The Berkeley Seismographic Station operated standard Wood—Anderson torsion seismographs from 8 April 1928 through 16 January 1994. These seismographs are historically significant in that their seismograms have been used to determine local (Richter) magnitude of earthquakes that occurred in northern and central California and adjacent regions, routinely since 1948 and ad hoc back to 1928. Broadband digitally recording seismographs were co-sited at four stations with Wood-Anderson instruments to compare the records. The Wood-Anderson seismographs became redundant for the purpose of determining the maximum horizontal trace amplitudes once procedures were developed to synthesize their seismograms accurately from the broadband digital recordings. Operation of the Wood-Anderson seismographs was subsequently discontinued. This article demonstrates the ability to determine an unbiased measure of local magnitude from synthesized Wood-Anderson seismograms, thereby maintaining a seamless catalog of local magnitude at Berkeley.

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