Hazardous geologic structures, such as faults, volcanoes, and shallow magma reservoirs, often juxtapose lithologies with contrasting magnetic properties. Aeromagnetic techniques are naturally suited for the exploration of these structures where they may be concealed below the surface and pose a threat to society. A variety of studies conducted during the past quadrennium focused attention on this important application of the aeromagnetic method. Here we highlight only a few significant developments related to earthquakes and volcanoes.