Mm: a variable-period mantle magnitude

E. A. Okal, J. Talandier

Research output: Contribution to journalArticlepeer-review

84 Scopus citations


This paper lays the theoretical groundwork for a variable period mantle magnitude, Mm, based on the measurement of the spectral amplitude X(ω) of very long period Rayleigh waves. We retain the concept of magnitude by restricting ourselves to single-station measurements, ignoring the focal mechanism and the exact depth of the shallow earthquakes considered. Our measurements are made at a series of periods (in all cases greater than 40 s), and the largest value is retained. This procedure effectively avoids the well-known interference effects leading to saturation of magnitude scales defined at a fixed period. Two corrections are used: a period-dependent distance correction Cp, and a source correction Cs, also period-dependent. The analysis of a data set of 256 records from the broadband seismograph at Papeete, Tahiti, the ultra-long period system at Pasadena, and stations of the GEOSCOPE network, shows that the mean error in the estimation of the seismic moment is on the order of 0.1-0.2 units of magnitude, with the standard deviation at each station also on the order of 0.2 units of magnitude. Both versions of the method lend themselves well to automation. -from Authors

Original languageEnglish (US)
Pages (from-to)4169-4193
Number of pages25
JournalJournal of Geophysical Research
Issue numberB4
StatePublished - Jan 1 1989

ASJC Scopus subject areas

  • Geophysics
  • Forestry
  • Oceanography
  • Aquatic Science
  • Ecology
  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth-Surface Processes
  • Atmospheric Science
  • Space and Planetary Science
  • Earth and Planetary Sciences (miscellaneous)
  • Palaeontology


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