Analysis of seismic noise at The Geysers geothermal area, California

The amplitude level and velocity of seismic noise at The Geysers area in California are different from the average pattern of background noise. The predominant peak in the spectrum of noise occurred at about 1 Hz. This noise was highly coherent over a distance of about 1 km, showed episodic bursts of energy, and appeared to come from the general region of major geothermal activity in the region. The predominant noise velocities were in the 4 to 7 km/sec range.