Calibration of Wilip-Galitzin, Sprengnether and Streckeisen Seismographs

As seismic instrumentation has evolved, three different three-component set of long-period/broadband seismographs have been installed and operated, with overlapping intervals, at Berkeley since the 1930's. Wilip-Galitzin (W-G) seismographs were operated on the northern most seismic piers in the basement of Haviland Hall on the Berkeley Campus (BRK) from August 28, 1930 until February 1, 1965. World Wide Standardized Station (WWSS) Sprengnether (SPR) long-period seismographs were operated in the Byerly Seismic Vault (BKS), located in Strawberry Canyon behind the Botanical Garden, from June 8, 1962 until September 30, 1991. Streckeisen (STS-1) broadband seismographs began recording in the Byerly Seismic Vault (BKS) on May 11, 1987 with a 16-bit PC-based recording system (Bolt et al., 1988) and a 20 second pendulum configuration and by August 8, 1991 they had evolved into the current 24-bit Quanterra Q680 data logger and 360 second very-broadband (VBB) pendulum configuration. The W-G and SPR seismographs operated concurrently, but not co-sited, from June 8, 1962 until February 1, 1965. The SPR and STS-1 seismographs operated concurrently at BKS from August 8 until September 30, 1991. Comparison of selected seismograms from these intervals allow us to verify the calibration and response of these seismographs and to demonstrate that, within appropriate passbands, the earlier instrument seismograms can be reliably synthesized from later instrument seismograms and that absolute ground motions can be reliably estimated. An example of a SPR seismogram, synthesized from the corresponding STS-1 seismogram, is shown in Figure 13.24. A Streckeisen STS-2 seismograph has operated at BRK since January 1, 1993 and a comparison of selected seismograms from the BKS STS-1 and the BRK STS-2 is used to quantify differences in their site responses. A comparison of the responses of these seismographs is shown in Figure 13.25.

Figure 13.25: A comparison of the velocity responses of the BRK W-G and STS-2 and the BKS SPR and STS-1 seismographs operated at Berkeley. The W-G and SPR instruments recorded galvanometrically on photographic paper and the paper seismograms are scanned at a resolution of 400 dots per inch. The STS-1 and STS-2 instruments record digitally via a high-resolution data logger. The velocity sensitivity is given in digital units per meter per second (DU/(M/S)). Two responses are given for the SPR because its natural period (Ts) was changed from 30 seconds to 15 seconds on May 12, 1965.
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