Determination of P Wave Onset Times by a Digital Computer

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  • 計算機による地震波の自働読み取りについて (P波検測)
  • ケイサンキ ニヨル ジシンハ ノ ジドウ ヨミトリ ニ ツイテ Pハ ケンソク

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Abstract

Programs for automatic reading of seismic P wave onset by a digital computer are introduced. These programs are composed of a series of simple processes as follows. A low cut recursive filter is used to increase S/N amplitude ratio. The arrival times of P waves are read by means of comparison with a threshold level corresponding to noise level before the P waves. Discrimination between P arrivals and noises are made by counting the number of points where amplitude of the wave exceeds the threshold level during a pre-set time interval. Then, the earlier of the closest two reading times among the three independently obtained from the three component data, is selected as the best P wave onset time.<br>As the result, 66% of microearthquakes observed at the Iwatsuki deep borehole observatory could be read within the time difference of 0.1sec between the automatic readings and ordinary visual readings.<br>Furthermore, an effective indicator of reliability of the finally adopted P onset times is discussed.

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