Initially, a set of approximately 100,000 waveforms from 255 candidate earthquakes recorded by 1160 horizontal channels (Station-Network-Channel-Location, or SNCL labels are used to describe each) from the AZ, BK, CI and NC networks were extracted. The candidate events were selected from the CISN 2000-2006 seismicity catalog by gridding the state into 50km square bins and selecting the largest 3+ event that occurred in each bin, and also (to obtain an adequate USArray data set) the largest 3+ event in 2006 (or second largest if the largest 2000-2006 event event in the bin occurred in 2006). The SNCL channels included both broadband and strong motion instruments.
Local magnitude () was calculated from each channel's trace by deconvolving the instrument response and convolving the response of a Wood-Anderson seismograph (Uhrhammer et al, 1996). For each event, differences for all SNCL pairs were calculated, giving a dataset with more than 10 million differential observations. These differences were simultaneously inverted to determine a station adjustment for each SNCL, (SNCL), and a function describing the amplitude decay as a function of distance, called .
Berkeley Seismological Laboratory
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