Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001geoji.146..731e&link_type=abstract
Geophysical Journal International, Volume 146, Issue 3, pp. 731-746.
Astronomy and Astrophysics
Astronomy
22
Crustal Structure, New Zealand, Plate Convergence, Seismic Velocity, Subduction, Tomography
Scientific paper
The Fiordland subduction zone, where subduction developed in the late Miocene, has been imaged with P and S-P arrival-time data from 311 earthquakes in a simultaneous inversion for hypocentres and 3-D VP and VP/VS models. The three-month microearthquake survey, recorded with 24 portable seismographs, provides excellent coverage, and, since earthquakes to depths of 130km are included, parts of the model are well-resolved to depths of 100km. The crustal features are generally consistent with geology. The low velocity in the upper 10km is associated with the Te Anau and Waiau basins. The Western Fiordland Orthogneiss is associated with a prominent feature from near-surface to over 40km depth, which includes the residue from the basaltic source rocks. It is defined by high VP (7.4kms-1 at 15km depth) and slightly low VP/VS, and has distinct boundaries on its southern and eastern margins. Adjacent to the deepest earthquakes, there is high-velocity Pacific mantle below 80km depth, inferred to be the mantle expression of ongoing shortening since the early Miocene. As the subducting slab moves down and northeast, it is hindered by the high-velocity body and bends to near-vertical. Bending is accommodated by distributed fracturing evidenced by high VP/VS and persistent deep earthquake activity. Buckling of the subducted plate pushes up the Western Fiordland Orthogneiss. In the transition to the Alpine fault in northern Fiordland, a prominent low-velocity crustal root is consistent with ductile thickening in combination with downwarp of the subducted plate.
Eberhart-Phillips Donna
Reyners Martin
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