A new source discriminant based on frequency dispersion for hydroacoustic phases recorded by T-phase stations

Jacques Talandier, Emile A. Okal*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

In the context of the verification of the Comprehensive Nuclear-Test Ban Treaty in the marine environment, we present a new discriminant based on the empirical observation that hydroacoustic phases recorded at T-phase stations from explosive sources in the water column feature a systematic inverse dispersion, with lower frequencies traveling slower, which is absent from signals emanating from earthquake sources. This difference is present even in the case of the so-called 'hotspot earthquakes' occurring inside volcanic edifices featuring steep slopes leading to efficient seismic-acoustic conversions, which can lead to misidentification of such events as explosions when using more classical duration-amplitude discriminants.We propose an algorithm for the compensation of the effect of dispersion over the hydroacoustic path based on a correction to the spectral phase of the ground velocity recorded by the Tphase station, computed individually from the dispersion observed on each record. We show that the application of a standard amplitude-duration algorithm to the resulting compensated time-series satisfactorily identifies records from hotspot earthquakes as generated by dislocation sources, and present a full algorithm, lending itself to automation, for the discrimination of explosive and earthquake sources of hydroacoustic signals at T-phase stations. The only sources not readily identifiable consist of a handful of complex explosions which occurred in the 1970s, believed to involve the testing of advanced weaponry, and which should be independently identifiable through routine vetting by analysts. While we presently cannot provide a theoretical justification to the observation that only explosive sources generate dispersed T phases, we hint that this probably reflects a simpler, and more coherent distribution of acoustic energy among the various modes constituting the wave train, than in the case of dislocation sources embedded in the solid Earth.

Original languageEnglish (US)
Pages (from-to)1784-1794
Number of pages11
JournalGeophysical Journal International
Volume206
Issue number3
DOIs
StatePublished - Sep 1 2016

Keywords

  • Hydrogeophysics
  • Pacific ocean

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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