ISSN:
1420-9136
Keywords:
Magnitude
;
moment magnitude
;
saturation of magnitude
;
peak factor
;
asperity
;
seismic force
;
Pareto distribution
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
,
Physics
Notes:
Abstract Several data sources appeared recently which enable one to construct an updated version of global average intermagnitude relationships. A set of nonlinear magnitude vsM w (or logM o ) curves is presented. Several regional scales are also included in the set. Utilization ofM w as a referential scale provides the optimal basis for extrapolation of return periods, strong motion amplitudes and source parameters from moderate to large earthquakes. Remarkable features of the constructed curves are: (1) practical coincidence of modifiedm b (m b * or $$\hat m_b$$ ) scale withm SKM of the Soviet Seismological Service (except the constant shift of 0.18); (2) the lack of true saturation of all scales butm b with the possible exception ofm B forM w 〉8.7; (3) almost common shape of curves for all short-period magnitudes (global as well as regional); (4) lack of a systematic world-averaged difference between American and SovietM s . ForM o large enough,m SKM (orm b * ) vs logM o trend has the slopeb=0.35. Data are compiled to estimate short-period spectral level vs logM o trend, and its slope seems to be near β=0.39. These two values and some additional assumptions, rather common, lead to the following conclusions regarding properties of the earthquake source and its short-period radiation: (1) peak to rms amplitude ratio (peak factor) of a short-period record grows asM o /0.11–0.13 , hence the Gaussian noise model of the record (predictingM o /0.03–0.04 ) can be definitely rejected, and some heavy-tailed peak distribution is to be assumed instead; (2) if one specifies this distribution to be the power-law (Pareto), then the estimate of the exponent α for this distribution approaches 2 for short-period teleseismic records (and this α value is the same as had been found previously for accelerogram peaks); (3) this may indicate the power law distribution of seismic force values of individual asperities; (4) there is a difference between our estimated β=0.39 and β=1/3 expected from the ω−2 model; data are not sufficient at present to show definitely that the difference is real.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00878585
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