Seismic magnitude scales Seismic magnitude scales Seismic magnitude scales are used to describe the overall strength or "size" of an earthquake. These are distinguished from seismic intensity scales that categorize the intensity or severity of ground shaking (quaking) caused by an earthquake at a given location. Magnitudes are usually determined from measurements of an earthquake's seismic waves as recorded on a seismogram. Magnitude scales vary on the type and component of the seismic waves measured and the calculations used. Different magnitude scales are necessary because of differences in earthquakes, and in the purposes for which magnitudes are used. The Earth's crust is stressed
Seismic noise Seismic noise In geology and other related disciplines, seismic noise is a generic name for a relatively persistent vibration of the ground, due to a multitude of causes, that is a non-interpretable or unwanted component of signals recorded by seismometers. Physically, seismic noise consists mostly of surface waves. Low frequency waves (below 1 Hz) are generally called microseisms; high frequency waves (above 1 Hz) are called microtremors. Its causes include nearby human activities (such as traffic or heavy machinery), winds and other atmospheric phenomena, and ocean waves. Seismic noise is relevant to any discipline that depends on seismology, such as