Self-noise spectra for 34 common electromagnetic seismometer/preamplifier pairs

Because of a lack of such information, computed self-noise spectra are presented for a total of 34 frequently used electromagnetic-seismometer/preamplifier combinations. For convenience, most of these data are given in three sets of units. Peterson's Low Noise Model is included on each plot for comparison. The self noises of nine frequently employed electromagnetic seismometers properly matched to their operational amplifier (op-amp) preamplifiers are plotted. In terms of amplitude density spectra in (m/sec**2)/Hz**0.5, the values of the self-noise spectra at resonance range from a low of 3 × 10−10 for the GS-13 to a high of 1.3 × 10−8 for the HS-1. Between these two seismometers, in order of increasing noise at resonance, are the SV-1, SL-210V, S-13, SS-1, L-4C, S-6000CD, and the L-22D. To show which seismometers exhibit the lowest noise with which operational amplifier preamplifiers, the self noises of the HS-1, L-22D, L-4C, GS-13, SV-1, and SL-210V are plotted each paired with four commonly used op-amps: the LT1028, OP-227, OP-77, and the LT1012. For the GS-13, the LT1012 was the quietest. For the rest, the OP-227 was the best. For a given seismometer, the differences in self noise between op-amps were frequently a factor of 2 or 3, and as large as 10 in one case. The use of these op-amps in the analog front ends of five current digital seismic recorders is discussed.