Extension of the energy-to-moment parameter Θ to intermediate and deep earthquakes

Nooshin Saloor*, Emile A. Okal

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


We extend to intermediate and deep earthquakes the slowness parameter Θ originally introduced by Newman and Okal (1998). Because of the increasing time lag with depth between the phases P, pP and sP, and of variations in anelastic attenuation parameters t, we define four depth bins featuring slightly different algorithms for the computation of Θ. We apply this methodology to a global dataset of 598 intermediate and deep earthquakes with moments greater than 1025 dyncm. We find a slight increase with depth in average values of Θ (from −4.81 between 80 and 135 km to −4.48 between 450 and 700 km), which however all have intersecting one-σ bands. With widths ranging from 0.26 to 0.31 logarithmic units, these are narrower than their counterpart for a reference dataset of 146 shallow earthquakes (σ=0.55). Similarly, we find no correlation between values of Θ and focal geometry. These results point to stress conditions within the seismogenic zones inside the Wadati-Benioff slabs more homogeneous than those prevailing at the shallow contacts between tectonic plates.

Original languageEnglish (US)
Pages (from-to)37-48
Number of pages12
JournalPhysics of the Earth and Planetary Interiors
StatePublished - Jan 2018

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Geophysics
  • Physics and Astronomy (miscellaneous)
  • Space and Planetary Science


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