The U.S. Geological Survey wants to warn you not to be alarmed if you see very low-flying planes around Spokane and North Idaho in the coming weeks.
The planes are piloted by experienced pilots specially trained for low-level flying and will measure the magnetic field of the Earth. The work is part of an ongoing USGS program to identify hidden geologic features, such as changes in rock types, ultimately providing a better understanding of the geology and hydrology of the area. For example, the survey may help map shallow faults responsible for a sequence of small earthquakes that occurred during the summer and fall of 2001 in Spokane.