The earth is shaken daily by strong earthquakes recorded by a number of seismic stations worldwide. Tectonic tremor, however, is a new type of seismic signal that seismologist started studying only within the last few years. Tremor is less hazardous than earthquakes and occurs at greater depth.  The link between tremor and earthquakes may provide clues about the more destructive earthquakes that occur at shallower depths. Geophysicists have collected seismic data of tectonic tremor in California. These data are now being evaluated in order to better understand this new seismic phenomenon.