Use of the mantle magnitude Mm for the reassessment of the moment of historical earthquakes - I: Shallow events

Emile A. Okal*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

68 Scopus citations


The mantle magnitude Mm is used on a dataset of more than 180 wavetrains from 44 large shallow historical earthquakes to reassess their moments, which in many cases had been previously estimated only on the basis of the earthquake's rupture area. We provide 27 new or revised values of Mo, based on the spectral amplitudes of surface waves recorded at a number of stations, principally Uppsala and Pasadena. Among them, and most significantly, we document a large low-frequency component to the source of the 1923 Kanto earthquake: the low-frequency seismic moment is 2.9×1028 dyn-cm, in accord with geodetic observations. On the other hand, we revise downwards the seismic moment of the 1906 Ecuador event, which did not exceed 6×1028 dyn-cm. Finally, the study of the 1960 Chilean and 1964 Alaskan earthquakes whose exceptionally large moments are properly retrieved through Mm measurements, serves proof that this approach performs flawlessly even for the very greatest earthquakes, and is therefore successful in its goal to avoid the saturation effects plaguing any magnitude scale measured at a fixed period.

Original languageEnglish (US)
Pages (from-to)17-57
Number of pages41
JournalPure and Applied Geophysics PAGEOPH
Issue number1
StatePublished - Mar 1 1992


  • Historical earthquakes
  • magnitudes
  • mantle waves
  • tsunamis

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology


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