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JELoWeb
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Short term geodetic measurements of horizontal island motion rates along the New Hebrides Trench reflect the far-field plate convergence rate in the southern section while the central section shows only a portion of the far-field rate. These results, if taken on their own merits, might lead to the interpretation of strong or at least moderate coupling in the central section and weak coupling in the southern section. It could also easily be argued that large, several thousand meter tall bathymetric features currently impinging the western margin of the central section are the likely sources for the greater coupling. However, the analysis here of nearly one hundred years of near-trench seismicity associated with active subduction along the trench reveals consistently low (10 to 30%) seismic coupling along both the southern and central sections. This suggests that although the d’Entrecasteaux Zone is present and likely to be responsible for deformation in the overriding plate in the form of episodic coral uplifts and aberrant horizontal convergence rates, seismicity data offers no evidence that it significantly increases the degree of coupling on the approximately one hundred year time scale. This is meaningful although not definitive. One hundred years may not be long enough to cover the seismic recurrence interval along the trench. Clearly, a greater duration of seismicity data and more complete geodetic coverage is necessary to provide a more detailed view and reconcile the apparent contradiction. To complement this, consideration of the effects of oblique convergence, possible variation in plate dip and depth of coupling along the trench axis, and even reevaluation of some of the more basic assumptions such as the earthquake average stress drop and physical properties of the plate material might assist in revealing more details of the tectonic processes active along the New Hebrides Trench. This, however can only be approached with the passage of time and future work. |
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© jlundy@wyoming.com 20 June 2003 |