Gillian Sharer accepted answer staff Oct. 10, 2013, 10:48 a.m.
There are many causes for transient signals. Long period transient signals can be caused by vault tilt (often resulting from weather systems or freezing/thawing ground), or local disturbances such as cattle, horses, or people. High frequency transient signals can be caused by fans, cars, or other nearby equipment. Other possibilities include calibration pulses or mass re-centers.