Near-source effect on radiation pattern of high-frequency S waves: Strong SH-SV mixing observed from aftershocks of the 1997 Northwestern Kagoshima, Japan, earthquakes

Hiroshi Takenaka, Yutaka Mamada, Hayato Futamure

Research output: Contribution to journalArticlepeer-review

29 Citations (Scopus)

Abstract

It has been empirically recognized that high-frequency components of S waves radiated from earthquake do not show a radiation pattern predicted from a double-couple source, while the low frequency components show the standard double-couple radiation pattern. In this paper, we investigate this frequency dependence of radiation pattern using the high quality single-station records from the aftershock events of the 26 March 1997 and 13 May 1997 Northwestern Kagoshima, Japan, earthquakes. We focus on frequency dependence of energy partition between SH and SV waves in the direct S-phase. From the variation of the SH energy fraction with frequency we find that the energy fraction can be well predicted by theoretical radiation coefficients for a double-couple source at frequencies lower than 2 Hz, while at 3.5 Hz or higher it cannot be predicted and shows stochastic behavior. The intermediate frequencies can be seen as a transition from deterministic to stochastic. This supports the assumption that the radiation patterns of SH and SV waves are purely stochastic for high frequencies. Analyses of events which are located close to each other suggest that this stochastic nature is ascribed to strong SH and SV mixing or coupling induced by local structural effects near the sources.

Original languageEnglish
Pages (from-to)31-43
Number of pages13
JournalPhysics of the Earth and Planetary Interiors
Volume137
Issue number1-4
DOIs
Publication statusPublished - May 15 2003
Externally publishedYes

Keywords

  • Northwestern Kagoshima earthquakes
  • Radiation pattern
  • S wave

ASJC Scopus subject areas

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

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