抄録
An empirical method is developed for determining magnitude calibration functions independently of the standardized approach after Gutenberg and Richter. The method is applied to the worldwide data in the Earthquake Data Report (EDR) Of NOAA and the Bulletins of the ISC. Magnitude calibration functions are derived through the method for events in the three seismic regions (a) Alaska-Aleutian Arc, (b) Andean South America, and (c) Japan-Kurile-Kamchatka. Characteristics of the calibration functions thus obtained are summarized for the three epicentral ranges of i) the near (0°≤Δ<20°), ii) the teleseismic (20°≤Δ<110°) and iii) the PKP (Δ°≥110°) distance ranges.
In the PKP distance range, variations of log (A/T) are interpreted in relation to the travel time of compressional core phases. It is shown that seismic signals at the PKP1-PKP2 caustic (142°-152°) from small events of magnitude about 4 can possibly be detected by observations under normal routine circumstances with a magnification of about 5×104 and the signals at the caustic range are highly suitable for worldwide magnitude determination.
