The other curves are the residual power spectra derived from pairs of channels, either electric or magnetic, from all three sites. Hx total and residual power spectra at PKD1 averaged over 8 days. Courtesy of S. Boyd. During these earthquakes all five EM sensors were functioning at Hollister. Hollister data on the left and Parkfield data on the right.
Vertical scale is counts and horizontal scale is time.
The lower five traces are seismic data. From Parkfield the 1 Hz seismic data comes from both PKD1, traces 6-8, and PKD, traces 9 and 10. Note, the first EM channel from Parkfield, Ex, is down. Courtesy of S. Boyd. A visual inspection of the 40 Hz Hollister EM time series reveals some interesting features due to both cultural and natural sources.