At 10:35 UT on May 5, 2005, a 3.4 earthquake occurred 4.6 km SE of CMSB at a depth of 5 km. The CMSB recording of this event demonstrates the signal-to-noise ratio and signal bandwidth that can be achieved using modern low-noise borehole emplanted accelerometers of an NHFN station and its capacity for providing high-resolution registration of a local earthquake. The absolute ground accelerations observed at CMSB are shown in Figure 5.4. Given the observed 3.4 magnitude and corresponding peak ground accelertion of 26,650 counts or 2.44 gal for this event and the effective acceleration clipping level of 196 gals for the CMSB hardware, the upper limit on the magnitude clipping level is estimated to be 5.3 (3.4 + log10(196/2.44)) for a local earthquake.
The corresponding vertical component (CL1) acceleration spectra shown in Figure 5.5 demonstrates the signal-to-noise ratio and signal bandwidth that can be achieved using modern low-noise borehole emplanted accelerometers. The signal bandwidth is 200 Hz and the SNR is above 50 dB in the 1-50 Hz band and the SNR is above 0 dB up to 170 Hz.
Berkeley Seismological Laboratory
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