 100	0.5 to 10	Induced magnetic fields due to sub-surface conductors	Electrical conductivity	Contaminant plume delineation
Very low frequency EM	1 to 10000	5 to 75	1 to 10	Secondary fields from navigational signals	Electrical conductivity	Faults, fracture zones
Magnetometry	1 to 10000	1 to 100	0.5 to 10	Magnitude and/or gradient of Earth’s magnetic field	Magnetization, magnetic susceptibility	Treatment monitoring (metals)
Seismic Reflection/Refraction	1 to 1000	1 to 500	1 to 10	Amplitude and arrival time of reflected elastic energy	Elastic wave velocities, attenuation	Depth of weathered zone, major fractures
Induced Polarization	1 to 1000	1 to 100	0.5 to 10	Decay in electrical potential following current pulse; frequency dependence of complex impedance	Imaginary part of the complex electrical conductivity at frequencies from mHz to kHz	Permeability estimation, amendment monitoring
Surface Nuclear Magnetic Resonance	10 to 100	1 to 100	1 to 10	Decay in nuclear magnetization following radiofrequency pulse	Relaxation time constant	Depth to groundwater, permeability, water content
Self Potential	1 to 1000	1 to 100	0.5 to 10	Electrical potentials arising from current sources in the earth	Electrodiffusion potential, redox potential, streaming potential	Groundwater flow directions