In the absence of earthquakes, seismometers record a wide range of signals generated from both natural and anthropogenic sources as well as from the instruments themselves. As these signals interfere with our ability to record earthquakes, they have been lumped together and given the term “noise.” Conceptually, these noise sources can be divided into the broad categories of (1) self-noise of seismic instruments, (2) non-seismic noise sources, and (3) non-earthquake sources of seismic energy. The self-noise of the seismometer and digitizer arises through both their electronics and thermally induced motions on the mass of the seismometer. Self-noise often increases drastically at lower frequencies. Non-seismic noise sources arise because seismic instruments are sensitive to environmental conditions such as thermal variations, magnetic fields, and changes in pressure. Finally, non-earthquake sources of seismic energy are being constantly recorded on seismic instruments across the planet. These arise from a multitude of naturally occurring surface processes (swell in large bodies of water, bedload transport in rivers, wind, etc.) as well as cultural activities. Recently, these signals have found applications in both seismic imaging as well investigating the processes generating them. In this webinar, I will discuss how these three types of noise sources are characterized. I will provide examples, some steps that can be taken to mitigate them, and touch on recent work using background noise to understand oceanic, atmospheric, and earth surface processes.
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