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Spectral and magnitude characteristics of anomalous Eurasian earthquakes

DEPARTMENT OF EARTH AND ATMOSPHERIC SCIENCES SAINT LOUIS UNIVERSITY, ST. LOUIS, MISSOURI 63156

Abstract

A number of main shock-aftershock sequences in the Eurasian interior contain some aftershocks whose m_b:M_S values are close to those of underground explosions. This paper is concerned with a study of the amplitude spectra of the P waves and Rayleigh waves for earthquakes of those main shock-aftershock sequences. It is found that for any given sequence studied, there is little if any variation in focal depth or focal mechanism. This rules out variations in these quantities as being the cause of anomalous m_b:M_S values. A study of the P-wave spectra establishes that one or both of the corner periods of anomalous earthquakes are smaller than those of non-anomalous earthquakes of the same moment. Thus the cause of anomalous m_b:M_S values of the earthquakes studied is a relative enrichment of the short-period portion of the spectrum of the anomalous events, which cannot be attributed to focal depth or focal mechanism.

Footnotes

^* Present address: Seismograph Service Corporation, Tulsa, Oklahoma.

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