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Rayleigh wave magnitude scaleM s (1973)

Marshall, P. D. ; Basham, P. W.

Springer

Pure and applied geophysics 103 (1973), S. 406-414

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ISSN: 1420-9136

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Summary TheM s Rayleigh wave magnitude formula is revised for purposes of eliminating the variable effects of near distances and propagation pats on the values computed from standard long period seismograms. The improved formulation employs a revised distance correction function and period dependent path correction that normalisesM s to large teleseismic distance, 20 second values. The method for computing the path corrections is described. The magnitude scale presented here givesM s values which are within ±0.1 magnitude units of the Gutenberg and Prague magnitude formulae.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00876419

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Variations with time in the detection thresholds of P for seismological stations reporting to the ISC (2005)

Young, J. B. ; Douglas, A. ; Marshall, P. D.

Springer

In: Journal of Seismology. 2005; 9(4): 405-412. Published 2005 Oct 01. doi: 10.1007/s10950-005-0268-x.

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Publication Date: 2005-10-01

Description: To determine maximum-likelihood magnitudes for a given seismological network requires estimates of the detection thresholds of short-period P for the individual stations. Ideally the detection threshold of a station with fixed instrumentation and operating procedures would be constant. However, some stations reporting to the International Seismological Centre (ISC) show systematic variations with time. Other stations are unreliable or report amplitudes (A) and periods (T) only intermittently. Ways are therefore needed for choosing stations that have a consistent performance over many years. Two rough measures are described here that can be used to look at variation in the apparent detection thresholds with time: One is the number of A/T observations (at distances greater than 20°) and the other log, for the P detections associated each month by the ISC; log(A/T) being the average log (A/T). Some of the factors that control detection thresholds and clearly revealed by these rough measures are: Array stations have lower thresholds than conventional observatories; installation of automatic detectors can lower the threshold; and annual variations in noise level are reflected in annual variations in detection thresholds. For some stations an apparent lowering of the threshold appears not to be due to changes at the station, but is a consequence of the lowering of the ISC reporting thresholds in the region around the station. For stations of the Swiss seismological network there is a slow rise in the threshold from the mid-1970s to 1992 which is difficult to explain but seems to be due to a gradual changes in the detail with which the seismograms are analysed. © Springer Science + Business Media, Inc. 2005.

Print ISSN: 1383-4649

Electronic ISSN: 1573-157X

Topics: Geosciences , Physics