Thursday, 17 June, 2010 at 7:30 pm
Geoscience Society NZ Meeting – How do tectonic plates lock together?
By Martin Reyners of GNS Science
Understanding how the interface between tectonic plates locks up is important for plate boundaries worldwide, because locked regions accumulate elastic strain which will eventually be released in large earthquakes. To better understand the distribution of plate locking beneath the North Island, we have compared the distribution of small earthquakes with interseismic geodetic locking of the plate interface from GPS and structure within both the Pacific and Australian plates from seismic tomography. The seismicity and structural data suggest a model where plate coupling is controlled by the ability of fluid to cross the plate interface. When an impermeable geological terrane in the overlying plate prevents such fluid flow, plate locking appears to be strong.
This new model has implications for where and when large earthquakes should occur in the subducted Pacific plate. We have thus carried out a detailed study of eight such events, going back to the Mw 6.8 Wairarapa earthquake of August 1942. The locations of these earthquakes are generally consistent with our plate locking model. In addition, our results suggest that a large earthquake in the subducted plate involves rupture of a localized asperity (rough spot) on an otherwise weak, reactivated fault. This finding provides a nice explanation of why aftershocks of such earthquakes are sparse, and die out very quickly.
Talk Details:
Thursday 17th June, 2010, 7:30 start
Science House, Turnbull St, Thorndon. All welcome.
Information: Bryan Davy, Ph. (04) 570-4811, e-mail: b.davy@gns.cri.nz
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