Comparison of manual and automatic onset time picking

The onset times for 78 teleseismic iP phases are picked by four seismic ana lysts and by three automatic picking algorithms, on both the single trace a nd on an array beam. The difference in the onset times picked by different analysts is on average +/- 0.067 sec with a standard deviation of 0.15 sec. The analysts on average pick times 0.1 sec earlier on the beam than on the single trace. The three automatic pickers are the picker described by Earle and Shearer(1 994), an autoregressive-Akaike information criteria (AR-AIC) picker (Leonar d and Kennett, 1999) and an adjusted AR-AIC picker, which is described in t his article. Of the three automatic pickers, the adjusted AR-AIC picker pic ks onset times closest to an experienced analyst. Compared to the three mos t experienced analysts, the difference in onset time is on average +/- 0.04 3 sec, with a standard deviation of 0.19 sec. These values are very similar to the differences between the analysts, suggesting that for many applicat ions, the time estimated by the adjusted AR-AIC picker can be used without review by a seismic analyst.