Repeat Measurements of Seismic Noise in the Waiotapu Geothermal Area, North Island, New Zealand

Abstract

The amplitudes of seismic ground noise were remeasured at 66 sites in the Waiotapu and Reporoa geothermal areas in 1995 to determine whether amplitudes had changed since the first survey in 1970. In both 1995 and 1970 high levels of seismic noise occurred in two localities, one at Waiotapu and one at Reporoa. The elevated levels of seismic noise at most sites are thought to be caused by or near-surface geothermal activity. At seven sites in the Waiotapu area seismic noise levels were almost the same in 1995as in 1970, indicating no change in the intensity of the source of the geothermal seismic noise. At most other sites the 1995 seismic noise levels were different to those measured in 1970, although at sites with high levels of seismic noise the differenceswere less than at siteswith low levels of seismic noise.