Isolated deep earthquakes beneath the North Island of New Zealand

Article English OPEN
Boddington, T. ; Parkin, C.J. ; Gubbins, D. (2004)

Seismicity shallows towards the south along the Tonga-Kermadec-Hikurangi margin, deep and intermediate seismicity being absent altogether in the South Island of New Zealand. Beneath the Taranaki region of the North Island the maximum depth of the main seismicity is 250 km, but very rare events occur directly below at 600 km. These could be associated with a detached slab or a vertical, aseismic continuation of the subducted Pacific Plate. Six small events that occurred in the 1990s were recorded extensively by digital instruments of the New Zealand National Network (NZNN) and temporary deployments. We relocate these events by a joint hypocentre determination (JHD) method and find their focal mechanisms using first motions and relative amplitudes of P and S arrivals. The earthquakes relocate to a remarkably uniform depth of 603 +/- 3 kmrelative error (+/- 10 km absolute error) in a line 30- km long orientated 40 NE, roughly parallel to the strike of the intermediate- depth seismicity. The only consistent component of the focal mechanisms is the tension axis: all lie close to horizontal and tend to align with the line of hypocentres. We interpret this deep seismic zone as a detached sliver of plate lying horizontally with the same orientation as the main subducted plate above. Volume change caused by a phase change controlled by the pressure at 600 km and temperature in the sliver produces a pattern of strain that places the sliver under tension along its length
  • References (24)
    24 references, page 1 of 3

    Adams, R.D., 1963. Source characteristics of some deep New Zealand earthquakes, New Zealand Journal of Geology and Geophysics, 6(2), 209- 220.

    Adams, R.D. & Ferris, B.G., 1976. A further earthquake at exceptional depth beneath New Zealand, New Zealand Journal of Geology and Geophysics, 19(2), 269-273.

    Brisbourne, A.M., 1998. Shear-wave structure of the Hikurangi subduction zone, North Island, New Zealand, PhD thesis, School of Earth Sciences, University of Leeds, UK.

    Douglas, A., 1967. Joint epicentre determination, Nature, 215, 47-48.

    Fukao, Y., Obayashi, M., Inoue, H. & Nenbai, M., 1992. Subducting slabs stagnant in the mantle transition zone, J. geophys. Res., 97, 4809-4822.

    Harvard Centroid Moment Tensor Catalog, 2003. http://www.

    ISC, 2003. International Seismological Centre, On-line Bulletin,, International Seismological Centre, Thatcham, UK, 2003.

    Kennett, B.L.N. & Engdahl, E.R., 1991. Traveltimes for global earthquake location and phase identification, Geophys. J. Int., 122, 429-465.

    Kirby, S.H., Durham, W.B. & Stern, L.A., 1991. Mantle phase-changes and deep-earthquake faulting in subducting lithosphere, Science, 252, 216- 225.

    Kirby, S.H., Stein, S., Okal, E.A. & Rubie, D.C., 1996. Metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere, Rev. Geophys., 34, 261-306.

  • Metrics
    views in OpenAIRE
    views in local repository
    downloads in local repository

    The information is available from the following content providers:

    From Number Of Views Number Of Downloads
    White Rose Research Online - IRUS-UK 0 30
Share - Bookmark