Study of calibration function for surface wave magnitude of DK1 seismographs

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Study of calibration function for surface wave magnitude of DK1 seismographs

The calibration function for surface wave magnitude of DK1 seismograph is deduced by using least squares method of error theory based on the records of DK1 seismograph from 1987 to 1993 and the M _s magnitude defined by International Seismological Center (ISC) as basic standard, which takes the form σ _DK1(Δ)=(1.66 ± 0.034)lg(Δ)+(3.2 ± 0.11) (10° ⩽ Δ ⩽ 130°, T = 8 ~ 20 s) From its physical essence, the calibration function for estimating surface wave magnitude by DK1 seismograph can be also deduced by means of the wave propagation theory in layer media, if the dispersion of seismic wave, absorption of media and the effect of the linear filter consisting of earth media and DK1 seismographs on the amplitudes and periods of surface wave are taken into account and it is also assumed that the maximum amplitude is response to Airy’s phase, which takes the form σ _DK1(Δ)=1.6611g(Δ)+3.3 (10° ⩽ Δ ⩽ 170°) No correction value is needed when using the calibration function deduced in this paper. Examination on surface wave magnitude of 315 events by 36 prompt earthquake stations and DK1 prompt network shows there exits no systematical error between surface magnitudes of M _s (DK1) and M _s (ISC) given by ISC and the average error is approximately zero.